Study of the Reported Indoor Radon Measurement Results for Residential Structures and Large Buildings in Florida

Indoor radon concentrations have been tested in thousands of residential housing units and large buildings during the past six a half years in the State of Florida. Beginning in 1989, testing has been conducted in compliance with the state radon regulations. These regulations mandate that periodic indoor radon testing be conducted in facilities that render services of public nature, and require certification for individuals providing radon measurement and mitigation services for a fee or remuneration in Florida. Reported indoor radon measurement results were developed into database resources, maintained by the Florida Department of Health and Rehabilitative Services (HRS). One resource generated from the mandatory testing results of facilities, and the other generated from the certified radon businesses reporting their measurement activities as a part of their license requirements. As of July 1996, HRS's databases contain indoor radon test results for 32,563 and 23,594 residential housing and nonresidential units, respectively. The residential part of these data sets is approximately 10-fold larger than the previous major survey performed in Florida during 1986-1987 by Geomet Technologies, Inc., in which only residential housing units was surveyed. Correlation analysis between the total number of buildings and the population geographical distribution, as variables, of HRS's data sets resulted in 0.85 and 0.97 correlation coefficients for residential housing and non-residential units, respectively. These coefficients indicate that both variables were independent and a reasonable random distribution exist, which qualifies the data sets to be used for statewide representation. A statewide weighted average indoor radon concentration of 1.55 pCiA is found to exist in Florida residential units with 11.8% of all housing units experiencing indoor radon levels exceeding 4 pCi/l. The statewide weighted average indoor radon concentration for non-residential units is 0.74 pCiA with approximately 6% of buildings with levels greater than 4 pCi/l. Applying correction factors for the average household occupancy and population growth to the 1994 population data, a conservative estimate of at least one half-million residential housing units in Florida are exposed to indoor radon concentrations exceeding the national action level.