26
DEPENDENCE OF RADON CONCENTRATION ON PRESSURE DIFFERENCE IN A CRAWL-SPACE

H. Kokotti, T. Keskikuru, R. Halonen and P. Kalliokoski
Department of Environmental Sciences, University of Kuopio
P:O:Box 1627, 70211 Kuopio, Finland

Radon concentration in a crawl space remained at the same level during autumn ( 756 Bq m -3 ) and in
winter ( 767 Bq m -3 ) because both air exchange rate and negative pressure (measured across the
foundation wall) increased after a installation of a new ventilation system in the crawl space. In
addition, relative humidity and water content remained constant in the crawl space air during the same
period of time. Radon entry rate was explained by the pressure difference across the crawl space wall
with percentages of 51 % (winter) and 76 % (autumn). The degree of explanation for the whole data
was found to be 75 %. Relative humidity and water content in the crawl space air were explained by
the pressure difference across the crawl space wall with 35 % and 28 %, respectively. Thus, both
radon and moisture from soil were carried similarly by the air flow driven by negative pressure in the
crawl space and a separate mechanical ventilation might be recommended to prevent also mold
problems.

Keywords: radon, moisture, relative humidity, a crawl space, pressure difference, ventilation.