A face mask (10) mechanically coupled to a lung demand valve (LDV) (12). The face mask (10) comprises a main mask and an inner mask (15) which fits over the wearer's mouth and nose. The interior of the inner mask (15) is in fluidic communication with the interior of the main mask (10) by means of non-return valves (16). The interior of the main mask is in fluidic communication with an inlet port (18) which is mechanically and fluidically coupled to a supply port (20) of an LDV. The LDV (12) includes a diaphragm and a cover (44) which comprises three parts (44a, 44b) and (44c). Exhaled air is used to flush the space around the diaphragm. Thus, any toxic or undesirable gas in the vicinity of the diaphragm is pushed out to atmosphere by the exhaled air flowing past and around the diaphragm.