increased use of manure storage facilities in agriculture there
have been numerous instances where a farmer, family member,
or employee has asphyxiated or succumbed to toxic gases from
the storage. Cases have been documented where several individuals
have died while attempting to rescue a coworker or family member
from an underground pit or a spreader tank.
What toxic gases are present around such storage facilities?
The four main gases produced from decomposing manure are Hydrogen
Sulfide, Methane, Ammonia, and Carbon Dioxide. In high concentrations,
each of these gases may pose a health threat to humans and livestock.
In animal housing facilities, where the manure pit is often
located below the facility floor, manure gases are generally
detectable in low concentrations throughout the year. When pits
are agitated for pumping, some or all of these gases are rapidly
released from the manure and may reach toxic levels or displace
oxygen, increasing the risk to humans and livestock.
Toxic or poisonous reactions in people or animals, oxygen depletion
which can result in asphyxiation and explosions that can occur
when oxygen mixes with the gases such as methane.
Hydrogen sulfide is considered the most dangerous of the byproducts
of manure decomposition. It has a, distinct rotten egg smell
and is heavier than air. After breathing this gas for a short
time, your sense of smell becomes fatigued and you can no longer
detect an odor.
At low concentrations H2S irritates the eyes and respiratory
tract while at moderate levels exposure causes headache, nausea,
and dizziness. At high concentrations H2S paralyzes the nerve
cells of the nose to the point where the person can no longer
smell the gas. Both carbon dioxide and hydrogen sulfide are
heavier than air, and will tend to settle to the lower areas
of the storage facility and remain in high concentrations even
Ammonia has a distinct, sharp, penetrating odor detectable at
very low concentrations. It is heavier than air, and at moderate
levels of concentration, it can irritate the eyes and respiratory
tract. At high concentrations it can cause ulceration to the
eyes and severe irritation to the respiratory tract. . Flushing
irritated skin or eyes with water is the best first-aid treatment
Carbon Dioxide is heavier than air and difficult to detect.
It replaces Oxygen in air and acts as an asphyxiate. At moderate
concentrations it causes shortness of breath and dizziness.
It is a major contributing factor to animal deaths by asphyxiation
in confinement buildings with faulty ventilation. In addition
to manure decomposition, carbon dioxide is also a byproduct
of livestock respiration.
Methane is odorless and lighter than air, so it tends to accumulate
at the top of manure pits. It is considered an asphyxiate at
extremely high concentrations. The main hazard is its flammable,
explosive nature. Methane is extremely difficult to detect without
gas detection instruments because it is odorless, but it should
be anticipated as being present in all manure storage areas.
Some systems for storing the manure are more dangerous than
others. Below ground storage facilities, or pits, are more hazardous
than above ground structures. Systems that are covered by lids,
caps or slotted floors are more hazardous than uncovered systems.
Pump-out pits or caps can also be very hazardous. Leaks from
storage structures may also cause significant losses of fish
and other aquatic species if near streams or lakes.
Construct manure storage pits outside confinement buildings,
above or below ground, and in a way that gases cannot move back
into the building.
Make sure that pumping equipment can be quickly and easily
removed for repairs or adjustment.
Attach a hinge or chain to covers or lids on storage areas
to prevent them from falling into the storage pit
Covered or enclosed tank facilities present the greatest danger,
especially when manure is being agitated or pumped out of the
structure. Little gas is produced or accumulates when the manure
is still and natural air movement or ventilation from fans prevents
The primary advantages of liquid manure storage facilities are
that they make the waste handling process less demanding on
your time and allow for applications of manure on croplands
at more convenient or appropriate times. In general, there are
three types of liquid manure storage systems being used.
a) Large manure storage tanks located directly underneath the
livestock housing area.
b) Manure storage located away from the livestock housing areas
in open lagoons or ponds.
c) Above ground, silo-type, manure storage structures.
In all three types, the manure is flushed from the livestock
housing area with added water and then agitated by various means
to form liquid slurry. This slurry is then pumped periodically
from the storage area into applicator tank wagons or through
irrigation systems for application on crop land as a valuable
fertilizer and soil conditioner.
When animal waste of any type is being stored in large quantities,
a number of hazards are present for both man and animal. The
most obvious hazard is the potential danger of falling into
one of the large open storage areas and drowning.
There is also the danger from manure gases, which are produced
as the manure is decomposed by bacterial action. During the
decomposition process, a variety of gases are released which
can be hazardous to both people and livestock.
Knowing the nature of these gases and the effects they might
have on you should reduce the potential risk of working around
manure storage areas.
In addition to adhering to proper construction and maintenance
procedures for liquid manure storage facilities, owners should
be encouraged to follow a few precautionary measures to protect
both workers and livestock from harmful manure gases.
They are as follows:
Know the physical effects of the various gases released during
manure decomposition. If at any time these effects are detected,
it is critically important that both workers and livestock are
evacuated from the area or ample ventilation provided.
Maintain adequate ventilation in all confined areas where
livestock are housed or livestock waste is stored. This is especially
true if the manure is being agitated, since agitation causes
a rapid release of gases. Even with the facility's ventilation
system operating, high levels of toxic gases can accumulate
quickly. Ventilation recommendations are available from a number
If the power fails, open all windows and doors and remove
livestock if possible. Many farmers with livestock confinement
operations have invested in portable or emergency power generating
units to insure livestock housing areas have continuous power
Since a methane/air mixture can be highly explosive, prohibit
smoking or other open flames in confined housing or manure storage
Concerning open storage of liquid manure in ponds or lagoons,
precautionary measures should also be taken to reduce the risks
to people and livestock.
Manure ponds or lagoons should, if at all possible, be fenced
in to prevent access by children or livestock. Open lagoons
can appear deceptively solid during warm weather and lure the
curious out onto the surface.
Signs should be posted around the perimeter of the lagoon
providing a clear warning of the existing hazards
- Remind children, visitors and any nonessential workers
to stay away from manure pits and transfer/holding tanks,
especially during agitation and pumping.
Do not allow people to enter livestock buildings during agitation
and pumping of manure pits under the building floor.
Full respiratory protection, in the form of self-contained
breathing units, should be utilized at all times. No one should
ever enter a manure storage pit - even to rescue a victim overcome
by gases -without a supply of air and assistance from a backup
crew using a lifeline.
- Avoid entering manure storage areas if at all possible.
Many deaths have occurred when people entered manure storage
areas without proper safety precautions.
- If you must enter a manure storage area, the following
confined space entry procedures will minimize, but not eliminate,
- Never enter a manure pit during or just after agitation
because there is always the possibility of deadly concentration
of this gas. Plumbing and pumping equipment should be installed
so that it can be easily removed for repairs.
Before agitation, take steps to ensure the welfare of the animals
and people working in the area.
- Remove all people and animals if possible. If animals
cannot be removed, maximize ventilation and agitate slurry
very slowly at first. Monitor the condition of the animals.
If the animals act restless or agitated or abnormal, stop
the agitation immediately and ventilate the area.
- Always keep at least one foot of space between the highest
manure level and the slats. This protects animals who lie
on the slats and inhale the gases that accumulate at the
surface of the pit.
- Do not enter manure pits without either:
- A self-contained air supply like those fire fighters
use. (Dust masks or other cartridge respirators will not
filter out the toxic gases nor will they provide the oxygen
requirement to work in confined spaces such as manure pits.)
- OR Test before entering. Test the oxygen level
to make sure that adequate oxygen is available. Also test
for hydrogen sulfide, a particularly toxic gas, to be sure
that concentrations are safe (less than 10 ppm).
- Provide additional forced ventilation. Additional ventilation
will increase oxygen and decrease hydrogen sulfide and other
- Monitor conditions. Agitation from working can increase
the toxic gas levels. Monitor conditions while working.
- When someone collapses in a pit, gases are so concentrated
that it is suicidal for anyone else to enter without a self-contained
- The only reasonable immediate action is to ventilate
the storage area and notify rescue personnel who can bring
the proper equipment.
- Barn fans may be activated to provide ventilation, but
do not lower fans into the pit because this could cause
- Use a safety line. A worker in a confined space or manure
storage area should wear a body harness with a safety line.
- The safety line should be held by enough people and/or
a winch so that the worker can be pulled out of the area
if a problem develops.
- Wear a supplied air respirator. Never a pit without one.
- The person using a respirator should be trained on the
use of the mask. It is particularly important that the mask
form a tight seal around the face.
- Provide a clear escape path. Make it as easy as possible
for the worker to exit the manure storage area quickly.
Don't block the path with tools or objects.
- Keep fire away. Methane gas is a byproduct of manure
degradation, and it is flammable. Keep fire and other ignition
sources such as electrical tools away from the manure storage
area. Test the methane level with an explosion meter.
- Know first aid. Someone on the site should be trained
in CPR and first aid.
- Recognize that conditions are of greatest risk when manure
is agitated or moved. Movement and agitation increase the
release of dangerous gases, sometimes several fold. When
agitating, pumping, or moving manure, take precautions to
be sure that extra ventilation is provided to nearby areas
(e.g., buildings over or near the manure storage).
- Due to the equipment requirements and inherent risks
associated with entering an area where there may be toxic
gases or insufficient oxygen, you should consider hiring
a professional trained in working in these areas to perform
maintenance tasks. If hiring a professional or using a SCBA
is not possible, the best advice is to stay out of the pit.
The information and recommendations contained in this publication
are believed to be reliable and representative of contemporary
expert opinion on the subject material. The Farm Safety Association
Inc. does not guarantee absolute accuracy or sufficiency of
subject material, nor can it accept responsibility for health
and safety recommendations that may have been omitted due to
particular and exceptional conditions and circumstances.
© 2002 Farm Safety Association Inc.
22-340 Woodlawn Road West, Guelph, Ontario (519) 823-5600.
Disclaimer and Reproduction Information: Information in
NASD does not represent NIOSH policy. Information included in
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