Guidelines for Use of Vapor Cloud Dispersion Models

The second edition of this essential reference updates and combines two earlier titles to capture the many technological advances for predicting the "footprint" of a vapor cloud release. Cited by EPA in its 1996 document, "Off–Site Consequence Analysis Guidance," the aim of the book is to encourage and facilitate the development and use of dispersion modeling as an everyday tool, providing practical understanding of basic physical and chemical principles, guidance in selecting release scenarios and the best available models, and information and examples on how to run some models and interpret outputs. Equally useful to beginners and experts, it compares 22 programs based on input from model developers, and presents 7 examples of typical accidental release scenarios. The book comes with a disk providing input and output data for scenarios.

Preface. Acknowledgments. Nomenclature. 1. Background and Objectives. 2. Overview of Modeling Procedures, Including Rationale for Selecting Scenarios for Worked Examples. 2.1 Types of Scenarios and Models. 2.2 Gross Screening Analysis. 2.3 Scenarios Selected for Worked Examples. 3. Input Data Required. 3.1 Source data. 3.2 Site Characteristics. 3.3 Meteorological Data and Formulas for Calculating Input Parameters. 3.4 Receptor Related Data. 4. Source Emission Models. 4.1 Conceptual Process for Source Term Determination. 4.2 Calculation of Source Terms. 4.2.1 Gas Jet Releases. 4.2.2 Liquid Jet Releases. 4.2.3 Two–Phase Jet Releases. 4.2.4 Liquid Pool Spreading. 4.2.5 Liquid Pool Evaporation. 4.3 Uncertainties in Source Term Estimation. 5. Dispersion Models. 5.1 Critical Richardson Number Criterion. 5.2 Jet Trajectory and Entrainment. 5.2.1 Momentum–Dominated Jets. 5.2.2 Elevated Dense Gas Jets. 5.2.3 Positively Buoyant Plumes. 5.3 Dense Gas Release at grade. 5.3.1 Background and Overview. 5.3.2 Dense Gas Clouds in the Absence of Heat Exchange. 5.3.3 Dense Gas Clouds in the Presence of Heat Exchanges. 5.4 Transport and Dispersion of Neutrally Buoyant of Passive Gas Clouds. 5.5 Simple Nomograms for Calculating the Dilution of Dense Gas Release. 5.6 Three–Dimensional Numerical Models of Dense Gas Dispersion. 5.7 Transport and Dispersion Near Buildings. 5.7.1 Plume Confinement by Canyons. 5.7.2 Concentrations on Building Faces Due to Releases from Vents. 5.7.3 Concentrations on the Building Downwind Face (the Near–Wake) Due to Releases from Sources on the Building. 5.7.4 Other Effects of Buildings. 5.8 Worst Case Meteorological Conditions. 5.9 Removal by Dry and Wet Deposition. 5.9.1 Gravitational Settling of Large Particles of Aerosols. 5.9.2 Dry Deposition of Small particles and Gases. 5.9.3 Removal of Particles and Gases by Participation and Clouds (Wet Deposition). 6. Averaging Times, Concentration Fluctuations, and Modeling Uncertainties. 6.1 Overview of Physical Considerations Related to Averaging Time. 6.2 Overview of Characteristics of Concentration Fluctuations in Plumes. 6.3 Predictions of Concentrations on the Plume Centerline at a Given Downwind Distance as a Function of Averaging Time, T