Farmers, Be on the Lookout for Silo Gas

AMES, Iowa – More Iowa farmers are cutting corn for silage this summer due to the extreme heat, dryness and crop conditions. Because of the increased silage production, the possibilities for silo gas and related health issues have increased, according to Chuck Schwab, Iowa State University Extension and Outreach farm safety and health specialist.

What is silo gas?

“Silo gas is a toxic, natural by-product of silage production,” said Schwab.“The gas occurs naturally as a result of ensiling. This hazard exists each year, but because of drought conditions, it could occur more frequently, since more farmers are ensiling this harvest season.”

As nitric gases from recently harvested plants leave the silage, the gases combine with oxygen from the air to produce another gas, called nitrogen dioxide. Nitrogen dioxide is a toxic gas that should be avoided. Carbon dioxide is also present. Silo gas forms when the nitrogen dioxide and carbon dioxide combine.

Silo gas usually forms within a few hours and up to three weeks after fresh plant material is added to the silo, silage bags or bunkers. The three-week period is the most dangerous time, and farmers should check for signs of silo gas. The gas is typically a problem in conventional, non-airtight silos. Open air usually prevents silo gas from reaching dangerous levels.

Silo-Filler’s Disease: What it is, and how to prevent it

Silo-filler’s disease is the term given to the injuries that result from exposure to silo gas. Inhaling even a small amount of silo gas can result in serious, permanent and sometimes fatal lung injuries. Symptoms of silo-filler’s disease include coughing, burning, shortness of breath, chills, fever headaches, nausea or vomiting.

Silo gas is almost invisible, but it can be seen as a yellow or red haze hanging just on top of the silo. Silo gas is heavier than air, and will settle on top of the silage and in any depression or cavity in it. It can travel down the silo chute and collect in adjoining buildings.

If signs of silo gas are detected, leave the area. See a doctor immediately if silo gas inhalation or exposure occurred, or could have occurred. To reduce the amount of silo gas formed:

  • Fill the silo quickly.
  • Fill the silo as full as possible.
  • Keep a blower running to provide as much air movement as possible during filling time.
  • After filling, keep the door between the feed room and barn closed and secured.

“It is important to remember this hazard exists, whether you make silage every year or are ensiling because of drought conditions this year,” Schwab said.

The Iowa Department of Public Health has prepared 2012 Iowa Harvest Exposure to Mold and Dust in Grain, a fact sheet addressing elevated human and animal health concerns about increased dust and mold exposure due to drought conditions. The fact sheet is available at