Air quality in an air ventilated fitness center reopening for pilot study during COVID-19 pandemic lockdown

During COVID-19 lockdowns less people were able to fulfill the WHO recommendations on physical activity. Also, fitness centers were associated to SARS-CoV-2 superspreader events. However, the risk of infection can be strongly reduced by outdoor air ventilation. To investigate whether a reopening of fitness centers can be justified, [Formula: see text] concentration was measured during four days in a fitness center. Except for one room, the observed [Formula: see text] concentrations were mainly under 800 ppm, which stands for high air quality. The strong decrease of [Formula: see text] concentration during the 15 min evacuations following each hour of workout, speaks for the functionality of the ventilation system. In particular, the number of people present in the studio has a strong impact on the estimated [Formula: see text] value. In a linear mixed model, an additional [Formula: see text] concentration of 2.24 ppm (95 % confidence interval [2.04, 2.43]) was estimated for this setting with a total volume of 4065 m [Formula: see text] in the fitness center and a possible air change rate per hour up to 10. This means, that for 45 visitors, 100 ppm can be added to the predicted concentration. To summarize, a combination of ventilation, restriction of the number of visitors and surveying the [Formula: see text] concentration allowing for further restrictions in case of need, seems to be an adequate means to reduce the risk of SARS-CoV-2 infection in fitness centers.