105 / 648
Safety and environmental standards for fuel storage sites
Final report
104
117 General guidance cannot be given beyond the need for a realistic case-by-case assessment
which may take into account environmental remediation and the rate at which penetration of the
ground takes place. These considerations will be site-specific and possibly specific to each tank.
Emergency warning systems and evacuation procedures
118 Emergency warning systems and evacuation procedures may allow people to escape in
the event of a storage tank overflow, and therefore avoid harm. However, great care is required
in taking credit for such systems in the LOPA because in their own right they only constitute a
means of, possibly, making a hazardous situation ‘safe’ (by preventing the consequence from
being realised). To be a complete protection layer they need to be combined with a means of
detecting an overflow, and therefore emergency warning systems and evacuation procedures
are better considered part of an overflow detection protection layer as an alternative to (or in
combination with) closing a valve or stopping a pump.
119 In judging the effectiveness of the emergency warning system and evacuation procedures,
the following should be considered:
The time it takes to activate the emergency warning system.
■
■
The coverage of the emergency warning system – can it be heard in all relevant parts of the
■
■
facility, including in noisy workplaces and inside vessels, vehicles and tanks?
Have the required emergency response actions been defined clearly and are they
■
■
communicated to all personnel at risk, including visitors and contractors?
How is assurance gained that personnel have understood their training and that they continue
■
■
to remember what to do?
Is it absolutely clear what needs to be done and how in responding to the alarm?
■
■
Do any decisions need to be made on how to respond to the alarm to deal with specific site
■
■
conditions at the time?
Are muster points clearly signed?
■
■
Is at least one muster point located in a safe place for foreseeable site conditions?
■
■
Can personnel access at least one muster point safely regardless of local conditions and will it be
■
■
obvious which muster point to go to and which route to use even in conditions of poor visibility?
How long will it take personnel to escape the hazardous area and how does this compare
■
■
with the time available before ignition might occur?
Are the evacuation procedures regularly tested by field tests, and what do the test results show?
■
■
120 Any credit taken for warning and evacuation systems should be fully justified in the LOPA
report.
121 While an overflow detection system combined with a warning alarm and evacuation
procedures may meet the requirements for an effective protection layer in considering the risk to
an individual, it may not do so for the overall exposed population.
122 Where the risk to a population is being considered, an overflow detection system with
a warning alarm and evacuation procedures may only be partially effective. Therefore such a
system would not meet the requirement of effectiveness for a LOPA layer of protection. In this
case, the contribution of any evacuation system should be considered in the determination of the
consequence and not as a protection layer.
Conditional modifiers
123 In this guidance, the term conditional modifiers is applied to risk reduction factors which are
either external to the operation of the facility (eg weather) or are part of the general design of the
facility without being specific to the prevention of a tank overflow (eg shift manning patterns, on-site
ignition controls). Conditional modifiers are represented in the LOPA by probabilities of occurrence,
as opposed to the probability of failure on demand used to represent a protection layer.