When BSAC created its Nitrox Training programme in 1995 the authors of these manuals and courses recommended a maximum PO2 (Partial Pressure of Oxygen) of 1.4 bar. This was from information known about the safe levels of oxygen to ensure the diver is kept well away from oxygen toxicity.
Partial pressure of oxygen
The maximum PO2 limit of 1.4 bar is recommended by all other training agencies. Some agencies start with a maximum PO2 of 1.6 bar and recommend reducing it when diving in more extreme conditions such as cold water, long decompression stops and a diver's higher work rate. Their recommendations could end up below 1.4 bar. These training agencies have recognised the increased risk of a problem in these more difficult conditions. BSAC took the initial view that our divers were being trained and diving in northern European waters and they face these harsher conditions most of the time in comparison to those diving abroad.
Other technical agencies reduce the maximum PO2 recommendation the more advanced, or more technical, the diving qualification becomes. For example, once Trimix is used, all agencies recommend a maximum PO2 of 1.4 bar for the bottom gas.
Decompression gas
In the UK, there is an HSE requirement to limit the PO2 to 1.4 bar at any depth. BSAC have successfully negotiated an increase to a PO2 of 1.6 as long as the diver is shallower than 10m, as at this point the diver is at the end of the dive and likely to be decompressing which has a low work rate and so is lower stress than during the start of the dive.
The recommendation for using Nitrox 80 as a decompression gas was not in opposition to using 100% oxygen but more to take advantage of the increased safety of using a weaker Nitrox mix as a decompression gas. When decompressing in challenging conditions, maintaining an accurate depth so as not to descend below the maximum operating depth of 100% oxygen can be difficult, for example in a large swell.
BSAC statement on the use and purchase of 100% oxygen
BSAC now endorses the use of 100% oxygen for suitably qualified members. For conditions of use see: BSAC Technical Safe Diving. The advice on maximum PO2 exposure should be considered when using 100% oxygen.
BSAC courses, which qualify our members to use and purchase 100%, oxygen are:
- BSAC Extended Range Diver
- BSAC Accelerated Decompression Procedures
- BSAC Mixed Gas Open Circuit diving using Trimix as a bottom gas
- BSAC Closed Circuit Divers
To purchase 100% oxygen evidence of qualification is required. Historically, BSAC ADP divers have been restricted to 80% oxygen. This statement can be used as evidence, with a qualification listed above, that our members can purchase 100% oxygen.
