Phase 1

Practice in a swimming pool or calm, shallow, protected body of water.

1. You and your buddy position yourselves 10m apart, neutrally buoyant, facing each other. Your buddy “runs out of air” and swims towards you without breathing.

2. When you see your buddy signal that they need air, prepare whichever of your second stage regulators is on the longer hose and give this to them when they arrive.

3. Begin air sharing then ascend slowly together. On arrival at the surface you auto-inflate your BCD while supporting your buddy as they orally inflate their BCD.

4. Repeat the drill, alternating roles and increasing the distance between you until you start experiencing significant stress as you approach your buddy. There is no need to take your regulator out during the non-breathing swim and, if you find you desperately have to inhale before you reach your buddy, just do it.

5. Then add a new level of difficulty. Still stationary in the water, face away from your buddy so you can’t see them coming. Don’t be surprised if, as the distance increases, your buddy just takes your long hose regulator rather than asking for it.

6. Finally, practice while you are both swimming at normal speed, one following the other, so your buddy is in the realistic position of having to catch up with a moving target in order to share air. Never end an air sharing drill underwater. It is important not to think that once you begin sharing air the emergency is over. It is not over until both divers are on the surface and positively buoyant, so every drill should end with an ascent.

Phase 2

To be practiced during ocean dives

1. Begin phase 2 only when you are completely comfortable with the phase 1 drills.

2. Once in a while, agree that one of you will initiate an out-of-air drill at some point towards the end of the dive. Advise anyone else diving with you that this is what you intend to do, so they don’t mistake it for a genuine emergency.

3. Then repeat what you did in the pool. At first, practice while you are swimming close together in the shallows then increase the level of difficulty as you gain confidence and become more accomplished.

4. Again, always follow an out-of-air drill with an ascent, including a safety stop if you have enough air, and the mutual establishment of surface buoyancy.

This post is adapted from a chapter in Scuba Confidential: An Insider's Guide to Becoming a Better Diver