Editing Decompression sickness (section)

=== Exposure to altitude ===
One of the most significant breakthroughs in the prevention of altitude DCS is oxygen pre-breathing. Breathing pure oxygen significantly reduces the nitrogen loads in body tissues by reducing the partial pressure of nitrogen in the lungs, which induces diffusion of nitrogen from the blood into the breathing gas, and this effect eventually lowers the concentration of nitrogen in the other tissues of the body. If continued for long enough, and without interruption, this provides effective protection upon exposure to low-barometric pressure environments.{{r|Dehart | Pilmanis}} However, breathing pure oxygen during flight alone (ascent, en route, descent) does not decrease the risk of altitude DCS as the time required for ascent is generally not sufficient to significantly desaturate the slower tissues.{{r|Dehart | Pilmanis}}

Pure aviator oxygen which has moisture removed to prevent freezing of valves at altitude is readily available and routinely used in general aviation mountain flying and at high altitudes. Most small general aviation aircraft are not pressurized, therefore oxygen use is an FAA requirement at higher altitudes.

Although pure oxygen pre-breathing is an effective method to protect against altitude DCS, it is logistically complicated and expensive for the protection of civil aviation flyers, either commercial or private. Therefore, it is currently used only by military flight crews and astronauts for protection during high-altitude and space operations. It is also used by flight test crews involved with certifying aircraft, and may also be used for high-altitude parachute jumps.

[[Astronauts]] aboard the [[International Space Station]] preparing for [[extra-vehicular activity]] (EVA) "camp out" at low atmospheric pressure, {{convert|10.2|psi|bar|abbr=on}}, spending eight sleeping hours in the [[Quest airlock]] chamber before their [[spacewalk]]. During the EVA they breathe 100% oxygen in their [[spacesuit]]s, which operate at {{convert|4.3|psi|bar|abbr=on}},{{r|tanner}} although research has examined the possibility of using 100% O<sub>2</sub> at {{convert|9.5|psi|bar|abbr=on}} in the suits to lessen the pressure reduction, and hence the risk of DCS.{{r|webb1989}}