Notes that some radon mitigation systems draw air with a high radon concentration from under the basement floors of houses and exhaust it outdoors. Describes a study to measure the reentry rates of radon released roof level and at ground level near a house to determine whether exhaust above the roof is necessary. This was done by using a portable mockup of a radon mitigation system exhaust, with SF6 as a tracer gas. States the roof- level exhaust produced maximum indoor SF6 concentrations that were significantly lower than those from the ground level exhaust. This suggests that the better radon discharge location is on the roof of a house.

KEYWORDS: Radon, tracers, indoor, air pollution, sulphur hexafluoride, exhaust gases, exhausts, recirculating