Welding on gas tanks is always interesting. Years ago when I was in the Army running a vehicle repair shop, we got in an M88 Tank recovery vehicle with a crack in the fuel tank (as opposed to the M60's with diesels, it had a gasser engine in it. A 750 hp Continental V12, IIRC). Anyway, we got the engine and the tank out of the tank.
and found the crack in the fuel tank. We flushed the 100+ gallon tank out with water twice, discharged a 5 lb CO2 fire extinguisher into it. I told the welder to go, and a short time after he struck the arc, it went
BOOMP! Everyone's eyes got a little bigger, and the welder backed off. But at that point, it had been "safed" by burning off all the vapor, and I told him to finish welding. Just a little excitement, but the job was done.
Have heard stories of guys cutting the tops off of oil drums with a torch winding up across the street. Don't do that.
