An apparatus for removing a sterilant from a sterilant containing atmosphere of a room includes an enclosure having an inlet to receive sterilant containing air from the room following sterilization of the room, outlet nozzles to return air from which sterilant has been removed to atmosphere, and a catalyst within the enclosure for removing sterilant from the air. A fan draws sterilant containing air from the inlet through the catalyst and thence to atmosphere. An additional fan is provided to circulate air containing sterilant from the room during a room sterilization process through that part of the enclosure which is downstream of the catalyst to ensure sterility of that part of the enclosure for the sterilant removal phase.