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1、 Evaluating Process Safety in the Chemical Industry A USERS GUIDE TO QUANTITATIVE RISK ANALYSIS J. S. Arendt D. K. Lorenzo EQE International, Inc. Knoxville, Tennessee American Chemistry Council 1300 Wilson Boulevard Arlington, Virginia 22209 Center for Chemical Process Safety 3 Park Avenue New York
2、, New York 10016 Copyright 2000 American Institute of Chemical Engineers 3 Park Avenue New York, New York 10016-5991 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, rec
3、ording, or otherwise without the prior permission of the copyright owner. ISBN 0-8169-0746-3 Library of Congress Cataloging-in-Publication Data (CIP data has been applied for) This guide was prepared by EQE International, Inc. (EQE), an ABS Group Company, as an account of work sponsored by the Ameri
4、can Chemistry Council, formerly the Chemical Manufacturers Association, and the Center for Chemical Process Safety (CCPS) of the American Institute of Chemi- cal Engineers (AIChE). It is sincerely hoped that the information presented in this document will lead to an even more impressive record for t
5、he entire industry; however, the American Institute of Chemical Engineers, the American Chemistry Council, its consultants, CCPS Subcommittee mem- bers, their employers, their employers officers and directors, and EQE International, Inc. and its employees disclaim making or giving any warranties or
6、representations, express or implied, including with respect to fitness, intended purpose, use or merchantability and/or correctness or accuracy of the content of the information presented in this document. As between (1) American Institute of Chemical Engineers, its consultants, CCPS Subcommittee me
7、mbers, their employers, their employers officers and directors, and EQE International, Inc. and its employees and (2) the user of this document, the user accepts any legal liability or responsibility whatsoever for the con- sequence of its use or misuse. PRINTED IN THE UNITED STATES OF AMERICA 10987
8、654321 PREFACE Quantitative risk analysis (QRA) is a powerful analysis approach used to help manage risk and improve safety in many industries. When properly performed with appropriate respect for its theoretical and practical limi- tations, QRA provides a rational basis for evaluating process safet
9、y and comparing improvement alternatives. However, QRA is not a panacea that can solve all problems, make decisions for a manager, or substitute for existing safety assurance and loss prevention activities. Even when QRA is preferred, qualitative results, which always form the foundation for QRA, sh
10、ould be used to verify and support any conclusions drawn from QRA. The American Chemistry Council, the Center for Chemical Process Safety, and their member companies recognize the need to provide deci- sionmakerswithaguidetoQRA. Chemicalprocessindustry(CPI)profes- sionals at every level (plant manag
11、ers, project managers, engineers, supervisors, etc.) need criteria for determining when risk analysis will provide information that will aid their decision making. Executives need help in understanding and evaluating QRA results that are often inscruta- bletononexperts. Andallneedadviceconcerninghow
12、detailedananaly- sismustbeifitistoprovideadequateinformationforaspecificdecision. ByillustratingthejudicioususeofQRA,thisguidewillhelpmanagersuse their limited resources more efficiently. This guide summarizes some of the wisdom accumulated by CPI risk analysispractitionersandsafetyprofessionals;dec
13、isionmakersconsider- ing the use of QRA can benefit from this collected experience. Even though this guideline does not address every issue and circumstance concerning the use of QRA, we believe that you will be able to blend your experience with the strategies provided in this guide to make more in
14、formed decisions about using QRA. xiii ACKNOWLEDGMENTS The American Chemistry Council, formerly the Chemical Manufacturers Association (CMA), and the American Institute of Chemical Engineers Center for Chemical Process Safety (AIChE/CCPS) have jointly published EvaluatingProcessSafetyintheChemicalIn
15、dustry:UsersGuidetoQuantitative Risk Analysis. This is a revised and updated edition of Evaluating Process Safety in the Chemical Industry: A Managers Guide to Quantitative Risk Analy- sis, published in 1989 by CMA. This book was written by Donald K. Lorenzo and J. Steven Arendt of EQE International
16、, Inc. (EQE), an ABS Group Company. The technical insights, experiences, suggestions, and peer review of the CCPS Risk Analysis Subcommittee (RASC), the American Chemistry Council Process SafetySubteam(PSS),andtheoriginal(1989)CMAProcessSafetyAnalysis Task Group (PSATG) were essential to the develop
17、ment of this guide. The CCPS RASC was chaired by Dennis C. Hendershot (Rohm Shell Chemical; ExxonMobil Chemical; Huntsman; Dow Chemical; Solutia; Celanese; Rohm Air Products and Chemicals, Inc.; Monsanto; Union Carbide; Montell; Eastman Chemical; and Lyondell. We are also indebted to the reviewers o
18、f this guide at EQE: John Farquharson for his technical review, Maureen Hafford for her editorial suggestions, Leslie Adair for proofreading the guide, and Angie Nicely and Paul Olsen for preparation of the manuscript for this guide. xv EXECUTIVE SUMMARY The art of making wise decisions is the hallm
19、ark of successful manage- ment and requires both pertinent information and good judgment. Safety-related decisions, in particular, have traditionally been based on hard-earned operating experience and intuition. As greater demand for improving the safety, health, environmental, and economic aspects
20、of facilities is placed on companies finite resources, the decision-making process becomes more difficult and the need for better information becomes more critical. Company management now recognizes that simply reacting to acci- dents and then determining where additional safety precautions are need
21、ed is no longer acceptable the potential effects of accidents are becoming increasingly catastrophic.Moreover, todays technical and social environment dictates that decision makers take a more proactive approach to safety-related decision making and that more thorough methods and strategies be used
22、to gain an increased understanding of the significance of risks from their companies operations. Risk is defined as the combination of the expected frequency and consequence of accidents that could occur as a result of an activity. Risk analysis is a formal process of increasing ones understanding o
23、f the risk associated with an activity. The process of risk analysis includes answer- ing three questions: What can go wrong? How likely is it? What are the impacts? Risk assessment is the subsequent process of taking risk analysis results and answering a fourth question: Are the risks tolerable? xv
24、ii Qualitative answers to one or more of these questions are often suf- ficient for making good decisions about the allocation of resources for safety improvements. But, as managers seek quantitative cost/benefit information upon which to base their decisions, they increasingly turn their attention
25、to the use of quantitative risk analysis (QRA). This guide provides information on the applicability of QRA to the chemicalprocessindustry(CPI). Althoughcompanieshavemanypossible applications for risk analysis (e.g., determining the investment risk of a new product), this guide focuses on how risk a
26、nalysis methods can be used for the improvement of process facilities. Moreover, while QRA can also be used to investigate economic, environmental, and health risks of process operations, this guide concentrates on QRAs use for estimating one particular type of riskthe risk of immediate injuries to
27、workers or the public from single accidents involving acute exposure to energy releases or harmful substances. Developing an appreciation of the benefits, limitations, relative costs, and complexities of using QRA is a necessity for CPI managers. To equip the potential user of QRA with this basic un
28、derstanding, this guide discusses three important aspects of QRA: How to decide whether to use QRA How to set up a QRA to provide specific risk information How to interpret and use QRA results This guide presents a framework to help you decide whether QRA can aid your decision making. Various factor
29、s influencing the decision to useQRAaredescribed,andthetypesofinformationQRAsmakeavailable tomanagersarediscussed. Managersareencouragedtofirstusequalita- tive techniques and risk screening methods as decision aids. Efficiency dictates that managers use QRA only in selected cases when decision- maki
30、ng information cannot be supplied by less elaborate means. But, appropriately scoped and applied, QRA can provide powerful insights for allocatingfiniteprocesssafetyresources.Thisguidecontainsaflowchart of questions and information you can use to help determine when to use QRA. If decision makers ch
31、oose to use QRA, they must then define the analysis objectives so the results will satisfy the particular decision- making requirement. Because the cost of performing QRA is dependent xviiiEXECUTIVE SUMMARY on depth and scope of study, this guide stresses the importance of defin- ing the right probl
32、em for analysis. An overview of QRA methods is pre- sented to help executives understand the options available when selecting QRA techniques. To help managers have realistic expectations, important limitations of QRA techniques are also discussed. Finally, this guide presents information on interpre
33、ting and using QRA results, outlining several methods for comparing results with expe- rience and for presenting results to enhance credibility. Because the way people view risk is an overriding concern in the use of QRA, various fac- tors that influence risk perception are also discussed. And the g
34、uide lists some pitfalls managers should avoid in using QRA results for decision making. WhenQRAisusedjudiciously,itsadvantagescanoutweightheasso- ciated problems. However, companies should resist the indiscriminate use of QRA as a means to solve all problems since this strategy could be aninefficie
35、ntuseoffinitesafetyimprovementresources,divertingatten- tion from other essential safety activities. Once executives can interpret and use QRA results, they will appreciate that the quality of their deci- sions largely rests on their ability to understand the salient analysis assumptions. Moreover,
36、they can use QRA to determine the impacts of important assumptions, and can use these sensitivity results to better understand the limitations of QRA studies. Quantitative risk analysis is an important tool for the CPI. But QRA mustcomplement(andnotreplace)otherhistoricallysuccessfulmethods for safe
37、ty assurance, loss prevention, and environmental control. A new, evolving technology, and still more of an art than a science, QRA will never make a decision for youit can only help to increase the informa- tion base you draw on when making a decision. More conventional pro- cess safety management p
38、ractices, such as good design standards, proper construction, accurate procedures, thorough training, periodic safety audits, and sound management judgment, will continue to form the foundation for a safe and productive chemical industry. EXECUTIVE SUMMARYxix ADVICE FOR THE READER This guide is desi
39、gned to equip you with a basic understanding of the benefits,limitations,andcomplexitiesofusingQRA. However,thisisnot a “how to” manual for QRA; nor does it concentrate on how to set up a corporate QRA program. (This information can be found in the CCPS Guidelines for Chemical Process Quantitative R
40、isk Analysis, Second Edition.24) Instead, this guide describes the role managers and sponsors should play in ensuring the success of QRA projects. To convey this information, we use the following steps: Establish a basic vocabulary (Glossary). Every discipline has its own jargon, and QRA is no diffe
41、rent Define a method for determining whether QRA can (or is needed to) help your decision making Describe what to reasonably expect from QRA ProvideabasisforunderstandingQRAresults,beyondtheobvious statistical meanings This guide may be read by an audience ranging from middle manag- ers to senior ex
42、ecutives who have different levels of knowledge about QRA. This guide may also be read by engineers and other technical staff who will be contributing to QRAs or using the results. We have, there- fore, designed the chapters to allow for differences in expertise and need. Chapter 1 defines QRA, disc
43、usses its essential elements, and dispels some misconceptions. Chapter 2 outlines considerations for deciding when to apply QRA. It presents some reasons for performing QRA and describes the types of information available from such studies.This chapteralsodescribespracticalsituationsinwhichQRAmaybeu
44、sedsuc- cessfully, as well as conditions that make QRA a less desirable choice. xxi OncethedecisionhasbeenmadetouseQRA,thenextstepistoexe- cute it effectively. Chapter 3 describes the process of setting up an indi- vidual QRA. This chapter discusses the importance of defining the right problem for a
45、nalysis and selecting the right analysis techniques; it also provides an overview (not a how to) of the various classes of QRA tech- niques. Chapter 4 discusses ways to interpret and use QRA results. Con- clusions about the future of QRA in the CPI are offered in Chapter 5. xxiiADVICE FOR THE READER
46、 ACRONYMS AIChEAmerican Institute of Chemical Engineers APIAmerican Petroleum Institute CCPSCenter for Chemical Process Safety CMAChemical Manufacturers Association CPIChemical process industry CPQRAChemical process quantitative risk analysis ERPGEmergency response planning guideline FARFatal accide
47、nt rate FMEAFailure modes and effects analysis HAZOPHazard and operability analysis LOPALayer of protection analysis P however, you may still need information on how likely the accident is. In other cases the quantification of poten- tial impacts alone will be adequate, and analysis of the likelihoo
48、ds is unnecessary. In practice, few decisions require explicit quantification of both frequency and consequence. 1.3. DEFINITION OF QRA QRA is the art and science of developing and understanding numerical estimates of the risk (i.e., combinations of the expected frequency and consequences of potenti
49、al accidents) associated with a facility or opera- tion. It uses a set of highly sophisticated, but approximate, tools for acquiring risk understanding. QRA methods can be used throughout all phases of the life of a process (laboratory development, detailed design, operation, demolition, etc.). However, QRA is most effective when used to analyze a process whose design characteristics have been specified (i.e., the piping and instrument diagrams P consistency with current industry practice). ThereareavarietyofwaystoexpressabsoluteQRAresults.Absolute freque
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