Quote Originally Posted by jrscgsr View Post
I'll just throw my 2 cents in if the original poster is still alive. My old boss filled a diesel truck gas tank with water to weld a small repair on it, after a couple seconds of welding the tank suddenly ballooned and push him back. The residual diesel on the inside of the tank turned to vapor with the welding heat then ignited despite being filled with water. He was lucky and didn't get hurt, but honestly the only way to safely weld/cut a fuel tank is to use a degreasing cleaner first then purge the tank with a non reactive gas. If I can't do that then I don't work on it.
Same thing happened to me years ago. Customer swore he flushed out the tank. It knocked me across the shop. Never again without purge.