Which brings us back to spontaneous human combustion.
I’d bet it has to do with the oils in the walnuts. An infamous source of garage fires is piles of linseed-oil soaked rags from people oiling their baseball bats. If I recall correctly it has to do with the degree of unsaturated carbon-carbon bonds in the oil which makes it reactive. Presumably lard-soaked rags wouldn’t exhibit the same problem.
In Una Persson’s impeccable report on spontaneous ignition of charcoal and coal (at least I’m not gonna peck it.) She spoke of a fire in a coal barge.
I worked in a tail light factory with a huge boiler room that supplied steam heat and air pressure (by steam-driven compressors) to the factory. It runs on natural gas now, but it was coal-fired for many years.
Anyway, in the winter months, the RR coal cars would sometimes come in frozen. They had a big car-shaker to break loose the coal, but sometimes the boiler room guys would have to start a fire under the coal car! :eek: :eek: I asked one about it one subzero day, but he shrugged it off, “Oh, yeah, we have to do this every year.” Still, it seemed kinda risky to me.
A fascinating article as usual from Una. I wish I had command performance from Cecil Adams on my resume!
I’m still confused on what role wetness plays. I assume that already wet coal would be in the process of drying, which the study showed is endothermic and tended to lower the temperature of the coal. Doesn’t that mean that wet coal is less likely to burn, not more? That would be more intuitive anyway. Wet stuff generally doesn’t burn.
The wild card is that making coal wet is exothermic. Why? I don’t know. That doesn’t really make sense to me, but that’s what the study says. If I accept the study as read, I would conclude that hosing down a pile of coal might be a bad idea, but once it was already wet, I would be safe for awhile. That seems to be exactly the wrong conclusion though. To quote Fred Willard from “A Mighty Wind”, wha’ happened?!
There’s a couple of complicated things happening which tend to be very specific to the situation that the coal is in, in addition to the type of coal. Here I am much less familiar with charcoal as used for cooking than with coal.
When the coal is in the ground and damp, the primary thing keeping it from combusting is lack of oxygen. In places where natural coal fires have started this often occurs at a large opening or crack in the ground, or at an exposed surface to the coal (sometimes coal can be dug out of stream and river banks). Once the oxygen is made available the oxidation and catalyzation reactions caused by the wetting speed up.
The wetting is not only adding heat, but is aiding in the catalysis of the volatile organic compounds in the coal.
The reason that wet coals like PRB will burn so readily is that it has been taken out of the ground, where it was wet but essentially unexposed to oxygen, and broken up so its surface area is tremendously increased. During the mining process a bit of surface moisture and some excess saturated moisture is lost, so the coal does dry out a bit. At this point, some parts of the coal which are still very wet can start to have chemical reactions with the oxygen in the air, and start the slow heating process. Depending on the availability of air and the insulation effects of the surrounding coal, the heat then can build up.
Sometimes the coal can be kept wet enough, by constant application of water and sprays, such that exposure to oxygen is minimized. This tends to be both expensive and messy, and the chemical-tainted water that runs off has to be disposed of.
I guess what I’m saying is, the real answer to your question is that you have to think of it on large scales and not small. The process results in a tendency towards combustion that is hard to predict on a small scale but not so hard on a large scale. In large coal piles (consisting of tens of thousands of tons) there are places where the wetness, packing, and exposure to oxygen are such that the combustion can occur. There are also going to be places where the coal is exposed to oxygen but not wet enough, and places where it is saturated with water to the point where oxygen exposure is very low. And once an area gets hot, the heat adds to the reaction and it goes on from there.
In looking back at charcoal, I looked very hard and found that it seems impossible to say or easily predict that any single bag or small collection of bags will self-ignite. I read through a few fire investigator’s reports where a wet bag of charcoal was blamed for a fire, but in all of these cases I saw there was no actual direct evidence of such. It really seemed to me that in at least one case they were sort of grabbing for an easy explaination.
I wonder if this is the same kind of thing.
Quite a few years ago (maybe 1960 or so) in my home town in Saskatchewan, a grain elevator full of wheat caught fire and collapsed. The fire certainly began in the wheat, and the investigators attributed it to storing the grain damp.
It took several days to clear the road, and weeks to remove the pile, hosing it down with every loader scoop and whenever the fire broke through to the surface. The area stank of smoke through the whole time.
Wet baled hay can combust while drying.
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