Gas Switching — What It Is and Why It Matters
Gas switching is the practice of changing between different breathing gas mixes during a single dive, most commonly during the ascent phase of a technical decompression dive. A diver might breathe a lean trimix at depth, switch to a richer nitrox mix at a mid-depth stop, and then switch to pure oxygen for the final shallow decompression stops to accelerate off-gassing.
Multi-gas dive computers support pre-programmed gas switches and will alert the diver when they reach the planned switch depth. Many prompt the diver to confirm the switch, at which point the computer recalculates all decompression obligations based on the new gas. This is a core feature of technical dive computers.
Frequently Asked Questions
How many gases can a dive computer track?
Recreational computers typically support 1 to 2 gas mixes. Mid-range technical computers handle 3 to 5. High-end computers like the Shearwater Perdix 2 support up to 5 gas mixes simultaneously, covering bottom gas plus multiple decompression gases.
What happens if I forget to switch gases on my computer?
The computer will continue calculating based on the previously active gas, which means your decompression schedule will be inaccurate. Most multi-gas computers will remind you at the pre-programmed switch depth. If you miss a switch, manually select the new gas as soon as you realize the error.
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