of Occupational Health and Safety, Fourth Edition Chapter 93 - Construction
and Safety Hazards in the Construction Industry
James L. Weeks
George Washington University
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build, repair, maintain, renovate, modify and demolish houses, office
buildings, temples, factories, hospitals, roads, bridges, tunnels, stadiums,
docks, airports and more. The International Labor Organization (ILO) classifies
the construction industry as government and private-sector firms erecting
buildings for habitation or for commercial purposes and public works such
as roads, bridges, tunnels, dams or airports. In the United States and
some other countries, construction workers also clean hazardous waste
Construction as a proportion of gross domestic product varies widely in
industrialized countries. It is about 4% of GDP in the United States,
6.5% in Germany and 17% in Japan. In most countries, employers have relatively
few full-time employees. Many companies specialize in skilled tradeselectricity,
plumbing or tile setting, for instanceand work as subcontractors.
The Construction Labor Force
A large portion of construction workers are unskilled laborers; others
are classified in any of several skilled trades (see table
93.1). Construction workers include about 5 to 10% of the workforce
in industrialized countries. Throughout the world, over 90% of construction
workers are male. In some developing countries, the proportion of women
is higher and they tend to be concentrated in unskilled occupations. In
some countries, the work is left to migrant workers, and in others, the
industry provides relatively well-paid employment and an avenue to financial
security. For many, unskilled construction work is the entry into the
paid labor force in construction or other industries.
93.1 Selected construction occupations
Bricklayers, concrete finishers and masons
Hazardous materials (e.g., asbestos, lead, toxic dumps) removal
Installers of floors (including terrazzo), carpeting
Installers of drywall and ceilings (including ceiling tile)
Insulation workers (mechanical and floor, ceiling and wall)
Iron and steel workers (reinforcement and structural)
Operating engineers (drivers of cranes and other heavy equipment
Painters, plasterers and paperhangers
Plumbers and pipefitters
Roofers and shinglers
Sheet metal workers
and Labor Instability
Construction projects, especially large ones, are complex and dynamic.
Several employers may work on one site simultaneously, with the mix of
contractors changing with the phases of the project; for example, the
general contractor is present at all times, excavating contractors early,
then carpenters, electricians and plumbers, followed by floor finishers,
painters and landscapers. And as the work developsfor instance,
as a buildings walls are erected, as the weather changes or as a
tunnel advancesthe ambient conditions such as ventilation and temperature
Construction workers typically are hired from project to project and may
spend only a few weeks or months at any one project. There are consequences
for both workers and work projects. Workers must make and remake productive
and safe working relationships with other workers whom they may not know,
and this may affect safety at the work site. And in the course of the
year, construction workers may have several employers and less than full
employment. They might work an average of only 1,500 hours in a year while
workers in manufacturing, for example, are more likely to work regular
40 hour weeks and 2,000 hours per year. In order to make up for slack
time, many construction workers have other jobsand exposure to other
health or safety hazardsoutside of construction.
For a particular project, there is frequent change in the number of workers
and the composition of the labor force at any one site. This change results
both from the need for different skilled trades at different phases of
a work project and from the high turnover of construction workers, particularly
unskilled workers. At any one time, a project may include a large proportion
of inexperienced, temporary and transient workers who may not be fluent
in the common language. Although construction work often must be done
in teams, it is difficult to develop effective, safe teamwork under such
Like the workforce, the universe of construction contractors is marked
by high turnover and consists mainly of small operations. Of the 1.9 million
construction contractors in the United States identified by the 1990 Census,
only 28% had any full-time employees. Just 136,000 (7%) had 10 or more
employees. The degree of contractor participation in trade organizations
varies by country. In the United States, only about 10 to 15% of contractors
participate; in some European countries, this proportion is higher but
still involves less than half of contractors. This makes it difficult
to identify contractors and inform them of their rights and responsibilities
under pertinent health and safety or any other legislation or regulations.
As in some other industries, an increasing proportion of contractors in
the United States and Europe consists of individual workers hired as independent
contractors by prime- or sub-contractors who employ workers. Ordinarily,
an employing contractor does not provide subcontractors with health benefits,
workers compensation coverage, unemployment insurance, pension benefits
or other benefits. Nor do prime contractors have any obligation to subcontractors
under health and safety regulations; these regulations govern rights and
responsibilities as they apply to their own employees. This arrangement
gives some independence to individuals who contract for their services,
but at the cost of removing a wide range of benefits. It also relieves
employing contractors of the obligation to provide mandated benefits to
individuals who are contractors. This private arrangement subverts public
policy and has been successfully challenged in court, yet it persists
and may become more of a problem for the health and safety of workers
on the job, regardless of their employment relationship. The US Bureau
of Labor Statistics (BLS) estimates that 9% of the US workforce is self-employed,
but in construction as many as 25% of workers are self-employed independent
on Construction Sites
are exposed to a wide variety of health hazards on the job. Exposure differs
from trade to trade, from job to job, by the day, even by the hour. Exposure
to any one hazard is typically intermittent and of short duration, but
is likely to reoccur. A worker may not only encounter the primary hazards
of his or her own job, but may also be exposed as a bystander to hazards
produced by those who work nearby or upwind. This pattern of exposure
is a consequence of having many employers with jobs of relatively short
duration and working alongside workers in other trades that generate other
hazards. The severity of each hazard depends on the concentration and
duration of exposure for that particular job. Bystander exposures can
be approximated if one knows the trade of workers nearby. Hazards present
for workers in particular trades are listed in table 93.2
93.2 Primary hazards encountered in skilled construction trades
Each trade is listed below with an indication of the primary hazards to
which a worker in that trade might be exposed. Exposure may occur to either
supervisors or to wage earners. Hazards that are common to nearly all
construction—heat, risk factors for musculoskeletal disorders and stress—are
of construction trades used here are those used in the United States.
It includes the construction trades as classified in the Standard Occupational
Classification system developed by the US Department of Commerce. This
system classifies the trades by the principal skills inherent in the trade.
dermatitis, awkward postures, heavy loads
dermatitis, awkward postures, heavy loads
from bonding agents, dermatitis, awkward postures
dust, heavy loads, repetitive motion
dust, walking on stilts, heavy loads, awkward postures
metals in solder fumes, awkward posture, heavy loads, asbestos dust
power installers and repairers
metals in solder fumes, heavy loads, asbestos dust
vapors, toxic metals in pigments, paint additives
from glue, awkward postures
fumes and particles, welding fumes
fumes and particles, welding fumes, asbestos dust
fumes, asbestos dust
trauma, awkward postures, glue and glue vapor
and terrazzo finishers
synthetic fibers, awkward postures
surfacing and tamping equipment operators
emissions, gasoline and diesel engine exhaust, heat
and track-laying equipment operators
tar, heat, working at heights
postures, heavy loads, noise
postures, heavy loads, working at heights
fumes, lead, cadmium
dust, whole-body vibration, noise
whole-body vibration, silica dust
and winch operators
and tower operators
and loading machine operators
dust, histoplasmosis, whole-body vibration, heat stress, noise
dozer and scraper operators
dust, whole-body vibration, heat noise
and street construction workers
emissions, heat, diesel engine exhaust
and tractor equipment operators
vibration, diesel engine exhaust
lead, dust, noise
As in other jobs, hazards for construction workers are typically of four
classes: chemical, physical, biological and social.
Chemical hazards are often airborne and can appear as dusts, fumes, mists,
vapors or gases; thus, exposure usually occurs by inhalation, although
some airborne hazards may settle on and be absorbed through the intact
skin (e.g., pesticides and some organic solvents). Chemical hazards also
occur in liquid or semi-liquid state (e.g., glues or adhesives, tar) or
as powders (e.g., dry cement). Skin contact with chemicals in this state
can occur in addition to possible inhalation of the vapor resulting in
systemic poisoning or contact dermatitis. Chemicals might also be ingested
with food or water, or might be inhaled by smoking.
Several illnesses have been linked to the construction trades, among them:
- silicosis among
sand blasters, tunnel builders and rock drill operators
- asbestosis (and
other diseases caused by asbestos) among asbestos insulation workers,
steam pipe fitters, building demolition workers and others
- bronchitis among
- skin allergies
among masons and others who work with cement
- neurologic disorders
among painters and others exposed to organic solvents and lead.
Elevated death rates
from cancer of the lung and respiratory tree have been found among asbestos
insulation workers, roofers, welders and some woodworkers. Lead poisoning
occurs among bridge rehabilitation workers and painters, and heat stress
(from wearing full-body protective suits) among hazardous-waste cleanup
workers and roofers. White finger (Raynauds syndrome) appears among
some jackhammer operators and other workers who use vibrating drills (e.g.,
stopper drills among tunnellers).
Alcoholism and other alcohol-related disease is more frequent than expected
among construction workers. Specific occupational causes have not been
identified, but it is possible that it is related to stress resulting
from lack of control over employment prospects, heavy work demands or
social isolation due to unstable working relationships.
are present in every construction project. These hazards include noise,
heat and cold, radiation, vibration and barometric pressure. Construction
work often must be done in extreme heat or cold, in windy, rainy, snowy,
or foggy weather or at night. Ionizing and non-ionizing radiation is encountered,
as are extremes of barometric pressure.
The machines that have transformed construction into an increasingly mechanized
activity have also made it increasingly noisy. The sources of noise are
engines of all kinds (e.g., on vehicles, air compressors and cranes),
winches, rivet guns, nail guns, paint guns, pneumatic hammers, power saws,
sanders, routers, planers, explosives and many more. Noise is present
on demolition projects by the very activity of demolition. It affects
not only the person operating a noise-making machine, but all those close-by
and not only causes noise-induced hearing loss, but also masks other sounds
that are important for communication and for safety.
Pneumatic hammers, many hand tools and earth-moving and other large mobile
machines also subject workers to segmental and whole-body vibration.
Heat and cold hazards arise primarily because a large portion of construction
work is conducted while exposed to the weather, the principal source of
heat and cold hazards. Roofers are exposed to the sun, often with no protection,
and often must heat pots of tar, thus receiving both heavy radiant and
convective heat loads in addition to metabolic heat from physical labor.
Heavy equipment operators may sit beside a hot engine and work in an enclosed
cab with windows and without ventilation. Those that work in an open cab
with no roof have no protection from the sun. Workers in protective gear,
such as that needed for removal of hazardous waste, may generate metabolic
heat from hard physical labor and get little relief since they may be
in an airtight suit. A shortage of potable water or shade contributes
to heat stress as well. Construction workers also work in especially cold
conditions during the winter, with danger of frostbite and hypothermia
and risk of slipping on ice.
The principal sources of non-ionizing ultraviolet (UV) radiation are the
sun and electric arc welding. Exposure to ionizing radiation is less common,
but can occur with x-ray inspection of welds, for example, or it may occur
with instruments such as flow meters that use radioactive isotopes. Lasers
are becoming more common and may cause injury, especially to the eyes,
if the beam is intercepted.
Those who work under water or in pressurized tunnels, in caissons or as
divers are exposed to high barometric pressure. Such workers are at risk
of developing a variety of conditions associated with high pressure: decompression
sickness, inert gas narcosis, aseptic bone necrosis and other disorders.
Strains and sprains are among the most common injuries among construction
workers. These, and many chronically disabling musculoskeletal disorders
(such as tendinitis, carpal tunnel syndrome and low-back pain) occur as
a result of either traumatic injury, repetitive forceful movements, awkward
postures or overexertion (see figure 93.1). Falls
due to unstable footing, unguarded holes and slips off scaffolding (see
figure 93.2) and ladders are very common.
93.1 Carrying without appropriate work clothing and protective equipment
93.2 Unsafe scaffolding in Kathmandu, Nepal, 1974
Biological hazards are presented by exposure to infectious microorganisms,
to toxic substances of biological origin or animal attacks. Excavation
workers, for example, can develop histoplasmosis, an infection of the
lung caused by a common soil fungus. Since there is constant change in
the composition of the labor force on any one project, individual workers
come in contact with other workers and, as a consequence, may become infected
with contagious diseasesinfluenza or tuberculosis, for example.
Workers may also be at risk of malaria, yellow fever or Lyme disease if
work is conducted in areas where these organisms and their insect vectors
Toxic substances of plant origin come from poison ivy, poison oak, poison
sumac and nettles, all of which can cause skin eruptions. Some wood dusts
are carcinogenic, and some (e.g., western red cedar) are allergenic.
Attacks by animals are rare but may occur whenever a construction project
disturbs them or encroaches on their habitat. This could include wasps,
hornets, fire ants, snakes and many others. Underwater workers may be
at risk from attack by sharks or other fish.
Social hazards stem from the social organization of the industry. Employment
is intermittent and constantly changing, and control over many aspects
of employment is limited because construction activity is dependent on
many factors over which construction workers have no control, such as
the state of an economy or the weather. Because of the same factors, there
can be intense pressure to become more productive. Since the workforce
is constantly changing, and with it the hours and location of work, and
many projects require living in work camps away from home and family,
construction workers may lack stable and dependable networks of social
support. Features of construction work such as heavy workload, limited
control and limited social support are the very factors associated with
increased stress in other industries. These hazards are not unique to
any trade, but are common to all construction workers in one way or another.
Risks of Underground Construction Work
Hygenic Institute of Prague
Underground construction work includes tunneling for roads, highways and
railroads and laying pipelines for sewers, hot water, steam, electrical
conduits, telephone lines. Hazards in this work include hard physical
labour, crystalline silica dust, cement dust, noise, vibration, diesel
engine exhaust, chemical vapours, radon and oxygen-deficient atmospheres.
Occasionally this work must be done in a pressurized environment. Underground
workers are at risk for serious and often fatal injuries. Some hazards
are the same as those of construction on the surface, but they are amplified
by working in a confined environment. Other hazards are unique to underground
work. These include being struck by specialized machinery or being electrocuted,
being buried by roof falls or cave-ins and being asphyxiated or injured
by fires or explosions. Tunneling operations may encounter unexpected
impoundments of water, resulting in floods and drowning.
The construction of tunnels requires a great deal of physical effort.
Energy expenditure during manual work is usually from 200 to 350 W, with
a great part of static load of the muscles. Heart rate during work with
compressed-air drills and pneumatic hammers reaches 150 to 160 per minute.
Work is often done in unfavorable cold and humid microclimatic conditions,
sometimes in cumbersome work postures. It is usually combined with exposure
to other risk factors which depend on the local geological conditions
and on the type of technology used. This heavy workload can be an important
contribution to heat stress.
The need for heavy manual labour can be reduced by mechanization. But
mechanization brings its own hazards. Large and powerful mobile machines
in a confined environment introduce risks of serious injury to persons
working nearby, who may be struck or crushed. Underground machinery also
may generate dust, noise, vibration and diesel exhaust. Mechanization
also results in fewer jobs, which reduces the number of persons exposed
but at the expense of unemployment and all of its attendant problems.
Crystalline silica (also known as free silica and quartz) occurs naturally
in many different types of rock. Sandstone is practically pure silica;
granite may contain 75%; shale, 30%; and slate, 10%. Limestone, marble
and salt are, for practical purposes, completely free of silica. Considering
that silica is ubiquitous in the earths crust, dust samples should
be taken and analyzed at least at the start of an underground job and
whenever the type of rock changes as work progresses through it.
Respirable silica dust is generated whenever silica-bearing rock is crushed,
drilled, ground or otherwise pulverized. The main sources of airborne
silica dust are compressed-air drills and pneumatic hammers. Work with
these tools most often occurs in the fore part of the tunnel and, therefore,
workers in these areas are the most heavily exposed. Dust suppression
technology should be applied in all instances.
Blasting generates not only flying debris, but also dust and nitrogen
oxides. To prevent excessive exposure, the customary procedure is to prevent
re-entry to the affected area until the dust and gases have cleared. A
common procedure is to blast at the end of the last work shift of the
day and to clear out debris during the next shift.
Cement dust is generated when cement is mixed. This dust is a respiratory
and mucous membrane irritant in high concentrations, but chronic effects
have not been observed. When it settles on skin and mixes with sweat,
however, cement dust can cause dermatoses. When wet concrete is sprayed
in place, it too can cause dermatoses.
Noise can be significant in underground construction work. Principal sources
include pneumatic drills and hammers, diesel engines and fans. Since the
underground work environment is confined, there is also considerable reverberant
noise. Peak noise levels can exceed 115 dBA, with time-weighted average
noise exposure equivalent to 105 dBA. Noise-reducing technology is available
for most equipment and should be applied.
Underground construction workers can also be exposed to whole-body vibration
from mobile machinery and to hand-arm vibration from pneumatic drills
and hammers. The levels of acceleration transmitted to the hands from
pneumatic tools can reach about 150 dB (comparable to 10 m/s2). Harmful
effects of hand-arm vibration can be aggravated by a cold and damp working
If soil is highly saturated with water or if construction is conducted
under water, the work environment may have to be pressurized to keep water
out. For underwater work, caissons are used. When workers in such a hyperbaric
environment make too rapid a transition to normal air pressure, they risk
decompression sickness and related disorders. Since the absorption of
most toxic gases and vapours depends on their partial pressure, more may
be absorbed at higher pressure. Ten ppm of carbon monoxide (CO) at 2 atmospheres
of pressure, for example, will have the effect of 20 PPM CO at 1 atmosphere.
Chemicals are used in underground construction in a variety of ways. For
example, insufficiently coherent layers of rock may be stabilized with
an infusion of urea formaldehyde resin, polyurethane foam or mixtures
of sodium water glass with formamide or with ethyl and butyl acetate.
Consequently, vapours of formaldehyde, ammonia, ethyl or butyl alcohol
or di-isocyanates may be found in the tunnel atmosphere during application.
Following application, these contaminants may escape into the tunnel from
the surrounding walls, and it may therefore be difficult to fully control
their concentrations, even with intensive mechanical ventilation.
Radon occurs naturally in some rock and may leak into the work environment,
where it will decay into other radioactive isotopes. Some of these are
alpha emitters that may be inhaled and increase the risk of lung cancer.
Tunnels constructed in inhabited areas can also be contaminated with substances
from surrounding pipes. Water, heating and cooking gas, fuel oil, petrol
and so on may leak into a tunnel or, if pipes carrying these substances
are broken during excavation, they may escape into the work environment.
The construction of vertical shafts using mining technology poses similar
health problems to those of tunneling In terrain where organic substances
are present, products of microbiological decomposition may be expected.
Maintenance work in tunnels used for traffic differs from similar work
on the surface mainly in the difficulty of installing safety and control
equipment, for example, ventilation for electric arc welding; this may
influence the quality of safety measures. Work in tunnels in which pipelines
for hot water or steam are present is associated with great heat load,
demanding a special regime of work and breaks.
Oxygen deficiency may occur in tunnels either because oxygen is displaced
by other gases or because it is consumed by microbes or by the oxidation
of pyrites. Microbes may also release methane or ethane, which not only
displace oxygen but, in sufficient concentration, may create the risk
of explosion. Carbon dioxide (commonly called blackdamp in Europe) is
also generated by microbial contamination. The atmospheres in spaces which
have been closed for a long time may contain mostly nitrogen, practically
no oxygen and 5 to 15% carbon dioxide.
Blackdamp penetrates into the shaft from the surrounding terrain due to
changes in the atmospheric pressure. The composition of the air in the
shaft may change very quicklyit may be normal in the morning, but
be deficient in oxygen by the afternoon.
Prevention of exposure to dust should in the first place be implemented
by technical means, such as wet drilling (and/or drilling with LEV), wetting
of the material before it is pulled down and loaded to the transport,
LEV of mining machines and mechanical ventilation of tunnels. Technical
control measures may not be sufficient to lower the concentration of respirable
dust to an acceptable level in some technological operations (e.g., during
drilling and sometimes also in the case of wet drilling), and therefore
it may be necessary to supplement the protection of the workers engaged
in such operations by the use of respirators.
The efficiency of technical control measures must be checked by monitoring
the concentration of airborne dust. In the case of fibrogenic dust, it
is necessary to arrange the programme of monitoring in such a way that
it allows the registration of the exposure of individual workers. The
individual exposure data, in connection with data about each workers
health, are necessary for the assessment of the risk of pneumoconiosis
in particular work conditions, as well as for the assessment of the efficiency
of control measures in the long-run. Last but not least, the individual
registration of exposure is necessary for evaluating the ability of individual
workers to continue in their jobs.
Due to the nature of underground work, protection against noise depends
mostly on the personal protection of hearing. Effective protection against
vibrations, on the other hand, can be achieved only by eliminating or
decreasing the vibration by mechanization of risky operations. PPE is
not effective. Similarly, the risk of diseases due to physical overload
of the upper extremities can be lowered only by mechanization.
Exposure to chemical substances can be influenced by the selection of
appropriate technology (e.g., the use of formaldehyde resins and formamide
should be eliminated), by good maintenance (e.g., of diesel engines) and
by adequate ventilation. Organization and work regime precautions are
sometimes very effective, especially in the case of the prevention of
Work in underground spaces in which the composition of the air is not
known demands strict adherence to safety rules. Entering such spaces without
isolating breathing apparatuses must not be allowed. The work should be
done only by a group of at least three peopleone worker in the underground
space, with breathing apparatus and safety harness, the others outside
with a rope to secure the inside worker. In case of accident it is necessary
to act quickly. Many lives have been lost in efforts to save the victim
of an accident when the safety of the rescuer was disregarded.
Pre-placement, periodic and post-employment preventive medical examinations
are a necessary part of the health and safety precautions for workers
in tunnels. The frequency of periodic examinations and the type and scope
of special examinations (x ray, lung functions, audiometry and so on)
should be individually determined for each workplace and for each job
according to the working conditions.
Prior to groundbreaking for underground work, the site should be inspected
and soil samples should be taken in order to plan the excavation. Once
work is underway, the work site should be inspected daily to prevent roof
falls or cave-ins. The workplace of solitary workers should be inspected
at least twice each shift. Fire suppression equipment should be strategically
placed throughout the underground work site.
Pekka Roto, Medicine
Tampere Regional Institute of Occupational Health
The construction industry forms 5 to 15% of the national economy of most
countries and is usually one of the three industries having the highest
rate of work-related injury risks. The following chronic occupational
health risks are pervasive (Commission of the European Communities 1993):
disorders, occupational hearing loss, dermatitis and lung disorders
are the most common occupational diseases.
- An increased risk
of respiratory tract carcinomas and mesothelioma caused by asbestos
exposure has been observed in all countries where occupational mortality
and morbidity statistics are available.
- Disorders resulting
from improper nutrition, smoking or use of alcohol and drugs are associated
especially with migrant workers, a substantial portion of construction
employment in many countries.
services for construction workers should be planned with these risks as
Types of Occupational Health Services
Occupational health services for construction workers consist of three
- specialized services
for construction workers
- occupational health
care for construction workers rendered by providers of broad-based occupational
- health services
provided voluntarily by the employer.
Specialized services are the most effective but also the most expensive
in terms of direct costs. Experiences from Sweden indicate that the lowest
injury rates on construction sites worldwide and a very low risk for occupational
diseases among construction workers are associated with extensive preventive
work through specialized service systems. In the Swedish model, called
Bygghälsan, technical and medical prevention have been combined.
Bygghälsan operates through regional centres and mobile units. During
the severe economic recession of the late 1980s, however, Bygghälsan
severely cut back its health service activities.
In countries that have occupational health legislation, construction companies
usually buy the needed health services from companies serving general
industries. In such cases, the training of occupational health personnel
is important. Without special knowledge of the circumstances surrounding
construction, medical personnel cannot provide effective preventive occupational
health programs for construction companies.
Some large multinational companies have well-developed occupational safety
and health program that are part of the culture of the enterprise. The
cost-benefit calculations have proved these activities economically profitable.
Nowadays, occupational safety program are included in quality management
of most international companies.
Because construction sites are often situated far from any established
providers of health services, mobile health service units may be necessary.
Practically all countries that have specialized occupational health services
for construction workers use mobile units for delivering the services.
The mobile units advantage is the saving of work time by bringing
the services to worksites. Mobile health centres are contained in a specially
equipped bus or trailer and are especially suitable for all types of screening
procedures, such as periodic health examinations. Mobile services should
be careful to arrange in advance for collaboration with local providers
of health services in order to secure follow-up evaluation and treatment
for workers whose test results suggest a health problem.
Standard equipment for a mobile unit includes a basic laboratory with
a spirometer and an audiometer, an interview room and x-ray equipment,
when needed. It is best to design module units as multipurpose spaces
so they can be used for different types of projects. The Finnish experience
indicates that mobile units are also suitable for epidemiological studies,
which can be incorporated into occupational health program, if properly
planned in advance.
preventive occupational health services
Identification of risk at construction sites should guide medical activity,
although this is secondary to prevention through proper design, engineering
and work organization. Risk identification requires a multidisciplinary
approach; this requires close collaboration between the occupational health
personnel and the enterprise. A systematic workplace survey of risks using
standardized checklists is one option.
Preplacement and periodic health examinations are usually conducted according
to requirements set by legislation or guidance provided by authorities.
The examinations content depends on the exposure history of each
worker. Short work contracts and frequent turnover of the construction
workforce can result in missed or inappropriate
health examinations, a failure to follow up on findings or unwarranted
duplication of health examinations. Therefore, regular standard periodic
examinations are recommended for all workers. A standard health examination
should contain: an exposure history; symptom and illness histories with
special emphasis on musculoskeletal and allergic diseases; a basic physical
examination; and audiometry, vision, spirometry and blood pressure tests.
The examinations should also provide health education and information
on how to avoid occupational risks known to be common.
disorders and their prevention
Musculoskeletal disorders have multiple origins. Lifestyle, hereditary
susceptibility and aging, combined with improper physical strain and minor
injuries, are commonly accepted risk factors for musculoskeletal disorders.
The types of musculoskeletal problems have different exposure patterns
in different construction professions.
There is no reliable test to predict an individuals risk for acquiring
a musculoskeletal disorder. Medical prevention of musculoskeletal disorders
is based on guidance in ergonomic matters and lifestyles. Preplacement
and periodic examinations can be used for this purpose. Nonspecific strength
testing and routine x rays of the skeletal system have no specific value
for prevention. Instead, early detection of symptoms and a detailed work
history of musculoskeletal symptoms can be used as a basis for medical
counseling. A program that performs periodic symptom surveys to identify
work factors that can be changed has been shown to be effective.
Often, workers who have been exposed to heavy physical loads or strain
think the work keeps them fit. Several studies have proved that this is
not the case. Therefore, it is important that, in the context of health
examinations, the examinees be informed about proper ways to maintain
their physical fitness. Smoking has also been associated with lumbar disk
degeneration and low-back pain. Therefore, anti-smoking information and
therapy should be included in the periodic health examinations, too (Workplace
Hazard and Tobacco Education Project 1993).
Occupational noise-induced hearing loss
The prevalence of noise-induced hearing loss varies among construction
occupations, depending on levels and duration of exposure. In 1974, less
than 20% of Swedish construction workers at age 41 had normal hearing
in both ears. Implementation of a comprehensive hearing conservation program
increased the proportion in that age group having normal hearing to almost
40% by the late 1980s. Statistics from British Columbia, Canada, show
that construction workers generally suffer significant loss of hearing
after working more than 15 years in the trades (Schneider et al. 1995).
Some factors are thought to increase susceptibility to occupational hearing
loss (e.g., diabetic neuropathy, hypercholesterolemia and exposure to
certain ototoxic solvents). Whole-body vibration and smoking may have
an additive effect.
A large-scale program for hearing conservation is advisable for the construction
industry. This type of program requires not only collaboration at the
worksite level, but also supportive legislation. Hearing conservation
program should be specific in work contracts.
Occupational hearing loss is reversible in the first 3 or 4 years after
initial exposure. Early detection of hearing loss will provide opportunities
for prevention. Regular testing is recommended to detect the earliest
possible changes and to motivate workers to protect themselves. At the
time of testing, the exposed workers should be educated in the principles
of personal protection, as well as the maintenance and proper use of protection
Occupational dermatitis is prevented mainly by hygienic measures. The
proper handling of wet cement and skin protection are effective in promoting
hygiene. During health examinations, it is important to stress the importance
of avoiding skin contact with wet cement.
Occupational lung diseases
Asbestosis, silicosis, occupational asthma and occupational bronchitis
can be found among construction workers, depending on their past work
exposures (Finnish Institute of Occupational Health 1987).
There is no medical method to prevent the development of carcinomas after
someone has been sufficiently exposed to asbestos. Regular chest x rays,
every third year, are the most common recommendation for medical surveillance;
there is some evidence that x-ray screening improves the outcome in lung
cancer (Strauss, Gleanson and Sugarbaker 1995). Spirometry and anti-smoking
information are usually included in the periodic health examination. Diagnostic
tests for the early diagnosis of asbestos-related malignant tumors are
Malignant tumors and other lung diseases related to asbestos exposure
are widely underdiagnosed. Therefore, many construction workers eligible
for compensation remain without benefits. In the late 1980s and early
1990s, Finland conducted a nationwide screening of workers exposed to
asbestos. The screening revealed that only one-third of the workers with
asbestos-related diseases and who had access to occupational health services
had been diagnosed earlier (Finnish Institute of Occupational Health 1994).
Special needs of migrant workers
Depending on the construction site, the social context, sanitary conditions
and climate may present important risks to construction workers. Migrant
workers often suffer from psychosocial problems. They have a higher risk
of work-related injuries than native workers. Their risk of carrying infectious
diseases, such as HIV/AIDS, tuberculosis, and parasitic diseases must
be taken into account. Malaria and other tropical diseases are problems
for workers in areas where they are endemic.
In many large construction projects, a foreign workforce is used. A preplacement
medical examination should be conducted in the home country. Also, the
spreading of contagious diseases must be prevented through proper vaccination
program In the host countries, proper vocational training, health and
safety education, and housing should be organized. Migrant workers should
be provided the same access to health care and social security as native
workers (El Batawi 1992).
In addition to preventing construction-related ailments, the health practitioner
should work to promote positive changes in lifestyle, which can improve
a workers health overall. Avoiding alcohol and smoking are the most
important and fruitful themes for health promotion for construction workers.
It has been estimated that a smoker costs the employer 20 to 30% more
than a nonsmoking worker. Investments in anti-smoking campaigns pay not
only in the short term, with lower accident risks and shorter sick leaves,
but also in the long term, with lower risks of cardiovascular pulmonary
diseases and cancer. In addition, tobacco smoke has harmful multiplier
effects with most dusts, especially with asbestos.
It is difficult to prove any direct economic benefit of occupational health
services to an individual construction company, especially if the company
is small. Indirect cost-benefit calculations show, however, that accident
prevention and health promotion are economically beneficial. Cost-benefit
calculations of investments in preventive program are available for companies
to use internally. (For a model used extensively in Scandinavia, see Oxenburg
Leen Akkers, Managing
the EC directive Minimum Regulations for Health and Safety on Temporary
and Mobile Building Sites typifies the legal regulations emanating from
the Netherlands and from the European Union. Their aim is to improve working
conditions, to combat disability and to reduce sickness absenteeism. In
the Netherlands, these regulations for the construction industry are expressed
in the Arbouw Resolution, Chapter 2, Section 5.
As is often the case, the legislation seems to be following the social
changes that began in 1986, when organizations of employers and employees
joined to establish the Arbouw Foundation to provide services for construction
companies in civil engineering and utility construction, earth works,
roadbuilding and water construction and the completion sectors of the
industry. Thus, the new regulations are scarcely a problem for the responsible
companies already committed to implement health and safety considerations.
The fact that these principles are often very difficult to put into practice,
however, has led to non-observance and unfair competition and, consequently,
the need for legal regulations.
The legal regulations focus on preventive measures before the construction
project is started and while it is in progress. This will yield the greatest
The Health and Safety Act stipulates that evaluations of risks must address
not only those arising from materials, preparations, tools, equipment
and so on, but also those involving special groups of workers (e.g., pregnant
women, young and elderly workers and those with disabilities).
Employers are obliged to have written risk evaluations and inventories
produced by certified experts, who may be employees or external contractors.
The document must include recommendations for eliminating or limiting
the risks and must also stipulate phases of the work when qualified specialists
will be required. Some construction companies have developed their own
approach to the evaluation, the General Business Investigation and Risk
Inventory and Evaluation (ABRIE), which has become the prototype for the
The Health and Safety Act obliges employers to offer a periodic health
examination to their employees. The purpose is to identify health problems
that may make certain jobs especially hazardous for some workers unless
certain precautions are taken. This requirement echoes the various collective
labor agreements in the construction industry which for years have required
employers to provide employees with comprehensive occupational health
care, including periodic medical examinations. The Arbouw Foundation has
contracted with the Federation of Occupational Health and Safety Care
Centres for the provision of these services. Over the years, a wealth
of valuable information has been accumulated which has contributed to
enhancement of the quality of the risk inventories and evaluations.
The Health and Safety Act also requires employers to have an absenteeism
policy which includes a stipulation that experts in this field be retained
to monitor and counsel disabled employees.
Many health and safety risks can be traced to inadequacies in the building
and organization choices or to poor planning of the work when setting
up a project. To obviate this, the employers, employees and the government
agreed in 1989 on a working conditions covenant. Among other things, it
specified cooperation between clients and contractors and between contractors
and subcontractors. This has resulted in a code of conduct which serves
as a model for the implementation of the European directive on temporary
and mobile building sites.
As part of the covenant, Arbouw formulated limits for exposure to hazardous
substances and materials, along with guidelines for the application in
various construction operations.
Under the leadership of Arbouw, the FNV Building Workers and Wood Workers
Union, the FNV Industry Union and the Mineral Wool Association, Benelux,
agreed to a contract that called for the development of glass wool and
mineral wool products with less dust emission, development of the safest
possible production methods for glass wool and mineral wool, formulation
and promotion of working methods for the safest use of these products
and performance of the research necessary to establish safe exposure limits
to them. The exposure limit for respirable fibers was set at 2/cm3
although a limit of 1/cm3 was regarded as feasible. They also
agreed to eliminate the use of raw and secondary materials that are health
risks, using as criteria the exposure limits formulated by Arbouw. Performance
under this agreement will be monitored until it expires on 1 January 1999.
Construction Process Quality
The implementation of the EC directive does not stand in isolation but
is an integral part of company health and safety policies, along with
quality and environmental policies. Health and safety policy is critical
part of the quality policy of the companies. The laws and regulations
will be enforceable only if the employers and employees of the construction
industry have played a role in their development. The government has dictated
the development of a model health and safety plan that is practicable
and can be enforced to prevent unfair competition from companies that
ignore or subvert it.
Doug J. McVitte, Manager
Construction Safety Association of Ontario
Diversity of Projects
and Work Activities
Many people outside the construction industry are unaware of the diversity
and degree of specialization of work undertaken by the industry, though
they see portions of it every day. In addition to traffic delays caused
by encroachments on roads and street excavations, the public is frequently
exposed to buildings being erected, subdivisions being constructed and,
occasionally, to the demolition of structures. What is hidden away from
view, in most cases, is the large amount of specialized work done either
as part of a new construction project or as part of the ongoing
repairs maintenance associated with almost anything constructed in the
The list of activities is very diverse, ranging from electrical, plumbing,
heating and ventilating, painting, roofing and flooring work to very specialized
work such as installing or repairing overhead doors, setting heavy machinery,
applying fireproofing, refrigeration work and installing or testing communications
The value of construction can be partially measured by the value of building
permits. Table 93.4 shows the value of construction
in Canada in 1993.
93.4 Value of construction projects in Canada, 1993 (based on value of
building permits issued in 1993)
Source: Statistics Canada
building (houses, apartments)
buildings (factories, mining plants)
buildings (offices, stores, shops etc.)
buildings (schools, hospitals)
buildings (airports, bus stations, farm buildings, etc.)
facilities (wharves, dredging)
and sewage systems
and oil (refineries, pipelines)
engineering construction (bridges, tunnels, etc.)
The health and safety
aspects of the work depend in large measure on the nature of the project.
Each type of project and each work activity presents different hazards
and solutions. Often, the severity, scope or size of the problem is related
to the size of the project as well.
Clients are the individuals, partnerships, corporations or public authorities
for whom construction is carried out. The vast majority of construction
is done under contractual arrangements between clients and contractors.
A client may select a contractor based on past performance or through
an agent such as an architect or engineer. In other cases, it may decide
to offer the project through advertising and tendering. The methods used
and the clients own attitude to health and safety can have a profound
effect on the projects health and safety performance.
For example, if a client chooses to pre-qualify contractors
to ensure that they meet certain criteria, then this process excludes
inexperienced contractors, those who may not have had satisfactory performance
and those without qualified personnel required for the project. While
health and safety performance has not previously been one of the common
qualifications sought or considered by clients, it is gaining in usage,
primarily with large industrial clients and with government agencies that
purchase construction services.
Some clients promote safety much more than others. In some cases, this
is due to the risk of damage to their existing facilities when contractors
are brought in to perform maintenance or to expand the clients facilities.
Petrochemical companies in particular make it clear that contractor safety
performance is a key condition of the contract.
Conversely, those firms who choose to offer their project through an unqualified
open bidding process to obtain the lowest price often end up with contractors
that may be unqualified to perform the work or who take short cuts to
save on time and materials. This can have an adverse effect on health
and safety performance.
Many people who are not familiar with the nature of the contractual arrangements
common in construction presume that one contractor performs all or at
least the major part of most building construction. For example, if a
new office tower, sports complex or other high-visibility project is being
constructed, the general contractor usually erects signs and often company
flags to indicate its presence and to create the impression that this
is its project. Years ago, this impression may have been relatively
accurate, since some general contractors actually undertook to perform
substantial parts of the project with their own direct-hire forces. However,
since the mid-1970s, many, if not most, general contractors have assumed
more of a project management role on large projects, with the vast majority
of the work contracted out to a network of subcontractors, each of which
has special skills in a particular aspect of the project. (See table
93.5 Contractors/subcontractors on typical industrial/commercial/institutional
Reinforcing steel contractor
Structural steel contractor
Finish carpentry/cabinet work contractor
Heating/ventilation/air conditioning contractor
As a result, the
general contractor could actually have fewer staff onsite than any of
several subcontractors on the project. In some cases the main contractor
has no workforce directly involved in construction activities, but manages
the work of subcontractors. On most major projects in the industrial,
commercial and institutional (ICI) sector, there are several layers of
subcontractors. Typically, the primary level of subcontractors have contracts
with the general contractor. However, these subcontractors may contract
part of their work out to other smaller or more specialized subcontractors.
The influence that this network of contractors may have on health and
safety becomes fairly obvious when it is compared with a fixed worksite
such as a factory or a mill. At a typical fixed-industry workplace, there
is only one management entity, the employer. The employer has sole responsibility
for the workplace, the lines of command and communication are simple and
direct, and only one corporate philosophy applies. At a construction project,
there may be ten or more employer entities (representing the general contractor
and the usual subcontractors), and the lines of communication and authority
tend to be more complex, indirect and often confused.
The attention given to health and safety by the person or company in charge
can influence the health and safety performance of others. If the general
contractor has attached a high degree of importance to health and safety,
this can have a positive influence on the health and safety performance
of the subcontractors on the project. The converse is also true.
Additionally, the overall health and safety performance of the site can
be adversely affected by the performance of one subcontractor (e.g., if
one subcontractor has poor housekeeping, leaving a mess behind as his
or her forces move through the project, it can create problems for all
of the other subcontractors onsite).
Regulatory efforts regarding health and safety are generally more difficult
to introduce and administer in these multi-employer workplaces. It may
be difficult to determine which employer has responsibility for which
hazards or solutions, and any administrative controls which appear to
be eminently workable in a single-employer workplace may need significant
modification to be workable on a multi-employer construction project.
For example, information regarding hazardous materials used on a construction
project must be communicated to those who work with or near the materials,
and workers must be adequately trained. At a fixed workplace with only
one employer, all of the material and the information accompanying it
is much more readily obtained, controlled and communicated, whereas on
a construction project, any of the various subcontractors may be bringing
in hazardous materials of which the general contractor has no knowledge.
Additionally, workers employed by one subcontractor using a certain material
may have been trained, but the crew working for another subcontractor
in the same area but doing something entirely different may know nothing
about the material and yet could be as much at risk as those using the
Another factor which emerges regarding contractor-contractor relationships
relates to the bidding process. A subcontractor who bids too low may take
shortcuts that compromise health and safety. In these cases, the general
contractor must ensure that subcontractors adhere to the standards, specifications
and statutes pertaining to health and safety. It is not uncommon on projects
where everyone has bid very low to observe continuing health and safety
problems coupled with excessive passing of responsibility, until regulatory
authorities step in to impose a solution.
A further problem relates to the scheduling of work and the impact this
can have on health and safety. With several different subcontractors on
the site at one time, competing interests may create problems. Each contractor
wants to get his or her work done as quickly as possible. When two or
more contractors want to occupy the same space, or when one has to perform
work overhead of another, problems can occur. This is typically a much
more common problem in construction than in fixed industry, where the
main competing interests tend to involve only operations versus maintenance.
The several employers on a particular project may have somewhat different
relationships with their employees than those common at most fixed industrial
workplaces. For example, unionized workers at a manufacturing facility
tend to belong to one union. When the employer needs additional workers,
it interviews and hires them and the new employees join the union. Where
there are former unionized workers on layoff, they are rehired generally
on a seniority basis.
In the unionized part of the construction industry, a completely different
system is used. Employers form collective associations which then enter
into agreements with building and construction trade unions. The majority
of the non-salaried direct-hire employees in the industry work through
their union. When, for example, a contractor needs five additional carpenters
at a project, he or she would call the local Carpenters Union and
place a request for five carpenters to show up for work at the project
on a certain day. The union would notify the five members at the top of
the employment list that they are to report to the project to work for
the particular firm. Depending on the provisions of the collective agreement
between the employers and the union, the contractor may be able to name
hire or select some of these workers. If there are no union members
available to fill the employment call, the employer may be able to hire
temporary workers who would join the union, or the union may bring in
skilled workers from other locals to help fill the demand.
In non-unionized situations, employers use different processes to obtain
additional staff. Prior employment lists, local employment centres, word
of mouth and advertising in local newspapers are the principal methods
It is not uncommon for workers to be employed by several different employers
in the course of a year. The employment duration varies with the nature
of the project and the amount of work to be done. This places a large
administrative load on the construction contractors compared with their
fixed-industry counterparts (e.g., recordkeeping for income taxes, workers
compensation, unemployment insurance, union dues, pensions, licensing
and other regulatory or contractual issues).
This situation presents some unique challenges compared to the typical
fixed-industry workplace. Training and qualifications must not only be
standardized but portable from one job or sector to another. These important
issues affect the construction industry much more profoundly than fixed
industries. Construction employers expect workers to come to the project
with certain skills and capabilities. In most trades, this is accomplished
by a comprehensive apprenticeship program. If a contractor places a call
for five carpenters, he or she expects to see five qualified carpenters
at the project on the day they are needed. If health and safety regulations
require special training, the employer needs to be able to access a pool
of workers with this training, since the training may not be readily available
at the time the work is scheduled to start. An example of this is the
Certified Worker Program required at larger construction projects in Ontario,
Canada, which involves having joint health and safety committees. Since
this training is not currently part of the apprenticeship program, alternative
training systems had to be put in place to create a pool of trained workers.
With growing emphasis on specialized training or at least confirmation
of skill level, training program conducted in conjunction with the building
and construction trades unions will likely grow in importance, number
The structure of organized labor mirrors the way in which contractors
have specialized within the industry. On a typical construction project,
five or more trades may be represented onsite at any one time. This involves
many of the same problems posed by multiple employers. Not only are there
competing interests to deal with, but lines of authority and communication
are more complex and sometimes blurred when compared with a single-employer,
single-union workplace. This influences many aspects of health and safety.
For example, which worker from which union will represent all workers
on the project if there is a regulatory requirement for a health and safety
representative? Who gets trained in what and by whom?
In the case of rehabilitation and reinstatement of injured workers, the
options for skilled construction workers are much more limited than those
of their fixed-industry counterparts. For example, an injured worker at
a factory may be able to return to some other job at that workplace without
crossing important jurisdictional boundaries between one union and another,
because there is typically only one union in the factory. In construction,
each trade has fairly clearly defined jurisdiction over the types of work
its members can perform. This greatly limits the options for injured workers
who may not be able to perform their normal pre-injury job functions but
could none the less perform some other related work at that workplace.
Occasionally, jurisdictional disputes arise over which union should perform
certain types of work which have health and safety implications. Examples
include scaffold erection, boom truck operation, asbestos removal and
rigging. Regulations in these areas need to consider jurisdictional concerns,
especially with respect to licensing and training.
The Dynamic Nature of Construction
Construction workplaces are in many respects quite different from fixed
industry. Not only are they different, they tend to be constantly changing.
Unlike a factory which operates at a given location day after day, with
the same equipment, the same workers, the same processes and generally
the same conditions, construction projects evolve and change from day
to day. Walls are erected, new workers from different trades arrive, materials
change, employers change as they complete their portions of the work,
and most projects are affected to some degree just by the changes in the
When one project is completed, workers and employers move on to other
projects to start all over again. This indicates the dynamic nature of
the industry. Some employers work in several different cities, provinces,
states or even countries. Similarly, many skilled construction workers
move with the work. These factors influence many aspects of health and
safety, including workers compensation, health and safety regulations,
performance measurement and training.
The construction industry is presented with some very different conditions
from those in fixed industry. These conditions must be considered when
control strategies are being contemplated and may help to explain why
things are done differently in the construction industry. Solutions developed
with the input from both construction labor and construction management,
who know these conditions and how to deal effectively with them, offer
the best chance for improving health and safety performance.
International Labour Office
Health and Safety
Construction companies are increasingly adopting the quality management
systems spelled out by the International Organization for Standardization
(ISO), such as the ISO 9000 series and the subsequent regulations that
have been based on it. Although no recommendations on occupational health
and safety are specified in this set of standards, there are cogent reasons
for including preventive measures when implementing a management system
such as that required by the ISO 9000.
Occupational health and safety regulations are written and implemented
and are continuously being adapted to technological progress as well as
to new safety techniques and to advances in occupational medicine. All
too often, however, they are not followed, either deliberately or out
of ignorance. When this occurs, models for safety management, such as
the ISO 9000 series, assist in integrating the structure and content of
preventive measures into management. The advantages of such a comprehensive
approach are obvious.
Integrated management means that occupational health and safety regulations
are no longer looked at in isolation, but gain relevance from the corresponding
sections of a quality management handbook, as well as in process and work
instructions, thus creating a fully integrated system. This integral approach
can improve the chances of greater attention to accident prevention measures
in daily construction practice and, thereby, reduce the number of workplace
accidents and injuries. Dissemination of a handbook that integrates occupational
health and safety procedures into the processes it describes is crucial
for this process.
New management methods are aimed at putting people closer to the centre
of the processes. Coworkers are being more actively involved. Information,
communication and cooperation are promoted across hierarchical barriers.
The reduction of absences due to illness or workplace accidents enhances
the implementation of the principles of quality management in construction.
With the development of new building methods and equipment, safety requirements
increase steadily in number. The increasing concern with environmental
protection makes the problem even more complex. Coping with the demands
of modern prevention is difficult without appropriate regulations and
a centrally directed articulation of the process and work instructions.
Clear divisions of responsibility and effective coordination for the prevention
plan should, therefore, be written into the quality management system.
Documentation of the existence of an occupational safety management system
is increasingly required when contractors submit bids for work, and its
effectiveness has become one of the criteria for awarding a contract.
The pressure of international competition could become even greater in
the future. It seems prudent, therefore, to integrate preventive measures
into the quality management system now, rather than waiting and being
forced by increasing competitive pressure to do so later, when the pressure
of time and the costs of personnel and financing will be much greater.
Furthermore, a not inconsiderable benefit of an integrated prevention/quality
management system is that having such a well-documented program in place
is likely to reduce the costs of coverage, not only for workers
compensation, but also for product liability.
Company management must be committed to the integration of occupational
health and safety into the management system. Goals specifying the content
and time-frame of this effort should be defined and included in the basic
statement of company policy. The necessary resources should be made available
and appropriate personnel assigned to accomplish the project goals. Specialized
safety personnel are generally required in large and mid-sized construction
companies. In smaller companies, the employer must take the responsibility
for the preventive aspects of the quality management system.
A periodic company management review closes the circle. The collective
experiences in utilizing the integrated prevention/ quality management
system should be examined and assessed, and plans for revision and for
subsequent review should be formulated by company management.
Assessment of results of the occupational safety management system that
has been instituted is the second step in the integration of preventive
measures and quality management.
The dates, kinds, frequency, causes and costs of accidents should be compiled,
analyzed and shared with all those in the company with relevant responsibilities.
Such an analysis enables the company to set priorities in formulating
or modifying process and work instructions. It also makes clear the extent
to which occupational health and safety experience affects all divisions
and all processes in the construction company. For this reason, defining
the interface between company processes and preventive aspects takes on
great importance. During bid preparation, the resources in time and money
needed for comprehensive preventive measures, such as those incurred in
clearing debris, can be precisely calculated.
When purchasing construction materials, attention should be paid to the
availability of substitutes for potentially dangerous materials. From
the beginning of a project responsibility for occupational health and
safety should be assigned for particular aspects and each phase of the
construction project. The need and availability for special training in
occupational health and safety as well as the relative risks of injury
and disease should be compelling considerations in the adoption of particular
construction processes. These conditions must be recognized early on so
that appropriately qualified workers can be selected and the courses of
instruction can be arranged in a timely manner.
The responsibilities and authorities of the personnel assigned to safety
and how they fit into the daily work should be documented in writing and
collated with the onsite task descriptions. The construction companys
occupational safety staff should appear shown in its organizational chart,
which, along with a clear responsibility matrix and schematic flowcharts
of processes, should appear in the quality management handbook.
In practice, there are four formal procedures and their combinations for
integrating occupational health and safety into a quality management system
that have been implemented in Germany:
- A quality management
handbook and a separate occupational safety management handbook are
developed. Each has its own procedures and work instructions. In
extreme cases, this creates ineffective, insular organizational solutions,
which require twice the amount of work and in practice do not accomplish
the desired results.
- An additional
section is inserted into the quality management handbook with the heading
Occupational health and safety. All statements on occupational
health and safety are organized in this section. This path is chosen
by some construction companies. Positioning a health and safety problem
in a separate section may well highlight the importance of prevention,
but it entails the risk being ignored as a fifth wheel and
serves more as an evidence of intent rather than a command for appropriate
- All aspects
of occupational health and safety are worked directly into the quality
management system. This is the most systematic implementation of
the basic idea of integration. The integrated and flexible structuring
of the presentation models of the German DIN EN ISO 9001-9003 permits
such an inclusion.
- The Underground
Construction Trade Organization (Berufs-genossenschaft) favors a modular
integration. This concept is explained below.
in Quality Management
Once the assessment is completed, at the latest, those responsible for
the construction project should contact the quality management officers
and decide on the steps for actually integrating occupational safety into
the management system. Comprehensive preparatory work should facilitate
setting common priorities during the work that promise the greatest preventive
The demands of prevention that come out of the assessment are first divided
into those that can be categorized according to the processes specific
to the company and those that should be considered separately since they
are more widespread, more comprehensive or of such a special character
that they demand separate consideration. The following question can be
of assistance in this categorization: Where would the interested reader
of the handbook (e.g., the customer or the worker) most likely
look for the relevant preventive policy, the section of a chapter devoted
to a process specific to the company, or in a special section on occupational
health and safety? Thus, it appears, a specialized procedural instruction
on transporting hazardous materials would make the most sense in almost
all construction companies if it were included in section on handling,
storing, packing, conserving and shipping.
Coordination and Implementation
After this formal categorization should come linguistic coordination to
ensure easy readability (this means presentation in the appropriate language(s)
and in terms easily understood by individuals with educational levels
characteristic of the particular workforce). Finally, the final documents
must be formally endorsed by the top management of the company. At this
juncture, it would be useful to publicize the significance of the changed
or newly-implemented procedures and work instructions in company bulletins,
safety circles, memos and any other available media, and to promote their
To assess the effectiveness of the instructions, appropriate questions
may be prepared for inclusion into general audits. In this manner, the
coherence of work processes and occupational health and safety considerations
is made unmistakably clear to the worker. Experience has shown that workers
may at first be surprised when an audit team on the construction site
in their particular division routinely asks questions on accident prevention
as a matter of course. The consequent increase in the attention paid to
safety and health by the workforce confirms the value of the integration
of prevention into the quality management program.
Jeffrey Hinksman, Health and Safety Consultant
The term construction industry is used worldwide to cover what
is a collection of industries with very different practices, brought together
temporarily on the site of a building or civil engineering job. The scale
of operations ranges from a single worker carrying out a job lasting minutes
only (e.g., replacing a roof tile with equipment consisting of a hammer
and nails and possibly a ladder) to vast building and civil engineering
projects lasting many years that involve hundreds of different contractors,
each with their own expertise, plant and equipment. However, despite the
enormous variation in scale and complexity of operations, the major sectors
of the construction industry have a great deal in common. There is always
a client (known sometimes as the owner) and a contractor; except for the
very smallest jobs, there will be a designer, either an architect or engineer,
and if the project involves a range of skills, it will inevitably require
additional contractors working as subcontractors to the main contractor
(see also the article Organizational factors affecting health and
safety [CCE05AE] in this chapter). While small-scale domestic or
agricultural buildings may be built on the basis of an informal agreement
between the client and builder, the vast majority of building and civil
engineering work will be carried out under the terms of a formal contract
between the client and contractor. This contract will set out details
of the structure or other work that the contractor is to provide, the
date by which it is to be built and the price. Contracts may contain a
great deal besides the job, the time and the price, but those are the
The two broad categories of construction projects are building
and civil engineering. Building applies to projects involving houses,
offices, shops, factories, schools, hospitals, power and railway stations,
churches and so onall those kinds of structures that in everyday
speech we describe as buildings. Civil engineering applies
to all the other built structures in our environment, including roads,
tunnels, bridges, railways, dams, canals and docks. There are structures
that appear to fall into both categories; an airport involves extensive
buildings as well as civil engineering in the creation of the airfield
proper; a dock may involve warehouse buildings as well excavation of the
dock and raising of the dock walls.
Whatever the type of structure, building and civil engineering both involve
certain processes such as building or erection of the structure, its commissioning,
maintenance, repair, alteration and ultimately its demolition. This cycle
of processes occurs regardless of the type of structure.
and the Self-employed
While there are variations from country to country, construction is typically
an industry of small employers. As many as 70 to 80% of contractors employ
less than 20 workers. This is because many contractors start out as a
single tradesperson working alone on small-scale jobs, probably domestic
ones. As their business expands, such tradespeople start to employ a few
workers themselves. The workload in construction is rarely consistent
or predictable, as some jobs finish and others start up at different times.
There is a need in the industry to be able to move groups of workers with
particular skills from job to job as the work requires. Small contractors
fulfill this role.
Alongside the small contractors there is a population of self-employed
workers. Like agriculture, construction has a very high proportion of
self-employed workers. These again are usually tradespeople, such as carpenters,
painters, electricians, plumbers and bricklayers. They are able to find
a place in either small-scale domestic work or as part of the workforce
on bigger jobs. In the boom construction period of the late 1980s, there
was an increase in workers claiming to be self-employed. This was partly
because of tax incentives for the individuals concerned and use by contractors
of so-called self-employed who were cheaper than employees. Contractors
were not faced with the same level of social security costs, were not
required to train self-employed persons and could get rid of them more
easily at the end of jobs.
The presence in construction of so many small contractors and self-employed
individuals tends to militate against effective management of health and
safety for the job as a whole and, with such a transitory workforce, certainly
makes it more difficult to provide proper safety training. Analysis of
fatal accidents in the United Kingdom over a 3-year period showed that
about half the fatal accidents happened to workers who had been onsite
for a week or less. The first few days on any site are especially hazardous
to construction workers because, however experienced they may be as tradespeople,
each site is a unique experience.
Public and Private Sectors
Contractors may be part of the public sector (e.g., the works department
of a city or district council) or they are part of the private sector.
A considerable amount of maintenance used to be done by such public works
departments, especially on housing, schools and roads. Recently there
has been a move to encourage greater competition in such work, partly
as a result of pressures for better value for money. This has led firstly
to a reduction in the size of public works departments, even their total
disappearance in some places, and to the introduction of mandatory competitive
tendering. Jobs previously done by public works departments are now done
by private-sector contractors under severe lowest tender wins
conditions. In their need to cut costs, contractors may be tempted to
reduce what are seen as overheads such as safety and training.
The distinction between public and private sectors may also apply to clients.
Central and local government (along with transportation and public utilities
if under the control of central or local government) may all be clients
for construction. As such they would generally be thought to be in the
public sector. Transportation and utilities run by corporations would
usually be considered to be in the private sector. Whether a client is
in the public sector sometimes influences attitudes towards inclusion
of some items of safety or training in the cost of construction work.
Recently public- and private-sector clients have been under similar constraints
as regards competitive tendering.
Work across National Boundaries
An aspect of public-sector
contracts of increasing importance is the need for tenders to be invited
from beyond national boundaries. In the European Union, for example, large-scale
contracts beyond a value set out in Directives, must be advertised within
the Union so that contractors from all member countries may tender. The
effect of this is to encourage contractors to work across national boundaries.
They are then required to work in accordance with the local national health
and safety laws. One of the aims of the European Union is to harmonize
standards between member states in health and safety laws and their application.
Major contractors working in parts of the world subject to similar regimes
must therefore be familiar with health and safety standards in those countries
where they carry out work.
In buildings, the
designer is usually an architect, although on small-scale domestic housing,
contractors sometime provide such design expertise as is necessary. If
the building is large or complex, there may be architects dealing with
design of the overall scheme as well as structural engineers concerned
with design of, for example, the frame, and specialist engineers involved
with design of the services. The architect for the building will ensure
that sufficient space is provided in the right places in the structure
to permit installation of plant and services. Specialist designers will
be concerned to ensure that the plant and services are designed to operate
to the required standard when installed in the structure in the places
provided by the architect.
In civil engineering, the lead in design is more likely to be taken by
a civil or structural engineer, although in high-profile jobs where visual
impact may be an important factor, an architect may have an important
role in the design team. In tunneling, railways and highways, the lead
in design is likely to be taken by structural or civil engineers.
The role of the developer is to seek to improve the utilization of land
or buildings and profit from that improvement. Some developers simply
sell the improved land or buildings and have no further interest; others
may retain ownership of land or even buildings and reap a continuing interest
in the form of rents that are greater than before the improvements.
The skill of the developer is to identify sites either as empty land or
underutilized and out-of-date buildings where application of construction
skills will improve their value. The developer may use his or her own
finances, but perhaps more often exercises further skills in identifying
and bringing together other sources of finance. Developers are not a modern
phenomenon; the expansion of cities over the last 200 years owes a great
deal to developers. Developers may themselves be clients for the construction
work, or they may simply act as agents for other parties who provide finance.
Types of Contract
In the traditional contract, the client arranges for a designer to prepare
a full design and specifications. Contractors are then invited by the
client to tender or bid for doing the job in accordance with the design.
The role of the contractor is largely confined to construction proper.
The contractors involvement in questions of design or specification
is then mainly a matter of seeking such changes as will make it easier
or more efficient to buildto improve buildability.
The other common arrangement in construction is the design and build contract.
The client requires a building (perhaps an office block or shopping development)
but has no firm ideas on detailed aspects of its design other than the
size of site, number of persons to be accommodated or scale of activities
to be carried out in it. The client then invites tenders from either designers
or contractors to submit both design and construction proposals. Contractors
working in design and build either have their own design organization
or have close links with an external designer who will work for them on
the job. Design and build may involve two stages in design: an initial
stage where a designer prepares an outline scheme which is then put out
to tender; and a second stage where the successful design and build contractor
will then carry out further design on detailed aspects of the job.
Maintenance and emergency contracts cover a wide variety of arrangements
between clients and contractors and represent a significant proportion
of the work of the construction industry. They generally run for a fixed
period, require the contractor to do certain types of work or to work
on a call-off basis (i.e., work that the client calls the
contractor in to do). Emergency contracts are widely used by public authorities
who are responsible for providing a public service that ought not to be
interrupted; government agencies, public utilities and transportation
systems make wide use of them. Operators of factories, particularly those
with continuous processes such as petrochemicals, also make wide use of
emergency contracts to deal with problems in their facilities. Having
entered such a contract, the contractor undertakes to make available suitable
workers and plant to carry out the work, often at very short notice (e.g.,
in the case of emergency contracts). The advantage to the client is that
he or she does not need to retain workers on payroll or have plant and
equipment that may only occasionally be used to deal with maintenance
Pricing of maintenance and emergency contracts may be on the basis of
a fixed sum per annum, or on the basis of time spent carrying out work,
or some combination.
Perhaps the most common publicly known example of such contractors is
maintenance of roads and emergency repairs to gas main or power supplies
that have either failed or been accidentally damaged.
Whatever the form of contract, the same possibilities arise for clients
and designers to influence the health and safety of contractors by decisions
made in the early stage of the job. Design and build perhaps permits closer
liaison between the designer and contractor on health and safety.
Price is always an element in a contract. It may simply be a single sum
for the cost of doing the job, such as building a house. Even with a single
lump sum, the client may have to pay part of the price in advance of the
job starting, to enable the contractor to buy materials. The price may,
however, be on a cost-plus basis, where the contractor is to recover his
or her costs plus an agreed amount or percentage for profit. This arrangement
tends to work to the disadvantage of the client, since there is no incentive
for the contractor to keep costs down. The price may also have bonuses
and penalties attached to it, so that the contractor will receive more
money if, for example, the job is completed earlier than the agreed time.
Whatever form the price takes for the job, it is usual for payments to
be made in stages as the work progresses, either on completion of certain
parts of the job by agreed dates or on the basis of some agreed method
of measuring the work. At the end of construction proper, it is common
for an agreed proportion of the price to be kept back by the clients until
snags have been put right or the structure has been commissioned.
During the course of the job, the contractor may encounter problems that
were not foreseen when the contract was made with the client. These might
require changes to the design, the construction method or the materials.
Usually such changes will create extra costs for the contractor, who then
seeks to recover from the client on the basis that these items become
agreed variations from the original contract. Sometimes recovery
of the cost of variations can make the difference for the contractor between
doing the job at a profit or loss.
The pricing of contracts can affect health and safety if inadequate provision
is made in the contractors tender to cover the costs of providing
safe access, lifting equipment and so on. This becomes even more difficult
where, in an attempt to ensure that they obtain value for money from contractors,
clients pursue a vigorous policy of competitive tendering. Governments
and local authorities apply policies of competitive tendering to their
own contracts, and indeed there may be laws requiring that contracts can
be awarded only on the basis of competitive tendering. In such a climate,
there is always a risk that the health and safety of construction workers
will suffer. In cutting costs, clients may resist a reduction in the standard
of construction materials and methods, but at the same time be totally
unaware that in accepting the lowest tender, they have accepted working
methods that are more likely to endanger construction workers. Even in
a situation of competitive tendering, contractors submitting tenders should
have to make clear to the client that their bid adequately covers the
cost of health and safety involved in their proposals.
Developers can influence health and safety in construction in ways similar
to clients, firstly by using contractors who are competent in health and
safety and architects who take health and safety into account in their
designs, and secondly in not automatically accepting the lowest tenders.
Developers generally want to be associated only with successful developments,
and one measure of success ought to be projects where there are no major
health and safety problems during the construction process
In the case of buildings, whether housing, commercial or industrial, projects
are subject to planning laws that dictate where certain types of development
may take place (e.g., that a factory may not be built among houses). Planning
laws may be very specific about the appearance, materials and size of
buildings. Typically areas identified as industrial zones are the only
places where factory buildings may be erected.
Often there are also building regulations or similar standards that specify
in precise detail many aspects of the design and specification of buildingsfor
example, the thickness of walls and timbers, depth of foundations, insulation
characteristics, size of windows and rooms, layout of electrical wiring
and earthing, layout of plumbing and pipework and many other issues. These
standards have to be followed by clients, designers, specifiers and contractors.
They limit their choices but at the same time ensure that buildings are
built to an acceptable standard. Planning laws and building regulations
thus affect the design of buildings and their cost.
Projects to build housing may consist of a single house or vast estates
of individual houses or flats. The client may be each individual householder,
who will then normally be responsible for maintenance of his or her own
house. The contractor will usually remain responsible for correcting defects
in construction for a period of months after building is finished. However,
if the project is for many houses, the client may be a public body, either
in local or national government, with responsibility for providing housing.
There are also large private bodies like housing associations for whom
numbers of houses may be built. Public or private bodies with responsibilities
for providing housing generally rent the finished houses to occupants,
retaining a greater or lesser degree of responsibility for maintenance
also. Building projects involving blocks of flats usually have a client
for the block as a whole, who then lets out individual flats under a leasing
arrangement. In this situation the owner of the block has responsibility
for carrying out maintenance but passes on the cost to the tenants. In
some countries ownership of individual flats in a block can rest with
the occupants of each flat. There has to be some arrangement, sometimes
through an estate management contractor, whereby maintenance can be carried
out and the necessary costs raised among the occupants.
Often houses are built on a speculative basis, by a developer. Specific
clients or occupants of those houses may not have been identified at the
outset but come on the scene after construction has begun and purchase
or rent the property like any other article. Houses are usually fitted
out with electrical, plumbing and drainage services and heating systems;
a gas supply may also be laid on. Sometimes in an attempt to cut costs,
houses are only partially finished, leaving it to the purchaser to install
some of the fittings and to paint or decorate the building.
Commercial buildings include offices, factories, schools, hospitals, shopsan
almost endless list of different types of buildings. In most cases these
buildings are constructed for a particular client. However, offices and
shops are often built on a speculative basis like housing, with the hope
of attracting buyers or tenants. Some clients require an office or shop
to be totally fitted out to their requirements, but very often the contract
is for the structure and main services, with the client making arrangements
to fit out the premises using specialist contractors in office and shop
Hospitals and schools are built for clients who have a clear idea of precisely
what they want, and the clients often provide design input into the project.
Plant and equipment in hospitals may cost more than the structure and
involve a great deal of design that has to satisfy stringent medical standards.
National or local government may also play a part in the design of schools
by laying down very detailed requirements on space standards and equipment
as part of its wider role in education. National governments usually have
very detailed standards as to what is acceptable in hospital buildings
and plant. Fitting out of hospitals and similarly complex buildings is
a form of construction work usually carried out by specialist subcontractors.
Such contractors not only require knowledge of health and safety in construction
in general, but also need expertise in ensuring that their operations
do not adversely affect the hospitals own activities.
Industrial building or construction involves use of the mass- production
techniques of manufacturing industry to produce parts of buildings. The
ultimate example is the house brick, but normally the expression is applied
to building using concrete parts or units that are assembled onsite. Industrial
construction expanded rapidly after the Second World War to meet the demand
for cheap housing, and it is more commonly found in mass housing developments.
Under factory conditions it is possible to mass produce cast units that
are consistently accurate in a way that would be virtually impossible
under normal site conditions.
Sometimes units for industrial construction are manufactured away from
the construction site in factories that may supply a wide area; sometimes,
where the individual development is itself very large, a factory is set
up onsite to serve that sole site.
Units designed for industrial construction must be structurally strong
enough to stand up to being moved, lifted and lowered; they must incorporate
anchorage points, or slots to permit safe attachment of lifting tackle,
and must also include appropriate lugs or recesses to permit the units
to fit together both easily and strongly. Industrial construction demands
plant for transporting and lifting units into position and space and arrangements
to store units safely when delivered to site, so that units are not damaged
and workers are not injured. This technique of building tends to produce
visually unattractive buildings, but on a large scale it is cheap; a whole
room can be assembled from six cast units with window and door openings
Similar techniques are used to produce concrete units for civil engineering
structures like elevated motorways and tunnel linings.
Some clients for industrial or commercial buildings containing extensive
complex plant wish simply to walk into a facility that will be up and
running from their first day in the premises. Laboratories are sometimes
constructed and fitted out on this basis. Such an arrangement is a turnkey
project, and here the contractor will ensure that all aspects of plant
and services are fully operational before handing the project over. The
job may be done under a design and build contract so that, in effect,
the turnkey contractor deals with everything from design to commissioning.
Civil Engineering and Heavy Construction
The civil engineering of which the public is most aware is work on highways.
Some highway work is the creation of new roads on virgin land, but much
of it is the extension and repair of existing highways. Contracts for
highway work are usually for state or local government agencies, but sometimes
roads remain under the control of contractors for some years after completion,
during which time they are permitted to charge tolls. If civil engineering
structures are being financed by government, then both the design and
actual construction will be subject to a high degree of supervision by
officials on behalf of government. Contracts for construction of highways
are usually let to contractors on the basis of a contractor being responsible
for a section of so many kilometers of the highway. There will be a main
contractor for each section; but highway construction involves a number
of skills, and aspects of the job such as steel work, concrete, shuttering
and surfacing may be subcontracted by the main contractor to specialist
firms. Highway construction is also sometimes carried out under management
contract arrangements, where a civil engineering consultancy will provide
management for the job, with all the work being done by subcontractors.
Such a management contractor may also have been involved in design of
Construction of highways requires the creation of a surface whose gradients
are suitable for the sort of traffic that will use it. In a generally
level terrain, creation of the foundation of the highway may involve earthmovingthat
is, shifting soil from cuttings to create embankments, building bridges
across rivers and driving tunnels through mountainsides where it is not
possible to go round the obstruction. Where labor costs are higher, such
operations are carried out using mechanically powered plant such as excavators,
scrapers, loaders and lorries. Where labor costs are lower, these processes
may be carried out manually by large numbers of workers using hand tools.
Whatever the actual methods adopted, highway construction requires high
standards of route surveying and planning of the job.
Highway maintenance frequently requires roads to remain in use whilst
repairs or improvements are carried out in part of the road. There is
thus a hazardous interface between traffic movement and construction operations
which makes good planning and management of the job even more important.
There are often national standards for signage and coning off of roadworks
and requirements as to the amount of separation there should be between
construction and traffic, which may be difficult to achieve in a confined
area. Control of traffic approaching roadworks is usually the responsibility
of the local police, but requires careful liaison between them and the
contractors. Highway maintenance creates traffic hold-ups, and accordingly
contractors are put under pressure to finish jobs quickly; sometimes there
are bonuses for finishing early and penalties for finishing late. Financial
pressures must not undermine safety on what is very dangerous work.
Surfacing of highways may involve concrete, stone or tarmacadam. This
requires a substantial logistical train to ensure that the required quantities
of surfacing materials are in place in the right condition to ensure that
surfacing proceeds without interruption. Tarmacadam requires special purpose
spreading plant that keeps the surfacing material plastic while spreading
it. Where the job is resurfacing, plant will be required including picks
and breakers so that the existing surface is broken up and removed. A
final finish is usually applied to the surfaces of highways involving
use of heavy powered rollers.
Creation of cuttings and tunnels may require use of explosives and then
arrangements to shift the muck displaced by the blasting. The sides of
cuttings may require permanent supports to prevent landslides or falls
of ground onto the finished road.
Elevated highways often require structures similar to bridges, especially
if the elevated section passes through an urban area when space is limited.
Elevated highways are often constructed from cast reinforced concrete
sections that are either cast in situ or cast in a fabrication area and
then shifted to the required position onsite. The work will require large-capacity
lifting machinery to lift cast sections, shuttering and reinforcing.
Temporary support arrangements or falsework to support sections
of either elevated highways or bridges while they are being cast in position
need to be designed to take into account the uneven loads imposed by concrete
as it is poured. Design of falsework is as important as design of the
Bridges in remote areas may be simple constructions from timber. More
commonly today bridges are from reinforced concrete or steel. They may
also be clad in brickwork or stone. If the bridge is to span a considerable
gap, whether above water or not, its design will require specialist designers.
Using todays materials, the strength of the bridge span or arch
is not achieved by mass material, which would be simply too heavy, but
by skillful design. The main contractor for a bridge building job is usually
a major general civil-engineering contractor with management expertise
and plant. However, specialist subcontractors may deal with major aspects
of the job like erection of steel work to form the span or casting or
placing cast sections of the span in place. If the bridge is over water,
one or both abutments that support the ends of the bridge may themselves
have to be constructed in water, involving piling, coffer dams, mass concrete
or stone work. A new bridge may be part of a new highway system, and approach
roads may have to be built, themselves possibly elevated.
Good design is especially important in bridge building, so that the structure
is strong enough to withstand the loads imposed on it in use and to ensure
that it will not require maintenance or repair too frequently. The appearance
of a bridge is often a very important factor, and again good design can
balance the conflicting demands of sound engineering and aesthetics. Provision
of safe means of access for maintenance of bridges needs to be taken into
account during design.
Tunnels are a specialized form of civil engineering. They vary in size
from the Channel Tunnel, with over 100 km of bores from 6 to 8 m in diameter,
to mini-tunnels whose bores are too small for workers to enter and which
are created by machines launched from access shafts and controlled from
the surface. In urban areas, tunnels may be the only way to provide or
improve transport routes or to provide water and drainage facilities.
The proposed route of the tunnel requires as detailed a survey as possible
to confirm the kind of ground that the tunnel workings will be in and
whether there will be groundwater. The nature of the ground, the presence
of groundwater and the end use of the tunnel all influence the choice
of tunneling method.
If the ground is consistent, like the chalk-clay beneath the English Channel,
then machine digging may be possible. If high groundwater pressures are
not encountered during pre- construction survey, then it is usually unnecessary
for the workings to be pressurized to keep out the water. If working in
compressed air cannot be avoided, this adds considerably to costs because
airlocks have to be provided, workers need to be allowed time to decompress,
and access to workings for plant and materials may be made more difficult.
A large tunnel for a road or railway in consistent non-hard-rock ground
might be dug using a full-face tunnel-boring machine (TBM). This is really
a train of different machines linked together and moving forward on rails
under its own power. The front face is a circular cutting head that rotates
and feeds spoil back through the TBM. Behind the cutting head are various
sections of the TBM that place the segments of tunnel lining rings in
position around the surface of the tunnel, grout behind the lining rings
and, in a very confined space, provide all the machinery to handle and
place ring segments (each weighing some tons), remove spoil, bring grout
and extra segments forward and house electric motors and hydraulic pumps
to power the cutting head and segment-placing mechanisms.
A tunnel in non-hard-rock ground which is not consistent enough to use
a TBM, may be dug using equipment such as roadheaders that bite into the
face of the heading. Spoil falling from the roadheader onto the tunnel
floor are to be collected by diggers and removed by lorry. This technique
permits digging of tunnels that are not circular in section. The ground
in which such a tunnel is dug will not usually have sufficient strength
for it to remain unlined; without some form of lining there might be falls
from roof and walls. The tunnel may be lined by liquid concrete sprayed
onto a steel mesh held in position by rock bolts (the New Austrian
tunneling method) or by cast concrete.
If the tunnel is in hard rock, the heading will be dug by means of blasting,
using explosives placed into shot holes drilled into the rock face. The
trick here is to use the minimum of blast to achieve a fall of rock in
the position and sizes required, thereby making it easier to remove the
spoil. On bigger jobs, multiple drills mounted on tracked bases will be
used along with diggers and loaders to remove spoil. Hard rock tunnels
are often simply trimmed to provide an even surface, but are not then
further lined. If the rock surface remains friable with a risk of pieces
falling, then a lining will be applied, usually some form of sprayed or
Whatever the method of construction adopted for the tunnel, the effective
supply of tunneling materials and removal of spoil are vital to the successful
progress of the job. Large tunneling jobs may require extensive narrow-gauge
construction rail systems to provide logistical support.
Dams invariably contain large quantities of earth or rock to provide mass
to resist the pressure from water behind them; some dams are also covered
in masonry or reinforced concrete. Depending on the length of the dam,
its construction often requires earthmoving on the very largest scale.
Dams tend to be built in remote locations dictated by the need to ensure
that water is available at a position where it is technically possible
to restrict the flow of the river. Thus temporary roads may have to be
built before dam building may start in order to get plant, materials and
personnel to the site. Workers on dam projects may be so far from home
that full-scale living accommodations have to be provided along with the
usual construction site facilities. It is necessary to divert the river
away from the site of the workings, and a coffer dam and temporary riverbed
may have be created.
A dam constructed simply from earth or rock that has been shifted will
require large scale excavation, digging and scraping plant as well as
lorries. If the dam wall is covered by masonry or cast concrete, it will
be necessary to employ high or long-reach cranes capable of depositing
masonry, shuttering, reinforcing and concrete in the right places. A continuous
supply of good-quality concrete will be necessary, and a concrete-mixing
plant will be necessary alongside the dam workings, with the concrete
either handled in batches by crane or pumped to the job.
Canals and docks
Construction and repair of canals and docks contain some aspects of other
jobs that have been described, such as roadworks, tunnels and bridges.
It is particularly important in canal building for surveying to be to
the highest standard before work begins, especially regarding levels and
to ensure that material that has had to be dug out can economically be
used elsewhere in the job. Indeed the early railway engineers owed a great
deal to the experience of canal builders a century before. The canal will
require a source for its water and will either tap into a natural source
such as a river or lake or create an artificial one in the form of a reservoir.
Digging of docks may start on dry land, but sooner or later has to link
up to either a river, a canal, the sea or another dock.
Canal and dock building requires excavators and loaders to open up the
ground. Spoil may be removed by lorry or water transport may be used.
Docks are sometimes developed on ground that has a long history of industrial
use. Industrial wastes may have escaped into such ground over many years,
and spoil removed in digging or extending the docks will be heavily contaminated.
Work in repairing a canal or dock is likely to have to be carried out
while adjacent parts of the system are kept in use. The workings may have
to rely on coffer dams for protection. Failure of a coffer dam during
extension of Newport Docks in Wales in the early years of this century
resulted in nearly 100 deaths.
Clients for canals and docks are likely to be public authorities. However,
sometimes docks are constructed for corporations alongside their major
production plants or for corporate clients to handle a particular type
of incoming or outgoing goods (e.g., motor cars). Repair and renovation
of canals is nowadays often for the leisure industry. Like dams, both
canal and dock construction may be in very remote situations, requiring
provision of facilities for workers beyond those of a normal construction
Construction of railroads or railways historically came after canals and
before major highways. Clients in railway construction contracts may be
rail operators themselves or governmental agencies, if the railways are
financed by government. As with highways, design of a railroad that is
economical and safe to build and operate depends on good surveying beforehand.
In general, locomotives do not operate effectively on steep gradients,
and therefore those designing layout of the track are concerned with avoiding
changes in levels, going round or through obstacles rather than over them.
Designers of railroads are subject to two constraints unique to the industry:
first, curves in the track layout must generally conform to very large
radii (otherwise trains cannot negotiate them); second, all the structures
connected with the railwayits bridge arches, tunnels and stationsmust
be capable of accommodating the envelope of the largest locomotives
and rolling stock that will use the track. The envelope is the silhouette
of the rolling stock plus clearance to allow safe passage through bridges,
tunnels and so on.
Contractors involved in building and repair of railroads require the usual
construction plant and effective logistical arrangements to ensure that
rail track and ballast as well as construction materials are always available
in what may be remote locations. Contractors may use the track they have
just laid to run trains supplying the works. Contractors involved in maintenance
of existing operational railways have to ensure that their work does not
interfere with the operations of the railway and endanger workers or the
The rapid expansion of air transportation since the middle of the 20th
century has resulted in one of the biggest and most complex forms of construction:
the building and extension of airports.
Clients for airport construction are usually governments at the national
or local level or agencies representing the government. Some airports
are built for major cities. Airports are rarely for private clients such
as business corporations.
Planning the work is sometimes made more difficult because of environmental
constraints that have been placed on the project in relation to noise
and pollution. Airports require a lot of space, and if they are located
in more heavily populated areas, creation of the runways and space for
terminal buildings and car parks may require reinstatement of derelict
or otherwise difficult land. Building an airport involves leveling a large
area, which may require earth moving and even land reclamation, and then
construction of a wide variety of often very large buildings, including
hangars, maintenance workshops, control towers and fuel storage facilities,
as well as terminal buildings and parking.
If the airport is being built on soft ground, buildings may require piled
foundations. Actual runways require good foundations; hardcore supporting
the surface layers of concrete or tarmac needs to be heavily compacted.
Plant used on airport construction is similar in scale and type to that
used in major highway projects, except that it is concentrated within
a limited area rather than over the many miles of a highway.
Airport maintenance is a particularly difficult type of work where resurfacing
the runways has to be integrated with continuing operation of the airport.
Usually the contractor is allowed an agreed number of hours during the
night when he or she can work on a runway that is temporarily taken out
of use. All the contractors plant, materials and workforce have
to be marshalled off the runways, prepared to move immediately to the
work site at the agreed start time. The contractor must finish his or
her work and get off the runways again at the agreed time when flights
may resume. Whilst working on the runway, the contractor must not impede
or otherwise endanger aircraft movement on other runways.
Health and Safety Consultant
All new buildings
and civil engineering structures go through the same cycle of conception
or design, groundworks, building or erection (including the roof of a
building), finishing and provision of utilities and final commissioning
before being brought into use. In the course of years, those once new
buildings or structures require maintenance including repainting and cleaning;
they are likely to be renovated by being updated or changed or repaired
to correct damage by weather or accident; and finally they will need to
be demolished to make way for a more modern facility or because their
use is no longer required. This is true of houses; it is also true of
large, complex structures like power stations and bridges. Each stage
in the life of a building or civil engineering structure presents hazards,
some of which are common to all work in construction (like the risk from
falls) or unique to the particular type of project (such as the risk from
collapse of excavations during preparation of foundations in either building
or civil engineering).
For each type of project (and, indeed, each stage within a project) it
is possible to forecast what will be the principal hazards to the safety
of construction workers. The risk from falls is common to all construction
projects, even those at ground level. This is supported by the evidence
of accident data which show that up to half of fatal accidents to construction
workers involve falls.
Physical hazards to those engaged in design of new facilities normally
arise from visits by professional staff to carry out surveys. Visits by
unaccompanied staff to unknown or abandoned sites may expose them to risks
from dangerous access, unguarded openings and excavations and, in a building,
to electrical wiring and equipment in a dangerous condition. If the survey
requires entry into rooms or excavations that have been closed for some
time, there is the risk of being overcome by carbon dioxide or reduced
oxygen levels. All hazards are increased if visits are made to an unlit
site after dark or if the lone visitor has no means of communicating with
others and summoning aid. As a general rule, professional staff should
not be required to visit sites where they will be on their own. They should
not visit after dark unless the site is well lit. They should not enter
enclosed spaces unless these have been tested and shown to be safe. Lastly,
they should be in communication with their base or have an effective means
of getting help.
Conception or design proper should play an important part in influencing
safety when contractors are actually working onsite. Designers, be they
architects or civil engineers, should be expected to be more than mere
producers of drawings. In creating their design, they should, by reason
of their training and experience, have some idea how contractors are likely
to have to work in putting the design into effect. Their competence should
be such that they are able to identify to contractors the hazards that
will arise from those methods of working. Designers should try to design
out hazards arising from their design, making the structure more
buildable as regards health and safety and, where possible,
substituting safer materials in the specifications. They should improve
access for maintenance at the design stage and reduce the need for maintenance
workers to be put at risk by incorporating features or materials that
will require less frequent attention during the life of the building.
In general, designers are able to design out hazards only to a limited
extent; there will usually be significant residual risks that the contractors
will have to take into account when devising their own safe systems of
work. Designers should provide contractors with information on these hazards
so that the latter are able to take both the hazards and necessary safety
procedures into account, firstly when tendering for the job, and secondly
when developing their systems of work to do the job safely.
The importance of specifying materials with better health and safety properties
tends to be underestimated when considering safety by design. Designers
and specifiers should consider whether materials are available with better
toxic or structural properties or that can be used or maintained more
safely. This requires designers to think about the materials that will
be used and to decide whether following previous practice will adequately
protect construction workers. Often cost is the determining factor in
choice of materials. However, clients and designers should realize that
while materials with better toxic or structural properties may have a
higher initial cost, they often yield much bigger savings over the life
of the building because construction and maintenance workers require less
expensive access or protective equipment.
Usually the first job to be done on the site after site surveys and laying
out of the site once the contract has been awarded (assuming there is
no need for demolition or site clearance) is groundworks for the foundations.
In the case of domestic housing, the footings are unlikely to require
excavations greater than half a meter and may be dug by hand. For blocks
of flats, commercial and industrial buildings and some civil engineering,
the foundations may need to be several meters below ground level. This
will require the digging of trenches in which work will have to carried
out to lay or erect the foundations. Trenches deeper than 1 m are likely
to be dug using machines such as excavators. Excavations are also dug
to permit laying of cables and pipes. Contractors often use special-purpose
excavators capable of digging deep but narrow excavations. If workers
have to enter these excavations, the hazards are essentially the same
as those encountered in excavations for foundations. However, there is
usually more scope in cable and pipe excavations or trenches to adopt
methods of working that do not require workers to enter the excavation.
Work in excavations deeper then 1 m needs especially careful planning
and supervision. The hazard is the risk of being struck by earth and debris
as the ground collapses along the side of the excavation. Ground is notoriously
unpredictable; what looks firm can be caused to slip by rain, frost or
vibration from other construction activities nearby. What looks like firm,
stiff clay dries out and cracks when exposed to the air or will soften
and slip after rain. A cubic meter of earth weighs more than 1 ton; a
worker struck by only a small fall of ground risks broken limbs, crushed
internal organs and suffocation. Because of the vital importance to safety
of selecting a suitable method of support for the sides of the excavation,
before work starts, the ground should be surveyed by a person experienced
in safe excavation work to establish the type and condition of the ground,
especially the presence of water.
Support for trench sides
Double-sided support. It is not safe to rely on cutting or battering
back the sides of the excavation to a safe angle. If the ground is wet
sand or silt, the safe angle of batter would be as low as 5 to 10°
above horizontal, and there is generally not enough room onsite for such
a wide excavation. The most common method of providing safety for work
in excavations is to support both sides of the trench through shoring.
With double-sided support, the loads from the ground on one side are resisted
by similar loads acting through struts between the opposing sides. Timber
of good quality must be used to provide vertical elements of the support
system, known as poling boards. Poling boards are driven into the
ground as soon as excavation begins; the boards are edge to edge, and
thus provide a timber wall. This is done on each side of the excavation.
As the excavation is dug deeper, the poling boards are driven into the
ground ahead of the excavation. When the excavation is a meter deep, a
row of horizontal boards (known as walings or wales) is
placed against the poling boards and then held in position by timber or
metal struts wedged between the opposing walings at regular intervals.
As digging proceeds, the poling boards are driven further into the ground
with their walings and struts, and it will be necessary to create a second
row of walings and struts if the excavation is deeper than 1.2 m. Indeed,
an excavation of 6 m could require up to four rows of walings.
The standard timber methods of support are unsuitable if the excavation
is deeper than 6 m or the ground is water bearing. In these situations,
other types of support for the sides of excavations are required, such
as vertical steel trench sheets, closely spaced with horizontal timber
walings and metal adjustable struts, or full-scale steel sheet piling.
Both methods have the advantage that the trench sheets or sheet piles
can be driven by machine before excavation proper starts. Also, trench
sheets and sheet piles can be withdrawn at the end of the job and reused.
Support systems for excavations deeper than 6 m or in water-bearing ground
should be custom designed; standard solutions will not be adequate.
Single-sided support. An excavation that is rectangular in shape
and too large for the support methods described above to be practicable
may have one or more of its sides supported by a row of poling boards
or trench sheets. These are themselves supported first by one or more
rows of horizontal walings which are themselves then held in place by
angled rakes back to a strong anchorage or support point.
Other systems. It is possible to use manufactured steel boxes of
adjustable width that may be lowered into excavations and within which
work can be carried out safely. It is also possible to use proprietary
waling frame systems, whereby a horizontal frame is lowered into the excavation
between the poling boards or trench sheets; the waling frame is forced
apart and applies pressure to keep the poling boards upright by the action
of hydraulic struts across the frame which can be pumped from a position
of safety outside the excavation.
Training and supervision. Whatever method of support is adopted,
the work should be carried out by trained workers under supervision of
an experienced person. The excavation and its supports should be inspected
each day and after each occasion that they have been damaged or displaced
(e.g., after a heavy rain). The only assumption one is entitled to make
regarding safety and work in excavations is that all ground is liable
to fail and therefore no work should ever be carried out with workers
in an unsupported excavation deeper than 1 m. See also the article Trenching
[CCE09AE] in this chapter.
Erection of the main part of the building or civil engineering structure
(the superstructure) takes place after completion of the foundation.
This part of the project usually requires work at heights above ground.
The biggest single cause of fatal and major injury accidents is falls
from heights or on the same level.
Even if the job is simply building a house, the number of workers involved,
the amount of building materials to be handled and, in later stages, the
heights at which work will have to be carried out all require more than
simple ladders for access and safe places of work.
There are limitations on the sort of work that can be done safely from
ladders. Work more than 10 m above ground is usually beyond the safe reach
of ladders; lengthy ladders themselves become dangerous to handle. There
are limitations on the reach of workers on ladders as well as on the amount
of equipment and materials they can safely carry; the physical strain
of standing on ladder rungs limits the time they can spend on such work.
Ladders are useful for carrying out short-duration, lightweight work within
safe reach of the ladder; typically, inspection and repair and painting
of small areas of the buildings surface. Ladders also provide access
in scaffolds, in excavations and in structures where more permanent access
has not yet been provided.
It will be necessary to use temporary working platforms, the most common
of which is scaffolding. If the job is a multistory block of flats, office
building or structure like a bridge, then scaffolding of varying degrees
of complexity will be required, depending on the scale of the job.
Scaffolds consist of easily assembled frameworks of steel or timber on
which working platforms may be placed. Scaffolds may be fixed or mobile.
Fixed scaffoldsthat is, those erected alongside a building or structureare
either independent or putlog. The independent scaffold has uprights
or standards along both sides of its platforms and is capable of remaining
upright without support from the building. The putlog scaffold has standards
along the outer edges of its working platforms, but the inner side is
supported by the building itself, with parts of the scaffold frame, the
putlogs, having flattened ends that are placed between courses of brickwork
to gain support. Even the independent scaffold needs to be rigidly tied
or secured to the structure at regular intervals if there are working
platforms above 6 m or if the scaffold is sheeted for weather protection,
thus increasing wind-loadings.
Working platforms on scaffolds consist of good-quality timber boards laid
so that they are level and both ends are properly supported; intervening
supports will be necessary if the timber is liable to sag due to loading
by people or materials. Platforms should never be less than 600 mm in
width if used for access and working or 800 mm if used also for materials.
Where there is a risk of falling more than 2 m, the outer edge and ends
of a working platform should be protected by a rigid guard rail, secured
to the standards at a height of between 0.91 and 1.15 m above the platform.
To prevent materials falling off the platform, a toe board rising at least
150 mm above the platform should be provided along its outer edge, again
secured to the standards. If guard rails and toe-boards have to be removed
to permit passage of materials, they should be replaced as soon as possible.
Scaffold standards should be upright and properly supported at their bases
on base plates, and if necessary on timber. Access within fixed scaffolds
from one working platform level to another is usually by means of ladders.
These should be properly maintained, secured at top and bottom and extend
at least 1.05 m above the platform.
The principal hazards in the use of scaffoldsfalls of person or
materialsusually arise from shortcomings either in the way the scaffold
is first erected (e.g., a piece such as a guard rail is missing) or in
the way it is misused (e.g., by being overloaded) or adapted during the
course of the job for some purpose that is unsuitable (e.g., sheeting
for weather protection is added without adequate ties to the building).
Timber boards for scaffold platforms become displaced or break; ladders
are not secured at top and bottom. The list of things that can go wrong
if scaffolds are not erected by experienced persons under proper supervision
is almost limitless. Scaffolders are themselves particularly at risk from
falls during erection and dismantling of scaffolds, because they are often
obliged to work at heights, in exposed positions without proper working
platforms (see figure 93.4).
93.4 Assembling scaffolding at a Geneva, Switzerland, construction site
without adequate protection
Tower scaffolds are either fixed or mobile, with a working platform
on top and an access ladder inside the tower frame. The mobile tower scaffold
is on wheels. Such towers easily become unstable and should be subject
to height limitations; for the fixed tower scaffold the height should
not be more than 3.5 times the shortest base dimension; for mobile, the
ratio is reduced to 3 times. The stability of tower scaffolds should be
increased by use of outriggers. Workers should not be permitted on the
top of mobile tower scaffolds while the scaffold is being moved or without
the wheels being locked.
The principal hazard with tower scaffolds is overturning, throwing people
off the platform; this may be due to the tower being too tall for its
base, failure to use outriggers or lock wheels or unsuitable use of the
scaffold, perhaps by overloading it.
Slung and suspended scaffolds. The other main category of scaffold
is those that are slung or suspended. The slung scaffold is essentially
a working platform hung by wire ropes or scaffold tubes from an overhead
structure like a bridge. The suspended scaffold is again a working platform
or cradle, suspended by wire ropes, but in this case it is capable of
being raised and lowered. It is often provided for maintenance and painting
contractors, sometimes as part of the equipment of the finished building.
In either case, the building or structure must be capable of supporting
the slung or suspended platform, the suspension arrangements must be strong
enough and the platform itself should be sufficiently robust to carry
the intended load of people and materials with guard sides or rails to
prevent them from falling out. For the suspended platform, there should
be at least three turns of rope on the winch drums at the lowest position
of the platform. Where there are no arrangements to prevent the suspended
platform from falling in the event of failure of a rope, workers using
the platform should wear a safety harness and rope attached to a secure
anchorage point on the building. Persons using such platforms should be
trained and experienced in their use.
The principal hazard with slung or suspended scaffolds is failure of the
supporting arrangements, either of the structure itself or the ropes or
tubes from which the platform is hung. This can arise from incorrect erection
or installation of the slung or suspended scaffold or from overloading
or other misuse. Failure of suspended scaffolds has resulted in multiple
fatalities and can endanger the public.
All scaffolds and ladders should be inspected by a competent person at
least weekly and before being used again after weather conditions that
may have damaged them. Ladders which have cracked styles or broken rungs
should not be used. Scaffolders who erect and dismantle scaffolds should
be given specific training and experience to ensure their own safety and
the safety of others who may use the scaffolds. Scaffolds are often provided
by one, perhaps the main, contractor for use by all contractors. In this
situation, tradespeople may modify or displace parts of scaffolds to make
their own job easier, without restoring the scaffold afterwards or realizing
the hazard they have created. It is important that the arrangements for
coordination of health and safety across the site deal effectively with
the action of one trade on the safety of another.
On some jobs, during both construction and maintenance, it may be more
practicable to use powered access equipment than scaffolding in its various
forms. Providing access to the underside of a factory roof undergoing
recladding or access to the outside of a few windows in a building may
be safer and cheaper than scaffolding out the whole structure. Powered
access equipment comes in a variety of forms from manufacturers, for example,
platforms that may be raised and lowered vertically by hydraulic action
or the opening and closing of scissor jacks and hydraulically-powered
articulated arms with a working platform or cage on the end of the arm,
commonly called cherry pickers. Such equipment is generally mobile
and can be moved to the place it is required and brought into use in a
matter of moments. Safe use of powered access equipment requires that
the job be within the specification for the machine as described by the
manufacturer (i.e., the equipment must not overreach or be overloaded).
Powered access equipment requires a firm, level floor on which to operate;
it may be necessary to put out outriggers to ensure that the machine does
not tip over. Workers on the working platform should have access to operating
controls. Workers should be trained in safe use of such equipment. Properly
operated and maintained, powered access equipment can provide safe access
where it may be virtually impossible to provide scaffolding, for example,
during the early stages of erection of a steel frame or to provide access
for steel erectors to the connecting points between columns and beams.
The superstructure of both buildings and civil engineering structures
often involves erection of substantial steel frames, sometimes of great
height. While responsibility for ensuring safe access for steel erectors
who assemble these frames rests principally with the management of steel
erection contractors, their difficult job can be made easier by the designers
of the steel work. Designers should ensure that patterns of bolt holes
are simple and facilitate easy insertion of bolts; the pattern of joints
and bolt holes should be as uniform as possible throughout the frame;
rests or perches should be provided on columns at joints with beams, so
that the ends of beams may rest still while steel erectors are inserting
bolts. As far as possible, the design should ensure that access stairs
form part of the early frame so that steel erectors have to rely less
on ladders and beams for access.
Also, the design should provide for holes to be drilled in suitable places
in the columns during fabrication and before the steel is delivered to
site, which will permit securing of taut wire ropes, to which steel erectors
wearing safety harnesses may secure their running lines. The aim should
be to get floor plates in place in steel frames as soon as possible, to
reduce the amount of time that steel erectors have to rely on safety lines
and harnesses or ladders. If the steel frame has to remain open and without
floors while erection continues to higher levels, then safety nets should
be slung below the various working levels. As far as possible, the design
of the steel frame and the working practices of the steel erectors should
minimize the extent to which workers have to walk steel.
While raising the walls is an important and hazardous stage in erecting
a building, putting the roof in place is equally important and presents
special hazards. Roofs are either flat or pitched. With flat roofs the
principal hazard is of persons or materials falling either over the edge
or down openings in the roof. Flat roofs are usually constructed either
from wood or cast concrete, or slabs. Flat roofs must be sealed against
entry of water, and various materials are used, including bitumen and
felt. All materials required for the roof have to be raised to the required
level, which may require goods hoists or cranes if the building is tall
or the quantities of covering and sealant are substantial. Bitumen may
have to be heated to assist spreading and sealing; this may involve taking
on to the roof a gas cylinder and melting pot. Roof-workers and persons
beneath can be burned by the heated bitumen and fires can be started involving
the roof structure.
The hazard from falls can be prevented on flat roofs by erecting temporary
edge protection in the form of guard rails of dimensions similar to the
guard rails in scaffolds. If the building is still surrounded by external
scaffolding, this can be extended up to roof level, to provide edge protection
for roof-workers. Falls down openings in flat roofs can be prevented by
covering them or, if they have to remain open, by erecting guard rails
Pitched roofs are most commonly found on houses and smaller buildings.
The pitch of the roof is achieved by erecting a wooden frame to which
the outer covering of the roof, usually clay or concrete tiles, is attached.
The pitch of the roof may exceed 45° above horizontal, but even a
shallower pitch presents hazards when wet. To prevent roof-workers from
falling while fixing battens, felt and tiles, roof ladders should be used.
If the roof ladder cannot be secured or supported at its bottom end, it
should have a properly designed ridge-iron that will hook over the ridge
tiles. Where there is doubt about the strength of ridge tiles, the ladder
should be secured by means of a rope from its top rung, over the ridge
tiles and down to a strong anchorage point.
Fragile roofing materials are used on both pitched and curved or barrel
roofs. Some roof lights are made of fragile materials. Typical materials
include sheets of asbestos cement, plastic, treated chipboard and wood-wool.
Because roof-workers frequently step through sheets they have just laid,
safe access to where the sheets are to be laid, and a safe position from
which to do it, are required. This is usually in the form of a series
of roof ladders. Fragile roofing materials present an even greater hazard
to maintenance workers, who may be unaware of their fragile nature. Designers
and architects can improve the safety of roof-workers by not specifying
fragile materials in the first place.
Laying of roofs, even flat roofs, can be dangerous in high winds or heavy
rain. Materials such as sheets, normally safe to handle, become dangerous
in such weather. Unsafe roof-work not only endangers roof-workers, but
also presents hazards to the public beneath. Erection of new roofs is
hazardous, but, if anything, maintenance of roofs is even more dangerous.
Renovation includes both maintenance of the structure and changes to it
during its life. Maintenance (including cleaning and repainting of woodwork
or other exterior surfaces, repointing of cement and repairs to walls
and the roof) presents hazards from falling similar to those of erection
of the structure because of the need to gain access to high parts of the
structure. Indeed, the hazards may be greater because during smaller,
short-duration maintenance jobs, there is a temptation to cut costs on
provision of safe access equipment, for example, by trying to do from
a ladder what can be safely done only from a scaffold. This is especially
true of roof work, where replacement of a tile may take only minutes but
there is still the possibility of a worker falling to his or her death.
Maintenance and cleaning
Designers, especially architects, can improve safety for maintenance and
cleaning workers by taking into account in their designs and specifications
the need for safe access to roofs, to plant rooms, to windows and to other
exposed positions on the outside of the structure. Avoiding the need for
access at all is the best solution, followed next by permanent safe access
as part of the structure, perhaps stairs or a walkway with guard rails
or a powered access platform permanently slung from the roof. The least
satisfactory situation for maintenance personnel is where a scaffold similar
to that used to erect the building is the only way to provide safe access.
This will be less of a problem for major, longer duration renovation work,
but on short-duration jobs, the cost of full scaffolding is such that
there is a temptation to cut corners and use mobile powered access equipment
or tower scaffolds where they are unsuitable or inadequate.
If renovation involves major re-cladding of the building or wholesale
cleaning using high-pressure water jetting or chemicals, total scaffolding
may be the only answer that will not only protect the workers but also
allow the hanging of sheeting to protect the public nearby. Protection
of workers involved in cleaning using high-pressure water jets includes
impervious clothing, boots and gloves, and a face screen or goggles to
protect the eyes. Cleaning involving chemicals such as acids will require
similar but acid-resistant protective clothing. If abrasives are used
to clean the structure a silica-free substance should be used. Since use
of abrasives will give rise to dust that may be injurious, approved respiratory
equipment should be worn by the workers. Repainting of windows in a tall
office building or block of flats cannot be done safely from ladders,
although this is usually possible on domestic housing. It will be necessary
to provide either scaffolding or to hang suspended scaffolds such as cradles
from the roof, ensuring that suspension points are adequate.
Maintenance and cleaning of civil engineering structures, like bridges,
tall chimneys or masts may involve working at such heights or in such
positions (e.g., above water) that prohibit the erection of a normal scaffold.
As far as possible, work should be done from a fixed scaffold slung or
cantilevered from the structure. Where this is not possible, work should
be done from a properly suspended cradle. Modern bridges often have their
own cradles as parts of the permanent structure; these should be checked
fully before being used for a maintenance job. Civil engineering structures
are often exposed to the weather, and work should not be permitted in
high winds or heavy rain.
Window cleaning presents its own hazards, especially where it is done
from the ground on ladders, or with improvised arrangements for access
on taller buildings. Window cleaning is not usually regarded as part of
the construction process, and yet is a widespread operation that can endanger
both the window cleaners and the public. Safety in window cleaning is,
however, influenced by one part of the construction process-design. If
architects fail to take into account the need for safe access, or alternatively
to specify windows of a design that can be cleaned from inside, then the
job of the window cleaning contractor will be much more hazardous. Whilst
designing out the need for external window cleaning or installing proper
access equipment as part of the original design may initially cost more,
there should be considerable savings over the life of the building in
maintenance costs and a reduction in hazards.
Refurbishment is an important and hazardous aspect of renovation. It takes
place when for example, the essential structure of the building or bridge
is left in place but other parts are repaired or replaced. Typically in
domestic housing, refurbishment involves stripping out windows, possibly
floors and stairs, along with wiring and plumbing, and replacing them
with new and usually upgraded items. In a commercial office building,
refurbishment involves windows and possibly floors, but also is likely
to involve stripping out and replacing cladding to a framed building,
installing new heating and ventilation equipment and lifts or total rewiring.
In civil engineering structures such as bridges, refurbishment may involve
stripping the structure back to its basic frame, strengthening it, renewing
parts and replacing the roadway and any cladding.
Refurbishment presents the usual hazards to construction workers: falling
and falling materials. The hazard is made more difficult to control where
the premises remain occupied during refurbishment, as is often the case
in domestic premises such as blocks of flats, when alternative accommodations
to house occupants are simply not available. In that situation the occupants,
especially children, face the same hazards as construction workers. There
may be hazards from power cables to portable tools such as saws and drills
required during refurbishment. It is important that the work be carefully
planned to minimize hazards to both workers and the public; the latter
need to know what will be going on and when. Access to rooms, stairs or
balconies where work is to be carried out should be prevented. Entrances
to blocks of flats may have to be protected by fans to protect persons
from falling materials. At the close of the working shift, ladders and
scaffolds should be removed or closed off in a manner that does not allow
children to get onto them and endanger themselves. Similarly, paints,
gas cylinders and power tools should be removed or stored safely.
In occupied commercial buildings where services are being refurbished,
it should not be possible for liftway doors to be opened. If refurbishment
interferes with fire and emergency equipment, special arrangements need
to be made to warn both occupants and workers if fire breaks out. Refurbishment
of both domestic and commercial premises may require removal of asbestos-containing
materials. This presents major health risks to the workers and the occupants
when they return. Such asbestos removal should be carried out only by
specially trained and equipped contractors. The area where asbestos is
being removed will need to be sealed off from other parts of the building.
Before the occupants return to areas from which asbestos has been stripped,
the atmosphere in those rooms should be monitored and the results evaluated
to ensure that asbestos fiber levels in air are below permissible levels.
Usually the safest way to carry out refurbishment is to totally exclude
occupants and members of the public; however, this is sometimes simply
Provision of utilities in buildings, such as electricity, gas, water and
telecommunications, is usually carried out by specialist subcontractors.
Principal hazards are falls due to poor access, dust and fumes from drilling
and cutting and electric shock or fire from electrical and gas services.
The hazards are the same in houses, only on a smaller scale. The job is
easier for contractors if proper allowance has been made by the architect
in designing the structure to accommodate the utilities. They require
space for ducts and channels in walls and floors plus sufficient additional
space for installers to operate effectively and safely. Similar considerations
apply to maintenance of utilities after the building has been taken into
use. Proper attention to the detailing of ducts, channels and openings
in the initial design of the structure should mean that these are either
cast or built into the structure. It will then not be necessary for construction
workers to chase out channels and ducts or to open up holes using power
tools, which create large quantities of harmful dust. If adequate space
is provided for heating and air conditioning ducts and equipment, the
job of the installers is both easier and safer because it is then possible
to work from safe positions rather than, for example, standing on boards
wedged across the inside of vertical ducts. If lighting and wiring have
to be installed overhead in rooms with high ceilings, contractors may
need scaffolding or tower scaffolds in addition to ladders.
Installation of utility services should be conform to recognized local
standards. These should, for example, cover all safety aspects of electrical
and gas installations so that contractors are in no doubt as to standards
required for wiring, insulation, earthing (grounding), fusing, isolation
and, for gas, protection for pipework, isolation, adequate ventilation
and fitting of safety devices for flame failure and loss of pressure.
Failure by contractors to deal adequately with these matters of detail
in the installation or maintenance of utilities will create hazards for
both their own workers and the occupants of the building.
If the structure is of brick or concrete, the interior finish may require
initial plastering to provide a surface which can be painted. Plastering
is a traditional craft trade. The principal hazards are severe strain
to the back and arms from handling bagged material and plaster boards
and then the actual plastering process, especially when the plasterer
is working overhead. After plastering, surfaces may be painted. The hazard
here is from vapors given off by thinners or solvents and sometimes from
the paint itself. If possible, water-based paints should be used. If solvent-based
paints have to be used, the rooms should be well ventilated, if necessary
by the use of fans. If materials used are toxic and adequate ventilation
cannot be achieved, then respiratory and other personal protection should
finishing may require the fixing of cladding or linings to the walls.
If this involves use of cartridge guns to secure the panels to timber
studding the hazard will principally arise from the way the gun is operated.
Cartridge-driven nails can easily be fired through walls and partitions
or can ricochet on striking something hard. Contractors need to plan this
work carefully, if necessary excluding other persons from the vicinity.
Finishing may require tiles or slabs of various materials to be fixed
to walls and floors. Cutting large quantities of ceramic tiles or stone
slabs using powered cutters gives rise to great quantities of dust and
should either be done wet or in an enclosed area. The principal hazard
with tiles, including carpet tiles, arises from the need to stick them
in position. Adhesives used are solvent based and give off vapors that
are harmful, and in an enclosed space they can be flammable. Unfortunately,
those laying tiles are kneeling down low over the point where vapors are
given off. Water-based adhesives should be used. Where solvent-based adhesives
have to be used, rooms should be well ventilated (fan assisted), the quantity
of adhesives brought into the workroom should be kept to a minimum and
drums should be decanted into smaller tins used by tilers outside the
If finishing requires installations of sound- or heat-insulation materials,
as is often the case in blocks of flats and commercial buildings, these
may be in the form of sheets or slabs that are cut, blocks that are laid
and fixed together or to a surface by a cement or in a wet form that is
sprayed. Hazards include exposure to dust that may both irritate and be
harmful. Asbestos-containing materials should not be used. If artificial
mineral fibers are used, respiratory protection and protective clothing
should be worn to prevent skin irritation.
Fire hazards in interior finishing
Many of the finishing operations in a building involve use of materials
that greatly increase the fire hazard. The basic structure may be relatively
nonflammable steel, concrete and brick. However, the finishing trades
introduce wood, possibly paper, paints and solvents.
At the same time that interior finishing is being performed work may be
going on nearby using electric powered tools, or the electrical services
may be being installed. Nearly always there is a source of ignition for
flammable vapor and materials used in finishing. Many very costly fires
have been ignited during finishing, putting workers at risk and usually
damaging not only the finishing of the building but also its main structure.
A building undergoing finishing is an enclosure in which possibly hundreds
of workers are using flammable materials. The main contractor should ensure
that proper arrangements are made to provide and protect means of escape,
keep access routes clear from obstructions, reduce the quantity of flammable
materials stored and in use inside the building, warn contractors of fire
and, when necessary, evacuate the building.
Some of the materials used in internal finishing may also be used on the
exterior, but exterior finishing is generally concerned with cladding,
sealing and painting. The cement courses in brick and block work are generally
pointed or finished as the bricks or blocks are laid and require
no further attention. The exterior of walls may be cement that is to be
painted or have an application of a layer of small stones, as in stucco
or roughcast. Exterior finishing, like general construction work, is done
outdoors and is subject to the effects of the weather. By far the greatest
hazard is the risk of falling, often heightened by difficulties in handling
components and materials. Use of paints, sealants and adhesives containing
solvents is less of a problem than in internal finishing because natural
ventilation prevents a buildup of harmful or flammable concentrations
Again, designers can influence the safety of exterior finishing by specifying
cladding panels that can be safely handled (i.e., not too heavy or large)
and making arrangements so that cladding can be done from safe positions.
The frames or floors of the building should be designed to incorporate
features like lugs or recesses that permit easy landing of cladding panels,
especially when placed in position by crane or hoist. Specification of
materials such as plastics for window frames and fascias eliminates the
need for painting and repainting and reduces subsequent maintenance. This
benefits the safety of both construction workers and the occupants of
house or flat.
Landscaping on a large scale may involve earth-moving similar to that
involved in highway and canal works. It may require deep excavations to
install drains; extensive areas may have to be slabbed or concreted; rocks
may have to be moved. Finally, the client may wish to create the impression
of a mature, well-established development, so that fully grown trees will
be planted. All of this requires excavation, digging and loading. It often
also requires considerable lifting capacity.
Landscape contractors are usually specialists who do not spend much of
their time working as part of construction contracts. The main contractor
should ensure that landscape contractors are brought to the site at an
appropriate time (not necessarily towards the end of the contract). Major
excavation and pipe laying may best be carried out early in the life of
the project, when similar work is being done for the foundations of the
building. Landscaping must not undermine or endanger the building or overload
the structure by heaping earth on or against it and its outbuildings in
a dangerous manner. If topsoil is to be removed and later placed back
in position, sufficient space to heap it in a safe manner will have to
Landscaping may also be required at industrial premises and public utilities
for safety and environmental reasons. Around a petrochemical plant it
may be necessary to level off the ground or provide a particular direction
of slope, possibly covering the ground with stone chips or concrete to
prevent the growth of vegetation. On the other hand, if landscaping around
industrial premises is intended to improve appearance or environmental
reasons (e.g., to reduce noise or hide an unsightly plant), it may require
embankments and erection of screens or planting of trees. Highways and
railroad tracks today have to include features that will reduce noise
if they are near urban areas or hide the operations if they are in environmentally
sensitive areas. Landscaping is not just an afterthought, because as well
as improving the appearance of the building or plant, it may, depending
on the nature of the development, preserve the environment and improve
safety generally. Therefore, it needs to be designed and planned as an
integral part of the project.
Demolition is perhaps the most dangerous construction operation. It has
all the hazards of working at heights and being struck by falling materials,
but it is carried out in a structure that has been weakened either as
part of the demolition, or as the result of storms, damage produced by
flood, fire, explosions or simple wear and tear. The hazards during demolition
are falls, being struck or buried in falling material or by the unintentional
collapse of the structure, noise and dust. One of the practical problems
with ensuring health and safety during demolition is that it can proceed
very rapidly; with modern equipment a great deal can be demolished in
a couple of days.
There are three principal ways of demolishing a structure: take it down
piecemeal; knock it or push it down; or blast it down using explosives.
Choice of method is dictated by the condition of the structure, its surroundings,
the reasons for the demolition and cost. Use of explosives will usually
not be possible when other buildings are close by. Demolition needs to
be planned as carefully as any other construction process. The structure
to be demolished should be thoroughly surveyed and any drawings obtained,
so that as much information as possible on the nature of the structure,
its method of construction and materials is available to the demolition
contractor. Asbestos is commonly found in buildings and other structures
that are to be demolished and requires contractors who are specialists
in handling it.
Planning of the demolition process should ensure that the structure is
not overloaded or unevenly loaded with debris and that there are suitable
openings for chuting of debris for safe removal. If the structure is to
be weakened by cutting parts of the frame (especially reinforced concrete
or other highly stressed types of structure) or by removing parts of a
building such as floors or internal walls, this must not so weaken the
structure that it may collapse unexpectedly. Debris and scrap materials
should be planned to fall in such a way that they can be removed or saved
safely and appropriately; sometimes the cost of a demolition job depends
on salvaging valuable scrap or components.
If the structure is to be demolished piecemeal (i.e., taken down bit by
bit), without using remotely operated powered picks and cutters, workers
will inevitably have to do the job using hand tools or handheld powered
tools. This means they may have to work at heights on exposed faces or
above openings created to allow debris to fall. Accordingly, temporary
scaffold working platforms will be necessary. The stability of such scaffolds
should not be endangered by removal of parts of the structure or fall
of debris. If stairs are no longer available for use by workers because
the stairwell opening is being used to chute debris external ladders or
scaffolds will be necessary.
Removal of points, spires or other tall features on the top of buildings
is sometimes done most safely by workers operating from properly-designed
buckets slung from the safety hook of a crane.
In piecemeal demolition, the safest method is to take the building down
in a sequence opposite to the way it was put up. Debris should be removed
regularly so that working places and access do not become obstructed.
If the structure is to be pushed or pulled over or knocked down, it is
usually pre-weakened, with the attendant hazards. Pulling down is sometimes
done by removing floors and internal walls, attaching wire ropes to strong
points on the upper parts of the building and using an excavator or other
heavy machine to pull on the wire rope. There is a real hazard from flying
wire ropes if they break due to overload or failure of the anchorage point
on the building. This technique is not suitable for very tall buildings.
Pushing over, again after pre-weakening, involves use of heavy plant such
as crawler-mounted grabs or pushers. The cabs of such equipment should
be shielded to prevent drivers from being injured by falling debris. The
site should not be allowed to become so obstructed by fallen debris as
to create instability for machine used to pull or push the building down.
The most common form of demolition (and if done properly, in many ways
the safest) is balling down, using a steel or concrete ball
suspended from a hook on a crane with a jib strong enough to withstand
the special strains imposed by balling. The jib is moved sideways and
the ball swung against the wall to be demolished. The principal hazard
is trapping the ball in the structure or debris, then trying to extricate
it by raising the crane hook. This grossly overloads the crane, and either
the crane cable or the jib may fail. It may be necessary for a worker
to climb up to where the ball is wedged and free it. However, this should
not be done if there is a risk of that part of the building collapsing
on the worker. Another hazard associated with less skilled crane operators
is balling too hard, so that unintended parts of the building are accidentally
Demolition using explosives can be done safely, but it must be carefully
planned and carried out only by experienced workers under competent supervision.
Unlike military explosives, the purpose of blasting to demolish a building
is not to totally reduce the building to a heap of rubble. The safe way
to do it is, after pre-weakening, to use no more explosive than will safely
bring down the structure so that debris can be safely removed and scrap
salvaged. Contractors carrying out blasting should survey the structure,
obtain drawings and as much information as possible on its method of construction
and materials. Only with this information is it possible to determine
whether blasting is appropriate in the first place, where charges should
be placed, how much explosive should be used, what steps may be necessary
to prevent ejection of debris and what sort of separation zones will be
required around the site to protect workers and the public. If there are
a number of explosive charges, electrical shotfiring with detonators will
usually be more practical, but electrical systems can develop faults,
and on simpler jobs the use of detonator cord may be more practical and
safer. Aspects of blasting that require careful preliminary planning are
what is to be done if there is either a misfire or if the structure does
not fall as planned and is left hanging in a dangerous state of instability.
If the job is close to housing, highways or industrial developments, the
people in the area should be warned; local police are usually involved
in clearing the area and halting pedestrian and vehicular traffic.
Tall structures like television towers or cooling towers may be felled
using explosives, providing they have been pre-weakened so that they fall
Demolition workers are exposed to high noise levels because of noisy machinery
and tools, falling debris or blasts from explosives. Hearing protection
will usually be required. Dust is produced in large quantities as buildings
are demolished. A preliminary survey should ascertain whether and where
lead or asbestos are present; if possible, these should be removed before
the start of the demolition. Even in the absence of such notable hazards,
dust from demolition is often irritating if not actually injurious, and
an approved dust mask should be worn if the work area cannot be kept wet
to control the dust.
Demolition is both dirty and arduous, and a high level of welfare facilities
should be provided, including toilets, washplaces, cloakrooms for both
normal clothing and work clothes and a place to shelter and take meals.
Dismantling differs from demolition in that part of the structure or,
more commonly, a large piece of machinery or equipment is disassembled
and removed from site. For example, removal of part or the whole of a
boiler from a power house in order to replace it, or replacement of a
steel girder bridge span is dismantling rather than demolition. Workers
involved in dismantling tend to do a great deal of oxyacetylene or gas
cutting of steel work, either to remove parts of the structure or to weaken
it. They may use explosives to knock over an item of equipment. They use
heavy lifting machinery to remove large girders or pieces of machinery.
Generally, workers engaged in such activities face all the same hazards
of falling, things falling on them, noise, dust and harmful substances
that are met in demolition proper. Contractors who carry out dismantling
require a sound knowledge of structures to ensure that they are taken
apart in a sequence that does not cause a sudden and unexpected collapse
of the main structure.
Work over and alongside water as in bridge building and maintenance, in
docks and sea and river defense work presents special hazards. The hazard
may be increased if the water is flowing or tidal, as opposed to still;
rapid water movement makes it more difficult to rescue those who fall
in. Falling in water presents the hazard of drowning (in even quite shallow
water if the person is injured in the fall as well as hypothermia if the
water is cold and infection if it is polluted).
The first precaution is to prevent workers from falling by ensuring that
there are proper walkways and workplaces with guard rails. These should
not be allowed to become wet and slippery. If walkways are not possible,
as perhaps in the earlier stages of steel erection, the workers should
wear harnesses and ropes attached to secure anchorage points. These should
be supplemented with safety nets slung beneath the work position. Ladders
and grablines should be provided to assist fallen workers to climb out
of the water, as, for example, at the edges of docks and sea defenses.
While workers are not on a properly boarded out platform with guard rails
or are traveling to and from their worksite, they should wear buoyancy
aids. Life buoys and rescue lines should be placed at regular intervals
along the edge of the water.
Work in docks, river maintenance and sea defenses often involves use of
barges to carry piling rigs and excavators to remove dredged out spoil.
Such barges are equivalent to working platforms and should have suitable
guard rails, life buoys and rescue and grab lines. Safe access from the
shore, dock or river side should be provided in the form of walkways or
gangways with guard rails. This should be so arranged as to adjust safely
with the changing levels of tidal water.
Rescue boats should be available, fitted with grablines and with life
buoys and rescue lines on board. If the water is cold or flowing, the
boats should be continuously staffed, and should be powered and ready
to carry out a rescue mission immediately. If water is polluted with industrial
effluent or sewage, arrangements should be made to transport those who
fall into such water to a medical center or hospital for immediate treatment.
Water in urban areas may be contaminated with the urine of rats, which
may infect open skin abrasions, causing Weils disease.
Work over water is often carried out in locations that are subject to
strong winds, driving rain or icing conditions. These increase the risk
of falls and heat loss. Severe weather may make it necessary to stop work,
even in the middle of a shift; to avoid excessive heat loss it may be
necessary to supplement normal wet or cold weather protective clothing
with thermal underclothing.
Diving is a specialized form of working underwater. The hazards faced
by divers are drowning, decompression sickness (or the bends),
hypothermia from the cold and becoming trapped below water. Diving may
be required during construction or maintenance of docks, sea and river
defenses and at piers and abutments of bridges. It is often required in
waters where visibility is poor or in locations where there is a risk
of entanglement for the diver and his or her equipment. Diving may be
carried out from dry land or from a boat. If the work requires only a
single diver, then as a minimum a team of three will be required for safety.
The team consists of the diver in the water, a fully equipped standby
diver ready to enter the water immediately in the event of an emergency
and a diving supervisor in charge. The diving supervisor should be at
the safe position on land or in the boat from which the diving is to take
Diving at depths less than 50 m is usually carried out by divers wearing
wet suits (i.e., suits that do not exclude water) and wearing self-contained
underwater breathing apparatus with an open face mask (i.e., SCUBA diving
gear). At depths greater than 50 m or in very cold water, it will be necessary
for divers to wear suits that are heated by a supply of pumped warm water
and closed diving masks, and equipment for breathing not compressed air
but air plus a mixture of gases (i.e., mixed-gas diving). Divers must
wear a suitable safety line and be able to communicate with the surface
and in particular with their diving supervisor. The local emergency services
should be advised by the diving contractor that diving is to take place.
Both divers and equipment require examination and testing. Divers should
be trained to a recognized national or international standard, firstly
and always for air diving and secondly for mixed-gas diving if this is
to take place. They should be required to provide written evidence of
successful completion of a diver training course. Divers should have an
annual medical examination with a doctor experienced in hyperbaric medicine.
Each diver should have a personal logbook in which a record of physicals
and of his or her dives is kept. If a diver has been suspended from diving
as a result of the physical, this also should be recorded in the logbook.
A diver under suspension should not be allowed to dive or act as a standby
diver. Divers should be asked by their diving supervisor if they are well,
especially whether they have any respiratory illness, before being allowed
to dive. Diving equipment, suits, belts, ropes, masks and cylinders and
valves should be checked every day before use.
Satisfactory operation of cylinder and demand valves should be demonstrated
by divers for their diving supervisor.
In the event of an accident or other reasons for the sudden ascent of
a diver to the surface, he or she may experience the bends or be at risk
of them and require to be recompressed. For this reason it is desirable
that the whereabouts of a medical or other decompression chamber suitable
for divers is located before diving starts. Those in charge of the chamber
should be alerted to the fact that diving is taking place. Arrangements
should be available for the rapid transport of divers requiring decompression.
Because of their training and equipment, plus all the backup required
for safety, use of divers is very expensive, and yet the amount of time
they are actually working on the riverbed may be limited. For these reasons
there are temptations for diving contractors to use untrained or amateur
divers or a diving team that is deficient in numbers and equipment. Only
reputable diving contractors should be used for diving in construction,
and particular care needs to be taken over the selection of divers who
claim to have been trained in other countries where standards may be lower.
Caissons are rather like a large inverted saucepans whose rims sit on
the bed of the harbor or river. Sometimes open caissons are used, which,
as their name implies, have an open top. They are used on land to sink
a shaft into soft ground. The bottom edge of the caisson is sharpened,
workers excavate inside the caisson, and it sinks into the ground as soil
is removed, thus creating the shaft. Similar open caissons are used in
shallow water, but their depth may be extended by adding sections on top
as the caisson sinks into the river or harbor bed. Open caissons rely
on pumping to control the entry of water and soil into the base of the
caisson. For deeper work still, a closed caisson will have to be used.
Compressed air is pumped into it to displace the water, and workers are
able to enter through an airlock, usually on top, and go down to work
in air on that bed. Workers are able to work under water but are freed
from the constraints of wearing diving equipment, and visibility is much
better. The hazards in pneumatic caisson work are the bends
and, as in all types of caisson including the simplest open caisson, drowning
if water gets into the caisson through any structural failure or loss
of air pressure. Because of the risk of entry of water, means of escape
such as ladders up to the entry point should be available at all times
in both open and pneumatic caissons.
Caissons should be inspected daily before they are used by someone competent
and experienced in caisson work. Caissons may be raised and lowered as
single units by heavy lifting equipment, or they may be constructed from
components in the water. Construction of caissons should be under the
supervision of a similarly competent person.
Tunneling, when carried out in porous ground beneath water, may need to
be done under compressed air. Driving tunnels for public transportation
systems in city centers beneath rivers is a widespread practice, owing
to lack of space above ground and environmental considerations. Compressed
air working will be as limited as possible because of its danger and inefficiency.
Tunnels beneath water in porous ground will be lined with concrete or
cast iron rings and grouted. But at the actual heading where the tunnel
is being dug and in the short length where tunnel rings are being placed
in position, there will not be a sufficiently watertight surface for the
work to proceed without some means of keeping out the water. Working under
compressed air may still be used for the tunnel head and ring or segment
placing part of the tunnel driving and lining process. Workers involved
in driving the heading (i.e., on a TBM operating the rotating cutting
head) or using hand tools, and those operating ring and segment placing
equipment, will have to pass through an airlock. The rest of the now lined
tunnel will not require to be compressed, and thus there will be easier
transit of personnel and materials.
Tunnelers who have to work in compressed air face the same hazard of the
bends as divers and caisson workers. The airlock giving access to the
compressed-air workings should be supplemented by a second airlock through
which workers pass at the end of the shift to be decompressed. If there
is only a single airlock, this may create bottlenecks and also be dangerous.
Hazards arise if workers are not decompressed sufficiently slowly at the
end of their shift or if lack of airlock capacity holds up entry of vital
equipment to the workings under pressure. Airlocks and decompression chambers
should be under the supervision of a competent person experienced in compressed-air
tunneling and proper decompression.
Jack L. Mickle & Associates
Trenches are confined
spaces usually dug to bury utilities or to place footings. Trenches are
normally deeper than they are wide, as measured at the bottom, and are
usually less than 6 m deep; they are also known as shallow excavations.
A confined space is defined as a space that is large enough for a worker
to enter and perform work, has limited means of entry and exit, and is
not designed for continuous occupancy. Several ladders should be provided
to enable workers to escape the trench.
Typically trenches are open only for minutes or hours. The walls of any
trench will eventually collapse; it is merely a matter of time. Short-term
apparent stability is a temptation for a contractor to send workers into
a dangerous trench in hopes of rapid progress and financial gain. Death
or serious injuries and mutilations can result.
In addition to being exposed to the possibility of collapsing trench walls,
workers in trenches, can be harmed or killed by engulfment in water or
sewage, exposure to hazardous gases or reduced oxygen, falls, falling
equipment or materials, contact with severed electrical cables and improper
Cave-ins account for at least 2.5% of annual work-related deaths in the
United States, for example. The average age of workers killed in trenches
in the US is 33. Often a young person is trapped by a cave-in and other
workers attempt a rescue. With failed rescue attempts, most of the dead
are would-be rescuers. Emergency teams trained in trench rescue should
be contacted immediately in the event of a cave-in.
Routine inspections of the trench walls and worker protection systems
are essential. Inspections should occur daily before the start of work
and after any occurrencesuch as rainstorms, vibration or broken
pipesthat may increase hazards. Following are descriptions of the
hazards and how to prevent them.
Trench Wall Collapse
The main cause of deaths related to trenching is collapsed trench walls,
which can crush or suffocate workers.
Trench walls may be weakened by activities outside but near a trench.
Heavy loads must not be placed on the edge of the wall. Trenches should
not be dug close to structures, such as buildings or railroads, because
the trenching may undermine the structures and weaken the foundations,
thus causing the structures and trench walls to collapse. Competent engineering
assistance should be sought in the planning stages. Vehicles must not
be permitted to approach too close to the sides of a trench; stop logs
or soil berms should be in place to prevent vehicles from doing so.
Types of soil and environment
Proper selection of a worker protection system depends on soil and environmental
conditions. Soil strength, the presence of water and vibration from equipment
or nearby sources affect the stability of trench walls. Previously excavated
soils never regain their strength. Accumulation of water in a trench,
regardless of depth, signals the most dangerous situation.
The soil must be classified and the construction scene evaluated before
an appropriate worker protection system is selected. A project safety
and health plan should address unique conditions and hazards related to
Soils can be divided into two main groups: cohesive and granular. Cohesive
soils contain a minimum of 35% clay and will not break when rolled into
threads 50 mm long and 3 mm in diameter and held by one end. With cohesive
soils, trench walls will stand vertically for short periods of time. These
soils are responsible for as many cave-in deaths as any other soil, because
the soil appears stable and precautions often are not taken.
Granular soils consist of silt, sand, gravel or larger material. These
soils exhibit apparent cohesion when wet (the sandcastle effect); the
finer the particle, the greater the apparent cohesion. When submerged
or dry, however, the coarser granular soils will immediately collapse
to a stable angle, 30 to 45°, depending on their particle angularity
Sloping prevents trench failure by removing the weight (of the
soil) that can lead to trench instability. Sloping, including benching
(sloping done in a series of steps), requires a wide opening at the top
of a trench. The angle of a slope depends on the soil and environment,
but slopes range from 0.75 horizontal: 1 vertical to 1.5 horizontal: 1
vertical. The slope of 1.5 horizontal: 1 vertical is set back 1.5 m on
each side at the top for each meter of depth. Even the slightest slope
is beneficial. However, the width requirements of slopes often make this
approach impracticable on construction sites.
Shoring can be used for all conditions. A shore consists of an
upright on each side of a trench, with braces in between (see figure
93.5 . Shores help prevent trench wall collapse by exerting outward
forces on a trench wall. Skip shores consist of vertical uprights and
cross braces with soil arching between; they are used in clays, the most
cohesive soils. Shores must be no more than 2 m apart from each other.
Greater distances between cross braces can be achieved by using wales
(or walings) to hold the uprights in place (see figure 93.6).
Close sheeting is used in granular and weaker cohesive soils; the trench
walls are covered entirely with sheeting (see figure 93.7).
Sheeting can be made of wood, metal or fiberglass; steel trench sheets
are common. Tight sheeting is used when flowing or seeping water is encountered.
Tight sheeting prevents water from eroding and bringing soil particles
into a trench. A shoring system must always be kept tight against the
soil to prevent collapse. Braces can be of wood or of screw, hydraulic
or pneumatic jacks. Wales can be of wood or metal.
93.5 Shores consist of uprights on each side of a trench with cross braces
93.6 Wales hold uprights in place, allowing greater distance between cross
93.7 Close sheeting is used in granular soils
trench boxes, are large personal protective devices; they do not prevent
trench wall collapse but protect workers who are inside. Shields are generally
made of steel or aluminum and their size commonly ranges from approximately
1 m to 3 m high and 2 to 7 m long; many other sizes are available. Shields
may be stacked on top of each other (figure 93.8).
Guard systems must be in place against hazardous movements of shields
in the event of a trench wall collapse. One way is to backfill on both
sides of a shield.
93.8 Shields protect workers from trench wall collapse
New products are available
that combine the qualities of a shore and a shield; some devices are useable
in particularly hazardous ground. Shield-shore units can be used as static
shields or can act as a shore by hydraulically or mechanically exerting
forces on the trench wall. The smaller units are particularly useful when
repairing breaks in utility pipes in city streets. Massive units with shield
panels can be forced into the ground by mechanical or hydraulic means. Soil
is then excavated from inside the shield.
Several steps are recommended to prevent engulfment by water or sewage in
a trench. First, known utilities should be contacted before digging to learn
where water (and other) pipes are located. Second, water valves that feed
pipes into the trench should be closed. Cave-ins that break water mains
or cause accumulations of water or sewage must be avoided. All utility pipes
and other utility equipment need to be supported.
Deadly Gases and Fumes and Insufficient Oxygen
Harmful atmospheres can lead to worker death or injury resulting from a
lack of oxygen, fire or explosion or toxic exposures. All trench atmospheres
where abnormal conditions are present or suspected should be tested. This
is especially true around buried garbage, vaults, fuel tanks, manholes,
swamps, chemical processors and other facilities that can release deadly
gases or fumes or deplete oxygen in the air. Construction equipment exhausts
must be dispersed.
Air quality should be determined with instruments from outside the trench.
This can be done by lowering a meter or its probe into the trench. The air
in trenches should be tested in the following order. First, oxygen must
be 19.5 to 23.5%. Second, flammability or explosibility must be no higher
than 10% of the lower flammable or explosive limits (LFLs or LELs). Third,
levels of potentially toxic substancessuch as hydrogen sulphide should
be compared with published information. (In the US, one source is the National
Institute for Occupational Safety and Health Pocket Guide to Chemical
Hazards, which gives, permissible exposure limits (PELs)). If the atmosphere
is normal, workers may enter. Ventilation may correct an abnormal atmosphere,
but monitoring must continue. Sewers and similar spaces where the air is
constantly changing usually require (or should require) a permit-entry procedure.
Permit-entry procedures require full equipment and a three-person team:
a supervisor, an attendant and an entrant.
Falls and Other Hazards
Falls into and within trenches can be prevented by providing safe and frequent
means for entering and exiting a trench, safe walkways or bridges where
workers or equipment are permitted or required to cross over trenches and
barriers adequate to stop other workers or bystanders or equipment from
approaching a trench.
Falling equipment or materials can cause death or injury through blows to
the head and body, crushing and suffocation. The spoil pile should be kept
at least 0.6 m from the edge of a trench, a barrier should be provided that
will prevent soil and rock material from rolling into the trench. All other
materials, such as pipes, must also be prevented from falling or rolling
into a trench. Workers must not be permitted to work under suspended loads
or loads handled by digging equipment.
All utilities should be marked prior to digging in order to prevent electrocution
or severe burns caused by contact with live power lines. Equipment booms
must not be operated near overhead power lines; if necessary, overhead lines
must be grounded out or removed.
Often, one death or severe injury in a trench is compounded by a poorly
thought-out rescue attempt. The victim and rescuers may become trapped and
overcome by deadly gases, fumes or lack of oxygen; drowned; or mutilated
by machines or rescue ropes. These compounded tragedies can be prevented
by following a safety and health plan. Equipment such as air testing meters,
water pumps and ventilators should be well-maintained, properly assembled
and available on the job. Management should train and require workers to
follow safe work practices and wear all necessary personal protective equipment.
Scott Schneider, Director
Occupational Safety and Health
Laborer's Health and Safety Fund
Tools are particularly
important in construction work. They are primarily used to put things
together (e.g., hammers and nail guns) or to take them apart (e.g., jackhammers
and saws). Tools are often classified as hand tools and power
tools. Hand tools include all non-powered tools, such as hammers and
pliers. Power tools are divided into classes, depending on the power source:
electrical tools (powered by electricity), pneumatic tools (powered by
compressed air), liquid-fuel tools (usually powered by gasoline), powder-actuated
tools (usually powered by an explosive and operated like a gun) and hydraulic
tools (powered by pressure from a liquid). Each type presents some unique
Hand tools include a wide range of tools, from axes to wrenches.
The primary hazard from hand tools is being struck by the tool or by a
piece of the material being worked on. Eye injuries are very common from
the use of hand tools, as a piece of wood or metal can fly off and lodge
in the eye. Some of the major problems are using the wrong tool for the
job or a tool that has not been properly maintained. The size of the tool
is important: some women and men with relatively small hands have difficulty
with large tools. Dull tools can make the work much harder, require more
force and result in more injuries. A chisel with a mushroomed head might
shatter on impact and send fragments flying. It is also important to have
the proper work surface. Cutting material at an awkward angle can result
in a loss of balance and an injury. In addition, hand tools can produce
sparks that can ignite explosions if the work is being done around flammable
liquids or vapors. In such cases, spark-resistant tools, such as those
made from brass or aluminum, are needed.
Power tools, in general, are more dangerous than hand tools, because
the power of the tool is increased. The biggest dangers from power tools
are from accidental startup and slipping or losing ones balance
during use. The power source itself can cause injuries or death, for example,
through electrocution with electrical tools or gasoline explosions from
liquid-fuel tools. Most power tools have a guard to protect the moving
parts while the tool is not in operation. These guards need to be in working
order and not overridden. A portable circular saw, for example, should
have an upper guard covering the top half of the blade and a retractable
lower guard which covers the teeth while the saw is not operating. The
retractable guard should automatically return to cover the lower half
of the blade when the tool is finished working. Power tools often also
have safety switches that shut off the tool as soon as a switch is released.
Other tools have catches that must be engaged before the tool can operate.
One example is a fastening tool that must be pressed against the surface
with a certain amount of pressure before it will fire.
One of the main hazards of electrical tools is the risk of electrocution.
A frayed wire or a tool that does not have a ground (that directs the
electrical circuit to the ground in an emergency) can result in electricity
running through the body and death by electrocution. This can be prevented
by using double-insulated tools (insulated wires in an insulated housing),
grounded tools and ground-fault circuit interrupters (which will detect
a leak of electricity from a wire and automatically shut off the tool);
by never using electrical tools in damp or wet locations; and by wearing
insulated gloves and safety footwear. Power cords have to be protected
from abuse and damage.
Other types of power tools include powered abrasive-wheel tools, like
grinding, cutting or buffing wheels, which present the risk of flying
fragments coming off the wheel. The wheel should be tested to make sure
it is not cracked and will not fly apart during use. It should spin freely
on its spindle. The user should never stand directly in front of the wheel
during startup, in case it breaks. Eye protection is essential when using
Pneumatic tools include chippers, drills, hammers and sanders.
Some pneumatic tools shoot fasteners at high speed and pressure into surfaces
and, as a result, present the risk of shooting fasteners into the user
or others. If the object being fastened is thin, the fastener may go through
it and strike someone at a distance. These tools can also be noisy and
cause hearing loss. Air hoses should be well connected before use to prevent
them from disconnecting and whipping around. Air hoses should be protected
from abuse and damage as well. Compressed-air guns should never be pointed
at anyone or against oneself. Eye, face and hearing protection should
be required. Jackhammer users should also wear foot protection in case
these heavy tools are dropped.
Gas-powered tools present fuel explosion hazards, particularly
during filling. They should be filled only after they have been shut down
and allowed to cool off. Proper ventilation must be provided if they are
being filled in a closed space. Using these tools in a closed space can
also cause problems from carbon monoxide exposure.
Powder-actuated tools are like loaded guns and should be operated
only by specially trained personnel. They should never be loaded until
immediately before use and should never left loaded and unattended. Firing
requires two motions: bringing the tool into position and pulling the
trigger. Powder-actuated tools should require at least 5 pounds (2.3 kg)
of pressure against the surface before they can be fired. These tools
should not be used in explosive atmospheres. They should never be pointed
at anyone and should be inspected before each use. These tools should
have a safety shield at the end of the muzzle to prevent the release of
flying fragments during firing. Defective tools should be taken out of
service immediately and tagged or locked out to make sure no one else
uses them until they are fixed. Powder-actuated fastening tools should
not be fired into material where the fastener could pass through and hit
somebody, nor should these tools be used near an edge where material might
splinter and break off.
Hydraulic power tools should use a fire-resistant fluid and be
operated under safe pressures. A jack should have a safety mechanism to
prevent it from being jacked up too high and should display its load limit
prominently. Jacks have to be set up on a level surface, centered, bear
against a level surface and apply force evenly to be used safely.
In general, tools should be inspected before use, be well-maintained,
be operated according to the manufacturers instructions and be operated
with safety systems (e.g., guards). Users should have proper PPE, such
as safety glasses.
Tools can present two other hazards that are often overlooked: vibration
and sprains and strains. Power tools present a considerable vibration
hazard to workers. The most well-known example is chain-saw vibration,
which can result in white-finger disease, where the nerves
and blood vessels in the hands are damaged. Other power tools can present
hazardous exposures to vibration for construction workers. As much as
possible, workers and contractors should purchase tools where vibration
has been dampened or reduced; anti-vibration gloves have not been shown
to solve this problem.
Poorly designed tools can also contribute to fatigue from awkward postures
or grips, which, in turn, can also lead to accidents. Many tools are not
designed for use by left-handed workers or individuals with small hands.
Use of gloves can make it harder to grip a tool properly and requires
tighter gripping of power tools, which can result in excessive fatigue.
Use of tools by construction workers for repetitive jobs can also lead
to cumulative trauma disorders, like carpal tunnel syndrome or tendinitis.
Using the right tool for the job and choosing tools with the best design
features that feel most comfortable in the hand while working can assist
in avoiding these problems.
Hans Goran Linder
National Board of Occupational Safety & Health
has undergone major changes. Once dependent upon craftsmanship with simple
mechanical aids, the industry now relies largely on machines and equipment.
New equipment, machinery, materials and methods have contributed to the
industrys development. Around the middle of the 20th century, building
cranes appeared, as did new materials like lightweight concrete. As time
went on, the industry began using prefabricated construction units along
with new techniques in the construction of buildings. Designers began
to use computers. Thanks to such equipment as lifting devices, some of
the work has become easier physically, but it has also become more complicated.
Instead of small, basic materials, such as bricks, tiles, board and light
concrete, prefabricated construction units are commonly used today. Equipment
has expanded from simple hand tools and transport facilities to complex
machinery. Similarly, methods have changed, for instance, from wheelbarrowing
to the pumping of concrete and from manual lifting of materials to the
lifting of integrated elements with the assistance of cranes.
Innovations in equipment, machinery and materials can be expected to continue
European Community Directives Relating to Workers Health and
In 1985, the European Community (EC) decided on a New Approach to
Technical Harmonization and Standards in order to facilitate the
free movement of goods. The New Approach directives are Community laws
which set out essential requirements for health and safety that must be
met before products may be supplied among member countries or imported
to the Community. One example of a directive with a fixed level of demands
is the Machine Directive (Council of the European Communities 1989). Products
meeting the requirements of such a directive are marked and can be supplied
anywhere in the EC. Similar systems exist for products covered by the
Construction Products Directive (Council of the European Communities 1988).
Besides the directives with such a fixed level of demands, there are directives
setting minimum criteria for workplace conditions. Community member states
must meet these criteria or, if they exist, satisfy a more stringent safety
level stipulated in their national regulations. Of specific relevance
to construction work are the Directive on the Minimum Safety and Health
Requirements for the Use of Work Equipment by Workers at Work (89/655/EEC)
and the Directive on the Minimum Safety and Health Requirements at Temporary
or Mobile Construction sites (92/57/EEC).
One of the types of construction equipment that frequently affects worker
safety is scaffolding, the primary means of providing a work surface at
elevations. Scaffolds are used in connection with construction, rebuilding,
restoration, maintenance and servicing of buildings and other structures.
Scaffold components may be used for other constructions such as support
towers (which are not considered scaffolds) or for the erection of temporary
structures such as grandstands (i.e., seating for spectators) and stages
for concerts and other public presentations. Their use is associated with
many occupational injuries, particularly those caused by falls from heights
(see also the article Lifts, escalators and hoists [CCE13AE]
in this chapter).
Types of scaffolds
Support scaffolds may be erected using vertical and horizontal tubing
connected by loose couplers. Prefabricated scaffolds are assembled from
parts manufactured in accord with standardized procedures that are permanently
attached to fixation devices. There are several types: the traditional
frame or modular type for building facades, mobile access towers (MATs),
craftsmen scaffolds and suspended scaffolds.
Vertical adjustment of the scaffold
The working planes of a scaffold are normally stationary. Some scaffolds,
however, have working planes that may be adjusted to different vertical
positions; they may be suspended from wires that raise and lower them,
or they may stand on the ground and be adjusted by hydraulic lifts or
prefabricated facade scaffolds
The erection of prefabricated facade scaffolds should follow the following
- Detailed erection
instructions should be provided by the manufacturer and kept at the
building site, and the work should be supervised by trained personnel.
Precautions should be taken to protect anyone walking under the scaffold
by blocking off the area, erecting additional scaffolding for the pedestrians
to walk under or creating a protective overhang.
- The base of the
scaffold should be placed on a firm, level surface. An adjustable steel
base plate should be placed on planking or boards to create a sufficient
surface area for weight distribution.
- A scaffold that
is more than 2 to 3.5 m off the ground should be equipped with fall
protection comprising a guard rail at a height of at least 1 m above
the platform, an intermediate guard rail and a toe board. To move tools
and supplies on or off the platform, the smallest possible opening in
the guard rail may be created with a foot stop and guard rail on either
side of it.
- Access to the
scaffold should normally be provided by stairs and not ladders.
- The scaffold should
be firmly secured to the wall of the building as directed by the manufacturers
- The stability
of the scaffold should be reinforced using diagonal elements (braces)
according to the manufacturers instructions.
- The scaffold should
be as close as possible to the facade of the building; if more than
350 mm, a second guard rail on the inside of the platform may be needed.
- If planks are
used for the platform, they must be secured to the scaffold structure.
A forthcoming European standard stipulates that the deflection (bending)
should be not more than 25 mm.
Earth-moving machinery is designed primarily to loosen, pick up, move,
transport and distribute or grade rock or earth and is of great importance
in construction, road-building and agricultural and industrial work (see
figure 93.9). Properly used, these machines are versatile
and can eliminate many of the risks associated with the manual handling
of materials. This type of equipment is highly efficient and is used worldwide.
93.9 Mechanical excavation at a construction site in France
that are used in construction work and in road-building include tractor-dozers
(bulldozers), loaders, backhoe loaders (figure 93.10),
hydraulic excavators, dumpers, tractor-scrapers, graders, pipelayers,
trenchers, landfill compactors and rope excavators.
93.10 Example of an articulated steer backhoe loader
The machine is versatile. It can be used for excavating, loading and lifting.
The angling of the machine (articulation) enables it to be used in confined
can endanger the operator and people working nearby. The following summary
of the hazards associated with earth-moving machines is based on the European
Community's Standard EN 474-1 (European Committee for Standardization
1994). It points out the safety related factors to be considered when
acquiring and using these machines.
The machine should provide safe access to the operators station
and maintenance areas.
The minimum space available to the operator should allow for all maneuvers
necessary for the safe operation of the machinery without excessive fatigue.
It should not be possible for the operator to have accidental contact
with the wheels or tracks or the working equipment. The engine exhaust
system should direct the exhaust gas away from the operators station.
A machine with an engine performance above 30 kW should be equipped with
an operators cab, unless the machine is being operated where the
year-round climate permits comfortable operation without a cab. Machines
having an engine performance less than 30 kW should be fitted with a cab
when intended for use where the air quality is poor. The airborne sound
power level of excavators, dozers, loaders and backhoe loaders should
be measured according to the international standard for measurement of
airborne exterior noise emitted by earth-moving machinery (ISO 1985b).
The cab should protect the operator against foreseeable weather conditions.
The interior of the cab should not present any sharp edges or acute angles
that may injure the operator if he or she falls or is thrown against them.
Pipes and hoses located inside the cab containing fluids that are dangerous
because of their pressure or temperature should be reinforced and guarded.
The cab should have an emergency exit separate from the usual doorway.
The minimum height of the ceiling above the seat (i.e., seat-index point)
depends on the size of the machines engine; for engines between
30 and 150 kW it should be 1,000 mm. All glass should be shatterproof.
The sound pressure level at the operators station should not exceed
85 dBA (ISO 1985c).
The design of the operators station should enable the operator to
see the traveling and work areas of the machine, preferably without having
to lean forward. Where the operators view is obscured, mirrors or
remote cameras with a monitor visible to the operator should enable him
or her to see the work area.
The front window and, if required, the rear window, should be fitted with
motorized windscreen wipers and washers. Equipment for defogging and defrosting
at least the front window of the cab should be provided.
Roll-over and falling object protection
Loaders, dozers, scrapers, graders, articulated steer dumpers and backhoe
loaders with an engine performance of more than 15 kW should have a structure
that will protect against roll-over. Machines intended for use where there
is a risk of falling objects should be designed for and fitted with a
structure that will protect the operator against falling material.
Machinery with provision for a seated operator should be fitted with an
adjustable seat that keeps the operator in a stable position and allows
him or her to control the machine under all expected operating conditions.
Adjustments to accommodate to the operators size and weight should
be easily made without the use of any tool.
The vibrations transmitted by the operators seat shall comply with
the relevant international vibration standard (ISO 1982) for tractor-dozers,
loaders and tractor-scrapers.
Controls and indicators
The main controls, indicators, hand levers, pedals, switches and so on
should be selected, designed and arranged so that they are clearly defined,
legibly labeled and within easy reach of the operator. Controls for machine
components should be designed so that they cannot accidentally start or
be moved, even if exposed to interference from radio or telecommunications
Pedals should have an appropriate size and shape, be surfaced with a nonskid
tread to prevent slipping and be adequately spaced. To avoid confusion
the machine should be designed to be operated like a motor vehicle, with
pedals located in the same way (i.e., with the clutch on the left, the
brake in the center and the accelerator on the right).
Remote-controlled earth-moving machinery should be so designed that it
stops automatically and remains immobile when controls are deactivated
or the power supply to them is interrupted.
should be equipped with:
- stop lights and
direction indicators for machines designed with a permissible traveling
speed over 30 km/h
- an audible warning
device controlled from the operators station and of which the
sound level should be at least 93 dBA at a 7 m distance from the front-end
of the machine and
- a device which
allows a flashing light to be fitted.
Creep (drift away) from the stopping position, for whatever reason (e.g.,
internal leakage) other than action of the controls, should be such that
it does not create a hazard to bystanders.
Steering and braking systems
The steering system should be such that the movement of the steering control
shall correspond to the intended direction of steering. The steering system
of rubber-tyred machinery with a traveling speed of more than 20 km/h
should comply with the international steering system standard (ISO 1992).
Machinery should be fitted with service, secondary and parking brake systems
that are efficient under all foreseeable conditions of service, load,
speed, ground conditions and slope. The operator should be able to slow
down and stop the machine by means of the service brake. In case it fails,
a secondary brake should be provided. A mechanical parking device should
be provided to keep the stopped machine from moving, and it should be
capable of remaining in the applied position. The braking system should
comply with the international braking system standard (ISO 1985a).
To permit night work or work in dusty conditions, earth-moving machines
should be fitted with large enough and bright enough lights to adequately
illuminate both the traveling and the work areas.
Earth-moving machinery, including components and attachments, should be
designed and constructed to remain stable under anticipated operating
Devices intended to increase the stability of earth-moving machinery in
working mode, such as outriggers and oscillating axle locking, should
be fitted with interlocking devices which keep them in position, even
in case of hydraulic hose failure.
Guards and covers
Guards and covers should be designed to be securely held in place. When
access is rarely required, the guards should be fixed and fitted so that
they are detachable only with tools or keys. Whenever possible, guards
should remain hinged to the machine when open. Covers and guards should
be fitted with a support system (springs or gas cylinders) to secure them
in the opened position up to a wind speed of 8 m/s.
Electrical components and conductors should be installed in such a way
as to avoid abrasion of wires and other wear and tear as well as exposure
to dust and environmental conditions which can cause them to deteriorate.
Storage batteries should be provided with handles and be firmly attached
in proper position while being easily disconnected and removed. Or, an
easily accessible switch placed between the battery and the earth should
allow the isolation of the battery from the rest of the electrical installation.
Tanks for fuel
and hydraulic fluid
Tanks for fuel and hydraulic and other fluids should have means for relieving
any internal pressure in case of opening and repair. They should have
easy access for filling and be provided with lockable filler caps.
The floor and interior of the operators station should be made of
fire-resistant materials. Machines with an engine performance exceeding
30 kW should have a built-in fire extinguisher system or a location for
installing a fire extinguisher that is easily reached by the operator.
Machines should be designed and built so that lubrication and maintenance
operations can be conducted safely, whenever possible with the engine
stopped. When maintenance can be performed only with equipment in a raised
position, the equipment should be mechanically secured. Special precautions
such as erecting a shield or, at least, warning signs, must be taken if
maintenance must be performed when the engine is running.
Each machine should bear, legibly and indelibly, the following information:
the name and address of the manufacturer, mandatory marks, designation
of series and type, the serial number (if any), the engine power (in kW),
the mass of the most usual configuration (in kg) and, if appropriate,
the maximum drawbar pull and maximum vertical load.
Other markings that may be appropriate include: conditions for use, mark
of conformity (CE) and reference to instructions for installation, use
and maintenance. The CE mark means that the machine meets the requirements
of European Community directives relevant to the machine.
When the movement of a machine creates hazards not obvious to a casual
spectator, warning signs should be affixed to the machine to warn against
approaching it while it is in operation.
Verification of safety requirements
It is necessary to verify that safety requirements have been incorporated
in the design and manufacture of an earth-moving machine. This should
be achieved through a combination of measurement, visual examination,
tests (where a method is prescribed) and assessment of the contents of
the documentation that is required to be maintained by the manufacturer.
The manufacturers documentation would include evidence that bought-in
components, such as windscreens, have been manufactured as required.
A handbook giving instructions for operation and maintenance should be
supplied and kept with the machine. It should be written in at least one
of the official languages of the country in which the machine is to be
used. It should describe in simple, readily understood terms the health
and safety hazards that may be encountered (e.g., noise and hand-arm or
whole-body vibration) and specify when personal protective equipment (PPE)
is needed. A space intended for the safekeeping of the handbook should
be provided in the operators station.
A service manual giving adequate information to enable trained service
personnel to erect, repair and dismantle machinery with minimum risk should
also be provided.
In addition to the above requirements for design, the instruction handbook
should specify conditions that limit use of the machine (e.g., the machine
should not travel at a greater angle of inclination than is recommended
by the manufacturer). If the operator discovers faults, damage or excessive
wear that may present a safety hazard, the operator should immediately
inform the employer and shut down the machine until the necessary repairs
The machine must not attempt to lift a load heavier than specified in
the capacity chart in the operating manual. The operator should check
how the slings are attached to the load and to the lifting hook and if
he or she finds that the load is not attached safely or has any concerns
about its safe handling, the lift should not be attempted.
When a machine is moved with a suspended load, the load should be kept
as near to the ground as possible to minimize potential instability, and
the travel speed should be adjusted to prevailing ground conditions. A
rapid change of speed should be avoided and care should be taken so the
load does not begin to swing.
When the machine is in operation, no one should enter the work area without
warning the operator. When the work requires individuals to remain within
a machines work area, they should observe great care and avoid unnecessarily
moving or remaining under a raised or suspended load. When someone is
within the work area of the machine, the operator should be particularly
careful and operate the machine only when that person is in the operators
view or his or her location has been signaled to the operator. Similarly,
for rotating machines, such as cranes and backhoes, the swing radius behind
the machine should be kept clear. If a truck must be positioned for loading
in a way such that falling debris might hit the drivers cab, no
one should remain in it, unless it is strong enough to withstand impact
of the falling materials.
At the beginning of the shift, the operator should check brakes, locking
devices, clutches, steering and the hydraulic system in addition to making
a functional test without a load. When checking the brakes, the operator
should make certain that the machine can be slowed down rapidly, then
stopped and safely held in position.
Before leaving the machine at the end of the shift, the operator should
place all operating controls in the neutral position, turn off the power
supply and take all necessary precautions to prevent unauthorized operation
of the machine. The operator should consider potential weather conditions
that might affect the supporting surface, perhaps causing the machine
to be frozen fast, tipped over or sunk, and take appropriate measures
to prevent such occurrences.
Replacement parts and components, such as hydraulic hoses, should be in
compliance with the specifications in the operating manual. Before attempting
any replacement or repair work in the hydraulic or compressed air systems,
the pressure should be relieved. The instructions and precautions issued
by the manufacturer should be observed when, for instance, a working attachment
is installed. PPE, such as a helmet and safety glasses, should be worn
when repair and maintenance work are done.
Positioning a machine for work
When positioning a machine, the hazards of overturning, sliding and subsidence
of the ground beneath it should be considered. When these appear to be
present appropriate blocking of adequate strength and surface area should
be provided to assure stability.
Overhead power lines
When operating a machine near overhead power lines, precautions against
contact with the energized lines should be taken. In this connection,
cooperation with the power distributor is advisable.
Underground pipes, cables and power lines
Prior to starting a project, the employer has the responsibility to determine
if any underground power lines, cables or gas, water or sewer pipes are
located within the work site and, if so, to determine and mark their precise
location. Specific instructions for avoiding them must be given to the
machine operator, for instance, through a call before you dig
Operation on roads with traffic
When a machine is operated on a road or other place open to public traffic,
road signs, barriers and other safety arrangements appropriate for the
traffic volume, vehicle speed and local road regulations should be used.
It is recommended that transport of a machine on a public highway should
be executed by truck or trailer. The hazard of overturning should be considered
when the machine is being loaded or unloaded, and it should be secured
so that it will not shift while in transit.
Materials used in construction include asbestos, asphalt, brick and stone,
cement, concrete, flooring, foil sealing agents, glass, glue, mineral
wool and synthetic mineral fibers for insulation, paints and primers,
plastic and rubber, steel and other metals, wallboard, gypsum and wood.
Many of these are covered in other articles in this chapter or elsewhere
in this Encyclopedia.
The use of asbestos for new construction is prohibited in some countries
but, almost inevitably, it will be encountered during the renovation or
demolition of older buildings. Accordingly, stringent precautions are
required to protect both the workers and the public against exposures
to asbestos that was previously installed.
Bricks, concrete and stone
Bricks are made of fired clay and grouped into facing bricks and brick
stones. They can be solid or designed with holes. Their physical properties
depend on the clay used, any added materials, the method of manufacture
and the incineration temperature. The higher the incineration temperature,
the less absorbency the brick will exhibit.
Bricks, concrete and stone containing quartz can produce silica dust when
cut, drilled or blasted. Unprotected exposures to crystalline silica can
increase susceptibility to tuberculosis and cause silicosis, a disabling,
chronic and potentially fatal lung disease.
Materials commonly used for interior flooring include stone, brick, floorboard,
textile carpeting, linoleum and plastic. The installation of terrazzo,
tile or wood flooring can expose a worker to dusts that can cause skin
allergies or damage the nasal passages or lungs. In addition, the glues
or adhesives used for installing tiles or carpeting often contain potentially
Carpetlayers can damage their knees from kneeling and striking a kicker
with the knee in stretching the carpeting to fit the space.
Glue is used to join materials through adhesion. Water-based glue contains
a binding agent in water and hardens when water evaporates. Solvent glues
harden when the solvent evaporates. Since the vapors can be harmful to
health, they should not be used in very close or poorly ventilated areas.
Glues consisting of components that harden when mixed can produce allergies.
Mineral wool and other insulation
The function of insulation in a building is to achieve thermal comfort
and to reduce energy consumption. To achieve acceptable insulation, porous
materials, such as mineral wool and synthetic mineral fibers, are used.
Great care must be taken to avoid inhaling the fibers Sharp fibers can
even penetrate the skin and cause an annoying dermatitis.
Paints and primers
Paints are used to decorate the exterior and interior of the building,
protect materials like steel and wood against corrosion or decay, make
objects easier to clean and provide signals or road-markings.
Lead-based paints are now being avoided, but they may be encountered during
the renovation or demolition of older structures, particularly those made
of metal, such as bridges and viaducts. Inhaled or swallowed fumes or
dusts can cause lead poisoning with kidney damage or permanent nervous
system damage; they are particularly dangerous for children who may be
exposed to lead dusts carried home on work clothes or shoes. Precautionary
measures must be taken whenever lead-based paints are used or encountered.
Use of cadmium- and mercury-based paints is prohibited for use in most
countries. Cadmium can cause kidney problems and some forms of cancer.
Mercury can damage the nervous system.
Oil-based paints and primers contain solvents which may be potentially
hazardous. To minimize solvent exposures, the use of water-based paints
Plastic and rubber
Plastic and rubber, known as polymers, can be grouped into thermoplastic
or thermosetting plastic and rubber. These materials are used in construction
for tightening, insulation, coating, and for products like piping and
fittings. Foil made of plastic or rubber is used for tightening and moisture-proof
lining and may cause reactions in workers sensitized to these materials.
Steel, aluminum and copper
Steel is used in construction work as a supporting structure, in reinforcement
rods, mechanical components and facing material. Steel may be carbon or
alloy; stainless steel is a type of alloy. Important steel properties
are its strength and toughness. Fracture toughness is important in order
to avoid brittle fractures.
The properties of steel depends on its chemical composition and structure.
Steel is heat-treated in order to release internal strain and to improve
weldability, strength and fracture toughness.
Concrete can withstand considerable pressure, but reinforcement bars and
nets are required for acceptable tensile strength. These bars typically
have a considerable carbon content (0.40%).
Carbon steel or mild steel contains manganese, which, when
released in fumes during welding, can cause a Parkinsons disease-like
syndrome, which can be a crippling nervous disorder. Aluminum and copper
can also, under certain conditions, be harmful to health.
Stainless steels contain chromium, which increases corrosion resistance,
and other alloy elements, such as nickel and molybdenum. But welding of
stainless steel can expose workers to chromium and nickel fumes. Some
forms of nickel can cause asthma or cancer; some forms of chromium can
cause cancer and sinus problems and nose holes (erosion of
the nasal septum).
Next to steel, aluminum is the most commonly used metal in construction,
because the metal and its alloys are light, strong and corrosion-resistant.
Copper is one of the most important metals in engineering, because of
its corrosion-resistance and high conductivity for electricity and heat.
It is used in energized lines, as roof and wall coating and for piping.
When used as a roof coating, copper salts in the rain runoff can be harmful
to the immediate environment.
Wallboard and gypsum
Wallboard, often coated with asphalt or plastic, is used as a protective
layer against water and wind and to prevent seepage of moisture through
the building elements. Gypsum is crystallized calcium sulphate. Gypsum
board consists of a sandwich of gypsum between two layers of cardboard;
it is widely used as wall covering, and is fire-resistant.
Dust produced when cutting wallboard can lead to skin allergies or lung
damage; carrying oversize or heavy board in awkward postures can cause
Wood is widely used for construction. It is important to use seasoned
timber for construction work. For beams and roof trusses of considerable
span, glue-laminated wood units are used. Measures are advisable to control
wood dust, which, depending on the species, can cause a variety of ailments
including cancer. Under certain conditions, wood dust can also be explosive.
Francis Hardy, Project
Construction Safety Association of Ontario
A crane is a machine
with a boom, primarily designed to raise and lower heavy loads. There
are two basic crane types: mobile and stationary. Mobile cranes can be
mounted on motor vehicles, boats or railroad cars. Stationary cranes can
be of a tower type or mounted on overhead rails. Most cranes today are
power driven, though some still operate manually. Their capacity, depending
on the type and size, ranges from a few kilograms to hundreds of tons.
Cranes are also used for pile driving, dredging, digging, demolition and
personnel work platforms. Generally, a cranes capacity is greater
when the load is closer to its mast (center of rotation) and less when
the load is further away from its mast.
Accidents involving cranes are usually costly and spectacular. Injuries
and fatalities involve not only workers, but sometimes innocent bystanders.
Hazards exist in all facets of crane operation, including assembly, dismantling,
travel and servicing. Some of the most common hazards involving cranes
hazards. Overhead powerline contact and arcing of electrical current
through the air can occur if the machine or hoist line is close enough
to the powerline. When powerline contact occurs, the danger is not just
limited to the operator of the hoist, but extends to all personnel in
the immediate vicinity. Twenty three percent of crane fatalities in
the United States, for example, in 19881989 involved powerline
contact. Aside from injury to humans, electrical current can cause structural
damage to the crane.
failure and overloading. Structural failure occurs when a crane
or its rigging components are overloaded. When a crane is overloaded,
the crane and its rigging components are subject to structural stresses
that may cause irreversible damage. Swinging or sudden dropping of the
load, using defective components, hoisting a load beyond capacity, dragging
a load and side-loading a boom can cause overloading.
failure. Instability failure is more common with mobile cranes than
stationary ones. When a crane moves a load, swings its boom and moves
beyond its stability range, the crane has a tendency to topple. Ground
conditions can also cause instability failure. When a crane is not leveled,
its stability is reduced when the boom is oriented in certain directions.
When a crane is positioned on ground that cannot bear its weight, the
ground can give way, causing the crane to topple. Cranes have also been
known to tip when traveling on poorly compacted ramps on construction
- Material falling
or slipping. Material can fall or slip if not properly secured.
Falling material can injure workers in the vicinity or cause property
damage. Undesired movement of material can pinch or crush workers involved
in the rigging process.
- Improper servicing,
assembling and dismantling procedures. Poor access, lack of fall
protection and poor practices have injured and killed workers when servicing,
assembling and dismantling cranes. This problem is most common with
mobile cranes where service is performed in the field and there is lack
of access equipment. Many cranes, particularly older models, do not
provide handrails or steps to facilitate getting to some sections of
the crane. Servicing around the boom and top of the cab is dangerous
when workers walk on the boom without fall-arrest equipment. On lattice-boom
cranes, incorrect loading and unloading as well as assembly and disassembly
of the boom has caused sections to fall onto the workers. The boom sections
were either not properly supported during these operations, or the rigging
of the lines to support the boom was improper.
- Hazard to the
helper or oiler. A very hazardous pitch point is created as the
upper portion of a crane rotates past the stationary lower section during
normal operations. All helpers working around the crane should stay
clear of the deck of the crane during operation.
- Physical, chemical
and stress hazards to the crane operator. When the cab is not insulated,
the operator can be subjected to excessive noise, causing loss of hearing.
Seats that are not properly designed can cause back pain. Lack of adjustment
to the seat height and tilt can result in poor visibility from operating
positions. Poor cab design also contributes to poor visibility. Exhaust
from gasoline or diesel engines on cranes contains fumes that are hazardous
in confined areas. There is also concern over the effect of whole-body
vibration from the engine, particularly in older cranes. Time constraints
or fatigue can also play a part in crane accidents.
Safe operation of a crane is the responsibility of all parties involved.
Crane manufacturers are responsible for designing and manufacturing cranes
that are stable and structurally sound. Cranes must be rated properly
so that there are enough safeguards to prevent accidents caused by overloading
and instability. Instruments such as load-limiting devices and angle and
boom length indicators aid operators in the safe operation of a crane.
(Powerline sensory devices have proved to be unreliable.) Every crane
should have a reliable, efficient, automatic safe- load indicator. In
addition, crane manufacturers must make accommodations in the design that
facilitate safe access for servicing and safe operation. Hazards can be
reduced by clear design of control panels, providing a chart at the operators
fingertips that specifies load configurations, handrails, non-glare windows,
windows that extend to the cab floor, comfortable seats and both noise
and thermal insulation. In some climates, heated and air-conditioned cabs
contribute to the workers comfort and reduce fatigue.
Crane owners are responsible for keeping their machines in good condition
by ensuring regular inspection and proper maintenance and employing competent
operators. Crane owners must be knowledgeable so that they can recommend
the best machine for a particular job. A crane assigned to a project should
have the capacity to handle the heaviest load it must carry. The crane
should be fully inspected by a competent person before being assigned
to a project, and then daily and periodically (as suggested by the manufacturer),
with a maintenance record kept. Ventilation should be provided to remove
or dilute engine exhaust from cranes working in enclosed areas. Hearing
protection, when necessary, should be provided. Site supervisors must
plan ahead. With proper planning operating near overhead powerlines can
be avoided. When work must be done near high-voltage power lines, clearance
requirements should be followed (see table 93.6 [CCE06TE]).
When working near powerlines cannot be avoided, the line should either
be de-energized or insulated.
93.6 Required clearance for normal voltage in operation near high-voltage
* Meters have been converted
from recommendations in feet. Source: ASME 1994.
in kilovolts (phase to phase)
clearance in meters (and feet)*
|Up to 50
|From 50 to 200
|From 200 to
|From 350 to
|From 500 to
|From 750 to
Signalers should be used to aid the operator near the limit of approach
around powerlines. The ground, including access in and around the site,
must have the ability to bear the weight of the crane and the load it is
lifting. If possible, the crane operating area should be roped off to prevent
injuries from overhead lifting. A signaler must be used when the operator
cannot see the load clearly. The crane operator and the signaler must be
trained and competent in hand signals and other aspects of the job. Proper
rigging attachments must be supplied so that riggers can secure the load
from falling or slipping. The rigging crew must be trained in the attachment
and dismantling of loads. Good communication is vital in safe crane operations.
The operator must carefully follow the manufacturers recommended procedures
when assembling and disassembling the boom before operating the crane. All
safety features and warning devices should be in working order and should
not be disconnected. The crane must be leveled and be operated according
to the crane load chart. Outriggers must be fully extended or set according
to manufacturers recommendations. Overloading can be prevented by
the operators knowing the weight to be lifted in advance and by using
load-limiting devices as well as other indicators. The operator should always
use sound craning practices. All loads must be fully secured before they
are lifted. Movement with a load must be slow; the boom should never be
extended or lowered so that it compromises the stability of the crane. Cranes
should not be operated when visibility is poor or when the wind can cause
the operator to lose control of the load.
Standards and Legislation
There are numerous written standards or guidelines for recommended manufacturing
and operating practices. Some are based on design principles, some on performance.
Subjects covered in these standards include methods of testing various safety
devices; design, construction and characteristics of the cranes; inspection,
testing, maintenance and operation procedures; recommended equipment and
control layout. These standards form the basis of government and company
health and safety regulations and operator training.
Escalators and Hoists
J. Staal, Technical
Secretary; John Quackenbush, International Representative
Federation Europeenne de la Manutention; International Union of Elevator
An elevator (lift) is a permanent lifting installation serving two or
more defined landing levels, comprising an enclosed space, or car, whose
dimensions and means of construction clearly permit the access of people,
and which runs between rigid vertical guides. A lift, therefore, is a
vehicle for raising and lowering people and/or goods from one floor to
another floor within a building directly (single push-button control)
or with intermediate stops (collective control).
A second category is the service lift (dumb waiter), a permanent lifting
installation serving defined levels, but with a car that is too small
to transport people. Service lifts transport foods and supplies in hotels
and hospitals, books in libraries, mail in office buildings and so on.
Generally, the floor area of such a car does not exceed 1 m2, its depth
1 m, and its height 1.20 m.
Elevators are driven directly by an electric motor (electric lifts; see
figure 93.11) or indirectly, through the movement
of a liquid under pressure generated by a pump driven by an electric motor
93.11 A cutaway view of an elevator installation showing the essential
Electric lifts are almost exclusively driven by traction machines, geared
or gearless, depending on car speed. The designation traction
means that the power from an electric motor is transmitted to the multiple
rope suspension of the car and a counterweight by friction between the
specially shaped grooves of the driving or traction sheave of the machine
and the ropes.
Hydraulic lifts have become widely used since the 1970s for the transport
of goods and passengers, usually for a height not exceeding six floors.
Hydraulic oil is used as pressure fluid. The direct-acting system with
a ram supporting and moving the car is the simplest one.
Technical Committee 178 of the ISO has drafted standards for: loads and
speeds up to 2.50 m/s; car and hoistway dimensions to accommodate passengers
and goods; bed and service lifts for residential buildings, offices, hotels,
hospitals and nursing homes; control devices, signals and additional accessories;
and selection and planning of lifts in residential buildings. Each building
should be provided with at least one lift accessible to handicapped people
in wheelchairs. The Association française de normalisation (AFNOR)
is in charge of the Secretariat of this Technical Committee.
General safety requirements
Every industrialized country has a safety code drawn up and kept up to
date by a national standards committee. Since this work was started in
the 1920s, the various codes have gradually been made more similar, and
differences now are generally not fundamental. Large manufacturing firms
produce units that comply with the codes.
In the 1970s the ILO, in close cooperation with the International Committee
for the Regimentation of Lifts (CIRA), published a code of practice for
the construction and installation of lifts and service lifts and, a few
years later, for escalators. These directives are intended as a guide
for countries engaged in the drafting or modification of safety rules.
A standardized set of safety rules for electric and hydraulic lifts, service
lifts, escalators and passenger conveyors, the object being the elimination
of technical barriers to trade among the member countries of the European
Community, is also under the purview of the European Committee for Standardization
(CEN). The American National Standards Institute (ANSI) has devised a
safety code for lifts and escalators.
Safety rules are aimed at several types of possible accidents with lifts:
shearing, crushing, falling, impact, trapping, fire, electric shock, damage
to material, accidents due to wear, and accidents due to corrosion. People
to be safeguarded are: users, maintenance and inspection personnel and
people outside the hoistway and the machine room. Objects to be safeguarded
are: loads in the car, components of the lift installation and the building.
Committees drawing up safety rules have to assume that all components
are correctly designed, are of sound mechanical and electrical construction,
are made of material of adequate strength and suitable quality and are
free from defects. Potential imprudent acts of users have to be taken
Shearing is prevented by providing adequate clearances between moving
components and between moving and fixed parts. Crushing is prevented by
providing sufficient headroom at the top of the hoistway between the roof
of the car in its highest position and the top of the shaft and a clear
space in the pit where someone can remain safely when the car is in its
lowest position. These spaces are assured by buffers or stops.
Protection against falling down the hoistway is obtained by solid landing
doors and an automatic cut off that prevents movement of the cab until
the doors are fully closed and locked. Landing doors of the power-operated
sliding type are preferred for passenger lifts.
Impact is limited by restraining the kinetic energy of closing power-operated
doors; trapping of passengers in a stalled car is prevented by providing
an emergency unlocking device on the doors and a means for specially trained
personnel to open them and extricate the passengers.
Overloading of a
car is prevented by a strict ratio between the rated load and the net
floor area of the car. Doors are required on all the cars passenger lifts
to keep passengers from being trapped in the space between the car sill
and the hoistway or the landing doors. Car sills must be fitted with a
toe guard of a height of not less than 0.75 m to prevent accidents, as
shown in figure 93.12 . Cars have to be provided
with safety gear capable of stopping and holding a fully loaded car in
the event of overspeed or failure of the suspension. The gear is operated
by an overspeed governor driven by the car by means of a rope (see figure
93.11). As passengers stand upright and move in a vertical direction,
the retardation during the operation of the safety device should lie between
0.2 and 1.0 g (m/s2) to guard against injuries (g = standard acceleration
of free fall).
93.12 Layout of the toe guard on the car sill to prevent trapping
Depending on national
legislation, lifts intended mainly for the transport of goods, vehicles
and motor cars accompanied by authorized and instructed users may have
one or two opposite car entrances not provided with car doors, under the
condition that the rated speed does not exceed 0.63 m/s, the car depth
is not less than 1.50 m and the wall of the hoistway facing the entrance,
including the landing doors, is flush and smooth. On heavy-duty freight
elevators (goods lifts), the landing doors are usually vertical BI-parting
power-operated doors, which usually do not meet these conditions. In such
a case, the required car door is a vertically sliding mesh gate. The clear
width of the lift car and the landing doors must be the same to avoid
damage to panels on the lift car by fork trucks or other vehicles entering
or leaving the lift. The whole design of such a lift has to take account
of the load, the weight of the handling equipment and the heavy forces
involved in running, stopping and reversing these vehicles. The lift car
guides require special reinforcement. When the transport of people is
permitted, the number allowed should correspond to the maximum available
area of the car floor. For example, the car floor area of a lift for a
rated load of 2,500 kg should be 5 m2, corresponding to 33 persons. Loading
and accompanying a load must be done with great care. Figure 93.13
shows a faulty situation.
93.13 Example of dangerous loading of a freight elevator (goods-lift).
All modern lifts are push-button and computer controlled, the car switch
system operated by an attendant having been abandoned.
Single lifts and those grouped in two- to eight-car arrangements are usually
equipped with collective controls which are interconnected in the case
of multiple installations. The main feature of collective controls is
that calls can be given at any moment, whether the car is moving or standstill
and whether the landing doors are open or closed. Landing and car calls
are collected and stored until answered. Regardless of the sequence in
which they are received, calls are answered in the order that most efficiently
operates the system.
Examinations and tests
Before a lift is put into service, it should be examined and tested by
an organization approved by the public authorities to establish the lifts
conformity with the safety rules in the country where it has been installed.
A technical dossier should be submitted to the inspector by the manufacturers.
The elements to be examined and tested and the way the tests should be
run are listed in the safety code. Specific tests by an approved laboratory
are required for: locking devices, landing doors (possibly including fire
tests), safety gear, overspeed governors and oil buffers. Certificates
of the corresponding components used in the installation should be included
in the register. After a lift is put into service, periodic safety examinations
should be conducted, with the intervals depending on traffic volume. These
tests are intended to ensure compliance with the code and the proper operation
of all safety devices. Components that do not function in normal service,
such as the safety gear and buffers, should be tested with a car empty
and at reduced speed to prevent excessive wear and stresses that can impair
the safety of a lift.
Maintenance and inspection
A lift and its components should be inspected and maintained in good and
safe working order at regular intervals by competent technicians who have
obtained skill and a thorough knowledge of the mechanical and electrical
details of the lift and the safety rules under the guidance of a qualified
instructor. Preferably the technician is employed by the supplier or erector
of the lift. Normally a technician is responsible for a specific number
of lifts. Maintenance involves routine servicing such as adjustment and
cleaning, lubrication of moving parts, preventive servicing to anticipate
possible problems, emergency visits in the case of breakdowns and major
repairs, which are usually done after consultation with a supervisor.
The overriding safety hazard, however, is fire. Because of the risk that
a lit cigarette or other burning object might fall into the crack between
the car sill and the hoistway and ignite lubricating grease in the hoistway
or debris at the bottom, the hoistway should regularly be cleaned out.
All systems should be at zero energy level before maintenance work is
begun. In single-unit buildings, before any work is started, notices should
be posted at each landing indicating that the lift is out of service.
For preventive maintenance, careful visual inspection and checks of free
movement, the condition of contacts and proper operation of the equipment
are generally sufficient. The hoistway equipment is inspected from the
top of the car. An inspection control is provided on the car roof comprising:
a BI-stable switch to bring it into operation and to neutralize the normal
control, including the operation of power-operated doors. Up and down
constant pressure buttons allow movement of the car at reduced speed (not
exceeding 0.63 m/s). The inspection operation must remain dependent on
the safety devices (closed and locked doors and so on) and it should not
be possible to overrun the limits of normal travel.
A stop switch on the inspection control station prevents unexpected movement
of the car. The safest direction of travel is down. The technician must
be in a safe position to observe the work environment when moving the
car and possess the appropriate inspection devices. The technician must
have a firm hold when the car is in motion. Before leaving, the technician
must report to the person in charge of the lift.
An escalator is a continuous moving, inclined stairway which conveys passengers
upward and downward. Escalators are used in commercial buildings, department
stores and railway and underground stations, to guide a stream of people
in a confined route from one level to another.
General safety requirements
Escalators consist of a continuous chain of steps moved by a motor-driven
machine by means of two roller chains, one at each side. The steps are
guided by rollers on tracks which keep the step treads horizontal in the
usable area. At the entrance and exit, guides ensure that over a distance
of 0.80 to 1.10 m, depending on the speed and rise of the escalator, some
steps form a horizontal flat surface. Step dimensions and construction
are shown in figure 93.14 . On the top of each balustrade,
a handrail should be provided at a height of 0.85 to 1.10 m above the
nose of the steps running parallel to the steps at substantially the same
speed. The handrail at each extremity of the escalator, where the steps
move horizontally, should extend at least 0.30 m beyond the landing plate
and the newel including the handrail at least 0.60 m beyond (see figure
93.15). The handrail should enter the newel at a
low point above the floor, and a guard should be installed with a safety
switch to stop the escalator if fingers or hands are trapped at this point.
Other risks of injury to users are formed by the clearances necessary
between the side of the steps and the balustrades, between steps and combs
and between treads and step risers, the latter more particularly in the
upward direction at the curvature where a relative movement between consecutive
steps occurs. The cleating and smoothness of the risers should prevent
Figure 93.14 Escalator step unit 1
X: Height to next step (not greater than 0.24m); Y: Depth (at least 0.38m);
Z: Width (between 0.58 and 1.10m); D: Grooved step tread; F: Cleated step
93.15 Escalator step unit 2
People may ride with
their shoes sliding against the balustrade, which can cause trapping at
the points where the steps straighten out. Clearly legible signs and notices,
preferably pictographs, should warn and instruct users. A sign should
instruct adults to hold the hands of children, who may not be able to
reach the handrail, and that children should stand at all times. Both
ends of an escalator should be barricaded when it is out of service.
The incline of an escalator should not exceed 30°, though it may be
increased to 35° if the vertical rise is 6 m or less and the speed
along the incline is limited to 0.50 m/s. Machine rooms and driving and
return stations should be easily accessible to specially-trained maintenance
and inspection personnel only. These spaces can lie inside the truss or
be separate. The clear height should be 1.80 m with covers, if any, opened
and the space should be sufficient to ensure safe working conditions.
The clear height above the steps at all points should be not less than
The starting, stopping or reversal of movement of an escalator should
be effected by authorized people only. If the country code permits operating
a system that starts automatically when a passenger moves past an electric
sensor, the escalator should be in operation before the user reaches the
comb. Escalators should be equipped with an inspection control system
for operation during maintenance and inspection.
Maintenance and inspection
Maintenance and inspection along the lines described above for lifts are
usually required by authorities. A technical dossier should be available
listing the main calculation data of the supporting structure, steps,
step driving components, general data, layout drawings, schematic wiring
diagrams and instructions. Before an escalator is put into service, it
should be examined by a person or organization approved by the public
authorities; subsequently periodic inspections at given intervals are
Moving Walkways (Passenger Conveyors)
A passenger conveyor, or power-driven continuous moving walkway, may be
used for the conveyance of passengers between two points at the same or
at different levels. Passenger conveyors are used to transport a great
number of people in airports from the main station to the gates and back
and in department stores and supermarkets. When the conveyors are horizontal,
baby carriages, pushcarts and wheelchairs, luggage and food trolleys can
be carried without risk, but on inclined conveyors these vehicles, if
rather heavy, should be used only if they lock into place automatically.
The ramp consists of metal pallets, similar to the step treads of escalators
but longer, or rubber belt. The pallets must be grooved in the direction
of travel, and combs should be placed at each end. The angle of inclination
should not exceed 12° or more than 6° at the landings. The pallets
and belt should move horizontally over a distance of not less than 0.40
m before entering the landing. The walkway runs between balustrades that
are topped with a moving handrail that travels at substantially the same
speed. The speed should not exceed 0.75 m/s unless the movement is horizontal,
in which case 0.90 m/s is permitted provided the width does not exceed
The safety requirements for passenger conveyors are generally similar
to those for escalators and should be included in the same code
Building hoists are temporary installations used on construction sites
for the transport of persons and materials. Each hoist is a guided car
and should be operated by an attendant inside the car. In recent years,
rack and pinion design has enabled the use of building hoists for efficient
movement along radio towers or very tall smoke stacks for servicing. No
one should ride a material hoist, except for inspection or maintenance.
The standards of safety vary considerably. In a few cases, these hoists
are installed with the same standard of safety as permanent goods and
passenger lifts in buildings, except that the hoistway is enclosed by
strong wire mesh instead of solid materials to reduce the wind load. Strict
regulations are needed although they need not be as strict as for passenger
lifts; many countries have special regulations for these building hoists.
However, in many cases the standard of safety is low, the construction
poor, the hoists driven by a diesel engine winch and the car suspended
by only a single steel wire rope. A building hoist should be driven by
electric motors to ensure that the speed is kept within safe limits. The
car should be enclosed and be provided with car entrance protections.
Hoistway openings at the landings should be fitted with doors that are
solid up to a height of 1 m from the floor, the upper part in wire mesh
of maximum 10 ´ 10 mm aperture. Sills of landing doors and cars
should have suitable toe guards. Cars should be provided with safety gear.
One common type of accident results when workers travel on a platform
hoist designed only for carrying goods, which do not have side walls or
gates to keep the workers from striking a part of the scaffolding or from
falling off the platform during the journey. A belt lift consists of steps
on a moving vertical belt. A rider is at risk of being carried over the
top, being unable to make an emergency stop, striking his or her head
or shoulders on the edge of a floor opening, jumping on or off after the
step has passed the floor level or being unable to reach the landing because
of power failure or the belts stopping. Accordingly, such a lift
should be used only by specially trained personnel employed by the building
owner or a designee.
Generally, the hoistway for any lift extends over the full height of a
building and interconnects the floors. A fire or the smoke from a fire
breaking out in the lower part of a building may spread up the hoistway
to other floors and, under certain circumstances, the well or hoistway
may intensify a fire because of a chimney effect. Therefore, a hoistway
should not form part of a buildings ventilation system. The hoistway
should be totally enclosed by solid walls of noncombustible material that
would not give off harmful fumes in case of a fire. A vent should be provided
at the top of the lift hoistway or in the machine room above it to allow
smoke to escape to open air.
Like the hoistway, the entrance doors should be fire resistant. Requirements
are usually laid down in national building regulations and vary according
to countries and conditions. Landing doors cannot be made smokeproof if
they are to operate reliably.
No matter how tall the building, passengers should not use lifts in case
of fire, because of the risks of the lift stopping at a floor in the fire
zone and of passengers being trapped in the car in the event of failure
of the electrical supply. In general, one lift that serves all floors
is designated as a lift for firefighters that can be put at their disposal
by means of a switch or special key on the main floor. The capacity, speed
and car dimensions of the firefighters lift have to meet certain
specifications. When firefighters use lifts, the normal operational controls
The construction, maintenance and refinishing of elevator interiors, installation
of carpeting and cleaning of the elevator (inside or out) may involve
the use of volatile organic solvents, mastics or glues, which can present
a risk to the central nervous system, as well as a fire hazard. Although
these materials are used on other metal surfaces, including staircases
and doors, the hazard is severe with elevators because of their small
space, in which vapor concentrations can become excessive. The use of
solvents on the outside of an elevator car can also be risky, again because
of limited air flow, particularly in a blind hoistway, where venting may
be impeded. (A blind hoistway is one without an exit door, usually extending
for several floors between two destinations; where a group of elevators
serves floors 20 and above, a blind hoistway would extend between floors
1 and 20.)
Lifts and Health
While lifts and hoists involve hazards, their use can also help reduce
fatigue or serious muscle injury due to manual handling, and they can
reduce labor costs, especially in building construction work in some developing
countries. On some such sites where no lifts are used, workers have to
carry heavy loads of bricks and other building materials up inclined runways
numerous floors high in hot, humid weather.
L. Prodan; G Bachofen,
Chief of Branch
CLUJ-NAPOCA; Swiss National Accident Insurance Organization
Adapted from the
3rd edition Encyclopedia of Occupational Health and Safety
articles Cement by L. Prodan and Concrete and reinforced
concrete work by G. Bachofen.
Cement is a hydraulic bonding agent used in building construction and
civil engineering. It is a fine powder obtained by grinding the clinker
of a clay and limestone mixture calcined at high temperatures. When water
is added to cement it becomes a slurry that gradually hardens to a stone-like
consistency. It can be mixed with sand and gravel (coarse aggregates)
to form mortar and concrete.
There are two types of cement: natural and artificial. The natural cements
are obtained from natural materials having a cement-like structure and
require only calcining and grinding to yield hydraulic cement powder.
Artificial cements are available in large and increasing numbers. Each
type has a different composition and mechanical structure and has specific
merits and uses. Artificial cements may be classified as Portland cement
(named after the town of Portland in the United Kingdom) and aluminous
The Portland process, which accounts for by far the largest part of world
cement production, is illustrated in figure 93.16
. It comprises two stages: clinker manufacture and clinker grinding. The
raw materials used for clinker manufacture are calcareous materials such
as limestone and argillaceous materials such as clay. The raw materials
are blended and ground either dry (dry process) or in water (wet process).
The pulverized mixture is calcined either in vertical or rotary-inclined
kilns at a temperature ranging from 1,400 to 1,450°C. On leaving the
kiln, the clinker is cooled rapidly to prevent the conversion of tricalcium
silicate, the main ingredient of Portland cement, into bicalcium silicate
and calcium oxide.
93.16 The manufacture of cement
The lumps of cooled clinker are often mixed with gypsum and various other
additives which control the setting time and other properties of the mixture
in use. In this way it is possible to obtain a wide range of different
cements such as normal Portland cement, rapid-setting cement, hydraulic
cement, metallurgical cement, trass cement, hydrophobic cement, maritime
cement, cements for oil and gas wells, cements for highways or dams, expansive
cement, magnesium cement and so on. Finally, the clinker is ground in
a mill, screened and stored in silos ready for packaging and shipping.
The chemical composition of normal Portland cement is:
Aluminous cement produces
mortar or concrete with high initial strength. It is made from a mixture
of limestone and clay with a high aluminum oxide content (without extenders)
which is calcined at about 1,400°C. The chemical composition of aluminous
cement is approximately:
- calcium oxide
(CaO): 60 to 70%
- silicon dioxide
(SiO2) (including about 5% free SiO2): 19 to 24%
- aluminum trioxide
(Al3O3): 4 to 7%
- ferric oxide (Fe2O3):
2 to 6%
- magnesium oxide
(MgO): less than 5%
Fuel shortages lead
to the increased production of natural cements, especially those using tuff
(volcanic ash). If necessary, this is calcined at 1,200°C, instead of
1,400 to 1,450°C as required for Portland The tuff may contain 70 to
80% amorphous free silica and 5 to 10% quartz. With calcination the amorphous
silica is partially transformed to tridimite and crystobalite.
- aluminum oxide
- calcium oxide
- ferric oxide (Fe2O3):
- silicon dioxide
Cement is used as a binding agent in mortar and concrete a mixture
of cement, gravel and sand. By varying the processing method or by including
additives, different types of concrete may be obtained using a single type
of cement (e.g., normal, clay, bituminous, asphalt tar, rapid-setting, foamed,
waterproof, microporous, reinforced, stressed, centrifuged concrete and
In the quarries from which the clay, limestone and gypsum for cement are
extracted, workers are exposed to the hazards of climatic conditions, dusts
produced during drilling and crushing, explosions and falls of rock and
earth. Road transport accidents occur during haulage to the cement works.
During cement processing, the main hazard is dust. In the past, dust levels
ranging from 26 to 114 mg/m3 have been recorded in quarries and cement works.
In individual processes the following dust levels were reported: clay extraction41.4
mg/m3; raw materials crushing and milling79.8 mg/m3; sieving 384 mg/m3;
clinker grinding140 mg/m3; cement packing 256.6 mg/m3; and loading,
etc.179 mg/m3. In modern factories using the wet process, 15 to 20
mg dust/m3 air are occasionally the upper short-time values. The air pollution
in the neighborhood of cement factories is around 5 to 10% of the old values,
thanks in particular to the widespread use of electrostatic filters. The
free silica content of the dust usually varies between the level in raw
material (clay may contain fine particulate quartz, and sand may be added)
and that of the clinker or the cement, from which all the free silica will
normally have been eliminated.
Other hazards encountered in cement works include high ambient temperatures,
especially near furnace doors and on furnace platforms, radiant heat and
high noise levels (120 dB) in the vicinity of the ball mills. Carbon monoxide
concentrations ranging from trace quantities up to 50 PPM have been found
near limestone kilns.
Other hazardous conditions encountered in cement industry workers include
diseases of the respiratory system, digestive disorders, skin diseases,
rheumatic and nervous conditions and hearing and visual disorders.
Respiratory tract diseases
Respiratory tract disorders are the most important group of occupational
diseases in the cement industry and are the result of inhalation of airborne
dust and the effects of macroclimatic and microclimatic conditions in the
workplace environment. Chronic bronchitis, often associated with emphysema,
has been reported as the most frequent respiratory disease.
Normal Portland cement does not cause silicosis because of the absence of
free silica. However, workers engaged in cement production may be exposed
to raw materials which present great variations in free silica content.
Acid-resistant cements used for refractory plates, bricks and dust contain
high amounts of free silica, and exposure to them involves a definite risk
Cement pneumoconiosis has been described as a benign pinhead or reticular
pneumoconiosis, which may appear after prolonged exposure, and presents
a very slow progression. However, a few cases of severe pneumoconiosis have
also been observed, most likely following exposure to materials other than
clay and Portland cement.
Some cements also contain varying amounts of diatomaceous earth and tuff.
It is reported that when heated, diatomaceous earth becomes more toxic due
to the transformation of the amorphous silica into cristobalite, a crystalline
substance even more pathogenic than quartz. Concomitant tuberculosis may
complicate the course of the cement pneumoconiosis.
Attention has been drawn to the apparently high incidence of gastroduodenal
ulcers in the cement industry. Examination of 269 cement plant workers revealed
13 cases of gastroduodenal ulcer (4.8%). Subsequently, gastric ulcers were
induced in both guinea pigs and a dog fed on cement dust. However, a study
at a cement works showed a sickness absence rate of 1.48 to 2.69% due to
gastroduodenal ulcers. Since ulcers may pass through an acute phase several
times a year, these figures are not excessive when compared with those for
Skin diseases are widely reported in the literature and have been said to
account for about 25% and more of all the occupational skin diseases. Various
forms have been observed, including inclusions in the skin, periungal erosions,
diffuse eczematous lesions and cutaneous infections (furuncles, abscesses
and panaritiums). However, these are more frequent among cement users (e.g.,
bricklayers and masons) than among cement manufacturing plant workers.
As early as 1947 it was suggested that cement eczema might be due to the
presence in the cement of hexavalent chromium (detected by the chromium
solution test). The chromium salts probably enter the dermal papillae, combine
with proteins and produce a sensitization of an allergic nature. Since the
raw materials used for cement manufacture do not usually contain chromium,
the following have been listed as the possible sources of the chromium in
cement: volcanic rock, the abrasion of the refractory lining of the kiln,
the steel balls used in the grinding mills and the different tools used
for crushing and grinding the raw materials and the clinker. Sensitization
to chromium may be the leading cause of nickel and cobalt sensitivity. The
high alkalinity of cement is considered an important factor in cement dermatoses.
Rheumatic and nervous disorders
The wide variations in macroclimatic and microclimatic conditions encountered
in the cement industry have been associated with the appearance of various
disorders of the locomotor system (e.g., arthritis, rheumatism, spondylitis
and various muscular pains) and the peripheral nervous system (e.g., back
pain, neuralgia and radiculitis of the sciatic nerves).
Hearing and vision disorders
Moderate cochlear hypoacusia in workers in a cement mill has been reported.
The main eye disease is conjunctivitis, which normally requires only ambulatory
Accidents in quarries are due in most cases to falls of earth or rock, or
they occur during transportation. In cement works the main types of accidental
injuries are bruises, cuts and abrasions which occur during manual handling
Safety and health measures
A basic requirement in the prevention of dust hazards in the cement industry
is a precise knowledge of the composition and, especially, of the free silica
content of all the materials used. Knowledge of the exact composition of
newly-developed types of cement is particularly important.
In quarries, excavators should be equipped with closed cabins and ventilation
to ensure a pure air supply, and dust suppression measures should be implemented
during drilling and crushing. The possibility of poisoning due to carbon
monoxide and nitrous gases released during blasting may be countered by
ensuring that workers are at a suitable distance during shotfiring and do
not return to the blasting point until all fumes have cleared. Suitable
protective clothing may be necessary to protect workers against inclement
All dusty processes in cement works (grinding, sieving, transfer by conveyor
belts) should be equipped with adequate ventilation systems, and conveyor
belts carrying cement or raw materials should be enclosed, with special
precautions being taken at conveyor transfer points. Good ventilation is
also required on the clinker cooling platform, for clinker grinding and
in cement packing plants.
The most difficult dust control problem is that of the clinker kiln stacks,
which are usually fitted with electrostatic filters, preceded by bag or
other filters. Electrostatic filters may be used also for the sieving and
packing processes, where they must be combined with other methods for air
pollution control. Ground clinker should be conveyed in enclosed screw conveyors.
Hot work points should be equipped with cold air showers, and adequate thermal
screening should be provided. Repairs on clinker kilns should not be undertaken
until the kiln has cooled adequately, and then only by young, healthy workers.
These workers should be kept under medical supervision to check their cardiac,
respiratory and sweat function and prevent the occurrence of thermal shock.
Persons working in hot environments should be supplied with salted drinks
Skin disease prevention measures should include the provision of shower
baths and barrier creams for use after showering. Desensitization treatment
may be applied in cases of eczema: after removal from cement exposure for
3 to 6 months to allow healing, 2 drops of 1:10,000 aqueous potassium dichromate
solution is applied to the skin for 5 minutes, 2 to 3 times per week. In
the absence of local or general reaction, contact time is normally increased
to 15 minutes, followed by an increase in the strength of the solution.
This desensitization procedure can also be applied in cases of sensitivity
to cobalt, nickel and manganese. It has been found that chrome dermatitisand
even chrome poisoningmay be prevented and treated with ascorbic acid.
The mechanism for the inactivation of hexavalent chromium by ascorbic acid
involves reduction to trivalent chromium, which has a low toxicity, and
subsequent complex formation of the trivalent species.
Concrete and Reinforced Concrete Work
To produce concrete, aggregates, such as gravel and sand, are mixed with
cement and water in motor-driven horizontal or vertical mixers of various
capacities installed at the construction site, but sometimes it is more
economical to have ready-mixed concrete delivered and discharged into a
silo on the site. For this purpose concrete mixing stations are installed
in the periphery of towns or near gravel pits. Special rotary-drum lorries
are used to avoid separation of the mixed constituents of the concrete,
which would lower the strength of concrete structures.
Tower cranes or hoists are used to transport the ready-mixed concrete from
the mixer or silo to the framework. The size and height of certain structures
may also require the use of concrete pumps for conveying and placing the
ready-mixed concrete. There are pumps which lift the concrete to heights
of up to 100 m. As their capacity is by far greater than that of cranes
of hoists, they are used in particular for the construction of high piers,
towers and silos with the aid of climbing formwork. Concrete pumps are generally
mounted on lorries, and the rotary-drum lorries used for transporting ready-mixed
concrete are now frequently equipped to deliver the concrete directly to
the concrete pump without passing through a silo.
Formwork has followed the technical development rendered possible by the
availability of larger tower cranes with longer arms and increased capacities,
and it is no longer necessary to prepare shuttering in situ.
Prefabricated formwork up to 25 m2 in size is used in particular for making
the vertical structures of large residential and industrial buildings, such
as facades and dividing walls. These structural-steel formwork elements,
which are prefabricated in the site shop or by the industry, are lined with
sheet-metal or wooden panels. They are handled by crane and removed after
the concrete has set. Depending on the type of building method, prefabricated
formwork panels are either lowered to the ground for cleaning or taken to
the next wall section ready for pouring.
So-called formwork tables are used to make horizontal structures (i.e.,
floor slabs for large buildings). These tables are composed of several structural-steel
elements and can be assembled to form floors of different surfaces. The
upper part of the table (i.e., the actual floor-slab form) is lowered by
means of screw jacks or hydraulic jacks after the concrete has set. Special
beak-like load-carrying devices have been devised to withdraw the tables,
to lift them to the next floor and to insert them there.
Sliding or climbing formwork is used to build towers, silos, bridge piers
and similar high structures. A single formwork element is prepared in situ
for this purpose; its cross-section corresponds to that of the structure
to be erected, and its height may vary between 2 and 4 m. The formwork surfaces
in contact with the concrete are lined with steel sheets, and the entire
element is linked to jacking devices. Vertical steel bars anchored in the
concrete which is poured serve as jacking guides. The sliding form is jacked
upwards as the concrete sets, and the reinforcement work and concrete placing
continue without interruption. This means that work has to go on around
Climbing forms differ from sliding ones in that they are anchored in the
concrete by means of screw sleeves. As soon as the poured concrete has set
to the required strength, the anchor screws are undone, the form is lifted
to the height of the next section to be poured, anchored and prepared for
receiving the concrete.
So-called form cars are frequently used in civil engineering, in particular
for making bridge deck slabs. Especially when long bridges or viaducts are
built, a form car replaces the rather complex falsework. The deck forms
corresponding to one length of bay are fitted to a structural-steel frame
so that the various form elements can be jacked into position and be removed
laterally or lowered after the concrete has set. When the bay is finished,
the supporting frame is advanced by one bay length, the form elements are
again jacked into position, and the next bay is poured
When a bridge is built using the so-called cantilever technique the form-supporting
frame is much shorter than the one described above. It does not rest on
the next pier but must be anchored to form a cantilever. This technique,
which is generally used for very high bridges, often relies on two such
frames which are advanced by stages from piers on both sides of the span.
Prestressed concrete is used particularly for bridges, but also in building
especially designed structures. Strands of steel wire wrapped in steel-sheet
or plastic sheathing are embedded in the concrete at the same time as the
reinforcement. The ends of the strands or tendons are provided with head
plates so that the prestressed concrete elements may be pretensioned with
the aid of hydraulic jacks before the elements are loaded.
Construction techniques for large residential buildings, bridges and tunnels
have been rationalized even further by prefabricating elements such as floor
slabs, walls, bridge beams and so on, in a special concrete factory or near
the construction site. The prefabricated elements, which are assembled on
the site, do away with the erection, displacement and dismantling of complex
formwork and falsework, and a great deal of dangerous work at height can
Reinforcement is generally delivered to the site cut and bent according
to bar and bending schedules. Only when prefabricating concrete elements
on the site or in the factory are the reinforcement bars tied or welded
to each other to form cages or mats which are inserted into the forms before
the concrete is poured.
Prevention of accidents
Mechanization and rationalization have eliminated many traditional hazards
on building sites, but have also created new dangers. For instance, fatalities
due to falls from height have considerably diminished thanks to the use
of form cars, form-supporting frames in bridge building and other techniques.
This is due to the fact that the work platforms and walkways with their
guard rails are assembled only once and displaced at the same time as the
form car, whereas with traditional formwork the guard rails were often neglected.
On the other hand, mechanical hazards are increasing and electrical hazards
are particularly serious in wet environments. Health hazards arise from
cement itself, from substances added for curing or waterproofing and from
lubricants for formwork.
Some important accident prevention measures to be taken for various operations
are given below.
As concrete is nearly always mixed by machine, special attention should
be paid to the design and layout of switchgear and feed-hopper skips. In
particular, when concrete mixers are being cleaned, a switch may be unintentionally
actuated, starting the drum or the skip and causing injury to the worker.
Therefore, switches should be protected and also arranged in such a manner
that no confusion is possible. If necessary, they should be interlocked
or provided with a lock. The skips should be free from danger zones for
the mixer attendant and workers moving on passageways near it. It must also
be ensured that workers cleaning the pits beneath feed-hopper skips are
not injured by the accidental lowering of the hopper.
Silos for aggregates, especially sand, present a hazard of fatal accidents.
For example, workers entering a silo without a standby person and without
a safety harness and lifeline may fall and be buried in the loose material.
Silos should therefore be equipped with vibrators and platforms from which
sticking sand can be poked down, and corresponding warning notices should
be displayed. No person should be allowed to enter the silo without another
Concrete handling and placing
The proper layout of concrete transfer points and their equipment with mirrors
and bucket receiving cages obviates the danger of injuring a standby worker
who otherwise has to reach out for the crane bucket and guide it to a proper
Transfer silos which are jacked up hydraulically must be secured so that
they are not suddenly lowered if a pipeline breaks.
Work platforms fitted with guard rails must be provided when placing the
concrete in the forms with the aid of buckets suspended from the crane hook
or with a concrete pump. The crane operators must be trained for this type
of work and must have normal vision. If large distances are covered, two-way
telephone communication or walkie-talkies have to be used.
When concrete pumps with pipelines and placer masts are used, special attention
should be paid to the stability of the installation. Agitating lorries (cement
mixers) with built-in concrete pumps must be equipped with interlocked switches
which make it impossible to start the two operations simultaneously. The
agitators must be guarded so that the operating personnel cannot come into
contact with moving parts. The baskets for collecting the rubber ball which
is pressed through the pipeline to clean it after the concrete has been
poured, are now replaced by two elbows arranged in opposite directions.
These elbows absorb almost all the pressure needed to push the ball through
the placing line; they not only eliminate the whip effect at the line end,
but also prevent the ball from being shot out of the line end.
When agitating lorries are used in combination with placing plant and lifting
equipment, special attention has to be paid to overhead electric lines.
Unless the overhead line can be displaced they must be insulated or guarded
by protective scaffolds within the work range to exclude any accidental
contact. It is important to contact the power supply station.
Falls are common during the assembly of traditional formwork composed of
square timber and boards because the necessary guard rails and toe boards
are often neglected for work platforms which are only required for short
periods. Nowadays, steel supporting structures are widely used to speed
up formwork assembly, but here again the available guard rails and toe boards
are frequently not installed on the pretext that they are needed for so
short a time.
Plywood form panels, which are increasingly used, offer the advantage of
being easy and quick to assemble. However, often after being used several
times, they are frequently misappropriated as platforms for rapidly required
scaffolds, and it is generally forgotten that the distances between the
supporting transoms must be considerably reduced in comparison with normal
scaffold planks. Accidents resulting from breakage of form panels misused
as scaffold platforms are still rather frequent.
Two outstanding hazards must be borne in mind when using prefabricated form
elements. These elements must be stored in such a manner that they cannot
turn over. Since it is not always feasible to store form elements horizontally,
they must be secured by stays. Form elements permanently equipped with platforms,
guard rails and toeboards may be attached by slings to the crane hook as
well as being assembled and dismantled on the structure under construction.
They constitute a safe workplace for the personnel and do away with the
provision of work platforms for placing the concrete. Fixed ladders may
be added for safer access to platforms. Scaffold and work platforms with
guard rails and toe boards permanently attached to the form element should
be used in particular with sliding and climbing formwork.
Experience has shown that accidents due to falls are rare when work platforms
do not have to be improvised and rapidly assembled. Unfortunately, form
elements fitted with guard rails cannot be used everywhere, especially where
small residential buildings are being erected.
When the form elements are raised by crane from storage to the structure,
lifting tackle of appropriate size and strength, such as slings and spreaders,
must be used. If the angle between the sling legs is too large, the form
elements must be handled with the aid of spreaders.
The workers cleaning the forms are exposed to a health hazard which is generally
overlooked: the use of portable grinders to remove concrete residues adhering
to the form surfaces. Dust measurements have shown that the grinding dust
contains a high percentage of respirable fractions and silica. Therefore,
dust control measures must be taken (e.g., portable grinders with exhaust
devices linked to a filter unit or an enclosed form-board cleaning plant
with exhaust ventilation.
Assembly of prefabricated elements
Special lifting equipment should be used in the manufacturing plant so that
the elements can be moved and handled safely and without injury to the workers.
Anchor bolts embedded in the concrete facilitate their handling not only
in the factory but also on the assembly site. To avoid bending of the anchor
bolts by oblique loads, large elements must be lifted with the aid of spreaders
with short rope slings. If a load is applied to the bolts at an oblique
angle, concrete may spill off and the bolts may be torn out. The use of
inappropriate lifting tackle has caused serious accidents resulting from
falling concrete elements.
Appropriate vehicles must be used for the road transport of prefabricated
elements. They must be approximately secured against overturning or slidingfor
example, when the driver has to brake the vehicle suddenly. Visibly displayed
weight indications on the elements facilitate the task of the crane operator
during loading, unloading and assembly on the site.
Lifting equipment on the site should be adequately chosen and operated.
Tracks and roads must be kept in good condition in order to avoid overturning
of loaded equipment during operation.
Work platforms protecting personnel against falls from height must be provided
for the assembly of the elements. All possible means of collective protection,
such as scaffolds, safety nets and overhead traveling cranes erected before
completion of the building, should be taken into consideration before recourse
is taken to reliance on PPE. It is, of course, possible to equip the workers
with safety harnesses and lifelines, but experience has shown that there
are workers who use this equipment only when they are under constant close
supervision. Lifelines are indeed a hindrance when certain tasks are performed,
and certain workers are proud of being capable of working at great heights
without using any protection.
Before starting to design a prefabricated building, the architect, the manufacturer
of the prefabricated elements and the building contractor should meet to
discuss and study the course and safety of all operations. When it is known
beforehand what types of handling and lifting equipment are available on
the site, the concrete elements may be provided in the factory with fastening
devices for guard rails and toe boards. The façade ends of floor
elements, for instance, are then easily fitted with prefabricated guard
rails and toe boards before the elements are lifted into place. The wall
elements corresponding to the floor slab may thereafter be safely assembled
because the workers are protected by guard rails.
For the erection of certain high industrial structures, mobile work platforms
are lifted into position by crane and hung from suspension bolts embedded
in the structure itself. In such cases it may be safer to transport the
workers to the platform by crane (which should have high safety characteristics
and be run by a qualified operator) than to use improvised scaffolds or
When post-tensioning concrete elements, attention should be paid to the
design of the post-tensioning recesses, which should enable the tensioning
jacks to be applied, operated and removed without any hazard for the personnel.
Suspension hooks for tensioning jacks or openings for passing the crane
rope must be provided for post-tensioning work beneath bridge decks or in
box-type elements. This type of work, too, requires the provision of work
platforms with guard rails and toe boards. The platform floor should be
sufficiently low to allow for ample work space and safe handling of the
jack. No person should be permitted at the rear of the tensioning jack because
serious accidents may result from the high energy released in the breakage
of an anchoring element or a steel tendon. The workers should also avoid
being in front of the anchor plates as long as the mortar pressed into the
tendon sheaths has not set. As the mortar pump is connected with hydraulic
pipes to the jack, no person should be permitted in the area between pump
and jack during tensioning. Continuous communication among the operators
and with supervisors is also very important.
Thorough training of plant operators in particular and all construction
site personnel in general is becoming more and more important in view of
increasing mechanization and the use of many types of machinery, plant and
substances. Unskilled laborers or helpers should be employed in exceptional
cases only, if the number of construction site accidents is to be reduced.
Pekka Roto, Medical
Tampere Regional Institute of Occupational Health
The most common form
of occupational dermatosis to be found among construction workers is caused
by exposure to cement. Depending on the country, 5 to 15% of construction
workersmost of them masonsacquire dermatosis during their
work lives. Two types of dermatosis are caused by exposure to cement:
(1) toxic contact dermatitis, which is local irritation of skin exposed
to wet cement and is caused mainly by the alkalinity of the cement; and
(2) allergic contact dermatitis, which is a generalized allergic skin
reaction to exposure to the water-soluble chromium compound found in most
cement. One kilogram of normal cement dust contains 5 to 10 mg of water-soluble
chromium. The chromium originates both in the raw material and the production
process (mainly from steel structures used in production).
Allergic contact dermatitis is chronic and debilitating. If not properly
treated, it can lead to decreased worker productivity and, in some cases,
early retirement. In the 1960s and 1970s, cement dermatitis was the most
common reported cause of early retirement among construction workers in
Scandinavia. Therefore, technical and hygienic procedures were undertaken
to prevent cement dermatitis. In 1979, Danish scientists suggested that
reducing hexavalent water-soluble chromium to trivalent insoluble chromium
by adding ferrous sulphate during production would prevent chromium-induced
dermatitis (Fregert, Gruvberger and Sandahl 1979).
Denmark passed legislation requiring the use of cement with lower levels
of hexavalent chromium in 1983. Finland followed with a legislative decision
at the beginning of 1987, and Sweden and Germany adopted administrative
decisions in 1989 and 1993, respectively. For the four countries, the
accepted level of water-soluble chromium in cement was determined to be
less than 2 mg/kg.
Before Finlands action in 1987, the Board of Labor Protection wanted
to evaluate the occurrence of chromium dermatitis in Finland. The Board
asked the Finnish Institute of Occupational Health to monitor the incidence
of occupational dermatosis among construction workers to assess the effectiveness
of adding ferrous sulphate to cement in order to prevent chromium-induced
dermatitis. The Institute monitored the incidence of occupational dermatitis
through the Finnish Register of Occupational Diseases from 1978 through
1992. The results indicated that chromium-induced hand dermatitis practically
disappeared among construction workers, whereas the incidence of toxic
contact dermatitis remained unchanged during the study period (Roto et
In Denmark, chromate sensitization from cement was detected in only one
case among 4,511 patch tests conducted between 1989 and 1994 among patients
of a large dermatological clinic, 34 of whom were construction workers.
The expected number of chromate-positive construction workers was 10 of
34 subjects (Zachariae, Agner and Menn J1996).
There seems to be increasing evidence that the addition of ferrous sulphate
to cement prevents chromate sensitization among construction workers.
In addition, there has been no indication that, when added to cement,
ferrous sulphate has negative effects on the health of exposed workers.
The process is economically feasible, and the properties of the cement
do not change. It has been calculated that adding ferrous sulphate to
cement increases the production costs by US$1.00 per ton. The reductive
effect of ferrous sulphate lasts 6 months; the product must be kept dry
before mixing because humidity neutralizes the effect of the ferrous sulphate.
The addition of ferrous sulphate to cement does not change its alkalinity.
Therefore workers should use proper skin protection. In all circumstances,
construction workers should avoid touching wet cement with unprotected
skin. This precaution is especially important in initial cement production,
where minor adjustments to molded elements are made manually.
National Center for Injury Prevention and Control
|Classes of bitumens/asphalts
|Class 1: Penetration
bitumens are classified by their penetration value. They are usually
produced from the residue from atmospheric distillation of petroleum
crude oil by applying further distillation under vacuum, partial oxidation
(air rectification), solvent precipitation or a combination of these
processes. In Australia and the United States, bitumens that are approximately
equivalent to those described here are called asphalt cements or
viscosity-graded asphalts, and are specified on the basis of viscosity
measurements at 60°C.
|Class 2: Oxidized
bitumens are classified by their softening points and penetration
values. They are produced by passing air through hot, soft bitumen
under controlled temperature conditions. This process alters the characteristics
of the bitumen to give reduced temperature susceptibility and greater
resistance to different types of imposed stress. In the United States,
bitumens produced using air blowing are known as air-blown asphalts
or roofing asphalts and are similar to oxidized bitumens.
|Class 3: Cutback
bitumens are produced by mixing penetration bitumens or oxidized
bitumens with suitable volatile diluents from petroleum crudes such
as white spirit, kerosene or gas oil, to reduce their viscosity and
render them more fluid for ease of handling. When the diluent evaporates,
the initial properties of bitumen are recovered. In the United States,
cutback bitumens are sometimes referred to as road oils.
4: Hard bitumens are normally classified by their softening
point. They are manufactured similarly to penetration bitumens, but
have lower penetration values and higher softening points (i.e., they
are more brittle).
|Class 5: Bitumen
emulsions are fine dispersions of droplets of bitumen (from classes
1, 3 or 6) in water. They are manufactured using high-speed shearing
devices, such as colloid mills. The bitumen content can range from
30 to 70% by weight. They can be anionic, cationic or nonionic. In
the United States, they are referred to as emulsified asphalts.
|Class 6: Blended
or fluxed bitumens may be produced by blending bitumens (primarily
penetration bitumens) with solvent extracts (aromatic byproducts from
the refining of base oils), thermally cracked residues or certain
heavy petroleum distillates with final boiling points above 350°C.
|Class 7: Modified
bitumens contain appreciable quantities (typically 3 to 15% by
weight) of special additives, such as polymers, elastomers, sulfur
and other products used to modify their properties; they are used
for specialized applications.
|Class 8: Thermal
bitumens were produced by extended distillation, at high temperature,
of a petroleum residue. Currently, they are not manufactured in Europe
or in the United States.
Asphalts can generally
be defined as complex mixtures of chemical compounds of high molecular
weight, predominantly asphaltenes, cyclic hydrocarbons (aromatic or naphthenic)
and a lesser quantity of saturated components of low chemical reactivity.
The chemical composition of asphalts depends both on the original crude
oil and on the process used during refining. Asphalts are predominantly
derived from crude oils, especially heavier residue crude oil. Asphalt
also occurs as a natural deposit, where it is usually the residue resulting
from the evaporation and oxidation of liquid petroleum. Such deposits
have been found in California, China, the Russian Federation, Switzerland,
Trinidad and Tobago and Venezuela. Asphalts are nonvolatile at ambient
temperatures and soften gradually when heated. Asphalt should not be confused
with tar, which is physically and chemically dissimilar.
A wide variety of applications include paving streets, highways and airfields;
making roofing, waterproofing and insulating materials; lining irrigation
canals and reservoirs; and the facing of dams and levees. Asphalt is also
a valuable ingredient of some paints and varnishes. It is estimated that
the current annual world production of asphalts is over 60 million tons,
with more than 80% being used in need construction and maintenance and
more than 15% used in roofing materials.
Asphalt mixes for road construction are produced by first heating and
drying mixtures of graded crushed stone (such as granite or limestone),
sand and filler and then mixing with penetration bitumen, referred to
in the US as straight-run asphalt. This is a hot process. The asphalt
is also heated using propane flames during application to a road bed.
Exposures and Hazards
Exposures to particulate polynuclear aromatic hydrocarbons (PAHs) in asphalt
fumes have been measured in a variety of settings. Most of the PAHs found
was composed of naphthalene derivatives, not the four- to six-ring compounds
which are more likely to pose a significant carcinogenic risk. In refinery
asphalt processing units, respirable PAH levels range from non-detectable
to 40 mg/m3. During drum-filling operations, 4 hour breathing zone samples
ranged from 1.0 mg/m3 upwind to 5.3 mg/m3 downwind. At asphalt mixing
plants, exposures to benzene-soluble organic compounds ranged from 0.2
to 5.4 mg/m3. During paving operations, exposures to respirable PAH ranged
from less than 0.1 mg/m3 to 2.7 mg/m3. Potentially noteworthy worker exposures
may also occur during the manufacture and application of asphalt roofing
materials. Little information is available regarding exposures to asphalt
fumes in other industrial situations and during the application or use
of asphalt products.
Handling of hot asphalt can cause severe burns because it is sticky and
is not readily removed from the skin. The principal concern from the industrial
toxicological aspect is irritation of the skin and eyes by fumes of hot
asphalt. These fumes may cause dermatitis and acne-like lesions as well
as mild keratoses on prolonged and repeated exposure. The greenish-yellow
fumes given off by boiling asphalt can also cause photosensitization and
Although all asphaltic materials will combust if heated sufficiently,
asphalt cements and oxidized asphalts will not normally burn unless their
temperature is raised about 260°C. The flammability of the liquid
asphalts is influenced by the volatility and amount of petroleum solvent
added to the base material. Thus, the rapid-curing liquid asphalts present
the greatest fire hazard, which becomes progressively lower with the medium-
and slow-curing types.
Because of its insolubility in aqueous media and the high molecular weight
of its components, asphalt has a low order of toxicity.
The effects on the tracheobronchial tree and lungs of mice inhaling an
aerosol of petroleum asphalt and another group inhaling smoke from heated
petroleum asphalt included congestion, acute bronchitis, pneumonitis,
bronchial dilation, some peribronchiolar round cell infiltration, abscess
formation, loss of cilia, epithelial atrophy and necrosis. The pathological
changes were patchy, and in some animals were relatively refractory to
treatment. It was concluded that these changes were a nonspecific reaction
to breathing air polluted with aromatic hydrocarbons, and that their extent
was dose dependent. Guinea pigs and rats inhaling fumes from heated asphalt
showed effects such as chronic fibrosing pneumonitis with peribronchial
adenomatosis, and the rats developed squamous cell metaplasia, but none
of the animals had malignant lesions.
Steam-refined petroleum asphalts were tested by application to the skin
of mice. Skin tumors were produced by undiluted asphalts, dilutions in
benzene and a fraction of steam-refined asphalt. When air-refined (oxidized)
asphalts were applied to the skin of mice, no tumor was found with undiluted
material, but, in one experiment, an air-refined asphalt in solvent (toluene)
produced topical skin tumors. Two cracking-residue asphalts produced skin
tumors. when applied to the skin of mice. A pooled mixture of steam- and
air-blown petroleum asphalts in benzene produced tumors. At the site of
application on the skin of mice. One sample of heated, air-refined asphalt
injected subcutaneously into mice produced a few sarcomas at the injection
sites. A pooled mixture of steam- and air-blown petroleum asphalts produced
sarcomas at the site of subcutaneous injection in mice. Steam-distilled
asphalts injected intramuscularly produced local sarcomas in one experiment
in rats. Both an extract of road-surfacing asphalt and its emissions were
mutagenic to Salmonella typhimurium.
Evidence for carcinogenicity to humans is not conclusive. A cohort of
roofers exposed to both asphalts and coal tar pitches showed an excess
risk for respiratory cancer. Likewise, two Danish studies of asphalt workers
found an excess risk for lung cancer, but some of these workers may also
have been exposed to coal tar, and they were more likely to be smokers
than the comparison group. Among Minnesota (but not California) highway
workers, increases were noted for leukemia and urological cancers. Even
though the epidemiological data to date are inadequate to demonstrate
with a reasonable degree of scientific certainty that asphalt presents
a cancer risk to humans, general agreement exists, on the basis of experimental
studies, that asphalt may pose such a risk.
Safety and Health Measures
Since heated asphalt will cause severe skin burns, those working with
it should wear loose clothing in good condition, with the neck closed
and the sleeves rolled down. Hand and arm protection should be worn. Safety
shoes should be about 15 cm high and laced so that no openings are left
through which hot asphalt may reach the skin. Face and eye protection
is also recommended when heated asphalt is handled. Changing rooms and
proper washing and bathing facilities are desirable. At crushing plants
where dust is produced and at boiling pans from which fumes escape, adequate
exhaust ventilation should be provided.
Asphalt kettles should be set securely and be leveled to preclude the
possibility of their tipping. Workers should stand upwind of a kettle.
The temperature of heated asphalt should be checked frequently in order
to prevent overheating and possible ignition. If the flash point is approached,
the fire under a kettle must be put out at once and no open flame or other
source of ignition should be permitted nearby. Where asphalt is being
heated, fire-extinguishing equipment should be within easy reach. For
asphalt fires, dry chemical or carbon dioxide types of extinguishers are
considered most appropriate. The asphalt spreader and the driver of an
asphalt paving machine should be offered half-face respirators with organic
vapor cartridges. In addition, to prevent the inadvertent swallowing of
toxic materials, workers should not eat, drink or smoke near a kettle.
If molten asphalt strikes the exposed skin, it should be cooled immediately
by quenching with cold water or by some other method recommended by medical
advisers. An extensive burn should be covered with a sterile dressing
and the patient should be taken to a hospital; minor burns should be seen
by a physician. Solvents should not be used to remove asphalt from burned
flesh. No attempt should be made to remove particles of asphalt from the
eyes; instead the victim should be taken to a physician at once.
James L. Weeks
School of Public Health and Health Services
Gravel is a loose
conglomerate of stones that have been mined from a surface deposit, dredged
from a river bottom or obtained from a quarry and crushed into desired
sizes. Gravel has a variety of uses, including: for rail beds; in roadways,
walkways and roofs; as filler in concrete (often for foundations); in
landscaping and gardening; and as a filter medium.
The principal safety and health hazards to those who work with gravel
are airborne silica dust, musculoskeletal problems and noise. Free crystalline
silicon dioxide occurs naturally in many rocks that are used to make gravel.
The silica content of bulk species of stone varies and is not a reliable
indicator of the percentage of airborne silica dust in a dust sample.
Granite contains about 30% silica by weight. Limestone and marble have
less free silica.
Silica can become airborne during quarrying, sawing, crushing, sizing
and, to a lesser extent, spreading of gravel. Generation of airborne silica
can usually be prevented with water sprays and jets, and sometimes with
local exhaust ventilation (LEV). In addition to construction workers,
workers exposed to silica dust from gravel include quarry workers, railroad
workers and landscape workers. Silicosis is more common among quarry or
stone-crushing workers than among construction workers who work with gravel
as a finished product. An elevated risk of mortality from pneumoconiosis
and other nonmalignant respiratory disease has been observed in one cohort
of workers in the crushed-stone industry in the United States.
Musculoskeletal problems can occur as a result of manual loading or unloading
of gravel or during manual spreading. The larger the individual pieces
of stone and the larger the shovel or other tool used, the more difficult
it is to manage the material with hand tools. The risk of sprains and
strains can be reduced if two or more workers work together on strenuous
tasks, and more so if draught animals or powered machines are used. Smaller
shovels or rakes carry or push less weight than larger ones and can reduce
the risk of musculoskeletal problems.
Noise accompanies mechanical processing or handling of stone or gravel.
Stone crushing using a ball mill generates considerable low-frequency
noise and vibration. Transporting gravel through metal chutes and mixing
it in drums are both noisy processes. Noise can be controlled by using
sound-absorbing or -reflecting materials around the ball mill, by using
chutes lined with wood or other sound-absorbing (and durable) material
or by using noise-insulated mixing drums.
Copyright © International Labour Organization 1998.
The ILO shall accept no responsibility for any inaccuracy, errors or omissions
or for the consequences arising from the use of this material.
Jeanne Mager Stellman, ed., Encyclopedia of Occupational Health and Safety,
Fourth Edition. Geneva: International Labour Office, III, 93 (52 pp.),
This paper appears in the eLCOSH website with the permission of the author
and/or copyright holder and may not be reproduced without their consent.
eLCOSH is an information clearinghouse. eLCOSH and its sponsors are not
responsible for the accuracy of information provided on this web site,
nor for its use or misuse.
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