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ILhemt FUNDAMENTALS OF PROCESS SAFETY Marshall and Steve Ruhemann Vjc The Authors Vic Marshalls tudied part-time for Associate Membership of the IChemE while working as a plant chemist for British Celanese. He went on to work for Theodore St. Just and Simon Carvesb eforej oining Bradford University, where he playeda major part in building up the new Chemical Engineering Department. After appearing as expert witness for the trades unions at the Flixborough Inquiry, he devotedt he rest of his career to safety, both as Directoro f Safety Services for the University and as a researchera nd consultant. Vic was a pioneer in the study and of practice process safety, publishingm any papers and a seminal book, Major Chemical Hazards. He served on the Major Hazards Committee of the Healtha nd Safety Commission and on many other advisory bodies. For this and related work he was awarded the Council, Franklin and Hanson Medalso f the IChemE. He died in 1996. Steve Ruhemann studied chemical engineering atI mperial College. He worked for Bataafsche PetroleumM aatschappij, the British Paper& Board Industry Research Association and AEI-Birlec Ltd before joining Bradford University'sC hemical Engineering Department, where he taught a varietyo f subjects. Since 1989 he has specialized in teaching ProcessS afety. Steve has served for many yearso n the local and national Executive Committees of the Association of University Teachers, and as its nationalP resident. of Fundamentals process safety Fundamentals of process safety Vie Marshall and Steve Ruhemann IChemE The information in this book is given in good faith and beliefi n its accuracy, but does not implyt he acceptance ofa ny legal liabilityo r responsibilityw hatsoever,b y the Institution, or by the authors, for the consequences of its use or misuse in any particularc ircumstances. This disclaimers hall have effecto nly to the extent permittedb y any applicablel aw. All rightsr eserved. Nop art of this publication may be reproduced, stored ina r etrievals ystem, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, withoutt he priorp ermissiono f the publisher. Published by Institutiono f ChemicalE ngineers (IChemE), Davis Building, 165—189 Railway Terrace, Rugby, Warwickshire CV21 3HQ, UK IChemEi s a Registered Charity © 2001 Steve Ruhemann ISBN0 85295 431 X Typesetb y TechsetC omposition Limited, Salisbury, UK Printedb y Bell& Bain Limited, Glasgow, UK 11 Foreword The chemicala nd process industries have broughtb enefitst o humanity which are so widespread that it is only possible for us tog ive af ew examples oft hem. Virtuallye verything we use today is a product,a t least partly,o f these industries. Houses, clothes, furniture, books,c omputers, health products, medicines and leisuree quipmenta re all, to a greater or lesser degree, products of these industries. Even the automotive industry, where raw materials are mainly metallic, requires rubber and plastics for indispensable items such as tyres, paint and seats. The finished product then requires fuel, produced by petroleumr efining,t o make it go. When things go wrong, however, these benefits can be costly, in terms of human injury and death, and damaget o property and the environment. Explo- sions, fires and toxic releases, exemplified by such disastersa s Flixborough, Seveso, Bhopal and Mexico City, are examples of what can happen ift hose who design or operate process plants get things badly wrong. Moreover, for every major event which makes the headlines,t here are perhaps hundreds of lessere vents, eachw ith itst oll of injury and damage. This book is concerned withh azards the situations whichh ave the poten- tial to give rise to such disasters— and the nature of the harm which may be inflicted on people, property or the environment when their potentials are realized. Our aim It ist he duty ofa ll int he processi ndustries to contribute ina ny wayt hey cant o reducet his toll of harm. To this end, thosew ho graduate from universities in the relevant disciplines, aspiring to gain responsible posts in these industries, mustu nderstandt heb asic principles whichu nderlie process safety. Oura im in writing this book, therefore, is to help them to do so. The study of this book alone will not adequately prepare graduates for immediate responsibility in industry. For this they still need to refer to more 111 specialistl iterature and will requires pecific practicalt raining,b oth initial and recurrent. In our view, however, it is not the responsibility of universitiest o provide such training,n or is itp racticalf or them to attemptt o do so. It is rather the role of enterprises to train their employees to apply these principles to the particularc ircumstances of their industry. The of study process safety The processi ndustries— or at least their more enlightened practitioners— have alwaysh ad ac oncernf or safety. Safety Rulesf or Use in ChemicalW orks' — the third edition of a work originally published in 1928 — gives some generalg uidance and many detailedi nstructions for the safe conducto f chemical processing operations. Its approach, however, is largely of the kind describeda s 'tactical' (see Chapter 6), reflectingt he relatively small scale of operations typical att he time. Thei ntervening yearsh ave seen an immense growthi n the scale of chemical manufacturing, with a corresponding increase in the severity of the harm caused when accidents occur. At the same time, public awarenesso f such events has been greatlye nhanced by theg rowtho ft he communications media, so that they have — quite properly— become matters of general concerno n which governments have been obliged to institute public enquiries and enact legislation. Manufacturing organizations, government agenciesa nd professionali nsti- tutions have thereforef ound itn ecessaryt o devotes ubstantial resources tot he study of the causes and consequences of such disasters and the means of preventing them and minimizing their effects. Early studies examined the disasters from the standpoint of the particulari nstallation and process, but it has become increasingly apparentt hat, in terms of science, engineering and management, all accidents have common features, even those arising in differentp lantsu sing differentp rocessest o make differentp roducts. The distincti dentityo ft he subject of process safety (manyp eople initially calledi t loss prevention, and some still do so) originatedi n the recognition of these commonf eatures,a nd iti s now explicitlya cknowledged, for example,b y the Institution of ChemicalE ngineers (IChemE)2. It is still ata n early stage of development as an academic subject, and there is continuing debate as to how it shouldb est be taught. It is hoped that this text will make a useful contribu- tiont o this debate and development. We acknowledge that process safety is actually a part of a wider area of concern dubbed by Marshall3 as 'social acceptability',w hich also includest he iv subject now becoming established as 'environmental protection'.W e believe that these subjects are closely related and shouldb e associated in academic study. on Existing publications process safety There are manyb ooks in print on the subject of process safety. The Centerf or Chemical Process Safety (CCPS)o ft he American Institute of Chemical Engi- neers (AIChE) and IChemE list, between them, some 40 books which have been published on various aspects of the subject. There are also a numbero f independently authored works in the area. There is aw ide range of guidance publications by governmental regulatory agencies, including thoseb y the Healtha nd Safety Executive (HSE)i n the UK and the NationalI nstitute for Occupational Safety and Health (NIOSH) in the USA. There is also ar ange of publications by the trade associations and indi- vidual firmsi nt he process industries. Of particularn ote is the seventh edition of Perry's Chemical Engineers' Handbook4, an extremely important reference work first published in 1934. 'Perry' has always been divided into sections covering distinct parts of the knowledge base oft he profession, butt he presente dition is the first to include one entitled 'process safety', an event which may perhaps be considered to reflectt he coming-of-age of the subject. The need for a different approachf or students It may seem,t herefore, that the subject area is alreadym ore than adequately covered. However, withoutw ishingt o minimize the importance oft hese publications, we believe that, with very few exceptions, theyh ave not been written for students, but rather for practisinge ngineers and technologists who have a considerable amount of knowledge and 'hands-on' experience. Some of them have also been writtenb y specialists, for specialists. a This book presents the fundamentals of process safetyi n way that canb e assimilatedb y students, who typically lack prior practical knowledge and experience. We have endeavoured to present this material within a coherent, integrated, academic framework, which is grounded in fundamental science, with the aim of making the subject more amenable to systematic study and more clearly related to the other subjects in their curriculum. v Theb ook is largelyb asedu pon a conceptual model which we have devised and which is expounded progressively in the course of the text. The model is founded on a set of defined and inter-related concepts. Students have limited time to study a subjectw hich is only a fairly small part of an undergraduate course. This makes it all the more importantt hat the book should concentrate on fundamentals. Even so, it can only provide the elementso f the subjecta nd, therefore, such important topics as, for example, quantitative risk assessment and gas dispersion, are treatedo nly in ani ntroduc- tory manner. Readership Early drafts of the book have been used successfully in the teaching of a process safety module to undergraduate students of chemical engineering at the Universityo f Bradford. We hope that it will prove suitable for students taking first degreesi n such subjects as chemical engineering, chemical technology, energy technology, petroleum engineering, and safety engineering. We hope, also, that it may be useful as an introductory text for graduates in thesed isciplines who have notr eceiveda ny formale ducation inp rocess safety and who now wish to study it. Finally, iti s our impression that lecturers attempting tot eacht he subjecta re significantly handicapped by the lack of a single text embodying it at an elementary level,e specially ifi t is not their primarya reao f specialization. We therefore hope that they will find support in this book. References I 1. ABCM, 1951, Safely Rules for Use in Chemical Works: Part ModelR ules, 3rd edn (Association of British Chemical Manufacturers, UK). 2. IChemE, 1998, Accreditation of University Chemical Engineering Degree Courses:a Guidef or Assessors and University Departments( IChemE,U K). 3. Marshall,V .C., 1990, The sociala cceptability of the chemicala nd process industries a proposal for an integrateda pproach, Trans IChemE, Part B, Proc Safe EnvProt, 68(B2): 83-93. 4. Perry,R H., Green, D.W. and Maloney, J.O. (eds), 1997, Perry's Chemical Engi- neers' Handbook, 7th edn (McGraw-Hill, UK). vi Acknowledgements In writingt his text we have inevitablyd rawn on av ery wider ange of sources. We have tried conscientiouslyt o acknowledgea ll of these by appropriate citations andI hope that we shall be forgivenf or any accidentalo missions. It isp erhapsa ppropriateh ere top ay a generalt ribute to the hundreds of authors who have contributedt o what has become, in recent years, a rich literature indeed. I owe ap articulard ebt to Dr I.M. Clark,w ho read a draft of the book and, thoughk indly givingi t his generala pproval,m ade a large number of sugges- tions for improvement, most of which I have been glad to incorporate. I am extremely gratefulf or the willing assistancew e have received from the Subject Librarians of the University of Bradford, specifically Anne I Costigan,M artin Wilkinson,P amelaT idswella ndK en Tidswell. have also had considerable help in the trackingd own of sources from John Williams, the University's Safety Advisor. My perseverancei n completingt he book owes much to the constant encouragement of my colleaguesi n the Univer- sity's Department of ChemicalE ngineering, whom I have to thank for many helpful discussions.T hanks are due also to the many students who have, by their responses and occasional criticisms, contributed significantly to its refinement (special mention should be made here of Mark Talford, who kindly undertookt o read the whole text). I have to thank Peter Dowhyj for drawing Figure 4.2 and Wendy Bailey and Jane Gibb for their clericala ssis- tance. Audra Morgan of IChemE has been extremely helpful in the final stages of preparationo f the book for publication. Notwithstanding all this help, such remaininge rrors as will surely come to light are of course the sole responsibilityo f the authors. It falls to me, as the surviving author, to express my gratitude for the of immensec ontribution my late colleaguea nd friendV ic Marshall.N ot only did he originallyc onceivet he idea oft he book and write the first draftso f the greaterp art, but the entiret ext has been informed by his pioneerings tudiesi n vii