THE NATIONAL RADON SURVEY IN IRELAND. S.G. Fennell, G.M. Mackin, J.S. Madden and A.T. McGarry

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1 Radon in the Living Environment, 136 THE NATIONAL RADON SURVEY IN IRELAND S.G. Fennell, G.M. Mackin, J.S. Madden and A.T. McGarry Radiological Protection Institute of Ireland, 3 Clonskeagh Square, Clonskeagh Road Dublin 14, Ireland This paper presents the results of the National Survey of Radon in Dwellings carried out by the Radiological Protection Institute of Ireland (RPII). Radon measurements were carried out in 11,319 houses throughout the country. Indoor annual average radon concentrations ranged from 10 Bq/m 3 to 1924 Bq/m 3. The measurement data were grouped on the basis of the 10 km grid squares of the Irish National Grid System and used to predict the percentage of dwellings in each grid square which exceeds the Reference Level of 200 Bq/m 3. Grid squares across the country in which this prediction exceeds 10% are designated High Radon Areas. Keywords: Radon, Survey, High Radon Areas INTRODUCTION In 1990, the Irish Government adopted an annual average radon concentration of 200 Bq/m 3 as the national Reference Level above which remedial action to reduce the indoor radon level in a dwelling should be considered. Results of a population-weighted radon survey carried out by the Experimental Physics Department of University College Dublin (UCD) between 1985 and 1989 estimated that 4% of the national housing stock have radon concentrations above this Reference Level [1]. During this survey measurements were carried out in 1300 houses throughout the country. The more recent National Survey, just completed by the RPII, measured radon in over 11,000 houses. Unlike the population weighted UCD study, this survey was geographically-based across the country. The primary objective of the survey was to determine, in detail, the geographical distribution of radon levels in dwellings in Ireland. As a compromise between the requirement for detailed mapping and the need for sufficient results within each area, the survey was based on small area units; in this case, the 10 km grid squares of the Irish National Grid System. Radon measurements were carried out in selected dwellings in each grid square and the data were used to predict the percentage of dwellings in each grid square with radon concentrations above the Reference Level. Grid squares where the predicted percentage of dwellings with radon concentrations above 200 Bq/m 3 is 10% or greater are designated High Radon Areas. It has been shown that the distribution of radon levels in dwellings approximates a log-normal distribution [2] and that such a log-normal approximation appears to hold whether a whole country, or a smaller area such as a 10 km grid square, is considered [3]. Modelling the distribution of indoor radon concentrations therefore allows the percentage of dwellings exceeding a reference concentration to be estimated [4]. The statistical procedure used in this survey is described by Daly [5] and is based on the approach of Liberman and Resnikoff [6]. SURVEY METHODOLOGY Although in a truly random survey, a valid prediction can be made based on a sample size of only three 1119

2 136 Radon in the Living Environment, dwellings per grid square, a minimum sample size of five dwellings was chosen for this survey. In order to ensure a sufficient sample size, a minimum of 70 householders per grid square were invited to participate. The householders' names and addresses were randomly selected from the Register of Electors. The householders were then invited by letter to participate in the survey. When agreeing to participate householders were asked to locate, as accurately as possible, the locations of their homes on the county map provided. This information was then used to assist in assigning the measurement for each dwelling to the correct grid square. Each participant was issued with two radon detectors, one to be placed in the main living area and the second in an occupied bedroom. The detectors used were CR-39 track etch detectors and the measurement period was twelve months. The measurement period was selected to avoid the necessity of having to correct the results for seasonal variations. On return to the Institute, the detectors were processed and the annual average radon concentration for each dwelling was calculated by averaging the results of the two measurements. The householders were individually notified of their measurement results and, where appropriate, recommendations were made regarding the necessity for remedial action. For grid squares with five houses or more the Geometric Mean (GM) and Geometric Standard Deviation (GSD) were estimated from the data and used to predict the percentage of houses with indoor radon levels exceeding 200 Bq/m 3. In grid squares where there are less than five valid measurements, predictions are made using data from surrounding grid squares. The smoothing technique used is described elsewhere [7]. RESULTS There are 26 counties in the Republic of Ireland, each of which was surveyed on a phased basis between 1992 and Invitations to participate in the survey were sent to approximately 53,000 householders and valid radon measurements were completed in 11,319 dwellings. This represents a sample rate of 1 in 93 houses. For the majority of grid squares, the number of valid measurements exceeded ten per grid square. A summary of the results of these measurements for each county is presented in Table 1. A total of 993 of the dwellings surveyed had radon concentrations in excess of the Reference Level of 200 Bq/m 3. The number of these dwellings, expressed as a percentage of the total number measured, is 8.6%. The summarised results for all the measurements are detailed in Table 2. The mean annual indoor radon concentration for the dwellings measured was 89 Bq/m 3. The maximum value of 1924 Bq/m 3 was measured in a house in the south west of the country. While the overall GSD for the measurements was 2.40, it should be noted that the GSD's for individual grid squares ranged from 1.23 to The radon measurement data presented in Table 1 were used to predict the percentage of dwellings with radon concentrations in excess of 200 Bq/m 3 in each grid square. The results are presented in the Radon in Irish Dwellings map, illustrated in Figure 1. The predictions are represented by 5 percentage bands i.e. <1%, 1-5%, 5-10%, 10-20% and >20%. The two percentage bands 10-20% and >20% delimit the High Radon Areas. For a number of the grid squares as many as 50% of dwellings are predicted to have radon levels greater than 200 Bq/m

3 Radon in the Living Environment, 136 DISCUSSION It is evident from figure 1 that there is considerable geographical variation in indoor radon concentrations across the country. Approximately one third of the grid squares have now been classified as High Radon Areas. In particular the south east of the country, and areas in the west, have a large number of affected squares. It is possible that the underlying geology may be a contributory factor to the prevalence of these High Radon Areas, and a detailed analysis of this correlation will be undertaken shortly. This survey is a geographically based survey. However, in estimating the scale of the radon problem, the housing density as well as the extent of High Radon Areas across the country must be taken into account. When the population distribution throughout the country is taken into consideration the percentage of houses predicted to have levels in excess of 200 Bq/m 3 is 5.3%. Based upon this figure it is estimated that approximately 55,000 houses in Ireland, or 190,000 householders, have indoor radon levels exceeding 200 Bq/m 3. In Ireland, an exposure-dose conversion factor where 40 Bq/m 3 over a 7000 hour year gives rise to an effective dose of 1 msv per year has been adopted [8]. Using this conversion factor it is estimated that approximately 190,000 householders are receiving doses greater than 5 msv per annum within their homes. It is now an objective of the RPII to encourage householders living in High Radon Areas to carry out measurements in their homes and to undertake the appropriate remedial measures if elevated levels of radon are found. Since July 1998, the Irish Building Regulations require that every new house incorporate some degree of radon preventive measures at the time of construction. The Technical Guidance Documents [9] which provide guidance on compliance with the requirements of the Building Regulations now require that the foundations in all new dwellings incorporate a potential means of extracting radon from the sub-structure. In addition, new dwellings in High Radon Areas must be fitted with a sealed membrane of low permeability. REFERENCES [1] McLaughlin, J.P. and Wasiolek, P., Radon levels in Irish dwellings. Radiation Protection Dosimetry, 24,(1/4), p [2] Commission of the European Communities, Exposure to natural radiation in dwellings of the European Communities. Luxembourg: Commission of the European Communities. [3] National Radiological Protection Board, Radon affected areas: Cornwall and Devon. Documents of the NRPB, 1,(4), p [4] Miles, J.C.H., Mapping the proportion of the housing stock exceeding a radon reference level. Radiation Protection Dosimetry, 56,(1/4), p [5] Daly, L., Personal communication. [6] Liberman, G.J. and Resnikoff, G.J., Sampling plans for inspection by variables. American Statistical Association Journal, June 1955, p [7] Fennell, S.G. et al., Radon Risk Mapping in Ireland. 137, Radon in the Living Environment, April 1999, Athens, Greece. [8] Madden, J.S. et al Radon in Selected Areas of Ireland RPII, - 94/3 [9] Department of the Environment, Building Regulations, Technical Guidance Document C site preparation and resistance to moisture. Department of the Environment. Dublin: Stationary Office. 1121

4 136 Radon in the Living Environment, Table 1: Summary of Survey Results for each county County No. of Dwellings Measured No. >200 Bq/m 3 (% of dwellings measured) Mean Max Carlow (15%) Cavan (3%) Clare (9%) Cork (6%) Donegal (4%) Dublin (4%) Galway (15%) Kerry (6%) Kildare (6%) Kilkenny (9%) Laois (5%) Leitrim (5%) Limerick (8%) Longford (6%) Louth (11%) Mayo (13%) Meath (8%) Monaghan (3%) Offaly (2%) Roscommon (7%) Sligo (20%) Tipperary (7%) Waterford (12%) Westmeath (7%) Wexford (12%) Wicklow (13%)

5 Radon in the Living Environment, 136 Table 2: National Survey Results Number of Dwellings Measured No. Measured >200 Bq/m 3 Min Max Mean GM GSD 11,

6 136 Radon in the Living Environment, Normal :48 >20% 10-20% 5-10% 1-5% <1% Insufficient Data Figure 1: Radon in Irish Dwellings 1124

The RPII s radon road shows. Hugh Synnott Scientific Officer Radon Advice Section

The RPII s radon road shows. Hugh Synnott Scientific Officer Radon Advice Section The RPII s radon road shows Hugh Synnott Scientific Officer Radon Advice Section 1 Structure of Presentation Background Main objectives of road shows Structure and format of road shows Impact of road shows