A method and apparatus for decontaminating a region with a gaseous or vaporous decontaminant (e.g., vaporized hydrogen peroxide) without dehumidification (e.g., without the use of a dryer). The saturation concentration of the decontaminant inside the region is monitored, and the concentration of the decontaminant inside the region is regulated to prevent condensation of the decontaminant. The bioburden reduction is continuously monitored during a decontamination phase to ascertain successful completion of a decontamination process in accordance with a target bioburden reduction.