Take Safety Precautions to Prevent Manure Pit Explosions

Provide continuous ventilation to prevent gas build-up.

Published on: Nov 27, 2009
Recent explosions and flash fires that occurred in livestock buildings with manure pits in Iowa and Minnesota prompt University of Nebraska-Lincoln Extension specialists and others to offer advice on how to avoid these potentially dangerous situations.

So far, the explosions have resulted in building damage with few animal losses and no personal injuries or fatalities, says Rick Stowell, UNL extension engineer.

Few, if any, explosions have been reported in Nebraska. However, the much-delayed harvest most likely has kept many farmers from agitating pits and moving manure to their fields yet this fall, Stowell says.

As farmers hustle to apply manure yet this fall, they need to be aware of potential safety concerns and take reasonable precautions.

A team of agricultural engineers, animal scientists and an industry consultant recently developed recommendations to help producers deal with the potential for danger.

When liquid manure is agitated to suspend the settled solids and create pumpable slurry, numerous gases are released into the air, Stowell says.

At elevated concentrations, some of these gases, such as hydrogen sulfide, are hazardous to those inside the building, both people and animals. However, methane, which is very flammable, also is released. If the methane concentration within the barn reaches its explosion threshold of 40,000 to 50,000 parts per million and there is an ignition source, such as a pilot light on a heater, an explosion likely will occur.

Stowell and this team of experts offer these suggestions:

--Producers should provide continuous ventilation to prevent a gas build-up and increased ventilation during agitation to quickly dissipate released gases. Sufficient ventilation or exchange of air in the barn is also essential to keep the concentration of methane below its explosive threshold. While agitating and pumping a manure pit, producers should provide 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, producers should 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. Also, producers need to make sure the normal ventilation inlets are open and operating properly to ensure good air distribution in the barn. This is also important in preventing animal deaths if animals must be present in barns during agitation and pumping of the manure pit.

--To prevent igniting an explosive concentration of methane, producers should turn off heater pilot lights and other non-ventilation electrical systems, such as the feeding system, that might produce an ignition spark. Without supplemental heat, producers may be restricted to pumping manure from a barn on warmer days or a warmer part of the day.

--When pumping pits that are nearly full, producers should 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.

--Foaming of manure pits is a growing and significant concern that might be related to explosion incidents. Some recent cases have seen foaming or extensive bubbling on the manure surface before the explosions. There are reports of several feet of foam developing in a matter of days in a building. Experts aren't certain what contributes to extensive foaming or how best to control it; they're studying it further.

Additional information can be found at the following Web sites:

University of Minnesota Extension's swine Web site: www.extension.umn.edu/swine/porkcast/barnventilation.html, or the Minnesota Pork Board Web site: www.mnpork.com/producers/index.php.