Gas 'im.
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Nitrogen works. :eek
You dont even know what it happening. I knew a guy who was working in a refinery and went into a vessel filled with nitrogen (he obivously did not know it). He said that one instant he was fine, and the next instant he woke up in the hospital. When he collapsed inside, another guy went after him and collapsed. Fortunately, the third guy was smart enough to stick an air hose in there, otherwise the two guys would be dead.