Disinfection by hydrogen peroxide at low concentration in air: The key role of condensation

Gazeous hydrogen peroxide (H₂O₂) is commonly used for disinfection of room surfaces or sterilization of medical devices. Disinfection and sterilization processes are controlled by mean values measured at sterilizer chamber or room level. However, the surface phenomena (adsorption/condensation) taking place on inoculum are essential and still not well-known. In the present study, a solution of water and H₂O₂ is sprayed in a room disinfection system (Glosair 400, ASP) for 12 min. Condensation mass, H₂O₂ concentration, relative humidity (RH), macro zoom observations and inactivation kinetics of various microorganisms (Staphyloccocus aureus, Pseudomonas aeruginosa Candida albicans, Aspergillus niger) are reported. Macro-zoom observations reveal condensation and bubbling activities. Microbial inactivation is found optimal at low initial RH, corresponding to high H₂O₂ vapor concentration and low condensed mass. H₂O₂ concentration in the condensate is high and probably boosted by fractional condensation. In surface disinfection processes, inactivation of microorganisms occurs in presence of condensation although excessive condensation, due to high initial RH conditions or the presence of salt, decreases the microbial inactivation efficiency by dilution. While the present experimental conditions differ from those prevailing in H₂O₂ sterilization (59 % H₂O₂ under vacuum) or industrial disinfection processes (30 % H₂O₂ at atmospheric pressure), they are partially transposable.