Editing Decompression sickness (section)

=== Ascent to altitude and loss of pressure from a pressurised environment===
The most common health risk on ascent to altitude is not decompression sickness but [[altitude sickness]], or acute mountain sickness (AMS), which has an entirely different and unrelated set of causes and symptoms. AMS results not from the formation of bubbles from dissolved gasses in the body but from exposure to a low partial pressure of oxygen and [[alkalosis]]. However, passengers in unpressurized aircraft at [[high altitude]] may also be at some risk of DCS.{{r|38uhms | Dehart | Pilmanis | Gerth}}

Altitude DCS became a problem in the 1930s with the development of high-altitude balloon and aircraft flights but not as great a problem as AMS, which drove the development of [[cabin pressurization|pressurized cabins]], which coincidentally controlled DCS. Commercial aircraft are now required to maintain the cabin at or below a [[pressure altitude]] of {{convert|2400|m|ft|abbr=on}} even when flying above {{convert|12000|m|ft|abbr=on}}. Symptoms of DCS in healthy individuals are subsequently very rare unless there is a [[Cabin pressurization#Unplanned decompression|loss of pressurization]] or the individual has been diving recently.{{r|NASA1999 | RRR1181}} Divers who drive up a mountain or fly shortly after diving are at particular risk even in a pressurized aircraft because the regulatory cabin altitude of {{convert|2400|m|ft|abbr=on}} represents only 73% of [[sea level pressure]].{{r|38uhms | Dehart | Vann1}}

Generally, the higher the altitude the greater the risk of altitude DCS but there is no specific, maximum, safe altitude below which it never occurs. There are very few symptoms at or below {{convert|5500|m|ft|abbr=on}} unless the person had predisposing medical conditions or had dived recently. There is a correlation between increased altitudes above {{convert|5500|m|ft|abbr=on}} and the frequency of altitude DCS but there is no direct relationship with the severity of the various types of DCS. A US Air Force study reports that there are few occurrences between {{convert|5500|m|ft|abbr=on}} and {{convert|7500|m|ft|abbr=on}} and 87% of incidents occurred at or above {{convert|7500|m|ft|abbr=on}}. {{r|FAA2005}} [[High-altitude military parachuting|High-altitude parachutists]] may reduce the risk of altitude DCS if they flush nitrogen from the body by [[Oxygen prebreathing|pre-breathing pure oxygen]].{{r|pmid14620473}} A similar procedure is used by astronauts and cosmonauts preparing for extravehicular activity in low pressure [[space suit]]s.