August 21, 2006

Don’t Risk Fire in Forage

Harvest moisture may seem like an unlikely problem during droughts, but fires can occur in forage, a North Dakota State University dairy expert warns.

“With forage so valuable, especially this year, take the time to assure yours is not lost, and your family and labor is safe,” NDSU Extension Service dairy specialist J.W. Schroeder says.

Hay fires are a danger anytime small bales are stacked at 20 percent moisture or higher, and big square or round bales are stacked at more than 16 percent moisture.

The quickest way to detect hot hay is to drive a long pipe or rod into the center of the stack and leave it there for 20 minutes, according to Schroeder. If the pipe or rod is too hot to hold when you’ve pulled it out of the stack, remove the hot hay immediately.

This process of forage heating up and burning typically is called spontaneous combustion. It usually occurs in hay within the first two months of storage. In silos, forage can dry down if air enters the silo through leaks in walls or doors. This results in the potential for fires throughout the year.

Spontaneous heating and combustion occur when sufficient moisture (above 25 percent and below 45 percent moisture content for forages), oxygen (air) and organic matter are together to support the growth of bacteria and molds. This growth results in an initial temperature peak of 54 to 65 degrees Celsius (130 to 150 degrees Fahrenheit). When the forage reaches this temperature range, a chemical process called the Maillard reaction may occur, causing additional heat generation. This reaction can be self-sustaining and does not require oxygen to continue. The gases produced will ignite if they reach a high enough temperature and are exposed to oxygen.

Here are the items Schroeder recommends producers use to create a hay probe:

• 1/2-inch pipe, threaded at each end; pipe lengths of 2, 4 and 6 feet provide maximum flexibility
• 1 1/4-foot by 1/2-inch coupler
• 4-inch by 1/2-inch connecting pipe, threaded on both ends
• Eight 3/16-inch holes for temperature sensing and water spray
• 3-inch by 1/2-inch machined pointed probe tip

He says producers also need lightweight wire to lower a thermometer into the probe to take temperature readings.

He suggests producers check the temperature of their hay daily if it’s above 120 degrees and twice a day if it’s 140 to 150 degrees. At 150 degrees, the hay is entering the danger zone, so check the temperature every two hours. If the temperature of the hay is between 150 and 160 degrees, start moving hay out of the stack.

“At 160 degrees or higher, call the fire department,” he says. “Have firemen on site before moving any hay.”

Schroeder says using a moisture tester is another way to avoid hay fires. Producers can purchase a tester or use a microwave to evaporate water from a hay sample to test moisture content.

He has this advice for preventing fires in silos:

• Make sure the silo is tight. Check doors regularly and repair loose or damaged fittings to keep air out of the silage. Air also can enter through damaged silo walls. Empty the silo completely every two years. Check the walls for damage and repair if necessary.
• Maintain adequate moisture content. Most silo fires occur because the silage is too dry. Silage should be between 45 percent and 65 percent moisture content. Silage below 40 percent moisture content, coupled with extra air from poor packing or air leakage into the silo, creates a risk of heat damage or fire.
• Cut silage to the proper length. It should be 3/8 inch to 1/4 inch. The short length aids packing (less voids, therefore less air) and makes unloading easier.
• Use a distributor to ensure adequate packing along silo walls. This also will help limit air movement into the silage from walls and doors.
• Fill the silo very rapidly for a good packing minimum of 2 feet per hour. This will reduce air trapped in silage and minimize air traveling through silage. Use temporary covers if you have long periods of time between fillings.

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Source: J.W. Schroeder, (701) 231-7663, jschroed@ndsuext.nodak.edu
Editor: Ellen Crawford, (701) 231-5391, ellen.crawford@ndsu.edu

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