Ah yes, "Cracker Barrel Cheese" keeps coming up. According to Sir Boverton Redwood, the interior of old oil barrels was coated with hot glue, glass, or glycerin to prevent leaks. The barrels were otherwise mainly comprised of white oak staves and iron hoops. Wood is a great heat insulator, so I would think it nearly impossible to ignite a barrel by throwing a fire cracker at it ... unless you are lucky enough to punch the bung.
