Abstract
Abstract: The commercial products of calcium hypochlorite (Ca（OCl) 2) , a solid hypochlorite salt, are hygroscopic because of the presence of calcium chloride as an impurity. In this study, we investigated the volatilization of gaseous hypochlorous acid (HOCl (g) ) from Ca (OCl) 2 tablets and its disinfection efficacy against Staphylococcus aureus on wet agar plates were studied in a 75 m3 room. HOCl (g) volatilization occurred spontaneously and continuously, even in ambient air. Under airflow conditions, the absorption of water vapor from the air into the Ca (OCl) 2 tablet was accelerated, and numerous droplets were formed on the tablet surface. The deliquescent property of calcium chloride indices these phenomena. When a glass Petri dish containing 10 Ca (OCl) 2 tablets was placed in the room under airflow conditions, HOCl (g) volatilization of was enhanced, and the HOCl (g) concentration in the room was maintained within the range of 60‒80 ppb for at least 24 h of volatilization. Viable S. aureus count on wet agar plates placed on the floor 1‒5 m away from the tablets decreased by 3.1-log after 1.5 h of exposure. This study indicates that sufficient concentrations of HOCl (g) can be volatilized from Ca (OCl) 2 tablets without the use of water, contributing to the disinfection of attached bacteria.
