Estimating the Flammable Mass of a Vapor Cloud

This CCPS Concept book shows designers and operators of chemical facilities how to realistically estimate the flammable mass in a cloud of accidentally released material that is capable of igniting. It provides information on industry experience with flammable vapor clouds, basic concepts of fires and explosions, and an overview of related computer programs.

JOHN L. WOODWARD, PhD, is Senior Principal Consultant in the Process Safety Division of Baker Engineering and Risk Consultants, Inc. in San Antonio, Texas. He has been actively involved in consequence modeling for both the DNV PHAST and BakerRisk SafeSite codes for many years. He was invited by the GAO as part of a team of LNG experts to review LNG safety issues.

Preface

xi

Acknowledgments

xiii

Glossary

xv

Nomenclature

xxiii

Introduction

1

(4)

Why Calculate Flammable Mass?

1

(1)

How Are Flammable Mass Estimates Used?

1

(1)

Other CCPS Publications

2

(3)

Overview

5

(6)

Context

5

(2)

Objectives

7

(1)

How to Use This Book

8

(3)

Industry Experiences With Flammable Vapor Clouds

11

(20)

Property Losses from Vapor Cloud Accidents

11

(1)

Examples of Vapor Cloud Events

11

(9)

Bangkok, Thailand, LPG Vapor Cloud

12

(2)

Saint Herblain, France, Gasoline Cloud, October 7, 1991

14

(2)

Pampa, Texas, Hoechst-Celanese Explosion, November 17, 1987

16

(1)

Monsanto Ethanol Explosion, Autumn, 1970

17

(1)

Mexico City Vapor Cloud and Explosion, November 19, 1984

18

(1)

Pasadena, Texas Fire and Explosion, October 23, 1989

18

(2)

Examples with Postaccident Determination of Flammable Mass

20

(11)

Flixborough Vapor Cloud Explosion, June 1, 1974

20

(4)

Piper Alpha North Sea Platform Fire, July 6, 1988

24

(2)

DSM Naphtha Cracker, Beek, the Netherlands, 7 November 1975

26

(5)

Basic Concepts---Fluid Flow, Fires, and Explosions

31

(100)

Discharge Characteristics

31

(29)

Single-Phase Discharge Rates from Tanks

32

(4)

Single-Phase Discharge Rates from Pipes

36

(1)

Two-Phase Discharge Rates from Tanks

37

(7)

Two-Phase Discharge Rates from Pipes

44

(5)

Aerosol Formation and Drop Size Correlations

49

(2)

Rainout

51

(5)

Pool Spread and Evaporation on Land

56

(4)

Dispersion Factors

60

(15)

Jet Mixing

60

(2)

Meteorology

62

(4)

Surface Roughness and Terrain

66

(3)

Averaging Time

69

(1)

Impingement and Cratering

70

(1)

Obstacle Effects

71

(4)

Sources of Ignition

75

(2)

Flame Characteristics

77

(17)

Flammable Limits

81

(3)

Flammable Limits with Inerts

84

(4)

Autoignition Temperature for Gases

88

(3)

Minimum Ignition Energy for Gases

91

(1)

Flash Point

91

(2)

Laminar Burning Velocity and Turbulent Flame Speed

93

(1)

Aerosol Flammability

94

(5)

Turbulence Effects

99

(5)

Turbulence Effects of Jet Plume Ignition

99

(3)

Turbulence and Pockets of Flammable Material

102

(2)

Flash Fires

104

(1)

Explosions

104

(20)

Confinement and Congestion

105

(3)

Effect of Concentration on Explosion Overpressure

108

(1)

TNT Equivalence Explosion Models

109

(5)

Volume Source Explosion Models

114

(6)

Determining Fuel Reactivity

120

(1)

Determining Degree of Confinement

121

(1)

Determining Level of Congestion

122

(2)

Multiple Congested Volumes

124

(1)

Minimum Flammable Mass for Vapor Cloud Explosions

124

(3)

Probability of Vapor Cloud Ignition and Explosion

127

(4)

Determination of Flammable Mass

131

(38)

Estimation Methods by Degree of Confinement

132

(1)

Methods for Finding the Flammable Mass in Unconfined Vapor Clouds

132

(25)

Screening: Rules of Thumb

135

(1)

Calculating Flammable Mass with Dispersion Models

136

(21)

Methods for Finding the Flammable Mass in Partially Confined Vapor Clouds

157

(2)

Estimating Flammable Mass for Potential Explosion Sites

158

(1)

Methods for Finding the Flammable Mass in Confined Vapor Clouds

159

(10)

Flammable Mass in Well-Mixed Room from Spill Outdoors

162

(3)

Flammable Mass from Indoor Release in Well-Mixed Room with Low Ventilation

165

(4)

Overview of Related Computer Programs

169

(14)

Worked Examples

183

(22)

Example 10, Unconfined Vapor Cloud---Vapor and Liquid Propane Releases

184

(2)

Example 11, Unconfined Vapor Cloud---Effect of Wind Speed

186

(1)

Example 12, Partially Confined Vapor Cloud Explosion---Vinyl Chloride Monomer Release

186

(6)

Example 13, Partially Confined Vapor Cloud Explosion---Total Petroleum LaMede Refinery Explosion, November 1992

192

(7)

Example 14, Partially Confined Vapor Cloud---Multiple Congested Areas

199

(2)

Example 15, Confined Vapor Clouds

201

(4)

Recommendations for Future Work

205

(4)

Calculating Flammable Mass Profiles Along a Vapor Cloud

205

(1)

Resolving the Minimum Explosive Mass Issue

205

(1)

Contribution of Aerosols to Explosive Mass

206

(1)

Dispersion Modeling Around Plant Structure

206

(1)

Improved Modeling of Jets Impacting Surfaces

207

(1)

Models That Account for Turbulence Spectra

207

(1)

Reconciling Indoor and Outdoor Explosion Models

207

(1)

Calculate Net Efficiencies for TNT Equivalent Models from Historical Events

207

(2)

Appendix A Atmospheric Stability Classification Schemes

209

(4)

Appendix B Vertical Wind Profiles

213

(2)

Appendix C Flammability Properties

215

(14)

Appendix D Correlation for Flash Point

229

(2)

Appendix E Polydisperse Drop Size Distributions

231

(2)

Appendix F Multicomponent Pool Evaporation for Spills on Land

233

(2)

Appendix G Generalized Indoor Concentration Build-Up or Decay

235

(2)

Appendix H Calculating Concentrations for Indoor Releases

237

(4)

Appendix I Evaluating Flammable Mass for Gaussian Dispersion Models: Instantaneous, Point Source

241

(4)

Appendix J Evaluating Flammable Mass for Gaussian Dispersion Models: Continuous Release, Approximate Method

245

(4)

Appendix K Evaluating Flammable Mass for Gaussian Dispersion Model---Continuous Release, Rigorous Solution

249

(8)

Appendix L Numerical Integration to Find Flammable Mass

257

(4)

Appendix M Expansion Velocity and Discharge Coefficients

261

(4)

Appendix N Conversion Factors

265

(2)

References

267

(18)

Index

285

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Estimating the Flammable Mass of a Vapor Cloud

Summary

Author Biography

Table of Contents

Supplemental Materials

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Estimating the Flammable Mass of a Vapor Cloud

Summary

Author Biography

Table of Contents

Supplemental Materials

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