Kurnal, you are perhaps correct. However, wasn't Buncefield built to prescriptive standards? I think we would all agree that we need benchmarks but the interesting thing is that we can veer either side of them if we carry out a risk analysis. Knowing what the benchmark is can be a start, knowing the risk a second and computing the risk against the benchmark may give you an answer. If we apply benchmark standards all the time nothing would get built, certainly not the Gherkin in London and other equally fine buildings across the UK. The substitution of one thing for another to enhance the opportunity to build has taken place for many years, we certainly would not build a Pyramid now. Surely the approach should be to analyse the risk against the benchmark standard, in this case HTM, and assess it. The interesting point of course, is where the prescription came from in the first instance, if anyone knows or can remember and, is it suitable now. "You cannot reverse a fire engine more than 20 metres, why, because horses in the long ago days would not walk backwards further than that or its imperial conversion rate". However, B5 and BS5588 Part 5 still say the same thing, is it relevant to those vast new trucks and their skilful drivers? I could be more boring, the point is do an FRA assess it all from benchmark standards and make a decision based on "as low as reasonably practicable" and defend that if necessary in a court of law.