Abstract: A closed circuit breathing apparatus with a simplified start-up procedure. The demand valve diaphragm (38) has in it a one way valve (51 and 52) that allows exhaled breath to escape from the apparatus. Movement of the diaphragm reciprocates a latch (63) through a series of stops (65 to 68). When the user inhales for the second time, the latch (63) escapes from the last stop (68), a spring (69) is released, the one-way valve is clamped shut by a plate (55), and a probe (73) releases a catch (35) and allows a breathing bag (13) to open.

Abstract: A self-rescue breathing apparatus has a radial-flow purifier 3 connected between a mouthpiece and a breathing bag 10. An outer plenum of the purifier is open at both ends, a central conduit is open only at the breathing-bag end. Flap valves 50A and 50B control the flow of gas so that exhaled breath passes radially inwards through the purifying medium which gas for inhalation passes freely up the outer plenum, reducing both the resistance to flow and the heating of the inhaled gas that the purifier (which works by exothermic chemical reaction) would otherwise cause.

Abstract: Closed-circuit compressed-oxygen breathing apparatus in which the oxygen supply is used to demist the visor 7 of the facemask 6 or cool the wearer's face before entering an oronasal mask 8 through a one-way valve 13 and mixing with the gas in the breathing circuit.