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Howard
J. Doss, Howard L. Person and William McLeod
Michigan State University Extension
Since
the increased use of manure pits by Michigan livestock producers,
there have been several instances where a farmer, family member,
or employee has asphyxiated or succumbed to toxic gases from
the pit. Cases have been reported where several individuals
have died while attempting to rescue a coworker or family
member from a pit.
Nationwide
data shows that most deaths occur during the summer months,
a time when many producers are emptying pits. Regardless of
the season, it is always best to presume that the pit contains
hazardous gases or lacks oxygen. Producers need to take protective
measures to protect themselves and others working in or around
the pit.
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 (see Table 1). In swine housing facilities, where
the manure pit is often located below the facility floor,
these 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
a d may reach toxic levels or displace oxygen, increasing
the risk to humans and livestock.
Table
1. Acute Effects of Swine Confinement Air Contaminants
on Humans* |
Gas
| Exposure
level
| Effect
or symptom
|
Hydrogen
Sulfide |
5
ppm |
RECOMMENDED
MAXIMUM FOR HUMAN HEALTH |
10
ppm |
Eye
irritation |
20
ppm for >20 minutes |
Irritation
to the eyes, nose and throat |
50
to 100 ppm |
Vomiting,
nausea, diarrhea |
200
ppm |
Dizziness,
nervous system depression, increased susceptibility to
pneumonia, fluid in the lungs with prolonged exposure |
500
ppm for 30 minutes |
Nausea,
excitement, unconsciousness |
600
ppm and above |
Rapid
death |
Ammonia |
5
ppm |
Lowest
concentration detectable by smell. |
7
ppm |
RECOMMENDED
MAXIMUM FOR HUMAN HEALTH |
6
- 20 ppm and above |
Eye
irritation and respiratory problems |
40
- 200 ppm |
Headache,
nausea, reduced appetite, irritation to airways, nose
and throat |
Carbon
Monoxide |
50
ppm |
RECOMMENDED
MAXIMUM FOR HUMAN HEALTH |
50
ppm for 8 hours |
Fatigue,
headaches |
500
ppm for 3 hours |
Chronic
headaches, nausea and impaired mental ability |
1,000
ppm for 1 hour |
Convulsions,
coma after prolonged exposure |
4,000
ppm and over |
Rapid
death |
Methane |
50,000
to 150,000 ppm |
Potentially
explosive |
500,000
ppm |
Asphyxiation |
Carbon
Dioxide |
1,500
ppm |
RECOMMENDED
MAXIMUM FOR HUMAN HEALTH |
20,000
ppm |
Deep,
rapid breathing |
40,000
to 60,000 ppm |
Heavy
breathing, drowsiness, for 30 minutes and headaches |
100,000
ppm and above |
Narcotic
effect, dizziness, unconsciousness |
250,000
ppm and above |
Death |
Dust |
2.4
mg/cubic meter |
RECOMMENDED
MAXIMUM FOR HUMAN HEALTH Cough and increased phlegm
(bronchitis), fewer episodes, chest tightness. |
Endotoxin |
0.08
micrograms/cubic meter |
RECOMMENDED
MAXIMUM FOR HUMAN HEALTH Decreased lung efficiency |
0.1
micrograms/cubic meter |
Organic
Dust Toxic Syndrome |
*
- Adapted from Baker J., Curtis S., Hogsett, O., et al
; Safety in swine production systems, Pork Industry Handbook,
publication PIH-104, Cooperative Extension Service, Purdue
University, West Lafayette, Indiana, 1986. Tables 1,2
and 3. |
Hydrogen
sulfide is considered the most dangerous gas in manure pits
because it is highly toxic and is rapidly released from decomposing
manure during agitation and pumping. Concentrations of hydrogen
sulfide can soar from 5 parts per million (ppm) to more than
500 ppm in seconds after agitation begins.
Concentrations
of hydrogen sulfide above 600 ppm can kill an individual after
taking only one or two breaths. The person falls immediately,
apparently unconscious and dies without moving again. A safe
evacuation of the individual can be made only if the rescuer
is wearing a self-contained breathing apparatus (SCBA). Generally,
a rescuer has about six minutes to begin cardiopulmonary resuscitation
(CPR) before brain damage/death occurs. Unless the rescuer
is wearing SCBA protective equipment (see section on personal
protective equipment), there is a strong likelihood that the
rescuer will also succumb to the toxic gases or lack of oxygen.
There have been numerous instances where several farmers have
been killed while attempting to remove someone from a pit
or facility.
At lower
concentrations, hydrogen sulfide can cause severe illness
and irritate the entire respiratory track and eyes. Symptoms
may include nausea, stomach distress, belching, coughing,
headache, dizziness, irritation of the eyes and blistering
of the lips.
It is
a common belief among farmers that it is safe to enter a facility
or pit if they cannot smell the putrid, rotten egg odor associated
with hydrogen sulfide. This is not necessarily true because
high concentrations of hydrogen sulfide paralyzes the nerve
cells of the nose to the point where the person can no longer
smell the gas.
Hydrogen
sulfide, because it is heavier than air, accumulates above
the liquid level of the pit. Individuals may be quickly overcome
with hydrogen sulfide when working around a pit, whether it
be climbing down a ladder to make repairs or when leaning
down to take a manure sample.
Ammonia
is easily recognized because of its pungent odor that is characteristic
of drying urine. This gas is released throughout the year from
urine and feces on the facility floor, or from a pit beneath
the floor. Ammonia is lighter than air and generally dissipates
from a well-ventilated facility.
Concentrations
ranging from 6 to 20 ppm and above will irritate the eyes
and throat. At higher concentrations, ammonia can irritate
the respiratory system and cause wheezing and shortness of
breath. Concentrations above 2500 ppm are considered to be
dangerous to human life, but individuals are not likely to
enter a facility with a concentration this high because of
the extremely strong odor.
Methane
is continuously produced in manure pits and released into the
air at a steady rate. A colorless, odorless, non-toxic gas that
is lighter than air, methane generally dissipates from a confinement
building. The primary danger of methane accumulation in a facility
is the risk of a fiery explosion from a spark if the methane/oxygen
mix is in proper proportions. The risk of fire is greater in
a poorly-ventilated structure.
Although
non-toxic to humans and livestock, methane can cause asphyxiation
if it displaces the oxygen in a closed facility.
Carbon
dioxide is produced by decomposing manure, animal respiration
and heating fuels. An odorless, colorless, non-toxic gas, carbon
dioxide is normally present at 300 ppm in the air. Concentrations
rise when ventilation systems are inadequate or functioning
improperly, This may result in oxygen being displaced in the
facility with carbon dioxide. Carbon dioxide, in combination
with rising temperatures and humidity, can kill hogs through
asphyxiation and heat stress if ventilation failure last for
several hours.
Pits
are unpredictable, they may have been safe to work around for
years, but suddenly, factors such as the stage of manure decomposition,
wind conditions, or other components are just right (or in this
case, wrong) for the pit to release deadly concentrations of
toxic gases. Always treat a pit as if it is a death trap and
take necessary precautions to protect yourself and others if
entry is necessary.
If
you must enter a manure pit where gases are suspected, a self-contained
breathing apparatus (SCBA) must be worn along with a safety
harness and preferable two persons available to assist in a
rescue.
A self-contained
breathing apparatus supplies the wearer with 15 to 30 minutes
of safe air to breath. A SCBA system, similar to those worn
by firefighters, has a small air tank and facemask that allows
the person to move about freely in an area where toxic gases
or insufficient oxygen is suspected.
There
are restrictions to wearing a SCBA that should be considered
before purchasing the equipment. Training on the use of a
SCBA is essential to ensure proper use. The facemask must
fit properly or toxic gases may enter the mask. The wearer
cannot have a beard because the facemask will not seal properly
around the face. Your local fire department is the best source
for information and training on its use. The cost of a SCBA
is about $1,700.
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.
Meters
and Ventilation
An alternative
to wearing a SCBA is to check gas and oxygen levels of a facility
or manure pit with a gas and oxygen testing meter before entering
(see Table 2 for types of meters and gases that they can detect).
Table
2. Gas Measuring Devices Useful in Confinement Buildings |
Gas
| Situations*
| Detector
Tubes
| Dosimeter
Tubes
| Solid
state Detectors
|
Ammonia |
routine
measurements |
satisfactory |
preferred |
Not
reliable |
Hydrogen
Sulfide |
routine
measurements |
preferred |
satisfactory |
satisfactory |
emergency
situations |
satisfactory |
too
slow |
preferred** |
Carbon
Monoxide |
routine
measurements |
preferred |
satisfactory |
satisfactory |
emergency
situations |
preferred |
too
slow |
preferred |
Carbon
Dioxide |
routine
measurements |
satisfactory |
satisfactory |
satisfactory |
emergency
situations |
preferred |
too
slow |
satisfactory |
Methane |
flammable
levels |
preferred |
not
available |
satisfactory |
*
- Routine is defined as typical daily average concentrations.
Emergency is defined as any non-routine situations such
as pit pump-out, ventilation or electrical failure, observation
of abnormal swine behavior, or unusual respiratory symptoms
in persons entering buildings which may indicate gas concentrations
immediately hazardous to human health.
** - Solid state detectors are preferred here because
of the speed or response and because they provide continuous
information on hydrogen sulfide concentrations.
|
Table
3. How to Measure Hydrogen Sulfide*, Carbon Monoxide,
and Carbon Dioxide During Emergency Situations** |
- Do
not enter the building. Open widows and doors from
the outside, turn on ventilators, and use any fans
available to blow air into the facility.
- Use
a detector tube with an extension hose to avoid the
possibility of breathing highly toxic air. The detector
tube must be specific for the gas to be measured (carbon
monoxide, carbon dioxide, or hydrogen sulfide). While
reaching through a window or other opening, place
the detector tube near floor level and use the vacuum
pump to draw air into the tube. Remove the detector
tube and read the gas concentration.
- If
measurement is low, borderline, or hard to read, take
additional measurements in different areas of the
building. One measurement may be inadequate to detect
high gas concentrations.
|
*
- Note that monitoring hydrogen sulfide concentrations
is recommended whenever a deep pit underneath a building
is being pumped, even if there are no indications of toxic
gases.
** - Emergency is defined as any non-routine situation
such as pit pump-out, ventilation or electrical failure,
malfunction of fossil fuel-burning heaters, observation
of abnormal swine behavior or death, or unusual respiratory
symptoms of persons entering the buildings. These symptoms
may indicate gas concentrations immediately hazardous
to human health. |
Metering
can also present problems if not done properly. Toxic gas concentrations
may vary throughout the area; higher levels may be detected
in dead air spaces where ventilation is inadequate; lower levels
are likely in areas near open windows and mechanically ventilated
areas. It should also be noted that gas levels can rapidly escalate
during agitation and pumping; meter readings that were at safe
levels before these activities may reach hazardous levels in
a few minutes. Continue to ventilate the area throughout the
entire process. Table 3 gives instructions on how to measure
some gases in emergency situations.
The
three basic types of meters are detector tube, dosimeter tube
and solid state detectors. Detector and dosimeter tubes use
inexpensive gas sampling devices that give reliable readings
for ammonia, hydrogen sulfide, carbon monoxide, carbon dioxide,
or other gases found on the farm. Dosimeters are best for
measuring average concentrations; detector tubes do the best
job of measuring instantaneous concentrations during emergency
situations. Solid state detectors give continuous readings
and have audible alarm systems, but are more expensive than
tube type detectors and must be calibrated frequently.
Additional
Equipment
Anyone entering
a pit should be equipped with an approved harness and a rescue
rope attached to a tripod and pulley system. Two people can
remove an unconscious individual from a pit in a few seconds
with this type of a emergency lift. Remember, you have only
six minutes to begin cardiopulmonary resuscitation (CPR) before
brain damage/death occurs.
Unsafe
Alternatives
The cost
of a self-contained breathing apparatus, metering, and approved
equipment to lift an unconscious individual from a pit may lead
you to consider less costly alternatives. Unfortunately, all
these alternatives have substantial safety risks.
- Lowering
an open flame into a pit to check oxygen levels may result
in an explosion from accumulation of methane gas. Also,
this only tells you that there is at least 16 percent oxygen
in the pit, but research shows that most individuals need
19.5 percent oxygen concentrations to live. Normal air contains
about 21 percent oxygen.
- An
alternative to an approved harness and safety lift may be
to tie a rope around the individual entering the pit. This
may work, but there is a substantial risk of breaking a
rib and puncturing a lung while making a rescue.
Do
not Enter any Confined 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
- Testing
the air for hydrogen sulfide, combustible gases or methane,
and oxygen with dependable and reliable equipment, AND
- Constant
and adequate ventilation of fresh air, AND
- An
approved harness/lifeline on the person entering the pit
with at least two people outside the pit who are capable
of pulling the person out of the pit if necessary, AND
- An
approved pulley and tripod or other suitably strong lifting
system that will make it possible to remove a limp body
from the pit.
Remember,
you have only six minutes after a person stops breathing to
begin mouth-to-mouth resuscitation before brain damage/death
occurs. Being prepared will greatly reduce the risk of panic,
ill adverse action, and needless death or injury.
Reducing
Hazards from Manure Gases
- Fence
around pits to keep children and other nonworkers away from
the pit. Keep gates locked to prevent anyone else from entering
the area.
- Provide
mechanical ventilation in closed buildings to provide as
much ventilation as possible during pit agitation. Turn
all fans on during agitation and throughout the entire pump-out
period. This is the time of greatest danger and when most
deaths and injuries occur.
- Keep
workers away from the pit and out of the building during
and immediately after agitation. Move animals out of the
building if possible.
- Post
warning signs at common potential entry points of confined
spaces where hazardous gas concentrations could occur.
- Warning
decals are available from the Michigan Department of Labor-S.E.T.
Division, P.O. Box 30015, 7150 Harris Dr., Lansing, MI 48909.
(Ask for SET #2054 confined space decal sign.)
- Thoroughly
ventilate and continue ventilation while working around
a pit. Have a second person standing by before attempting
to enter a building to rescue an animal or coworker. If
thorough ventilation is not immediately possible, a self-contained
breathing apparatus should be worn. Failure to use this
equipment could result in death or serious health impairment
of the rescuer.
- Consider
installing railings on all walkways and permanent ladders
on the inside wall of the tank. Construct lids or tops on
all ground level pits, or fence around them where possible.
- If
possible, remove clogged or damaged pumps from the tank
to make repairs instead of entering the pit. Remind children,
visitors and any non-essential 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.
Livestock
confinement operators should consult a physician whenever they
experience one or more of the following symptoms:
- Persistent
cough, especially a cough accompanied by large amounts of
phlegm, shortness of breath, or a feeling of chest tightness.
- Wheezing,
chest tightness, or shortness of breath which develops while
working in a confinement building.
- Episodes
of flu-like illness with fever, headache, muscle aches,
cough, chest tightness, and shortness of breath that develops
several hours after entering the confinement building.
- Excessive
and persistent shortness of breath at any time.
- Excessive
fatigue or intolerance to exercise.
- Any
respiratory symptoms following a known exposure to high
concentrations of gas associated with pit agitation.
- Livestock
confinement operators should also consider having a yearly
physical examination which will enable the physician to
examine the patient:s respiratory condition and compare
any changes in lung function from year to year.
- Swine
Confinement and Respiratory Health, University of Iowa,
Institute of Agricultural Health and Occupational Medicine,
1989.
- Hazardous
Gases in Manure Tanks in Livestock Operations, 1989,
Michigan State University, Agricultural Engineering Information
Series, AEIS #573.
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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
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
Michigan
State University, Agricultural Engineering Department.
Howard
J. Doss, Extension Agricultural Safety Specialist; Howard
L. Person, Extension Agricultural Engineer; and William McLeod,
Agricultural Engineering, Michigan State University Extension,
East Lansing, Michigan 48824. 5/93. Funded by the National
Institute of Occupational Safety and Health - #UO5/CC-4506052-02.
This
information is for educational purposes only. Reference to
commercial products or trade names does not imply endorsement
by the MSU Extension or bias against those not mentioned.
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