Understanding Scuba Diving Tanks
Air, Not Oxygen
The first thing know about a scuba diving tank, or cylinder, is that nearly always the recreational diver will have it filled with clean air, not oxygen. This is contrary to what many television programs would have us believe! It is not an oxygen tank – it is an air cylinder.
If it was filled with pure oxygen, diving deeper than around 6m and breathing pure oxygen could actually kill the diver!
What Is In It Then?
Believe it or not, just plain, pure, clean compressed air. Nothing fancy! Your dive centre will use a compressor to suck in air, filter it to remove particles and water and squash it into the cylinder so that there is plenty to breath on your dive!
Is It Always Just Fresh Air?
A cylinder does not always just contain fresh air. Specialist divers use nitrox or trimix to allow them to diver deeper and for longer and occasionally, pure oxygen during decompression stops – but only shallower than 6 metres!
What Is A Scuba Diving Tank Made Of?
The solid, and frequently heavy, tanks are made of aluminum or steel. Pick one up and you will know by the weight which it is – the steel ones are far heavier. For this reason, divers in dry suits, who need more weight to correct the positive buoyancy effects of the exposure suit, may tend to wear the heavier steel tanks to prevent carrying so many loose weights.
How Long Does The Air In A Cylinder Last?
This is actually a very complicated question. In short, the deeper you go, the smaller the tank, the heavier you breath, the harder you are swimming etc the shorter the time you will get out of a tank.
The problem is that it takes more air molecules to fill your lungs at depth then on the surface because of the effects of pressure at depth. So at 20 or 30 metres, you are taking a lot more out of the tank with each breath – in fact 3 and 4 times as much respectively.
Swimming hard makes you breath harder and, of course, a 12 litre cylinder carries a lot less air than a 15 litre cylinder. But, a novice diver should be able to make a 40 to 50 minute dive as long as they aren’t going excessively deep!
Why Does The Tank Feel Lighter After A Dive
Believe it or not, the difference in weight is the weight of the air that you have breathed! That weight difference is how much air you have gone through during the dive.
What Safety Precautions Should Be Followed?
Obviously, take care when lifting a dive tank – it is heavy! But it is also full of compressed air, so make sure that it is not going to fall over. Take care not to damage the top part where you plug in your regulators, nor loose the o-ring. Also, a tank should never be fully drained. The pressure inside stops moist air from getting in, which could cause rust and damage the inside of the tank.