A decontamination enclosure, comprised of a plurality of preformed panels joined together to form a structure defining a totally enclosed chamber. A door is formed in at least one of the panels, the door being movable between an opened position and a closed position to allow access to the chamber. A circulation system is attached to the structure for circulating vaporized hydrogen peroxide through the chamber. A controller is provided for controlling the amount of vaporized hydrogen peroxide introduced into the chamber.