The study presented here examined the factors influencing the effectiveness of surface decontamination with hydrogen peroxide vapor. The impact of relative humidity and hydrogen peroxide gas concentrations was investigated and compared to a dew point analysis of these various sterilant atmospheres. For this purpose, a series of different H 2 O 2 decontamination cycles were developed and tested for antimicrobial effectiveness using biological indicators inoculated with greater than 10 6 spores of Geobacillus stearothermophilus. The results indicate that an increasing concentration of hydrogen peroxide in the gas phase and higher humidity levels result in a faster inactivation of the test organisms. The higher the H 2 O 2 gas phase concentration was, the more independent the inactivation effect from the humidity level. At lower H 2 O 2 concentrations, the same kill was achieved with higher humidity. Subvisible condensation was found to be necessary for short inactivation times, but condensation in the visible range did not further enhance the sporicidal activity. The molecular deposition of water and hydrogen peroxide on the target surface represents the determining factor for microbial inactivation, whereas the hydrogen peroxide concentration in the gas phase is of secondary importance.

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