The Complete Handbook of Oxygen Tanks

Chapter 1: Understanding Oxygen Tanks

The oxygen tank you are most likely to encounter, whether you are a respiratory therapist setting up a portable unit or a welder connecting a cylinder to a regulator, is a thick-walled pressure vessel holding anywhere from a few hundred to more than two thousand liters of gas compressed to some fraction of 2,200 pounds per square inch. At standard atmospheric pressure, that's a very large volume of gas. The tank's entire purpose is to store a very large amount of breathing or process gas in a compact, portable, and safe container. It works because, under pressure, a gas that occupies a huge volume at ambient pressure will occupy a small fraction of that volume inside a strong container. Oxygen, like most gases, behaves approximately as an ideal gas, so the general relationship holds that pressure multiplied by volume stays constant, and the amount of gas you can store in a fixed container is directly proportional to the pressure you can safely put into it.

That "safely" is the most important word in the previous paragraph. The engineering, the manufacturing, and most of the regulations that govern oxygen tanks exist for a simple reason: a tank full of compressed gas is a small bomb with a valve. If a tank is overfilled, structurally compromised, or damaged, the stored energy of the compressed gas is released. A catastrophic failure of a cylinder is not a gentle leak; it is a violent rupture that sends shrapnel through