Anthony R Denman

Radon in the Creswell Crags permian limestone caves

An investigation of radon levels in the caves of Creswell Crags, Derbyshire, an important Site of Special Scientific Interest (SSSI) shows that the Lower Magnesian Limestone (Permian) caves have moderate to raised radon gas levels (27-7800 Bq m(-3)) which generally increase with increasing distance into the caves from the entrance regions. This feature is partly explained in terms of cave ventilation and topography. While these levels are generally below the Action Level in the workplace (400 Bq m(-3) in the UK), they are above the Action Level for domestic properties (200 Bq m(-3)). Creswell Crags has approximately 40,000 visitors per year and therefore a quantification of effective dose is important for both visitors and guides to the Robin Hood show cave. Due to short exposure times the dose received by visitors is low (0.0016 mSv/visit) and regulations concerning exposure are not contravened. Similarly, the dose received by guides is fairly low (0.4 mSv/annum) due in part to current working practice. However, the risk to researchers entering the more inaccessible areas of the cave system is higher (0.06 mSv/visit). This survey also investigated the effect of seasonal variations on recorded radon concentration. From this work summer to winter ratios of between 1.1 and 9.51 were determined for different locations within the largest cave system.

A review of the cost effectiveness of radon mitigation in domestic properties in Northamptonshire

The costs of remedial work, and the radon level reduction achieved, have been studied in a series of domestic properties in Northamptonshire, which is a radon affected area. The cost-effectiveness of the series is similar to published theoretical estimates for proposed national remediation programmes, and five times more effective than our similar analysis for the National Health Service workplace, if it is assumed that 100% of householders discovering levels above 300 Bq m-3 implement remediation. In practice, in the UK, far fewer of those who arrange an initial radon test proceed to remediation, but this domestic programme could be cost effective if more than 5% carry out remediation. Our series confirms that a considerable number of householders with radon levels in the 200 to 300 Bq m-3 range do not seek or implement remediation work.

Time activity modelling of domestic exposures to radon.

Radon gas occurs naturally in the environment with a variable distribution. In some areas radon concentrates sufficiently within the built environment that it is considered as a public health risk. It is possible, successfully, to reduce radon levels in the built environment, and it has been shown that such remediation programmes can be justified in terms of the costs and benefits accruing. However, the estimated dose received by people in their homes depends on the time spent indoors. The research presented here uses data derived from time activity surveys in Northamptonshire, together with radon data from a representative home, to model potential exposures for different population sub-groups. Average home occupancy ranged from 14.8h (probable error 2.5h) for students to 17.7 (3.1) h for adults; schoolchildren spent an average of 14.9 (1.2) h at home. Over a quarter of adults, however, were in the home for 22 h on more. These differences in occupancy patterns lead to substantial differences in radon exposure. In a home with an average hourly ground floor radon concentration of 467 Bqm(-3), modelled hourly average exposures ranged from ca. 250 Bqm(-3) for students and school children, to over 340 Bqm(-3), for women based at home. Modelled exposures show a non-linear association with total time spent at home, suggesting that exposure estimates based on linear models may provide misleading estimates of health risks from radon and the potential benefits of radon remediation. Highest hourly exposures are likely to be experienced by people with highly occupancy, living in single-storey, ground floor accommodation (for example, the elderly the infirm and non-working young mothers). Since these may be least aware of radon risks, and least able to take up remediation measures, they should be specifically targeted for radon monitoring and for assistance in remediation schemes.

Lorenz Curve and Gini Coefficient: novel tools for analysing seasonal variation of environmental radon gas.

Using a methodology derived from Economics, the Lorenz Curve and Gini Coefficient are introduced as tools for investigating and quantifying seasonal variability in environmental radon gas concentration. While the Lorenz Curve presents a graphical view of the cumulative exposure during the course of the time-frame of interest, typically one year, the Gini Coefficient distils this data still further, to provide a single-parameter measure of temporal clustering. Using the assumption that domestic indoor radon concentrations show annual cyclic behaviour, generally higher in the winter months than in summer, published data on seasonal variability of domestic radon concentration levels, in various areas of the UK, Europe, Asia and North America, are analysed. The results demonstrate significantly different annual variation profiles between domestic radon concentrations in different countries and between regions within a country, highlighting the need for caution in ascribing seasonal correction factors to extended geographical areas. The underlying geography, geology and meteorology of a region have defining influences on the seasonal variability of domestic radon concentration, and some examples of potential associations between the Gini Coefficient and regional geological and geographical characteristics are proposed. Similar differences in annual variation profiles are found for soil-gas radon measured as a function of depth at a common site, and among the activity levels of certain radon progeny species, specifically (214)Bi deposited preferentially in human body-fat by decay of inhaled radon gas. Conclusions on the association between these observed measures of variation and potential underlying defining parameters are presented.

Tidal synchronicity of built-environment radon levels in the UK

In our recent work on radon in UK homes the authors have observed tidal-periodic variations in built-environment radon levels and here report results from our ongoing investigations. These tidal variations have been quantified using a variety of analytical techniques, including a novel correlation technique developed as part of this investigation. The observed variations are cyclic at the 14-15 day tidal period and lag new/full moons by varying periods of days, the magnitude of the variation and lag being dependent on factors such as location, underlying geology and rock/soil hydration. As well as quantification and discussion of tidal effects on radon levels, the potential effects of such phenomena on the reliability of short-term radon measurements are discussed.

A cost-effectiveness analysis of a residential radon remediation programme in the United Kingdom

SummaryAs residential radon programmes of identification and remediation have proceeded, so questions have been raised about their costs and benefits. This study presents a generalizable model for estimating the cost-effectiveness of a radon mitigation programme using the methodological framework now considered appropriate in the economic evaluation of health interventions. Its use will help to inform future discussion of radon remediation and lung cancer prevention programmes. Data from Northamptonshire were analysed, resulting in a societal cost-effectiveness ratio of £13250 per life-year gained in 1997. The percentage of houses found to be over the action level, and the percentage of householders who decide to remediate are shown to be important parameters for the cost-effectiveness analysis. Questions are raised about the particular importance of perspective in this type of analysis and suggestions are made for future research directions.

The health benefits and cost effectiveness of the radon mitigation programme in NHS properties in Northamptonshire

A comprehensive radon remediation programme in NHS properties in Northamptonshire, where 11 100 staff are employed working on 83 separate sites, has been in progress since 1992, and has resulted in many locations with raised radon levels being identified and remediated. This paper considers the dose saving achieved and costs of the remediation to derive a value for the cost-effectiveness of the programme. A value of £184 000 per Man-Sievert of annual dose reduction was obtained, which is around half the figure calculated by the NRPB in its recent initiative to reduce patient doses from dental x-rays in the UK, based on cost-benefit analysis. Thus similar comprehensive radon remediation programmes in any workplace in Radon Affected Areas can be justified. The cost of this workplace programme is, however, a factor of about 4 times more expensive than the theoretical estimates for domestic radon mitigation programmes found in the literature, and the reasons for this difference are considered.

Using the European Community Radon Software to estimate the individual health benefits of a domestic radon remediation programme

Radon can be present in domestic properties at high enough levels to pose a health risk. Such levels can usually be reduced by simple means. Studies on a group of radon-remediated homes in Northamptonshire, a radon affected area, have estimated the health benefits and cost effectiveness from remediation and have shown that remediation can be justified. These assessments have been based on collective population-average risk coefficients. The advent of the European Community Radon Software (ECRS) permits the consideration of individual risk. In particular, it can take into account individual smoking habits, which significantly affect risk, as current scientific opinion is that risks from radon and smoking are multiplicative. This note indicates how the software can be used, and the usefulness of this approach.

Do the UK workplace Radon Action Levels reflect the radiation dose received by the occupants

In the UK, Action Levels for radon have been established at 400 Bq m(-3) for the workplace and 200 Bq m(-3) for the home. We have estimated the dose received by occupants of rooms with radon levels near or above the Action Level, using hourly radon readings, and a questionnaire to record occupancy. In the workplace, results for 73 staff suggest that doses are lower than expected, partly due to part-time working and partly due to the mobility of staff. The 75% quantile for the series, corrected to a 37 hour week, is 5.2 mSv at 400 Bq m(-3). Compared to the current annual limit for radiation workers, the Action Level could be increased, but the current Action Level is compatible with the recent EEC Directive requiring a lower dose limit. However, when raised radon levels in the workplace were reduced by remediation in the series we studied, the dose reduction to staff was consistently around half of the radon level reduction. Although it would be appropriate to study more locations, this suggests an Action Level for remediated workplaces of 200 Bq m(-3). Finally, in a limited series of dose assessments in domestic properties, we found that doses could considerably exceed 5 mSv at the 200 Bq m(-3) Action Level, primarily because the sample included an example of high occupancy, in our case several Asian wives in purdah, whose occupancy was almost total.

Effectiveness of secondary radon protection in Northamptonshire houses

Northamptonshire is classified as a radon affected area, with greater than 1 per cent of houses being above the UK action level of 200Bq/m–3. New houses, in areas where >10 per cent are above the action level, have to have primary protection of a radon‐proof membrane and secondary measures such as a non‐activated radon sump. New houses, in areas where 3‐10 per cent are above the action level only need the secondary measures. This research calls into question the effectiveness of this strategy. The use of radon potential maps, rather than radon in building maps, would have demonstrated that radon “hot spots”, where a very high percentage of houses are over the action level, can occur on a range of geology. One estate, at Higham Ferrers, had 35 per cent over the action level, even though it had been classified as only requiring secondary measures. The reluctance of occupiers in the UK to instigate monitoring and remediation means that very few will have their house tested for radon and activate the sump, by fitting a fan, if that is required. This paper provides arguments that support the view that it would be more effective to have primary and secondary measures introduced in all new houses in radon affected areas.