PRENTICE HALL INTERNATIONAL SERIES
IN THE PHYSICAL AND CHEMICAL ENGINEERING SCIENCES
NEAL R. AMUNDSON, SERIES EDITOR, University of Houston
ADVISORY EDITORS
ANDREAS ACRIVOS, Stanford University
JOHN DAHLER, University of Minnesota
H. SCOTT FOGLER, University of Michigan
THOMAS J. HANRATTY, University of Illinois
JOHN M. PRAUSNITZ, University of California
L. E. SCRIVEN, University of Minnesota
BALZHISER, SAMUELS, AND ELIASSEN Chemical Engineering Thermodynamics
BEQUETTE Process Dynamics
BIEGLER, GROSSMAN, AND WESTERBERG Systematic Methods of Chemical Process Design
CROWL AND LOUVAR Chemical Process Safety: Fundamentals with Applications
CONSTANTINIDES AND MOSTOUFI Numerical Methods for Chemical Engineers with MATLAB Applications
CUTLIP AND SHACHAM Problem Solving in Chemical Engineering with Numerical Methods
DENN Process Fluid Mechanics
DOYLE Process Control Modules: A Software Laboratory for Control Design
ELLIOT AND LIRA Introductory Chemical Engineering Thermodynamics
FOGLER Elements of Chemical Reaction Engineering, 3rd edition
HIMMELBLAU Basic Principles and Calculations in Chemical Engineering, 6th edition
HINES AND MADDOX Mass Transfer
KYLE Chemical and Process Thermodynamics, 3rd edition
PRAUSNITZ, LICHTENTHALER, AND DE AZEVEDO Molecular Thermodynamics of Fluid-Phase Equilibria, 3rd edition
PRENTICE Electrochemical Engineering Principles
SHULER AND KARGI Bioprocess Engineering, 2nd edition
STEPHANOPOULOS Chemical Process Control
TESTER AND MODELL Thermodynamics and Its Applications, 3rd edition
TURTON, BAILIE, WHITING, AND SHAEIWITZ Analysis, Synthesis and Design of Chemical Processes
WILKES Fluid Mechanics for Chemical Engineering
Prentice Hall International Series in the Physical and Chemical Engineering Sciences
Chemical Process Safety
Fundamentals with Applications
Second Edition
Prentice Hall PTR
Upper Saddle River, New Jersey 07458
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Printed in the United States of Amerigca
10 9 8 7 6 5 4 3 2 1
ISBN: 0-13-018176-5
Pearson Education Ltd.
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Contents
1-3 Accident and Loss Statistics
1-6 The Nature of the Accident Process
1-8 Four Significant Disasters
2-1 How Toxicants Enter Biological Organisms
2-2 How Toxicants Are Eliminated from Biological Organisms
2-3 Effects of Toxicants on Biological Organisms
2-6 Models for Dose and Response Curves
OSHA: Process Safety Management
3-2 Industrial Hygiene: Identification
3-3 Industrial Hygiene: Evaluation
Evaluating Exposures to Volatile Toxicants by Monitoring
Evaluation of Worker Exposures to Dusts
Evaluating Worker Exposures to Noise
Estimating Worker Exposures to Toxic Vapors
3-4 Industrial Hygiene: Control
4-1 Introduction to Source Models
4-2 Flow of Liquid through a Hole
4-3 Flow of Liquid through a Hole in a Tank
4-4 Flow of Liquids through Pipes
4-5 Flow of Vapor through Holes
4-6 Flow of Gases through Pipes
4-8 Liquid Pool Evaporation or Boiling
4-9 Realistic and Worst-Case Releases
5 Toxic Release and Dispersion Models
5-1 Parameters Affecting Dispersion
5-2 Neutrally Buoyant Dispersion Models
Case 1: Steady-State Continuous Point Release with No Wind
Case 3: Non-Steady-State Continuous Point Release with No Wind
Case 4: Steady-State Continuous Point Source Release with Wind
Case 5: Puff with No Wind and Eddy Diffusivity Is a Function of Direction
Case 8: Puff with No Wind and with Source on Ground
Case 9: Steady-State Plume with Source on Ground
Case 10: Continuous Steady-State Source with Source at Height Hr above the Ground
Limitations to Pasquill-Gifford Dispersion Modeling
5-5 Effect of Release Momentum and Buoyancy
6-2 Distinction between Fires and Explosions
6-4 Flammability Characteristics of Liquids and Vapors
Flammability Limit Dependence on Temperature
Flammability Limit Dependence on Pressure
Estimating Flammability Limits
6-5 Limiting Oxygen Concentration and Inerting
Blast Damage Resulting from Overpressure
Energy of Mechanical Explosions
Boiling-Liquid Expanding-Vapor Explosions
7 Designs to Prevent Fires and Explosions
Combined Pressure-Vacuum Purging
Vacuum and Pressure Purging with Impure Nitrogen
Advantages and Disadvantages of the Various Pressure and Vacuum Inerting Procedures
Using the Flammability Diagram To Avoid Flammable Atmospheres
Energy from Electrostatic Discharges
Energy of Electrostatic Ignition Sources
7-3 Controlling Static Electricity
General Design Methods To Prevent Electrostatic Ignitions
Increasing Conductivity with Additives
Handling Solids without Flammable Vapors
Handling Solids with Flammable Vapors
7-4 Explosion-Proof Equipment and Instruments
Area and Material Classification
7-7 Miscellaneous Designs for Preventing Fires and Explosions
9-1 Conventional Spring-Operated Reliefs in Liquid Service
9-2 Conventional Spring-Operated Reliefs in Vapor or Gas Service
9-3 Rupture Disc Reliefs in Liquid Service
9-4 Rupture Disc Reliefs in Vapor or Gas Service
9-5 Two-Phase Flow during Runaway Reaction Relief
9-6 Deflagration Venting for Dust and Vapor Explosions
Vents for Low-Pressure Structures
Vents for High-Pressure Structures
9-7 Venting for Fires External to Process Vessels
9-8 Reliefs for Thermal Expansion of Process Fluids
10-1 Process Hazards Checklists
10-3 Hazards and Operability Studies
11-1 Review of Probability Theory
Interactions between Process Units
Revealed and Unrevealed Failures
Determining the Minimal Cut Sets
Quantitative Calculations Using the Fault Tree
Advantages and Disadvantages of Fault Trees
Relationship between Fault Trees and Event Trees
Sources of Ignition in Vessels
Miscellaneous Aids to Diagnosis
Conductor in a Solids Storage Bin
Nitrobenzene Sulfonic Acid Decomposition
Phenol-Formaldehyde Runaway Reaction
Conditions and Secondary Reaction Cause Explosion
Appendix A: Unit Conversion Constants
Appendix B: Flammability Data for Selected Hydrocarbons
Appendix C: Detailed Equations for Flammability Diagrams
Equations Useful for Placing Vessels into and out of Service
Appendix D: Formal Safety Review Report for Example 10-4
Appendix E: Saturation Vapor Pressure Data
Preface
This second edition of Chemical Process Safety is designed to enhance the process of teaching and applying the fundamentals of chemical process safety. It is appropriate for an industrial reference, a senior-level undergraduate course, or a graduate course in chemical process safety. It can be used by anyone interested in improving chemical process safety, including chemical and mechanical engineers and chemists. More material is presented than can be accommodated in a 3-credit course, providing instructors with the opportunity to emphasize their topics of interest.
The primary objective of this textbook is to encapsulate the important technical fundamentals of chemical process safety. The emphasis on the fundamentals will help the student and practicing scientist to understand the concepts and apply them accordingly. This application requires a significant quantity of fundamental knowledge and technology.
The second edition has been rewritten to include new process safety technology and new references that have appeared since the first edition was published in 1990. It also includes our combined experiences of teaching process safety in both industry and academia during the past 10 years.
Significant modifications were made to the following topics: dispersion modeling, source modeling, flammability characterization, explosion venting, fundamentals of electrostatics, and case histories. This new edition also includes selected materials from the latest AICHE Center for Chemical Process Safety (CCPS) books and is now an excellent introduction to the CCPS library.
This second edition also includes more problems (now 30 per chapter). A complete set of problem solutions is available to instructors using the book in their curriculum. These changes fulfill the requests of many professors who have used this textbook.
We continue to believe that a textbook on safety is possible only with both industrial and academic inputs. The industrial input ensures that the material is industrially relevant. The academic input ensures that the material is presented on a fundamental basis to help professors and students understand the concepts. Although the authors are (now) both from universities, one has over 30 years of relevant experience in industry (J. F. L.) and the other (D. A. C.) has accumulated significant industrial experience since the writing of the first edition.
Since the first edition was published, many universities have developed courses or course content in chemical process safety. This new emphasis on process safety is the result of the positive influences from industry and the Accreditation Board for Engineering and Technology (ABET). Based on faculty feedback, this textbook is an excellent application of the fundamental topics that are taught in the first three years of the undergraduate education.
Although professors normally have little background in chemical process safety, they have found that the concepts in this text and the accompanying problems and solutions are easy to learn and teach. Professors have also found that industrial employees are enthusiastic and willing to give specific lectures on safety to enhance their courses.
This textbook is designed for a dedicated course in chemical process safety. However, we continue to believe that chemical process safety should be part of every undergraduate and graduate course in chemistry and chemical and mechanical engineering, just as it is a part of all the industrial experiences. This text is an excellent reference for these courses. This textbook can also be used as a reference for a design course.
Some will remark that our presentation is not complete or that some details are missing. The purpose of this book, however, is not to be complete but to provide a starting point for those who wish to learn about this important area. This book, for example, has a companion text titled Health and Environmental Risk Analysis that extends the topics relevant to risk analysis.
We thank many of our friends who continue to teach us the fundamentals of chemical process safety. Those who have been especially helpful include G. Boicourt and J. Wehman of the BASF Corporation; W. Howard and S. Grossel, who have extensive industrial experience and are now consultants; B. Powers from Dow Chemical Company; D. Hendershot from Rohm and Haas; R. Welker of the University of Arkansas; R. Willey of Northeastern University; and R. Darby of Texas A&M University.
We also continue to acknowledge and thank all the members of the Undergraduate Education Committee of the Center for Chemical Process Safety and the Safety and Loss Prevention Committee of the American Institute of Chemical Engineers. We are honored to be members of both committees. The members of these committees are the experts in safety; their enthusiasm and knowledge have been truly educational and a key inspiration to the development of this text.
Finally, we continue to acknowledge our families, who provided patience, understanding, and encouragement throughout the writing of the first and second editions.
We hope that this textbook helps prevent chemical plant and university accidents and contributes to a much safer future.
Daniel A. Crowl and Joseph F. Louvar
Nomenclature
a |
velocity of sound (length/time) |
A |
area (length2) or Helmholtz free energy (energy); or process component availability |
At |
tank cross sectional area (length2) |
ΔA |
change in Helmoltz free energy (energy/mole) |
C |
mass concentration (mass/volume) or capacitance (Farads) |
C0, C1 |
discharge coefficients (unitless) or concentration at a specified time (mass/volume) |
Cm |
concentration of dense gas (volume fraction) |
Cp |
heat capacity at constant pressure (energy/mass deg) |
CV |
heat capacity at constant volume (energy/mass deg) |
Cppm |
concentration in parts per million by volume |
Cvent |
deflagration vent constant (pressure1/2) |
〈C〉 |
average or mean mass concentration (mass/volume) |
d |
diameter (length) |
dp |
particle diameter (length) |
df |
diameter of flare stack (length) |
D |
diffusion coefficient (area/time |
Dc |
characteristic source dimension for continuous releases of dense gases (length) |
Di |
characteristic source dimension for instantaneous releases of dense gas (length) |
D0 |
reference diffusion coefficient (area/time) |
Dm |
molecular diffusivity (area/time) |
Dtid |
total integrated dose due to a passing puff of vapor (mass time/volume) |
Ea |
activation energy (energy/mole) |
ERPG |
emergency response planning guideline (see Table 5-6) |
EEGL |
emergency exposure guidance levels (see section 5.4) |
f |
Fanning friction factor (unitless) or frequency (1/time) |
f(t) |
failure density function |
fv |
mass fraction of vapor (unitless) |
F |
frictional fluid flow loss term (energy mass) or force or environment factor |
FAR |
fatal accident rate (fatalities/108 hours) |
FEV |
forced expired volume (liters/sec) |
FVC |
forced vital capacity (liters) |
g |
gravitational acceleration (length/time2) |
gc |
gravitational constant |
go |
initial cloud buoyancy factor (length/time2) |
G |
Gibbs free energy (energy/mole) or mass flux (mass/area time) |
GT |
mass flux during relief (mass/area time) |
ΔG |
change in Gibbs free energy (energy/mole) |
h |
specific enthalpy (energy/mass) |
hL |
fluid level above leak in tank (length) |
|
initial fluid level above leak in tank (length) |
hs |
leak height above ground level (length) |
H |
enthalpy (energy/mole) or height (length) |
Hf |
flare height (length) |
Hr |
effective release height in plume model (length) |
ΔH |
change in enthalpy (energy/mole) |
ΔHc |
heat of combustion (energy/mass) |
ΔHr |
release height correction given by Equation 5-64 |
ΔHv |
enthalpy of vaporization (energy/mass) |
I |
sound intensity (decibels) |
ID |
pipe internal diameter (length) |
IDLH |
immediately dangerous to life and health (see section 5.4) |
I0 |
reference sound intensity (decibels) |
Is |
streaming current (amps) |
ISOC |
in-service oxygen concentration (volume percent oxygen) |
j |
number of inerting purge cycles (unitless) |
J |
electrical work (energy) |
k |
non-ideal mixing factor for ventilation (unitless) |
k1, k2 |
constants in probit a equations |
ks |
thermal conductivity of soil (energy/length time deg) |
K |
mass transfer coefficient (length/time) |
Kb |
backpressure correction for relief sizing (unitless) |
Kf |
excess head loss for fluid flow (dimensionless) |
Ki, K∞ |
constants in excess head loss, given by Equation 4-38 |
KG |
explosion constant for vapors (length pressure/time) |
Kj |
eddy diffusivity in x, y or z direction (area/time) |
KP |
overpressure correction for relief sizing (unitless) |
KSt |
explosion constant for dusts (length pressure/time) |
KV |
|
K0 |
reference mass transfer coefficient (length/time) |
K* |
constant eddy diffusivity (area/time) |
L |
length |
LEL |
lower explosion limit (volume %) |
LFL = LEL |
lower flammability limit (volume %) |
LOC |
limiting oxygen concentration (volume percent oxygen) |
m |
mass |
m0 |
total mass contained in reactor vessel (mass) |
mTNT |
mass of TNT |
mv |
mass of vapor |
M |
molecular weight (mass/mole) |
M0 |
reference molecular weight (mass/mole) |
Ma |
Mach number (unitless) |
MOC, MSOC |
See LOC |
MTBC |
mean time between coincidence (time) |
MTBF |
mean time between failure (time) |
n |
number of moles |
OSFC |
out of service fuel concentration (volume percent fuel) |
p |
partial pressure (force/area) |
pd |
number of dangerous process episodes |
ps |
scaled overpressure for explosions (unitless) |
P |
total pressure or probability |
Pb |
backpressure for relief sizing (psig) |
PEL |
permissable exposure level (see section 5.4) |
PFD |
probability of failure on demand |
Pg |
gauge pressure (force/area) |
Pmax |
maximum pressure for relief sizing (psig) |
Ps |
set pressure for relief sizing (psig) |
Psat |
saturation vapor pressure |
q |
heat (energy/mass) or heat intensity (energy/area time) |
qf |
heat intensity of flare (energy/time area) |
qg |
heat flux from ground (energy/area time) |
qs |
specific energy release rate at set pressure during reactor relief (energy/mass) |
Q |
heat (energy) or electrical charge (coulombs) |
Qm |
mass discharge rate (mass/time) |
|
instantaneous mass release (mass) |
Qv |
ventilation rate (volume/time) |
r |
radius (length) |
R |
electrical resistance (ohms) or reliability |
|
Sachs scaled distance, defined by equation 6-25 (unitless) |
Rd |
release duration for heavy gas releases (time) |
RHI |
reaction hazard index defined by Equation 13-1 |
rf |
vessel filling rate (time–1) |
Rg |
|
Re |
Reynolds number (unitless) |
S |
entropy (energy/mole deg) or stress (force/area) |
Sm |
material strength (force/area) |
SPEGL |
short term public exposure guideline (see section 5.4) |
t |
time |
td |
positive phase duration of a blast (time) |
te |
emptying time |
tp |
time to form a puff of vapor |
tv |
vessel wall thickness (length) |
tw |
worker shift time |
Δtv |
venting time for reactor relief |
T |
temperature (deg) |
Td |
material decomposition temperature (deg) |
Ti |
time interval |
TLV |
threshold limit value (ppm or mg/m3 by volume) |
Tm |
maximum temperature during reactor relief (deg) |
Ts |
saturation temperature at set pressure during reactor relief (deg) |
TWA |
time weighted average (ppm or mg/m3 by volume) |
TXD |
toxic dispersion method (see section 5.4) |
u |
velocity (length/time) |
ud |
dropout velocity of a particle (length/time) |
|
average velocity (length/time) |
〈u〉 |
mean or average velocity (length/time) |
U |
internal energy (energy/mole) or overall heat transfer coefficient (energy/area time) or process component unavailability |
UEL |
upper explosion limit (volume %) |
UFL = UEL |
upper flammability limit (volume %) |
v |
specific volume (volume/mass) |
vf |
specific volume of liquid (volume/mass) |
vg |
specific volume of vapor (volume/mass) |
vfg |
specific volume change with liquid vaporization (volume/mass) |
V |
total volume or electrical potential (volts) |
Vc |
container volume |
W |
width (length) |
We |
expansion work (energy) |
Ws |
shaft work (energy) |
x |
mole fraction or Cartesian coordinate (length) |
Xf |
distance from flare at grade (length) |
y |
mole fraction of vapor (unitless) or Cartesian coordinate (length) |
Y |
probit variable (unitless) |
YG |
gas expansion factor (unitless) |
z |
height above datum (length) or Cartesian coordinate (length) or compressibility (unitless) |
ze |
scaled distance for explosions (length/mass1/3) |
Greek Letters
α |
velocity correction factor (unitless) or thermal diffusivity (area/time) |
β |
thermal expansion coefficient (deg–1) |
δ |
double layer thickness (length) |
ε |
pipe roughness (length) or emissivity (unitless) |
εr |
relative dielectric constant (unitless) |
ε0 |
permittivity constant for free space (charge2/force length2) |
η |
explosion efficiency (unitless) |
φ |
nonideal filling factor (unitless) |
γ |
heat capacity ratio (unitless) |
γc |
conductivity (mho/cm) |
χ |
function defined by Equation 9-6 |
λ |
frequency of dangerous episodes |
λd |
average frequency of dangerous episodes |
μ |
viscosity (mass/length/time) or mean value or failure rate (faults/time) |
μv |
vapor viscosity (mass/length/time) |
ψ |
overall discharge coefficient used in Equation 9-15 (unitless) |
ρ |
density (mass/volume) |
ρL |
liquid density (mass/volume) |
ρref |
reference density for specific gravity (mass/volume) |
ρv |
vapor density (mass/volume) |
σ |
standard deviation (unitless) |
σx, σy, σz |
dispersion coefficient (length) |
τ |
relaxation time |
τi |
inspection period for unrevealed failures |
τ0 |
operation period for a process component |
τr |
period required to repair a component |
τu |
period of unavailability for unrevealed failures |
ζ |
zeta potential (volts) |
Subscripts
a |
ambient |
c |
combustion |
f |
formation or liquid |
g |
vapor or gas |
H |
higher pressure |
i |
initiating event |
j |
purges |
L |
lower pressure |
m |
maximum |
s |
set pressure |
o |
initial or reference |
Superscripts
° |
standard |
’ |
stochastic or random variable |