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Safety and environmental standards for fuel storage sites
Final report
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Firewater management and control measures
233 Well-planned and organised emergency response measures are likely to significantly reduce
the potential duration and extent of fire scenarios, and so reduce firewater volumes requiring
containment and management. Site-specific planning of firewater management and control
measures should be undertaken with active participation of the local Fire and Rescue Service, and
should include consideration of:
bund design factors such as firewater removal pipework, aqueous layer controlled overflow to
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remote secondary or tertiary containment (for immiscible flammable hydrocarbons);
recommended firewater/foam additive application rates and firewater flows and volumes at worst-
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case credible scenarios (including severe pool fire or multiple tank / multiple bund fire); and
controlled-burn options appraisal, and pre-planning/media implications.
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Tertiary containment
234 This guidance applies only to the loss of secondary containment from bunds containing
tanks within the scope (the COMAH CA Containment Policy has a wider scope). At installations
where bunds contain tanks within scope, operators should assess the requirement for tertiary
containment, on the basis of environmental risk, and to make site action plans for improvement.
Provision of tertiary containment should also take into account safety aspects – for example the
flows and accumulations of hazardous liquids on and around a site.
235 Tertiary containment minimises the consequences of a failure in the primary and secondary
containment systems by providing an additional barrier preventing the uncontrolled spread of
hazardous liquid. Tertiary containment is achieved by means external to and independent of the
primary and secondary containment systems, such as site drainage and sumps, diversion tanks,
impervious liners and/or flexible booms. Tertiary containment will be utilised when there is an
event that causes the loss of containment (for example bund joint failure or firewater overflowing
from a bund during a prolonged tank fire), and is intended to ensure that loss of control of
hazardous materials does not result from such an event.
Risk assessment
236 A risk assessment should be undertaken to determine the extent of the requirement for
tertiary containment, taking into account:
foreseeable worst-case scenario – severe pool fire or multiple tank/multiple bund fire (following
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an explosion or due to escalation);
foreseeable bund failure modes, including:
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the amount of spilled substances, including hydrodynamic effects of catastrophic tank
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failure and emergency response actions such as fire fighting;
the potential impact of fire on bund integrity including joints in walls and floors;
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worst-case foreseeable delivered firewater volumes including fire fighting agents (see IP19
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); and
passive and active firewater management measures.
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environmental setting, including:
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all relevant categories of receptors as specified in
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Guidance on the interpretation of Major
Accident to the Environment
;
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proximity of receptor, for example groundwaters under the site;
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site and surrounding topography;
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geological factors affecting the permeability of surrounding land and environmental pollution
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pathways; and
hydrogeological factors affecting liquid pollutant flows and receptor vulnerabilities;
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known pathways and potential pathways to environmental receptors in the event of failure of
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secondary containment;
likely environmental impact consequences, in terms of extent and severity, of the pollutant
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and/or firewater quantities and flows resulting from foreseeable bund failure scenarios.