The value of Seasonal Correction Factors in assessing the health risk from domestic radon: a case study in Northamptonshire, UK

Following an intensive survey of domestic radon levels in the United Kingdom (UK), the former National Radiological Protection Board (NRPB), now the Radiation Protection Division of the Health Protection Agency (HPA-RPD), established a measurement protocol and promulgated Seasonal Correction Factors applicable to the country as a whole. Radon levels in the domestic built environment are assumed to vary systematically and repeatably during the year, being generally higher in winter. The Seasonal Correction Factors therefore comprise a series of numerical multipliers, which convert a 1-month or 3-month radon concentration measurement, commencing in any month of the year, to an effective annual mean radon concentration. In a recent project undertaken to assess the utility of short-term exposures in quantifying domestic radon levels, a comparative assessment of a number of integrating detector types was undertaken, with radon levels in 34 houses on common geology monitored over a 12-month period using dose-integrating track-etch detectors exposed in pairs (one upstairs, one downstairs) at 1-month and 3-month resolution. Seasonal variability of radon concentrations departed significantly from that expected on the basis of the HPA-RPD Seasonal Correction Factor set, with year-end discontinuities at both 1-month and 3-month measurement resolutions. Following this study, monitoring with electrets was continued in four properties, with weekly radon concentration data now available for a total duration in excess of three and a half years. Analysis of this data has permitted the derivation of reliable local Seasonal Correction Factors. Overall, these are significantly lower than those recommended by HPA-RPD, but are comparable with other results from the UK and from abroad, particularly those that recognise geological diversity and are consequently prepared on a regional rather than a national basis. This finding calls into question the validity of using nationally aggregated Seasonal Correction Factors, especially for shorter exposures, and the universal applicability of these corrections is discussed in detail.     

The effects of geology and the impact of seasonal correction factors on indoor radon levels: a case study approach

Geology has been highlighted by a number of authors as a key factor in high indoor radon levels. In the light of this, this study examines the application of seasonal correction factors to indoor radon concentrations in the UK. This practice is based on an extensive database gathered by the National Radiological Protection Board over the years (small-scale surveys began in 1976 and continued with a larger scale survey in 1988) and reflects well known seasonal variations observed in indoor radon levels. However, due to the complexity of underlying geology (the UK arguably has the world's most complex solid and surficial geology over the shortest distances) and considerable variations in permeability of underlying materials it is clear that there are a significant number of occurrences where the application of a seasonal correction factor may give rise to over-estimated or under-estimated radon levels. Therefore, the practice of applying a seasonal correction should be one that is undertaken with caution, or not at all. This work is based on case studies taken from the Northamptonshire region and comparisons made to other permeable geologies in the UK.     

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 critical comparison of the cost-effectiveness of domestic radon remediation programmes in three counties of England

Radon remediation programmes in domestic dwellings were carried out in five areas, from three counties of England, and the total costs obtained. A single company, which abided by the Code of Practice of the Radon Council of Great Britain, carried out the remediation. The dose savings from the programmes were calculated and used to estimate the number of lung cancers averted. The data obtained allowed the cost-effectiveness of the remediation programmes in each area to be calculated. The remediation programmes in three areas (Northants 2, 3 and North Oxfordshire) were cost-effective whereas those in two areas (Northants 1 and North Somerset) were not. To be cost-effective, the Northants I and North Somerset areas would need to increase the number of householders that carried out remediation, if they were over the UK Action Level. Health policy makers should concentrate their resources on communities in areas where there is a significant proportion of dwellings above the UK Action Level and where the number of properties being remediated is low.     

The practical use of electrets in a public health radon remediation campaign

As part of a long-term assessment of domestic radon in Northamptonshire, England, a batch of 50 commercially available electrets was deployed for nearly 1,000 exposures, individual exposure periods ranging from one to eight weeks. Responsivity was comparable with that of recently-calibrated Durridge RAD-7 continuously-monitoring equipment. Voltage history analysis indicated mean voltage decay during manufacturers' QA assessment of 0.059+/-0.026 Vday(-1), increasing to 0.114+/-0.073 Vday(-1) during storage to first use and to 0.204+/-0.49 Vday(-1) during inter-deployment storage. At a representative elevated radon concentration of 500 Bqm(-3), the resulting perturbation is 3% over a 7-day deployment; at the typical mean Northamptonshire level of 80 Bqm(-3) it approaches 22%. Each electret can be used for up to 25 measurements, which makes the technology attractive for organisational use. It is not suited for deployment by individual householders.     

Time-integrating radon gas measurements in domestic premises: comparison of short-, medium- and long-term exposures

To identify the most applicable technology for the short-term assessment of domestic radon levels, comparative assessments of a number of integrating detector types, including track-etch, electret and activated charcoal were undertaken. Thirty-four unremediated dwellings in a high-radon area were monitored using track-etch detectors exposed for one-month and three-month periods. In parallel, one-week measurements were made in the same homes at one-month intervals, using co-located track-etch, charcoal and electret detectors exposed simultaneously, while three of the homes were also monitored by continuous-sampling detectors at hourly intervals over extended periods. Calibration of dose-integrating devices against each other and against continuous-monitoring systems confirmed good responsivity and linearity. Although track-etch, charcoal and electret devices are suitable in principle for one-week measurements, zero-exposure offset and natural radon variability cause many one-week results to be equivocal, necessitating repetition of the measurement. One-week exposures can be reliable indicators in low-radon areas or for new properties, but in high-radon areas, the use of three-month exposures is indicated. This analysis also established confidence limits for short-term measurements.