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talking point

A more sensible approach is needed towards precautions against geological carbon dioxide, says Graham Cannon.

As someone who earns much of his living by testing for landfill gas, you might expect me to want sites to be investigated for as long and as comprehensively as possible. Putting aside my own profit, I feel it is very important that the problems associated with landfill gases are looked at more rigorously in comparison with the other risks we face in our daily lives.

After a house in Loscoe, Derbyshire, was destroyed in 1986 in an explosion caused by methane gas from a nearby landfill site, a lot of research and consideration was given to landfill gases and guidelines were developed to overcome methane difficulties.

I have no wish to challenge the recommendations for this difficult gas, which is explosive at relatively low concentrations (5%). However, following on methane's coat tails comes concern about carbon dioxide.

Recommendations are given (by CIRIA and others) on building precautions where underground carbon dioxide is found, and it is interesting to compare these thresholds with common sources of the gas.

Where levels in the ground exceed 1.5%, a gas-proof membrane is required;

greater than 5% and special underfloor ventilation is also needed.

However, all humans exhale large volumes of carbon dioxide at 3%, an ordinary family car churns out vast quantities of carbon dioxide at 12%, not to mention far more toxic CO, NOX and ozone. (How many readers have an integral garage? ) In other words, we are placing membranes under a building to keep out trivial levels of carbon dioxide, whereas in their homes people, pets and equipment are generating far greater quantities in higher concentrations.

Testing guidance is based on waste management reports which are concerned with landfill sites where concentrations of gas are high. These state that tests should be carried out regularly over three months, including tests at barometric pressures below 1,000mb. On a project close to a landfill site, or on suspect material, this is very appropriate, but on a more typical site, it can be overkill.

I have many projects on my files where small extensions to buildings (which have no gas protection) more than 200m from possible landfill sources, on clay soils, are requiring high specification gas monitoring boreholes and long-term testing. This adds to building costs and, in the long term, reduces the UK's competitiveness.

Perhaps a greater concern than the cost is the insistence on three-month testing, which frequently seriously delays fast-track projects and can mean that business opportunities are missed.

In recent years, professionals have embraced the idea of the risk assessment approach to landfill gas but, once a judgement has been made, the regulatory authorities must accept that risks are abundant in life. They seem to be looking for a 'risk elimination' outcome. The precautionary principle will be appropriate in new or hazardous activities, such as genetically modified crops, the nuclear industry, genetic medical science, but there is little point in attempting to reduce problems from carbon dioxide to infinitesimal levels when there are day-to-day hazards staring us the face.

Let us stand back a little and look at the broad picture.

More than 3,000 people are killed on Britain's roads every year. Millions are killed by self-inflicted smoking; if someone has been a serious smoker for 30 years or so, their chances of living through that period are worse than Russian roulette. In any one year, every person has a one in 80 chance of dying.

In contrast, despite the vast majority of British homes having no protective membranes, I know of no UK incidents of householder deaths resulting from groundsourced carbon dioxide. You are more likely to be injured by a wooden spoon.

I am not looking to discard the recommendations on carbon dioxide, but would like to see a pragmatic 'can do' attitude to overcoming these difficulties rather than the box-ticking, audit-style regime that is developing.

I know it is going to mean less work for me, but let us take a sensible view on these risks and spend the nation's precious resources on things that are more worthwhile.

lGraham Cannon is principal engineer of Worms Eye Geotechnical, a Lancashirebased contaminated land investigation company.

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