Self combustion from "oily rags" is a real threat, but not from petroleum
soaked
rags. Oils which can result in spontaneous combustion are linseed and tung
oils,
(there may be others, but I do not know of any). The reason that linseed and
tung
oils are used on wood (as a finish or combined with dyes as a stain/finish) is
that
they polymerize (sp?) in a process combining with oxygen in an exothermic (ie:
released heat) reaction. So, lets say that you soak a rag with on of these
oils and
spread it on some wood, then drop the rag in a heap and go take a lunch break.
The
oil on the wood begins combining with oxygen and begins both hardening and
releasing
heat. The amount of oil on the surface of the wood is pretty little and the
surface
area is large - hence no noticeable rise in the temperature of the wood surface
and
no risk. The rag on the floor, however, has a large amount of oil saturating it
and
the temperature begans to rise. The speed of chemical reations (like the oil
combining with oxygen) doubles with every 10 degree F rise in temperature. So
as the
rag warms up, the chemical reaction speeds up warming the rag faster and
faster. If
the temperature rises high enough one can get smoke and eventually flames.
There is
a house not too far from where I live which burned down to the ground a few
months
ago from a wood staining rag igniting in the middle of the night.
I am not a chemist either, but I don't think that any oil which is stable in
air can
cause spontaneous combustion. If the oil skims over in a can and hardens on
contact
with air, be careful. I don't think that common cooking oils are a concern.
-Roger
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