As I remember it... this is called 'spontanious combustion'... we learned to respect this when I was employed as an aircraft mechanic.
In a nutshell: The higher the O2 content (%) in the air surrounding a combustible material, the lower the temp at which it will combust. In PURE O2... oil and grease will ignite at room temp... NOT KIDDING.
We were VERY careful when we added O2 to a corp jet... one has to wipe the fittings with a clean rag (not even your hand)... to be SURE there was no oil or combustible material in the joint when topping off the O2 tank.
There was a case of a corp jet back in 1978 or 79 (I think it was a G2) which burned, due to O2 getting into grease in the nosewheelwell...where the O2 filling fitting is...
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Romans Ch's 5-6-7-8
2 Chronicles 7:14