Radon entry into buildings: Effects of atmospheric pressure fluctuations and building structural factors

Abstract

An improved understanding of the factors that control radon entry into buildings is needed in order to reduce the public health risks caused by exposure to indoor radon. This dissertation examines three issues associated with radon entry into buildings: 1) the influence of a subslab gravel layer and the size of the openings between the soil and the building interior on radon entry; 2) the effect of atmospheric pressure fluctuations on radon entry; and 3) the development and validation of mathematical models which simulate radon and soil-gas entry into houses.Experiments were conducted using two experimental basements to examine the influence of a subslab gravel layer on advective radon entry driven by steady indoor-outdoor pressure differences. These basement structures are identical except that in one the floor slab lies directly on native soil whereas in the other the slab lies on a high-permeability gravel layer. Our measurements indicate that a high permeability subslab gravel layer increases the advective radon entry rate into the structure by as much as a factor of 30. The magnitude of the enhancement caused by the subslab gravel layer depends on the area of the openings in the structure floor; the smaller the area of these openings the larger the enhancement in the radon entry rate caused by the subslab gravel layer. A three-dimensional, finite-difference model correctly predicts the effect of a .. 11 DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document.subslab gravel layer and open area configuration on advective radon entry driven by steady indoor-outdoor pressure differences; however, the model underpredicts the absolute entry rate into each structure by a factor of 1.5.Experiments were conducted in the structure with the subslab gravel layer to examine the importance of radon entry driven by atmospheric pressure fluctuations. Continuous measurements of soil-gas and radon entry driven by atmospheric pressure fluctuations were made for a range of steady indoor-outdoor pressure differences. In the absence of a steady indoor-outdoor pressure difference, atmospheric pressure fluctuations drive 1.5 times more radon entry into the experimental structure than diffusion. Pressurizing or depressurizing the interior of the structure diminishes the contribution of atmospheric pressure fluctuations to the long-term radon entry rate into the experimental structure.To explain the effect of atmospheric pressure fluctuations on radon entry into houses, we present a detailed analysis of soil-gas flow driven by these fluctuations. A theoretical framework is developed to predict transient soil-gas entry into houses. Utilizing this framework, we examine and compare the measurements of soil-gas flow and the predictions of an analytical and a numerical model in both the time and frequency domains. Two scaling parameters are identified from a dimensional analysis of the analytical model to characterize how changes in water tab...

Definition and Sensitivity Analysis of a CFD Model for the Study of Radon Entry and Accumulation in Buildings

“…In locations with high radon content, indoor mitigation processes are based on preventing the penetration of the gas. To this end, it is essential to understand the transport and entry mechanisms, that cause radon generated within the soil to move through the soil and penetrate the building envelope [3]. These mechanisms are influenced both by the properties of the soil [4] and the building envelope, as well as by temporary actions, such as weather or building use [5][6].…”

A full-scale experimental study of sub-slab pressure fields induced by underground perforated pipes as a soil depressurisation technique in radon mitigation

“…An understanding of those matters helps optimise depressurisation system design. Some have been studied experimentally by analysing the pressure fields associated with different slab/soil conditions (Collignan et al, 2004;Reddy et al, 1991;Robinson, 1996) and activating the system with sumps. In contrast, here the facility used consisted of perforated pipes (of the sort normally used for drainage).…”