Many folks have asked me about how to perform a gas switch. So I figured I would type up the procedures here. Please keep in mind that these procedures do not replace sound, high quality technical dive training, but act as a supplement to that training. If you are not trained in technical diving, do not try to perform these procedures.

Many people believe that the gas switching process is performed by an individual. That is not correct. Performing a gas switch is a team effort and the focus during the gas switch must be on the team. That way the team deco can be optimized. The gas switch is a time where the awareness of the entire team must be raised to a higher level. As each member of the team switches to a high partial pressure of oxygen, the risk of oxygen toxicity is greatly increased. The team must be focused on each member during the switch to be able to respond to any problems that may occur and to verify that each member of the team is on the right gas.

There are many things that must go on prior to entering the water with a deco bottle. First, the gas inside the bottle must be analyzed. This must happen right before the dive, regardless if the bottle was previously analyzed and marked. Be prudent and re-analyzed just before entering the water or getting on the boat. I always tell my students to analyze the gas just prior to the regulator being put on. Second, after you analyze the bottle, you must mark the bottle with the contents/result of the gas analysis. There are many fancy stickers people use for contents labels. I choose to use the most cost effect method of gray duct tape. On the contents label, I mark the results of the gas analysis, date of analysis, my initials, and the MOD. Deco bottles must have a minimum of four markings on them. 1) Visual inspection sticker, 2) gas contents sticker, 3) clearly identifiable MOD on the outside (facing away from the diver when worn), and 4) clearly identifiable MOD on the inside (facing towards the diver when worn). Item 3 is used by the team to verify the MOD of the bottle being switched to. Item 4 is used by the individual to verify the MOD of the bottle switching to. Deco bottle valves are turned on at the start of the dive and then turned off. This pressurizes the regulator so that it will not come loose during the dive. If the valve was left on, it runs the risk of losing the gas from the bottle without the diver ever knowing it.

To preform a proper gas switch, the steps are as follows:
1) Signal to the team that it you are preforming a gas switch
2) Verify that your at the target depth and not deeper than the planned MOD of the gas switch
3) Verify that the maximum operation depth (MOD) of the deco bottle to switch to and that you are at or above that depth
4) Verify that the regulator is still pressurized and the first stage regulator is seated properly. If the regulator has no pressure, make sure it is seated properly and then partially turn on the valve and re-close it. This pressurizes the regulator.
5) Deploy the second stage regulator from the deco bottle and loop the hose around your neck
6) Re-verify your depth so that you are not violating the MOD of the bottle you are switching to
7) Remove the regulator from your mouth with the left hand.
8.) Insert the deco regulator into your mouth with the right hand.
9) Quickly move the regulator from step 7 to your right hand.
10) As you breath from the deco regulator, watch the SPG on the deco bottle. If the pressure gauge loses pressure greatly, then you are breathing the right bottle. If it doesn’t move, then switch back to the regulator in your right hand and verify the bottle is turned on or you have the correct regulator. To do this, remove the regulator and hose from around your neck and trace the hose back to the bottle. When wearing one deco bottle, this is quite simple, but if you are wearing two deco bottles it must be performed.
11) If step 10 goes smoothly, turn on the valve for the deco bottle completely
12) Re-verify your current depth such that you are not violating the MOD for the bottle breathing
13) Clip off the long hose to the right chest d-ring to keep it out of the way. If you are switching off another deco bottle, remove the deco regulator and hose from around your neck and re-stow it back on the deco bottle.
14) Signal to the team/buddy to verify the MOD of the bottle being breathed and that you are breathing from the right bottle.
15) If the team/buddy signals OK, move to the next team member to perform the gas switch. If you are the last person to switch, then the deco leader will start the deco time for the team. Deco time does not start until the entire team has performed the gas switch. This is why the gas switch procedure must be as efficient as possible so that team members are not sitting on a high PPO2/using up precious deco gas while waiting for others to switch.

If for some reason, you fumble the deco bottle second stage and it falls out of your hand or mouth, quickly go to your bungee backup regulator under your chin. Remove the deco regulator and hose from around your head and trace the hose to the correct deco bottle. Then perform the switch again. We do this so that we do not accidentally grab the wrong second stage (such as our long hose) and breath the wrong gas and not know it. Many people believe that the deco regulator should be deployed prior to arriving at the switch depth in order to make the switch go faster. We don’t do this for the single reason of fumbling the deco regulator and accidentally breathing a gas below it’s MOD. Once you get proficient with the gas switch, the team should be able to switch in less than 2 minutes, assuming a three man team. Two man teams can switch within a minute. Thus removing the need to deploy the deco regulator deeper than the switch depth. Remember, try not to develop bad habits and focus on sound skills.

As you can see, we are always prudent when performing gas switches. Analyze, analyze, analyze your gas and always verify and re-verify your depth so that you do not violate the MOD of the gas being breathed. Always err on the side of caution.

I hope you enjoyed this article and feel free to leave any feedback or ask any questions.

Dive Safe,
Duane
www.precisiondiving.net