An apparatus for determining the efficiency of a vaporizer in a decontamination system, having a first sensor for generating a first signal indicative of the concentration of a decontaminating chemical in a liquid decontaminate before vaporization by a vaporizer, and a second sensor for generating a second signal indicative of the concentration of vaporized decontaminate after vaporization by said vaporizer, and means for determining efficiency in accordance with said first and second signal.