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Decompression equipment
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<p>There are several categories of decompression equipment used to help divers <a href="/facts/Decompression_practice/eBKHl82s">decompress</a>, which is the process required to allow divers to return to the surface safely after spending time underwater at higher ambient pressures. </p><p>Decompression obligation for a given <a href="/facts/Dive_profile/BCffhVPt">dive profile</a> must be calculated and monitored to ensure that the risk of <a href="/facts/Decompression_sickness/aSpCCQaU">decompression sickness</a> is controlled. Some equipment is specifically for these functions, both during planning before the dive and during the dive. Other equipment is used to mark the underwater position of the diver, as a position reference in low visibility or currents, or to assist the diver's ascent and control the depth. </p><p>Decompression may be shortened ("accelerated") by breathing an oxygen-rich "decompression gas" such as a <a href="/facts/Nitrox/SvhHPlPY">nitrox</a> blend or pure <a href="/facts/Oxygen/acyn6o8r">oxygen</a>. The high partial pressure of oxygen in such decompression mixes produces the effect known as the <a href="/facts/Oxygen_window/A7LXl3xj">oxygen window</a>. This decompression gas is often carried by scuba divers in side-slung cylinders. <a href="/facts/Cave_diving/WacIQn2q">Cave divers</a> who can only return by a single route, can leave decompression gas cylinders attached to the guideline ("stage" or "drop cylinders") at the points where they will be used. <a href="/facts/Surface-supplied_diving/ucetQS99">Surface-supplied divers</a> will have the composition of the breathing gas controlled at the <a href="/facts/Gas_panel/ucetQS99">gas panel</a>. </p><p>Divers with long decompression obligations may be decompressed inside gas filled <a href="/facts/Hyperbaric_chamber/K0uRU4RY">hyperbaric chambers</a> in the water or at the surface, and in the extreme case, <a href="/facts/Saturation_diving/YWm5hEPg">saturation divers</a> are only decompressed at the end of a project, contract, or tour of duty that may be several weeks long. </p>