the mask 10 in this position the clip 30 is inaccessible while the mask is being worn by a patient once the mating portion 22 of the vent connector piece 28 has been inserted through the aperture 12 and the locking clip placed in the annular groove the conduit end assembly 20 and the mask 10 cannot be separated without first removing the mask from the patient an exploded view of one embodiment of the anti asphyxia valve and conduit connector assembly is shown in fig2 as illustrated in fig2 the end of the elbow 26 adjacent the mask 10 is fitted with an anti asphyxia valve arrangement that provides an air passage to the patient in the event of failure of the gas delivery apparatus consisting of a valve membrane 27 fitted into the end of elbow 26 and vents 31 in the vent connector piece 28 during proper operation of the gas delivery system the valve membrane remains in the orientation shown in fig2 closing off the vents 31 in the event of a drop in pressure below a predetermined level the valve membrane 27 flips to a reverse orientation opening the vents 31 the construction and operation of the anti asphyxia valve is described in more detail in the applicant 39 s australian patent application no 65527 99 the contents of which are incorporated herein by reference and described herein resilient detents 42 on the elbow 26 pass through and engage behind slot forming formations 44 in the vent connector piece 28 to provide releasable engagement of the two parts the vent connector piece has a collar 47 that abuts a corresponding surface of the mask 10 to limit the.