I scuba diving, as in life, a rapid ascent can bring problems. At the weekend I had the job of taking a couple of divers in to test a rescue skill needed for their qualification. It’s that thing you need when you’re out of air! Not a recommended situation and not something that should happen in the course of a normal dive. Still we train so that if it does happen we are prepared.

Under normal conditions a diver should not exceed 15 metres per second when returning to the surface. If a diver is out of air for some reason they should signal to their buddy and take the spare regulator (breathing mouthpiece) so both can carefully get to the surface together. My trainees had completed one careful lift from 10 to 6 metres depth and dropped to change roles (hero becomes victim). All systems checked. Everybody neutrally buoyant (nicely floaty, like in space) and off we go. This should have been easy. For what ever reason my trainees shot up like a rocket and ended up breaking surface. One complained that the computer was beeping and would not stop so we made for the exit slipway and did not continue out dive.

Sitting on the café over a brew we discussed the issue. Checking my computer I could see that we came up at twice the recommended rate and then some. These were not novice divers and have done this manoeuvre many times in practice. For whatever reason when it is being watched by an instructor everything goes to pieces. When you dive you take on air (or other gases) at pressure so your lungs stay inflated. Which means you take in more of every gas that is in air (in this case). Still at 21% oxygen and 79% nitrogen but at higher concentrations. The issue is the nitrogen. Too high a concentration and you get a ‘bend’ or decompression Illness. If you come up slowly some of the nitrogen flushes from your system. Come up too quickly….

Contrary to logic you should dump air from your buoyancy system as you rise to the surface. The air inside will expand as the pressure (caused by the depth) lessens. Forget to take the air out….result rocket speed. If you are at any real depth this can cause you to pass out. De brief over we returned to our respective homes. Now the nice thing about a nitrogen overdose is that you have to rest, complete rest, when you get home. The nasty stuff can be a rash, nausea, dizziness aching joints (hence the bends) and all manner of things. So home to the pyjamas and the sofa.

All divers involved are fit and well two days later. No trip to the chamber for us. Lessons learned.