Air management and out-of-air situations

In short

The air in your cylinder is your lifeline underwater: you need to know how much you use, plan the dive so that you come back with a reserve, and watch your gauge and your buddy's. Running out of air is much easier to prevent than to manage. If it happens, the answer is almost always the same: the "out of air" signal, sharing air with your buddy and a controlled ascent together.

Why it matters

Running out of air is rarely caused by equipment: most often, the diver did not check their gauge or underestimated their consumption. It causes stress and can lead to an ascent that is too fast, with a risk of barotrauma or decompression sickness. Good air management avoids these situations and makes diving more relaxed.

Air consumption

Your consumption depends on many factors:

• Depth: at 10 m, the pressure is twice that at the surface, and each breath uses twice as much air; at 30 m, four times as much. The same cylinder therefore lasts much less time at depth.
• Exertion: finning fast or against the current greatly increases consumption.
• Cold: the body uses more energy.
• Stress: it speeds up breathing.
• Experience: a relaxed, well-balanced diver uses less air.

Estimating your consumption

Note your pressure at the start and at the end, the average depth and the duration of a calm dive. Dividing the air used by the duration and by the average ambient pressure gives a "surface" consumption in litres per minute. It is often between 15 and 25 l/min at rest and increases with exertion. This figure helps you predict the gas supply for a dive; recalculate it from time to time.

Planning your gas supply

• Reserve: you surface with an agreed amount of air (often 50 bar, sometimes more depending on the dive and the cylinder). This reserve is not meant to be used: it is there to deal with the unexpected.
• Half pressure: on an out-and-back dive, turn around at the latest when you have used half of the air available above the reserve.
• Rule of thirds: in demanding environments (strong current, overhead environments), one third out, one third back, one third for safety.
• Team plan: the dive is organised around the diver who uses the most air. Turn and return pressures are announced at the briefing.

Monitoring

• Check your gauge regularly, for example every five minutes and at each change of depth.
• Tell the guide or your buddy your pressure when asked, and signal half pressure and reserve on your own initiative.
• Watch your buddy too: their breathing rate, their bubbles, their behaviour.

Running out of air

Prevention

• cylinder filled and valve fully open, checked before the dive;
• gauge checked often;
• location and operation of your buddy's alternate air source known before the dive;
• distance to your buddy: always within arm's reach.

Response

1. Give the "out of air" signal to your buddy, clearly.
2. Share air: your buddy gives you their alternate second stage (octopus) or, depending on the procedure you were taught, their primary second stage while switching to the alternate.
3. Stabilise and hold on to each other, by the arm or a strap, face to face or side by side.
4. Ascend together, at a controlled speed, with a safety stop if conditions allow, then signal at the surface.

An independent emergency ascent, breathing out all the way up, remains a last resort when no buddy is within reach. It is taught in training and requires control of your ascent rate.

Equipment failure

• Free flow: the second stage keeps delivering air. You can keep breathing from it, letting the excess escape from the corner of your mouth, signal the problem and ascend. With a twin-outlet valve, your buddy can close the outlet of the failing regulator while you breathe from the other.
• Leak from a hose or fitting: signal and end the dive.
• Valve: if the valve was not opened properly, your buddy can open it; closing and opening a valve underwater is learned with an instructor.

In every case, end the dive with your buddy.

Key takeaways

• Consumption increases with depth, exertion, cold and stress.
• Always come back with your reserve and turn around at half pressure.
• Check your gauge often and watch your buddy.
• Out of air: "out of air" signal, share air, controlled ascent together.
• An independent emergency ascent is a last resort.

Further reading

Sessions recorded by the watch keep the dive profile and events, which helps you compare the actual duration with your previous dives. The app does not measure cylinder pressure: note your start and end pressures to track your consumption. The guides on hand signals and on the dive team complement this one.