Models of Radon Entry

This paper reviews existing models of radon entry into houses. The primary mechanism of radon entry in houses with high indoor concentrations is, in most cases, convective entry of radon-bearing soil gas from the surrounding soil. The driving force for this convective entry is the small indoor-outdoor pressure difference arising from the stack effect and other causes. Entry points for the soil gas generally are the cracks or gaps in the basement sub-structure, or through other parts of the building shell directly in contact with the soil, although entry may also occur by means of flow through permeable concrete or cinder block walls of the sub-structure. Models using analytical solutions to idealised geometrical configurations with simplified boundary conditions obtain analytical tractability of equations to be solved at the cost of severe approximations; their strength is in the insights they offer with their solutions. Models based on lumped parameters attempt to characterise the significant physical behavioural characteristics of the soil gas and radon flow. When realistic approximations are desired for the boundary conditions and terms in the governing equations, numerical models must be used; these are usually based on finite difference or finite element solutions to the governing equations. Limited data are now available for experimental verification of model predictions. The models are briefly reviewed and their strengths and limitations are discussed.