Guidelines for Use of Vapor Cloud Dispersion Models, Second Edition

278 Pages·9.924 MB·English

GUIDELINES FOR
Use of Vapor Cloud
Dispersion Models
Publications Available from the
CENTER FOR CHEMICAL PROCESS SAFETY
of the
AMERICAN INSTITUTE OF CHEh4ICAL ENGINEERS
Guidelines for Use of Vapor Cloud Dispersion Models, Second Edition
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GUIDELINES FOR
Use of Vapor Cloud
Dispersion Models
SECOND EDITION
CENTER FOR CHEMICAL PROCESS SAFETY
of the
American Institute of Chemical En,’O ineers
345 East 47th Street, New York, NY 10017
Copyright 0 1996
American Institute of Chemical Engineers
345 East 47th Street
New York, New York 10017
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 othemise
without the prior permission of the copyright owner.
Library of Congress Cataloging-in Publication Data
Guidelines for use of vapor cloud dispersion models / Center for
Chemical Process Safety of the American Institute of Chemical
Engineers.
P. cm.
Includes bibliographical references and index.
ISBN 0-81694702-1
1. Atmospheric diffusion-hlathematical models. 2. Hazardous
substances-Environmental aspects-Mathematical models.
3. Vapor clouds-Mathematical models. I. American Institute of
Chemical Engineers. Center for Chemical Process Safety.
QC880.4.DUC85 1996
628.5'3'01 1 3 4 ~ 2 0 96-26950
I I
This book is available at a special discount when ordered in bulk quantities.
For information, contact the Center for Chemical Process Safe@ of the
American Institute of Chemical Engineers at the address shorn above.
It is sincerely hovd that the information presented in this document will lead to an evcn more
impressive saiery record for the entire indusu).: hoaever. the Amencan Institute of Chemcal
Engineers. its consultants. CCPS subcornnunee members. their employers. their employers'
officers and directon and E.ARTH TECH disclam mhng or gibing an)- amanues or
representations. exprtss or implied. including nith respect to fitness. intended purpose. use or
merchantabilit> andlor correcmess or accurac) of the content of the informauon presented in
this document. .As between I 1 ) the American Institute of Chemcal Engmeen. its consultants.
CCPS subcommittee membcn. their employers. their employers' officen and directors and
EARTH TECH and (21 the user of this document. the user accepts any legal liability or
responsibility a harswber for the consequence of ~tsus e or misuse.
Contents
PREFACE ix
ACKNOWLEDGMENTS xi
NOMENCLATURE xiii
1. Background and Objectives 1
2. Overview of Modeling Procedures,
Including Rationale for Selecting
Scenarios for Worked Examples 3
2.1. Types of Scenarios and Models 3
2.2. Gross Screening Analysis 7
2.3. Scenarios Selected for Worked Examples 9
3. Input Data Required 11
3.1. Source Data 11
3.2. Site Characteristics 13
3.3. Meteorological Data and Formulas for Calculating Input Parameters 13
3.4. Receptor-Related Data 16
4. Source Emission Models 19
4.1. Conceptual Process for Source Term Determination 20
4.2. Calculation of Source Terms 23
4.2. I. Gas Jet Releases 25
V
vi Contents
4.2.2. Liquid Jet Releases 29
4.2.3. Two-Phase Jet Releases 31
4.2.4. Liquid Pool Spreading 36
4.2.5. Liquid Pool Evaporation 39
4.2.6. Multicomponent Evaporation 46
4.3. Uncertainties in Source Term Estimation 47
5. Dispersion Models 49
5.1. Critical Richardson Number Criterion 49
5.2. Jet Trajectory and Entrainment 52
5.2.1. Momentum-Dominated Jers 52
5.2.2. Elevated Dense Gas Jets 54
5.2.3. Positively Buoyant Plumes 58
5.3. Dense Gas Release at Grade 59
5.3.1. Background and Overview 59
5.3.2. Dense Gas Clouds in the Absence of Heat Exchange 61
5.3.3. Dense Gas Clouds in the Presence of Heat Exchanges 72
5.4. Transport and Dispersion of Neutrally Buoyant
or Passive Gas Clouds 74
5.5. Simple Nomograms for Calculating the Dilution
of Dense Gas Release 78
5.6. Three-Dimensional Numerical Models of Dense Gas Dispersion 83
5.7. Transport and Dispersion Near Buildings 88
5.7.1. Plume Confinement by Canyons 89
5.7.2. Concentrationso n Building Faces Due to
Releases from Vents 89
5.7.3. Concentrationso n the Building Downwind Face (the
Near- Wake) Due to Releases from Sources on the Building 91
5.7.4. Other Effects of Buildings 91
5.8. Worst Case Meteorological Conditions 93
5.9. Removal by Dry and Wet Deposition 94
5.9.1. GravitationalS ettling of Lorge Pam'cles or Aerosols 94
5.9.2. Dry Deposition of Small Particles and Gases 96
5.9.3. Removal of Particles and Gases by Precipitation
and Clouds (Wet Deposition) 98
Contents vii
6. Averaging Times, Concentration Fluctuations,
and Modeling Uncertainties 101
6.1. Overview of Physical Considerations Related to Averaging Time 101
6.2. Overview of Characteristics of Concentration Fluctuations in Plumes 103
6.3. Predictions of Concentrations on the Plume Centerline at a Given
Downwind Distance as a Function of Averaging Time, Ta 104
6.4. Predictions of Concentrations at a Given Receptor Position as a
Function of Averaging Time, Ta 109
6.5. Threshold Crossing Probability 113
6.6. A General Structure for the Analysis of Model Uncertainties 113
7. Overview of Operational Vapor Cloud Models
in Common Use 119
7.1. Summary of Commonly Used Models 1 I9
7.2. Characteristics of Commonly Used Vapor Cloud Dispersion Models 121
8. Evaluation of Models with Field Data 127
8.1. Description of Field Data Sets 127
8.2. Model Evaluation Procedures 133
8.3. Models Evaluated 135
8.4. Results of Model Evaluations 137
9. Summary of Seven Worked Examples 147
9.1. Description of Seven Scenarios Used for Worked Examples 147
Properties of Released Material 149
Source Configuration 153
Source Strength 154
Meteorological Conditions 154
Site Conditions 155
Concentrations of Interest 155
Sensitivity Runs 156
9.2. Overview of Predicted Concentrations 156
APPENDIX A
Scenario 1 : Release of Pressurized Liquid Chlorine 159
viii Contents
APPENDIX B
Scenario 2: Liquid (Cryogenic) Spill of Refrigerated Chlorine 177
APPENDIX C
Scenario 3: Liquid (Noncryogenic) Spill of Liquid Acetone 195
APPENDIX D
Scenario 4: Vertical Jet Release of a Dense Gas (Normal Butane) 207
APPENDIX E
Scenario 5: Release of SO3 within a Building and Subsequent
Dispersion of H2S04 from a Vent on the Building 22 1
APPENDIX F
Scenario 6: Pressurized Horizontal Gas Jet Release of
a Multicomponent Mixture 235
APPENDIX G
Scenario 7: Transient (Mitigated) Area-Source Release
of Hydrogen Fluoride 243
REFERENCES 259
INDEX 267
Preface
For 40 years the American Institute of Chemical Engineers (AIChE) has
been involved with process safety and loss control issues in the chemical,
petrochemical, hydrocarbon process, and related industries and facilities.
AIChE publications and symposia are information resources for the chemi-
cal engineering and other professions on the causes of process incidents and
the means of preventing their occurrences and mitigating their consequences.
The Center for Chemical Process Safety (CCPS), a directorate of
AIChE, was established in 1985 to develop and disseminate technical
information for use in the prevention of major chemical process incidents.
With the support and direction of the CCPS Advisory and Managing Boards,
a multifaceted program was established to address the need for process
safety management systems to reduce potential exposures to the public,
facilities, personnel, and the environment. This program involves the
development and publication of guidelines related to specific areas of
process safety management; organizing convening, and conducting semi-
nars, symposia, training programs, and meetings on process safety-related
matters; and cooperation with other organizations, both internationally and
domestically, to promote process safety. CCPS’s activities are supported by
funding and expertise from over 90 entities.
In 1987 CCPS published Guidelinesf or Use of Vapor Cloud Dispersion
Models, and in 1989, Workbook of Test Cases for Vapor Cloud Source
Dispersion Models. These books have served well but are now outdated.
At nearly a decade old, they refer to an earlier generation of vapor cloud
models.
The present book has been expanded to include both source term models
and vapor cloud dispersion models, and it incorporates worked examples
with the model descriptions.
ix
Acknowledgments
The American Institute of Chemical Engineers and the Center for Chemical
Process Safety (CCPS) express their gratitude to all the members of the
Vapor Cloud Modeling Subcommittee for their unstinting efforts and
technical contributions in the preparation of this Guidelines. The members
of this distinguished group are:
Ronald J. Lantzy, Chair Rohm and Haas Company
Gib R. Jersey, Vice Chair Mobil Technology Company
William J. Hague, Past Chair AlliedSignal, Inc.
Douglas N. Blewitt Amoco Corporation
Sanford G. Bloom Lockheed Martin Energy Systems
Donald J. Connolley AKZO Nobel Chemicals, Inc.
George E. DeVaull Shell Oil Company
Seshu Dharmavaram DuPont Company
Ebrahim Esmaili Exxon Research and Engineering Co.
David J. Fontaine Chevron Research and Technology Co.
Gene K. Lee Air Products and Chemicals, Inc.
John T. Marshall Dow USA, Texas Operations
David McCready Union Carbide Corporation
Robert Moser Cigna Property and Casualty
Ronald D. Myers Rohm and Haas Company
Malcolm L. Preston ICI Engineering Technology
Jerry M. Schroy Monsanto Company
Kenneth W. Steinberg Exxon Research and Engineering Co.
Jawad Touma US. Environmental Protection Agency
xi