The forum system notification warned me about necroing this topic… but it is Friday the 13’th so I choose to live dangerously…
Today (well actually couple of days ago after learning from this thread how often people in Germany set fire to things 
) I learned that spontaneous combustion really is a thing.
Industrial and mining combustion of coal dust excluded, it appears that for the average home D.I.Y.'er that something as seemingly innocuous as Linseed oil can lead to a fire due to the exothermic reaction as the oil dries (not on your Std 6 wood work chess board but the discarded rags in the bin).
Basic example
