Careful. If you're breathing pure helium, the time between feeling woozy and passing out is much shorter than you think. I helped a friend set up and tear dow

Careful. If you're breathing pure helium, the time between feeling woozy and passing out is much shorter than you think. I helped a friend set up and tear down an art project involving a 12-foot weather balloon filled with helium. At some point, I felt it was pretty wasteful to be just venting the helium without even playing with it. I sat down on the rubber gym floor for safety and had a friend watching. Two breaths of pure helium in a row was enough to make me pass out. I felt woozy and said "whoah", and I heard my head thump the rubber floor of the gymnasium. I was out just long enough for my friend to realize I wasn't joking around. Had I been using a heavier gas (lower effusion rate and tendency to pool in the lungs) or not exhaled and inhaled when I started to feel woozy, I very easily could have required resuscitation.