So I was told a story from an old mechanic. Gas tank was leaking on a customer's car. The old shop owner told him to fix it. He didn't know how. Old guy showed him. Start the car on the lift, cover exhaust with a hose, feed other end in gas tank filler neck so all exhaust is blowing in the tank. Grabbed the welder, and welded the tank, right there, while running with gas in tank. He freaked. Old guy says, won't blow up without air, the carbon monoxide will not let it ignite!! This person never tried it himself, was a mechanic his whole life and 100% honest. I would never, but it is said to have taken place. Scary ****