Safe Diving Practices G
| Gas analysing |
| Gas mixtures (Tech. diving) |
| Gas requirements |
Gas analysing
When nitrox and / or mixed gases are being used, all gases must be analysed prior to the dive.
All cylinders must be clearly marked with their oxygen and helium percentages and MOD (Maximum operating depth).
The partial pressures of oxygen (pO2) should not exceed 1.4 bar for travel (ascent and descent) and primary gases. For suitably qualified divers, the partial pressure of oxygen must not exceed 1.6 bar for any chosen decompression gas mixture. For divers not holding appropriate technical qualifications, the pO2 of 1.4 bar should not be exceeded for any gas mixes including decompression gases.
The BSAC recommend a suitable equivalent narcotic depth (END) with regard to the dive conditions and a personal narcotic tolerance.
When gas mixes involving helium are used in technical diving, wherever practicable, the helium content of the mix should also be analysed by an appropriate instrument (e.g. helium analyser) as a confirmation of the precise mix.
Gas mixtures (Technical diving)
Technical divers should only use gas mixes for which they hold a recognised qualification:
Appropriate safeguards should be put in place to avoid premature gas loss and to ensure that the respective maximum operating depths of all open circuit gases carried are observed.
All divers are strongly advised not to use an hypoxic gas unless the depth requires it to reduce the pO2 to a breathable value.
Gas requirements
All divers should carry the gas they need to complete the dive safely. They should also have a plan to access back up cylinders in case of a gas failure. (See Air reserve)
For technical divers using open circuit equipment this includes bottom gas, travel gas and decompression gas. They should also have a plan to access back up cylinders in case of a gas failure. Reserve requirements for travel (descent & ascent) and primary gas should be calculated on the rule of thirds.
Reserve gas for decompression is normally calculated as double the amount of gas required for the planned decompression schedule.
Page last modified: 1st Jun 2007 - 09:27:19