Air change rates and radon accumulation in rooms with various levels of window and door closure

Dwellings in Israel must include a residential protected room made of thick concrete slabs and walls, with an extremely airtight window and outward opening extremely airtight steel door. An inward opening regular door is applied for everyday usage. Being multipurpose, the residential protected room raised concern regarding long-term radon exposure. This article presents the stage of air change rate investigation (using SF6 as tracer gas) and radon monitoring in a multidisciplinary research performed by two teams. It comprised six residential protected rooms in a tall unoccupied building, including various scenarios of window and door closure. The teams established a common theoretical model and addressed sensitivity to differences in assumptions and methods of analysis. Similar orders of magnitude of air change rates and free surface exhalation rates were obtained, but with nonnegligible discrepancies between specific values. Tracer gas method results were more sensitive to calculation assumptions and radon monitoring results to measurement uncertainties. Measured air change rates were as follows: fully sealed residential protected room: <0.03 ACH (air changes per hour); closed window and regular door: <0.25 ACH; tilted window and closed door: 1-3 ACH; one component open and the other closed: 3-20 ACH; and both components somewhat open: 20-100 ACH. It was shown that expected maximal radon concentrations in a residential protected room under conditions of regular usage or emergency protection would not reach the limit value of 200 Bq/m3.