How You Use Your Tank Valve May Be Wrong: The Quarter Turn That Can Kill

We divers are creatures of habit. We like to do things the way we always have. Instructors who teach their trainees exactly what their instructor taught them exacerbate these habits. Outdated techniques and theories are handed down like gospels. Sometimes, a better way presents itself, but there is often a reluctance to step off the well-trodden path into the undergrowth of a new experience.

Take the tank valve. It's like a faucet. 'It's lefty loosey, righty tighty.' One shouldn't need to know more than that. However, with a tank valve, you'll want it either fully open or fully closed. This is where old habits can interfere with good practice.

Back in the day, tank valves could jam if they were opened too far. Older divers were taught to open the valve all the way and then close it a quarter of a turn. All well and good if you are precise in your habits, but what of the diver who does that and then forgets he's opened the tank and closes it by mistake, turning it back open a quarter of a turn? His air supply will be uninterrupted at the surface, but as he goes deeper, it will become harder and harder to breathe. If he's lucky, he'll see his pressure gauge drop to zero on each inhalation before returning to the full-tank position. If he's unlucky...well?

Today's tank valves don't jam in the open position, so open the tank all the way and leave it there. When you want to shut off the gas, close it all the way. No halfmeasures, no quarter turns, and you'll stay safe.

If you are using higher percentages of oxygen, you should know to open a tank valve cautiously, especially the O2 tank on a rebreather. A sudden rush of oxygen could cause a fire.

This outdated habit simply refuses to die. Changing the habit of a lifetime can save your reputation as a serious diver, maybe even save your life.