However, manure accumulations within enclosed buildings generate gases which can be both toxic and asphyxiating when improperly managed. Another problem is unvented heaters in poorly ventilated buildings that lack enough oxygen for complete fuel combustion. This situation can increase carbon monoxide levels. Dust resulting from automated feeding systems, animal hair and dander, and dried manure on floors and animals can irritate respiratory systems. The severity of these problems is seasonal in that the atmosphere within enclosed buildings is often much better during the summer than the winter because ventilation rates are not reduced for heat energy conservation.

The potential danger of stored manure gases must be respected. Livestock have died as a result of ventilation failures or stored manure agitation. Human fatalities have occurred from entering a manure collection or storage pit without insuring adequate ventilation or without being equipped with proper breathing apparatus. In addition, manure storage pits or tanks and lagoons, like any water impoundment, should be respected for the drowning potential.

Hydrogen Sulfide (H2S). Hydrogen sulfide is the most toxic gas associated with the decomposition of swine manure. It is believed to have been responsible for most of the deaths of livestock and humans that have occurred around liquid manure storage pits. It is colorless, heavier than air, and highly soluble in water; it has the characteristic odor of rotten eggs. However, the odor of hydrogen suNide can be deceiving. It is first detected, by most people, at concentrations below one part per million (ppm) by volume. (One ppm is the equivalent of one volume of gas mixed in one million volumes of air.) Above 6 ppm, the odor will only increase slightty even though the concentration of hydrogen sulfide increases significantly. The gas at 150 ppm can have a deadening effect on the sense of smell making detection extremely difficuK.

A common level of hydrogen sulfide gas in environmentally controlled swine units is around 5 ppm. But during the first stages of stored manure agitation and pumping liquid manure, hydrogen sulfide can reach dangerous concentrations. Levels of 200 to 300 ppm have been reported to exist within a few minutes after agitation begins, and levels can go as high as 1,500 ppm. The effects hydrogen suitide can have on humans and swine, at dfflerent levels, are shown in Table 1.

The National Institute ot Occupational Safety and Health (NIOSH) maximum recommended safe concentration of hydrogen sulfide for workers in a building during an eight-hour work period five days per week is 10 ppm. Human evacuation is recommended when levels exceed 50 ppm.

Even if a person does not lose consciousness after inhaling heavy doses of hydrogen sulfide, medical attention still should be sought since fluids can accumulate in the lungs following exposure.

Ammonia (NHa). During storage and decomposition, significant amounts of ammonia are released from manure and urine. Sources of ammonia include urine and feces on the top of slats or solid floors and in the pit. Ammonia gas is an irrnant which is colorless, lighter than air, and highly water soluble. It has a sharp pungent odor that becomes detectable at levels as low as 5 ppm.

Typical ammonia levels in well-ventilated environmentally regulated buildings are 10-20 ppm with liquid manure systems and 50 ppm where manure and urine are deposited on solid floors. Levels can exceed 50 ppm with lower winter ventilation rates and reach 100-200 ppm in poorly vennilated buildings. The effects of exposure to ammonia gas are presented in Table 2. The NIOSH maximum recommended safe ammonia concentration for workers in a building for an eight-hour work period is 25 ppm.

Calbon Dloxide (CO2>. The earth's atmosphere normally contains 300 ppm of carbon dioxide. At considerably higher concentrations, it can asphyxiate people by reducing the amount of oxygen present.

Manure decomposnion and the nommal breathing process of animals can increase the level ot carbon dioxide in confined spaces. Typical concentrations inside ventilated buildings range trom 1,000 ppm during well-ventilated periods to 10,000 ppm during winter. The effects of excessive concentrations ot carbon dioxide are presented in Table 3. The NIOSH maximum recommended safe carbon dioxide concentration for workers is 5,000 ppm.

Methane (CH4). Methane is produced during natural decomposnion of manure and is nontoxic. It is rarely a problem in swine buildings. However, high concentrations can cause headaches and even asphyxiation. The major safety concern about methane is that it is highly tiammable and can be explosive at levels ranging from 50,000 to 150,000 ppm (5 to 15 percent). Because methane is lighter than air, it tends to rise and accumulate near the higher stagnant parts of enciosed buildings and tightly closed manure storage pits. This colorless, odorbss gas is only slightly soluble in water. Bun if a unit is well-ventilated, concentrations should be well below the minimum explosive point.

The NIOSH maximum recommended safe methane concentration for workers during an eight-hour period is 1,000 ppm. Its effects on humans and swine are presented in Table 4.

Carbon monoxide (CO). When fuels burn incompletely, as all fuels do to some extent, carbon monoxide is produced. This is 8 gas which is most notorious for killing people who operate their car engines inside closed garages.

Inside a building, carbon monoxide can build up in poorly ventilated areas where heating units malfunction, where there are unvented heaters, or where there are gas catalytic heaters. Winter is the most dangerous period because buildings are usually closed and ventilation rates are lowest. A victim can be unaware of the presence of carbon monoxide because it is colorless and odorless. The NIOSH maximum recommended safe working carbon monoxide concentration for adults during an eight-hour period is 50 ppm. Pregnant female workers should be aware that an unborn fetus is more susceptible to carbon monoxide than adults. Carbon monoxide has the same density as air and is insoluble in water. Table 5 presents the effects of carbon monoxide exposure.

Table 1. Effects of hydrogen sulfide exposure on humans and swine.
Exposure level	Effects or symptom
On humans
10 ppm	Eye irritation
20 ppm for more than 20 min.	Irritation to the eyes, nose, and throat
50 to 100 ppm	Vomiting, nausea, diarrhea
200 ppm for 1 hr.	Dizziness, nervous system depression,increased susceptibility to pneumonia
500 ppm tor 30 min.	Nausea, excitement, unconsciousness
600 ppm and above	Rapid death
On swine
20 ppm, exposed continually	Fear of light, loss of appetite, nervousness
200 ppm	Possible pulmonary edema (water in the lungs) with breathing difficulties and possible loss of consciousness and death

Table 2. Effects of ammonia gas exposure on humans and swine.
Exposure level	Effects or symptom
On humans
6 to 20 ppm and above	Eye irritant, respiratory problems
100 ppm tor 1 hr.	Irrration to mucous surfaces
400 ppm for 1 hr.	Irritation to eyes, nose, and throat
700 ppm	Immediate irritation to eyes, nose, and throat
5,000 ppm	Respiratory spasms, rapid suffocation
10,000 ppm and above	Death
On swine
50 ppm	Reductions in performance and health. Long-term exposure increases the possibility of pneumonia and other respiratory diseases.
100 ppm	Sneezing, salivation, and loss of appetite thereby reducing animal performance.
300 ppm and above	Immediate irritation of nose and mouth. Prolonged exposure causes extremely shallow and irregular beathing followed by convulsions.

Table 3. Effects of excess carbon dioxide exposure on humans and swine.
Exposure level	Effects or symptom
On humans
60,000 ppm for 30 minutes	Heavy tereathing, drowsiness, and headaches
100,000 ppm (10%) and above	Narcotic effect, dizziness, unconsciousness
250,000 ppm (25%) and above	Death
On swine
40,000 ppm	Increased rate of breatzmg
90,000 ppm	Discomfort
200,000 ppm (20%)	Cannot be tolerated by market hogs for more than one hour

Another potential problem is inhalation of animal feed dust containing antibiotics. These inhaled particles could cause a person to become sensitive to certain antibiotics. It is possible for some workers to contract infections that are resistant to antibiotics. When a person breathes dusty air for an extended time there may be several cwnsequences:

• Chronic bronchitis (frequent cough bringing up phlegm) may result.
• The respiratory system's capacity to take in and exhale oxygen may be reduced.
• There may be an increased susceptibility to respiratory diseases such as colds and pneumonia.
• Episodes of flu-like illness with fever might deveiop.
• Adverse allergic reactions may result.

Manure agitation. When liquid manure that has been stored for a prolonged period is agitated, toxic levels of hydrogen sulfide gas will be released This situation can create lethal conditions, even when there is full ventilation. The greatest hazard exists almost immediately after vigorous agitation of stored manure tregins. When this occurs, high concentrations of gases are released near the building's exhaust fans as well as at the area around the point of agitation

Table 4. Effects of methane exposure on humans and swine.
Exposure level	Effects or symptom
50,000 to 150,000 ppm	Potentially explosive
500,000 ppm	Asphyxiation

Entering a manure storage. A manure storage pit should never be entered without full respiratory protection Even ii it has been ventilated or recently emptied a person could be killed by hydrogen sulfide gas or by the lack of oxygen. Moreover, the methane gas that accumulates in the upper stagnant-air areas of enclosed tanks can create an explosive condition

Open manure storage pits, tanks, or lagoons. When an opening into a deep manure storage pit or tank is unguarded, it invites an accident. Workers and animals could san into the pit and drown. Surface scums and crusts can be deceiving since they may appear capabk of supporting a person's weight, especially a child's, when in fact, they cannot..

Heaters and engines. Unless there is adequate ventilation where unit heaters, catalytic heaters, and radiant heaters are used, carbon monoxide can reach deadly concentrations. Another hazard is the use of auxiliary generators that are not vented to the outside.

In addition to maintaining adequate ventilation, observe these management tips:

• Maintain the ventilation systems by frequently removing dust accumubtions from exhaust tans, fan shutters, and air inlet screens.
• Place ducts to be used for underfloor exhaust fans below the slats and above the highest level the manure will reach. Use them to exhaust air outside.
• Provide the maximum amount of mechanical ventilation possible whenever stored manure is agitated.

  In a naturally ventilated building, agitate only when there is a brisk breeze; and even then, consider removing livestock from the building betore agitating the manure.

• Install an alarm system to warn of power failures that would affect the mechanical ventilation system. Check and maintain the alamm system and power unit on a weekly basis. If power fails, an emergency power generating unit should start immediately. If an auxiliary unH is not available, open all windows and doors and consider removing livestock from the building where manure is stored.
• Use proper manure storage management. Do not overfill underfloor manure storage pits. These pits should be pumped or drained when the liquid level rises to within 1 foot of the shts or to within 4 inches of the bottom of slat support beams. Clean the manure pits regularly. After emptying the pit, add enough liquid to cover the remaining residue and manure solids. Hydrated agricultural lime can be added to manure storage contents at the rate of 1 pound per 1,000 cubic feet of stored manure to maintain the pH near 7. Alkaline conditions suppress the release of hydrogen sulfide but increase ammonia emissions.
• Placement of gas traps in drain lines connecting outside manure storage structures with enclosed buildings is recommended.
• Unvented heaters should never be installed unless continuous ventilation is provided, in other words, vent all engine and heater exhausts to the outside to minimMe carbon monoxide levels.

Table 5. Effects of carbon monoxide exposure on humans and swine.
Exposure level	Effects or symptom
On humans
50 ppm for 8 hr.	Fatigue, headaches
500 ppm for 3 hr.	Chronic headaches, nausea and impaired mental ability
l,000 ppm for 1 hr.	Convulsions; coma after prolonged exposure
4,000 ppm and over	Death
On swine
200-250 ppm	Baby pigs are less vigorous
150 ppm and over	Causes abortions in late term sows, and an increased incidence of stillborn pigs. Reduces growth rate of young pigs.

• If possible, evacuate all animals and workers from buildings before stored manure is agitated. If animal evacuation is not possible, observe from a distance start agitation slowly and be ready to turn off the pump at the first sign of trouble or discomfort. See Tables 1-5 for effects of exposure to gases. Do not agitate vigorously at the start. Instead, begin agitating at near tractor idle speed and slowly build up the pump speed.
• Never bok into a manure storage when agitating. Never try to rescue a distressed animai or person without being equipped with seH-contained breathing apparatus that has its own oxygen supply.
• Enter a manure storage pit or tank only when it is absolutely necessary. Even then, only do so if it is well-ventilated and if you are wearing a self-contained breathing apparatus with a lifeline attached. Make certain a similarly eQuipped person who is capable of retrieval is ready and strategically located lor rescue.
• Be aware of the signs which indicate gas has reached toxic levels. These signs include rapid blackening of copper pipes, electrical wiring, or lead-pigmented paint - or white deposits of zinc sulfate on galvanized steel. Approved commercial gas monitors, measuring devices, or kits can be used to check gas levels.
• To help prevent the risk of drowning, construct covers for ground-level and below-ground manure collection and storage tanks. Once installed, keep these access covers in place. Covers should be round or chained to the floor to prevent them from falling into the pit. Install railings around all manure storage pit or tank openings, walkways alongside the structures, and piers or catwalks over the open storage areas. Attach pemnanent ladders made of noncorrosive material to the inside wall of all deep manure storage structures.

• Fence in earthen manure storage basins and lagoons to keep out animals and people. Remind people, by posting warning signs, to exercise utmost caution.
• Prohibit smoking, welding, or the use of open flames in poorly ventilated buildings or enclosed manure storage areas until the areas have been thoroughly ventilated.
• Use explosion-proof electric motors. Keep light fixtures and electric wiring around storage structures in good condition. All electrical wiring should meet the National Electric Code.
• Place flame arrestors on the gas lines that lead to heating units or generator engines.
• The area around the anaerobic digester systems for methane production should have "Caution-Flammable" signs posted in plain view.
• Keep all guards and safety shields in place on equipment such as pumps, manure spreaders, and power units.
• Stand clear of "tipping bucket" flush tanks when they rotate.
• When working in enclosed buiidings for a prolonged period, reduce inhalation of dusty air by wearing a disposable dust mask which has been approved by the American National Standard Practices for Respiratory Protection, or NIOSH.

• Be able to recognize symptoms of gas poisoning and the physical effects that occur as a result of exposure to manure decomposition and/or heating units.
• Rescue equipment and first-aid supplies that meet the approved standards of a consuning physician should be located near the manure storage area.
• Post the phone number of the local fire department or rescue squad near rescue equipment and beside all telephones.
• Do not attempt to rescue a victim from a storage pit unless you are equipped with a self-contained breathing apparatus.
• When phoning for emergency medical help, make sure rescuers know what the situation involves so they can determine the need for special equipment.
• If the victim can be safely moved, get him or her to fresh air.
• If the gases have simply irritated a part of the body, flush the affected areas with fresh water.
• If the victim is not breathing, start cardiopulmonary resuscitation (CPR, if properly trained) immediately and continue until medical heip anives.

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