It’s the time of year when pork producers will be pumping out their deep pits and that means recognizing and planning for hazards that can accompany the job. If foam is present, the hazards are multiplied.

While manure pit fires and explosions have occurred, not all such incidents happened during agitation and pumping, nor has foam been present in every case. Iowa State University Extension agricultural engineers point out that such episodes highlight why it’s so important to be cautious when agitating and pumping manure from deep pits.

Liquid manure in pits decomposes slowly, which creates several gases, including methane and hydrogen sulfide. The gas release can increase dramatically when the manure is agitated during pumping. This is especially true for hydrogen sulfide, which can have a lethal paralyzing effect.

When excessive foam is involved it’s believed that it prevents the normal release of methane. If the foam is disturbed by agitation or activities such as power-washing, the captured methane can be released quickly and when mixed with fresh air it can create an explosive mixture. If this mixture comes into contact with an ignition source, it can cause a flash fire or explosion.

Here are some steps to minimize risks:

  • Review emergency action plans with all workers; emergency contact numbers available on site. The publication “Emergency Action Plans,” accessible at, has more information.
  • Before agitation or pumping, turn off electrical power to all non-ventilation equipment such as lights and feed motors. Extinguish any pilot lights or other ignition sources. Open all ventilation curtains or ventilation pivot-doors, but leave walk-in doors locked to prevent human entry.
  • Run ventilation fans at maximum speed.
  • Ensure that all people are out of the building and tag all doors to prevent entry during agitation and pumping. Most state pork producer associations have such warning tags available, or contact the National Pork Board at (800) 456-7675.
  • If there is significant foam, consider pumping without agitation to reduce fire or explosion risk, and monitor solids accumulation. This will influence agitation needs during the next pumping event.
  • Do not agitate until the manure level is at least two feet below the slats.
  • During agitation keep the jet of pressurized manure below the liquid surface—do not let it strike walls or columns in the pit.
  • Stop agitation when the manure level does not allow agitation below the liquid surface.
  • Continue maximum ventilation for 30 minutes to one hour after pumping has ended; do not let anyone re-enter the building before then.
  • Never enter a building or manure storage structure when liquid manure is being agitated or pumped. You can review a video discussing safety practices online at