Estimating airborne trichloramine levels in indoor swimming pools using the well-mixed box model

Exposure to airborne disinfection by-products, especially trichloramine (TCA), could cause various occupational health effects in indoor swimming pools. However, TCA concentration measurements involve specialized analysis conducted in specific laboratories, which can result in significant costs and time constraints. As an alternative, modeling techniques for estimating exposures are promising in addressing these challenges. This study aims to predict airborne TCA concentrations in indoor swimming pools using a mathematical model, the well-mixed box model, found in the IHMOD tool, freely available on the American Industrial Hygiene Association website. The model’s predictions are compared with TCA concentrations measured during various bather load scenarios. The research involved conducting 2-hr successive workplace measurements over 16- to 18-hr periods in four indoor swimming pools in Quebec, Canada. TCA concentrations were estimated using the well-mixed box model, assuming a homogeneous mixing of air within the swimming pool environment. A novel approach was developed to estimate the TCA generation rate from swimming pool water, incorporating the number of swimmers in the model. Average measured concentrations of TCA were 0.24, 0.26, 0.14, and 0.34 mg/m³ for swimming pools 1, 2, 3, and 4, respectively. The ratio of these measured average concentrations to their corresponding predicted values ranged from 0.51 to 1.30, 0.67 to 1.04, 0.57 to 1.14, and 0.68 to 1.49 for the respective swimming pools. In a worst-case scenario simulating the swimming pool at full capacity (maximum bathers allowed), TCA concentrations were estimated as 0.23, 0.36, 0.14, and 0.37 mg/m³ for swimming pools 1, 2, 3, and 4. Recalculated concentrations by adjusting the number of swimmers so as not to exceed the recommended occupational limit concentration of 0.35 mg/m³ gives a maximum number of swimmers of 63 and 335 instead of currently 80 and 424 for swimming pools 2 and 4, respectively. Similarly, for swimming pools 1 and 3, the maximum number of swimmers could be 173 and 398 (instead of the current 160 and 225, respectively). These results demonstrated that the model could be used to estimate and anticipate airborne TCA levels in indoor swimming pools across various scenarios.

暴露于空气传播消毒副产物，尤其是三氯胺（trichloramine, TCA），可能会对室内游泳池从业人员造成多种职业健康损害。然而，TCA浓度检测需在特定实验室开展专业分析，这会带来显著的成本与时间约束。作为替代方案，用于估算暴露量的建模技术在解决上述挑战方面极具应用前景。本研究借助美国工业卫生协会（American Industrial Hygiene Association）官网免费发布的IHMOD工具中的完全混合箱式模型（well-mixed box model）这一数学模型，对室内游泳池内空气中的TCA浓度进行预测。将该模型的预测结果与不同游泳负荷场景下实测得到的TCA浓度进行对比分析。本研究在加拿大魁北克省的4座室内游泳池中，于16至18小时的监测周期内开展了连续2小时的现场作业测量。本研究假设游泳池环境内空气均匀混合，采用完全混合箱式模型估算TCA浓度，并开发了一种新方法，将游泳人数纳入模型参数以估算游泳池水体的TCA生成速率。四座游泳池（编号1至4）的TCA平均实测浓度分别为0.24、0.26、0.14和0.34 mg/m³。各泳池实测平均浓度与对应预测值的比值范围依次为：1号泳池0.51~1.30，2号泳池0.67~1.04，3号泳池0.57~1.14，4号泳池0.68~1.49。在模拟游泳池满负荷运行（即允许的最大游泳人数）的最坏场景下，1至4号泳池的TCA预测浓度分别为0.23、0.36、0.14和0.37 mg/m³。通过调整游泳人数重新计算浓度，使其不超过推荐的职业接触限值0.35 mg/m³，结果显示：2号和4号泳池的最大允许游泳人数应分别从当前的80人和424人调整为63人和335人；同理，1号和3号泳池的最大允许游泳人数可分别调整为173人和398人（相较于当前的160人和225人）。上述结果证实，该模型可用于估算和预测不同场景下室内游泳池空气中的TCA水平。