DOnt use gas, since you are likely to die.
Here is the only worth while ways of sound deadening removal.
Dry ice. Spread it over the sound deadening, and let it sit at least 25 mins. Then hit it with a hammer and chisle.
Air Chisle.
Hammer, and chisle.
Once thats gone, use a large while wheel and remove all the residue, and then take asitone, and whipe it clean.
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