June 30, 2009
Some barns in Pennsylvania got a whole lot warmer than expected in recent weeks. The combination of wetter than normal hay and warm summer weather sparked a rash of barn fires cause by hot hay igniting via spontaneous combustion, reports Davis Hill, Penn State Extension's director of Agricultural Emergencies program.
By baling hay wetter than normal to escape a forecasted rain, you take a chance, says Hill. Field-dried to 20% moisture or less, baled hay can cure properly. But some have had to bale at 25% moisture. With moisture content that high and no preservative, stored hay will generate more heat than can be safely dissipated into the atmosphere.
How to check hay
Smoldering hay gives off a strong, pungent odor, indicating that a fire is occurring. If even the slightest smell is present, attempt to take temperature readings of the stack, he advises. It's the only real way of determining how bad the potential fire problem is before flames arrive.
Infrared thermometers and digital thermometers are accurate. Local fire companies may be willing to come out with thermal imaging cameras to evaluate a situation, says Hill. "Most would prefer to come out prior to an actual fire to help avoid a catastrophic fire. A number of fire companies and silo-fire experts also have probes available that can be borrowed to monitor a stack of hay."
A stack core temperature between 150 and 174 degrees Fahrenheit is entering the danger zone. Temperatures should be checked twice daily, and if possible the stack should be disassembled to allow more air to cool it.
At 175 degrees, hot spots and pockets of fire are likely. Stop all air movement around the hay and alert a fire service to a possible hay fire incident.
At 190 degrees, remove hot hay with the help of a fire service. Be prepared for the hay to burst into flames as it contacts the air.
At 200 degrees or higher, a fire is almost certain to develop. Call a fire service and have the hay removed. Again, expect the hay to burn as it contacts fresh air.
It's better to have a fire away from your main hay storage or barn. Use caution when moving heated bales. Wetting hot bales down before moving them can help keep them from bursting into flame.
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