Barn Fires: Avoid Hay Bale Combustion

Experienced agricultural producers in the southern Great Plains know that low wind speeds, high humidity, moist hay, and hot temperatures can be a recipe for disaster.

Under such a set of circumstances, tightly stacked hay bales have been known to combust. Without proper preventive measures, hay barns or any other structures close to the blazing bales potentially might be lost.

"When you go in and immediately harvest these forages, they have a high water content, which continues the process of respiration," said Daren Redfearn, MS, PhD, Oklahoma State University Cooperative Extension forage specialist.

Respiration is a normal process that plants use to produce food. Unfortunately, it also produces heat. The respiration process will continue to produce heat until the moisture content of the hay drops below 40%. At 20% moisture, the hay is considered dry.

However, Redfearn reminds producers that mold will grow through respiration and will produce heat until that point. This heat can mix with oxygen and cause combustion. Combustion typically takes place along the surface of the bales because oxygen has trouble penetrating into the middle.

Before this happens, there are some preventive measures that should be taken.

"Make hay while the sun is shining," Redfearn said. "Producers need to get their hay dried as quickly as possible."

If there is any question as to whether the hay was baled at the correct moisture, the temperature of the bales should be closely monitored. A bale that measures less than 120°F is in little danger.

Redfearn said bales between 120° and 140° need some attention. These bales should be removed from a barn or structure and separated so that they can cool off. Once the temperature of a bale exceeds more than 140°, it is generally too late.

"Once you start moving them at that temperature, that's when you really get the danger," he said.

Combustion issues typically occur within five days to seven days of baling.

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