A cost-effectiveness analysis of radon protection methods in domestic properties: a comparative case study in Brixworth, Northamptonshire, UK
Introduction
Radon is a naturally occurring radioactive gas, which, as it decays, produces radioactive progeny that can deliver a dose of radiation to those exposed to it (Hughes, 1999). When concentrated in domestic properties radon will, because of associated radiation, threaten human health. A number of studies in recent years have demonstrated a link between high levels of radon in domestic properties and a higher incidence of lung cancer among those living in the properties (Lubin and Boice, 1997, Denman and Phillips, 1998, Darby et al., 1998, Darby et al., 2001, Darby et al., 2005, Kreienbrock et al., 2001, Krewski et al., 2005).
Faced with the threat to human health that radon represents, the National Radiological Protection Board (NRPB) in the UK (since 2005 part of the UK's Health Protection Agency) identified in 1990 an “Action Level” of 200 Becquerels per cubic metre (Bq m−3). Areas where more than 1% of domestic properties have radon readings above this level are classified by the NRPB as radon “Affected Areas” and, if readings above the Action Level occur in specific existing domestic properties, householders are advised to remediate against the gas' effects. The primary method of remediation in the UK is to install an under floor sump fitted with a fan that captures and then expels the radon into the atmosphere. The method can also be applied in new properties, the sump and fan being fitted during construction, but an alternative available in these is to install a radon-proof membrane during construction that prevents the gas from entering the property.
As a consequence of evidence emerging on radon's effects, the Building Research Establishment (BRE) (1992) recommended that all new properties in specified geographical areas in the UK be built with radon protection, advice recognised by legislation in 1993. This was updated in 1999 since when regulations require that all new properties have a membrane installed if 3% or more of existing properties in an area are above the Action Level (BRE, 1999). The regulations do not apply, therefore, in all Affected Areas. New properties must also be fitted with a sump if more than 10% of properties in an area have readings above the Action Level. A fan can then be added if subsequent tests reveal that one is needed to reduce radon levels further.
The current regulations are in force in the village of Brixworth, Northamptonshire, UK, the geographical location of which is shown in Fig. 1. Brixworth lies in a radon Affected Area and is well known for its high-indoor radon levels. Green et al. (2002) report 16.2% of properties to be above the Action Level in the postcode sector (NN6 9) that covers the village. This sector, it should be noted, covers a wider geographical area than that of Brixworth, so the value is not an exact representation of radon levels in the village. It is, however, the most detailed available in the public domain. Moreover, all other villages within the postcode sector share the geology that gives rise to the elevated radon levels in Brixworth. The local bedrock is of Inferior Oolite material and the villages are situated on hills of Northamptonshire Sand (Hains and Horton, 1969), a permeable rock formation regarded as a significant radon source in Northamptonshire (Sutherland and Sharman, 1996). The proportion of properties above the Action Level reported by Green et al. (2002) is, therefore, highly likely to reflect radon levels in Brixworth.
Despite BRE regulations, however, Denman et al. (2005) found, when they tested a sample of properties for radon in the village, all of which were fitted with membranes and sumps, that a significant number had readings above the Action Level. This result is consistent with those from two Irish studies reported upon by Synnott et al. (2004), suggesting that experience with the sample is not an isolated case. These failures are most likely caused by problems during construction, although later alterations or settling of properties after construction may also be factors.
Potential problems with membranes could have implications for their cost-effectiveness and it is this aspect of their use in the sample of properties tested by Denman et al. (2005) that is considered in this study. Their estimated cost-effectiveness is then compared with that of an alternative regulatory regime. While the results relate to the particular case of Brixworth, the analysis has wider implications for protecting new properties against radon's effects and for the regulations that support this aim.
In Section 2, the nature of the alternative regulatory regime considered is outlined briefly. Section 3 then describes the method used to estimate the cost-effectiveness of the two regimes. The results obtained from applying the method described are presented in Section 4. These show the alternative regime to be more cost-effective than the current one. The subsequent discussion in Section 5 considers the implications of the results and their limitations. Section 6 concludes with proposals for further research to establish whether a change in the current regulatory approach is justified.
Section snippets
An alternative regulatory regime
Although membrane use has been the method required by building regulations in the UK for some years, it is possible to envisage alternative regimes in which protection against radon in new properties is achieved by different means. The alternative regulatory regime considered in this study is the following:
- 1.
construct all new properties without protection against radon;
- 2.
upon completion, test all new properties for radon using NRPB protocols (Wrixon et al., 1988);
- 3.
remediate properties above the
Method
Analysis of the two regimes was based on results from the radon tests reported in Denman et al. (2005), who also detail how the sample and readings were obtained. The tests were conducted between December 2003 and May 2004 in 65 houses built in Brixworth since 1992. All the properties had membranes and sumps installed during construction, a point confirmed with the house builders concerned. The cost-effectiveness of both regimes was estimated using cost per “quality-adjusted life-year” (QALY)
Results
The distribution of hypothetical readings for the 65 properties in the sample, shown in Fig. 3, was the starting point for considering the effects of both regimes. For the current regime, when these values were compared with the actual test readings from Denman et al. (2005) the reduced exposure to radon in the properties and the consequent fall in radiation dose due to the membranes and sumps could be estimated. Results for these two effects are given in Table 1. Also summarised in Table 1 are
Discussion
Given these results, the alternative regime would appear for the Brixworth sample to be both more cost-effective than installing membranes and sumps and more robust to changing certain assumptions. That said, the cost-effectiveness of both regimes compares well with those of other medical interventions, as Fig. 5 demonstrates. Similarly, both estimates are considerably below the threshold of £30 000 per QALY gained implicitly adopted by the UK's National Institute for Health and Clinical
Conclusions
Overall, the evidence presented suggests the alternative regime for protecting those in new properties against the effects of radon is more cost-effective in Brixworth than the current regime, and makes a prima facie case for re-examining the present approach. It also raises concerns that the current trigger of 3% of properties above the Action Level for installing membranes and sumps is suspect. If the proposed alternative regime is more cost-effective than installing membranes and sumps in
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