Preventing Hay Fires

While the threat of hay fires is often greater in the late spring and early summer months, it can affect hay storage anytime hay is put up with high moisture concentrations.

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Q. As several hay fires and the loss of barns and other property made the news recently, an inquiry came into the UK Ag Equine Programs office: What information is available about the prevention and control of hay fires? Can that information be made available publicly?


A. According to Ray Smith, PhD, professor and forage extension specialist at the University of Kentucky, and a publication he helped author while he was a faculty member at Virginia Tech University, hay moisture concentration has a major effect on the microbial activity that can lead to hay fires.

Smith said producers should cure hay to the proper moisture concentration prior to baling--a concentration of 20% or less for small rectangular bales and 18% or less for large or round bales. (Note, however, that experts caution that a moisture concentration greater than 16.5% in square bales puts those bales at a greater risk of mold during storage).

Many of the hay fires that occur happen within six weeks of baling, when hay spontaneously combusts. Kentucky and several states in the Southeast had a wetter-than-average late spring, which affected many farmers’ hay baling schedules as well as the quality of some of the hay that was put up.

While the threat of hay fires is often greater in the late spring and early summer months, it can affect hay storage anytime hay is put up with high moisture concentrations.

Smith recommends farmers or horse owners check the temperatures of hay that has been baled at a higher-than-desirable moisture concentration twice a day during that six-week window post-baling. When temperature readings come back at lower than 130 degrees Fahrenheit, continue monitoring them twice per day. If those temperatures fall within the 130-140-degree range, Smith recommends rechecking that reading in a few hours. If the temperature is measured at 150 degrees, it is likely that number will continue to rise. At that point, he recommends moving the hay to allow air circulation and cooling and to monitor temperatures every few hours. (Note that experts also suggest moving affected hay with a fire department close at hand in case the increased oxygen serves as the tipping point to fire). If temperature readings are greater than 175 degrees, it is likely that a hay fire is imminent or already occurring. At that point, call the fire department immediately.

You can monitor temperatures inside hay using a probe and thermometer. Commercial temperature probes are available but are often too short to monitor the maximum interior temperature. The following article referenced by Smith describes how to make a simple temperature probe with an iron pipe.

The Virginia Tech educational paper about hay fire prevention and control referenced can be found in its entirety at http://pubs.ext.vt.edu/442/442-105/442-105.html.

Holly Wiemers, MA, APR, is communications director for UK Ag Equine Programs.


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