Blackdamp (also known as stythe or choke damp), sometimes found in enclosed environments such as mines, sewers, wells, tunnels and ships' holds, is an asphyxiant, reducing the available oxygen content of air to a level incapable of sustaining human or animal life. It is not a single gas but a mixture of unbreathable gases left after oxygen is removed from the air; it typically consists of nitrogen, carbon dioxide and water vapour. The term is etymologically and practically related to terms for other underground mine gases such as fire damp, white damp, stink damp, and afterdamp.