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- I use my air too quickly
What is happening
You often reach the agreed turn pressure before everyone else, and the group has to shorten the plan. You may swim with your head higher than your fins, use your hands, or make frequent BCD adjustments, all of which add effort and gas consumption.
Why it happens
Ordered from the most common cause down. Open one to see the mechanism behind it.
Speed, current, dangling equipment and diagonal trim increase resistance in the water. To overcome it, your body works harder and your breathing rate rises.
- swimming too fast
- diagonal trim
- dangling gauge console or octopus
Your regulator delivers gas at ambient pressure, which increases with depth. The same volume of breaths at depth uses more gas from the cylinder than it does at the surface.
- a deeper profile
- time spent at maximum depth
- no personal SAC for planning
Excess lead requires more gas in your BCD to stay neutral. The larger volume increases drag and can lift your upper body, making swimming harder.
- too much lead
- a large gas bubble in the BCD
- an upright profile
Stress can increase minute ventilation even more than vigorous effort. When you see your gas supply falling, anxiety can make your breathing speed up further.
- nerves before or during the dive
- fixation on the SPG
- a demanding environment or task
In cold water, your body works harder to maintain its core temperature. That increases energy demand and breathing-gas use.
- getting cold during the dive
- an unsuitable exposure suit
- shivering
What to try on your next dive
One thing, not ten. Give it a full dive before you judge it.
Establish a personal SAC baseline at a constant depth
- Choose a known, constant depth and stay with your buddy.
- Set neutral buoyancy without working to hold depth.
- Record your starting pressure, time and depth.
- Swim comfortably at the same depth, then record the ending pressure and calculate SAC.
- Secure your gauge console and octopus so no equipment dangles.
- Swim with slow, deliberate movements and horizontal trim.
How you will know it is working
| Published reference | Value | Source |
|---|---|---|
| Planning value for average surface consumption | 25 L/min | CMAS Europe — Air Consumption |
| Reference point for a relatively experienced diver | 14–16 L/min | TDI/SDI — Air Management |
At a constant depth, record pressure used and time. Calculate SAC by dividing bar used by minutes and ATA; for RMV, multiply SAC by the cylinder's water volume.
- Breathe naturally and continuously. Never hold your breath or skip-breathe to save gas.
- Do not use your lungs as the primary buoyancy tool or make your regulator harder to breathe from.
- If your actual consumption cannot support the planned profile, tell your buddy or divemaster and end or change the plan. Do not use all your gas to complete a safety stop.