Active air stripping and direct point exhaust of trichloramine (NCl₃) from indoor pools

Control of gas-phase trichloramine (NCl₃) in indoor swimming pool environments has been identified as a priority within the swimming community because of the ability of NCl₃ to function as a respiratory system irritant and a corrosive agent. Conventional heating, ventilation, and air conditioning (HVAC) systems in indoor pool facilities are generally incapable of controlling episodes of high gas-phase NCl₃, which are often observed during periods of high bather load. To address this issue, an active air stripping system was installed at the venue for the Olympic and Paralympic swimming competitions in Paris, France during the period of July-September 2024. The active air stripping system promoted net liquid→gas transfer of volatile compounds (including NCl₃), with venting directly to the outside. This system was demonstrated to reduce the liquid-phase combined chlorine concentration in a manner that was consistent with stripping of NCl₃. More importantly, active air stripping also reduced the gas-phase NCl₃ concentration in the air above the pool. Because the air flow rate through the active stripping system was less than 1% of the outside air flow rate through the HVAC system, active stripping presents a method to improve indoor air quality in indoor pool facilities while also reducing HVAC system operating costs and energy consumption.