A filtering mask assembly includes a housing including a fan and an outlet valve. A filter is releasably mounted onto the housing and is adapted to substantially follow a shape and contour of the housing to seal the housing. A face seal is interposed between the wearer's face and the housing to provide a resilient conformity to the wearer's face when the mask assembly is worn. The mask assembly defines an inner space between the mouth and nose of the wearer and an inner side of the mask assembly, and an intermediate space between the housing and the filter and an outer space separated from the inner space by an outer side of the mask assembly. The fan is positioned on a downstream side of the filter to draw air through the filter. The mask assembly prevents the breathing of any air which has not passed through the filter.