Volatilization of gaseous hypochlorous acid from calcium hypochlorite product induced by the deliquescent property of calcium chloride

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.