Â DWELLINGS CONSTRUCTED WITH SUSPENDED TIMBER FLOORS
Dwellings in the UK with suspended timber floors and high radon levels are proving difficult to remedlate. This paper reports on the experience of the Building Research Establishment in dealing with such dwellings. Remediation techniques are discussed in some detail and attention is given to the drawbacks of each system. Details of the remediation of 18 dwellings are given, and comparisons are made between the effectiveness of the different techniques adopted. Sump systems are shown to be very effective at reducing radon levels, but unfortunately they are not practical to inatall fbr the majdly of cases. Natural vatilatim, mecbical supply veatilationand rnuhnid extract ventilation are three alternative techniques that have been used successfully.
Radon entry into houses having a crawl space.
The transport of 222Rn from soil, through a vented crawl space, and into the living space of single-family residences was studied. Two houses were monitored in detail for periods of 5 and 7 weeks. With crawl space vents open, the average indoor 222Rn concentrations were 1.2 and 0.6 pCi 1.-1 (44 and 22 Bq m-3); with the vents sealed the averages rose to 2.2 and 1.0 pCi 1.-1 (81 and 37 Bq m-3). The data suggest that, of the Rn released into the crawl space from the soil beneath the house, a significant fraction, perhaps 50% or more, enters the living space. The effect of 3 meteorological parameters--wind speed, indoor-outdoor temperature difference, and rate of barometric pressure change--on Rn concentration and entry rate were examined. In 1 of the houses a higher temperature difference corresponded to a higher indoor concentration, suggesting that the increased infiltration rate is more than compensated by an increase in the Rn entry rate. On the other hand, a high wind speed tended to reduce the indoor concentration, presumably by increasing both cross-ventilation of the crawl space and the infiltration rate of the living space. Results suggest that Rn transport into the crawl space of at least 1 of the houses occurred by pressure-driven flow, rather than solely by molecular diffusion. The diffusion coefficient of 222Rn through polyethylene sheeting, such as was present on the ground beneath this house, was measured in the laboratory and found to range from 0.65 X 10(-7) cm2 s-1 at 11 degrees C to 1.6 X 10(-7) cm2 s-1 at 25 degrees C, implying that the maximum diffusive flux through the sheet was many times smaller than that necessary to account for the rate of Rn entry into the house. A third house was studied using a tracer gas injected into the crawl space at a controlled rate. The fraction of air leaving the crawl space that entered the living space ranged from 0.3 to 0.65, in good agreement with results for Rn transmission in the other 2 houses, assuming that the 222Rn flux into the crawl space was comparable to that which would have resulted from molecular diffusion from soil having a 222Rn diffusion length of 1.0 m. By sealing leaks in the floor of this house, the average infiltration rate was reduced by 25%, but the indoor concentration of the tracer gas remained constant.
Improved Low‐Level Alpha‐Scintillation Counter for Radon
A low counter background is obtained by use of steel for the shell and quartz for the counter window, while marked improvement in the stability is obtained by coating the window with an electrically conducting layer of tin oxide. The distribution of radon and its daughters within the counter under various conditions was determined by comparison of observed and calculated counting efficiencies. A stable counting efficiency of 5.58±0.05 cpm/μμc radon and a background counting rate of 0.08 cpm is obtained. The usefulness of this counter is augmented by adsorbing the radon on charcoal. The radon is then easily transferred to the counter with a small volume of helium and a Sigmamotor pump. This system is suitable for the analysis of samples of radon as small as 10−14 c or concentrations in air smaller than 10−16 C radon/liter.