MSU Extension

Severe burns, pig deaths and building fires have been reported in recent years on farms where foam and methane have accumulated in manure pits. While foaming manure pits may be a new phenomenon to some, there are reports of foaming pits dating back to 1969 (Burns, 2009). The number of farms experiencing foaming pits appears to be increasing. A recent survey of Midwest pork producers indicated 25% were experiencing some foam (Jacobson et al, 2011). Fall is a time to spread manure. Fall is also a time of cooler temperatures and corresponding reduced ventilation rates in finishing facilities. Consequently, there are increased risks associated with manure hauling; particularly when there is foam in manure pits.

Any livestock farmer with foaming manure pits needs to take precaution. Hog barns with significant foam are a risk to pigs, caretakers and the structure itself.

As the foam bubbles form on the manure, surface gases associated with storing manure in deep pits—most notably methane—are captured in the foam. Bubbles may contain 60–70% methane. Under normal circumstances, the foam is left undisturbed and there is minimal risk. However, when the foam is disturbed through what are considered regular management activities such as manure agitation and/or pumping and power washing, large amounts of methane may be released into the air space above the slats. The released methane is easily ignited and may lead to barn explosions and flash fires. Minimum ventilation rates, such as those used when pigs are small, increase the risk of methane ignition. 

While the concerns with foam have garnered the attention of Extension and University researchers at institutions across the Midwest, both ‘what causes’ foam and ‘what reduces’ foam remain elusive. The University of Minnesota (Jacobson, 2011) survey of Midwest producers was unable to find a clear link between pits that foam and pig diet, age of pig, barn management, barn-pit design, or pig genetics. Researchers are continuing to work on finding answers.

In the meantime, farmers need to review safety procedures they are using on their farm. They need to be sure they are following all safety precautions to avoid personal injury, pig losses, and facility damage. Although these precautions are appearing in several other popular publications and National Pork Board press articles this fall, we think that the need to be safe justifies repeating them here.

• Steps to reduce the risk of explosion and flash fires in swine barns with foaming pits include:
• When hauling manure do not enter and do not let any employees enter the room being pumped. The risk to human life is too great to allow for visual monitoring.
•  Be extremely cautious when power washing rooms over foaming pits.
• Turn off all heaters, pilot lights and non-ventilation electrical equipment in the room being pumped or power washed. Enforce no smoking rules in and around barns.
• Open all air inlets slightly to reduce static pressure and prevent incoming ventilation air from short circuiting through the pump out opening. Lowering static pressure also helps ensure the wall fans don’t overpower the pit ventilation and draw pit gases up into the air space above the slats.
• Maximize ventilation during warmer weather.
• During cool weather set the pit ventilation at its maximum level and run at least one wall fan (20–30 CFM per pig minimum).
• Continue to run pit ventilation while the room is empty between groups of pigs. Many of the flash fires that have been reported happened while the barn was sitting empty.
• If the pit is nearly full of manure or a combination of manure and foam, don’t agitate the manure until there is 2-3 feet of head space in the pit. Lack of head space reduces the effectiveness of the pit ventilation and allows gases to escape into the air space above the slats.
• Discharge all agitated manure under the manure surface. Do not shoot manure over the pit surface (rooster tail) and do not shoot manure against walls and pillars. As the pit empties shut down the agitation when the returning stream begins to disturb the manure surface.
• Allow the ventilation system to operate at increased levels for at least 30 minutes after disturbance to the foam has been complete.

In conclusion, farmers should prepare for safety this fall when hauling manure from swine barns. They definitely should have a plan on what to do if there is foam in the pit, if pigs are in the building, and if there is only a limited number of days to get the manure spread on the fields.

Resources and further reading:

Burns, R., 2009, Deep Pit Swine Facility Flash Fires and Explosions: Sources, Occurrences, Factors, and

Management, National Pork Board, Available: 09-252-BURNS-ISU.pdf

Iowa Pork Producers Association, 2010, Understanding Manure Foam and Pump Out Safety, Available:

http://www.iowapork.org/Portals/iowapork/Headlines%20Fall%202010.pdf

Jacobson L., D. Schmidt and C. Clanton, 2011, Manure Foaming in Midwestern Deep Pit Swine Barns,

University of Minnesota Extension bulletin in press