English

The very high indoor radon concentrations found in the western part of Switzerland in the early80th were at the origin of an extended research programme between 1987 and 1991. The resultsobtained showed a real need for a further detailed radon programme. This should be based on thestate of knowledge, take economical aspects into account and be practically orientated. The mainaim is to deal with elevated concentrations.

In 1995 and 1996 radon concentrations and effective air flows were measured in about 1500 Dutchdwellings built between 1985 and 1993. The goal of this investigation was to describe the trend inthe average radon concentration by supplementing the first survey on dwellings built up to 1984and to quantify the contributions of the most important sources of radon. In the living room of newdwellings the average radon concentration was 28 Bq m-3, which is 50% higher than in dwellingsbuilt before 1970.

For over ten years STUK (The Radiation and Nuclear Safety Authority, Finland) has performedsystematic indoor radon mapping with municipal health authorities. In the most radon-proneprovinces (Uusimaa, Kymi and Hme) there are about 480,000 low-rise dwellings. It is expectedthat in 51,000 homes the action level of 400 Bq/m3 is exceeded, of which about 6,000 have beendetected. In the rest of Finland the numbers are: 820,000 low-rise dwellings, 17,000 expectedcases of exceeding the limit, of which 800 were detected, respectively.

The relation between an increased risk for lung cancer and exposure to indoor radon is assessed inepidemiological studies. Both the quality and reliability of smoking data and the radon exposuredata are of primary importance. Contemporary measurement of radon concentration in thedwellings of the individuals in a case-control study is traditionally used to assess the past radonhistory. These assessments contain large uncertainties since the contemporary measured radonconcentration might not be representative for the situation a long time ago.

A data set of long-term radon measurements in about 2200 houses in southern Belgium has been collectedin an on-going national Rn survey. The spatial variation of indoor Rn concentrations is modelled byvariograms. A radon distribution map is produced using the lognormal kriging technique. A GIS is usedto digitise, process and integrate a variety of data, including geological maps, Rn concentrationsassociated with house locations and an administrative map etc. It also allows to evaluate the relationshipsbetween various spatial data sets with the goal of producing radon risk maps.

It is estimated that more than 5000 householders in the UK have taken steps to reduce high radonlevels in their homes. In 1993 a number of homes with successful remedies installed were asked toparticipate in a study to determine the long term reliability of those systems. This involved the annualremeasurement of the radon concentration in each dwelling.

A soil gas measurement method developed earlier [1] was applied to boreholes drilled to belowfoundation depth. Radon concentration and permeability were measured at 50 cm intervals. Inradon prone areas permeability showed to increase with depth over several orders of magnitude,indicating a low permeability top layer with a thickness of 0.5 m and more. A radon availabilityindex (RAI) was empirically defined and the maximum RAI of each boring proved to be a reliableindicator for radon problems in nearby houses.

Within the Belgian Radon Programme the Belgian Building Research Institute is responsible for theinvestigation of techniques for prevention and mitigation of radon problems in dwellings. One of themost regular actions is the installation of a sub-slab depressurisation (SSD) system. As there are noready-to-use systems available on the Belgian market, a system has to be designed for every specificsituation.

First, models (room models) published in the international literature allowing the exposure togamma radiation indoors due to building materials to be assessed are reviewed and discussed. Forone of them, a sensitivity analysis regarding the effect of changing the parameters (e.g. dimensionsof the room, thickness and density of the walls, etc.) used in calculations is performed.

This paper presents a history of the development of a formalized training and technology transferprogram for radon testers and mitigators in the United States. It explores the experiences andchallenges of the last fifteen years in providing training to an emerging radon industry so that they, inturn, can provide high-quality measurement and mitigation services to the general public.