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My most-dramatic experience was at a brewery, in Boulder, CO.
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A friend, of mine (and, the brewer, he knew, there) took me on a tour. Eventually, we came-upon one o' those plastic 55-gal. barrels, where the CO2 was being expelled. A hose, from the vat, ran into that barrel....that was (approx.) 2/3 filled with water. I was told..."Go ahead and take a hit outta that barrel!!" I'd assumed they were talking about a smell. When I put my face just-below the top-edge of the barrel...and, attempted to take a "hit"....I almost blacked-out...but, was caught, before I hit the floor. Because of it's density, that CO2 goes nowhere....except over the top-edge of the barrel, as volume increases.
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