A Reminder About Silo Gas

Posted: October 2, 2012

Every year, we usually hear of at least one farmer being overcome by silo gas. Since there is still some silage corn standing across PA, it doesn’t hurt to remind ourselves about the dangers surrounding silo gas.

The following information is taken from a Penn State Press release:

During the fermentation process of silage, a number of gases are given off, Davis Hill, senior extension associate explained. Of particular concern is a family of gases called oxides of nitrogen -- often referred to as silo gas. "The formation of these gases peaks in one to two days after filling and can last for 10 days to two weeks after the fresh, green forage is chopped and blown into the silo," he said.

Silo gas sometimes has a bleach-like odor and under certain conditions can be visible as a fog from a distance (often mistaken for smoke). If the gas is high enough in concentration, this fog will appear to be yellow to reddish brown in color, and the silage surface, silo wall, base of the chute and other structures of the silo may be stained (yellow, orange, reddish) from the gas. This gas is heavier than air, which means it will settle at the surface of the silage instead of rising to the top of the silo, exiting through the fill door. This is an important factor, Hill pointed out.

"The highest concentration of gas will be at the surface of the silage, which is where a person will be going if he or she needs to enter the silo for any reason," he said. "Also, if a silo door is open near the surface of the silage, the high concentration of gas -- being heavier than air -- could exit the silo through this door, flow down the chute and settle at the base of the silo in the feed room or in the barn area. If there is little ventilation in the barn, a dangerous buildup of silo gas can occur, which can affect livestock or people who enter the area.

The presence and concentration of silo gas is dependent on the storage structure and the quality of the forage material that is chopped. Those crops that have received nitrogen fertilizer (corn) and those crops that have suffered prolonged drought or especially prolonged drought conditions followed by rain just prior to harvest often lead to high gas production.

Some precautions to take include:

  • Assure all spaces at the base of the silos are well ventilated and that silo doors are closed well above the level of the silage surface.
  • Stay out of the silo for three weeks after filling the silo and always ventilate the silo with the silo blower for at least 20 minutes prior to entry (however, this is only effective if the silo is over half full).
  • Consider leaving the lower 10-12 inches of stalk in the field (chop higher than normal) as this part of the plant may have the highest level of nitrates accumulated.

Individual reactions to silo gas depend on the concentration of gas that is inhaled and the length of exposure, Hill said. Very high concentrations of gas will cause immediate distress, which will result in a person collapsing and dying within minutes.

"More mild concentrations could cause upper respiratory congestion, watering eyes, coughing, difficulty breathing, fatigue and nausea. If symptoms are mild, an individual may stay in the area to finish the job at hand. This can make the effects of silo gas worse, as these effects can last for many hours in the body, causing symptoms to become progressively worse over the course of the next day or two." People experiencing any of these symptoms when inside or near a freshly filled silo should immediately exit to fresh air and leave the task for another day. They also should go immediately to their doctor or the hospital emergency room and report that they have had a serious "silo gas poisoning" exposure.

One aftereffect of silo gas poisoning is fluid in the lungs leading to chemical pneumonia and perhaps death if not treated promptly. The effects of fluid filling the lungs may not present itself until several hours after the exposure—and then it may be too late.

Contact Information

Dwane Miller
  • Extension Educator, Agronomy
Phone: 570-622-4225 x14