A decontamination enclosure, comprised of: a totally enclosed chamber; a circulation system attached to a structure for circulation of gas through said chamber, said circulation system having: a duct disposed along the exterior of said structure, said duct being connected to said enclosure and communicating with said chamber at a first location to define an outlet from said chamber and being connected to said enclosure and communicating with said chamber at a second location and at a third location to define inlets to said chamber; and a blower disposed in said duct for conveying a stream of gas through said duct in a first direction, said blower disposed in said duct downstream from said first location and upstream from said second and third locations (134, 136); a vaporized hydrogen peroxide generator connected to said duct for introducing vaporized hydrogen peroxide into said stream of gas at said third location; and a controller for controlling the amount of vaporized hydrogen peroxide introduced into said chamber and for controlling the flow of said gas to said second location and said third location; characterized in that said decontamination enclosure is further comprised of: a plurality of preformed, rigid structural panels (22, 24) joined together to form a modular structure defining said totally enclosed chamber, a door formed in at least one of said panels (22, 24), said door movable between an opened position and a closed position to allow access to said chamber; a catalyst disposed in said duct at said second location; wherein said structure formed by said plurality of preformed, rigid structural panels (22,24) supports said circulation system, said catalyst, said vaporized hydrogen peroxide generator and said controller. a totally enclosed chamber; a circulation system attached to a structure for circulation of gas through said chamber, said circulation system having: a duct disposed along the exterior of said structure, said duct being connected to said enclosure and communicating with said chamber at a first location to define an outlet from said chamber and being connected to said enclosure and communicating with said chamber at a second location and at a third location to define inlets to said chamber; and a blower disposed in said duct for conveying a stream of gas through said duct in a first direction, said blower disposed in said duct downstream from said first location and upstream from said second and third locations (134, 136); a duct disposed along the exterior of said structure, said duct being connected to said enclosure and communicating with said chamber at a first location to define an outlet from said chamber and being connected to said enclosure and communicating with said chamber at a second location and at a third location to define inlets to said chamber; and a blower disposed in said duct for conveying a stream of gas through said duct in a first direction, said blower disposed in said duct downstream from said first location and upstream from said second and third locations (134, 136); a vaporized hydrogen peroxide generator connected to said duct for introducing vaporized hydrogen peroxide into said stream of gas at said third location; and a controller for controlling the amount of vaporized hydrogen peroxide introduced into said chamber and for controlling the flow of said gas to said second location and said third location; a plurality of preformed, rigid structural panels (22, 24) joined together to form a modular structure defining said totally enclosed chamber, a door formed in at least one of said panels (22, 24), said door movable between an opened position and a closed position to allow access to said chamber; a catalyst disposed in said duct at said second location; wherein said structure formed by said plurality of preformed, rigid structural panels (22,24) supports said circulation system, said catalyst, said vaporized hydrogen peroxide generator and said controller.