I think there is a lot of speculation here. Compost does not spontaneously combust.
Microbes can not operate without moisture, and can not survive temps higher than 100 Celsius. Moisture does not exist past 100 Celsius either. Fire starts around 300 degrees. You still need a spark, and dry material, regardless of the act of composting.
I have composted at projects in the sub arctic, desert, and tropics, and have worked with hundreds more, none has ever experienced spontaneous combustion.
Composting results in a lot of chemical reactions going on. These reactions result in a lot of heat being generated.
That said, that’s usually not smoke. It’s steam. While compost piles do get hot they are (supposed to be) really moist. It’s certainly possible for that to be smoke, and a compost pile can ignite, but that’s rare and means something has gone wrong.
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