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Air Force have concluded that personnel are likely to notice the symptoms before loss of consciousness only if those personnel have previously undergone hypoxia training in a controlled environment, as 94% of untrained pilots experience loss of consciousness despite education about hypoxia’s symptoms. 5 While hypoxia has signs and symptoms that can be recognizable, studies by the U.S. 2 Hypoxia is the leading cause of fatality for rebreather divers at 38.9% of deaths, while in contrast hyperoxia is responsible for only 9.6%. Rebreather diving is the activity with the second highest fatality rate in the world per hour of performance, second only to BASE jumping. The oxygen sensing mechanism is therefore simultaneously responsible for both pO 2 adjustment and safety monitoring, thus failure can result in either hypoxia (possibly causing loss of consciousness) or hyperoxia (possibly causing seizure due to oxygen toxicity). This package measures and injects oxygen to maintain a preset desired oxygen partial pressure (pO 2). Pure oxygen rebreathers use a mechanical injection system, but most mixed-gas closed circuit rebreathers (CCRs) use an electronics package comprised of oxygen sensors, a computer, and a solenoid.
Rebreathers remove expired carbon dioxide via a passive chemical reaction with a “scrubber” material, and in fully closed rebreather models, more oxygen is injected as it is used by the diver. Rebreathers are devices that recycle a diver’s exhaled breathing gas rather than venting it, unlike open-circuit SCUBA (Self-Contained Underwater Breathing Apparatus). These devices, if configured for underwater use, could provide a practical and inexpensive alarm system to warn of impending loss of consciousness in a manner that is redundant to the rebreather. Pulse oximeters placed on the forehead and clipped on the nasal ala provided a mean of 32 s (☑0 s SD) of warning time to divers with falling oxygen levels, prior to risk of loss of consciousness. The subjects were immersed in water in four separate environmental scenarios, including cold and warm water, and monitored using pulse oximeters placed at multiple locations. Twenty-eight volunteer human subjects breathed on a mixed-gas rebreather in which the oxygen addition system had been disabled. The purpose of this study was to determine whether a pulse oximeter could provide a useful amount of warning time to a diver with a rebreather after failure of the oxygen addition mechanism. However, rebreathers’ need to replace oxygen used by breathing creates a failure mechanism that can and frequently does lead to hypoxia, loss of consciousness, and death. Divers who wish to prolong their time underwater while carrying less equipment often use devices called rebreathers, which recycle the gas expired after each breath instead of discarding it as bubbles.