Farm Safety Association, Inc.
Liquid
manure storage systems have come into prominent use in recent
years. Many dairy, beef and hog operations (and to a limited
extent poultry operations) now use liquid manure systems as
a fast and economical method of handling animal wastes. These
systems, particularly if they are incorporated into the barn
construction, may pose a serious hazard because of gases produced.
Decomposing animal manure gives off a variety of gases including
hydrogen sulphide, carbon dioxide and methane. Of all these
gases, hydrogen sulphide or more commonly called manure gas,
is the most dangerous. Hydrogen Sulphide (H2S) has
been responsible for many animal deaths as well as occasional
human deaths.
Hydrogen
Sulphide is formed as a result of decomposing animal manure.
The decomposition process begins as soon as it is excreted by
the animals. Micro-organisms utilize the manure to synthesize
new cellular material and to furnish energy for synthesis. This
process takes place with or without oxygen. However, the type
of microbes, and the type of gases that are produced, are dependent
on the type of environment in which degradation takes place.
In anaerobic conditions (without oxygen), typical of most liquid
manure systems, hydrogen sulphide will be given off.
Hydrogen
sulphide is produced continuously in all un-aerated manure
storage systems, including shallow barn gutters, underground
storage tanks or outside manure holding ponds or lagoons.
Depending on temperatures and other factors, the rate of release
of the gas is slow in undisturbed storage.
Hydrogen
sulphide is a clear, colourless gas that can be identified in
relatively low concentrations, by a characteristic "rotten-egg"
odour. Hydrogen sulphide is approximately 20 percent heavier
than air, with a specific gravity of 1.19. Hydrogen sulphide
odours can be recognized in concentrations of less than 1 mg/kg
(air). The odour of hydrogen sulphide will increase as the gas
becomes more concentrated. However, in concentrations of 150
or greater mg/kg (air), a person's ability to detect the gas
is affected by temporary paralysis of the olefactory nerves
in the nose. Owing to this unique property of Hydrogen sulphide,
relying totally on the sense of smell to warn against the gas,
can be extremely dangerous. In high concentrations, the ability
to smell the gas is lost instantaneously, the disappearance
of the odour could mean that the gas concentrations have increased.
Hydrogen
sulphide is classified as a toxic chemical, in high concentrations
it will lead to almost instantaneous poisoning and death. High
concentrations will result in the complete arrest of respiration.
A person over come by this gas should promptly be removed from
the contaminated area and given immediate artificial respiration.
Exposure
to lesser concentrations may result in nausea, stomach distress,
belching and coughing. Moderate concentrations may result
in eye irritation.
Because
hydrogen sulphide is heavier than air, the gas has a tendency
to accumulate on the surface of the manure. Over a period of
time, the undisturbed accumulation of the gas, along with a
rising level of liquid manure in the storage system, may force
the gas above floor level. When this happens animals are usually
doomed. Above ground air currents may also result in localized
concentrations of the gas, this usually explains why livestock
losses occur in certain areas of a particular barn.
The greatest
danger of exposure to hydrogen sulphide exists during agitation
and pumping. Clean out during the fall months after several
months of warm temperature storage accelerates gas production,
or clean out after a prolonged period of time increases the
potential danger. During agitation, hydrogen sulphide is released
from the manure in the same manner as carbon dioxide is liberated
after shaking a carbonated soft drink.
The
following precautions are essential to the safe management of
a liquid manure system located in a livestock building:
- Under
no circumstances should anyone enter a liquid manure pit
without wearing a self-contained breathing apparatus, even
if the pit is empty. Use a life line that is connected to
someone outside the danger area.
- Never
allow the manure pit to fill completely. Allow 1 to 2 feet
of air space to accommodate concentrations of gas.
- If
possible, lower the level of liquid manure in the storage
facility before commencing agitation. This will further
reduce the possibility of gas being forced above floor level.
- Keep
the agitator below the liquid surface. Gas will be released
in greater volumes if vigorous surface agitation occurs.
- Provide
strong ventilation during pumping and agitation. The building
interior should be off limits to people, and if possible,
animals should be evacuated.
- Because
of the dangers presented by the agitation and pumping operations,
these procedures should involve two people, connected by
a life line, with one person always outside of the danger
area.
- Consult
with your physician if you have been exposed to hydrogen
sulphide in concentrations severe enough to cause irritation
to the respiratory tract.
SPREADER
TANKS
The danger of hydrogen sulphide in spreader tanks is as great, or greater than that of a liquid manure pit. Under no circumstances should a spreader tank be entered without using a self contained breathing apparatus and a life line attached to someone outside of the danger area.
PROPERTIES
OF HYDROGEN SULPHIDE *
Chemical
Formula |
H2S |
Odour |
Rotten
Egg |
Boiling
Point |
60°
C |
Odour
Threshold |
0.13
mg/kg (Oxygen) |
Specific
Gravity |
1.19 |
*
American Industrial Hygiene Association, 1962. |
|
DESIGN
AND CONSTRUCTION OF NEW FACILITIES
The following
factors should be taken into consideration if you are considering
incorporating a liquid manure system into a new building:
- All
manure pit pump-out openings should be located outside the
building, thereby eliminating the danger of working in a
confined area.
- Liquid
manure storage should be separated from the livestock buildings.
Connecting drains, gutters and channels should be fitted
with gas traps, or some other means, to prevent gases from
re-entering the building.
- In-barn
liquid manure collection pits should be kept to a minimum
volume and divided into small compartments to eliminate
the need for agitation.
PHYSIOLOGICAL
RESPONSE OF ADULT HUMANS TO HYDROGEN SULPHIDE **
Effect |
Concentration
Mg (H2S)/1 Kg (Air) |
Least
Detectable Odour |
0.01-0.7 |
Offensive
Odour |
3-5 |
Eye
Irritation |
10 |
Irritation
Mucous Membranes
and Lungs |
20 |
Irritation
of Respiratory Tract |
50-100 |
Olefactory
Nerve Paralysis |
150 |
Headache,
Dizziness |
200 |
Nausea,
Excitement, Unconsciousness |
500-600 |
Rapidly
Fatal |
700-2000 |
**
Source Nordstron, G.A.: J.B. McQuilty: "Manure
Gases in the Animal Environment." University of
Alberta - 1976. |
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
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
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.
Fact Sheet
NO.
F-006
SEPTEMBER 1985
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