No-decompression dive

Flying and ascent to altitude after diving

Exposure to reduced atmospheric pressure during the period after a dive when the residual gas levels have not yet stabilized at atmospheric saturation levels can incur a risk of decompression sickness. Rules for safe ascent are based on extension of the decompression model calculations to the desired altitude, but are generally simplified to a few fixed periods for a range of exposures. For the extreme case of an exceptional exposure dive, the US Navy requires a surface interval of 48 hours before ascent to altitude. A surface interval of 24 hours for a Heliox decompression dive and 12 hours for Heliox no-decompression dive are also specified. More detailed surface interval requirements based on the highest repetitive group designator obtained in the preceding 24‑hour period are given on the US Navy Diving Manual Table 9.6, both for ascents to specified altitudes, and for commercial flights in aircraft nominally pressurized to 8000 ft.