Help finding a movie title

Saw a movie in the 80's or 90's about a bank robbery and I can't remember the name of it.

It was a well thought out bank heist where they came in through the sewers had all the equipment, including a meter to let them know if the gasses etc. in the sewer were too dangerous. They get the money but on the way out, the gas becomes too toxic and one of the guys ends up spending the weekend trapped in the vault.
Monday comes and somehow the guy just walks out of the front door of the bank (I think with the money) where his friends are waiting for him and they drive off getting away with the money.

Hope this helps even though it's vague.

Thanks in advance for all help.

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Loophole (1981)
http://en.wikipedia.org/wiki/Loophole_(1981_film)

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That's it! Wow there were quite a few more details than I had remembered. Will have to see if I can find it again.
Thank you 'will' that was so quick. I'll have to try and find something a bit harder for you next time. lol