well my face is a little red.
the last one is from a movie.
The only reason I bring doubt is because they expressly design gas tanks not to explode. I had a lengthy talk about this with a few automotive engineers in the safety group. On top of that inside a gas tank there's not enough oxygen to make a big boom. A compromised tank such as in a bad accident will go up, but 1 gallon of gas left in a busted tank won't .
I would never recommend welding on a gas tank like that. but it's a myth that one little spark will turn a car gas tank into a mushroom cloud. if it catches fire it can quickly set the whole car ablaze.
for instance
http://www.youtube.com/watch?v=7KK48hQ78Kkhttp://www.youtube.com/watch?v=QgAaj3DkA-w&feature=related before the guy pulled the nozzle out of the container the first was far from a mushroom cloud.
In fact the right thing to do if your car catches on fire is to leave the nozzle inside
but I'll repeat it's pretty stupid to weld on a gas tank like that.