The Helicopter Aircrew Breathing Device or HABD (also known as a Helicopter Emergency Egress Device HEED or SEA [clarification needed] [1]) is an item of survival equipment which was adopted by the military to increase the chances of survival for embarked troops and aircrew trapped in an aircraft which has ditched (crashed into a body of water).
It is a form of self contained underwater breathing apparatus (scuba) which consists of a small cylinder pressurized with atmospheric air and first stage regulator worn in a pouch on the user's life vest; a pressure gauge; an air hose and a second-stage demand regulator that delivers air to the user's mouth when the internal pressure of the mouthpiece drops during inhalation, and is ruggedly constructed to survive impacts associated with emergency ditchings.
Since a full-size scuba cylinder would be prohibitively bulky and heavy, especially for troops already laden with full combat gear, the HABD must be small and thus limited in capacity.
Jet fuel and hydraulic fluid may seep into the cabin and can cause blindness to open eyes and lung damage if inhaled.
Immersion in cold water evokes a "gasp" response in humans, which can reduce their breath-holding ability to as little as 15 seconds.