Spontaneous Combustion of Hay a Real Threat

By Jim PathFinder Ewing

On my daily bike ride (which is more like every other daily maybe), I saw an interesting sight: Spontaneous combustion of a hay bale.

I was riding my bike and kept smelling smoke — not uncommon with people burning off their fields from winter stubble. I came over a rise and there was the hay bale, off the side of the road: smoldering.

I’ve seen it only very rarely. With round bales, it occurs where wet hay and dry hay are rolled up together. The heat from natural degradation or unintentional composting of the wet hay causes the dry hay to ignite. It can happen in stacked square bales, too.

Here’s more on the mechanics of it and how to avoid it from Washington State University: http://ext.wsu.edu/hay-combustion.html

Here’s a photo I took:

Spontaneous combustion of a hay bale occurs when damp and dry hay is mixed.

Spontaneous combustion of a hay bale occurs when damp and dry hay is mixed. Photo by Jim PathFinder Ewing c. blueskywaters.com

What to look out for? According to the WSU article:

There will be early warning signs. Watch for steam rising from bale surfaces and condensing on the roof and eves of the barn. Often molds will start to grow on all these surfaces, too. There will be an acrid, hot, tobacco smell rising from the bales. Even before these visual signs appear, it is wise to take the temperature of the bales in the stack.

If the hay is in round bales, probe the bale ends. If in square bales, probe from the sides. If you do not have a long temperature probe, you can use a crowbar. If the haystack is large, push the crowbar in between bales as deep as you can go. Leave the crowbar there for about two hours. Remove the bar and feel with your bare hands. If the crowbar is easily handled, without feeling heat or discomfort, the hay in that area has not heated yet.
If the crowbar can only be held for a short time, the hay temperature is approaching 130 Fº. If the bar can only be touched briefly, hay temperatures are about 140 Fº. At 150 Fº, the bar is too hot to hold.

There’s an important lesson here: Pay attention when cutting hay for storage. If that smoldering bale had been in an enclosed structure with other bales and other flammable materials, it could have posed a substantial danger. As it is, the farmer is out the $90 or so the bale could have fetched or the cost of feed that s/he would have to shell out to replace it.

Jim PathFinder Ewing is a journalist, author, writer, editor, and blogger. His latest book titled Conscious Food: Sustainable Growing, Spiritual Eating (Findhorn Press) is in bookstores now. For more, see: http://www.linkedin.com/in/jimpathfinderewing/, Facebook or his webpage, blueskywaters.com

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