CDOIF Guidance

Safety and environmental standards for fuel storage sites

Final report

44 The MIIB’s third progress report

indicated that there was a problem with the tank level

monitoring system at Buncefield.

45 Overfill protection systems using high-level switches or other two-state detectors may be

inactive for long periods and may develop unrevealed faults. Such faults cause the system to

fail to danger. Therefore, overfill protection systems should be tested periodically to identify and

correct unrevealed faults.

46 These systems should be designed, implemented, documented, and have a regime of safety

lifecycle management necessary to achieve the required SIL in compliance with BS EN 61511.

Management of instrumented systems for fuel storage tank installations

47 This guidance does not replace or detract from the requirements of BS EN 61511, but is a

summary of some of the main requirements that are relevant to in-scope tanks. It does not cover

all the requirements of BS EN 61511 – for more detail refer to the standard.

48 The suitability and continuing integrity of instrumented systems is essential to ensure the

safety of an installation and in particular the primary containment system. The functional integrity

of overfill protection systems is critical to primary containment. Overfill protection systems may

be in a dormant state without being required to operate for many years. For this reason periodic

testing is an essential element in assuring their continuing integrity.

49 BS EN 61511 requires that for all SIS implementing safety instrumented functions of SIL 1 or

higher there is a management system in place for the whole of the lifecycle of the SIS, which will

manage all appropriate measures.

50 BS EN 61511 does not cover requirements for systems providing a risk reduction of less than

ten; however, they may still provide a contribution to the safety function and where these systems

are part of the risk reduction they should comply with the management systems requirements of

BS EN 61511 so far as is reasonably practicable.

Part 2 Protecting against loss of

primary containment using high

integrity systems

MIIB Recommendation 2

Operators of Buncefield-type sites should, as a priority, review and amend as necessary their

management systems for maintenance of equipment and systems to ensure their continuing

integrity in operation. This should include, but not be limited to reviews of the following:

(a) the arrangements and procedures for periodic proof testing of storage tank overfill prevention

systems to minimise the likelihood of any failure that could result in loss of containment; any

revisions identified pursuant to this review should be put into immediate effect;

(b) the procedures for implementing changes to equipment and systems to ensure any such

changes do not impair the effectiveness of equipment and systems in preventing loss of

containment or in providing emergency response.