Irish Times: Mayo gas pipeline controversy: “Five people are in prison because they refuse to allow a powerful multinational to put a gas pipeline through their land. They believe that a pipeline for crude natural gas with a design pressure of 345 Bar is an enormous danger to themselves and their families”: Wednesday 13 July 2005
A chara, - Five people are in prison because they refuse to allow a powerful multinational to put a gas pipeline through their land. They believe that a pipeline for crude natural gas with a design pressure of 345 Bar is an enormous danger to themselves and their families.
Shell and the Government tell us that a quantified risk assessment (QRA) and its subsequent review have shown that the risk is minimal.
QRAs are a useful tool in the right context. That context exists when substantial reliable historical data from similar projects are available. For instance it would be possible to provide reliable QRAs for a new ammonia production plant because so many virtually identical plants have been built and substantial historical data is available.
Unfortunately no such body of historical data exists for the proposed Mayo pipeline because it will be the first of its kind. This means that any QRA can be constructed only by analogy, assumption and perhaps extrapolation. All of these rely on the judgment of the professionals involved. None of them can ever be as reliable as accumulated historical evidence. The mathematics will be just as impressive, but the mathematics will be based essentially on conjecture. It cannot be otherwise since no historical precedents exist against which the risk assessment can be tested.
Engineers (this one included) are not prophets. We know this well and so we rely only on mathematical models which are validated by experimental data. Our models may look wonderful but without experimental confirmation they are no more than speculation. In my own area of limited expertise (chemical engineering), inherited wisdom dictates that any radically innovative process will first be tested by a full-scale pilot plant at perhaps a scale of 10 per cent of full operational level.
This would be particularly true where high-pressure explosive gas was involved. We need pilot plants because common sense and accumulated experience tells us that you cannot forecast everything that might happen in an entirely new and untested process.
So it comes as no surprise to discover there is a glorious confusion about a central aspect of the development. The pipeline is designed to work at 345 Bar and we are told it will be tested up to about 415 Bar. But Shell assures us - and the authors of the QRA confirm - that it will rarely (never?) operate above 120 Bar.
So why is it being so significantly over-designed? Presumably because the designers accept it will have to handle the maximum pressure on occasion but neither they nor Shell are sure how often or under what circumstances. For if they knew why and how often, they could produce a design that would guarantee that such allegedly rare events could be disposed of in a manner that guaranteed the maximum pressure would never be reached in the pipeline. One concludes they don't have sufficient certainty to design for that and that consequentially there is a large measure of uncertainty at the core of this design.
That sense of uncertainty is compounded by the first review of the QRA which concludes that failure in the pipeline could be 15 times more likely than previously forecast. The review also noticed that "vehicles can run off the road" (QRA Review, paragraph 4.9). How much it cost to elicit that high-tech observation we don't know. But it does motivate the authors to recommend that the concrete protection for road crossings of the pipeline should be extended to the full width of the road.
QRAs based on limited or non-existent data are inevitably open to uncertainty. The differences between the BPA review and the original QRA illustrate this but don't guarantee that other uncertainties don't exist. How much else is uncertain? I don't know and most assuredly they don't know.
Uncertain risk is unacceptable risk. Shell should be required to process its gas by tried and tested methods where historic data can be used to do a genuine QRA. One can only hope that in that context the high-powered designers will remember that "vehicles can run off the road". - Is mise,
Senator BRENDAN RYAN (B.E., Chemical Engineering), Seanad Eireann, Dublin 2.
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