Farmers often know the hay they are baling is wetter than they'd like, but they are taking a chance, hoping to save a better-quality product versus letting the rain cause the crop to deteriorate in the field. Unfortunately, moist hay can quickly become hot hay which can ignite through spontaneous combustion.
Most farmers strive to bale hay that is field dried to 20 percent or less in moisture. At this moisture content, the baled hay can cure properly and maintain quality. With moisture content higher than 20%, hay under storage conditions will generate more heat than can safely be dissipated into the atmosphere. As temperatures rise, dangers of spontaneous combustion increase. Farmers need to be diligent in checking their hay, especially if they know they baled hay that was wetter than normal. Smoldering hay gives off a strong, pungent odor. This odor is an indication that a fire is occurring. If even the slightest smell is present, farmers should take temperature readings of the stack.
Reaching inside a hay stack will give an initial clue. If it feels warm or hot to the touch, that's a good indication that problems may exist. Knowing the temperature of the hay is the only real way of determining how serious the potential fire problem is before flames ignite.
Hay temperature and related actions:
- Temperature 125 degrees F -- No action needed.
- Temperature 150 degrees F -- Entering the danger zone. Temperatures should be checked twice daily. If possible, stacked hay should be disassembled to allow more air to move around heated bales for cooling.
- Temperature 160 degrees F -- Reaching the danger zone. Temperature should be checked every two hours. If possible, stacked hay should be disassembled to allow more air to move around heated bales for cooling.
- Temperature 175 degrees F -- Hot spots or fire pockets are likely. If possible, stop all air movement around hay. Alert fire service of a possible hay fire incident.
- Temperature 190 degrees F -- Remove hot hay. This should be done with the assistance of the fire service. The fire service should be prepared for hay to burst into flames as it contacts fresh air.
Keeping a watchful eye on heating hay can save your barn or storage building. Checking the temperature of suspected or hot hay can help you make critical decisions. If you see the temperature rising toward the 150 degree range, you might consider moving the hay to a remote location, away from any buildings or combustible material. Use caution when moving heated bales, because they can burst into flames when they are exposed to fresh air. Wetting hot bales down before moving them can help control this hazard.