NDSU Extension - Burke County


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Check Your Hay!

County Agent News
Dan Folske
September 30, 2019


Check Your Hay!

            Wet conditions for haying and heavy recent rains have contributed to hay fires and spoiling hay around the state. Some heating of hay following baling is normal but when moisture levels at baling are too high microbial action can cause excessive heating and even spontaneous combustion. This is especially true when bales are stacked into large piles with limited airflow.

            High-moisture haystacks and bales can catch on fire because they have chemical reactions that build heat. Hay insulates, so the larger the haystack, the less cooling that occurs to offset the heat. When hay’s internal temperature rises above 130 degrees Fahrenheit (55 degrees Celsius), a chemical reaction begins to produce flammable gas that can ignite if the temperature goes high enough. 

Fire is possible in hay that’s loose, in small or large bales or stacks, and stored inside or outside. Hay fires are a danger at any time in stacked small bales when the hay’s moisture content is 20 percent or higher, and in stacked big square or round bales when the hay’s moisture content is more than 16 percent. Hay fires usually occur within six weeks of baling.

Heating occurs in all hay above 15 percent moisture, and it generally peaks at 125 to 130 F in three to seven days with minimal risk of combustion or forage quality losses. Then the temperature in a stack should decrease to safe levels in the next 15 to 60 days, depending on bale and stack density, ambient temperature, humidity and rainfall the hay absorbed.

  • Check your hay regularly. If you detect a slight caramel odor or distinct musty smell, chances are your hay is heating. At this point, checking the moisture is too late; you'll need to keep monitoring the hay's temperature.
  • If you suspect your hay is heating, insert a simple probe into the haystack to monitor the temperature. You can make a probe from a 10-foot piece of pipe or electrical tubing. Sharpen one end of the pipe or screw a pointed dowel to one end, then drill several 1/4-inch-diameter holes in the tube just above the dowel. Drive the probe into the haystack and lower a thermometer on a string into the probe. Insert the probe in several parts of the stack and leave the thermometer in place for 10 minutes at each site.
  • If the internal temperature is 125 degrees F or less, there is no action needed.
  • At 150 degrees F, hay is entering the danger zone. At this point, check the temperature twice daily and disassemble stacked hay bales to promote air circulation to cool the hay.
  • At an internal temperature of 175 degrees F, hot spots or fire pockets are likely! Alert fire services to the possible hay fire incident immediately.  Do not move bales as airflow could cause the hay to ignite!
  • Hay treated with preservatives containing ethoxyquin and butylated hydroxytoluene produce hydrogen cyanide gas at about 240 F (115 C). This gas is deadly, so use extreme caution when fighting a fire in this hay.

The proper procedure for controlling a hay fire is:

  • Knock down visible flames. A straight-tip nozzle will penetrate deeper into the hay.
  • Probe for hot spots and inject water through the probe to cool the hay and raise it to a moisture content that will prevent burning.
  • When the hot spots appear to have cooled sufficiently, begin removing the hay from the barn or stack. Keep a hose handy in case of missed or insufficiently cooled hot spots.


Filed under: Burke news
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