My Dad said he saw a guy in the shop that wanted to make a burn barrel out of a 55 gallon sealed drum. As soon as he burned thru the end with the torch, Kaboom and he was dead. I think he said the drum has some kind of glue in it. Who knows what the glue solvent was, but something flammable. All it takes is just the fumes left in the barrel.
Doesn't matter what you use, make certain the barrel is clean and has no flammable material in it. People have been killed using a chisel to take the tops off and a jig saw can still create a spark.
Barrels are not nice to work on unless they have been properly cleaned and that is not as easy to do as one would think.
$30 gets a drum deheader on E-bay. Like a big can opener. Leaves a smooth edge too.