seal  Purdue News

September 8, 2003

Silo gas a deadly hazard on the farm

WEST LAFAYETTE, Ind. – Silos, a necessity on many farms, can be dangerous, especially days after filling when deadly gasses are building up inside, said Gail Deboy, a Purdue University Cooperative Extension agriculture safety specialist.

Last October a Michigan farmer died from exposure to silo gas after entering a silo three days after it was filled. Deboy said farmers can combat the dangers of silo gas by taking precautions.

"The greatest amount of silo gas occurs one to three days after crops, especially corn, have been put into the silo," Deboy said.

Because silo gas forms as a result of the fermentation that takes place in chopped forage shortly after it's placed in the silo, farmers can lower the risk of exposure by waiting one month before entering a newly filled silo. Even then, all doors, hatches and vents should be open and the blower should be operated for one hour prior to entry, Deboy said.

It's also important to remember that whenever fermentation or heating takes place, or when spoiled material is removed from the top of the silo, a potential for exposure exists, he said.

Richard Huntrods, superintendent at the Feldun-Purdue Ag Center, knows firsthand the dangers of silo gas exposure. One day while working at another farm, Huntrods and a co-worker opened a silo that had been filled with high-moisture corn the day before.

"We needed to start feeding out of that silo, so one of the guys went up the chute and opened the door," he said. "Unfortunately, he opened the door just above the corn instead of a door farther up like I told him. And instead of shutting it quickly when he realized there was gas coming out, he kicked it completely open."

Huntrods saw the worker overcome by silo gas and went to help him.

"I tried to hold my breath so I could catch the guy, but I took a couple of breaths and that's all it took," he said.

Another worker saw what was happening and ran to the house to call 9-1-1. When the pair regained consciousness, they were on the conveyor belt below the chute.

Deboy said if the men had fallen into the silo they probably wouldn't have survived.

Fermentation is to blame for the deadly gasses. As fermentation occurs, a variety of gases, including carbon dioxide and nitric oxide, are released. Carbon dioxide can cause suffocation in concentrations of 30 percent or higher, Deboy said, but that's unlikely to occur in a silo.

It's the other chemical, nitric oxide, that packs the punch. When it combines with oxygen, it becomes highly toxic nitrogen dioxide. Federal regulations state that 50 parts per million of nitrogen dioxide is an immediate hazard, Deboy said.

"When inhaled, this gas may be fatal or cause permanent lung damage, even in such low concentrations," he said.

Silo gas causes severe irritation of the upper respiratory tract and may lead to inflammation of the lungs. However, that doesn't mean there will be immediate pain or discomfort. Sometimes, but not always, a person experiences coughing, throat irritation and chest pain, Deboy said.

"A farmer may inhale silo gas for a short period of time, notice little inconvenience and die in his sleep several hours later," Deboy said. Without medical assistance, fluid produced by the irritation can build up in the lungs and lead to suffocation.

People who've been exposed to silo gas and have recovered often relapse one to two weeks after the incident. Relapse symptoms are similar to those for pneumonia. Once again, they should seek medical assistance.

Deboy said that if it's absolutely necessary to enter the silo within one month of the filling date, a self-contained breathing apparatus and other confined-space entry procedures should be used. He said farmers generally will not have the expensive, specialized equipment necessary, but local fire departments do, and can be of assistance.

Confined-space entry practices can be found in 29 CFR 1910 OSHA General Industry Regulations. Deboy said copies of the OSHA regulations are available for a fee from the Hoosier Safety Council online or by calling (800) 537-5346.

Writer: Kay Hagen, (765) 494-6682,

Sources: Gail Deboy, (765) 496-2377,

Rich Huntrods (812) 279-8554,

Ag Communications: (765) 494-2722; Beth Forbes,;

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