Extinguish the chance of hay fires

If you run a farm, you’re probably aware that of the potential sources for fire on your operation — lightning strikes, piles of oily rags, electrical shorts caused by dust or cobwebs, etc. — and you take steps to mitigate them.

There’s one fire starter that may not be on your radar, though, because it’s counterintuitive: wet hay. However unlikely this might seem, according to Grinnell Mutual’s Loss Control bulletin on the spontaneous ignition of hay, hay is a leading cause of fires in barn and storage buildings every year. According to one report from the Animal Welfare Institute, over one four-year period (2018-2021), barn fires in the U.S. took the lives of nearly 3 million animals. And then there’s the risk to your facilities, machinery, and maybe even your home.

Hay fires usually get their start in the first six weeks after baling, in hay that was not cured properly after it was cut. Excessive moisture in the hay fosters the growth of bacteria and other microorganisms. This produces heat which, while it kills some microorganisms, leaves heat-loving bacteria unaffected. These continue to thrive, heating up more and drying out the surrounding hay. Eventually, if there’s also enough oxygen present, the hay mass will reach a temperature at which it can spontaneously ignite. These fires usually result in a total loss of the storage building and its contents.

What you can do

Of course, it’s best never to allow a hay fire to start in the first place. To help mitigate fire danger, you should cut the hay under dry conditions and store it only after the moisture content is below 20 percent. There are also conditioners that can help remove excessive moisture and dry the hay faster.

Hay storage barns or buildings should be weather tight. Ideally, you should store hay bales so air circulates freely above, below, and around them, and avoid storing hay directly on the ground. Storing the bale on gravel or on objects can help prevent ground moisture from penetrating the bale and allow air to circulate underneath it. If you’re storing your hay outside, make sure it’s tightly tarped.

After you’ve put up your hay, keep a careful eye on it, particularly during the first six weeks. Check the temperature in the center of the bale or haystack twice a day, leaving the thermometer in place for at least 10 minutes. As long as the internal temperature of a bale remains below 130 degrees Fahrenheit, you should be safe. But if the temperature starts to climb or vary erratically, you should take steps — such as moving the hay to improve air circulation and getting it away from structures.

Hay stored for longer than six weeks still has the potential to get wet, which could kick off the heating process that leads to a fire. In the event your bale’s internal temperature is above 175 degrees Fahrenheit, you should avoid moving it. It’s likely a fire has already started, and moving the hay could expose the fire to more oxygen. Instead, move any livestock or flammable objects away, evacuate the area, and call the fire department.

The information included here was obtained from sources believed to be reliable, however Grinnell Mutual Reinsurance Company, SI, and its employees make no guarantee of results and assume no liability in connection with any training, materials, suggestions, or information provided. It is the user’s responsibility to confirm compliance with any applicable local, state, or federal regulations. Information obtained from or via Grinnell Mutual Reinsurance Company, SI, should not be used as the basis for legal advice and should be confirmed with alternative sources.

Source: New Jersey Agricultural Experiment Station

1/2025