HOW TO SCREEN FOR RN-222 IN LARGE BUILDINGS

Rn-222 measurements have been made in over 10,000 ground-contact rooms in 908 federal buildings. These data were examined statistically to c ompare parametric distributions that might be useful in the design and execution of future surveys of indoor Rn-222 in large buildings. In 1 52 of the 365 buildings with the most measurements per building, the l ognormal distribution was acceptable. Many other distributions were ob served in the other 213 buildings, including bi- and tri-modal distrib utions. In contrast, when data from entire facilities were examined, t he data were usually described by a lognormal distribution. Because of the above observations, we propose that any future surveys of indoor Rn-222 in large buildings be done in two phases, screening and assessm ent. During the screening phase, all facilities may be surveyed with a comparatively low sampling density, perhaps, one measurement per 465 m(2) (5,000 ft(2)) of floor space. Based on the results presented here , it is expected that statistical analysis of the screening data will reveal any facilities with substantial evidence of a high incidence of rooms with elevated indoor Rn-222 concentrations (e.g., above 150 Bq m(-3)). In the assessment phase, the identified facilities sill be sur veyed with a sampling density of one measurement for every ground-cont act roam or about one per 84 m(2) (900 ft(2)). Using numerical simulat ion techniques, we have tested the proposed screening phase protocol a gainst data from sixteen facilities. The results of the simulated scre enings support the feasibility of a two-phased approach to the task of identifying facilities having rooms with elevated Rn-222 concentratio ns.