The Nimrod Review - Official Documents

The Nimrod Review
ALARP
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expressly stated that “the use of numerical estimates of risk by themselves can ... be misleading and lead to
decisions which do not meet adequate levels of safety”. Thus, in general, qualitative learning and numerical risk
estimates from QRA should be combined with other information from engineering and operational analyses in
making an overall decision. 34
9.19 I have referred above to the ALARP principle, derived from sections 2 and 3 of the HSWA, i.e. the principle that
risks should be reduced to “As Low As Reasonably Practicable”. In the Piper Alpha report, Lord Cullen illustrated
this principle using the (carrot) diagram35 depicted in Figure 9.1 (from which, in due course, the tables in BP1201
that I set out below were derived).
9.20
9.21
Figure 9.1: Lord Cullen’s ALARP diagram
A similar diagram re-appeared in the HSE R2P2 document. What the diagram seeks to illustrate is the principle
that, above a certain level, a risk is regarded as intolerable and cannot be justified on any grounds, except
perhaps in extraordinary circumstances (the ‘INTOLERABLE’ level). At a lower level, a risk can be regarded as broadly
acceptable when the risk becomes truly negligible in comparison with other risks that the individual or society
runs (the ‘BROADLY ACCEPTABLE’ region). Between the broadly acceptable and intolerable regions an activity is
allowed to take place provided that the associated risks have been made ALARP (‘TOLERABLE’).
36 37 In R2P2, the HSE set out its guidance as to what was meant by reducing risks to a level that was ALARP. The
HSE referred, in this respect, to the key case of Edwards v National Coal Board [1949] 1 KB 704, in which the
Court of Appeal held that “… in every case, it is the risk that has to be weighed against the measures necessary
to eliminate the risk. The greater the risk, no doubt, the less will be the weight to be given to the factor of
34 HSE Publication “Reducing Risks, Protecting People”, 2001, page 31.
35 Cullen, fig 17.1. The diagram was introduced to the Piper Alpha Inquiry by Dr. M. S. Hogh, Manager of Projects and External Affairs, Group Safety
Centre, BP International.
36 See paragraph 9.18 above.
37 See also the HSE’s subsequent publication “Principles and guidelines to assist HSE in its judgment that duty-holders have reduced risk as low as
reasonably practicable” dated 13 December 2001.