section_path: Applications/Life support and recreational use
section_name: Life support and recreational use
paragraph_text: Life support and recreational use
  
  An application of O as a low-pressure breathing gas is in modern space suits, which surround their occupant's body with the breathing gas. These devices use nearly pure oxygen at about one-third normal pressure, resulting in a normal blood partial pressure of O. This trade-off of higher oxygen concentration for lower pressure is needed to maintain suit flexibility.
  
  Scuba and surface-supplied underwater divers and submarines also rely on artificially delivered O. Submarines, submersibles and atmospheric diving suits usually operate at normal atmospheric pressure. Breathing air is scrubbed of carbon dioxide by chemical extraction and oxygen is replaced to maintain a constant partial pressure. Ambient pressure divers breathe air or gas mixtures with an oxygen fraction suited to the operating depth. Pure or nearly pure O use in diving at pressures higher than atmospheric is usually limited to rebreathers, or decompression at relatively shallow depths (~6 meters depth, or less), or medical treatment in recompression chambers at pressures up to 2.8 bar, where acute oxygen toxicity can be managed without the risk of drowning. Deeper diving requires significant dilution of O with other gases, such as nitrogen or helium, to prevent oxygen toxicity.
  
  People who climb mountains or fly in non-pressurized fixed-wing aircraft sometimes have supplemental O supplies. Pressurized commercial airplanes have an emergency supply of O automatically supplied to the passengers in case of cabin depressurization. Sudden cabin pressure loss activates chemical oxygen generators above each seat, causing oxygen masks to drop. Pulling on the masks "to start the flow of oxygen" as cabin safety instructions dictate, forces iron filings into the sodium chlorate inside the canister. A steady stream of oxygen gas is then produced by the exothermic reaction.
  
  Oxygen, as a mild euphoric, has a history of recreational use in oxygen bars and in sports. Oxygen bars are establishments found in the United States since the late 1990s that offer higher than normal O exposure for a minimal fee. Professional athletes, especially in American football, sometimes go off-field between plays to don oxygen masks to boost performance. The pharmacological effect is doubted; a placebo effect is a more likely explanation. Available studies support a performance boost from oxygen enriched mixtures only if it is inhaled during aerobic exercise.
  
  Other recreational uses that do not involve breathing include pyrotechnic applications, such as George Goble 's five-second ignition of barbecue grills.