PPM-Hrs: Chlorine Dioxide Gas Treatment by Dosage

Previously, accurate measurement of other decontaminating agents was not consistent or reliable.  During large facility decontamination, it is not uncommon that the target concentration cannot be reached.  This may be due to loss, consumption, absorption or reaction with organic load. Since chlorine dioxide gas has a visible color, it is easily and accurately measured. This allows us to monitor the overall dosage accumulated during the decontamination and only complete the process once the correct dosage has been met.

To test this, ClorDiSys performed tests at different concentrations (0.3, 0.5, 1, 5, 10 & 20 mg/L) all with the same dosage. Dosage is described as an exposure at a concentration (parts per million) multiplied by an amount of time, typically hours (Hrs). For CD, this is referred to as PPM-Hrs. To determine the PPM-Hrs, the concentration in PPM is accumulated every minute. This accumulation then accrues PPM-Hrs. 6-log biological indicators were used to test the efficacy of chlorine dioxide gas when the overall dosage is held constant, but the concentration and contact times are varied. All of the varied chlorine dioxide gas concentrations (0.3, 0.5, 1, 5, 10 & 20 mg/L) with BI’s exposed to various exposure times with each cycle having a fixed target dosage of 720PPM-Hrs exhibited complete decontamination. The 20 mg/L run had the shortest gas time (14 minutes), and 0.3mg/L had the longest gas time (355 minutes). 

Data shows that the concentration of chlorine dioxide gas used does not affect the overall efficacy of the sterilization cycle as long as the overall exposure dosage of 720 ppm-hr has been met. Therefore, when the target concentration cannot be reached due to loss, consumption, or absorption, the cycle can still be successful. This confirms that the overall goal of an exposure is to achieve a certain dosage (720ppm-hrs) regardless of the concentration or exposure time.