Iowa State University Extension
In typical
modern livestock housing, where animals are densely confined,
dusts from the animals, their feed, and their feces, ammonia
(NH3) which comes primarily from the animals' urine and feces,
and hydrogen sulfide (H2S) from manure pits, especially during
agitation and emptying, can rise to harmful levels. Dust and
gas levels are highest in winter, although dust levels increase
whenever animals are fed, handled, or moved. Hazardous dusts
and gases induce the strongest and most frequent human respiratory
responses in swine confinement buildings. This unit concentrates
on workers in these buildings, although similar respiratory
responses could occur among poultry confinement workers or
(less commonly and severely) workers in other types of confinement
operations.
Confinement
dusts and gases can affect any exposed person within a short
time, and in extreme cases have caused sudden death or have
forced owners, employees, and veterinarians to stay out of
confinement buildings or seek other employment. Responses
often vary from person to person, may affect any part of the
respiratory tract, and may include irritant, toxic, or allergic
processes. Potential responses include acute or chronic bronchitis
(the most common reaction), increased airways reactivity,
asthma, chronic airways obstruction, and a systemic influenza-like
reaction, the toxic organic dust syndrome or TODS. When manure
pits constructed underneath confinement buildings are agitated
for emptying, the level of H2S can rise to lethal levels within
seconds; this has caused a number of deaths. Researchers suspect
that chronic obstructive pulmonary disease may occur among
confinement workers with long-term exposure.
When
diagnosing and treating respiratory illness in confinement
workers, physicians should make a conscientious attempt to
discover links between exposure to dusts and gases in the
houses and the illness. This will avoid use of nonspecific
treatments that are ineffective in the long run. Instead a
patient must be protected by reducing dust and gas levels
in the confinement house through engineering and management
practices, or by use of respirators. Confinement house workers
should be monitored for development of chronic respiratory
problems. Manure pits should never be entered without proper
respiratory protection, and when pits are being agitated or
emptied, workers should stay out of the pits and out of the
buildings above them.
Compared
to conventional livestock housing, the typical confinement
system is more enclosed and tightly constructed. A much higher
density of animals is housed in these buildings, usually for
24 hours a day from birth to shipment to the slaughter house.
Because large numbers of animals are confined in small spaces,
these buildings must include devices to ventilate and heat
the buildings and to dispose of animal wastes. Often, feeding
and watering operations are semiautomatic or automatic. (See
Fig. 1) Poultry confinement operations first appeared in the
United States in the late 1950's. Swine confinement operations
came into use a decade later. Today sheep, beef cattle, dairy
cattle, and veal calves also are housed in confinement buildings,
although far less commonly than swine and poultry. Quarters
for these other animals often are not completely enclosed,
or the animals may be kept outside for at least part of the
year.
Manure
is handled by one of two systems: it either drops through
a slatted floor into a pit beneath the house where it remains
until the manure slurry is pumped out to be distributed on
fields (usually twice a year), or it is removed through any
of several mechanisms to a storage pit or lagoon outside the
building. Outside storage is typical of most newer systems,
but a large number of older buildings with pits directly below
the house remain in operation.
What
toxic dusts and gases are found in confinement houses?
Dust
is generated from animals and their feed, and dust and gases
from animal wastes. These dusts and gases accumulate to concentrations
that may be hazardous to human and animal health.
Each
confinement house contains its own complex mixture of dusts
and gases, which is dependent on numerous factors including
ventilation of the building, the type of animals, how they
are fed, and how their wastes are handled. (See Fig. 2) Dust
and gas composition change within a single house over time.
The types of confinement operations and corresponding dust
and gas exposures are listed in Table 1. This unit concentrates
on swine operations, where potentially hazardous dusts and
gases and resulting health problems are best studied and are
thought to be most extreme. Similar responses would occur
most commonly among poultry confinement workers.
Table
1
Dusts
and Gases In Various confinement Operations: Implications
for Human Health
Type
of
Confinement Gases
operation Dusts NH2 H2S(following manure
agitation)
=================================================================
swine major concern moderate major concern
concern
poultry moderate concern major none (manure is
concern stored as solid)
sheep minimal concern moderate major concern, if
veal calf (lower dust concern have liquid manure
dairy cattle concentrations, system
beef cattle resulting in
fewer and less
severe inflammatory
reactions)
Dust
particles contain approximately 25% protein, and range in
size from less than 2 microns to 50 microns in diameter. One-third
of the particles are within the respirable size range (less
than 1011 in diameter). 125 Fecal material particles including
proteins from gut epithelium are quite small and constitute
the major alveolar burden, while large particles of feed grains
form the major airways burden. Also present are animal dander,
broken bits of hair, bacteria, bacterial endotoxins, pollen
grains, insect parts, and fungal spores. The dust absorbs
NH3 and possibly other toxic or irritating gases (e.g. H2S),
multiplying the potential hazards of each gas individually.
Ammonia, for example, may adsorb to respirable particles and
be drawn deep into the lungs where it possibly could cause
irritation or increase inflammatory responses to the dust.
Toxic,
irritating, and asphyxiating gases are continuously generated
in the manure pit, and can rise into a confinement house.
Of the 40-plus gas types in anaerobically degenerating manure,
H2S, carbon dioxide (CO2), methane (CH4), and carbon monoxide
(CO) are present most commonly and in highest concentrations.
The majority of NH3 is thought to be released by bacterial
action on urine and feces on the confinement house floors.
Carbon monoxide and CO2 may be produced by heating systems
in winter, as well as by the animals' respiration (CO2 only).
Who
is exposed to these dusts and gases, and when?
Dust
and gas concentrations in swine confinement buildings can
be high enough to affect anyone who enters, but persons with
long-term occupational exposures are in greatest danger of
developing chronic problems and possibly irreversible lung
damage. Confinement house owners and managers, hired hands,
and farm family members may work in the houses anywhere from
a few hours a week to eight or more hours daily. (See Fig.
3) During this time, workers are preparing feed, feeding animals,
cleaning the building, sorting and moving animals from one
building to another, and performing routine vaccinations,
treatments, or other management and maintenance procedures.
The turnover rate of hired swine confinement house workers
is quite high, and some owners have had to sell their operations
because they could not work in their own units, reportedly
because of respiratory problems. Some veterinarians who entered
houses sporadically to treat sick animals have reported that
the severity of their respiratory reactions forces them to
stay out of these buildings, or to use respirators effective
in reducing exposure.
Dust
and gas loads increase in winter when the houses are tightly
closed to conserve heat, and when CO and CO2 are released
from poorly vented or improperly functioning heaters. Dust
loads also increase when animals are being moved, handled,
and fed. Ventilation systems frequently do not reduce dust
or gas levels adequately, so that levels remain unhealthful
for humans. When ventilation systems fail for several hours,
CO2 from animal respiration, heaters, and manure pits can
rise to asphyxiating levels. Although some massive animal
losses have been attributed to this situation, it is probably
not a human health threat.
Hydrogen
sulfide from manure pits is most hazardous when the pits are
fully or partially beneath the houses. However, if gases from
outside pits are permitted to backflow, they too can enter
confinement units. Manure pit gases pose an acute hazard when
the liquid manure slurry is agitated, a common operation performed
to suspend solids so that pits can be pumped empty. During
agitation, H2S can be released rapidly, soaring from usual
ambient levels of less than 5 ppm to lethal levels of over
500 ppm within seconds.20 Animals have died and workers have
become seriously ill in swine confinement buildings when H2S
has risen from agitated pits underneath. Several workers have
died when entering a pit during or soon after the emptying
process to repair pumping equipment or clean out solids.20
Persons attempting to rescue these workers also have died.
Workers may be exposed to high H2S levels when they enter
the pit to retrieve animals or tools, or to repair ventilation
systems or cracks in the cement.
Swine
confinement houses and resulting health problems are concentrated
in the Corn Belt of the Midwest, but are also found in western
Nebraska, Kansas, Colorado, and in southeastern states including
North Carolina and Georgia. Poultry confinement houses and
resulting respiratory problems are concentrated in the Northeast,
Southeast, Midwest, and Far West. Other types of confinement
operations are ,primarily located in the Midwest's Corn Belt.
How
commonly does such exposure occur?
In the
United States, an estimated 700,000 persons work in confinement
operations. This number includes owner-operators, spouses,
children, employees, and veterinarians. In a highly agricultural
state such as Iowa, over 80,000 persons (or an estimated 53%
of the people working with swine) work in swine confinement
buildings. Included in this number are spouses and children
who may work short periods of time.
The
largest group of exposed workers with the most frequent and
severe health problems is associated with swine confinement
houses. Here, the average dust load is six milligrams per
cubic meter. Buildings with 10 to 20 milligrams are common,
concentrations high enough so that one is unable to see clearly
across a 100 foot room. Concentrations of H2S, CO2, and CO
may exceed levels recommended as safe in industrial occupational
settings. Nearly 70% of swine confinement workers experience
one or more symptoms of respiratory illness or irritation.
Prevalence of respiratory illness among workers in nonswine
confinement operations is lower.
GASES
Inhalation
of confinement house dusts and gases produces a complex set
of respiratory responses. An individual's response depends
on characteristics of the inhaled components (such as composition,
particulate size, and antigenicity) and on the individual's
susceptibility, which is tempered by extant respiratory conditions
(including allergies and asthma), reactivity of the bronchi,
and smoking history. Irritant, toxic, or allergic processes
may be involved, alone or in combination. Since dusts include
both respirable (~10 microns ) and larger (10--50 microns
) particles, lung tissues, large airways, and small airways
may all be affected. For the most part, responses cannot be
tied to a specific dust or gas component. Specific mechanisms
involved often cannot be defined, and conditions may be described
symptomatically.
Acute,
delayed, and chronic responses are described in following
paragraphs and outlined in Table 3. Descriptions concentrate
on health problems of swine confinement workers. Hazardous
exposures of other types of confinement operations have been
listed in Table 1; respiratory problems vary accordingly.
Symptoms
of swine confinement workers are listed in Table 2. The most
common respiratory symptoms (cough, sputum production, chest
tightness, shortness of breath, and wheezing) are manifestations
of airways disease, composed of bronchitis often associated
with increased airways reactivity Evidence suggests that those
exposed become increasingly reactive to the confinement environment
with increasing exposure (greater than two hours per day and
six years work experience). In general, the symptoms increase
among smokers and also increase as the number of swine raised
increases. Health effects are also greater among those with
pre-existing respiratory problems (hay fever, bronchitis)
and among those with heart trouble or allergies. Chest tightness,
coughing, nasal, and eye symptoms have been experienced in
some persons within 30 minutes of entering these houses for
the first time, but usually two or more hours of exposure
are required. These symptoms usually disappear 24 to 48 hours
after leaving the unit, although they can persist for several
days or weeks or even months among workers exposed for several
years. A small percentage, 12%, of these cases are thought
to be specific allergic-mediated illnesses such as asthma
(classical type 1 reactions), while the remaining proportion
appears to be nonallergic reactions.
Table
2 Symptoms of Swine Confinement Workers
Symptom Prevalence
Cough 67%
Sputum or phlegm 56%
Scratchy throat 54%
Runny nose 45%
Burning or watering eyes 39%
Headaches 37%
Tightness of chest 36%
Shortness of breath 30%
Wheezing 27%
Muscle aches and pains 25%
Manure
pit agitation can result in the sudden release of large quantities
of H2S causing H2S intoxication (See Fig. 4) At moderately
high concentrations (100-400 ppm), H2S produces rhinitis,
cough, dyspnea, tracheobronchitis, and possibly pulmonary
edema; at higher concentrations, sudden collapse associated
with respiratory paralysis and pulmonary edema occurs. A number
of deaths of confinement workers have resulted from this exposure.
Delayed
responses include a toxic organic dust syndrome (TODS) experienced
four to six hours after working for several hours in a confinement
house during particularly dusty operations such as handling,
moving, or sorting animals. Symptoms include fever, malaise,
muscle aches and pains, headache, cough, and tightness of
chest. This episodic problem, experienced by about 10% of
workers in confinement buildings,1 may be the same toxic syndrome
resulting from exposure to decayed plant material (see Unit
2) and grain dusts (see Unit 3). Inhaled endotoxins from aerosolized
gram-negative bacteria might cause this syndrome.
Chronic
health effects are manifest as chronic bronchitis with or
without airways obstruction, experienced by 58% of all swine
confinement workers. This is the most commonly defined chronic
health problem of this occupational group, and is suffered
by three times as many swine confinement workers as farmers
who work in conventional swine housing units or in agricultural
operations other than swine or poultry production. Symptoms
include chronic cough, with excess production of phlegm and
sometimes chronic wheezing. Smokers experience a greater prevalence
and severity of chronic bronchitis than do nonsmokers. Most
workers removed from the confinement house environment become
asymptomatic (in the absence of smoking) within a few months,
but bronchitic symptoms in some workers can persist for two
years or more.
Chronic
or irreversible airways obstruction other than chronic bronchitis
has not been identified, but long-term lung damage may be
occurring. Confinement workers' lung functions do not differ
significantly from those of workers in conventional swine
buildings when baseline PFT's (FEV and FVC) are measured in
the morning, before work begins.1721 However, these pulmonary
function values of most confinement house workers do decrease
significantly through the workday. In addition, the severity
of chronic bronchitic symptoms increases in workers with a
longer history of confinement house work. This suggests that
chronic obstructive pulmonary disease may occur among these
workers in future years. Evidence of permanent lung damage
has not yet been found, possibly because swine confinement
houses are a relatively new innovation or because there have
been no systematic clinical studies to assess confinement
workers. In 1981, the average swine producer with confinement
structures had used these structures for only six years.
Because
of the high concentrations of animals and associated microorganisms,
infectious diseases transmissible to humans are especially
hazardous when contracted by confined animals. Some of these
infectious diseases are described in Unit 7.
Diagnosis
Use
of diagnostic aids is of secondary importance to a detailed
clinical and occupational history. Remember that a patient's
response to confinement dusts and gases is variable, and that
one or more conditions may be occurring simultaneously. Question
a patient in detail about chief complaints, including questions
on how long symptoms have been present and the time relationship
of symptoms to work exposure. Take an in-depth personal and
family medical history, including questions on allergies,
asthma, and hobbies or personal habits (such as smoking) that
might complicate the issue. Ask how many hours per day or
week the patient works in confinement buildings, how long
the patient has held this job, and what conditions prevail
within the confinement building.
Physicians
may fail to relate a patient's symptoms to exposure to a confinement
house atmosphere. In addition, misdiagnosis and subsequent
treatment of confinement-related respiratory conditions as
allergic responses are not uncommon; such treatment may provide
symptomatic relief through bronchodilation, but is nonspecific
and probably ineffective in the long run.
Table
3 Occupational Respiratory Conditions Associated with Swine
Livestock Confinement--Diagnosis, Treatment, and Control
Symptoms/History:
Cough, with sputum production, possibly tightness of
chest.
Very frequently seen among swine confinement workers;
somewhat less often in poultry workers.
Smoking associated with increased frequency and more
severe symptoms.
Symptoms continuing for 2 or more years classified as
chronic bronchitis.
Work Exposure:
Usually occurs in those who work in swine confinement for
2 or more hours per day. More frequent and severe for
those who have worked 6 or more years in confinement.
Generally occurs in buildings with poor environment:
dusty (appears hazy and dust accumulates on accumulates
on horizontal surfaces) poor ventilation, often older
building (built before 1975). Nursery buildings and
those with manure pits under slatted floors may be
biggest offenders. Usually worst during cold weather.
Diagnostic Aids:
Symptoms and history usually sufficient for diagnosis.
PFT may show decreased flow rates.
Skin tests or other immunological tests not indicated.
Treatment/Control:
Protection from environment most important action.
Medications usually not indicated.
Antihistamines, decongestants, antibiotics may provide
temporary relief of symptoms but should not be used
long-term.
Improved ventilation crucial.
Employ management procedures to limit dust generation
(i.e. frequent cleaning).
Install dust and gas control technology.
Establish a respirator program.
Abstain from smoking.
Prognosis:
Most improve if environmental exposure is controlled
through engineering, management, or use of respirator.
Cessation of smoking also crucial.
Temporary removal from the environment or use of a
respirator may help until other measures can be taken.
Long-term or permanent damage has not been reported to
date.
Usually not necessary to quit working.
Symptoms/History:
Chest tightness, mild dyspnea, some restriction and
obstruction during breathing.
Often accompanied by bronchitis.
Very common in exposed workers.
History similar to bronchitis, but often with a
nonproductive cough.
Work Exposure:
Identical to bronchitis (above).
Diagnostic Aids:
PFT following a workshift shows flow decreased flow
rates, primarily FEV, and FEV25-75.
Respiratory challenge with methacholine or histamine show
decreased PFT flow rates.
Treatment/Control:
Identical to bronchitis (above).
Prognosis:
Identical to bronchitis (above).
Symptoms/History:
Wheezing within minutes (immediate asthma) or for up to
24 hours (delayed asthma) following exposure.
Only seen in small percentage of workers (less than 10%).
Work Exposure:
: Among atopics or those who already have asthma from
another source, often occurs with first exposure.
: With other workers, a period of sensitization is
required, which may vary from a few months to several
years.
Extent of exposure not as important (environment may be
relatively clean, and a person may spend very small
amount of time in building).
Diagnostic Aids:
Same as asthma from any other source: obstructive air
flow patterns following exposure; skin test often
positive to one or more of feed grains, hog dander, hog
hair, various molds, dusts; associated with atopic status
and increased airways reactivity. Reversible with
bronchodilators.
Treatment/Control:
Medication and treatment same as any asthmatic.
Attempts to control exposures by environmental control
and respirators may or may not be helpful.
Desensitization usually not applicable because of
multiple antigens and irritant gases.
Prognosis:
Same as for any asthmatic.
Depending on degree of sensitivity, may be almost
impossible to protect these people from their
environment.
This may be one condition for which patient must quit
working in confinement house.
Increased airway reactivity and asthma may continue past
employment.
Symptoms/History:
: Fever, muscle aches, chest tightness, cough, malaise.
Symptoms develop 4-6 hours following exposure.
Self-limited symptoms usually resolve 24-72 hours.
Recurrent episodes common.
Seen in 10-15% of the swine farming population.
Often observed in clusters where 2-3 workers have similar
exposure.
Work Exposure:
Usually condition associated with work in a totally
enclosed building.
Usually follows a particularly heavy exposure (e.g. 4-6
hours of very dusty work such as handling or sorting
hogs).
Diagnostic Aids:
Elevated white blood cell count, usually neutrophilia.
PFT will show decreased FEV, and diminished flow rates.
PO2 may be decreased.
Bronchoalveolar lavage usually shows PMN response.
May show serum precipitins to various molds or dust
extracts, but these are not diagnostic.
X-ray may show scattered patchy infiltrates.
Lung biopsy may show inflammatory polymorphonuclear cell
infiltrates.
Treatment/Control:
: Symptomatic treatment in acute stages may include oxygen,
IV fluids to correct acid-base imbalance and dehydration.
Aspirin may be used to control fever.
Most cases do not seek medical attention; often confused
with influenza.
Prognosis:
Usual recovery period 3-4 days, but patient may feel
tired and have shortness of breath for several weeks.
Subsequent attacks may occur in future following heavy
exposure.
Symptoms/History:
Sudden and immediate onset of nausea, dizziness, possibly
sudden collapse, respiratory distress, apnea.
May lead to sudden death or patient may recover if
removed from environment, often with dyspnea, hemoptysis,
and pulmonary edema, following intensive treatment.
Work Exposure:
: Almost always occurs with agitation of a liquid manure
pit while emptying it.
: Respiratory effects will occur within seconds of
encountering high concentration of H2S.
Diagnostic Aids:
If patient survives: - x-ray often shows pulmonary edema.
- possibly presence of sulfhemoglobin and sulfide in
blood.
If deceased: - autopsy shows pulmonary edema, froth in
trachea, possibly greenish tinge to viscera. - blood
contains sulfide and sulfhemoglobin.
Treatment/Control:
Avoidance.
Remove exposed person from environment (without exposing
others) and resuscitate. May have to ventilate.
Seek medical care, watch for and control pulmonary edema.
Prognosis:
If patient survives initial exposure, will probably
recover usually with minimal loss of lung function.
Recovery period may be from days to 2-3 years, depending
on severity of exposure.
Table
3 lists the primary respiratory conditions associated with
confinement dusts and gases, including symptoms and signs,
associated work exposure, and specific diagnostic aids. This
table was developed from experience with swine confinement
operations. Conditions provoked within other types of confinement
buildings may differ.
Treatment
Medically,
little can be prescribed excluding treatment of some of the
acute illnesses (asthma, pulmonary edema from H2S intoxication).
These treatments, specific control measures, and the prognosis
for these illnesses are listed in Table 3.
Respiratory
conditions must be controlled through protecting the patient
from the environment, either by reducing dust and gas levels
or by isolating the patient from these substances. A patient
may need to get in touch with a consulting veterinarian or
agricultural engineer who has knowledge of environmental control.
The local veterinarian or the Cooperative Extension Service
agricultural engineer should be able to recommend an appropriate
expert.
Physicians
need to address the patient's anxiety as well as the patient's
medical problems. Confinement workers often are told to quit
working in confinement structures if they are having respiratory
problems. Usually this recommendation is unnecessary. It may
produce extreme mental stress, and should only be given once
the cause and prognosis of illness have been determined and
other avenues of controlling harmful exposures have been fully
explored. In many instances, the farmer has no reasonable
occupational choice other than to continue working in the
confinement building. Also, quitting farming is leaving a
life-style as well as a job.
Farmers
are becoming increasingly aware of confinement-associated
respiratory conditions. A physician can explain potential
long-term respiratory conditions but also instill confidence
regarding maintenance of the farmer's health status, and assist
in protecting the farmer from health problems of the work
environment. Monitoring the patient's respiratory status may
be reassuring to many patients. An initial exam should include
a thorough occupational history, spirometry, and a chest x-ray
if patients are symptomatic. These can be repeated if clinically
indicated at later annual check-ups.
Health
hazards associated with confinement houses must be addressed
through improvements in the environment and protection of
the individual. Techniques for reducing or eliminating the
sources of dusts and gases include delivering feed by extension
spouts into covered feeders, rather than letting feed fall
freely several feet from automatic delivery systems into open
feeders (See Fig. 5), frequently and systematically washing
buildings with power sprayers to keep them as clean as possible,
using wire mesh floors which are more self-cleaning, and assuring
that heating units are clean, vented, and functioning properly.
Control techniques can be assessed by measuring dust and gas
concentrations (see Unit 8).
Because
it is impossible to eliminate the formation of dusts and gases,
techniques for removing contaminants from the air of confinement
houses are critically important. Ventilation will reduce gases,
but not necessarily dusts, to healthful levels. Ventilation
systems must be properly designed and maintained, and ventilation
rates adjusted to include consideration of air quality. These
rates often are kept low in winter because of concerns for
conserving heat, causing dust and gas concentrations to rise.
A number of engineering techniques (e.g. use of heat exchangers
which allow increased ventilation while capturing some waste
heat) have been tried with varying degrees of success.
Anyone
working in a swine or poultry confinement house would be wise
to wear a dust mask. Persons exposed to houses with high dust
or gas concentrations, or persons with respiratory conditions,
may need to use a more sophisticated respirator such as a
half-mask cartridge respirator or air helmet. (See Unit 9)
Preventing
exposure to high concentrations of H2S from manure pits requires
stringent controls. General safety measures include constructing
manure pits outside of the confinement building, constructing
openings so that lids or other objects cannot fall into the
pit requiring a worker to enter the pit for retrieval, and
erecting safety guards and warning signs. Whenever a pit that
is under a confinement house is being agitated, people should
stay out of the building, ventilation of the house should
be maximized, and animals should be removed or observed from
outside the building.
Even
when not being agitated, manure pits can seldom be entered
safely. If entrance is imperative, only a self-contained breathing
apparatus, worn by an individual trained in its use, will
provide adequate protection. All operators should understand
that high concentrations of H2S cannot be smelled and that
H2S above 1000 ppm produces unconsciousness in only one to
three breaths.
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The
National Dairy Database (1992)
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