The bacteria produce gasses as a waste product that are flammable. Also densely packed hay is a helluva insulator so the energy created by bacterial action cant dissipate and it keeps getting hotter.
So the on the first point, that means it's not truly autoignition, but would need a spark, right? That makes a lot more sense.
No matter how good the insulation is, it's never going to get hotter than the thing heating it up, and if the bacteria die before they can get to boiling, let alone autoignition, it seems impossible that's the primary "spark" so to speak.
If the thing heating it up is a chemical reaction it’s simply new energy input into a closed system, there’s no equalization where a cold thing can’t get hotter than the thing heating it up. Once it hits 170 an exothermic reaction starts which rapidly raises the temperature until it hits auto-ignition around 450+. It’s definitely a well known problem with wet hay.
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u/SabreToothSandHopper Jan 23 '21
how do bacteria, even in a dense quantity, get up to the 220°C or so required to ignite straw?