Radon decay products concentration

Rudnick, S.N., W.C. Hinds, E.F. Maher, and M.W. First, Effect of Plateout, Air Motion and Dust Removal on Radon Decay Product Concentration in a Simulated Residence, Health Phvs. 45 463-470... 

Measures to reduce radon concentrations have been studied in an old house in which the radon decay-product concentration initially exceeded 0.3 Working Level (WL). Some of the measures were only partially successful. Installation of a concrete floor, designed to prevent ingress of radon in soil gas, reduced the radon decay-product concentration below 0.1 WL, but radon continued to enter the house through pores in an internal wall of primitive construction that descended to the foundations. Radon flow was driven by the small pressure difference between indoor air and soil gas. An under-floor suction system effected a satisfactory remedy and maintained the concentration of radon decay products below 0.03 WL. 

Before standards for indoor exposure to radon can be formally established, work is necessary to determine whether remedies are feasible and what is likely to be involved. Meanwhile, the Royal Commission on Environmental Pollution (RCEP) in the UK has considered standards for indoor exposure to radon decay products (RCEP, 1984). For existing dwellings, the RCEP has recommended an action level of 25 mSv in a year and that priority should be given to devising effective remedial measures. An effective dose equivalent of 25 mSv per year is taken to correspond to an average radon concentration of about 900 Bq m 3 or an average radon decay-product concentration of about 120 mWL, with the assumption of an equilibrium factor of 0.5 and an occupancy factor of 0.83. 

The range of radon decay-product concentrations found in houses in southwest England spans three orders of magnitude. A few dwellings have been found where levels exceed 0.6 WL. It is clear that there are likely to be an appreciable number of houses in this region with indoor concentrations higher than 120 mWL. In 1982, the Department of the Environment identified two local authorities in the county of Cornwall that were willing to lend council property to test... 

Figure 2. Variation 1n radon decay-product concentration over a 10 day period and wind speed.

Figure 3a shows the radon decay-product concentration in the sitting room, together with the wind speed, for the 25 day period... 

Figure 3. Variation in radon decay-product concentration and wind speed, (a) before and (b) after laying polythene.

Figure 4. Radon decay-product concentrations on removing polythene sheet from sitting room floor.

F varies from 0.1, when only 218Po is present, to unity at equilibrium. Figure 5 shows the changes in the aggregate radon decay-product concentration, the concentration of 218Po, and the variation in F achieved by operating the electrostatic precipitators. The radon decay-product concentration was reduced by more than a factor of 10. 

In all rooms the concentration of the radon decay products was decreased by mechanical ventilation (Table I). The smallest decrease occurred in the office, indicating that this room had the highest radon production rate whereas the polythene sheeting reduced ingress of radon into the sitting room. Apart from the office, reduction in radon decay-product concentration was larger than could be explained by the increased ventilation rate. 

After the concrete floor had been installed, measurements indicated radon decay-product concentrations of 160 mWL and 140 mWL on the ground floor and upstairs, respectively. There were noticeable gaps between the concrete floor and the wall surfaces in a number of places, some of which extended to the foundations. The radon production rate was estimated to be 1300 Bq m"3 h"1, more than four times the value found in the initial study with all internal doors open. Radon was obviously entering the dwelling with ease, even though the area of underlying material exposed in gaps between the floor and the walls was much smaller than that exposed beneath... 

Figure 9. Radon decay-product concentrations and ventilation rates showing the effect of covering the fire-places.

The fans were switched on at time E, causing a further decrease in concentration. Low concentrations were maintained for 4 days, at the end of which only one of the fans was kept in operation (office system F to G, sitting room system G to H). The increase in the concentration of radon decay-products after switching off one or both fans is evident. After time I, the radon decay-product concentration decreased, but less rapidly than in the first trial and the final value was not as low. However, a trend to still lower values was apparent when the exercise was concluded on day 19. Measurements of the concentration of radon in the exhausts of the two suction systems were made on three days and the results are given in Table II. 

Figure 11. Variation in radon decay-product concentrations before and during the operation of the underfloor under-pressure system.

The subsoil is the principal source of radon in this house. Both the activity concentration of radium-226 in subsoil and of radon in soil gas are above levels for building ground that might result in significant indoor radon concentrations. The radon decay-product concentration in the dwelling before remedial measures were taken was substantially higher than the reference value of 120 mWL. 

The highest radon production rates occurred in rooms with suspended wooden floors through which air could pass readily. Simple ventilation of the underfloor space with a 30 W fan was effective in reducing radon decay-product concentrations in these rooms, but not below the reference value in all rooms. More rigorous application of this technique with multiple extraction points and a larger fan could clearly serve as an effective remedy. 

Electrostatic precipitators were effective in reducing the radon decay-product concentration below the reference level, but analysis of the room aerosol indicated that the reduction was largely offset by an increase in lung dose per unit exposure. 

Mechanical ventilation of room air reduced the radon decay-product concentration below the reference level by a larger... 

A new concrete floor incorporating barriers to radon transport from the subsoil appeared to be only partially successful in reducing radon decay-product concentrations. It was shown that the Venturi effect of the wind across two chimney stacks caused pressure-driven flow of radon from the ground. Covering the fireplaces to eliminate this effect resulted in concentrations below the reference level. 

D22.05 D6327-98 Standard Test Method for Determination of Radon Decay Product Concentration and Working Level in Indoor Atmospheres by Active Sampling on a Filter... 

Maximum average annual radon decay product concentration (Including background) as a result of Inactive uranium processing sites, In any occupied or habitable building... 

In order to determine radon decay product concentrations, the build-up and decay methods are used (Cliff, 1978 Trembley et al., 1979). The following timetable is used the collection period is 28 min, the first waiting period is 2 min and there are four time-measurement periods of 10 min with a 2-min interval for the readout between them. Using the counting data from the resulting measurements, radon decay product concentrations are estimated by the least square method. 

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