Covariation amongst pool management, trichloramine exposure and asthma for swimmers in Norway

The association between asthma and exposure to the air in swimming facilities has been acknowledged. However, the variation in, long-term exposure to and management of the respiratory irritant trichloramine (NCl₃) is not well understood. In this study, 313 swimmers above 18 years of age licensed by the Norwegian Swimming Association answered a questionnaire about health and swimming. The prevalence of asthma amongst the most-exposed swimmers was 36%. Two facilities, those with the highest and lowest reported prevalence of asthma, were chosen for further investigation. For each facility, a one-week-long monitoring campaign was performed, during which pool management, air and water quality were investigated. The results of this study showed that time of day, occupancy and pool management affect the concentration of NCl₃, which ranged from 58 μg/m³ to 461 μg/m³. Furthermore, in one of the facilities, the concentration of CO₂ was measured to evaluate whether this contaminant could be used to predict the number of pool occupants as well as the concentration of NCl₃ in the air. The concentration of CO₂ was significantly correlated with occupancy level (ρ = 0.82, p = 0.01) and NCl₃ concentration (r = 0.80, p = 0.01). Furthermore, according to the random intercept model the concentration of CO₂ explained 52% of the variation observed in the air concentration of NCl₃. CO₂ sensors to control the air supply can help reduce the air concentrations of NCl₃ and balance the air supply based on occupancy level.