Released July 20, 2009
STILLWATER, Okla. – 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 preventative 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, 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 percent. At 20 percent moisture, the hay is considered dry.
However, Redfearn reminds producers that mold will grow through respiration and produce heat until that point. The heat produced, along with the hay itself, 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 preventative measures that should be taken.
“Make hay while the sun is shining,” Redfearn said, referring to an old adage that has a lot of truth to it. “Producers need to get their hay dried as quickly as possible.”
The summer months in Oklahoma provide adequate drying conditions. There are high temperatures, a slight breeze and low humidity.
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 degrees Fahrenheit is in little danger.
Redfearn said bales between 120 degrees and 140 degrees 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 degrees, it is generally too late.
“Once you start moving them at that temperature, that’s when you really get the danger,” he said. “That’s when you are putting yourself in danger.”
Combustion issues typically occur within five days to seven days of baling.
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Writer: Sean Hubbard, 405-744-4490, sean.hubbard@okstate.edu
