Heating anything that has been exposed to hydrocarbons may be VERY DANGEROUS!
Dried gunk deposited on the item may be vaporized by heat and cause an explosion.
I have seen a picture of three firefighters engulfed in flames when they tried to cut an empty oil drum with a K12 saw (a disc saw which generates heat and sparks)
Any hydrocarbon heated enough can produce vapors that can be explosive - for instance grease, and even coal. Coal and oil furnaces do not have a secure latch, just a short hook, so that they can blow open if there is an explosion.
Putting tin foil over an opening in a gas tank may be OK to keep vapors in, but if you drive the car, fuel sloshing may pop the tin foil off or burst the foil
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