The assembly 10 comprises a housing having a fan 13 and an outlet valve (40, fig 4a), a filter 11 releasably mounted onto the housing to seal the housing from the environment and a face seal 15 to provide a resilient conformity to the wearer's face when worn. The housing may comprise a main frame 12 and an internal chassis 14 with chambers 17 for holding a rechargeable power source of the fan. The fan may comprise a casing (21, fig 2) which tapers from its inlet to its outlet having a diameter of less than 60 mm and a thickness of less than 20 mm. The mixed-flow fan rotator may generate a pressure increase of between 5 to 18 mm water gauge with flow rates between 0.25 to 10.5 litres per second when operating in a range of between 4000 to 7000 rpm.
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