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Agriculture - Tips on preventing hay fires on the farm

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FARMING FACTS by BRYCE ROBERTS/Agriculture Extension Agent

You can prevent hay bale or barn fires if you bale hay at appropriate moisture levels and monitor the temperature of recently baled hay.

Generally, hay will begin a heating phase within one to two days after baling. During this time, you should monitor hay to make sure it does not reach temperatures that can damage the hay or lead to spontaneous combustion.

It is not unusual for the temperature within a bale of hay to reach 100 degrees Fahrenheit, and may go as high as 130 degrees before beginning to decline. If the temperature peaks below 130 degrees, there may be some loss of quality but no danger of fire. With free air circulation around a bale, both heat and moisture can easily dissipate. A single bale rarely heats enough to catch on fire, but when they are placed close together or stacked with other bales that are also heating, it is much more difficult for the heat to leave the bales. A good practice is to leave bales scattered in the barn or in the field for 3 to 4 weeks before placing them in a stack.

If the bales are wetter than they should be, the temperatures can easily rise above 130 degrees. At 140 to 150 degrees more microbial growth and chemical reactions within the hay cause it to generate heat at an increasingly rapid rate.

If hay temperatures reach 150 degrees, you will need to move bales to allow for better air circulation and you should check the temperature at least two to three times per day. At 180 degrees, fire is imminent, and at 200 degrees, it is likely to be present. In either case, the fire department should be notified. It is best to wait for them to arrive before removing the hay from the stack in case of a flame up.

Smoke from hay that has been treated with an acid preservative may contain toxic fumes, so keep people away from the smoke and inform the firefighters of the treatment that was applied.

To check the temperature of hay, you can use several types of thermometers. Find one that is durable and easy to use and will measure up to 200 degrees.

One way to use a simple glass thermometer is by attaching a string or thin wire and lowering or pushing it into a probe that has been inserted into the center area of the hay stack. Do not insert them directly into the hay because they break very easily. It is best to use only spirit-filled glass thermometers. That prevents any risk of accidentally contaminating hay with mercury from a broken thermometer.

You can also use electronic thermometers with remote sensors and a digital readout. Avoid LED displays because they are often hard to read in bright light. An LCD is a better choice. If you are also moisture testing your hay, some of the electronic moisture meters also measure temperature.

Long stem thermometers, commonly called compost thermometers, are probably the most rugged and reliable when measuring temperatures in one bale at a time. With these types, the price increases with the dial size and length of the stem. It may be tempting to stick these directly into a hay bale, but the stem can easily bend and destroy the accuracy or operation of the thermometer.

It is best and necessary in most cases to use some kind of hay probe. You can easily make one yourself using steel pipe or electrical conduit. You can also purchase commercial probes.

When you are using a thermometer, measure the wettest hay first. Probe square bales from the side and round bales from the end. You should insert the probe near the center of the bale. In round bales, if the core is loosely formed, probe six to 12 inches away from the center where the hay will be more tightly packed.

In large stacks, it may be difficult to reach the center, but it is important to get at least five to 10 feet down from the top or in from the side. The most critical factor is to reach where the wettest hay is stored. It is best to probe at several locations and at different depths within a stack to locate the warmest spot.

When checking hay for moisture and temperature, always err on the side of caution.  If temperatures are in an upward mode, monitor hay until it becomes stabilized under 130 degrees Fahrenheit or until the interior of the bale or the hay stack reaches ambient temperature.

Feel free to contact me at your Spencer County Cooperative Extension Service at 477-2217 or you can email me at broberts@uky.edu.  You can visit the Spencer County Extension Services’ website at www.spencerextension.com.