I grew up in the welding business and some of the guys would come in in the morning, presumably after a "big night" and turn on the O2 side of the acetylene torch and take several deep breaths to clear out the cobwebs. O2 and caffeine, what a combination! Well, why not! I hadn't tied one on but a little pick-me-up in the AM couldn't hurt, could it? Until one morning when I nonchalantly turned on the acetylene instead of the oxygen! No, it isn't really poisonous (which I read later) but the taste was excruciatingly bitter. Beyond that, as you may know, it is extremely explosive. I was lucky. No sparks were flying at the time. Needless to say, I curtailed my morning hits of O2!

Many years later I read of some kids in a high school welding class who, while the instructor wasn't looking, were taking mouthsful of acetylene and blowing it out over an open flame. Great fun, huh? Well, one kid goofed up somehow and sucked in and burned his lungs and died from it! As I remember, this was over in the Sacramento areas in the 1990's. If you are going to be breathing anything other than God-given air you ought to know what you are doing or have professional direction. Lung are pretty irreplaceable.