Safe Gas Switching Procedure for Technical Diving

Switching gases correctly is critical in technical diving, as gas-switching errors are a major cause of incidents among open-circuit technical divers. Each agency has its own mnemonic for safe gas switching, but for those who find these hard to recall, here’s a clear, structured approach to follow instead.

Objective of the Gas Switch Procedure

The purpose of this procedure is to create a safe, error-resistant sequence for switching gases underwater. Safety protocols are carefully vetted and tested to ensure that they minimize human error. Even as guidelines evolve, our focus remains on reducing underwater errors through simplicity and clarity in the gas-switching sequence.

Key Steps for Safe Gas Switching

1. Signal and Gain Attention
   • Signal your intent to switch to your buddy and team. Clearly indicate which gas you are switching to.
   • The goal here is to capture their full attention, as distracted divers can miss important cues.
2. Check the Cylinder Neck Label
   • Verify the label on your cylinder to ensure it's the correct gas. The label should be clear and easy to read.
3. Confirm Your Depth
   • Check that you’re above the minimum switch depth for the gas. Ensure you are stable at this depth, not drifting upward or downward.
4. Prepare and Deploy the Regulator
   • Unclip and prepare the regulator you intend to use. Briefly depress the purge button to confirm it's functioning properly.
5. Get Buddy Confirmation
   • Look to your buddy for external confirmation. They should acknowledge that switching to this gas is appropriate based on your current depth and gas plan.
6. Verify Regulator and Cylinder Match
   • Double-check that the regulator in your hand is indeed connected to the intended cylinder.
7. Switch Your Computer to the Correct Gas Mix
   • Update your dive computer to reflect the current gas mix. This ensures accurate decompression data and helps avoid surprises during the dive.

Common Errors and How to Avoid Them

1. Premature External Confirmation
   • The most common error occurs when divers ask for confirmation before completing their own checks. Always conduct personal checks first and then seek external verification.
2. Excessive Cylinder Labeling
   • Keep cylinder labels simple:
     • A) MOD Label: Place a maximum operating depth (MOD) label on the cylinder, aligned with the valve for easy visibility.
     • B) Your Initials: Place your initials near the MOD label to identify the cylinder as yours.
     • C) Neck Label: A smaller label on the neck should include MOD, gas percentage, and your initials at a minimum. Avoid excessive details to prevent confusion.
3. Avoid Unstandardized Gas Percentages
   • Stick to standard mixes (e.g., 32% for 32m, 50% for 21m, 80% for 9m, 100% for 6m) to simplify decision-making underwater.
4. Use Durable Labels
   • Avoid painters’ tape or duct tape that may fall off or damage the cylinder. Use adhesive designed for underwater use and label cylinders when dry.
5. Analyze and Label Your Own Gas on Dive Day
   • Always analyze the gas yourself, as shop labels may be unreliable. Don’t rely solely on third-party analysis.

Recommended Gas Switching Sequence

1. Review Dive Plan and Verify Depth
   • Confirm your current depth matches your planned switch depth.
2. Signal Intent to Switch
   • Signal to your buddy that you’re switching to the appropriate gas.
3. Check Cylinder Neck Label
   • Confirm the neck label matches the gas you intend to switch to.
4. Deploy Regulator
   • Take the second stage of the intended gas mix, tracing the hose back to ensure it's from the correct first stage.
5. Purge and Activate Regulator
   • Partially press the purge button to verify the regulator and gauge stability, then fully open the valve.
6. Reconfirm Depth Stability
   • Check your depth to ensure you haven’t drifted.
7. Get Final Buddy Confirmation
   • Look to your buddy for a specific switch confirmation (e.g., "Switch50") rather than a generic "OK" signal.
8. Switch Regulators, Stow Long Hose, Update Computer
   • Place the new regulator in your mouth, stow your primary long hose, and update your computer with the new gas mix.

Hand Positioning for Switching Procedure

1. Left Hand Deploys Regulator
   • Use your left hand to retrieve the new regulator, then transfer it to your right hand.
   • This allows your left hand to operate the valve.
2. Switching Hands for Regulator Placement
   • After final buddy confirmation, hold the regulator in your left hand to keep the right hand free for removing and stowing the long hose, this is a clear wide motion keeping both 2nd stages away from each other.
3. Stowing Procedure
   • Clip off the long hose, ensuring the hands do not cross over. A 100cm hose is recommended for the deco regulator, after you've secured your long hose and placed the deco regulator in your mouth you can position the deco reg hose
     behind your head by simply pulling it over your head.

Switching Back to Back Gas (BG)

If you need to revert to back gas:

1. Remove the Deco Gas Regulator from Your Neck
   • Use your left hand to remove the deco regulator hose from your neck so you can see it free and unsnagged.
2. Unclip the Long Hose
   • Use your right hand to unclip and switch back to the primary long hose, while your left hand takes the deco 2nd stage out of your mouth.
   • Close the deco cylinder valve, remove the cylinder from your side and neatly re-stow the hose and 2nd stage.
3. Reposition the Deco Cylinder
   • Securely re-clip the deco cylinder at the bottom of your cylinder stack or onto a rear D-ring, preparing for the next deco gas deployment.

This procedure offers a comprehensive, systematic approach to ensure safe gas-switching while minimizing the chance for errors during technical dives. By following this structured process, you can make your gas-switching safer and more reliable.

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