Pork producers, commercial pumpers and barn workers need to watch for foam on the surface when pumping manure pits. This foam contains numerous gases hazardous to people and animals.

Methane, one of the gases contained in the foam, can cause explosions or flash fires.

During pit pumping last fall, several incidents in Minnesota and Iowa were reported where explosions or flash fires occurred in livestock buildings with manure pits. This fall, another similar incident occurred in central Iowa and severely injured one person. Some of the cases have reported foaming or extensive bubbling on the manure surface prior to the explosions. 

Some reports indicate several feet of foam can develop in a matter of days. No consistent solution has yet been found to control the foaming in livestock manure pits and systems that are generating foam should be regarded as potential fire hazards.

“If a 6-inch thick or greater layer of foam is present and it is disturbed during normal pit agitation and pumping, a sudden release of dissolved gases will occur,” said Larry Jacobson, an agricultural engineer with University of Minnesota Extension. Without adequate barn ventilation, this can result in methane concentrations reaching the lower explosive level of 5 percent or 50,000 parts per million (ppm). “An explosion is then likely if an ignition source is present from a pilot light, electric spark from a motor, or cigarette,” said Jacobson.

Carefully following recommended precautions and informing all workers involved of safety measures can prevent such occurrences from happening.

Agricultural engineers, animal scientists and pork industry consultants have developed the following recommendations to help producers address this serious safety concern:

Before agitating or pumping begins, review your emergency action plan with all workers, and have emergency contact numbers available at the site.

Ensure that all people are out of the building and clearly tag all doors, noting that the building is unsafe for entry during agitation and pumping.

Provide continuous ventilation to prevent a gas build-up. Increase ventilation during agitation to quickly dissipate released gases. Sufficient ventilation or exchange of air in the barn is always essential to keep the concentration of methane below its explosive threshold.

  • Sufficient air exchange in a barn while agitating and pumping a manure pit is at least two to three times the minimum ventilation rate (or around 10 air changes per hour) for the barn.
  • If the pit is full or nearly full, do not rely only on pit fans to supply this airflow rate, since these fans may be severely restricted. It may be better to use only wall fans to supply this air exchange while agitating/pumping the barn’s manure pit since methane gas is lighter than air.
  • Make sure your normal ventilation inlets are open and operating properly to ensure good air distribution in the barn. If animals must be present in barns) This is also important in preventing animal deaths during agitation and pumping of the manure pit.

Turn off heater pilot lights and other non-ventilation electrical systems (such as the feeding system) that might produce an ignition spark. Not providing supplemental heat in the barn may be problematic for cases when there are no animals in the barn or there are only small animals that require warmer inside temperatures. This may restrict when you pump manure from such a barn to warmer days or a warmer part of the day.

When pumping pits that are close to being full, pump without agitation until manure is about 2 feet below the slats. This will allow pit fans (if available and used) to perform properly during agitation and provide more dilution space for methane and other gases that are released.

Researchers do not yet understand all the factors such as diet, manure pH and others that cause this problem. Several research projects are ongoing to better understand the causes and eventually provide solutions to this serious problem, according to Jacobson. 

Additional information on this issue can be found at the following websites:

University of Minnesota Extension’s swine website:

Manure Pit Foaming. Iowa Manure Certification Workshop. January 2011.  

For more information on safety practices during manure removal, see http://bit.ly/ripLOy

Source: University of Minnesota