The safe isolation of plant and equipment

This is a free-to-download, web-friendly version of HSG253 (second edition, published 2006). This version has been adapted for online use from HSE’s current printed version.

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ISBN 978 0 7176 6171 8 Price £12.95

This book is a useful reference for duty holders in the onshore and offshore oil and gas industry, chemical manufacturing, and pipelines associated with these industries. It will help duty holders to develop, review and enhance their own isolation standards and procedures. It also has general application to all industries where process isolations are made, and to mobile offshore drilling units where relevant.

It provides guidance on how to isolate plant and equipment safely, and how to reduce the risk of releasing hazardous substances during intrusive activities such as maintenance and sampling operations. It includes a methodology for selecting ‘baseline’ process isolation standards and outlines preventive and risk reduction measures.

HSE Books Page 1 of 81

© Crown copyright 2006

First published 1997

ISBN 978 0 7176 6176 8

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the prior written permission of the copyright owner.

Applications for reproduction should be made in writing to: The Office of Public Sector Information, Information Policy Team, Kew, Richmond, Surrey TW9 4DU or e-mail: licensing@opsi.gov.uk

This guidance is issued by the Health and Safety Executive. Following the guidance is not compulsory and you are free to take other action. But if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to this guidance as illustrating good practice.

Contents Foreword 4

Introduction 5 Scope and target audience 5 Legal considerations 6 Risk reduction and ALARP 6 Overview of isolation hazards 7

Management of isolations 7 Basic principles 7 Design 8 Human factors 10 Roles and responsibilities 12 Training and competence 14 Monitoring, audit and review 15 Setting performance indicators for isolation activities 17

Safe systems of work for isolation activities 17 Work control systems 17 Documentation 17 Controlling interactions with other work/systems 18 Controlling changes 19

Key stages of process isolation 21 Hazard identification 22 Risk assessment and selection of isolation scheme 23 Planning and preparation of equipment 31 Installation of the isolation 32 Draining, venting, purging and flushing 34 Testing and monitoring effectiveness of the isolation 35 Reinstatement of the plant 38

Isolation situations requiring specific considerations 39 Own isolations 39 Arrangements for large-scale isolations 41 Extended isolations 42

Appendices 42 1 Legal requirements 42 2 Non-process isolation hazards 44 3 Checklists for monitoring and review 47 4 Valve types and issues 50 5 Isolation methods 52 6 Example of a selection tool to establish the ‘baseline standard’ for a final isolation 59 7 Pipeline isolation requirements 68 8 Draining, venting, purging and flushing activities 72 9 Isolations for instrument work 75

References and further reading 77

Glossary 79

Foreword Failures during the isolation and reinstatement of process plant are one of the main causes of loss-of-containment incidents, and may lead to major accidents. High standards of isolation and rigorous management control are required for plant isolation and reinstatement, particularly in major hazard industries.

This guidance reflects current industry ‘good practice’ standards. It has been developed by a joint working group, including members from industry, trade unions and the Health and Safety Executive. It replaces the Oil Industry Advisory Committee’s 1997 document The safe isolation of plant and equipment (ISBN 0 7176 0871 9).

This revised guidance reflects our increased appreciation of the importance of human factors in safe isolations. Analysis confirms that where incidents occur, the root causes often include human failures.

We recommend the review of company procedures against the principles and practical guidance contained in this publication. An action plan should then be prepared for the implementation of any necessary improvements.

Effective and lasting improvement can be achieved where all concerned, from senior management to those carrying out work on the plant, share a genuine commitment to achieving and maintaining isolation procedures of a high standard.

We would like to thank the following individuals, their employers and industry groups for their contribution.

Ian Darlington Shell UK Oil Products UKPIA Kevin Dixon-Jackson* CIBA Speciality Chemicals plc CIA Martyn Foote Cresent UKOOA Stuart Kennedy National Grid UKOOA Peter Thompson BP Exploration Operating Company Ltd UKOOA Ron Wood* Shell UK Oil Products TGWU Mike Young Petrofac Facilities Management UKOOA

*CDOIF member

Introduction Scope and target audience

1 This publication provides guidance on the general principles of safe process isolations. It describes how to isolate plant and equipment safely, and how to reduce the risk of releasing hazardous substances during intrusive activities such as maintenance and sampling operations.

2 It includes a methodology for selecting ‘baseline’ process isolation standards and outlines preventive and mitigatory risk reduction measures. It is intended for use as a reference to assist duty holders to develop, review and enhance their own isolation standards and procedures.

3 The guidance applies to the following industries:

■■ the onshore and offshore oil and gas industry; ■■ chemical manufacturing; and ■■ pipelines associated with these industries.

It also has general application to all industries where process isolations are made, and applies to mobile offshore drilling units where relevant (eg well test facilities, underbalanced drilling etc).

4 This guidance is primarily intended for senior operational managers who are responsible for their companies’ isolations systems, and for the health and safety professionals who advise them. It will also be of interest to employee representatives and to anyone who monitors, audits and reviews isolations systems. Organisations responsible for the design and modification of plant should use this guidance to ensure that their designs provide adequate isolation facilities.

5 Key issues for this guidance include:

■■ the importance of good design (for new plant and for plant modifications); ■■ the critical role of human factors in preventing loss of containment; ■■ a revised and recalibrated selection tool; ■■ plant reinstatement as a critical element of isolation activity; ■■ guidance on the use of ‘variations’ from company standards; ■■ advice on controlling own isolations and extended term isolations; and ■■ the inclusion of medium and low pressure gas distribution networks within the scope of the document.

6 The guidance is intended to reflect industry ‘good practice’ for the design of new plant. It applies to existing plant to the extent that it is reasonably practicable to do so. Any alterations required to reduce risks for existing plant to ‘as low as reasonably practicable’ (see paragraphs 13-16) should be identified and carried out within an appropriate timescale.

7 The primary concern of this guidance is with process isolations eg for intrusive maintenance on live plant. The principles are also relevant for non-intrusive isolations that involve breaking the containment envelope and for controlling long- term process plant configurations. The guidance is not intended for emergency situations where loss of containment has occurred and immediate isolation of inventory is required. It does not apply to non-process plant and equipment (eg powered access equipment used during isolation activities).

8 The main focus is on risks to the safety of people, particularly where activities present potential major accident hazards. Avoiding loss of containment will also improve environmental protection and reduce business interruption.

9 The effectiveness of an isolation system depends on the adequacy of other arrangements, including work control systems (especially permit-to-work), operating procedures, training and competence, management of change and contingency plans. The References and further reading section gives sources of more detailed guidance on such topics.

Terms ‘should’, ‘may’ and ‘must’ 10 Throughout this publication, verbs with specific meanings are used:

■■ should – primary verb for statements of guidance; ■■ may – where the guidance suggests options; and ■■ must – only where there is a specific legal/statutory requirement for the measures described, or where the dangers of not taking that course of action are self-evident.

Legal considerations

11 Relevant legislation is listed in Appendix 1.

Contractors and subcontractors 12 The client company is responsible for operational health and safety, irrespective of where its resources come from – whether its own staff, contract, subcontract or agency staff or self-employed workers. Duties in relation to contract staff (eg training, provision of information, co-operation between employers) are further discussed in Management of health and safety at work.1

Risk reduction and ‘as low as reasonably practicable’ (ALARP)

13 The Health and Safety at Work etc Act 1974, and associated legislation, requires duty holders to reduce risk, so far as is reasonably practicable. The qualification as low as reasonably practicable (ALARP), which has been used throughout this document, is interpreted in the same way.

14 To show that you have reduced risks to this level, you must identify the risk reduction measures available and determine the level of risk reduction that can be achieved and the associated cost. Unless the sacrifice involved in implementing the risk reduction measure is grossly disproportionate to the benefits of the risk reduction, then you must implement the measure. Where available measures are not taken, you must justify this decision.

15 The greater the potential hazard, the more effective, secure and controlled the isolation should be. Where a number of options for risk reduction exist, you must use the lowest-risk option that is reasonably practicable. Engineering solutions are preferred to procedural controls or to reliance on the use of personal protective equipment (PPE).

16 In some circumstances, the risks associated with an isolation may be intolerable.2 In such cases the work should not go ahead. No individual step in an isolation procedure should be associated with an intolerable risk. Instead, you should find an alternative approach (eg plant shutdown) that does not involve intolerable risk. This guidance does not attempt to define a criterion for isolations of intolerable risk. These will be situation-specific.

Overview of isolation hazards

17 Oil refineries, oil and gas production installations and chemical processing plants are characterised by long lengths of continuously welded pipework and pipelines connecting process vessels, plant and installations. The contents are often hazardous substances, which may be flammable and/or toxic and are often at high temperatures and/or pressures.

18 Any intrusive activity could allow the escape of hazardous substances. The implementation of adequate isolation practices is critical to avoiding loss of containment. You should minimise isolation requirements, wherever practicable, by planning intrusive maintenance for shutdown periods. When maintenance work has to be carried out on live plant a high standard of management will be required.

19 Release of hazardous substances due to inadequate process isolation may lead to:

■■ local immediate effects to people (death or injury) and to the environment. Long-term effects to people and the environment may be equally serious; and/ or ■■ escalation of the initial release, causing wider damage to plant and other systems (eg damage resulting in further releases of inventory).

20 This guidance is focused mainly on loss of containment hazards, but personal injury hazards and non-process isolation hazards should also be considered (see Appendix 2). These include:

■■ mechanical equipment; ■■ electrical equipment (including process control systems); ■■ hazardous atmospheres in confined spaces; and ■■ special hazards such as radioactive sources and static electricity.

21 Plant reinstatement is a critical aspect of any intrusive activity. Incorrect or incomplete reinstatement is likely to result in loss of containment.

Management of isolations Basic principles

22 The requirements for risk management are discussed in Management of health and safety at work.1 The basic principles are to:

■■ avoid risk wherever possible; ■■ carry out risk assessment to evaluate risks that cannot be avoided; ■■ take action to reduce risks to ALARP levels; and ■■ reduce risks at source wherever possible.

23 The HSE publication Successful health and safety management3 describes the principles and management practice that provide a framework for effective management of health and safety.

24 This guidance sets out expectations for managing isolations activities, ie that you:

■■ set a policy and standards for isolation activities, to reduce risk to ALARP; ■■ set procedures/processes, with worker participation, to achieve secure isolations in normal operating conditions and in other foreseeable conditions; ■■ assess any proposed deviations from company procedures, authorise these at an appropriate level and record/monitor them; ■■ monitor and periodically audit your isolations procedures and use that information in the review of your isolations policy (a checklist for reviewing the adequacy of the overall arrangements is given at Appendix 3); and ■■ have, for multi-site operations, an element of corporate oversight4 in standard- setting and assurance (for example, central reporting of objective information on the performance of isolations systems).

25 The potential for human failure during isolations, and its importance, is discussed in paragraphs 42-46. It is important that you both understand and act upon this knowledge. Critical aspects of people’s role within isolations systems include:

■■ setting roles and responsibilities for key personnel; ■■ training, competence and authorisation; and ■■ the management activities of monitoring, audit and review and then taking action.

Design

Principles 26 Good design maximises inherent safety and is fundamental to achieving safe and effective isolation without placing unnecessary constraints on plant operation. Some intrusive maintenance or internal inspection tasks will always require plant shutdown. Where isolation to enable intrusive activities is appropriate, suitable isolation arrangements on the plant should be clearly specified at the design stage.

27 The opportunity to achieve an inherently safer design is greatest for new plant and equipment. Wherever reasonably practicable, the same approach should be followed for plant modifications (see paragraphs 137-140).

28 The potential for human failure, including error, should be addressed and, wherever possible, minimised in the design.

29 At an early point in the design process the client should specify the intentions for normal and alternative mode(s) of operation, sparing of equipment, and the equipment maintenance strategy. Where possible, this should anticipate the intended lifecycle of the plant, including foreseeable modifications (for example addition of equipment). This philosophy should be documented and will determine the plant’s outline isolation requirements. Any proposed deviation from the agreed design basis once the plant is operational should be justified through risk assessment before alternative isolation arrangements are used.

30 The following issues should be considered and included within the design documentation:

■■ alternative modes of plant operation using differing flow routes; ■■ requirements for intrusive plant operations (for example filter change-out, sampling or removal of pipeline pigs from launchers and receivers) and requirements for access into equipment for inspection and/or maintenance; and ■■ the detail of isolation arrangements, including valve types, spacers/spading points or spectacle blinds, test points and associated vents and drains for venting, flushing and purging.

Positive isolation requirements 31 Design of new plant should include facilities for positive isolation (including the valved isolation to install the positive isolation) in the following situations:

■■ for vessel entry, where a requirement for entry cannot be eliminated by equipment design (see paragraph 97); ■■ for isolation of toxic fluids; or ■■ to control segregation of parts of the plant which, in alternative operating modes, might otherwise be exposed to overpressure conditions. This applies where it is not reasonably practicable for the installed safety systems to protect all foreseeable operating configurations, for example the separation of a high-pressure plant from its drainage system.

Plant Identification 32 A scheme to uniquely identify all process plant, piping, and valves should be drawn up. All items should be readily identifiable on the plant and referenced on the piping and instrumentation diagrams (P&IDs). In addition, you should permanently label key items of equipment. Formal, simple, easily visible and unambiguous labelling should be provided wherever mistakes in identification could occur and could result in significant consequences.5, 6

Pipework 33 Pipework layout should minimise trapped inventories and allow easy removal of fluid for isolation purposes. Ensure that pipework:

■■ is of sufficient size and design to minimise the possibility of becoming blocked in service; and ■■ is robust and able, where appropriate, to cope with the repetitive stresses imposed by vibration, pulsating pressure and temperature cycling.7

34 Any piece of pipework intended for physical disconnection should be easily removable. Pipework supports should provide adequate support during disconnection. Provide supports where temporary hoses will be required for bleeding.

Valves 35 Specify suitable isolation valves for the service fluid and operating conditions (see Appendix 4). Ensure that you can indicate and effectively secure the position of manually operated valves.

Pressure safety valves 36 Isolation valves should be provided downstream of pressure safety valves for safe isolation from a shared flare or vent system if intrusive maintenance is intended at any time when the remainder of the flare or vent system is in operation. Also, where an isolation valve is downstream from a pressure safety valve, you should be able to secure the isolation valve in the open position at all times when the pressure safety valve is on-line. Standards for safety systems in unfired pressure vessels are given in BS EN 764-7.8

37 Where pressure safety valves are spared and continued plant operation is intended, suitable isolation facilities must also be provided upstream of the pressure safety valves. Appropriate arrangements are required to ensure that the isolation valves do not impair the performance of the pressure safety valves in service, and that closure of the downstream isolation valve does not expose pipework downstream of the off-line pressure safety valve to over-pressure from the live plant.

Spared equipment 38 For spared or parallel-operated equipment, isolation arrangements should allow complete segregation from on-line equipment for operational and/or maintenance reasons. The arrangements should also provide for operational/ maintenance requirements of associated shared services, including control systems and fluid disposal systems such as flare headers.

Location of isolation and testing facilities 39 Unless risk assessment indicates otherwise, isolation and bleed points should be as close as possible to the plant item. Concentration of