Deep air/extended range diving
One of the more divisive subjects in technical diving concerns using compressed air as a breathing gas on dives below 130 feet (40 m).
[9] While mainstream training agencies still promote and teach such courses (TDI,
[10] IANTD and DSAT/PADI), a minority (NAUI Tec, GUE, UTD) argue that diving deeper on air is unacceptably risky, saying that helium mixes should be used for dives beyond a certain limit (100–130 feet (30–40 m), depending upon agency). Such courses used to be referred to as "deep air" courses, but are now commonly called "extended range" courses.
Deep air proponents base the proper depth limit of air diving upon the risk of
oxygen toxicity. Accordingly, they view the limit as being the depth at which partial pressure of oxygen reaches 1.4 ATA, which occurs at about 186 feet (57 m).
Helitrox/triox proponents argue that the defining risk should be
nitrogen narcosis, and suggest that when the partial pressure of nitrogen reaches approximately 4.0 ATA, which occurs at about 130 feet (40 m), helium is necessary to offset the effects of the narcosis.
[citation needed] Both sides of the community tend to present self-supporting data. Divers trained and experienced in deep air diving report less problems with narcosis than those trained and experienced in mixed gas diving trimix/heliox, although scientific evidence does not show that a diver can train to overcome any measure of narcosis at a given depth, or become tolerant of it.
[11]
The
Divers Alert Network does not formally reject deep air diving per se, but indicates the additional risks involved.
[12]