Radon indoor concentrations

Radon gas is formed in the process of radioactive decay of uranium. The distribution of naturally occurring radon follows the distribution of uranium in geological formations. Elevated levels have been observed in certain granite-type minerals. Residences built in these areas have the potential for elevated indoor concentrations of radon from radon gas entering through cracks and crevices and from outgassing from well water. 

Outdoor inhalation exposure is mainly due to traffic, energy production, heating, and natural factors such as pollen and mineral dusts. These outdoor sources of pollution also affect indoor air quality. The indoor concentration is typically 20-70% of the corresponding outdoor concentration. Occasionally the indoor concentrations of an external pollutant (especially radon) may even exceed the concentrations outdoors. ... 

In the radon surveys the primary quantity determined is the indoor air mean radon activity concentration. From a radiological health perspective it is the dose arising from the inhalation of radon daughters that is of interest. The conversion from radon exposure to annualised effective dose equivalent for the survey was carried out using the factors given in Table I which are similar to those being used in other European surveys. The occupancy and equilibrium factors given in this table are assumed mean values for Irish... 

It is to be noted that the conversion factor of 20 mSv effective dose equivalent per 200 Bq m 3 equilibrium equivalent radon concentration, considered by the ICRP (ICRP, 1984) in recommending an Action Level for remedying high indoor radon concentrations, corresponds to a dose rate of about 40 pGy per y per Bq m 3 radon gas concentration. 

Bergman, H., and O. Axelson, Passive smoking and indoor radon daughter concentrations, Lancet 1308-1309 (1983). 

A. There is no correlation between Mr and Mn this means, for example, that the average indoor concentration of radon in various counties is not correlated with the amount of cigarette smoking in those counties... 

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... 

Initial studies of the indoor concentrations of radon and its decay products were carried out with all exterior doors and windows closed, but with all internal doors fully opened. The radon production rate for the whole house was determined by measuring the 218Po concentration in indoor air and in the air outside the dwelling and by determining the ventilation rate. The radon production rate, K, is given by (Cliff, 1978b) ... 

Most of the early measurements of radon levels were made outdoors however, it has become apparent that the indoor concentrations are generally several times higher than those outdoors. Because people in Western countries spend only 15% of their time outdoors, most of the exposure to radon therefore occurs indoors. Additionally, the trend toward the construction of more energy-efficient housing (more air-tight) has also enhanced the concentrations of radon-222 indoors. 

Indoor radon levels were measured in homes located in the Reading Prong area of Pennsylvania. This area has an unusual abundance of homes with high radon concentrations that is presumed to be from geologically produced emanation of radon. Indoor levels of radon in this area ranged from 4 to 20 pCi/L (150 to 740 Bq/m ) in 29% of the homes to >80 pCi/L (3,000 Bq/m ) in 1% of the homes (Fleischer 1986). 

Nero A. 1987. Indoor concentrations of radon-222 and its daughters sources, range, and environmental influences. In Gammage R, Kaye S, eds. Indoor air and human health. Chelsea, Ml Lewis Publishers, Inc., 43-67. 

Location Geochemical background Indoor concentration [Bq m" ] Radon [79, 80] Thoron [81] Outdoor radon concentration [Bq m ] [81]... 

Like most other indoor air contaminants, radon can be controlled by keeping it out of the house, or reducing the concentration by mixing it with fresh air after it has already entered. The following approaches have been tried or suggested9 ... 

Radon mitigation by SSD has been proven to be very effective, often decreasing indoor radon concentrations by 90% or more following mitigation. 

In theory, the application of radon barriers should be adequate to avoid elevated radon levels in houses. In practice, however, a backup radon mitigation system has been found essential for maintaining indoor radon concentrations below 4 pCi/L in most homes studied. In the recent radon-resistant residential construction projects conducted by U.S. EPA and/or private builders, several of the homes designed to be radon resistant have contained radon concentrations above 4 pCi/L. In each of those houses, a backup system consisting of an active (fan-assisted), or passive (wind-and-stack-effect-assisted), SSD system was installed at the time of construction. When mechanical barriers failed to adequately control radon, the soil depressurization methods were made operational. 

In addition to the above measurements, indexes using soil concentrations in combination with permeability measurements have been suggested by some researchers.4142 As elaborated on later in this section, these methods have been successful in establishing relationships between some of the site measurements and indexes, and indoor radon concentrations for specific areas and regions. 

In buildings with indoor radon concentrations greater than 4pCi/L, the majority of the radon is produced in the soil and enters the building through foundation openings. The radon gas found in soils is... 

Several studies have been attempted to make simple correlations between radon or radium concentrations in the soil and indoor radon concentrations.4344 No significant correlations were made between these variables. 

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