The Safe Isolation Of Plant And Equipment (HSG253)
Health and SafetyExecutiveThe safe isolation of plantand equipmentThis is a free-to-download, web-friendly version of HSG253(second edition, published 2006). This version has been adapted for onlineuse from HSE’s current printed version.You can buy the book at www.hsebooks.co.uk and most good bookshops.ISBN 978 0 7176 6171 8Price 12.95This book is a useful reference for duty holders in the onshore and offshoreoil and gas industry, chemical manufacturing, and pipelines associated withthese industries. It will help duty holders to develop, review and enhance theirown isolation standards and procedures. It also has general application to allindustries where process isolations are made, and to mobile offshore drillingunits where relevant.It provides guidance on how to isolate plant and equipment safely, and howto reduce the risk of releasing hazardous substances during intrusive activitiessuch as maintenance and sampling operations. It includes a methodology forselecting ‘baseline’ process isolation standards and outlines preventive and riskreduction measures.HSE BooksPage 1 of 81
Health and SafetyExecutive Crown copyright 2006First published 1997ISBN 978 0 7176 6176 8All rights reserved. No part of this publication may be reproduced, stored ina retrieval system, or transmitted in any form or by any means (electronic,mechanical, photocopying, recording or otherwise) without the prior writtenpermission 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.ukThis guidance is issued by the Health and Safety Executive. Following the guidanceis not compulsory and you are free to take other action. But if you do follow theguidance you will normally be doing enough to comply with the law. Health andsafety inspectors seek to secure compliance with the law and may refer to thisguidance as illustrating good practice.Page 2 of 81
Health and SafetyExecutiveContentsForeword 4Introduction 5Scope and target audience 5Legal considerations 6Risk reduction and ALARP 6Overview of isolation hazards 7Management of isolations 7Basic principles 7Design 8Human factors 10Roles and responsibilities 12Training and competence 14Monitoring, audit and review 15Setting performance indicators for isolation activities 17Safe systems of work for isolation activities 17Work control systems 17Documentation 17Controlling interactions with other work/systems 18Controlling changes 19Key stages of process isolation 21Hazard identification 22Risk assessment and selection of isolation scheme 23Planning and preparation of equipment 31Installation of the isolation 32Draining, venting, purging and flushing 34Testing and monitoring effectiveness of the isolation 35Reinstatement of the plant 38Isolation situations requiring specific considerations 39Own isolations 39Arrangements for large-scale isolations 41Extended isolations 42Appendices 42123456789Legal requirements 42Non-process isolation hazards 44Checklists for monitoring and review 47Valve types and issues 50Isolation methods 52Example of a selection tool to establish the ‘baseline standard’ for a finalisolation 59Pipeline isolation requirements 68Draining, venting, purging and flushing activities 72Isolations for instrument work 75References and further reading 77Glossary 79The safe isolation of plant and equipmentPage 3 of 81
Health and SafetyExecutiveForewordFailures during the isolation and reinstatement of process plant are one of themain causes of loss-of-containment incidents, and may lead to major accidents.High standards of isolation and rigorous management control are required for plantisolation and reinstatement, particularly in major hazard industries.This guidance reflects current industry ‘good practice’ standards. It has beendeveloped by a joint working group, including members from industry, tradeunions and the Health and Safety Executive. It replaces the Oil Industry AdvisoryCommittee’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 ofhuman factors in safe isolations. Analysis confirms that where incidents occur, theroot causes often include human failures.We recommend the review of company procedures against the principles andpractical guidance contained in this publication. An action plan should then beprepared for the implementation of any necessary improvements.Effective and lasting improvement can be achieved where all concerned, fromsenior management to those carrying out work on the plant, share a genuinecommitment to achieving and maintaining isolation procedures of a high standard.We would like to thank the following individuals, their employers and industrygroups for their contribution.Ian DarlingtonKevin Dixon-Jackson*Martyn FooteStuart KennedyPeter ThompsonRon Wood*Mike YoungShell UK Oil ProductsCIBA Speciality Chemicals plcCresentNational GridBP Exploration Operating Company LtdShell UK Oil ProductsPetrofac Facilities ManagementUKPIACIAUKOOAUKOOAUKOOATGWUUKOOA*CDOIF memberThe safe isolation of plant and equipmentPage 4 of 81
Health and SafetyExecutiveIntroductionScope and target audience1 This publication provides guidance on the general principles of safe processisolations. It describes how to isolate plant and equipment safely, and how toreduce the risk of releasing hazardous substances during intrusive activities such asmaintenance and sampling operations.2 It includes a methodology for selecting ‘baseline’ process isolation standardsand outlines preventive and mitigatory risk reduction measures. It is intended foruse as a reference to assist duty holders to develop, review and enhance their ownisolation standards and procedures.3The 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 whoare responsible for their companies’ isolations systems, and for the health andsafety professionals who advise them. It will also be of interest to employeerepresentatives and to anyone who monitors, audits and reviews isolationssystems. Organisations responsible for the design and modification of plant shoulduse this guidance to ensure that their designs provide adequate isolation facilities.5Key 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; andthe inclusion of medium and low pressure gas distribution networks within thescope of the document.6 The guidance is intended to reflect industry ‘good practice’ for the design ofnew plant. It applies to existing plant to the extent that it is reasonably practicableto do so. Any alterations required to reduce risks for existing plant to ‘as low asreasonably practicable’ (see paragraphs 13-16) should be identified and carried outwithin an appropriate timescale.7 The primary concern of this guidance is with process isolations eg forintrusive maintenance on live plant. The principles are also relevant for non-intrusiveisolations that involve breaking the containment envelope and for controlling longterm process plant configurations. The guidance is not intended for emergencysituations where loss of containment has occurred and immediate isolation ofinventory is required. It does not apply to non-process plant and equipment (egpowered access equipment used during isolation activities).The safe isolation of plant and equipmentPage 5 of 81
Health and SafetyExecutive8 The main focus is on risks to the safety of people, particularly whereactivities present potential major accident hazards. Avoiding loss of containment willalso improve environmental protection and reduce business interruption.9 The effectiveness of an isolation system depends on the adequacy of otherarrangements, including work control systems (especially permit-to-work), operatingprocedures, training and competence, management of change and contingencyplans. The References and further reading section gives sources of more detailedguidance 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 themeasures described, or where the dangers of not taking that course of actionare self-evident.Legal considerations11 Relevant legislation is listed in Appendix 1.Contractors and subcontractors12 The client company is responsible for operational health and safety, irrespectiveof where its resources come from – whether its own staff, contract, subcontractor agency staff or self-employed workers. Duties in relation to contract staff (egtraining, provision of information, co-operation between employers) are furtherdiscussed in Management of health and safety at work.1Risk 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. Thequalification as low as reasonably practicable (ALARP), which has been usedthroughout this document, is interpreted in the same way.14 To show that you have reduced risks to this level, you must identify the riskreduction measures available and determine the level of risk reduction that can beachieved and the associated cost. Unless the sacrifice involved in implementingthe risk reduction measure is grossly disproportionate to the benefits of the riskreduction, then you must implement the measure. Where available measures arenot taken, you must justify this decision.15 The greater the potential hazard, the more effective, secure and controlled theisolation should be. Where a number of options for risk reduction exist, you mustuse the lowest-risk option that is reasonably practicable. Engineering solutions arepreferred to procedural controls or to reliance on the use of personal protectiveequipment (PPE).16 In some circumstances, the risks associated with an isolation may beintolerable.2 In such cases the work should not go ahead. No individual stepin an isolation procedure should be associated with an intolerable risk. Instead,you should find an alternative approach (eg plant shutdown) that does not involveintolerable risk. This guidance does not attempt to define a criterion for isolations ofintolerable risk. These will be situation-specific.The safe isolation of plant and equipmentPage 6 of 81
Health and SafetyExecutiveOverview of isolation hazards17 Oil refineries, oil and gas production installations and chemical processingplants are characterised by long lengths of continuously welded pipework andpipelines connecting process vessels, plant and installations. The contents areoften hazardous substances, which may be flammable and/or toxic and are oftenat high temperatures and/or pressures.18 Any intrusive activity could allow the escape of hazardous substances. Theimplementation of adequate isolation practices is critical to avoiding loss ofcontainment. You should minimise isolation requirements, wherever practicable, byplanning intrusive maintenance for shutdown periods. When maintenance work hasto be carried out on live plant a high standard of management will be required.19 Release of hazardous substances due to inadequate process isolation maylead 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 othersystems (eg damage resulting in further releases of inventory).20 This guidance is focused mainly on loss of containment hazards, but personalinjury hazards and non-process isolation hazards should also be considered (seeAppendix 2). These include: mechanical equipment;electrical equipment (including process control systems);hazardous atmospheres in confined spaces; andspecial hazards such as radioactive sources and static electricity.21 Plant reinstatement is a critical aspect of any intrusive activity. Incorrect orincomplete reinstatement is likely to result in loss of containment.Management of isolationsBasic principles22 The requirements for risk management are discussed in Management of healthand 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; andreduce risks at source wherever possible.23 The HSE publication Successful health and safety management3 describesthe principles and management practice that provide a framework for effectivemanagement of health and safety.The safe isolation of plant and equipmentPage 7 of 81
Health and SafetyExecutive24 This guidance sets out expectations for managing isolations activities, ie thatyou: set a policy and standards for isolation activities, to reduce risk to ALARP; set procedures/processes, with worker participation, to achieve secureisolations in normal operating conditions and in other foreseeable conditions; assess any proposed deviations from company procedures, authorise these atan appropriate level and record/monitor them; monitor and periodically audit your isolations procedures and use thatinformation in the review of your isolations policy (a checklist for reviewing theadequacy of the overall arrangements is given at Appendix 3); and have, for multi-site operations, an element of corporate oversight4 in standardsetting and assurance (for example, central reporting of objective information onthe performance of isolations systems).25 The potential for human failure during isolations, and its importance, isdiscussed in paragraphs 42-46. It is important that you both understand and actupon this knowledge. Critical aspects of people’s role within isolations systemsinclude: setting roles and responsibilities for key personnel; training, competence and authorisation; and the management activities of monitoring, audit and review and then takingaction.DesignPrinciples26 Good design maximises inherent safety and is fundamental to achieving safeand effective isolation without placing unnecessary constraints on plant operation.Some intrusive maintenance or internal inspection tasks will always require plantshutdown. Where isolation to enable intrusive activities is appropriate, suitableisolation 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 plantand equipment. Wherever reasonably practicable, the same approach shouldbe 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 intentionsfor normal and alternative mode(s) of operation, sparing of equipment, and theequipment maintenance strategy. Where possible, this should anticipate theintended lifecycle of the plant, including foreseeable modifications (for exampleaddition of equipment). This philosophy should be documented and will determinethe plant’s outline isolation requirements. Any proposed deviation from theagreed design basis once the plant is operational should be justified through riskassessment before alternative isolation arrangements are used.The safe isolation of plant and equipmentPage 8 of 81
Health and SafetyExecutive30 The following issues should be considered and included within the designdocumentation: 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) andrequirements for access into equipment for inspection and/or maintenance; and the detail of isolation arrangements, including valve types, spacers/spadingpoints or spectacle blinds, test points and associated vents and drains forventing, flushing and purging.Positive isolation requirements31 Design of new plant should include facilities for positive isolation (includingthe valved isolation to install the positive isolation) in the following situations: for vessel entry, where a requirement for entry cannot be eliminated byequipment design (see paragraph 97); for isolation of toxic fluids; or to control segregation of parts of the plant which, in alternative operatingmodes, might otherwise be exposed to overpressure conditions. This applieswhere it is not reasonably practicable for the installed safety systems to protectall foreseeable operating configurations, for example the separation of ahigh-pressure plant from its drainage system.Plant Identification32 A scheme to uniquely identify all process plant, piping, and valves should bedrawn up. All items should be readily identifiable on the plant and referenced on thepiping and instrumentation diagrams (P&IDs). In addition, you should permanentlylabel key items of equipment. Formal, simple, easily visible and unambiguouslabelling should be provided wherever mistakes in identification could occur andcould result in significant consequences.5, 6Pipework33 Pipework layout should minimise trapped inventories and allow easy removal offluid for isolation purposes. Ensure that pipework: is of sufficient size and design to minimise the possibility of becoming blockedin service; and is robust and able, where appropriate, to cope with the repetitive stressesimposed by vibration, pulsating pressure and temperature cycling.734 Any piece of pipework intended for physical disconnection should beeasily removable. Pipework supports should provide adequate support duringdisconnection. Provide supports where temporary hoses will be required for bleeding.Valves35 Specify suitable isolation valves for the service fluid and operating conditions(see Appendix 4). Ensure that you can indicate and effectively secure theposition of manually operated valves.Pressure safety valves36 Isolation valves should be provided downstream of pressure safety valves forsafe isolation from a shared flare or vent system if intrusive maintenance is intendedat 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 beable to secure the isolation valve in the open position at all times when the pressuresafety valve is on-line. Standards for safety systems in unfired pressure vessels aregiven in BS EN 764-7.8The safe isolation of plant and equipmentPage 9 of 81
Health and SafetyExecutive37 Where pressure safety valves are spared and continued plant operation isintended, suitable isolation facilities must also be provided upstream of the pressuresafety valves. Appropriate arrangements are required to ensure that the isolationvalves do not impair the performance of the pressure safety valves in service,and that closure of the downstream isolation valve does not expose pipeworkdownstream of the off-line pressure safety valve to over-pressure from the live plant.Spared equipment38 F
Page 1 of 81 Health and Safety Executive 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. You can buy the book at www.hsebooks.co.uk and most good bookshops. ISBN 978 0 7176 6171 8
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Le genou de Lucy. Odile Jacob. 1999. Coppens Y. Pré-textes. L’homme préhistorique en morceaux. Eds Odile Jacob. 2011. Costentin J., Delaveau P. Café, thé, chocolat, les bons effets sur le cerveau et pour le corps. Editions Odile Jacob. 2010. 3 Crawford M., Marsh D. The driving force : food in human evolution and the future.
