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HSE plans new approach to societal risk

Posted on May 26 2009
News archive >> OPINION

HSE has recently released several documents concerning the assessment of Societal Risk. This concept, long familiar to operators of major hazard installations, is at last to be introduced into the regime of land-use planning near such installations.

Until now, HSE has based its land-use planning advice around major hazard installations on calculations of either the worst credible hazard or Individual Risk, depending on the nature of the hazards present. Societal Risk has been accounted for implicitly, with HSE being readier to advise against a development if it would introduce larger numbers of people, particularly vulnerable people, into the hazard range.

HSE set out its doctrine in a 1989 publication (Risk criteria for land-use planning in the vicinity of major industrial hazards) and, until recently, it has remained largely unaltered – although its implementation has altered radically (see here).


Hazard: A physical situation with a potential for human injury, damage to property, damage to the environment or some combination of these.

Individual Risk: The likelihood that a particular person in some fixed relation to a hazard (e.g. at a particular location, level of vulnerability, protection and escape) might sustain a specified level of harm.

Societal Risk: The relationship between frequency and the number of people sustaining a specified level of harm in a given population due to the realisation of specified hazards.

Recently, however, for a variety of reasons, HSE had begun to consider whether (and if so, how) Societal Risk might be taken into consideration explicitly in land-use planning. This study received added impetus from recommendations following the Buncefield incident.

Societal Risk calculations are lengthy and potentially expensive to carry out, and the results are not always easy for Local Planning Authorities to comprehend; indeed, their interpretation can be contentious even among risk specialists. For these reasons, HSE has over the last decade or so developed several ‘quick and dirty’ surrogates for a quantified Societal Risk assessment, none of which is without serious shortcomings.

Recently, following a public consultation, a Societal Risk Technical Advisory Group has been convened to advise on how Societal Risk estimates should be carried out, and also on how tolerability criteria should be set for Societal Risk.

Intriguingly, HSE’s briefing note to the Technical Advisory Group doesn’t confine itself to the Societal Risk issues, but invites the Group to question several assumptions in HSE’s approach to land-use planning around major hazard installations:

- Is the evaluation of societal risk to be based on the presence of hazardous substances as the operator stored or uses them on a daily basis (“as is”) or on the potential for their presence permitted within their hazardous substances consent (“as consented”)?

- Should explicit attention be given to all current risk reduction measures (e.g. including non-passive measures or other measures not routinely accounted for in assessments… because they are not considered enforceable under health and safety or planning legislation)?

- What attention, if any, should be paid to mitigation claimed for buildings (by chance or by design) and for emergency response?”

Some of our clients will recall HSE’s response when we attempted to discuss these questions in the run-up to recent planning inquiries…

In our opinion, there is a latent flaw running through the entire Societal Risk methodology, of which HSE is only partially aware. Alas, we can only sigh, with Fermat, that this newsletter is too narrow to contain our marvellous proof – but we will return to this subject. The flaw is in HSE’s treatment of “scale aversion”: society is said to be more averse to a single incident claiming, say, 50 lives than to 50 disconnected individual fatalities.

The problem is that HSE claims that its suggested Societal Risk tolerability criterion is “scale neutral”, while in fact it has a strong built-in scale aversion factor. HSE has noticed this, but has dismissed its importance, or at least suggested that it was a moot point whether this was a real or apparent effect – that it depended on your point of view. However, we will show conclusively that the aversion factor is real and is far from negligible.

The issue here is not whether an aversion factor should be used – this is not a technical but a sociopolitical question – but that if it is used, it should be explicit and decision makers need to be made aware of its existence and true magnitude.

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Last changed: May 27 2009 at 7:18 PM


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