Assessing the annual representativeness of a 120-hour radon measurement methodology in Switzerland

In Switzerland, official radon measurements typically require yearlong or at least three-month passive dosimetric measurements during the heating season. For faster results, the Swiss Federal Office of Public Health (FOPH) introduced a 120-hour measurement protocol in 2018. This method aims to replicate winter conditions year-round to estimate the probability of exceeding the reference value of 300 Bq/m3. While widely used, its representativeness and the necessity of depressurization of a building have not been thoroughly evaluated. This study compares the 120-hour methodology, carried both in summer and winter, with yearlong and three-month measurements and assesses the impact of summer depressurization. Measurements were conducted in five homes during winter without depressurization, and summer with and without depressurization. Results showed good consistency between 120-hour and official measurements in three out of five homes, both during winter and summer periods, validating the method's general reliability. However, in two homes, the 120-hour approach overestimated radon risk. No significant differences were observed between summer measurements with and without depressurization, supporting the simplification of the protocol by omitting depressurization in non-heating seasons. However, our results indicated that the 120-hour methodology may not be able to replace long-term measurements as it requires broader validation to confirm its representativeness.