- This often occurs from carbonic acid gas, or "choke-damp," on entering wells or old cellars; this gas being heavier than air, falls and rests at the bottom. Before entering such places, test by lowering a lighted candle; if the flame is extinguished it is unsafe to enter until the gas has been removed, by throwing down a bundle of lighted shavings or blazing paper, sufficient to cause a strong upward current. When a person is overcome by this gas, he must be immediately rescued by another, who must be rapidly lowered and drawn out, as he must do all while holding his breath; a large sack is sometimes thrown over the person who goes to the rescue. As soon as brought out, place the person on his back, bare the neck and throat, loosen clothing and strip as quickly as possible; if he has not fallen in the water, dash cold water freely overhead, neck, and shoulders, standing off several feet and throwing it with force; artificial respiration should be used meantime, as in case of drowning, with as little cessation as possible. If the person has fallen into the water when overcome by the gas, place in a warm bed, and use the means of artificial respiration vigorously.

Suffocation from burning charcoal, from anthracite or bituminous coal, or from common burning gas, or the foul gases from drains and cess-pools, is treated as if from carbonic acid gas.