The Beauly–Denny pylons: more about relative risk

h/tip to Kate

Scottish Government plans to build a power line between Beauly (Cromarty) and Denny (Stirlingshire) have given rise to protest on health grounds. The line will carry 400 kilo volts and cross 137 miles at a height of 53 metres. Parts of an existing line will be dismantled and parts will go underground, but no underground work is expected at Stirling, the major centre of population on the route.

A Daily Record report earlier this year mentions leukaemia as a known risk of living under electricity pylons.  It claims that childhood leukaemia rates under high voltage lines are twice what they are away from such lines, and also mentions depression and suicide as further risks associated with high voltage lines. Dr Richard Simpson MSP criticises the absence of any proper discussion of these health issues.

A doubling of risk is fairly low. To compare with the risks from secondary smoke: the risks (of lung cancer or heart attack) commonly said to result from exposure to secondary smoke are around 24 per cent, or a relative risk of 1.24, which is considerably less than 2 (indicated by a doubling of risk). Many risks have to be at least 3 before they are taken seriously enough to merit investigation as to whether they can constitute a cause of an outcome.

Dr Richard Simpson does himself some credit in this instance. He is clearly a man who believes in the precautionary principle: he favours smoking restrictions on health grounds – even though a risk of 1.24 does not constitute a meaningful risk in any sense of the word. A doubling of risk (an increase by a factor of 2) is perhaps another matter, especially when discussing childhood cancers, rather than the alleged ill effects of secondary smoke, which are generally diseases of old age. As Dr Simpson says: we may decide after an investigation about the likely health impact that we still want to have the project, but we are not even having the discussion about health. Stirling residents see the government burying the power lines in areas of scenic significance but not in areas where large populations live.

This link discusses some of the issues around electro magnetic fields (EMFs) that surround pylons. Paragraph 12 helpfully gives the exposure risk rates and compares pylons with both active and passive smoking. It says that secondary smoke exposure increases risk of heart attack from 10 in 100,000 non-smokers to 12 in 100,000 exposed non-smokers. Leukaemia rates increase from 3 in 100,000 to about 11 in 100,000 following exposure to EMFs. This is much more than double but the rate varies according to the strength of exposure, generally with results between 2 and 4.

Officially the verdict goes like this: 'the evidence does not establish that exposure to EMFs is a cause of cancer although it does provide some evidence to suggest the possibility exists'. That's probably fair, for a relative risk reaching 4. So the Scottish Government should recognise the fears of the Stirling residents and acknowledge that there is at least some ground for their fears, rather than ignoring the issue altogether.

As for the Scottish Government's view of secondary smoke, if it can make light of a relative risk of up to 4 on childhood leukaemia so far as to expose whole communities to such a risk, it is hard to understand how a risk of 1.24 (alleged risk from secondary smoke) is so serious that it can deprive every pub, club, bingo club, bowling alley (ad infinitum) in the land of any discretion in how this problem should be managed.