Scuba Diving

Abstract

In scuba diving, air is obtained from tanks for breathing. For recreational diving, scuba tanks are usually filled with normal compressed air up to 200 bar. Via different stages, the pressure is reduced to a level so that the diver can breathe normally. Tanks are made either of steel or aluminium. However, aluminium scuba tanks are only allowed in certain countries. Aluminium scuba tanks are lighter than the one made of steel. Both can be filled up to 200 bar. Scuba tanks shouldn’t be emptied completely for safety and maintenance reasons. They always should have more than 50 bar left at the end of each dive. If tanks are completely emptied, moist air might enter and cause the inside to rust. Rust particles in return might block of the sinter filter and block off air supply. Additionally, pressure display on poorly maintained pressure gauges might not reflect the real pressure in scuba tanks. That bears the risk of running out of air under water even when the pressure gauge displays that some air is still left. Besides, residual, “spare”, air should always be kept in case of emergency situations, which could arise at anytime. Scuba tanks have to be serviced in regular intervals. Tanks made of steel have to undergo a visual test usually every 2.5 years and a hydrostatic test every 5 years. These dates vary in different countries. Aluminium bottles have to be serviced every 6 years. Information about the permitted filling pressure, the last maintenance and the gas mixture can be seen on the stamp marking on the scuba tank’s top, close to the outlet. Tanks can capture something between 3 and 18 l. The most common type of scuba tanks for sport divers has around 10–11 l (◘ Fig. 3.1).