Introduction to Fire Safety Management

Figure 13.11 Fire fi ghting run-off
fog, low pressure water sprays rather than main jets,
controlled burn and the possible recycling of fi re fi ghting
water, where safe and practicable to do so. The fi re
fi ghting strategy will need to be discussed with the Fire
and Rescue Service and those discussions should be
informed by data relating to the environmental impact
of each of the options. As a principle of course the best
possible strategy to prevent environmental pollution is
not to have a fi re in the fi rst place.
A main jet used for fi re fi ghting produces large
quantities of fi rewater run-off. In many cases, primary
and local containment either by temporary or fi xed
bunding may prevent an incident from causing pollution.
However, where local containment is not provided, or
the fi re risk assessment indicates that additional control
measures are required, for example to contain fi re -
water run-off, which may amount to thousands of cubic
metres, ‘remote containment’ systems may be appropriate.
Remote containment systems may be used by
themselves, or in combination with on-site containment
arrangements. They may be required to protect both
surface and foul water drainage systems.
Quantities of water used for fi re fi ghting
Due of the uncertain nature of an incident and the potential
responses of the emergency services, it is diffi cult to
calculate the capacity of containment areas, including
bunded enclosures in a way that makes a realistic allowance
for fi re fi ghting media that may be used to deal with
an incident. However, since many incidents are likely to
involve fi re, and almost all ‘worst case’ scenarios involve
fi re, making adequate provision for retention of fi re fi ghting
and cooling water is of critical importance.
When considering the capacity required for containing
fi rewater run-off, a distinction needs to be made between
local and remote containment arrangements or combined
containment in terms of what may be achievable.
Environmental impact of fi re
Allowance for fi re fi ghting agents in designing
on-site bund capacity
It is impracticable to design a bunded area with suffi -
cient capacity to contain all the potential fi re fi ghting and
cooling water that would be used in a major fi re. In many
cases this would result in very high bund walls. This in
turn would not only cause construction, operational and
safety problems, but is also likely to adversely affect fi re
fi ghting operations. For bunded areas, therefore, it is
normal to merely provide suffi cient freeboard (above the
height of bund required to contain released substances)
to retain a blanket of fi re fi ghting foam, and some additional
capacity for cooling water. It is normally considered
adequate to provide something over 100 mm of freeboard
for the containment of foam.
Allowance for fi re fi ghting agents in the design of
remote and combined systems
Remote and combined systems should be designed so
that they have suffi cient capacity to retain such fi re fi ghting
and cooling water as could reasonably be expected to
be used in a major fi re. It is essential to consult fully with
the Fire and Rescue Service to agree an estimate of the
required capacity. In order to achieve a realistic estimate
it will be necessary to consider the following factors:
➤ The size and layout of the plant
➤ The nature of the materials present and the processes
carried out
➤ Cooling water from automatic fi re fi ghting systems
(e.g. fi xed sprinkler installations, on-site fi re fi ghting
capability)
➤ The Fire and Rescue Service’s own contingency
strategy for dealing with an incident
➤ The Fire and Rescue Service’s own fi re fi ghting
capability.
In the light of this information the designer must then
decide, in consultation with the regulators and the plant
operators, the capacity of containment required.
On sites where there is the potential for any containment
capacity to be signifi cantly overrun, it may be
necessary to install additional fi xed fi re systems, or
compartmentalise the plant or site, or gain the agreement
of the Fire and Rescue Service, the Environment Agency
and the operators to a ‘controlled burn’ response
strategy. For sites with a low hazard or risk rating it will
be harder to justify the costs of full containment for fi re
fi ghting and cooling water and the designer should seek
to strike a reasonable balance between protection and
cost, in consultation with the Fire and Rescue Service,
the regulators and the site operators.
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