The (literally) Smoking Gun: Hay Fires

Photo from Alabama Cooperative Extension: 
https://www.aces.edu/blog/topics/forages-livestock/reducing-the-risk-hay-fire/

Even though temperatures have consistently stayed in the 80's, the shorter days tell us that winter is approaching.  Many of us have started our winter preparations, which can (and should) include stocking up on quality hay.  However, baled hay can be its own fuel and ignition, and can result in a hay fire.

Hay fires are unique to the horse and agriculture industry.  The majority of hay fires occur within 6 weeks of baling, usually due to an excessive amount of moisture in the bale.  This is thanks to the growth and multiplication of mesophilic (warm temperature) bacteria naturally found in forages.  Much like with composting, the mesophilic bacteria release heat within the bale and can cause the temperature to rise between 130-140 degrees Fahrenheit.  The ideal moisture level for hay being baled is 15-18% moisture.  At this moisture level, at 130-140 degrees Fahrenheit the bacteria begin to die and the internal temperature of the bale begins to cool.  However, in bales with higher moisture content, the heat created from mesophilic bacteria provides a breeding ground for thermophilic (heat-loving) bacteria, which in turn creates hotter temperatures (up to 170 degrees Fahrenheit).  Bales with higher moisture content also sustain these higher temperatures for longer periods.  For example, a bale with 30% moisture may have a higher interior bale temperature for up to 40 days.  It's easy to see how spontaneous combustion can occur in these situations.

Other factors that can have added risk of hay fires include the volume/density of the bale, and ventilation or airflow around stacked bales.  Bales with a lower density/not packed as tight, that are stacked lower and have good airflow have a lower risk of overheating and combusting.

If you are concerned that hay may have been baled at too high a moisture content, make sure to monitor the internal bale temperature 2x a day for the first 6 weeks after baling.  You can use a temperature probe ($20 at most ag supply stores).  When taking temperatures, drive the probe into the center of the bale and leave it there for 15-20 minutes to get an accurate reading.  You can use the chart below for further actions to take depending on the internal temperature of your hay bales.

In the event of a fire, or even if your hay is smoldering, contact the fire department immediately.  Always remember to protect your own life first!  You can always replace hay, buildings, and equipment, but there is only 1 you.

If you do take action to fight the fire, here are some actions to consider first:

• Check the surrounding area for flammable products, like gasoline cans.  If they are present, LEAVE IMMEDIATELY and make sure to notify firefighters of the flammable products upon their arrival.
• Remove any extra vehicles or machinery from the area around the fire to make room for fire service equipment.
• Move any bale moving equipment out of the way, but make sure it is also readily available if needed.
• Turn off electricity to the building (if you have any).

For an in-depth review on how barn fires can start and how to prevent them, check out Penn State's Fire Safety in Horse Stables publication.