Vapourized hydrogen peroxide:
Determining successful gassing cycle characteristics for IVC air handling units and cage change stations.

There is increasing interest in new fumigation systems capable of replacing established agents ,such as formaldehyde gas, ethylene oxide (ETO), ammonia or peracetic acid, whose use may be associated with residual toxicity and/or damage to metal , plastic or electronic components . Air handling units and cage change stations used with Individually Ventilated Cage systems present a particular challenge to fumigants , either during routine disinfection or prior to their introduction into microbiologically clean areas . Vaporized hydrogen peroxide may offer an alternative to established agents because of its microbiocidal activity and low toxicity .

The objective of this study was to determine the dose range , exposure time and other conditions necessary for vaporized hydrogen peroxide to achieve a 100% of kill of indicator microorganisms (Staphylococcus aureus, Escheria coli, Pseudomonas aeruginosa, Aspergillus niger, Candida albicans and spores of Geobacillus stearothermophilus and Bacillus atrophaeus) during the fumigating cycle of IVC air handling units and cage changing stations. Microbiological indicators were randomly distributed inside the equipment and exposed to different volumes ( 75 to 225ml ) of vaporized hydrogen peroxide delivered either via a direct loop connection to a hydrogen peroxide generator or indirectly , where a generator was connected to a modified rack washer used as a gassing enclosure.

The trials showed that the microbicidal action of the vaporized hydrogen peroxide depended on the sensitivity of the test organism ( at lower concentrations Pseudomonas aeruginosa and Aspergillus niger were more resistant than G.steaorothermophilus and Bacillus atrophaeus spores) , the quantity of hydrogen peroxide and the method of delivery, exposure time , environmental temperature and relative humidity . Several trials were necessary to determine the appropriate combination of concentration of hydrogen peroxide, delivery method and other aspects of the gassing phase that allowed the definition of precise and successful cycle characteristics .