Introduction to Safety Integrity Level (SIL) Studies

Introduction to Safety Integrity Level (SIL) Studies

1. Purpose

The purpose of this procedure is to describe the recommended practice for performing Safety Integrity Level (SIL) assessment & verification studies of identified Instrumented Protective Functions.

2. Scope

This procedure applies to the performance of SIL Studies on Oil & Gas facilities projects executed by EPC companies. The recommended practice outlined in this procedure shall be adopted on a project where client’s specific guidelines are not available.

3. Reference documents

• IEC 61508, Functional safety of electrical/electronic/programmable electronic safety-related systems
• IEC 61511, Functional Safety – safety instrumented systems for the process industry sector
• PFD data from vendors
• Safety Equipment Reliability Handbook, by OREDA or any other handbook for generic data.

4. General

Instrument and control systems play a significant role in the management of hazards on oil and gas installations. Shutdown systems are traditionally recognized as safety systems which contribute to reducing the likelihood and consequences of dangers to personnel, but also limiting risks to environment, to assets and to continued production. Therefore, instrumented protective functions need to be reviewed through a systematic assessment process to determine any requirement for increased reliability and/ or higher integrity and hence reducing risks.

The main objective of the SIL study is to assess the integrity level for all instrumented protection functions that have been provided for all process systems through a SIL Assessment Workshop, in accordance with IEC 61511 and to verify through SIL Verification calculations that the design meets the integrity levels.

Fire & Gas Detection system is not generally considered for the SIL Assessment as most of the operators decide the minimum integrity level requirement for the F&G system based on their internal standards or regulatory requirements.

SIL Assessment workshop is conducted to perform a systematic review of plant process systems to identify failures in E/E/PE safety related control systems at each plant, which have the potential for harm to personnel (through illness and injury or loss of life) or to the environment (temporary or permanent). A secondary objective will be to identify where such failures have the potential to cause significant economic loss due to production loss and/or damage to capital equipment. The safety and environmental harm and the economic loss will generally arise due to loss of containment, either of the product or of a substance hazardous to health.

The SIL Assessment shall also include the failure of control functions leading to high consequence events, which are identified during HAZOP review.

5. Roles and Responsibilities

The SIL Assessment team should consist of the following persons:

Chairman: Responsible for chairing the SIL review meeting and ensuring the process runs smoothly in accordance with the procedure. The Chairman shall ensure the team remain focused and do not deviate from the objective of the study. The chairman shall have experience of conducting SIL Assessment Workshop or similar studies. The Chairman shall bring the SIL Assessment software. The SIL Assessment and SIL Verification report shall be prepared by the Chairman.

Secretary: Responsible for recording the discussion of the meeting, using the worksheets. It is preferable that the SIL Secretary has a technical background in Instrumentation.

Lead HSE Design Engineer:  The Lead HSE (Design) Engineer on the project shall ensure that the SIL is performed to the standards set out in this procedure. The Lead HSE (Design) Engineer shall ensure the administrative tasks necessary to perform the SIL study completed (organization of team, distributing the documents, Chairman Selection, selection of venue, etc).

Lead Instrument Engineer:  Lead Instrument Engineer shall be responsible to ensure completion of Project design documents necessary prior to SIL study including vendor documents. He shall provide Chairman the list of tags, initiating devices, final elements and service description for each SIF to include into the worksheets.

Lead Process Engineer:  Lead Process Engineer shall ensure that the P&ID’s are updated in line with the recommendations given in the HAZOP.

Follow-up: The Follow-up Coordinator shall be nominated by Project Engineering Manager (PEM) who can make project decisions on the conflicting requirements. The co-ordinator shall act on behalf of the PEM to facilitate and expedite the satisfactory close-out of recommendations raised by the SIL study. The overall responsibility of SIL close-out process lies with PEM.

6. SIL Team Composition

Presence of following team members both from Contractor and the Operating

Company is essential during the full duration of the review:

• · Process Engineer
• · Control and Instrumentation Engineer
• · HSE/ Safety Engineer
• · Operation’s Representative
• · Other discipline engineers (Mechanical, Civil, layout etc.) shall be available on need basis

7. SIL Study Schedule and Pre-requisites

SIL Assessment

The SIL Assessment Workshop should be scheduled after completion of HAZOP study and incorporation of major HAZOP recommendations onto the P&IDs and Cause & Effects Charts.

The following project specific documents (latest revisions) shall be made available prior to the SIL Assessment workshop:

• Piping & Instrumentation Diagrams
• Cause and Effects Chart
• HAZOP Report
• QRA Reports
• Plot plans
• Approved SIL Assessment Methodology

The SIL Assessment Report, which is the outcome of the SIL Assessment Workshop, shall be produced to document the entire workshop proceedings and the final assessed Integrity Levels for the IPFs / SIFs, as concluded in the SIL Assessment Workshop.

SIL Verification

The SIL Verification exercise shall be taken up based on the findings of the SIL Assessment Workshop to ensure that the ultimate design meets the Integrity Level assessed. SIL Verification study requires the following information to start with –

• SIL Assessment Report
• Failure Data from Vendors / Established / recognized sources
• Piping & Instrumentation Diagrams
• Vendor Safety Manual
• Cause and Effect
• Safeguarding System Philosophy
• Process Operating and Control Philosophy
• Make/Model and Data Sheet of SIF Components