Guidelines for vapor release mitigation

GUIDELINES FOR Vapor Release Mitigation Prepared by Richard W. Prugh Center for Chemical Process Safe& and Robert W . Johnson Battelle Columbus Division for CENTER FOR CHEMICAL PROCESS SAFETY of the American Institute of Chemical Engineers 345 East 47th Street, New York, NY 10017 This page intentionally left blank GUIDELINES FOR Vapor Release Mitigation This page intentionally left blank GUIDELINES FOR Vapor Release Mitigation Prepared by Richard W. Prugh Center for Chemical Process Safe& and Robert W . Johnson Battelle Columbus Division for CENTER FOR CHEMICAL PROCESS SAFETY of the American Institute of Chemical Engineers 345 East 47th Street, New York, NY 10017 Copyright 6 1988 American Institute of Chemical Engineers 345 East 47th Street, New York, NY 10017 All rights resemed 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 permission of the copyright owner. Libtwy of Congreae Cataloging-in-Publicatwn Data Prugh, Richard W. Guidelines for vapor release mitigation Bibliography: p. Includes index. Environmental aspects. 2. Petro1. Chemical plants leum chemicals industry - Environmental aspects. 3. Vapors - Environmental aspects. 4. Hazardous substances - Environmental aspects. L Johnson, Robert W. (Robert William), 1955II. American Institute of Chemical Engineers. Center for Chemical Process Safety. IlI. Title. TD888.C5P78 1987 660.2’804 87-26987 ISBN 0-8169-0401-4 - I This book is available at a special discount when ordered in bulk quantities. For information, contact the Center for Chemical Process Safety at the address shown above. I It is sincerely hoped that the information presented in this document will lead to an even more impressive safety record for the entire industry; however, neither the American Institute of Chemical Engineers, nor the Battelle Memorial Institute can accept any legal liability or responsibility whatsoever for the consequences of its use or misuse by anyone. CONTENTS Preface Acknowledgments Summary Glossary 1. Introduction 1.1 Objective 1.2 Hazard of Accidental Vapor Cloud Releases 1.3 Types of Vapor Clouds 1.3.1 Flammable Vapor Clouds 1.3.2 Toxic Vapor Clouds 1.3.3 Flammable-Toxic Vapor Clouds 1.3.4 Other Types of Vapor Clouds 1.4 Forms of Vapor Release 1.5 Release Causes 1.6 Possible Consequences of Vapor Cloud Releases 1.6.1 Toxic Effects 1.6.2 Fires 1.6.3 Explosions 1.7 Analysis of the Need for Mitigation 1.8 Vapor Release Mitigation Approaches 2. Mitigation through Inherently Safer Plants 2.1 Inventory Reduction 2.2 Chemical Substitution 2.3 Process Modification 2.3.1 Refrigerated Storage Guidelines for VaporRelease Mitigation vi 2.3.2 Dilution 2.4 Siting Considerations 19 20 3. Engineering Design Approaches to Mitigation 3.1 Plant Physical Integrity 3.1.1 Design Practices 3.1.2 Materials of Construction 3.2 Process Integrity 3.2.1 Identification of Reactants and Solvents 3.2.2 Limits on Operating Conditions 3.2.3 Process Control Systems 3.2.4 Pressure Relief Systems 3.2.4.1 Relief Devices 3.2.4.2 Relief Headers 3.3 Process Design Features for Emergency Control 3.3.1 Emergency Relief Treatment Systems 3.3.1.1 Active Scrubbers. 3.3.1.2 Passive Scrubbers 3.3.1.3 Stacks 3.3.1.4 Flares 3.3.1.5 Catchtanks for Vapor-Liquid Separation 3.3.1.6 Incinerators 3.3.1.7 Absorbers 3.3.1.8 Adsorbers 3.3.1.9 Condensers 3.3.2 Emergency Process Abort Systems 3.3.3 Emergency Isolation of Leak/Break 3.3.3.1 Isolation Devices 3.3.3.2 Remote Isolation. 3.3.3.3 Inspection and Testing of Isolation Devices 3.3.4 Emergency Transfer of Materials 3.3.4.1 Transfer of Vapor/Cover Gas to Reduce Driving Pressure 3.3.4.2 Transfer of Liquids to Reduce Inventory Available for Release 3.4 Spill Containment 3.4.1 Double Containment 3.4.2 Enclosures and Walls 3.4.3 Dikes, Curbs, Trenches, and Impoundments 23 24 24 25 27 27 4. Process Safety Management Approaches to Mitigation 4.1 Operating Policies and Procedures 63 63 66 4.2 Training for Vapor Release Prevention and Control 28 29 30 30 31 33 33 34 36 37 40 43 45 46 46 47 47 49 50 52 52 53 54 56 57 57 57 58 Contents Audits and Inspections Equipment Testing Maintenance Programs Modifications and Changes Methods for Stopping a Leak 4.7.1 Patching 4.7.2 Freezing 4.8 Security 4.3 4.4 4.5 4.6 4.7 5. Mitigation through Early Vapor Detection and Warning 5.1 Detectors and Sensors 5.1.1 Types of Sensors 5.1.1.1 Combustion 5.1.1.2 Catalytic 5.1.1.3 Electrical 5.1.1.4 Chemical Reaction 5.1.1.5 Visual 5.1.1.6 Absorption/Scattering 5.1.2 Response Time of Sensors 5.1.3 Positioning of Sensors 5.2 Detection by Personnel 5.2.1 Odor Warning Properties 5.2.2 Color or Fog 5.3 Alarm Systems 6. Mitigation through Countermeasures 6.1 Vapor/Liquid Releases 6.2 Vapor Release Countermeasures 6.2.1 Water Sprays 6.2.2 Water Curtains 6.2.3 Steam Curtains 6.2.4 Air Curtains 6.2.5 Deliberate Ignition 6.2.6 Ignition Source Control 6.3 Liquid Release Countermeasures 6.3.1 Dilution 6.3.2 Neutralization 6.3.3 Covers 6.3.3.1 Liquids 6.3.3.2 Foams 6.3.3.3 Solids 6.3.3.4 Application 6.4 Avoidance of Factors that Aggravate Vaporization vii 67 68 70 71 73 73 74 75 77 77 78 78 78 78 78 79 79 79 81 81 82 82 84 87 87 88 88 89 90 91 91 92 93 94 94 94 94 95 96 96 96 viii Guidelinesfor Vapor Release Mitigation 7. On-Site Emergency Response 7.1 On-Site Communications 7.2 Emergency Shutdown Equipment and Procedures 7.3 Site Evacuation 7.4 Havens 7.5 Escape from Vapor Cloud 7.6 Personal Protective Equipment 7.7 Medical Treatment 7.8 On-Site Emergency Plans, Procedures, Training, and Drills 101 8. Alerting Local Authorities and the Public 8.1 Alerting Systems 8.1.1 Capabilities 8.1.2 Input requirements 8.2 Roles and Lines of Communication 8.3 Information to Be Communicated 113 9. Selection of Mitigation Measures 9.1 Risk Analysis 9.2 Methods for Hazard Identification 9.3 Methods for Estimating the Consequences of Accidents 9.4 Methods for Estimating the Probability of Accidents 117 102 103 104 104 106 106 108 108 114 114 115 115 116 118 120 120 122 Appendix A. Loss-of-ContainmentCauses in the Chemical Industry 123 Appendix B. Properties of Some Hazardous Materials. 129 Appendix C. Derivation of Fog Correlations 131 Appendix D. Catchtank Design 133 Appendix E. Capacity of Havens 137 Appendix F. Sources to Vapor-Mitigation Equipment Vendors 141 Subject Index 143 PREFACE The American Institute of Chemical Engineers (AIChE) has a 30-year history of involvement with process safety and loss control for chemical and petrochemical plants. Through its strong ties with process designers, plant builders and operators, safety professionals, and academia, the AIChE has enhanced communication and fostered improvement in the high safety standards of the industry. Their publications and symposia have become an information resource for the engineering profession on the causes of accidents and means of prevention. Early in 1985, AIChE established the Center for Chemical Process Safety (CCPS) to serve as a focus for a continuing program for process safety. The first CCPS project was the preparation of Guidelines for Hazard Evaluation Procedures. One of the CCPS projects for 1987 was the preparation of this document, Guidelinesfor Vapor Release Mitigation. The goal of this project was to publish available information on generic techniques designed to reduce the consequences of unplanned hazardous vapor releases. Sources of information will be major chemical companies as well as recent open literature, governmental agencies, transport systems, and engineering organizations. The CCPS will solicit information from major chemical companies and by so doing provide these companies a mechanism for making any special knowledge available to the engineering community and the public. Thus, Guidelines for Vapor Release Mitigation is a survey of current industrial practice for controlling accidental releases of hazardous vapors and preventing their escape from the source area. To prepare this document, CCPS reviewed the available literature for de- X Guidelines for Vapor Release Mitigation scriptions of existing and proposed vapor-control equipment and visited industrial sites. CCPS also obtained equipment designs and procedures for dealing with vapor releases from chemical and petrochemical companies. These guidelines are intended to represent current industrial practice rather than theory. However, some of the suggested practices and equipment have not been fully tested; that is, they may not have been used to mitigate an actual vapor release. These guidelines present methods for attaining improvement and are a starting point for further development; however, they are not proposed as standards to be achieved by the industry, and companies are not expected to employ all of the methods presented. Further, there are wide variations in toxicity (acute, chronic, and latent), resistance to corrosion and erosion, flammability (explosive limits and ignition energies), and physical properties (vapor pressure and vapor density) among the fluids involved. Therefore, the applicability of the guidelines should be evaluated or tested in terms of particular fluids and proposed construction materials. Guidelinesfor Vapor Release Mitigation should be useful to both experienced and inexperienced engineers, but because of the rapid evolution in plant design and operation, it is unlikely that this volume includes all the useful methods for mitigating vapor hazards. Current literature--particularly the journals of AIChE and its British counterpart, the Institution of Chemical Engineers--contains additional guidance on existing and novel methods of vapor control. Eliminating the cause of releases and reducing their frequency are effective mitigation methods, in the broader sense of the term. Techniques for analyzing processes to identify vapor release sources and evaluate their likelihood are presented in Guidelines for Hazard Evaluation Procedures and in a forthcoming CCPS volume, Guidelines for Chemical Process Quantitative Risk Assessment Procedures. Methods for preventing vapor releases are also addressed in Guidelines for Safe Storage and Handling of High Toxic Hazard Material. Although methods for reducing the likelihood of vapor releases are included in the present volume, these guidelines emphasize methods for reducing the size, duration, and consequences of vapor releases. ACKNOWLEDGMENTS The AIChE wishes to thank the members of the Technical Steering Committee of the Center for Chemical Process Safety for their advice and support. Under the auspices of the Technical Steering Committee, the Vapor Mitigation Subcommittee of the CCPS provided guidance in this work. The chairman of the subcommittee was Stanley J. Schechter (Rohm and Haas), with Edwin J. Bassler (Stone & Webster) and G. A. Viera (Union Carbide) also on the subcommittee. Thomas W. Carmody and Russell G. Hill of the Center for Chemical Process Safety were responsible for overall administration and coordination of this project. The subcommittee acknowledges the assistance of the following people in commenting on various aspects of the drafts: D. E. Wade (Monsanto), R. A. Smith (Dow), R. F. Schwab (Allied-Signal), R. G. Holmes (Westinghouse), R. W. Ormsby (Air Products), P. Rasch (Celanese), R. J. Hawkins (Celanese), S. S . Grossel (HoffmanLaRoche), and J. Hagopian (Arthur D. Little). The principal author of Guidelines for Vapor Release Mitigation was Richard W. Prugh, a staff member of the Center for Chemical Process Safety, with significant technical and editorial contributions by Robert W. Johnson of Battelle Memorial Institute’s Columbus Division. Important editorial contributions from William H. Goldthwaite of Battelle Columbus Division are gratefully acknowledged. xi This page intentionally left blank SUMMARY The purpose of this document is to make generally available the approaches and measures that are currently being used by many companies in the chemical process industry for mitigating the likelihood and consequences of vapor cloud releases. Many of the major chemical accidents that have occurred recently have involved the release of toxic or flammable vapors in quantities sufficient to have severe health and environmental impacts. The release of dangerous amounts of toxic and flammable vapors can be minimized and the severity of their effects can be reduced by a variety of mitigation measures. The choice of mitigation measure depends upon the particular hazard of concern, the amount of material involved, the siting of the facility, the processes involved, and other characteristics of the facility in question. Nevertheless, there is a hierarchy or preference order to the approaches that should be considered in choosing an approach for any particular mitigation concern. The mitigation approach which is generally most effective is to make the plant inherently safer. A chemical process facility will be inherently safer if, for example, the inventory of hazardous material can be eliminated by substitution of a nonhazardous material in the process, or reduced to a level where total release would not pose a threat 'to employees or the public. This is being done in several facilities by manufacturing the hazardous material in situ and limiting the inventory to that which is in the pipes and reaction vessels. Another approach that is sometimes possible with new plants is to choose a site far enough removed from populated or sensitive areas that it would be impossible for a hazardous concentration to develop there. It folxiii XiV Guidelines for VaporRelease Mitigation lows that this buffer zone must somehow be kept inviolate for the life of the plant or process. There are a variety of engineering approaches to mitigation of hazardous vapor releases that are next in order of preference. The first is to ensure plant integrity so that the probability of a release is minimized. Attention to design and construction codes is an important aspect of this. Ensuring that materials of construction are chosen to maintain plant integrity while containing the process materials under the process conditions and under process upset conditions is essential. Inspection and testing of materials and equipment before start-up and at intervals during operation of the process are also necessary. "Process integrity" is also high on the preference order of approaches to mitigation. Process integrity involves the chemistry of plant design and operation, and includes ensuring that only the proper reactants and solvents are used and that they are of the required purity for the process and equipment. Knowing and maintaining the conditions of operation within limits that are known to be safe is also essential to process integrity. Avoiding processes that are sensitive to parameter deviations and providing measurement and control of those parameters are helpful in avoiding upsets that lead to loss-ofcontainment accidents. Pressure relief systems, properly chosen and configured and venting into other containment or disposal systems such as scrubbers, stacks, and flares, are another way of enhancing process integrity. The approaches to mitigation that have been mentioned above are at the top of the preference order because they can work toward preventing the release of dangerous amounts of hazardous vapors. However, mitigation after loss of containment can also be effective and usually must be provided for in the process design stage. Secondary containment by concentric piping, double-walled vessels, or enclosures may be warranted. In the event of the release of a volatile liquid to the environment by a leak or a rupture of a line or vessel, containing the liquid in a restricted area or minimizing its surface area can reduce the quantity of material released as vapor. This can be accomplished by using dikes, curbs, and trenches leading to strategically located impoundments. An added incentive is to help keep the liquid source of the vapor away from sensitive areas with respect to people, process, and the environment. There are other effective mitigation measures that are more concerned with the start-up, operation, and maintenance of the facility than With facility and process design. These include procedure development and communication, training, inspections and tests, documentation and the protocol for maintenance and modifications. In each Summary xv instance, accuracy and clarity of procedures are important to avoid errors which could lead to upsets and vapor release accidents. Should loss of containment develop, there are methods for temporarily stopping a leak through patching or, with some materials, freezing that may be useful. Mitigation by early detection and warning can be effective in preventing on-site health effects and in limiting the off-site release to nonhazardous levels. There are several detection methods ranging from various types of sensors to detection by personnel by odor or sight. Warning may involve alarms, communication systems, and accident analysis systems. Lower on the preference order, but still important, are the systems or equipment that can be provided for mitigation by countermeasures. These provide mitigation by controlling, to as great a degree as possible, the dilution and dispersion of the hazardous vapors. Systems such as water curtains, steam curtains and water sprays have been studied and used, to a limited extent, to control the movement and concentration of the vapor. If the spilled liquid has been confined by a dike or impoundment, reducing the vapor generation rate can often be done by covering the liquid source with foams, with compatible liquids, and, in some cases, with granular solids. On-site and off-site emergency response can provide effective mitigation of health effects in many instances if adequately planned and effectively implemented. This requires both equipment and training--both tailored to the materials and types of accidents that are most likely to be involved. The preference order of mitigation measures that have been mentioned and are described in this volume is important to selection of the most appropriate measures for a particular facility. Also important is an understanding of the types of accident that can occur and result in a vapor release and the possible consequences of such a release. Methods for identifying and evaluating accident scenarios, both with and without particular mitigation measures, can be valuable in the selection process. Other AIChE-CCPS volumes, referenced in this text, describe these identification and evaluation procedures. This page intentionally left blank