Handbook of Radon.
51. Radon protection and affected areas: a perspective.
It is known that radon levels in the ground can be misleading as an indicator of possible problems indoors. Radon is ubiquitous in rocks and soils in the UK, as elsewhere, and its discovery at 30,000 Bq/m3 in soil gas is unremarkable. Thus, it can become necessary to consider application of radon protection methods to new houses within defined areas.
It is an attractive idea for houses and other buildings to be constructed so as to guarantee that they will have low radon levels. Indeed, the Institution of Environmental Health Officers have suggested that radon protection be extended across the UK. Calculations of marginal cost-effectiveness do not support such widespread application, especially in view of the limited data on performance yet available.
However for the key affected counties, or at least those parts that are significantly affected, it may represent good value to incorporate radon protection, since some of the possible methods are far easier to install at time of initial construction.
It must be remembered that even in Devon and Cornwall only around 10 to 15% of new houses would, on average, be expected to exceed 200 Bq/m3 if built conventionally. The percentage having much higher levels would be expected to be tiny, perhaps 1% overall but concentrated on a few sites.
Many of the highest level radon houses discovered to date are in areas where there will be little new building work, because of protection afforded by National Park or Outstanding Natural Beauty status.
The NRPB have defined as "affected by radon" areas of the country that (from their surveys) they could suggest had a more than 1% chance of a house above 200 Bq/m3. This now includes all of Devon, Cornwall, and Northants, and parts of Derbyshire and Somerset. Scotland may also have areas delineated.
What is meant by an affected area is that there is a greater than 1% chance of finding a house above the action level of 200 Bq/m3, or in other words, a house that presents a calculated risk to the occupants about equal to smoking one cigarette per day for non-smokers. Recent EPA figures show an even lower risk factor for people who have never smoked.
Whatever the exact risk, it seems of the same order as sharing an office or home with a smoker. Therefore, it could be suggested that areas of the country be declared as being affected by passive smoking if more than one home or office out of a hundred gave rise to the same risk factor as is calculated for 200 Bq/m3 of radon. A sense of perspective may be needed in delineating affected areas, because of the costs of radon protection measures.
The essential technique employed to date in the UK for passive radon protection is to lay an airtight membrane, usually a plastic sheet, completely across the site. Effectiveness is achieved if air flow from the ground can be precluded. It is of little significance if the membrane is permeable to radon, since diffusion flow alone will not usually give rise to high indoor radon levels. The difficulties of radon protection as practised to date are simply those of quality control and practicability on site.
No detailed results have yet been published from the UK field trials in 1989/90 and in over 450 houses in 1990/91. The discussion that has appeared seems simplistic in view of the available data set. In the meantime passive stack vents are being evaluated as an adjunct to across-site membranes. Performance is expected to be strongly a function of stack design and location.
What is required is an analysis of the cost and effectiveness of various methods, to include running costs. For new housing these may be lower than for typical older stock because floor designs that are ideal for sub-floor suction can be specified. Small fans or even passive stack vents may suffice.