Keep track of hay temperatures after it goes into the barn is part of the process to prevent barn fires. Photo from Michigan State University.

By Jeff Burbrink
Extension Educator Ag & Natural Resources, Purdue Extension LaGrange County

LAGRANGE — Our region is one the largest hay producing areas in the state, and as a result, we have seen more than our share of hay fires over the years.

Jeff Burbrink

Keith Johnson, Purdue Extension’s forage specialist, reminds us of the importance of checking hay several times after it goes into the barn. It is normal for hay to heat a bit as it cures in the barn. That’s part of the process of preserving the nutrients for later use. But, when the temperatures exceed 125 F, there is a real possibility that trouble is coming.

It has been my observation that people keep a close eye on the hay for five days or so, and then assume it’s okay. In reality, most fires break out two to four weeks after being stacked.

What causes the fire? The root cause is excessive moisture. The target moisture for beginning to bale hay without a preservative is 20% for small rectangular bales, 18% for large round bales, and 17% for large rectangular bales.  Moisture levels higher than this result in microorganisms creating mold, reduced protein in the hay, reduced forage quality and the possibility of spontaneous combustion.

The critical temperatures to watch for in stored hay are:

• 125 F or lower – No action needed
• 150 F — Entering the danger zone. Check temperature twice daily. If possible, disassemble stacked hay to allow more air to move around and cool heated bales.
• 160 F — The hay is reaching the danger zone. Check temperature every couple of hours. If possible, disassemble stacked hay to allow more air to move around and cool heated bales.
• 175 F — Hot spots or fire pockets are likely. Continue to check temperature frequently. If possible, stop all air movement around hay. Alert fire service of possible hay fire incident.
• 190 F — Fire is likely. Remove hot hay with fire service assistance. The fire service should be prepared for the hay to burst into flames as it contacts fresh air.
• 200 F or higher — Fire is imminent. Remove hot hay with fire service assistance. The fire service should be prepared for the hay to burst into flames as it contacts fresh air.

Remember, the probe is measuring where it was inserted. Five or 10 feet over, the temperature can vary considerably. If you find hay at 175 degrees, you might want to assume it is higher elsewhere in the stack.

There are numerous internet sites, catalogs and farm stores where you can purchase hay temperature probes. Look for probes that are strong enough to penetrate through tightly packed bales to a length of around 6 feet. Another nice feature is the ability to insert a thermometer with a probe.

If you find yourself pulling hay out of a barn, be careful where you stack it. I talked to someone who learned the hard way not to place the hot hay under power lines!