Increasing the probability of surviving loss of consciousness underwater when using a rebreather

Re-circulating underwater breathing apparatus (rebreathers) have become increasingly popular amongst sport divers. In comparison to open-circuit scuba, rebreathers are complex life support equipment that incorporates many inherent failure modes and potential for human error. This individually or in combination can lead to an inappropriate breathing gas. Analysis of rebreather diving incidents suggests that inappropriate breathing gas is the most prevalent disabling agent. This can result in spontaneous loss of consciousness (LoC), water aspiration and drowning. Protecting the airway by maintaining the diver/rebreather oral interface may delay water aspiration following LoC underwater; the possibility of a successful rescue is, thus, increased. One means of protecting the airway following LoC underwater is the use of a full-face mask (FFM). However, such masks are complex and expensive; therefore, they have not been widely adopted by the sport diving community. An alternative to the FFM used extensively throughout the global military diving community is the mouthpiece retaining strap (MRS). A recent study documented 54 LoC events in military rebreather diving with only three consequent drownings; all divers were reported to be using a MRS. Even allowing for the concomitant use of a tethered diving partner system in most cases, the low number of fatalities in this large series is circumstantially supportive of the efficacy of the MRS. Despite drowning featuring as a final common pathway in the vast majority of rebreather fatalities, the MRS has not been widely adopted by the sport rebreather diving community.