CDOIF Guidance

61 / 648

Safety and environmental standards for fuel storage sites
Final report
60
243 Some tertiary containment assessments have considered the environmental receptors
surrounding the installation and potential pathways for pollution flows. However, many
concentrated solely on assessing the maximum practical use of installed containment
capacity, and determining the consequent fire-fighting attack duration. Buncefield showed that
consequences might be much more extensive than expected.
244 Assessment of tertiary containment should start with an initial worst-case assumption that
available secondary containment will fail or capacity will be exceeded, and the consequent
firewater flows and directions should be identified and estimated. Based on this, implementation
of basic good practice measures should be considered, for example site kerbing/banking,
sleeping policemen/ramps, permanent or temporary measures to close off potential environmental
pathways and/or direct flows, and temporary emergency containment provision. This could
include the provision of pollution containment equipment, for example pipe-blockers, drain sealing
mats and land booms.
245 Further assessment should consider firewater volumes from worst-case credible scenarios.
Implementation of additional measures should be considered by means of a cost-benefit
analysis comparison versus the expected value of the consequences. Consideration of tertiary
containment measures beyond basic good practice should be informed by an integrated risk
assessment of the primary/secondary/tertiary controls as a whole.
Published guidance
246 General guidance on the design of remote containment systems (including lagoons, tanks
and temporary systems such as sewerage storm tanks and sacrificial areas such as car parks,
sports field and other landscape areas) is available in numerous documents including CIRIA 164,
and PPG18.44
247 Catchment areas used for tertiary containment often serve a dual purpose, for example
roadways, hard standing, car parks. Such areas are normally routinely drained to surface
water drainage systems. Therefore, to be considered for emergency tertiary containment, such
areas must be capable of reliable emergency sealing of drains and interception of pollutants.
Furthermore, arrangements must not compromise emergency access or unduly compromise day-
to-day operations.
248 Major accident case studies provide valuable approaches to tertiary containment design, for
example:
Allied Colloids, Bradford (July 1992). ■
■
Monsanto, Wrexham (1985). ■
■
Sandoz, Switzerland (1986). ■
■
The first two of these are described in CIRIA 164, chapter 6.
Risk assessment guidance
249 Suitable and precautionary methodologies should be used for the above risk assessment.
In view of the high uncertainties in modelling the transport of entrained or dissolved pollutants in
liquids escaping secondary containment, it is recommended that assessments concentrate on
quantifiable physical parameters such as those indicated in Table 5.
250 Two important references for an overall approach to environmental risk assessment are the
Energy Institute Environmental Risk Assessment of Bulk Liquid Storage Facilities: A Screening
Tool45 and Guidance on the Environmental Risk Assessment Aspects of COMAH Safety Reports46
–
assessment.pdf