GUIDELINES FOR

Use of Vapor Cloud

Dispersion Models

SECOND EDITION

CENTER FOR CHEMICAL PROCESS SAFETY

of the

American Institute of Chemical Engineers345 East 47th Street, New York, NY 10017

Copyright © 1996American Institute of Chemical Engineers345 East 47th StreetNew 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 anymeans, electronic, mechanical, photocopying, recording, or otherwisewithout the prior permission of the copyright owner.

Library of Congress Cataloging-in Publication DataGuidelines for use of vapor cloud dispersion models / Center for

Chemical Process Safety of the American Institute of ChemicalEngineers.

p. cm.Includes bibliographical references and index.ISBN 0-8169-0702-11. Atmospheric diffusion—Mathematical models. 2. Hazardous

substances—Environmental aspects—Mathematical models.3. Vapor clouds—Mathematical models. I. American Institute ofChemical Engineers. Center for Chemical Process Safety.QC880.4.D44G85 1996628.5T0113—<ic20 96-26950

This book is available at a special discount when ordered in bulk quantities.For information, contact the Center for Chemical Process Safety of theAmerican Institute of Chemical Engineers at the address shown above.

It is sincerely hoped that the information presented in this document will lead to an even moreimpressive safety record for the entire industry: however, the American Institute of ChemicalEngineers, its consultants. CCPS subcommittee members, their employers, their employers'officers and directors and EARTH TECH disclaim making or giving any warranties orrepresentations, express or implied, including with respect to fitness, intended purpose, use ormerchantability and/or correctness or accuracy of the content of the information presented inthis document. As between (1 ) the American Institute of Chemical Engineers, its consultants.CCPS subcommittee members, their employers, their employers' officers and directors andEARTH TECH and (2) the user of this document, the user accepts any legal liability orresponsibility whatsoever for the consequence of its use or misuse.

Preface

For 40 years the American Institute of Chemical Engineers (AIChE) hasbeen 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 andthe means of preventing their occurrences and mitigating their consequences.

The Center for Chemical Process Safety (CCPS), a directorate ofAIChE, was established in 1985 to develop and disseminate technicalinformation 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 processsafety management systems to reduce potential exposures to the public,facilities, personnel, and the environment. This program involves thedevelopment and publication of guidelines related to specific areas ofprocess safety management; organizing convening, and conducting semi-nars, symposia, training programs, and meetings on process safety-relatedmatters; and cooperation with other organizations, both internationally anddomestically, to promote process safety. CCPS's activities are supported byfunding and expertise from over 90 entities.

In 1987 CCPS published Guidelines for Use of Vapor Cloud DispersionModels, and in 1989, Workbook of Test Cases for Vapor Cloud SourceDispersion Models. These books have served well but are now outdated.At nearly a decade old, they refer to an earlier generation of vapor cloudmodels.

The present book has been expanded to include both source term modelsand vapor cloud dispersion models, and it incorporates worked exampleswith the model descriptions.

Acknowledgments

The American Institute of Chemical Engineers and the Center for ChemicalProcess Safety (CCPS) express their gratitude to all the members of theVapor Cloud Modeling Subcommittee for their unstinting efforts andtechnical contributions in the preparation of this Guidelines. The membersof this distinguished group are:

Ronald J. Lantzy, Chair

Gib R. Jersey, Vice ChairWilliam J. Hague, Past ChairDouglas N. BlewittSanford G. BloomDonald J. ConnolleyGeorge E. DeVaullSeshu DharmavaramEbrahim EsmailiDavid J. Fontaine

Gene K. LeeJohn T. MarshallDavid McCreadyRobert MoserRonald D. MyersMalcolm L. PrestonJerry M. SchroyKenneth W. SteinbergJawad Touma

Rohm and Haas Company

Mobil Technology CompanyAlliedSignal, Inc.Amoco CorporationLockheed Martin Energy SystemsAKZO Nobel Chemicals, Inc.

Shell Oil CompanyDuPont CompanyExxon Research and Engineering Co.Chevron Research and Technology Co.

Air Products and Chemicals, Inc.Dow USA, Texas Operations

Union Carbide CorporationCigna Property and CasualtyRohm and Haas CompanyICI Engineering TechnologyMonsanto CompanyExxon Research and Engineering Co.U.S. Environmental Protection Agency

CCPS guidance and counsel were appropriately provided by its recentdirector, Bob G. Perry, and its current director, Jack Weaver. Liaisonbetween the Subcommittee and CCPS was provided by William J. Minges,CCPS Staff.

The contract for preparing the Guidelines was awarded to EARTH TECH(formerly Sigma Research Corp.), Concord, MA. The following people arethe authors of this book:

Steven R. Hanna, EARTH TECH.Peter J. Drivas, Gradient Corp.Joseph J. Chang, EARTH TECH.

We acknowledge the dozens of scientists and engineers who prepareduseful discussions of their models, who took the time to complete question-naires, and who sent copies of relevant manuscripts to EARTH TECH.

CCPS also expresses its appreciation to members of the TechnicalSteering Committee for their valuable advice and support.

The group to whom the Subcommittee is especially indebted consistsof those who volunteered to provide peer review:

J. Steven Arendt JBF Associates, Inc.Daniel A. Crowl Michigan Technological UniversityThomas O. Gibson Dow Chemical CompanyKenneth Harrington BattelleMichael J. Hitchler Westinghouse Savannah River CompanyJohn A. Hoffmeister Lockheed Martin Energy SystemsJohn Hudson PC/?, Inc.Dimitrios Karydas Factory Mutual Research Corporation

Steven Kent Raytheon Engineers and Constructors, Inc.Georges A. Melham Arthur D. Little, Inc.Kenneth Mosig AIU Energy/Starr Technical Risks Agency, Inc.John A Noronha Eastman Kodak CompanyFrank P. Ragonese Mobil Oil Corporation

Nomenclature

First mention

SECT. EQ. NO.

al9a2 Entrainment constants 5.2.2 (5-7)

A (m2) Effective cross-sectional building area 5.7.2 (5-66)

A1 ? A2 Constants in cloud depth formulas 5.3.2 (5-34)

Ah(m2) Puncture area 4.2.1 (4-2)f\

A (m) Area of pipe or pool 4.2.1 (4-6)

Bc (m s~ ) Buoyancy flux for continuous plume 5.1 (5-3a)

B{ (m4s~2) Buoyancy flux for instantaneous cloud 5.1

SjOnV1) Continuous liquid spill rate 4.2.4 (4-19)

с (ms"1) Speed of sound in gas 4.2.2 (4-10)

c2(10"12m2(im~2) Conversion factor 5.9.1 (5-67)

снт (J s^m'2^1) Heat transfer coefficient 4.2.5 (4-23)

c0 Discharge coefficient 4.2.1 (4-2)

cp (J kg^Kr1) Gas specific heat at constant pressure 4.2.1

cpa (J kg^K'1) Specific heat of air 5.6 (5-54)

cpl (J kg^K'1) Liquid heat capacity 4.2.3.2 (4-15)

cpm (J kg^K"1) Specific heat of hazardous gas 5.6 (5-54)

cps (J kg^KT1) Specific heat of underlying surface 5.3.3 (5-37)

cv (J kg^KT1) Gas specific heat at constant volume 4.2.1

C(kgm~3) Concentration 2.1 (2-1)

С Dimensionless concentration 5.7.2 (5-63)

C* (kg m"3) Concentration threshold 6.5

C(kgnT3)

C0'(kgm-3)

Cp'(kgm-3)

C^kgkg-1)

C/'Ckgkg-1)Ccl(kgnf3)

c,Cm(kgnf3)QCkgrn-3)C0(kgm-3)Cp(kgm-3)C^Ckgm-3)

4(m)

D (mV1)

DB (mV1)

Dc(m)

Я;(т)

D0(m)

£p(m)/>р(цт)

ERPG

/

/area

F^CkgnrV1)Fwet (kg m~2s~1)FAC2FB

g (ms~2)

£0(ms-2)GCkgs-V2)

hc (Wm"2 K"1)

Mm>

Mean or average concentration

Observed concentration random variability

Predicted concentration random variability

Concentration of gas in plume

Concentration of liquid in plumeConcentration on plume centerlineCloudiness indexMean concentrationInitial concentrationObserved concentrationPredicted concentrationPeak concentration

Tank diameterMolecular diffusivity of pollutant gasBrownian diffusivity for particlesSource dimension for continuous releaseSource dimension for instantaneous releaseInitial cloud widthPipe diameter

Particle diameter

Emergency Response Planning Guidelines

Pipe friction factorArea view factorParticle deposition fluxWet deposition fluxFraction within a factor of twoFractional bias

<2Acceleration of gravity (9.8 ms )

Reduced gravity = g(p0 - pa)/pa

Mass emission rate per unit area

Heat transfer constantInitial cloud depth

6.3

6.6 (6-18)

6.6 (6-19)

5.6 (5-51)

5.6 (5-53)6.34.2.5 (4-25)5.55.2.2 (5-13)6.6 (6-18)6.6 (6-18)6.3

4.2.2 (4-11)5.9.2 (5-75b)5.9.2 (5-76)5.55.55.1 (5-1)4.2.1 (4-6)

5.9.1 (5-67)

3.4

4.2.1 (4-6)4.2.5 (4-24)5.9.1 (5-69)5.9.2 (5-80)8.2 (8-4)8.2 (8-5)

3.3 (3-1)

5.54.2.3.2(4-15)

5.3.3 (5-38)5.3.2

Лр(т)Ag(m)Яв(т)Hf(mKs~l)Я, (т)tfs(WnT2)

#vap(Jkg~')

#wc (m>

/fcgCms-1)

Plume centerline height above ground

Stack height

Building height

Sensible heat flux

Height of liquid above puncture

Convective heat flux

Heat of vaporization of liquid

Plume depth, worst case

Intermittency of concentration record

Mass transfer coefficient

fcs (J s"1 m~1K~1)Thermal conductivity of soil

KF, K^, Kg

К (т2 s'1)

L(m)

Mm)

Mm)Mm)LAI

т (kg)

ntj (kg)mt (kg)

Dimensionless factors

Eddy diffusivity vector

Monin-Obukhov length

Length of building wake or cavity

Length of pipe

Length of tank

Leaf Area Index

Liquid mass in pool

Mass of gas component j

Total mass in pipeline

M (kg kg-mole"1 ) Molecular weight

Mi (kg kg-mole~ ) Molecular weight of gas component у

M0(mV2)

MG

«To

^Re

^Sc

^Sh

"st

P

p (N m"2)

Initial plume momentum flux

Geometric mean

Total moles of liquid

Reynolds number

Schmidt number

Sherwood number

Stokes number

Probability density function

Tank pressure

5.4 (5-40)

5.1 (5-4a)

5.7.1 (5-62)

3.3 (3-1)

4.2.2 (4-10)

5.3.3 (5-38)

4.2.3.1 (4-14)

2.1 (2-1)

6.4 (6-13)

4.2.5.2 (4-29)

4.2.5.1 (4-28)

4.2.1 (4-6)

5.6 (5-49)

3.3 (3-1)

5.7.4

4.2.1 (4-6)

4.2.2 (4-13)

5.9.2 (5-78b)

4.2.5 (4-22)

5.3.2 (5-17)

4.2.1 (4-5)

4.2.1

5.3.2 (5-17)

5.2.1 (5-17)

8.2 (8-1)

4.2.6 (4-34)

4.2.5.2 (4-30)

4.2.5.2 (4-30)

4.2.5.2 (4-30)

5.9.2 (5-77)

6.3 (6-6)

4.25.1 (4-1)

pa(Nm-2)

P,s(Nm-2)

/>0(NnT2)

Pv(NnT2)

P (mm ЬГ1)

P

^(kgs-'nT2)

«condCJs'1)

<?conv (J s ')

^evapCJs"1)

^(JS4)

««mCJs'1)eckgs-1)Gangs'1)GfCkgs-1)

6i(kg)e.ckgs-1)GoCkgs-1)

r(m)

r.Csm-1)

rcut (s nf1)

r^sm"1)

rgtsnT1)

r,(m)

rs (s m-1)rt (s m'1)

R

R(m)

R (J КГ1 kg'1)

R*

Ri*

».

'̂o

Ambient pressure

Saturation vapor pressure of component i

Stagnation pressure

Vapor pressure

Precipitation rate

Cumulative density function

Evaporation rate per unit area

Conduction heat transfer from ground

Convection heat transfer from air

Heat loss due to evaporation

Radiative heat transfer from air

Incident solar radiation

Source mass emission rate

Evaporation rate of liquid pool

Mass emission rate of liquid that flashes

Mass in instantaneous cloud release

Liquid mass flow rate

Initial source mass emission rate

Distance on building from source to receptor

Aerodynamic resistance

Cuticle resistance

Stomate resistance

Resistance to transfer across surface

Liquid pool radius

Surface resistance

Transfer resistance

Correlation coefficient

Plume radius

Gas constant for specific gas

4.2.1 (4-1)

4.2.6 (4-34)

4.2.3.2(4-15)

4.2.3.2(4-15)

5.9.2 (5-81)

6.3 (6-7)

4.2.6 (4-34)

4.2.5 (4-22)

4.2.5 (4-22)

4.2.5 (4-22)

4.2.5 (4-22)

4.2.5 (4-22)

2.1 (2-1)

4.2.5 (4-26)

4.2.3.1 (4-14)

5.4 (5-4)

4.2.2 (4-10)

4.2.1 (4-4)

5.7.2 (5-64)

5.9.2 (5-70)

5.9.2 (5-78b)

5.9.2 (5-78b)

5.9.2 (5-78b)

4.2.4 (4-18)

5.9.2 (5-70)

5.9.2 (5-70)

8.2 (8-3)

5.2.2 (5-7)

5.3.2 (5-17)

Universal gas constant (83 10 J K~l kg-mole"1) 4.2. 1

Local cloud Richardson number

Ambient Richardson number

Critical Richardson number

5.3.2 (5-30)

5.6 (5-60)

5.1 (5-1)

s(m)

•̂ CF

t(s)

fe(s)Г(К)

Г* (К)ГЬ(К)rd(s)r,(s)

. Г0(К)

ГР(К)

Г,(8)

^soil(K)

w (m s"1)

и (m s'1)

u (m s"1)

M! (m s~ )

w* (m s~l)

wa (m s"1)

we (m s-1)

мн (m s"1)

ws (m s"1)

wst (m s'1)

wwc (m s'1)

v (m s"1)

vd (m s'1)vedge (m S"1)

v^kg-1)

vs (m s'1)vtop (m s'1)VctmV1)

^(mV1)

Distance along plume axis

Slip correction factor

Time

Exposure time

Temperature turbulent fluctuation

Temperature, air

Normal boiling point of liquid

Time duration of release

Integral time scale

Temperature, tank

Pool temperature

Sampling time

Soil temperature

Wind speed

Wind speed turbulent fluctuation

Wind vector

Wind speed at height of 1 m

Friction velocity

Advection velocity of cloud

Entrainment rate

Wind speed at height of building

Plume speed along axis

Wind speed at stack height

Wind speed, worst case

Gross entrainment velocity

Dry deposition velocity

Edge entrainment velocity

Difference in specific volume between

liquid and gas

Gravitational settling speed

Top entrainment velocity

Volume flow rate

Initial volume flow rate

5.2.2 (5-7)

5.9.1 (5-68)

4.2.1 (4-4)

6.5

3.3 (3-3)

3.1

4.2.3.1 (4-14)

5.5

6.3 (6-9)

4.2.1

4.2.5 (4-22)

6.3

4.2.5.1 (4-28)

3.3 (3-4)

3.3 (3-2)

5.6 (5-49)

9.1

3.3 (3-1)

5.3.2 (5-20)

5.2.1

5.7.2 (5-63)

5.2.2 (5-7)

E (E-9)

2.1 (2-1)

5.3.2 (5-26)

5.9.2 (5-70)

5.3.2 (5-28a)

4.2.3.2(4-15)

5.9.1 (5-67)

5.3.2 (5-28a)

5.3.2 (5-28a)

5.1 (5-1)

V j (m3)Vio(m3)

V, (m3)

Mm3)VG

w(ms-1)

w' (m s"1)

w0 (m s"1)

W(m)

WB(m)

Wc(m)

Wwc (m)

*(m)

*g(m)о

xix0(m)

xv(m)

y(m)

?o(m)

z(m)

Zd(m)

«„(т)zp(m)

a

as (m2 s-1)

P(s)

Y=Vc v

8

AC0(kgnT3)

ACp(kgm-3)

Volume of instantaneous cloud

Initial volume of instantaneous cloud

Volume of liquid in tankVolume of instantaneous spill

Geometric variance

Local jet vertical speed

Vertical wind speed fluctuation

Initial jet velocity

Plume widthWidth of building

Width of canyon between buildings

Plume width, worst case

Distance from cloud to receptor

Distance where plume touches ground

Initial liquid mole fraction of component i

Alongwind position of cloud center

Virtual source distance

Lateral position

Lateral centerline position of plume

Height above ground

Reference height (usually 10 m)

Roughness length

Plume height above source

Mass conservation factor

Thermal diffusivity of soil

Time constant for release from pipe

Gas specific heat ratio

Dirac delta function

Data error in observed concentration

Error in predicted concentrationdue to data errors

5.3.2 (5-18)

5.1 (5-2)

4.2.2 (4-11)4.2.4 (4-18)

8.2 (8-2)

5.2.1

3.3 (3-3)

5.2.1

8.4

5.7.2

5.7.1 (5-61)

2.1 (2-1)

5.1 (5-2)

5.2.2 (5-12)

4.2.6 (4-34)

5.4 (5-41)

5.4

5.4 (5-40)

5.4 (5-40)

3.3 (3-4)

5.9.2 (5-71)

3.2

5.2.1 (5-5)

4.2.1 (4-4)

4.2.5.1 (4-28)

4.2.1 (4-4)

4.2.1 (4-1)

6.4 (6-13)

6.6 (6-18)

6.6 (6-19)

Ah (т)

^upwind (m>

Ay(m)

^initial (m)

V

8

ed (m2 s-3)

A(s-!)

fiCkgnfV 1)

v(m2 s"1)

Ф.П

Фpa(kgnT3)

Paer (kg m"3)

p! (kg пГ 3)

p0(kgnT3)

Ppo (kg m""3)Ps(kgm-3)

psp (kg пГ3)

pw(kgnT3)

ac (kg m-3)

Maximum rise of dense plume

Distance dense cloud travels upwind

Crosswind distance traveled by plume

Distance cloud spreads laterally at source

Del operator

Liquid emissivity

Eddy dissipation rate

Wet removal inverse time scale

Air viscosity

Molecular viscosity of air

Solar angle above horizon

Dimensionless function of Ri

Ambient air density

Mass of aerosol per unit cloud volume

Liquid density

Gas density in tank

Initial plume density

Density of underlying surface

Solid particle density

Density of water

Standard deviation of concentrationfluctuations

OSB = 5.67 x 10~8 J s'V^K"4 Stefan-Boltzmann constant

cx(m)

Sy(m)

Gyi (m)az(m)

ene^0)

Alongwind dispersion parameter

Lateral dispersion parameter

Lateral dispersion of instantaneous puff

Vertical dispersion parameter

Angle of plume axis with horizontal

Angle of liquid surface in tank

5.2.2 (5-11)

5.3.2 (5-22)

5.2.1 (5-6)

5.3.2 (5-23)

5.6 (5-49)

4.2.5 (4-24)

5.2.2 (5-15)

5.9.2 (5-79)

5.9.1 (5-67)

5.9.2 (5-75a)

4.2.5 (4-25)

5.6 (5-57)

5.1 (5-1)

5.3.2 (5-16)

4.2.2 (4-11)

4.2.1 (4-2)

5.1 (5-1)

5.3.3 (5-37)

5.9.1 (5-67)

4.2.4 (4-20)

6.4 (6-15)

4.2.5 (4-24)

5.4 (5-41)

5.3.1

6.3 (6-3)

5.3.1

5.2.2 (5-7)

4.2.2 (4-13)