Pig bang theory: Hog manure explosions vex scientists

Researchers say "manure foam" explosions on Midwest pig farms could be related to the animals' diet.

After several years of research, scientists have been unable to pinpoint the cause of fiery and exploding poop on Midwest pig farms.

In the past five years, about 30 to 40 "manure foam" flash fires and blasts have been reported, University of Minnesota researchers say. One explosion was so powerful it leveled a barn in northern Iowa, killing 1,500 pigs.

The fires and explosions have been occurring at manure pits where farmers store pig waste. A bubbling layer of foam — sometimes several feet high — mysteriously builds up at the surface of the manure, releasing a high concentration of volatile methane gas. All it takes is a tiny spark — from a running motor, for example — for disaster to strike.

Incidences of spontaneous manure foaming have increased significantly since the phenomenon started cropping up at factory-scale hog farms in the upper Midwest. Explosions have killed thousands of pigs, costing farmers millions of dollars.

"No human deaths have been reported during these events, but workers have been injured after being blown by a blast or exposed to intense heat," University of Minnesota researchers said in a report last year.


Just last month, says Chuck Clanton, a University of Minnesota professor and agricultural engineer, a flash fire from foaming manure in south-central Minnesota burned the inside of a building and plastic water and feed lines. There were also three flash fires at upper Midwest farms last fall, Clanton told MSN News.

Pig farm explosions: Damage from manure foam fire.Chuck Clanton

"The flash fires are more of a blue flame moving across the manure surface from one end of the building to the other and sometimes gets hot enough to melt or burn plastic (feed and water) lines and warp the sheet metal," Clanton said in an email.

Larry Jacobson, a professor and extension engineer at the University of Minnesota, told Mother Jones magazine that about a quarter of operations in the hog-heavy regions of Minnesota, Illinois and Iowa are experiencing foam. He said that "the number may be higher, because some operators might not know that they have it."

Clanton said one manure foam explosion a few years ago destroyed a barn on a farm in northern Iowa, killing 1,500 pigs and severely burning a worker. He declined to go into detail about the case. "These individuals have been through enough and do not want to rehash events," he said.


Researchers aren't sure what's causing the manure foaming. Among the "Pig Bang" theories is one that suggests it's connected to the hogs' diet. It's become an increasingly popular practice among farmers to mix swine feed with dried distillers grains, a byproduct of corn processing for ethanol, in part to cut down on the cost of feeding pigs. Researchers say distillers grains contain high levels of fatty acids that pass through the pigs' digestive system and help form bubbles in the manure foam.

"We hope to start research to look into this this summer," Clanton said.

In the meantime, scientists are recommending that pig farmers add monensin, an antibiotic widely used to make cows gain weight, to the pig manure pits to control foaming. Monensin decreases the amount of acetic acid, a precursor for methane buildup.

Clanton said the use of monensin is only a Band-Aid until scientists can pinpoint the root cause of the manure foaming.

Angela Kent, an associate professor in the Department of Natural Resources and Environmental Sciences at the University of Illinois, told Mother Jones that scientists "are in the midst of a large multi-institution investigation focused on finding the cause of this very serious problem."

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