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Watch for deep-pit manure foam

September 22, 2015  by Chuck Clanton PE professor University of Minnesota College of Food Agricultural and Natural Resource Sciences and Larry Jacobson PE agricultural engineer and professor University of Minnesota Extension

September 22, 2015, St. Paul, MN — Manure deep-pits under swine barns in the Upper Midwest are getting full in this time of year, and concern over pit foaming is especially high. Pork producers should be vigilant.

Although the frequency of flash fires or barn explosions in deep-pit pig buildings has been significantly reduced since the peak of this problem in 2009, foam still can occur. Tragically, that resulted in two fatalities earlier in 2015.

To prevent an explosion or a flash fire, ventilate or exchange air in the barn to dilute the concentration of methane gas in the air.

The presence of foam bubbles on top of liquid manure in a deep pit contains about 70 percent methane. Any activity that disrupts the foam releases this stored methane or natural gas can be dangerous. Methane is extremely explosive when between 4 and 15 percent of the air by volume. If you are not sure if foam is present or if there is only a thin layer, take precautions.


Always check for foam when there is any interruption in normal activities. This includes changing (turning) groups of pigs, running soaking nozzles or power washing, agitating and pumping liquid manure in the pit, or any maintenance work (such as welding) inside the barn. These activities disrupt the foam and release methane.

If foam is detected in the manure pit prior to any of these activities, immediately take these precautions:

Run the exhaust fans in the barn to at least the mild weather or fall/spring ventilation rate. This will provide roughly 25 to 35 air exchanges per hour in the barn or, for a grow-finish barn, 30 to 40 cfm/pig. Use of wall fans are preferable in addition to pit fans, since the airflow rates from pit fans are commonly compromised or reduced significantly by high manure levels in the pit and duct transitions on pit fans.

When foam is present, eliminate all ignition sources inside the barn: pilot lights or electrostatic spark on water and space heaters, sparking switches on lights and non-enclosed electric motors, welding, grinding, cigarettes, cigars or pipes.

Extension and research personnel from the University of Minnesota, Iowa State University and University of Illinois developed warning stickers in English and Spanish to post inside pig barns. Stickers will be available from pork producer associations in all three states.

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