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Keeping Hay Fires from Spontaneous Combustion

Excerpt from Montana State University / D. Cash & R. Johnson

Every farmer has heard stories of someone affected by a hay fire. It certainly isn’t a minor incident since it can damage property and threaten lives. While hay fires can occur during transportation, they are more likely to be caused by spontaneous combustion once the bales are at the farm.

Actually, wet hay is more likely to lead to spontaneous combustion than dry hay. If wet hay with more than 22% moisture is stored in a barn or stacked then the risk of spontaneous combustion is increased. Further, the wet hay loses in forage quality.

When the internal temperature of hay rises above 130 degrees Fahrenheit (55 degrees C) it provokes a chemical reaction producing flammable gases that can ignite. Most hay fires occur within 6-weeks of baling. Heating occurs in all hay above 15% moisture, but generally peaks at 125 to 130 degrees F within three to seven days with a minimal risk of combustion or forage quality loss. In the next 15 to 60-days depending on stack density, external temperatures, humidity and rainfall the internal temperature will decline to a safe level.

As with all bales – there is a need to gauge the temperature:
At 150 degrees – check temperature daily
At 160 degrees – measure temperature every 4 hours and inspect the stacks
At 175 degrees – wet hay down, remove it from the barn or dismantle the stack away from other bales and buildings and Contact the Fire Department
At 185 degrees – hot spots or pockets may be expected. Flames will most likely develop
At 212 degrees – this is critical – hay will almost certainly ignite

Play it Safe and Take Precautions:

  • To avoid hay fires, small, rectangular bales should not exceed 18 to 22% moisture and large round or rectangular bales should not exceed 16 to 18% moisture for safe storage.
  • Check fresh hay daily. If there is a distinct musty smell or a slight caramel odor, there is the likelihood that the hay is heating – keep monitoring the temperature.
  • Prior to entering a barn place long planks on top of the hay. Always tie a rope around your waist and have another person on the other end at a safe location to pull you out should the surface of the hay collapse into a fire pocket.
  • Know the composition of the feed – hay treated with preservatives can be a dangerous combination.
  • Dry ice, liquid nitrogen or carbon dioxide gas pumped into the hay can prevent combustion by eliminating the oxygen from the hay mass. While farmers in the past sprinkled salt on wet hay to prevent spoilage – it will not prevent spontaneous combustion.

Adopting good storage practices will help to avoid spontaneous combustion and ensure better quality hay.