National
Institute for Occupational Safety and Health
NIOSH
ALERT: May 1990
DHHS (NIOSH) Publication No. 90-103
Many farm workers have died after entering manure pits. |
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The National
Institute for Occupational Safety and Health (NIOSH) requests
assistance in preventing deaths of farm workers in manure pits.
An urgent need exists to inform farm owners and workers about
the dangers of enter such pits, where oxygen-deficient, toxic
and/or explosive atmospheres often result from fermentation
of the wastes in confined areas. These hazards have been known
for several years. However, recent NIOSH investigations conducted
under the NIOSH Fatal Accident Circumstances and Epidemiology
(FACE) Program suggest that farm workers are unaware of the
danger, and many deaths continue to occur as a result of entry
into manure pits.
This
Alert describes seven deaths from asphyxiation (suffocation)
that occurred during two incidents involving entry into manure
pits. The recommendations included in this Alert should be
followed by all farm owners and operators who have manure
pits on their property. Editors of appropriate trade journals,
agriculture extension agents, farm owners and operators, and
those in the agricultural trades are requested to bring the
recommendations in this Alert to the attention of all workers
who are at risk.
Of the
approximately 2.3 million farms in the United States [USDA
1985], an unknown number contain manure pits or tanks. Manure
pit systems are used primarily on livestock farms (including
dairy operations) to allow for the easy cleaning of animal
confinement buildings and the efficient underground storage
of large amounts of raw manure. Because large areas of the
confinement building can be cleaned with a water hose or other
similar methods, such handling of manure is more efficient
than the historical method of shoveling solid animal waste.
Inside
the pit, the manure undergoes anaerobic digestive fermentation
to form fertilizer. The digestive process can generate four
potentially dangerous gases:
- Methane
- Hydrogen
sulfide
- Carbon
dioxide
- Ammonia
The
accumulation of these gases within the confined space of the
manure pit can produce an oxygen-deficient, toxic, and/or
explosive environment.
The
National Traumatic Occupational Fatality (NTOF) Data Base
indicates that from 1980 through 1985, 16 deaths resulted
from the asphyxiation (suffocation) of workers in manure pits
or similar waste tanks [NIOSH 1989a]. These deaths resulted
from nine separate incidents, but five of them involved multiple
fatalities. Because the NTOF Data Base includes only work-related
deaths of U.S. workers aged 16 or older, it may underestimate
the number of deaths resulting from entry into manure pits
during 1980-85.
Under
the Fatal Accident Circumstances and Epidemiology (FACE) Program,
NIOSH investigated two 1989 incidents described in this Alert.
These two incidents resulted in seven fatalities and suggest
that many farm workers are unaware of the hazards of entering
manure pits. These pits are designed as confined spaces with
limited means of entry and unfavorable ventilation. The gases
generated by the bacterial decay of the manure may accumulate
sufficiently to create deadly oxygen-deficient (less that
19.5% oxygen), toxic, and/or explosive atmospheres [NIOSH
1987].
In these
two incidents and in those reported earlier, the fatalities
often involved more than one victim. Two or more workers often
died when rescue was attempted without appropriate safety
equipment and procedures. Such a chain of events is consistent
with the findings of other FACE investigations, which show
that 39% of the victims in confined-space incidents were coworkers
or others who attempted to rescue the initial victim [Manwaring
and Conroy (in press)].
No Occupational
Safety and Health Administration (OSHA) standard exists for
work in and around manure pits. OSHA is reviewing a proposed
rule on confined-space procedures that would address safety
in confined spaces such as manure pits [54 Fed. Reg. 24080
(1989)], but even this standard would not be enforced by OSHA
on farms with 10 or fewer workers (calculated as an annual
average). The absence of a standard and the lack of knowledge
about the dangers of these pits increase the potential for
deaths such as those described in this Alert.
NIOSH
has published criteria for a recommended standard for working
in confined spaces [NIOSH 1979], an Alert on confined-space
hazards [NIOSH 1986], and a guide for working in confined
spaces [NIOSH 1987].
|
Table
1. Health effects associated with various percentages
of oxygen in the atmosphere |
| %
oxygen in atmosphere |
Health
effects |
21
(normal oxygen content in air) |
None
|
19.5
(minimum oxygen level for safe entry) |
None
|
16
|
Impaired
judgment and breathing |
14
|
Faulty
judgment, rapid fatigue |
6
|
Difficult
breathing, death in minutes |
Source:
NIOSH [1987]. |
|
The following is a brief summary of the physiological effects of gases commonly encountered in manure pits. Because all of the gases generated in these pits can displace oxygen (O2), atmospheric conditions inside the pit can become oxygen-deficient. Table 1 lists the health effects associated with various percentages of oxygen in the atmosphere [NIOSH 1987].
Methane
Methane
(CH4), is an odorless gas that is flammable or
explosive at concentrations of 5% to 15% by volume of air
[NIOSH 1985b]. At high concentrations, methane can displace
enough oxygen to cause death by suffocation. Because this
gas is lighter than air, it occurs near the top of the pit.
Methane should be expected to be present in manure pits.
Hydrogen
Sulfide
Hydrogen
sulfide (H2S) is a highly toxic gas with a "rotten
egg" odor at low concentrations [NIOSH/OSHA 1981]. At
high concentrations, hydrogen sulfide can paralyze the olfactory
senses [NIOSH 1979]. Because this gas is heavier than air,
it can settle near the bottom of the manure pit. Hydrogen
sulfide is a severe eye irritant and may cause tissue damage
[NIOSH/OSHA 1981]. At low concentrations, gas can cause dizziness,
headache, nausea, and irritation of the respiratory tract.
At high concentrations, hydrogen sulfide can cause unconsciousness,
respiratory failure, and death within minutes. In addition,
hydrogen sulfide may be explosive at a wide range of concentrations
in air--4.3% to 46% by volume [NIOSH 1985a].
Carbon
Dioxide
Carbon
dioxide (CO2) is an odorless that is normally in
the atmosphere [NIOSH/OSHA 1981]. Because this gas is heavier
than air, it can settle near the bottom of the manure pit.
At low concentrations, carbon dioxide can result in labored
breathing, drowsiness, and headache. At high concentrations,
carbon dioxide can displace enough oxygen to cause death by
suffocation.
Ammonia Ammonia
(NH3) has the sharp odor characteristic of household
ammonia [NIOSH/OSHA 1981]. This gas can severely irritate
the eyes, nose, throat, and lungs. Exposure to high concentrations
can be fatal.
The
two incidents described below were investigated by NIOSH as
part of its FACE Program. These incidents suggest that many
farm workers may be unaware of the hazards of entering manure
pits. Furthermore, both incidents involved the deaths of would-be
rescuers who were members of the same family. Family members
may be more apt than others to attempt a rescue.
Case
No. 1--Two Fatalities
On June
26, 1989, a 31-year-old male dairy farmer and his 33-year-old
brother died after entering a 25-foot-square, 4-1/2-foot-deep
manure pit inside a building on their farm. A pump intake
pipe in the pit had clogged, and the farmer descended into
the pit to clear the obstruction. While in the pit, he was
overcome and collapsed. The victim's brother was standing
at the entrance of the pit and apparently saw the victim collapse.
He entered the pit an attempt to rescue him. The brother was
overcome and collapsed inside the pit. Four hours later, another
family member discovered the two victims inside the pit and
called the local fire department to rescue them. The victims
were pronounced dead at the scene by the coroner. The coroner's
report attributed the cause of death in both cases to methane
asphyxiation [NIOSH 1989b].
Case
No. 2--Five Fatalities On July
26, 1989, five farm workers died after consecutively entering
a manure pit on their farm. The pit measured 20 by 24 feet
and was 10 feet deep. The victims were a 65-year-old dairy
farmer, his two sons aged 37 and 28, a 15-year-old grandson,
and a 63-year-old nephew. The younger son initially entered
the pit to replace a shear pin on an agitator shaft. (NOTE:
Agitation of the manure, which is required to facilitate transfer,
causes a rapid release of the gases formed during decomposition.)
While attempting to climb out of the pit, the initial victim
was overcome and fell to the bottom. The grandson then entered
the pit to attempt a rescue. He too was overcome and collapsed.
The nephew, the older son, and the dairy farmer then entered
the pit one at a time, attempting to rescue those already
overcome. Each was overcome and collapsed in turn. A carpet
installer working at the farm house then entered the pit to
attempt a rescue. He too was overcome but was rescued by his
assistant and subsequently recovered. Finally, the owner of
a local farm implement business arrived on the scene with
two of his workers and, using a rope, extricated the five
victims from the pit. When the local emergency rescue squad
arrived on the scene approximately 20 minutes after the incident,
they immediately began cardiopulmonary resuscitation. The
nephew was pronounced dead at the scene. The remaining four
victims were transported to the local hospital. The farmer
and his younger son were pronounced dead on arrival, and the
older son died an hour after reaching the emergency room.
The grandson was transferred to a major trauma center by helicopter
but he died approximately 6 hours after his removal from the
pit. Reports of the medical examiner cite methane asphyxiation
as the cause of these five deaths [NIOSH 1989c].
Many
farm workers appear to be unaware of the immediate danger
posed by entry into manure pits. Like other types of confined
spaces, manure pits present special problems regarding worker
awareness of hazards. The dangerous atmospheric conditions
may exist intermittently. In both of the incidents described
in this Alert, the pits had been entered on numerous occasions
without problems. Previous uneventful entries may lead farm
workers to feel safe about entering these pits.
The
decomposition of waste that occurs in manure pits can create
oxygen-deficient, toxic, and/or explosive atmospheres. The
anaerobic bacterial action that breaks down the manure can
generate methane, hydrogen sulfide, carbon dioxide, and ammonia.
These gases may produce toxic effects, but more important,
they can displace oxygen in a confined space. Deaths can occur
from lack of oxygen or from the toxic effects of these gases
[Donham 1983; CES 1980]. In addition, methane and hydrogen
sulfide may present an explosion hazard.
The
two incidents reviewed in this Alert occurred during hot weather,
which may result in increased gas accumulation in manure pits.
All 16 deaths identified in the NTOF Data Base occurred from
April through September, with the highest number occurring
in August. Although this information indicates that summer
is the most dangerous period, the potential for an oxygen-deficient,
toxic, and/or explosive atmosphere is always present in a
manure pit.
Manure
pits on farms should be treated like any other type of confined
space. As such,
- all
manure pits should be ventilated,
- the
atmosphere within the pit should be tested before entry,
- a
standby person should be in constant contact and ready to
lift the worker to safety with mechanical lifting equipment
(winch, hoist, or pulley), and
- anyone
entering a manure pit should wear a safety belt or harness
with a lifeline tied to the mechanical lifting device.
In addition,
a positive-pressure, self-contained breathing apparatus (SCBA)
should be used by individuals entering the pit if an oxygen-deficient
or toxic atmosphere is detected. However, because the required
training and specialized equipment may not be readily available
to farm workers, NIOSH recommends that they take the following
MINIMUM precautions wherever manure pits are in use:
- NEVER
enter a manure pit unless absolutely necessary and only
when proper safeguards have been taken!
- Post
hazard signs on all manure pits. The signs should be understandable
to workers who cannot speak English or read. Signs in more
than one language may be necessary in some areas.
- Provide
a powered, continuous fresh air ventilation system for each
manure pit. Ventilation is especially important when agitation
of waste is initiated after it has been fermenting for some
time. Because this system should consist of both supply
and exhaust ventilation, two openings are required in the
waste pit. Portable fans can be used if they have an explosion-proof
design and are sufficiently large enough to provide a continuous
change of air within the pit. An alternative is a ventilation
system that uses a large, high-velocity, high-volume fan
of explosion-proof design to force fresh air into a manure
pit that has an exhaust vent located as far from the supply
fan as possible. All exhaust from the pit should be directed
outside and away from workers and livestock.
Explosion-proof ventilation equipment must be used because
methane and hydrogen sulfide gas can be explosive. The
pit should be ventilated continuously. Contact local agriculture
extension agents for additional information on ventilating
manure pits.
- NEVER
enter a manure pit unless someone is standing by and maintaining
constant visual or auditory contact. This standby person
must
--remain at the opening of the pit during the entire
time the pit is occupied,
--have a mechanical device (winch, hoist, or pulley)
in place to help remove the person from the pit,
--be physically capable of using the mechanical device
to lift an unconscious victim from the pit without entering
it,
--resolve all details of the rescue plan, including
availability of rescue equipment, before anyone enters
the pit, and
--remember that a delay of even a few minutes could
be fatal in an emergency.
- ALWAYS
wear a harness or safety belt with a lifeline when entering
a manure pit. Secure the end of this lifeline to the mechanical
lifting equipment outside the pit. The use of a harness
or safety belt with a lifeline is critical because it is
the only safe means for a standby person to rescue a worker
from the pit without proper respiratory protection (i.e.,
positive-pressure, self-contained breathing apparatus).
- NEVER
enter a manure pit to attempt a rescue without proper respiratory
protection (i.e., positive-pressure, self-contained breathing
apparatus). Rescuers who enter the pit without such equipment
will almost certainly become victims. Instead, call the
local fire department or rescue squad immediately. They
have the training and equipment needed to accomplish such
a rescue without endangering other lives.
NIOSH
further recommends that the following actions be taken by
farm owners and operators as well as manufacturers and providers
of equipment for animal waste pit systems:
- Provide
the information in this Alert to all farm workers.
- Fit
all openings to manure pits with substantial metal grill
covers to provide some natural ventilation and to prevent
accidental falls or entries into the pits. Remember, however,
that natural ventilation alone cannot maintain a safe atmosphere
within the pit. Powered ventilation must be used before
anyone enters the manure pit.
- Eliminate
the need for entry into the pit by providing access to all
serviceable parts (shears, pins, cleanouts, etc.) from the
outside:
--Modify existing systems to relocate serviceable parts
to the outside.
--Engineer new manure pit systems to provide access
to all serviceable parts from the outside.
- Provide
all purchasers of equipment designed for manure pit systems
with the following:
--Information on the hazards of these pits
--Information (diagrams, etc.) on installing the equipment
to permit servicing without entry into the pit.
Comments
or questions concerning this Alert should be directed to Dr.
Thomas R. Bender, Director, Division of Safety Research, 944
Chestnut Ridge Road, Morgantown, West Virginia 26505-2888;
telephone (304) 291-4595.
J. Donald
Millar, M.D., D.T.P.H. (Lond.)
Assistant Surgeon General
Director, National Institute for Occupational Safety and Health
Centers for Disease Control
CES
[1980]. Beware of on-farm manure storage hazards, S-82. West
Lafayette, IN: Cooperative Extension Service, Purdue University.
Donham,
KJ [1983]. Livestock confinement. In: Parmeggiani L, ed. Encyclopedia
of Occupational Safety and Health. 3rd ed., Vol. 2. Geneva,
Switzerland: International Labor Organization, pp. 1239-1241.
54 Fed.
Reg. 24080 [1989]. U.S. Department of Labor, Occupational
Safety and Health Administration: 29 CFR 1910. Permit required
confined spaces; notice of proposed rulemaking.
Manwaring
JC and Conroy C [in press]. Occupational confined space-related
fatalities: surveillance and prevention. Journal of Safety
Research.
NIOSH
[1979]. Criteria for a recommended standard: working in confined
spaces. Morgantown, WV: U.S. Department of Health, Education,
and Welfare, Public Health Service, Centers for Disease Control,
National Institute for Occupational Safety and Health, DHEW
(NIOSH) Publication No. 80-106.
NIOSH
[1985a]. NIOSH pocket guide to chemical hazards. Cincinnati,
OH: U.S. Department of Health and Human Services, Public Health
Service, Centers for Disease Control, National Institute for
Occupational Safety and Health, DHHS [NIOSH] Publication No.
85-114.
NIOSH
[1985b]. Safety and health in confined workspaces for the
construction industry. Cincinnati, OH: U.S. Department of
Health and Human Services, Public Health Service, Centers
for Disease Control, National Institute for Occupational Safety
and Health.
NIOSH
[1986]. NIOSH alert: Request for assistance in preventing
occupational fatalities in confined spaces. Cincinnati, OH:
U.S. Department of Health and Human Services, Public Health
Service, Centers for Disease Control, National Institute for
Occupational Safety and Health, DHHS (NIOSH) Publication No.
86-110.
NIOSH
[1987]. A guide to safety in confined spaces. Cincinnati,
OH: U.S. Department of Health and Human Services, Public Health
Service, Centers for Disease Control, National Institute for
Occupational Safety and Health, DHHS (NIOSH) Publication No.
87-113.
NIOSH
[1989a]. Five family members die after entering manure waste
pit on a dairy farm. Morgantown, WV: U.S. Department of Health
and Human Services, Public Health Service, Centers for Disease
Control, National Institute for Occupational Safety and Health,
Division of Safety Research, Fatal Accident Circumstances
and Epidemiology (FACE) Report 89-46.
NIOSH
[1989b]. National traumatic occupational fatality (NTOF) data
base. Morgantown WV: U.S. Department of Health and Human Services,
Public Health Service, Centers for Disease Control, National
Institute for Occupational Safety and Health, Division of
Safety Research.
NIOSH
[1987c]. Two farm laborers die in oxygen-deficient manure
pit. Morgantown, WV: U.S. Department of Health and Human Services,
Public Health Service, Centers for Disease Control, National
Institute for Occupational Safety and Health, Division of
Safety Research, Fatal Accident Circumstances and Epidemiology
(FACE) Report 89-44.
NIOSH/OSHA
[1981]. Occupational health guidelines for chemical hazards.
Cincinnati, OH: U.S. Department of Health and Human Services,
Public Health Service, Centers for Disease Control, National
Institute for Occupational Safety and Health, DHHS (NIOSH)
Publication 81-123.
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and Reproduction Information: Information in NASD does not represent
NIOSH policy. Information included in NASD appears by permission
of the author and/or copyright holder. More
NASD Review: 04/2002
This NIOSH
Update is DHHS(NIOSH) Publication number
81-123
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This page was last updated: 2/11/97.
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