Many are unaware that wet hay has a greater risk of causing fire than dry hay. You may be wondering why right now. Logically, it seems odd that something wet could suddenly burst into flames as the opposite seems to make more sense. However, those who advise you to check your wet hay are right, and in this post you can find out why and how to prevent this.

In a recent article, Esther Inglis-Arkell explains how wet hay can just spontaneously burst into flames, and I will do my best to summarize it here. Spontaneous combustion is an interesting process; it seems far-fetched or supernatural that something perfectly fine and at rest, suddenly bursts into flames. Yet, Inglis-Arkell assures us it “sounds a lot more mysterious than it is…There are barns, hay fields, forests, compost heaps, and, once, a two-ton pile of wood chips that have spontaneously caught fire.”

Why? Water is the cause. Water enables the biological processes that discharge heat. As plant cells die, heat and water is released. The greener something is, or the more water it has inside it, the more heat that will exit. From there, our least-favorite friends, bacteria and fungi, go crazy. In their now warm, wet home they begin to eat and produce even more heat as they reproduce. Eventually, the temperature “hits a critical point, and the pile begins to smolder.” The hay itself insulates the fire, and causes it to grow hotter. Further, if there is no oxygen present, the heat will slowly increase until “someone rakes into it and exposes the super-heated material to air. Then it bursts into flame from the inside out.”

Now, what does this mean for you and your stable?

  1. I advise against hay lofts in your barn. Instead, a smaller room can be designated to store small amounts (I recommend up to a 7 day storage maximum), while a larger, separate building can hold the bulk of it. This helps isolate a potential cause of fire.
  2. You don’t want to provide a warm, wet home for fungi to grow. For this, and many other reasons, I advocate for plenty of natural light.
  3. Never stack wet hay (anything with more than 22 percent moisture) and with the hay you do stack, make sure it has plenty of airflow. This will help dry out the hay further. It is wise to stack the hay off the ground so air can get under it to aid the drying process. Further, we add screened ventilation vents to many of our hay storage areas so that air can surround the hay. This allows air to circulate further as hot air rises out of the vents in the roof by the Chimney effect.
  4. If at all possible, refuse any hay delivery that has encountered rain on transport. If it is raining when it arrives, keep it covered and on the truck until the rain stops. Better yet, provide a hay barn in which the hay truck can pull under a roof to unload.
  5. Check your hay regularly and keep vigilant for a caramel odor or musty smell, which is a sign that your hay is heating. Using a temperature probe, you can evaluate the danger level of the hay. 150 degrees F is the start of the danger zone; at 175, call a fire department. Please, if your hay does reach a dangerous level, contact the fire department before addressing it yourself. They will most likely tell you to wet the hay down, remove it from the barn, and dismantle the stack. At this point, there is likely fire pockets and potential for injury. At 190, be prepared for the stack to burst into flames when it contacts the air.

Fire is always a big concern for stables. Yet, with the knowledge of danger, comes the ability to prevent it. Check out Inglis-Arkell’s article for more information on the process and this website that provides further tips.