September 11, 2003

 

Manure Agitation May Be a Life or Death Process

Hydrogen sulfide causes sudden death in humans and livestock by stopping breathing. It is released from manure decomposing under oxygen free conditions. Exposure to hydrogen sulfide occurs when people enter a confined space which contains or has contained manure or other decomposing organic matter. These spaces may include under-floor manure storage pits, manure pump pits, septic tanks or sewer lines.

"People have frequently entered pits without incident, but then one day, conditions are different and people die," explains Ken Hellevang, NDSU Extension Service engineering specialist.

People and animals have died or been injured during agitation of under-floor manure pits. "During agitation, hydrogen sulfide is suddenly released from manure. At a high enough concentration, it can kill," Hellevang says. "The problem is not predictable – after many agitations without problems, conditions can change and cause a death or injury."

What are the conditions that result in a problem? Hellevang says that Canadian researchers found that splashing liquid manure into the air during agitation causes hydrogen sulfide to be suddenly released into the air. They also found that operating the pit ventilation system so air is drawn from the barn into the pit through slotted floors keeps hydrogen sulfide from entering the barn.

They also noted that operating barn wall exhaust fans could increase the concentration of hydrogen sulfide in the barn space as the fans draw hydrogen sulfide from the pit into the barn. This is of special concern when wall exhaust fans are more powerful than pit exhaust fans or when inlet size is inadequate for the high airflow rate.

These results have led Canadian researchers to make the following recommendations to manage hydrogen sulfide release into a barn during manure pit agitation:

• Pump the liquid surface down two feet below the floor beams before agitation. This allows the pit fans to draw air from throughout the pit, moves the release surface farther from the slotted floor and allows agitation without splashing on the beams.
• Operate agitation equipment so liquid agitation occurs below the liquid surface. Don't throw liquid over the top of the surface.
• Operate pit exhaust fans at full capacity while agitating. Turn off barn exhaust fans (in the walls) so they don't pull gases out of the pit. This recommendation is contrary to what has been recommended in the past.
• Install alarms to warn if pit exhaust fans fail to operate during agitation.

Research suggests the following practices also may be beneficial.

• Before agitation, be sure pit fans are operating and exhausting air from the pit.
• Make sure openings into the pit from outside are sealed so air is not drawn into the pit causing a ventilation system short circuit. These openings may be around fan housings and at the agitation port in the wall.
• Remove animals from the barn if possible (agitate after load out).
• Do not allow workers in the barn while agitating. Place signs on entrance doors warning of the hazard within.
• If animals remain in the barn, there is no way to assure they will survive the manure agitation process. Consider covering all or part of the slotted floor with a barrier such as plastic sheets to limit gas entry into the barn. This may work best if located above the agitation spot and the pit fans. Where possible, fence animals away from floor openings near the agitation area.
• If pits must be agitated during high temperature periods, turning off barn exhaust fans may result in excessive animal heat stress. Avoid emptying pits at this time or provide a positive pressure ventilation (fans blow into barn) system. Locate fans so they do not cause air turbulence near the slatted floor. Allow air to exit barn through pit.
• Never enter a manure pit unless it has been properly tested for adequate oxygen (more than 21 percent) and safe levels of hydrogen sulfide (less than 20 ppm), or you are wearing self-contained breathing apparatus.

To learn more about designing and managing livestock ventilation systems, you can order a copy of Mechanical Ventilating Systems for Livestock Housing, (MWPS-32) from MidWest Plan Service, 122 Davidson Hall, Iowa State University, Ames, IA 50011-3080. You can call toll free 800-562-3618, fax 515-294-9589, or email mwps@iastate.edu. Orders can also be made on the Web site at www.mwpshq.org .

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Source: Ken Hellevang, (701) 231-7243, kjh-eng@ndsuext.nodak.edu
Editor: Tom Jirik, (701) 231-9629, tjirik@ndsuext.nodak.edu