The gas switch is one of the most hazardous parts of any extended range dive and as such it is a procedure conducted with a team mate and with a clearly defined sequence of key points
Whether it is an open-circuit Extended Range Diver switching to a decompression gas in order to increase their off-gassing efficiency during a decompression dive, or an SCR Extended Range Diver who must bailout to their decompression gas if their unit should malfunction, this switch from one breathing gas to another is a critical procedure to master in order to prevent accidents due to breathing a gas at an unsafe depth.
The gas switch is one of the most hazardous parts of any extended range dive and as such it is a procedure conducted with a team mate and with a clearly defined sequence of key points. To make it easier for team mates to spot a potential mistake from happening some decompression regulators are often in a different colour such as green which designates a higher oxygen decompression gas.
In SSI we use the acronym SWITCH to help divers learn and master the correct sequence:
SIGNAL to the team mate that your intention is to make a gas switch
Check on your personal dive computer to see at what WATER DEPTH you are currently at
IDENTIFY on the cylinder via the markings, the maximum depth of the gas in the cylinder and cross check this against your dive computer to ensure that you are either equal to or shallower than that depth
TURN on the cylinder valve, pull out the second stage hose from its retainers, purge the second stage to ensure the tank is open whilst looking at the SPG
Turn to your team mate and show them the maximum depth markings on the cylinder and wait for them to CONFIRM that the current depth is either equal to or shallower than that depth
Make the gas switch, confirm that the regulator is breathing ok, switch gases on the computer and note when HANG TIME begins
The SSI XR gas switch procedure can be viewed by clicking here.
For more information on the training to become an SSI Extended Range Diver and learn how to perform a safe gas switch along with other skills head to: https://www.divessi.com/info/en-IC/extended-range-program/extended-range-specialities.html/