Mine is 24' x 24', block walls with steel roof built in 1979, I've tried, but even I have been unable to burn it down. Though, I have had to replace the windows and the service door. I don't like to talk about an acetylene leaks/explosions but I will say that when my neighbor called the volunteer fire dept after a big boom and fireball and there was no fire to put out when they finally arrived, the volunteers were kind of pissed off. They wanted me to pay for the call. When the ringing in my ears subsided, I said I didn't call them and exactly what fire/explosion were they talking about; I didn't "see" anything of the sort. Of course my welding helmet might have obscured my vision of the alleged explosion at the time.
