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Dennis
J. Murphy
Pennsylvania State University Cooperative Extension
On-farm storage of animal manure each year is becoming more
common in Pennsylvania. Dairy, beef, swine, and veal enterprises
are all making increased use of manure storage systems as
a part of their operation. With each additional installation,
the probability that a fatal accident will result increases.
Tragically, experiences in several states indicate that when
an accident does occur, it is likely to involve two or three
fatalities (see Figure 1). Also, there have been several cases
of large numbers of livestock perishing due to manure gases.
There
are various types of manure storage systems, and some are
more hazardous than others. Below ground storages, or pits,
are more hazardous than above ground storages. Systems that
are substantially covered by slotted floors, or have storage
lids or caps, are more hazardous than those that have no type
of top covering (see Figure 2). Thus, storages that are potentially
the most dangerous utilize pits within buildings or directly
beneath livestock. Pump-out pits with lids or caps can also
be very hazardous.
Manure
storage hazards include gases that are toxic (hydrogen sulfide),
corrosive (ammonia), asphyxiant (carbon dioxide), and explosive
(methane). Drowning is also possible. All of these hazards
exist with covered pit type storages. Danger is most severe
when manure is being agitated or pumped out, and after emptying
if the pit is covered. At other times, gas production is very
slight and ventilation from fans or natural air movement usually
prevents hazardous buildup of the gases. Because open storages
and above ground tanks are not covered, oxygen depletion and
toxic and explosive gas buildup is less likely to occur. Therefore,
the only potential hazard normally associated with these systems
is drowning.
Hydrogen sulfide is the most hazardous manure gas. It is colorless,
heavier than air, and can cause death within seconds at high
concentration. Hydrogen sulfide is identified by a rotten
egg odor and can be detected at low levels. However, the sense
of smell is deadened from concentrations much less than that
which is lethal. Additionally, the smell is often masked by
many other smells common to livestock facilities. The amount
of the gas can be increased a thousand-fold during agitation
nd emptying. Hydrogen sulfide is associated with most of the
fatalities from manure storages, both human and animal.
Carbon
dioxide is a non-toxic gas, but it does replace oxygen and,
therefore, can asphyxiate humans and animals. Because it is
colorless and odorless, carbon dioxide is impossible to detect
without gas detection equipment. Since it is heavier than
air, it usually accumulates near the bottom of the storage.
Carbon dioxide does not usually build up to the point that
it becomes lethal unless all ventilation into and around the
pit has been eliminated for a few hours.
Ammonia
can cause severe damage to the eyes, throat, and lungs. This
gas combines with moisture in the eyes and respiratory tract
to form an alkaline base, which results in severe burns. Ammonia
is lighter than air and has a strong bleach-like smell. Because
of its irritating nature, people usually leave the area quickly.
Therefore, it is not suspected to have caused any human deaths.
However, constant low-level exposure to ammonia can have a
discomforting effect on humans and livestock.
Methane
is a highly flammable and explosive gas. It, too, is odorless
and colorless, and impossible to detect without gas detection
instruments. Methane is lighter than air and readily rises
out of storage areas. It can collect under hoods, roof ridges,
and corners. It's most likely to accumulate during hot weather
if ventilation is poor. There have been a few methane explosions
resulting from lighting torches and sparks from a shorted
electrical wire.
There are several things an operator can do to minimize hazards
associated with stored manure. However, none is more important
than keeping people and animals out of buildings and providing
strong, constant ventilation during agitation and emptying.
Continue to ventilate for a few hours after pumping has stopped.
Ventilation systems should be equipped with alarms to warn
of failure, and auxiliary ventilation should be available
in case of power failure. Another recommendation is not to
fill your storage to capacity. Allow one to two feet of air
space to accommodate concentrations of gases. Also, always
keep the agitator below the liquid surface; use gas traps
in pipelines emptying into storages to keep gas from flowing
back into buildings; and forbid smoking, open flames, or spark
producing operations in the immediate vicinity of the storage
area.
Rescuing
a person from a pit is a no win operation. Unfortunately,
when someone collapses in a pit, gases are so high that it
is literally suicide for anyone else to enter without a self-contained
breathing apparatus (see Figure 3). The only reasonable action
that can be taken is to provide ventilation into the storage
and wait for rescue personnel with the proper equipment. Barn
fans and silo blowers are sources of ventilation that may
be used. However, do not lower fans into the pit because of
possible methane gas buildup.
Uncovered
storages at ground level should be fenced to keep people and
animals off the crust-like surface that normally develops.
The surface crust may harden in very dry or extended cold
periods, but the hardening will be uneven. As the crust softens
with changing weather conditions, a person or animal can suddenly
break through. Do not leave ladders leaning against above
ground tank storages. A person who accidentally falls into the
tank will be trapped because he or she will be unable to limb
the smooth surface.
Warning
signs should be placed near open storages and above ground
tanks, and a rescue pole and rope should be appropriately
located in the area. Remember to warn visitors and guests
of the hazards or manure storages because you are legally
responsible for their safety while on your property.
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Disclaimer
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 document
was published in 1991 as Pennsylvania State University Fact
Sheet Safety
28
, Pennsylvania Cooperative Extension Service. For more
information, contact Pennsylvania State University College
of Agricultural Sciences, Agricultural Engineering Department,
246 Agricultural Engineering Building, University Park, PA
16802.
Dennis
J. Murphy, professor, Agricultural Engineering Department,
Cooperative Extension Service, Pennsylvania State University,
University Park, PA 16802.
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