Scuba diving is a mode of underwater diving where the diver uses a self-contained underwater breathing apparatus (scuba) which is completely independent of surface supply, to breathe underwater.[1] Scuba divers carry their own source of breathing gas, usually compressed air,[2] allowing them greater independence and freedom of movement than surface-supplied divers, and longer underwater endurance than breath-hold divers.[1] Open circuit scuba systems discharge the breathing gas into the environment as it is exhaled, and consist of one or more diving cylinders containing breathing gas at high pressure which is supplied to the diver through a regulator.