Haypiles and compost piles may self-ignite because of heat
produced by bacterial fermentation.
Linseed oil in a partially confined space can oxidize
leading to a build-up of heat and thus ignition.
Coal can ignite spontaneously when exposed to oxygen which
causes it to react and heat up when there is insufficient ventilation for
Pyrite oxidation is often the cause of coal spontaneous
ignition in old Mine tailings.
Pistachio nuts are highly flammable when stored in large
quantities, and are prone to self-heating and spontaneous combustion.
Large manure piles can spontaneously combust during
conditions of extreme heat.
Cotton and linen. When these materials come into contact
with polyunsaturated vegetable oils (linseed, massage oils), bacteria slowly
decompose the materials, producing heat. If these materials are stored in a way
so the heat cannot escape, the heat build-up increases the rate of
decomposition and thus the rate of heat build-up increases. Once ignition
temperature is reached, combustion occurs.