Safety Critical Systems Handbook

A Straight forward Guide to Functional Safety, IEC 61508 (2010 EDITION) and Related Standards, Including Process IEC 61511 and Machinery IEC 62061 and ISO 13849

David J. Smith, Kenneth G. L. Simpson

• Publisher: Butterworth-Heinemann
• Year: 2010
• ISBN:
  9780080967820
• Topic: Technology & Engineering
• Subtopic: Industrial Health & Safety
• Index: Technology & Engineering

Safety Critical Systems Handbook: A Straightfoward Guide to Functional Safety, IEC 61508 (2010 Edition) and Related Standards, Including Process IEC 61511 and Machinery IEC 62061 AND ISO 13849, Third Edition, offers a practical guide to the functional safety standard IEC 61508. The book is organized into three parts. Part A discusses the concept of functional safety and the need to express targets by means of safety integrity levels. It places functional safety in context, along with risk assessment, likelihood of fatality, and the cost of conformance. It also explains the life-cycle approach, together with the basic outline of IEC 61508 (known as BS EN 61508 in the UK). Part B discusses functional safety standards for the process, oil, and gas industries; the machinery sector; and other industries such as rail, automotive, avionics, and medical electrical equipment. Part C presents case studies in the form of exercises and examples. These studies cover SIL targeting for a pressure let-down system, burner control system assessment, SIL targeting, a hypothetical proposal for a rail-train braking system, and hydroelectric dam and tidal gates.

• The only comprehensive guide to IEC 61508, updated to cover the 2010 amendments, that will ensure engineers are compliant with the latest process safety systems design and operation standards
• Helps readers understand the process required to apply safety critical systems standards
• Real-world approach helps users to interpret the standard, with case studies and best practice design examples throughout

Appendix 1 Functional Safety Management

Template Procedure

This procedure could be part of a company's Quality Management System (e.g. ISO 9001). It contains those additional practices (over and above ISO 9001) necessary to demonstrate Functional Safety Capability as would be audited by a reviewing body (see Chapter 7).

A large organization, with numerous activities and product types, might require more than one procedure, whereas a small company would probably find a single procedure satisfactory.

Again, the activities covered by a designer and manufacturer of instruments or systems will differ from those of a plant operator, which, in turn, will differ for a functional safety consultant/assessor.

This template has been successfully used by companies in the safety systems integration field and in consultancy firms. It consists of a top-level procedure and eight work practices to cover details of safety assessment (see Annex 1).

The terms used (e.g. Safety Authority, Safety Engineering Manager) are examples only, and will vary from organization; xxxs are used to designate references to in-house company procedures and documents.

This template should not be copied exactly as it reads but tailored to meet the company's way of operating.

Company Standard xxx Implementation of Functional Safety

Contents

1. Purpose of Document
2. Scope
3. Functional Safety Policy
4. Quality & Safety Plan
5. Competencies
6. Review of Requirement and Responsibilities
   1. Source of the requirement
   2. Contract or project review
   3. Assigning responsibilities
7. Functional Safety Specification
8. Life Cycle Activities
   1. Integrity Targeting
   2. Random Hardware Failures
   3. ALARP
   4. Architectures
   5. Life-cycle activities
   6. Functional Safety Capability
9. Implementation
10. Validation
11. Work Instruction xxx/001 – Random Hardware Failures & ALARP
12. Work Instruction xxx/002 – Integrity Targeting
13. Work Instruction xxx/003 – Life Cycle Activities
14. Work Instruction xxx/004 – Architectures (SFF)
15. Work Instruction xxx/005 – Rigour of Life Cycle Activities
16. Work Instruction xxx/006 – Functional Safety Competence
17. Work Instruction xxx/007 – Functional Safety Plan
18. Work Instruction xxx/008 – Functional Safety Specification

1 Purpose of document

This standard provides detail of those activities related to setting and achieving specific safety-integrity targets and involves the design, installation, maintenance and modification stages of the life-cycle. Where the activity in question is already catered for elsewhere in the XYZ Ltd quality management system, this document will provide the appropriate cross-reference.

The purpose of this procedure is to enable XYZ Ltd to provide in-house expertise in functional safety such as to meet the requirements of IEC 61508. Since IEC 61508 is not a prescriptive standard the issue is one of providing a risk based “safety argument” that is acceptable to one's regulator/auditor/HSE. A functional safety assessment consists of evidence showing that the areas of the standard have been adequately addressed and that the results are compatible with the current state of the art.

This requires a proactive risk-based approach rather than a slavish adherence to requirements.

2 Scope

The standard shall apply to all products and documentation designed, produced, installed or supported by XYZ Ltd except where contract requirements specifically call for an alternative.

In the case of simple designs, and modifications to existing plant, these activities may be carried using in-house resources and skills. Larger projects may require the use of external resources.

Additional detail (to assist Project Safety Engineers or subcontractors) is supplied in Work Instructions/001 – /008.

The following diagram shows the relationship of relevant procedures:

3 Functional safety policy

Paragraph x of the Quality Manual emphasizes that capability in respect of functional safety is a specific design capability within XYZ Ltd. Some contracts will relate to safety-related applications. Some developments will specifically target safety-integrity conformance as a design requirement.

If the project is deemed to be safety-related then the Project Manager shall appoint an independent Project Safety Assessor. However, a project may be declared sufficiently minor that formal hazard identification is not required and that the remainder of this procedure need not apply. That decision will only be undertaken or ratified by the Company Functional Safety Manager.

In the case of minor modifications this review process is satisfied by means of the impact analysis which shall be recorded on the change request.

4 Quality & safety plan

Every project shall involve a Quality & Safety Plan which is the responsibility of the Project Manager. It will indicate the safety-related activities, the deliverables (e.g. Safety-Integrity assessment report) and the competent persons to be used. The Project Manager will consult the competency register and will review the choice of personnel with the Safety Authority.

The tasks are summarized in Section 5 of this standard. Minimum SR items required in the Quality & Safety Plan are shown in WI/007.

See also , Appendix 7 of this book

5 Competencies

The HR department will maintain a “safety-related competence register” containing profiles of those individuals eligible to carry out functional safety assessment and design tasks. Periodically the Managing Director and Functional Safety Manager will review the list.

The list will be updated from:

• Individuals’ attendance at relevant off-the-job courses
• Records of SR experience from each project (on-the-job training) (Project Managers will provide this information to the Personnel Manager)
• Details of new employees or contractors.

Sample entry in the competency register

See , Chapter 2 Figure 2.5 of this book

Examples of specific jobs involving SR competencies include:

Functional Safety Manager

T...

Table of contents

• Cover
• Title Page
• Copyright
• Table of Contents
• IEC 61508
• A Quick Overview
• The 2010 Version of IEC 61508
• Acknowledgements
• Part A: The Concept of Safety Integrity
• Part B: Specific Industry Sectors
• Part C: Case Studies in the Form of Exercises and Examples
• Appendix 1: Functional Safety Management
• Appendix 2: Assessment Schedule
• Appendix 3: Betaplus CCF Model, Scoring Criteria
• Appendix 4: Assessing Safe Failure Fraction and Diagnostic Coverage
• Appendix 5: Answers to Examples
• Appendix 6: References
• Appendix 7: Quality and Safety Plan
• Appendix 8: Some Terms and Jargon of IEC 61508
• Index