System for reducing pathogens in a breathable airstream

A personal respiratory protection device, comprising:

• a) a housing configured to be worn by a user and having at least one air inlet and at least one air outlet;
• b) an airflow path extending through the housing from the at least one air inlet to the at least one air outlet;
• c) an ultraviolet irradiation assembly disposed in the airflow path, the ultraviolet irradiation assembly comprising:
• i) an array of ultraviolet light emitters mounted on a circuit substrate;
• ii) a first ultraviolet-transmissive substrate positioned in close proximity to the array of ultraviolet light emitters;
• iii) a diffuse reflective coating disposed on the first ultraviolet-transmissive substrate and defining a plurality of apertures aligned with respective ones of the ultraviolet light emitters, each aperture having an area greater than an emitting area of its corresponding ultraviolet light emitter;
• and
• iv) a second diffuse reflective surface spaced from the first ultraviolet-transmissive substrate to define, together with the first diffuse reflective coating, a reflective irradiation cavity,
• wherein the plurality of apertures are configured to couple a majority of ultraviolet radiation generated by the ultraviolet light emitters into the reflective irradiation cavity while limiting direct line-of-sight emission into the airflow path;
• d) at least one fan configured to move air through the reflective irradiation cavity;
• and
• e) a control system operatively coupled to the ultraviolet light emitters and the at least one fan,
• whereby air passing through the reflective irradiation cavity is exposed to multiple diffuse reflections of ultraviolet radiation to produce an increased and spatially uniform photon density prior to delivery of treated air to a breathing zone of the user.