Methane production in deep manure pits is unavoidable and if not managed carefully can present a fire risk in swine facilities. Managing this risk is a primary concern in maintaining a safe environment in deep pit swine production facilities.
“To our knowledge there have been eight fires in Iowa that have occurred in deep pit facilities in Fall of 2009; it’s possible that more have occurred,” says Robert Burns, agriculture and biosystems engineering professor, Iowa State University. Burns has investigated five of the fires that occurred looking for common denominators.
“Fires resulting from methane produced in deep pit swine facilities can result in varying amounts of damage,” says Burns. “Flash fires can race through the barn causing significant damage but leaving the structure intact.” However, other fires can destroy the entire facility, Burns adds.
Fires can result in deep pit facilities if ventilation is inadequate and methane is present in 5 percent to 15 percent concentrations. “Methane is obviously a fuel and if present in this concentration can explode if an ignition source is present,” warns Burns. Ignition of these fires can be explosive.
Hydrogen sulfide and phosphine gas, if present in adequate concentrations, also can present a risk. “We don’t believe, however, that hydrogen sulfide or phosphine are resulting in the fires,” says Burns. “Methane is what we believe is fueling the fires.”
Foam production in deep pit manure systems is a complicating factor and an increasing problem in some facilities. “We’ve discovered that foam can contain from 50 percent to 75 percent methane,” says Burns. “When we break up that foam and the air mixes upward into the housing area, the methane can be diluted down to the explosive limits.” If an ignition source is present in this situation, such as a heater, a flash fire may occur.
Of the five recent swine facility fires investigated by Burns, all five had foam present in the manure pit. As a result of foam build-up, pit fan effectiveness may be reduced. Breaking up the foam can have dangerous consequences. Barn heaters were identified as ignition sources in four of the five fires Burns investigated.
Unfortunately, foam production in deep pit manure systems is not fully understood at the present time. Burns’ study of the barn fires revealed two things: methane is the main cause of deep pit fires and heaters are the primary ignition source in most cases.