I can tell you smth about this
It so happens that I live in Eastern Europe and my father has seen what you call "Spontaneous Combustion " or at leas what was left of him
My father then was 25 and he was a criminal detective at police.
When they arrived at the place[investigation group], they saw a chair. There was a pile of ash on the chair, and the witnesses claimed there was a man there. Latter analysis prooved tht tht ash could be human. What was signifficant is tht. there were signs of extreme temperature, but the chair was merely burnt[slyghtly burnt, toned brown].
There have also been other cases in EE. so because you say tht
Spontaneous Combustions happen only in west is [I think] that you live there. I myself have never heard of Spontaneous Combustions in West, but tht doesen't mean tht there aren't any.
I would say tht these combustions are caused by our body chemistry. I saw on discovery channel tht there are chemicals in people tht can couse the combustion, the only thing tht remains unclear is what triggers this combustion.
If you like, I can ask my father for more details, he told me about this case some two years ao and I don't remember alll clearly.
Bye!