The most important thing for a scuba diver is air, without it one would surely drown. Knowing how much air you have is important.
I was recently on a dive and there were a few unaware divers on it. It was obvious that they didn’t have a clue. One was yo-yoing from the bottom to the surface, another was trailing through the reef leaving a path of destruction in her wake, and the third was flailing and flapping like a bird. It would come as no surprise that these divers would be the ones to have problems on the dive. I kept my eye on them but it wasn’t my responsibility to look after them. They are certified divers and they should know what they are doing.
One of the dive leaders was asking us, each in turn, what air we had left. When he checked with the flailing one, let’s call her Flappy, she couldn’t signal how much air she had left so the DL had to check her gauge himself. You could see his eyes pop out, even through his mask. It transpired that Flappy hadn’t been paying attention to the amount of air that she was using. She had 500psi (approximately 35 bar): we weren’t even 10 minutes into the dive. The DL took her straight to the surface and had her taken out of the water. The saga continued when we all got back on board, the DL started bollocking her for not checking her air. Flappy had no idea what was wrong, perhaps there was a language barrier, perhaps she had always dived with someone who constantly checked her air, perhaps she had a death wish. But she looked stunned that she had been brought back 30 minutes early.
That situation had been an accident waiting to happen. If she had been diving without the aid of a DL then what would she have done? She as at 20m (66ft) and out of air at almost twice the depth that you practice doing a CESA from. Would her buddies have known what to do? Chances are probably not. Many divers don’t think about doing rescue training, seeing it as something that someone else does.
So the first step in becoming a good diver is knowing how much air is left in your cylinder. A friend of mine told me, while he was doing his DM, that he started guessing how much was left in his cylinder before he looked at the gauge. He said that eventually he started to get a feeling for it, a sixth sense. I have been practising this skill since he told me about it. It does become like a sixth sense and I know how much air I have in my cylinder.
Knowing how much air you have becomes even more important when you are deep diving. You can easily be using 4 times as much air and the contents of your cylinder can easily slip away from you. There is a general trend in diving that once you get to half your cylinder you should turn around. This is a good idea, but it can mean that those that are guzzlers are embarrassed to say when they get half way because they don’t want to spoil everyone else’s dive. Cave divers use the rule of thirds. One third to get there, one third to get back, and the last third is just in case there is a problem.
A good dive is when everyone gets back safe, I think it would spoil your dive more if someone ran out of air. It’s your responsibility to check your air, but it’s also your responsibility to check you buddies air.
One of the other two divers did have another problem. The yo-yoing diver had a rapid ascent and surfaced while she was meant to be doing her safety stop. She could easily have suffered from a lung over expansion injury. Buoyancy control is as important as air awareness.