How to Switch your Diving Gas

By Michael Thornton and Josh Thornton

Scuba Diver Switching Gas

Switching your diving gas in 8 easy steps

Safe technical diving begins with awareness. The first step is being aware of yourself. As you gain experience and comfort you become aware of yourself and your gear. The highest level of awareness is when you are aware of yourself, your gear, and your surroundings including your dive team. When you add complications, emergencies or any kind of stress your awareness will diminish.

Not being aware of you, your gear or your surroundings during something as critical as a gas switch can be fatal. It is important to follow a strict protocol while staying aware during any gas switch to minimize risk.

As with most diving skills there is more than one way to do things. By establishing a set protocol and adhering to it every time, the risk of making a mistake is reduced. The most common problems that arise during a gas switch are losing control of your buoyancy and changing depths unintentionally or breathing the incorrect gas mixture for the respective depth.

All deco bottles should be pressurized but with valves closed when not in use. This prevents losing gas unintentionally and minimizes the risk of breathing off of the incorrect regulator. Pressurizing is necessary to keep water out of the system and your gear working.

When performing a gas switch, the following steps will help:

  1. Confirm you are at the correct depth to make the planned switch and achieve neutral buoyancy. (Also have team verify)
  2. Identify the correct cylinder by verifying the MOD marking on the cylinder. (Also have team verify)
  3. Deploy the second stage and follow the hose back to the first stage to verify you have the correct second stage.
  4. After you have confirmed you have the correct second stage and cylinder, open the valve.
  5. Purge the second stage to remove any debris that may have entered during the dive, and confirm functionality.
  6. Swap regulators and breathe. (Signal team you are okay)
  7. Clip off primary regulator.
  8. Change gases on your computer(s). (Signal this and confirm it with your team)

As a team you should discuss where your cylinders will be mounted. Some common mounting protocols are: 1) rich mixes on the right and lean mixes on the left or 2) all cylinders on the left side and rotate them for easy access at the appropriate depths. Whichever protocol you choose make sure you can easily access all of the cylinders and verify with visual and tactile methods the various cylinders. Team gas switching protocols call for individuals to verify proper gas switches within the team. Some teams prefer to complete the switch one at a time to allow maximum control.

Labeling the cylinder near the neck allows the diver to see it (and in turn, verify the mix). An additional label on the side near the bottom of the cylinder allows the team to see the markings as well.

When switching from one deco/stage gas to another it is important to follow the same verification procedures listed above. To avoid confusion, switch to your back gas. This will allow you to stow the regulator from the first deco/stage cylinder and turn off the valve prior to deploying the second deco/stage regulator.

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