METHODS: CC Environmental Health and Hazardous Material Program investigators inspected the facility. California Department of Public Health (CDPH) investigators reviewed records of non-agricultural chlorine exposures provided by the California Department of Pesticide Regulation.
RESULTS: CC Environmental Health investigators measured the pool water’s free chlorine residual at 13.5 ppm (allowable maximum is 10 ppm per California Code of Regulations section 65529), and the pH at 6.8 (allowable minimum 7.2). They noted that before the chlorine gas release, the pool recirculation pump was not in operation, yet chemical controller data revealed a continuous release of muriatic acid and sodium hypochlorite into the pool recirculation line. When the recirculation pump was reactivated, excess levels of these chemicals reacted to form elevated levels of chlorine gas affecting pool patrons. The park was closed for further investigation into the cause of the incident, and to install a new chemical controller. CC Hazardous Material Program inspection identified violations including an incomplete emergency response plan, failure to provide and document initial and refresher employee training, inadequate procedures to prevent exposures and mitigate hazards related to a potential release, and operating an underground storage tank containing hazardous material without appropriate controls or permit. CDPH identified 19 incidents of chlorine exposures at recreational swimming pools from 2008 to 2015. Of these, 7 resulted in inhalational exposure to chlorine impacting a total of 121 persons (2 –30 persons per incident), and in each incident, either sensor failure, human error, or mechanical failure was identified as the cause for the chlorine release. In 6 incidents, major maintenance or repairs were conducted while bathers were in the pool.
CONCLUSIONS: These investigations identified work practices, policies, and procedures critical to preventing mass chlorine exposures at recreational swimming pools: 1) safe handling and storage of pool chemicals; 2) adequate training for handling pool chemicals and equipment; 3) monitoring pool chemical concentrations to maintain within safe limits; 4) maintenance of chemical controllers; and 5) compliance with hazardous material reporting.