Indoor chlorine gas release in a natatorium: A case study

Pool chemicals are utilized in pools to inactivate pathogens, optimize pH, and increase water clarity. This is conducted to ensure public health and safety by reducing bacteria concentrations and allowing distressed swimmers to be detected underwater. In commercial recreational facilities, muriatic acid and gaseous CO₂ are typically used to maintain pH. Chlorine, which can take the form of liquid or solid tablets of sodium hypochlorite or granular calcium hypochlorite, is used to sanitize pool water, and is the most used chemical treatment in the world for swimming pools disinfection. If chlorine is mixed with muriatic acid, chlorine gas is formed, which can lead to severe injuries and fatalities (SIFs) to exposed individuals. This work illustrates an incident that occurred as a result of the simultaneous injection of muriatic acid and liquid sodium hypochlorite into a recreational natatorium chemical feed line. This led to the release of chlorine gas in the indoor environment, which resulted in injuries to five patrons. Furthermore, strategies are proposed to prevent this from occurring and to reduce the likelihood of similar incidents in the future. These include the implementation of fail-safe logic to prevent the controller from malfunctioning and ensuring that controller program settings do not permit simultaneous chemical injection.