Scuba Diving - Breathing Underwater

Breathing Underwater

Water normally contains the dissolved oxygen from which fish and other aquatic animals extract all their required oxygen as the water flows past their gills. Humans lack gills and do not otherwise have the capacity to breathe underwater unaided by external devices. Although the feasibility of filling and artificially ventilating the lungs with a dedicated liquid (liquid breathing) has been established for some time, the size and complexity of the equipment allows only for medical applications with current technology.

Early diving experimenters quickly discovered it is not enough simply to supply air to breathe comfortably underwater. As one descends, in addition to the normal atmospheric pressure, water exerts increasing pressure on the chest and lungs—approximately 1 bar (14.7 pounds per square inch) for every 33 feet (10 m) of depth—so the pressure of the inhaled breath must almost exactly counter the surrounding or ambient pressure to inflate the lungs. It becomes virtually impossible to breathe unpressurised air through a tube below three feet under the water.

By always providing the appropriate breathing gas at ambient pressure, modern demand valve regulators ensure the diver can inhale and exhale naturally and without excessive effort, regardless of depth.

Because the diver's nose and eyes are covered by a diving mask; the diver cannot breathe in through the nose, except when wearing a full face diving mask. However, inhaling from a regulator's mouthpiece becomes second nature very quickly.