HID's approach to ALARP decisions



1.  This note summarises the approach that HID expects inspectors to take when making case-specific decisions on whether risks are as low as reasonably practicable (ALARP) during assessment of safety cases/reports (or other formal documents), or enforcing compliance with the law. This note does not cover the normal management arrangements (adequate supervision, peer review, etc.) that are in place to ensure that the approach is properly implemented. This SPC replaces SPC/Permissioning/09 which has been withdrawn.


2.   HID's approach to ALARP decisions mirrors that explained in "Reducing Risks, Protecting People; HSE's decision-making process" and "Principles and Guidelines to assist HSE in its judgements that duty holders have reduced risks as low as reasonably practicable".

3.  R2P2 emphasises that people increasingly rely upon regulators like HSE as a source of reassurance about the arrangements put in place by duty holders for protecting people. If that trust is not to be threatened, HID must properly discharge its function to ensure that duty holders have put in place all necessary measures to prevent major accidents and limit their consequences.   

4.  HID's approach to ensuring compliance with the requirements of the permissioning regimes within its remit needs to be fully consistent with the Governments Enforcement Concordat as amplified in HSE's enforcement policy statement.

5.  HID's approach to ALARP decisions needs to ensure that all staff involved in case-specific ALARP decisions:

Interpretation of the legal basis of ALARP judgements

6.  Generic guidance on the legal basis for making ALARP judgements is given in the HSE principles and guidelines document. The main points are:

The sacrifice (normally expressed in monetary terms) is that needed to implement additional measures to reduce risks. Benefits gained by duty holders (eg reduced plant replacement costs) should be offset against costs. The comparison is between the net sacrifice and the benefits of risk reduction (lives saved, reduced costs of the emergency services etc). The assessment needs to be proportionate (see sector specific guidance for further information on proportionality).

Making ALARP judgements

7.  HSE is only concerned with the risks to people, although we should be mindful that measures intended to reduce risks to people may conflict with the need to reduce risks to the environment. For the risks to people to be reduced ALARP all necessary measures must be in place. HID will assess this by scrutinising the duty holders conclusions that:

8.  Some duty holders may regard this as a new approach, but it is not. Such an approach is inherent in the 1974 Health and Safety at Work Act.

Judging whether risks to people are ALARP

9.  Under the legislation specific to HID, as for the HSW Act, it is for duty holders to demonstrate that the necessary measures are in place to reduce risks ALARP, and for HID to assess that demonstration and/or verify through inspection that duty holders are complying with their legal obligations. How duty holders make the demonstration is for them to decide, but clearly they, at least, need to address the arguments that are outlined in HSE's approach ( see R2P2, particularly Part 3) to decision taking in respect of tolerability of risk.

10.  HID will therefore expect that:

11.  In the interests of transparency and consistency, HID Inspectors should consider HSW Act S2 and S3 risks separately (if appropriate) and proportionately. However, the approach for S2 and S3 risks is identical:

12.  If neither HID nor the operator can identify further prima-facie risk reduction measures , over and above the measures described in the duty holders demonstrations, then the risks are ALARP. Views on options for risk reduction measures are a team effort, and face-to-face discussions with the duty holder are required whenever the societal risks are appreciable.

Judging gross disproportion

13.  Determining that risks have been reduced ALARP involves an assessment of the risk to be avoided, of the sacrifice (in money, time and trouble) involved in taking measures to avoid that risk, and a comparison of the two. HSE has not provided any specific guidance, but the disproportion between risk and sacrifice must be gross for all possible options.

14.  Consistent and proportionate judgments can be supported by the R2P2 TOR framework (see R2P2 paragraphs 118 et seq.) by considering individual and societal risks separately. If either consideration indicates that a risk reduction option is reasonably practicable it must be implemented. The judgement on gross disproportion must be a collective one - by the Assessment Team in the case of safety case/report assessment, or by the Inspection team in the case of enforcement action.

15.  Consideration of costs and benefits requires estimates of the likelihood and consequences of particular accidents. Both estimates involve uncertainty, which in the case of event frequency may be an order of magnitude or more. Many decisions can be made by exercising professional judgment based on estimates of the costs of a measure and the number of casualties saved by implementation, possibly informed by a crude cost benefit analysis (CBA).

16.  R2P2 (paragraphs 101-108 and Annex 3), discusses CBA and the estimation of the cost of preventing a fatality (CPF, ie the total final cost of the risk reduction measure divided by the total fatalities prevented). By comparing this with the value of preventing a fatality (VPF, ~£1m) an estimate of the disproportion factor (ie CPF/VPF) can be made. Further guidance is given in the CBA Checklist.

17.  When the proportion factor is 1 or less (or even 2 or less - remember that the disproportion must always be gross, and 2 may not be significantly different from 1 when uncertainty is considered) the measure must be implemented, even when the risks are close to being broadly acceptable. Judgement on whether the proportion factor is grossly disproportionate depends on the levels of individual and societal risks (and possibly the societal concern in certain circumstances). Inspectors should also consider the significance of uncertainties in the calculation of CPF.

18.  Providing the risk analysis is based on cautious best estimates and the costs are realistic (not needlessly inflated beyond the provision of a fit for purpose solution), HID will use the following as the basis for exercising judgement:

19.  HID will attach more weight to consequences where a hazard has attributes which makes it likely that it will give rise to societal risks, such as the potential for severe detriment, eg a major explosion in a built-up area (see Principles and Guidelines document, paragraph 34). Other factors, such as vulnerable groups where societal concerns have previously been expressed, will also be considered as appropriate. For example, for onshore non-nuclear sites, the number of children and elderly persons likely to be affected, and the presence of hospitals and schools may be an input to the ALARP decision.

20.  HID will expect new technology to be implemented, in line with HSE's policy on harnessing new technology, unless gross disproportion can be demonstrated unequivocally.

21.  The precautionary principle (see R2P2 paragraph 91) will be invoked where:

22.  HID expect that the vast majority of decisions can be made relatively quickly once a safety case/report or other form of demonstration has been assessed. Risk reduction measures that are judged prima facie reasonable should be discussed with the duty holder and the way forward agreed. HID expects inspectors to take a "firm but fair" line to ensure that HID and HSE policy on enforcing what is required by the regulations is not compromised.

Further Information

23.  For further information, contact HID CI5A, 2.2 Redgrave Court, Bootle.

Updated 2022-04-26