CDOIF Guidance

Safety and environmental standards for fuel storage sites

Final report

Societal Risk assessment

44 The scenario of an explosion following a tank overflow may contribute significantly to the

societal risk associated with an establishment. If this is the case, then the scenario should be

included in the Societal Risk assessment within the safety report for the establishment. As

described in the HSE COMAH SPC/Permissioning/12:

‘Societal Risk is the relationship between frequency of an event and the number of people

affected. Societal concern includes (together with the Societal Risk) other aspects of

society’s reaction to that event. These may be less amenable to numerical representation

and include such things as public outcry, political reaction and loss of confidence in the

regulator, etc. As such, Societal Risk may be seen as a subset of societal concern.’

45 Assessing a scenario in terms of the numbers of potential fatalities does not address

all aspects of societal concern, but is an indicator of the scale of the potential societal

consequences. The fatalities may be onsite and/or offsite. Other aspects of societal concern are

outside of the scope of this risk assessment guidance.

46 A scenario with the potential for more than ten fatalities may contribute significantly to the

level of Societal Risk from the hazardous establishment. Therefore the scenario should also be

considered as part of the safety report Societal Risk assessment.

47 A scenario with the potential for ten or less fatalities may not represent a significant Societal

Risk and a judgment will need to be taken over its inclusion.

Reducing risks, protecting people

provides one Societal Risk tolerance criterion, that the

fatality of ‘50 people or more in a single event should be regarded as intolerable if the frequency

is estimated to be more than one in five thousand per annum’ (paragraph 136). This risk criterion

is applied to a ‘single major industrial activity’ as a whole, where a single major industrial

activity means an industrial activity from which risk is assessed as a whole, such as all chemical

manufacturing and storage units within the control of one company in one location or within a site

boundary.

49 There is currently no nationally agreed risk tolerance criterion to determine when the level of

Societal Risk is ‘broadly acceptable’. This assessment is site-specific, and would therefore need to be

performed for the establishment as part of the safety report demonstration and agreed with the CA.

50 LOPA is not normally used to assess Societal Risk because a Societal Risk assessment

typically requires the evaluation of a range of scenarios. This is typically carried out using

quantified risk assessment techniques such as fault and event trees. There is no universally

agreed method of presenting the results of a Societal Risk assessment, but commonly used

methods include F-N curves and risk integrals.

Scenario-based environmental risk assessment

51 There are currently no published environmental risk criteria for Great Britain with the same

status as those for safety in

Reducing risks, protecting people

. Information on tolerability of

environmental risk has also been produced for options assessment in section 3.7 of

Integrated

Pollution Prevention and Control (IPPC) and Environmental Assessment and Appraisal of BAT

IPPC H1 Version 6 July 2003.

The tolerability criteria from this reference is summarised in matrix

form in Table 9 below. Further guidance on environmental risk matrix can be found in Annex 5 of

HSE’s SPC/Permissioning/11.

52 Dutyholders seeking to demonstrate compliance with the COMAH Regulations should adopt

an approach consistent with the information provided in Tables 9 and 10 and with that in their

COMAH safety reports and pollution prevention control permit applications.