Extended Use of the Mask Mounted Anti-Suffocation Valve
Claire Peckover and John Ernsting
The anti-suffocation valve employed in RAF oxygen masks provides inward relief in situations where the wearer is required to breathe ambient air. Such a situation may arise following separation of the man portion of the personal equipment connector, failure of the breathing gas supply or on selection of continuous flow bypass.
The level of suction required to open the anti-suffocation valve (12-14 cm wg) is such that opening of the valve during normal operation of the oxygen system is avoided but on cessation of the normal delivery of breathing gas the valve will open without imposing an unacceptable level of inspiratory resistance on the wearer. The level of suction also ensures that the wearer is able to detect the valve is open.
Whilst the mask mounted anti-suffocation valve has been used successfully in-Service, data relating to its acceptability is limited to short periods of use, up to 10 minutes. During recent laboratory based studies, naive subjects were able to breath through the anti-suffocation valve whilst exercising at up to 70 watts for 45 minutes without any adverse effects on respiration. Further studies are currently being carried out to extend this work whilst measuring additional physiological variables in order to evaluate more thoroughly the effects of using the anti-suffocation valve facility for periods of up the 1 hour. These results will be presented.
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