Determination of optimal ventilation rates in educational environment in terms of radon dosimetry

摘要

Introduction: New and renovated energy efficient buildings with minimised ventilation rates together with increased building airtightness are often associated with higher indoor radon concentrations compared to the concentrations in existing buildings. The purpose of our study is to analyse the problem associated with the increased radon concentration and ventilation requirements and recommendations in schools. The radon concentration was critically assessed by varying the design ventilation rates (DVRs) within fifteen cases according to legislative requirements and recommendations. The case study is a branch primary school in western part of Slovenia situated in a radon prone area. Methods: Radon (222Rn) concentrations were simulated in the classroom, using CONTAM 3.2. program. For validation, measurements were performed on 8 measuring days in September and 6 measuring days in March. The simulated and measured 222Rn concentrations are well correlated for all measurement days, with the simulated/measured ratio of 0.85?1.39. In order to define optimal DVRs in terms of dosimetry, the effective dose and its ratio to the worldwide average effective dose at workplace, received by radon progeny in 950 h (expected effective dose, 0.13 mSv/y), were calculated for each case. Results: Simulations showed that the highest radon concentrations were observed in case 1 with a DVR of 79.6 m3/h (621 Bq/m3) and case 4 with a DVR of 69.4 m3/h (711 Bq/m3), both defined by national regulations. The calculated values in both cases exceeded the national reference value for radon (300 Bq/m3) by 2.1 times and 2.4 times, and the WHO guideline value (100 Bq/m3) by 6.2 times and 7.1 times, respectively. The simulations are in line with the results of radon dosimetry. Both DVRs correspond to the highest effective doses, 1.88 mSv/y (about 14-fold higher than expected effective dose) for case 1 and 2.15 mSv/y (about 17-fold higher than expected effective dose) for case 4. Case 11_Cat I with a DVR of 1999.7 m3/h defined by EN 15251: 2007 resulted in minimal Rn concentration (35 Bq/m3) and corresponds to the lowest effective dose 0.11 mSv/y and its ratio to the expected effective dose 0.8. Conclusions: Ventilation is an immediate measure to reduce radon concentration in a classroom and it must be performed in line with other holistic measures to prevent and control radon as a health risk factor.