SI057002_MNL - Gasoline Overfill Protection SIS IMMEAS-SIS1 Management Manual

7 / 76

Safety Instrument System
Tank Overfill Protection - Management of Functional Safety
P & I Design Ltd DOCUMENT NO: SI277102_RPT
2 Reed Street, Thornaby, UK, TS17 7AF ISSUE: B DATE:10.10.12
Tel: + 44 (0)1642 617444 PAGE 5 OF 22
Fax: + 44 (0)1642 616447
5.0 SAFETY INSTRUMENT SYSTEM
The Safety Instrument Functions of the Safety Instrumented Systems are:
1. Tank Overfill Protection – SIL 2
6.0 FUNCTIONAL SAFETY
This document will provide the control of the design review assessments and Functional
Safety Assessment through the lifecycle of the SIS to ensure the necessary objectives of
functional safety are met. It will identify the means of evaluating the system together with all
stages of the review process. Design reviews and Functional Safety Assessments (FSA) will
be documented in separate documents but referenced within this document.
As part of the continuous assessment process a Compliance Document Ref SI277101_RPT
will be completed at various lifecycle phases. The purpose of this document is to ensure
compliance to the standard at each phase.
In accordance with BS EN 61511 the defined stages for FSA are:
 Stage 1 – After the HAZOP and risk assessment has been carried out, the
required protection layers have been identified and the safety requirement
specification (SRS) has been developed.
 Stage 2 - After the SIS has been designed.
 Stage 3 After the installation, pre-commissioning and final validation of the
SIS has been completed and operating and maintenance procedures have been
developed.
 Stage 4 – After gaining experience in operating and maintenance.
 Stage 5 – After modification and prior to decommissioning of the SIS.
The number, size and scope of Functional Safety Assessments is decided upon specific
circumstance considering the following:
 Size of project;
 Degree of complexity;
 Safety integrity Level;
 Duration of Project;
 Consequence in the event of failure;
 Degree of standardisation of design features;
 Safety regulatory requirements;
 Previous experience with a similar design.
The constitution of the FSA team is based upon the following:
 The scope of the FSA;
 Who is to participate in the FSA;
 The skills, responsibilities and authorities of the FSA team
 The information that will be generated as a result of the FSA;
 The identity of any safety bodies if required;
 The resources required to complete the FSA;
 The level of independence of the FSA team;
 The means by which the FSA will be revalidated after modifications.