Buddy breathing

Buddy breathing is a rescue technique used in scuba diving "out-of-gas" emergencies, when two divers share one demand valve, alternately breathing from it. Techniques have been developed for buddy breathing from both twin-hose and single-hose regulators, but to a large extent it has been superseded by safer and more reliable techniques using additional equipment, such as the use of a bailout cylinder or breathing through a secondary demand valve on the rescuer's regulator.

Running out of breathing gas most commonly happens as a result of poor gas management, but it can also happen due to unforeseen exertion, stress, or breathing equipment failure. Equipment failure resulting in the loss of all gas could be caused by failure of a pressure retaining component such as an O-ring or hose in the regulator or, in cold conditions, a freezing of water in the regulator resulting in a freeflow from the demand valve. The need for buddy breathing can be avoided by use of alternative techniques and equipment.

Buddy breathing originated from military diving following a prohibition on the training and practice of free ascents. Minor variations on the basic technique were taught by different agencies at different times, and different techniques were needed for single hose and twin hose regulators. As buddy breathing has been found to require more intensive practice than is usually provided during entry level training to be reliably used in a real emergency without endangering the buddy, and more reliable alternatives are affordably available, the procedure has been deprecated by most recreational diver training agencies in favour of more reliable and safer alternatives which are quicker to learn, and where appropriate, emergency swimming ascent.

The term has also been used for air sharing between scuba divers using an octopus demand valve, and between firefighting breathing apparatus.