page_title: Decompression sickness
section_title: Underwater diving
hierarchical_section_title: Decompression sickness / Prevention / Underwater diving
caption_attribution_description: English: Display of Aladin Pro personal dive computer
context_page_description: Decompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurisation. DCS most commonly refers to problems arising from underwater diving decompression, but may be experienced in other depressurisation events such as emerging from a caisson, flying in an unpressurised aircraft at high altitude, and extravehicular activity from spacecraft. DCS and arterial gas embolism are collectively referred to as decompression illness.
  Since bubbles can form in or migrate to any part of the body, DCS can produce many symptoms, and its effects may vary from joint pain and rashes to paralysis and death. Individual susceptibility can vary from day to day, and different individuals under the same conditions may be affected differently or not at all. The classification of types of DCS by its symptoms has evolved since its original description over a hundred years ago. The severity of symptoms varies from barely noticeable to rapidly fatal.
  Risk of DCS caused by diving can be managed through proper decompression procedures and contracting it is now uncommon.
context_section_description: To prevent the excess formation of bubbles that can lead to decompression sickness, divers limit their ascent rate—the recommended ascent rate used by popular decompression models is about 10 metres (33 ft) per minute—and carry out a decompression schedule as necessary. This schedule requires the diver to ascend to a particular depth, and remain at that depth until sufficient gas has been eliminated from the body to allow further ascent. Each of these is termed a "decompression stop", and a schedule for a given bottom time and depth may contain one or more stops, or none at all. Dives that contain no decompression stops are called "no-stop dives", but divers usually schedule a short "safety stop" at 3 m (10 ft), 4.6 m (15 ft), or 6 m (20 ft), depending on the training agency.
  The decompression schedule may be derived from decompression tables, decompression software, or from dive computers, and these are commonly based upon a mathematical model of the body's uptake and release of inert gas as pressure changes. These models, such as the Bühlmann decompression algorithm, are designed to fit empirical data and provide a decompression schedule for a given depth and dive duration.
  Since divers on the surface after a dive still have excess inert gas in their bodies, decompression from any subsequent dive before this excess is fully eliminated needs to modify the schedule to take account of the residual gas load from the previous dive. This will result in a shorter allowable time under water without obligatory decompression stops, or an increased decompression time during the subsequent dive. The total elimination of excess gas may take many hours, and tables will indicate the time at normal pressures that is required, which may be up to 18 hours.
  Decompression time can be significantly shortened by breathing mixtures containing much less inert gas during the decompression phase of the dive (or pure oxygen at stops in 6 metres (20 ft) of water or less). The reason is that the inert gas outgases at a rate proportional to the difference between the partial pressure of inert gas in the diver's body and its partial pressure in the breathing gas; whereas the likelihood of bubble formation depends on the difference between the inert gas partial pressure in the diver's body and the ambient pressure. Reduction in decompression requirements can also be gained by breathing a nitrox mix during the dive, since less nitrogen will be taken into the body than during the same dive done on air.
  Following a decompression schedule does not completely protect against DCS. The algorithms used are designed to reduce the probability of DCS to a very low level, but do not reduce it to zero. The mathematical implications of all current decompression models are that provided that no tissue is ingassing, longer decompression stops will decrease decompression risk, or at worst not increase it.
caption: The display of a basic personal dive computer shows depth, dive time, and decompression information.
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