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F. W. �
I�ve become puzzled about spontaneous generation of fire in hay. I take it on faith, and in warm moist weather I poke a long
thermometer probe deep into the end of freshly rolled round bales after they have lain in the field for a day or so. Typically
in summer (ambient temp of 100 to 105 degrees F) I�ll find a few with temps of 145 degrees F or above while the rest are down
below 120. Maybe 6 or 7 out of 100. We just leave those hot bales alone �till they cool off, and stack the rest end-to-end
in open hay-traps. But I�m uneasy about what would happen if we chanced to butt several of the hot ones together.
How can fire start? Newton�s Law of Cooling requires that heat flows away from hot spots, toward cooler spots. The ignition
temperature for dry hay is claimed to be about 400 degrees F, and the microbes who are busy digesting the moist hay and making
all that heat are bound to die well below that temperature..
Now in oily cotton waste or rags, I can see the process � in that case there is a tremendous amount of confined surface covered
with a very thin layer of oil, and the normally slow oxidation of the oil surface produces (a little) heat. This in turn speeds
up the oxidation, and off we go with positive feedback.
But how about the bacteria in the hay? Do they make some oil or alcohol in their digestive process which stays behind after
they cook, and which does the final high heat part of the reaction? Or what?
Comment?
Spurgeon Smith (near Elgin, TX)
