HomeMy WebLinkAboutRISK MANAGEMENT 3687 MT. DIABLO BLVD.
LAFAYETTE, CA 94549
TELEPHONE (41'5) 283-8860
LOSS CONTROL CONSULTANTS ·
FIRE PROTECTION ENGINEERS
11w FPE ~;foup Momo From:
Dan Cox
,
USES OF EPIcode','-
response personnel and emergency planners with a sol't-
ware tool to help evaluate the atmospheric release ol' toxic
substances. ~Plcode allows fast estimatlon and assess-
ment of chemlcal-release scena~os associated wlth acc~-
dents from indust~ and transpo~ation.
The software can also be used for s~ety-analysis planmng
pu~oses on facilities handling toxic materials. Addition-
ally, this program can provlde a rapid Brst-order check
against complex and more e~ens~ve models runmng on
larger computers. ~Plcode ~11 promde a reasonable level
of accuracy for a timely i~tlal assessment.
The program conta~s a libra~ of over 600 chemical sub-
stances along wlth the associated ~posure levels accepted
by various professlonal organ~atlons and regulato~
agencies. ~en developing ~Plcode, we made eve~ effort
to ensure that it is easy to use, potable, and rellable for
on-the-spot applicatlons.
The sol. are is completely menu-d~ven and requires
mimmal user traimng. Chemical i~o~ation can be
retrieved l~om the libra~ by entering either the substance
name or a common synon~, the U.S. Depa~ment of
~anspgFrat'~on (DOT) Number, or the Chemlcal Abstract
Se~lce (CAS) Number. EPIcode also contains a ~Browser"
utlli~ that allows easy searching of the chemical llbra~ ff
you do not ~ow the ~act spelling or chemical number.
the instructions tn this manual. As a quick reference, we
EPIcode will run on an IBM PC, XT, AT, or compatible, ???~!?~iiiii??~!!!i??~i~::~::~::~:/:~::~ have included a step-by-step flow chart to follow during
with a mininmm of 512 kbytes of RAM and a single floppy your first few uses of EPIcode.
;~" disk drive. However, the program runs most efficiently
· when it resides on a hard disk. The software is available
CODE BASIS ~
on either 5 1/4" or 3 1/2" diskettes, and is not copy-pro- ~
tected for the purpose of personal backup only. See
Backup and Hard Disk Systems on page 39. EPIcode uses the well-established Gaussian Plume
Model, which is widely used for initial emergency assess-
The software supports either monochrome or color mon- merit or safety analysis planning of a chemical release.
itors. The only operating system software required is MS- The Gaussian Plume Model generally produces results in
DOS version 2.1 or later, good agreement with experimental data. The appendices
to this manual describe the code basis and all algorithms
Output can be directed to the computer monitor, printer, used.
or to a disk file. The ASCII-fore, at disk l'ile can be read or
altered using any standard word processor. This feature
allows you to include EPIcode estimates in formal reports. £Plcocte TM LIBRARY
The disk file can also be imported to any commercial . ,'
database or spreadsheet package where the data can be The EPIcode library contains information on over 600
manipulated and displayed using the additional graphics toxic substances listed in the Threshold Limit Values and
(' capabilities in other software. Biological Exposure Indices for 1987-1988, published by
the American Conference of Governmental Industrial
Hygienists. IDLH (Immediately Dangerous to Life or
Health) and STEL (Short Term Exposure Limit) values are
included when available (National Institute for Occupa-
tional Safety and Health).
This library of chemical information is protected from
inadvertent modification, but a user can easily supple-
ment the standard database with a personal subset of
additional chemicals you may frequently encounter.
These additional chemicals will automatically supplement
any future EPIcode Library upgrades; you do not need to
re-enter these substances each time.
APPENDIX A
EPIcode ALGORITHMS
In the preceding sections of this manual, you have learned
enough detail to use the EPIcode software. This Appendix
documents the codes and outlines the algorithms used in
the program for better background and to emphasize the
utility, and limitations, of EPIcode estimates.
COOI~DINATE SYSTEM
In the EPIcode system, we have placed the coordinate
origin (x = O, y = 0, z = 0) at ground level, beneath the point
at which the chemical substance is released. The x axis is
the downwind axis, extending horizontally with the ground
in the average wind direction. The y axis is the crosswind
axis, perpendicular to the downwind axis, also extending
horizontally. The altitude axis'(z axis) extends vertically. A
plume travels along, or parallel to, the downwind axis. The
figure below illustrates the EPIcode coordinate system.
Y
Crosswind~'"'""'"~
-y
axis
The 'puiP equation is used for an instantaneous term BASIC EQUATION
release, and the ~eontinuous~ equation is used for a eon-
tinuous release. For a non-instantaneous term release
{e.g,, 0.5 min., 120 min., etc.) EPIeode automatically The origin of the Oaussian model is found in work by
selects the appropriate equation. This selection process is Sutton (1932), Pasqufll (1961, 1974), and Gifford {1961,
{' based upon the plume length {release duration x wind 1968). Additional background and supplemental informa-
speed) relative to the c~ at the specific downwind location tlon on the Oaus~ian model can be found tn Turner {1969)
× and Hanna et a1.~(1982).
being considered. We assume that ~ = ~ . For a term
X
release when the plume length is less thaYn c~x, the plume
diffusion process is more accurately characterized by the We use the following Gaussian model equations to deter-
Puff equation. The Continuous equation is used whenever mine the concentration for a gas or an aerosol (particles
the plume length is greater than or equal to 2ox. For less than approximately 20 p_m in diameter).
plume lengths between ~x and 2c~x, a combination of both
equations is used.
Continuous Phase: ·
If the lnversion Layer optlon is in effect, and c~z exceeds the Q [ 1 (~y)~{ [ i(E-H]21
inversion height L, the following equations are used. C (x.y,z,H) -2~C~y~zu exp - ~ exp - 2~, % y J +
Continuous Phase, % >L: i ~[
.. exp - z+H 121~
{ C(x,y,z,H) = ,/-2~u exp - -~
Puff Phase:
Puff Phase, ~z > L: C (x,y,z,H) = (2~)3/2Ox~yOz exp - ¥ exp - °z JJ
9r 1 y
The values of % and °z are representative of a sampling where C = atmospheric concentration (ppm, mg/ma)
time often minutes. Concentrations directly downwind Q = source term {g/s, ma/s, etc.),
from a source decrease with sampling time pl-/marily or for a term release
because of a larger %due to increased meander of wind Q = Q~./release duration (g/s, etc.)
direction. For sampling times greater than ten minutes, QT = total release (g, ma, etc.)
and less than the total release time for term releases, the H = effective height of chemical substance release
following equation can be used to predict the sampling x = downwind distance (m)
results {Turner, 1969): y = crossla, ind distance {m)
( 10 )0.2 z = vertical axis distance (m)
Cs = C~.-~-sj c~x = standard deviation of the concentration
distribution in the downwind axis direction
where C. = the concentration averaged over t minutes. {x axis, meters) ox = %.
' % = standard deviation of the concentration
For example, you run an air sampler for one hour (60 min) distribution In the crosswind direction
at a particular downwind location. The EPIcode estimate {y axis, meters)
at this location ls 25 mg/m3. However. the one-hour aver- c~z = standard deviation of the concentration
distribution In the vertical direction
age concentration expected from the previous equation is: (z axis, meters)
~ u = average wind speed at the effective release
Cs = 25mg/m3 10mini= 17mg/m3 height {m/s. mph)
60 min
= inversion layer height (m).
EFFECTIVE RELEASE HEIGH1~ An upwind virtual point source, which results in an initial
c~y equal to the effective radius of the area source, is used to
model an area release.
The actual plume height may not be the physical release
height, e.g., the stack height. Plume rise can occur be-
cause of the velocity of a stack emission, and the tempera-
ture differential between the stack effluent and the sur-
rounding air. The rise of the plume results in an increase
in the release height, as shown in the figure at the top of
the next page.
This effective increase in release height leads to lower
concentrations at the ground level. If you are not able to
visually estimate or calculate the effective release height,
we recommend you use the actual physical release height
(i.e., the height of the stack)--or use zero height for a
ground-level release. This will always yield conservative
estimates.
For users who are not familiar with the different stability
classifications commonly used in meteorology, EPIcode will
select the appropriate stability classification with informa-
tion you provide from direct observations. Or, a user can
directly select and force a particular stability classification.
The simplified method requires selection of the solar insola- ~/ N---.----
tion factor and ground wind speed (at a 2 meter height). ~ -:
EPIcode then automatically determines the atmospheric
stability category from the matrix given in Table 1. This
table contains criteria for the six stability classes, which H
are based on five categories of surface wind speeds and /
four categories of solar insolation. This scheme is widely ~ ~ X
used in meteorology and is accepted for stability class
estimation.
If the release is from a stack, and you know additional
Table 1. Meteorological conditions used to define the information on the stack discharge velocity, temperature,
Atmospheric Stability Categories, A-F, used in EPIcode. and stack diameter (i.e., if you are designing a new stack
for a building), EPIcode can automatically calculate the
Sun conditions effective release height. This can also be applied to an area
release ff the effective release radius is less than fifty
Low in meters.
Ground wind High in sky or
speed (m/s) sky cloudy Nighttime
Select Calculate PLUME RISE by typing PR from the
<2 A B F release height prompt. EPIcode calculates both the
2-3 A C E momentum plume rise (Briggs, 1969) and the buoyant
3--4 B C D plume rise (Briggs, 1975) and chooses the greater of the
4-6 C D D two results. The recommended methodologies in the above
>6 C D D two references are strictly followed.
Pasquill Stability Types:
A: Extremely Unstable D: Neutral
B: Moderately Unstable E:Slightly Stable STABILITY CLASSIFICATION
c: slightly Unstable F: Moderately Stable
Meteorologists distinguish several states of the atmospheric
surface layer: unstable, neutral, and stable. These eatego-
The user may also select the stability class, A-F, directly ties refer to how a parcel of air would react when it is
from the table. In addition to these six stability classes, displaced adiabatically in the vertical direction. The
EPIeode also allows you to enter w for the worst-case EPIcode model offers two ways to select the atmospheric
scenario. If w is selected, EPIeode uses a/1 stability classes stability category.
to determine the downwind concentration, then chooses
only the class resulting in the highest contaminant concen-
tration for the particular ground-level location. For
For brief (puff) releases of less than ten minutes, the ex- documentation purposes the displayed output indicates
per/mental data indlcate that that oy and % are smaller by which stability class gave rise to the worst case at each
about a factor of two (Slade, 1968). EPIcode automatically downwind location.
uses the following algorithms to determine the short-term
standard deviations, o/and az'. These values replace the
o~ and oz in the basic Gauss/an equation. DETERMINATION OF ~y AND ~z
The new o~ and oz' are a factor of two smaller than ov and The standard dewatlons of the crosswind and vertical
oz for release durations less than or equal to one minute, concentrations frorn the basic equation arc c~ and
For durations between one and ten minutes, the factor is respectively.
linearly interpolated, as shown below.
Once the atmospheric stability category has been deter-
Release Duration, t mined, EPIcode uses the equations given in Table 2 to es-
(m/n] o,' o,' t/mate o~ and oz for two terrain types--Standard and City.
The City terrain factor accounts for the increased plume
t > 10 o, % dispersion from crowded structures and the heat retention
1 < t _< 10 o,/(-0.1 It + 2.11) %/(-0.1 It + 2.11) characteristics of urban surfaces, such as asphalt and con-
t < 1 o,/2 %/2 crete. The City terrain factor will estimate lower concentra-
tions than the Standard factor, due to the increased disper-
sion from large urban structures and materials. Choosing
In a term release and for plume travel times [distance/u(H)l Standard terrain will give the most conservative estimates.
longer than 10,000 seconds, the ~continuous' plume os are
more characteristic of the observed diffusion process. For Table 2. Equations used to determine o~ and o.. This
long plume travel times, only continuous-plume os are methodology is derived from Briggs, 1973.
used. The transition between ~)uff and continuous os
begins at plume travel times of 1000 seconds and is cam- Pasquill (~y Oz
plete by 10,000 seconds, type (m) (m)
Open Country
Wind Speed Var/at/on with Height ^ 0.22x (1 + O.O001x)-I/2 0.20x
The wind speed a user inputs to EPIcode is the estimate for B 0.16x (1 + 0.0001x)-1/2 0.12x -1/2
C 0.1 lx (1 + 0.0001x)-1/2 0.08x (1 + 0.0002x)_1/2
a height of two meters. However, the Gaussian plume D 0.08x (1 + 0.0001x)-1/2 0.06x )1 + 0.0015X)_l
equation requires the wind speed at height H, the effective E 0.06x (1 + 0.0001x)-1/2 0.03x (1 + 0.0003x) ,
release height. EPIcode automatically uses the following F 0.04x (1 + 0.0001x)-1/2 0.016x (1 + 0.0003x~-~
power-law formula to determine the wind speed for all
effective heights greater than two meters.
City
FH__]P A-B 0.32x (1 + 0.0004x)-1/2 0.24x (1 + 0.001x)1/2
u(H) = u(2)L2J C 0.22x (1 + 0.0004x)-1/2 0.20x
0 00^- ,-1/2 -1/2
0.14x (1 + 0.0003x) 1/2
D 0.16x (l + ^.^^~uq, x!_l/2 0.0ax {1 + O. O0015X)" '
where u(2) = surface wind speed/m/s) at 2 meters height. E-F 0.1 lx (1 + u.uuu~xj
H = effective release height (m).
P = factor from Table 3. x = downwind distance, rn
where: Table 3. Exponential factor used by EPIcode for calcu-
lating wind speed variation with height (from Irwin
DF{x) = Depletion factor. (1979).
x = Downwind distance.
C ' v = Deposition velocity. The deposition velocity Stability Class
· is empirically defined as the ratio of the ob-
served deposition rate (e.g., mg/m2. s) and A i B C D E F
the observed air concentration near the "
ground surface (e.g., mg/m3). City 0.15 0.15 0.20 0.25 0.40 0.60
u = Average ground level (2 m) wind speed. Standard
H = Effective release height of chemical, terrain 0.07 0.07 0.10 0.15 0.35 0.55
oz {x) = Standard deviation of the air concentration
distribution in the vertical direction {z axis)
for either Standard or City terrain, as
applicable.
PLUME DEPLETION
Tile default values I'or the deposition velocities used iii
EPIcode are:
Very small particles and gases or vapors are deposited on
Physical form surfaces as a result of turbulent diffusion and Brownian
motion. Chemical reactions, tmpaction, and other bio-
.... of substance v (cm/s) logical, chemical, and physical processes combine to keep
Solid 1 the released substance at ground level. As this material
Gas/vapor 0.1 deposits on the ground, the plume above becomes depleted,
Unknown 0.1 EPIcode uses a source-depletion algorithm to adjust the air'
concentration in the plume to account for this removal of
material.
These default values can be changed by the user if more
applicable information is available (e.g., increased deposi- The source term in EPIcode is allowed to decrease with
tion due to chemical reactivity, etc.), downwind distance. The code accomplishes this by multi-
plying the original source term by a source-depletion factor,
DF(x). The evaluation of this depletion factor has been
VERIFICATION ............ described by Van der Hoven (in Slade, 1968).
The Gaussian model is still the basic workhorse for atmos- The equation used in EPIcode is: v /-~
--fi
pheric dispersion calculations and has found its way into ~x 1
most governmental guidebooks. The Gaussian model has DF (X) = e. xpJO 2 dx
(' also been used and accepted by the Enmronmental Pro- 1 H
tection Agency. The adequacy of this model for making ~z (x) exp ~
initial dispersion estimates has been tested and verified
for many years.
APPENDIXB ' EPIcode strictly £ollo,vs a well-established implementation
of the Gaussian model. EPIcode uses no "black-box"
techniques. All algorithms are presented and fully refer-
NFPA HAZARD CLASSIFICATIONS' enced ii1 this manual.
ACCURACY
The National Fire Protection Association uses a color-coded
Hazard Classification scheme, which EPIcode adopts for its The many uncertainties associated with the variables in the
color displays. This Appendix gives details on the NFPA Gaussian model, such as l'luctuations in the meteorological
classification system, conditions, or type of terrain, result in a degree o£ impreci-
sion in the calculated ground level concentrations. I1'
The color red is used to denote lqammability, blue to denote inappropriate meteorological data, source term assump-
a health hazard, and yellow to denote chemical reactivity, tions, effective stack height, etc., are input into the pro-
Each o£ these colors also contains a number from 0-4 to gram, large errors are possible in the EPIcode estimates.
indicate the magnitude o£ the threat. This classification Given accurate input assumptions, the standard deviation
system also uses a fourth color category, ~vhite, for special of the ground concentration as calculated by EPIcode is
hazards, the most common of which is Hi" indicating that thought to be approximately a factor of five. In other
water should not be used. The special symbol used in the words, 68% of the time (i.e., the percentage of observations
NFPA hazard classifications is shoxvn below, within +_ 1 standard deviation, assuming a Gaussian distri-
bution) the calculated ground-level concentration will be
xvithin a factor ol' 5.
~ ...- Flammability
Health Signal Signal (Red) Other percentages can be in£erred l¥om the Gaussian
(Blue) distribution. I£ C is the calculated ground-level concen-
tration, this means that 50% of the time the true concen-
tration should lie between C/3 and 3C; and 80% of the
time between C/8 and 8C. For example, ff the calculated
value xvere 300 ppm, at least half o£ the time you would
(Yellow) The Examples section compares EPIcode estinmtes ~vith
Special Hazard ~ actual test releases of ammonia and other chemicals.
Information (Wkite)
BLUE--Health Hazard
4 Materials that on very short exposure could
cause death or major residual injury even i£ prompt medi-
cal treatment is given.
BLUE--continued
3 Materials that on short exposure could cause
serious temporary or residual injury even if prompt medical
treatment is given. .
2 Materials that on intense or continued exposure
could cause temporary incapacitation or possible residual :.
injury unless prompt medical treatment is given.
i Materials that on exposure would cause irritation
but only minor residual injury even ff no treatment is given.
0 Materials that on exposure under fire conditions
would offer no hazard beyond that of ordinary combustible ..
material.
REDwFlammability '
4 Materials that will rapidly or completely vaporize ~:.
at atmospheric pressure and normal ambient temperature,
or that are readily dispersed in air and will burn rapidly. ·
3 Liquids and solids that ~an be ignited under
almost all ambient temperature conditions.
2 Materials that must be moderately heated or ex-
posed to relatively high ambient temperatures before
igmtion can occur.
1 Materials that must be preheate'd before ignition
can occur. '~:!!
0 Materials that will not burn.
APPENDIX C
YELLOWtReactivity
4 Materials that in themselves are readily capable
LIST OF CHEMICALS INTHE or detonation or explosive decomposition or reaction at
EPIcodeTM LIBRARY normal temperatures and pressures.
3 Materials that in themselves are capable of deto-
nation or explosive reaction but require a strong initiating
source or that must be heated under confinement before
Chemical Name CAS number initiation, or that react explosively with water.
ACETAi. DEHYDE 75-07-0 2 Materials that in themselves are normally un-
ACETIC ACID 64-19-7 stable and readily undergo violent chemical change but
ACETIC ANHYDRIDE 108-24-7 do not detonate. Also materials that may react violently
ACETONE 67-64-1 with water or that may form potentially explosive mixtures
ACETONITRI LE 75-05-8
ACE'I~LENE 74-86-2 with water.
ACE'I~LEN E TETRABROMIDE 79-27-6
ACETYI.SALICYI.IC ACH) 50-78-2 1 Materials that in thernselves are nom~ally stable,
ACROLEIN 107-02-8 but that can become unstable at elevated temperatures and
ACRYLAMID E 79-06-1
ACRYLIC ACID 79-10-7 pressures, or that may react with water with some release
ACRYLONITRILE 107-13-1 Of energy but not violently.
ALDRIN 309-00-2
07-18-6 ':~
ALLYLALLYL ALCOHOLcHLORIDE 1107-5-1 0 Materials that in themselves are normally stable,
ALLYL GLYC1DYL ETI-IER 106-92-3 even under fire exposure conditions, and that are not
ALLYL PROPYL DISULFIDE 2179-59-1 reactive with water.
ALPHA-ALUMI NA 1344-28-1
-AMI NO[) I PH EN YL 92-67-1
2-AMINOPYRIDINE 504-29-0
AMITROLE 61-82-5
AMMONIA 7664-41-7 WHITE--Other
AMMONIUM CHLORIDE FUME 12125-02-9
AMMONIUM SU LFAMATE 7773-06-0
SEC-AMYL ACETATE 626-38-0 W Materials that react so violently with water that a
N-AMYL ACETATE 628-63-7 ??:ii~i~i::i possible hazard results when they come in contact with
ANILINE 62-53-3 .....................::~i: water, as in a fire situation. Similar to Reactivity Class-
AN I s I D I N E 29191 - 52 - 4 i:i::!i!?:i::i~!i~::il .......... '.:
?~:~:~:~:~:~:~:~: ification 2.
ANTIMONY TRIOXIDE 1309-64-4 :i:i:~:~::i:i ......
ANTU 86-88-4 ::::::::::::::::::::::::::::::::::::Oxy Oxidizing material; any solid or liquid that readily
ARGON 7440-37-1 .......................... yields oxygen or other oxidizing gas, or that readily reacts
ARSENIC 7440-38-2 to oxidize combustible materials.
ARSENIC TRIOXIDE 1327-53-3
ARSINE 7784-42-1
ASBESTOS 1332-21-4
ASPHALT 8052-42-4
ATRIZINE 1912-24-9
AZINPHOS-METHYL 86-50-0
Chemical Name CAS number Chemical Name CAS number
BARI U M 7440- 39-3
CARBOFURAN 1563-66-2 BARIUM SULFATE 7727-43-7
CARBON BLACK BENOMYL 17804-35-2
1
333-86-4
CARBON DIOXIDE 124-38-9 BENZENE 71-43-2
CARBON I)ISULIql)E 75-15-0 BENZII)INE , 92-87-5
CARBON MONOXIDE 630-08-0 BENZO(A)PY~ENE 50-32-8
CARBON TETRABROMIDE 558-13-4 BENZOYL PEROXi DE 94-36-0
CARBON TETRACHLORIDE 56-23-5 BENZYL CHLORIDE 100-44-7
CARBONYL FLUORIDE 353-50-4 BERYLLIUM 7440-41-7
CATECHOL 120-80-9 BIPHENYL 92-52-4
CELLULOSE 9004-34-6 BISMUTH TELLURIDE 1304-82-1
CESIUM HYDROXIDE 21351-79- 1 BORON OXIDE 1303-86-2
CHLORDANE 57-74-9 BORON TRIBROMIDE 10294-33-4
CHLORINATED CAMPHENE 8001-35-2 BORON TRIFLUORIDE 7637-07-2
CHLORINATED DIPHENYL OXIDE 55720-99-5 BROMACIL 314-40-9
CHLORINE 7782-50-5 BROMINE 7726-95-6
CHLORINE DIOXIDE 10049-04-4 BROMINE PENTAFLUORIDE 7789-30-2
CHLORINE TRIFLUORIDE 7790-91-2 BROMOFORM 75-25-2
CHLOROACETALDEHYDE 107-20-0
ALPHA-CHLOROACETOPHE NONE 532-27-4 1,3-BUTAD1ENE 106-99-0
BUTANE 106-97-8
CHLOROACETYL CHLORII')E 79-04-9 2-BUTOXYETHANOL 111-76-2
CHLOROBENZENE 108-90-7 N-BUTYL ACETATE 123-86-4
O-CHLOROBENZYLIDENE MALONONITRILE 2698-41- t SEC-BUTYL ACETATE 105-46-4
CHLOROBROMOMETHANE 74-97-5 TERT- BUTYL ACETATE 540-88-5
CHLORODIFLUOROMETHANE 75-45-6 BUTYL ACRYLATE 141-32-2
CHLORODIPHENYL (42% CHLORINE) 53469-21-9 N-BUTYL ALCOHOL 71-36-3
CHLORODIPHENYL (54% CHLORINE) 11097-69- 1 SEC-BUTYL AL(~OHOL 78-92-2
CHLOROFORM 67-66-3 TERT-BUTYL ALCOHOL 75-65-0
BIS(CHLOROMETHYL) ETHER 542-88-1 BUTYl. AMINE 109-73-9
CHLOROMETHYL METHYL ETHER 107-30-2 TERT-BUTYL CHROMATE 1189-85-1
1-CHLORO~ 1-NITROPROPANE 600-25-9 N-BUTYL GLYCIDYL ETHER 2426-08-6
CHLOROPENTAFLUOROETHANE 76-15-3 N-BUTYL LACTATE 138-22-7
CHLOROPICRIN 76-06-2 BUTYL MERCAPTAN 109-79-5
BETA-CHLOROPRENE 126-99-8
O-SEC-BUTYLPHENOL 89-72-5
O-CHLOROSTYRENE 2039-87-4
P-TERT-BUTYLTOLUENE 98-51 - 1
O-CHLOROTOLUENE 95-49-8
C HLORPYRIFOS 2921-88-2
CHROMITE CADMIUM 7440-43 -9
CHROMIUM 7440-47-3 CADMIUM OXIDE 1306-19-0
CHROMYL CHLORIDE 14977-61-8 CALCIUM CARBONATE 1317-65-3
CHYRSENE 218-01-9 CALCIUM CYANAM1DE 156-62-7
CLOPIDOL 2971-90-6 CALCIUM HYDROXIDE 1305-62-0
COAL TAR 65996-93-2 CALCIUM OXIDE 1305-78-8
COBALT 7440-48-4 CALCIUM SILICATE 1344-95-2
COBALT CARBONYL 10210-68-1 CALCIUM SULFATE 7778-18-9
COBALT HYDROCARBONYL 16842-03-8 CAMPHOR 76-22-2
COPPER 7440-50-8 CAPTAFO L 2425-06~ 1
C O'1"I'O N DUST CAPTAN 133-06-2
CRESOL 1319-77-3 CARBARYL 63-25-2
CROTONALD EHYD E 4170-30-3
Chemical Name CAS number Chemical Name CAS number
2-D I ETHYLAMINOETHAN OL 100-37-8 CRUFOMATE 299-86-5
.... DIETHYLENE TRIAMINE 111-40-0 CUMENE 98-82-8
DIETHYL KETONE 96-22-0 CYANAMIDE 420-04-2
DIETHYL PHTHALATE 84-66-2 CYANIDES ~ 151-50-8
DIFLUORODIBROMOMETHANE 75-61-6 CYANOGEN ! 460-19-5
DIGLYCIDYL ETHER 2238-07-5 CYANOGEN CHLORiDE 506-77-4
DIlSOBUTYL KEri'ONE 108-83-8 CYCLOHEXANE 110-82-7
DII SOPROPYLAMINE 108-18-9 CYCLOHEXANOL 108-93-0
DIMETHYLAC ETAMI D E 127-19-5 CYCLOHEXANONE 108-94-1
DIMETHYLAMINE 124-40-3 CYCLOHEXENE 110-83-8
DIMETHYLANILINE 121-69-7 CYCLOH EXYLAMI NE 108-91-8
DIMETHYL CARBAMOYL CHLORIDE 79-44-7 CYCLONITE 121-82-4
DIMETHYLFORMAMIDE 68-12-2 CYCLOPENTADIENE 542-92-7
1,1 -DIMETHYLHYDRAZINE 57-14-7 CYCLOPENTANE 287-92-3
DIMETHYLPHTHALATE 131 - 11-3 CYHEXATIN 13121-70-5
DIMETHYL SULFATE 77-7.8- 1
DINITOLMIDE 148-01-6
DINITROBENZENE 528-29-0 2,4-D 94-75-7
DINITRO-O-CRESOL 534-52-1 DDT 50-29-3
DINITROTOLUENE 121 - 14-2 DECABORANE 17702-41-9
DIOXANE 123-91 - 1 DEMETON 8065-48-3
DIOXATHION 78-34-2 DIACETONE ALCOHOL 123-42-2
DIPHENYLAMINE 122-39-4 DIAZINON 333-41-5
DIPROPYLENE GLYCOL METIIYL ~H-1ER 34590-94-8 DIAZOMETHANE 334-88-3
DIPROPYL KETONE 123-19-3 DIBORANE 19287-45-7
DIQUAT 85-00-7 2-N-DIBUTYLAMINOETHANOL 102-81-8
DI-SEC-OCTYL PHTHALATE 117-81-7 DIBUTYL PHOSPHATE 107-66-4
DISULFIRAM 97-77-8 DIBUTYL PHTHALATE 84-74-2
DISULFOTON 298-04-4 1,1 -DICHLORO- 1-NITROETHANE 594-72-9
2,6-DI-TERT-BUTYL-P-CRESOL 128-37-0 1,3-DICHLORO-5,5-DIMETHYL HYDANTOIN 118-52-5
DIURON 330-54-1 DICHLOROACETYLENE 7572-29-4
DM NYL BENZENE 1321-74-0 O-DICHLOROBENZENE 95-50- 1
P-DICHLOROBENZENE 106-46-7
3,3'-DICHLOROBENZIDINE 91-94- 1
EMERY 112-62-9 DICHLORODIFLUOROMETHANE 75-71-8
ENDOSULFAN 115-29-7 1,1 -DICHLOROETHANE 75-34-3
ENDRiN 72-20-8 1,2-DICHLOROETHYLENE 540-59-0
EPICHLOROHYDRIN 106-89-8 DICHLOROETHYL ETHER 111-44-4
EPN 2104-64-5 DICH LOROFLUOROMETHANE 75-43-4
ETHANE 74 -84 -0 DICHLOROPROPENE 542-75-6
ETHANOLAMINE 141-43-5 2,2-DICHLOROPROPIONIC ACID 75-99-0
ETHION 563-12-2 DICHLOROTETRAFLUOROETHANE 76-14-2
~.- 2-ETHOXYETHANOL 110-80-5 DICHLORVOS 62-73-7
f 2-ETHOXYETHYL ACETATE 111 - 15-9 DICROTOPHOS 141-66-2
ETHYL ACETATE 141-78-6 DICYCLOPENTADIENE 77-73-6
ETHYL ACRYLATE 140-88-5 DICYCLOPENTADIENYL IRON 102-54-5
ETHYL ALCOHOL 64-17-5 DIELDRIN 60-57-1
ETHYLAMINE 75-04-7 DIETHANOLAMINE 111-42-2
ETHYL AMYL KETONE 541-85-5 DIETHYLAMINE 109-89-7
Chemical Name CAS number Chemical Name CAS number
ETHYL BENZENE 100-41-4
HEXACHLOROBUTADIENE 87-68-3 ETHYL BROMIDE 74-96-4
HEXACHLOROCYCLOPENTADIENE 77-47-4 ETHYL BUTYL KETONE 106-35-4
HEXACHLOROETHANE 67-72-1 ETHYL CHL/DRIDE 75-00-3
HEXACHLORONAPHTHALENE 1335-87-1 ETHYLENE ~ 74-85-1
HEXAFLUOROACETONE 684-16-2 ETHYLENE CHLOROHYDRIN 107-07-3
HEXAMETHYL PHOSPHORAMIDE 680-31-9 ETHYLENEDIAMINE 107-15-3
HEXANE 110-54-3 ETHYLENE DIBROMIDE 106-93-4
SEC-HEXYL ACETATE 108-84-9 ETHYLENE DICHLORIDE 107-06-02
HEXYLENE GLYCOL 107-41-5 ETHYLENE GLYCOL 107-21-1
HYDRAZINE 302-01-2 ETHYLENE GLYCOL DINITRATE 628-96-6
HYDROGEN 1333-74-0 ETHYLENE OXIDE 75-21-8
HYDROGENATED TERPH ENYLS 61788-32-7 ETHYLENIMINE 151-56-4
HYDROGEN BROMIDE 10035-10-6 ETHYL ETHER 60-29-7
HYDROGEN CHLORIDE 7647-01-0 ETHYL FORMATE 109-94-4
HYDROGEN CYANIDE 74-90-8 ETHYLIDENE NORBORNENE 16219-75-3
HYDROGEN FLUORIDE 7664-39-3 ETHYL MERCAPTAN 75-08-1
HYDROGEN PEROXIDE 7722-84-1
HYDROGEN SELENIDE 7783-07-5 N-ETHYLMORPHOLINE 100-74-3
HYDROGEN SULFIDE 7783-06-4 ETHYL SILICATE 78-10-4
HYDROQUINONE 123-31-9
2-HYDROXYPROPYL ACRYLATE 999-61-1 FENAMIPHOS 22224-92-6
FENSULFOTHION 115-90-2
FENTHION 55-38-9
INDENE 95-13-6 FERBAM 14484-64-1
INDIUM 7440-74-6 FERROVANADIUM DUST 12604-58-9
IODINE 7553-56-2 FIBROUS GLASS DUST
IODOFORM 75-47-8 FLUORIDES 16984-48-8
IRON OXIDE 1309-37-1 FLUORINE 7782-41-4
IRON PENTACARBONYL 13463-40-6 FONOFOS 944-22-9
ISOAMYL ACETATE 123-92-2 FORMALDEHYDE 50-00-0
ISOAMYL ALCOHOL 123-51-3 FORMAMIDE 75-12-7
ISOBU'IYL ACETATE 110-19-0 FORMIC ACID 64-18-6
ISOBUTYL ALCOHOL 78-83-1 FURFURAL 98-01-1
ISOOCTYL ALCOHOL 26952-21-6 FURFURYL ALCOHOL 98-00-0
ISOPHORONE 78-59-1
ISOPHORONE DIISOCYANATE 4098-71-9
ISOPROPOXYETHANOL 109-59-1 GASOLINE 8006-61-9
ISOPROPYL ACETATE 108-21-4 GERMANUIM TETRAHYDRIDE 7782-65-2
ISOPROPYL ALCOHOL 67-63-0 GLUTARALDEHYDE 111-30-8
ISOPROPYLAMINE 75-31-0 i::iii::i::iiiiiii::i::i::ii!i?:!! GLYCERIN 56-81-5
N-ISOPROPYLANILINE 768-52-5 GLYCIDOL 556-52-5
ISOPROPYL ETHER 108-20-3 GRAPHITE 7782-42-5
ISOPROPYL GLYCIDYL ETHER 4016-14-2
HAFN I U M 7440- 58 -6
KAOLIN HELIUM 7440-59-7
KETENE 463-51-4 HEPTACHLOR 76-44-8
HEPTANE 142 -82 -5
Chemical Name CAS number Chemical Name CAS number
METHYLENE CHLORIDE 75-09-2 LEAD 7439-92-1
4,4' METHYLENE DIANILINE 101-77-9 LEAD ARSENATE 10102-48-4
METHYL ETHYL KETONE 78-93-3 LEAD CHROMATE 7758-97-6
METHYL ETHYL KETONE PEROXIDE 1338-23-4 LINDANE ~ 58-89-9
METHYL 2-CYANOACRY1.ATE 137-05-3 LITH 1UM HYDRI DE 7580-67-8
MI'~I'HYL FORMATE 107-31-3 LPG 68476-85-7
METHYL HYDRAZI NE 60-34-4
METHYl. IODIDE 74-88-4
METHYL ISOAMYL Ki~YrONE 110-12-3 MAGNESITE 546-93-0
METHYl. ISOBUTYL CARBINOL 108-11-2 MAGNESIUM OXIDE 1309-48-4
METHYL ISOBUTYL KETONE 108-10-1 MALATHION 121-75-5
METHYL ISOCYANATE 624-83-9 MALEIC ANHYDRIDE 108-31-6
METHYL ISOPROPYL KE~.FONE 563-80-4 MANGANESE 7439-96-5
METHYL MERCAPTAN 74-93-1 MANGANESE CYCLOPENTADIENYL
METHYL METHACRYLATE 80-62-6 TRICARBONYL 12079-65-1
METHYL PARATHION 298-00-0 MANGANESE TETROXIDE 1317-34-6
METHYL PROPYL KETONE 107-87-9 MERCURY 7439-97-6
METHYL SILICATE 681-84-5 MESITYL OXIDE 141-79-7
ALPHA-METHYL STYRENE 98-83-9 METHACRYLIC ACID 79-41-4
METI~,I B UZIN 21087-64-9 ME'THANE 74-82-8
.,_ MEVINPHOS 7786-34-7 METHOMYL 16752-77-5
(~ MICA 12001-25-2
METHOXYCHLOR
72-43-5
· MOLYBDENUM 7439-98-7 2-METHOXYETHANOL 109-86-4
MONOCROTOPHOS 6923-22-4 2-METHOXYETHYL ACETATE 110-49-6
MORPHOLINE 110-91-8 4-METHOXYPHENOL 150-76-5
METHYL ACETATE 79-20-9
NALED 300-76-5 METHYL ACETYLENE 74-99-7
NAPHTHALENE 91-20-3 METHYL ACETYLENE-PROPADIENE
BETA-NAPHTHYLAMINE 91-59-8 MIXTURE
NICKEL 7440-02-0 METHYL ACRYLATE 96-33-3
NICKEL CARBONYL 13463-39-3 METHYLACRYLONITRILE 126-98-7
NICOTI NE 54-11-5 METHYLAL 109-87-5
NITRAPYRIN 1929-82-4 METHYL ALCOHOL 67-56-1
I ii~iii}i!ii METHYLAMINE 74-89-5
NITRIC ACID 7697-37-2 ii!iiiiiiiiiiiiiiiii?::iii::~::i::ii ::!i!!!il METHYL N-AMYL KETONE 110-43-0
NITRIC OXIDE 10102-43-9 iiiiiiiiill iiiiiii~I N-METHYL ANILINE 100-61-8
P-NITROANILINE 100-01-6 ii?!i~ii?iiiii~iiii!iiiii iii~iiii!i METHYL BROMIDE 74-83-9
NITROBENZENE 98-95-3 i~?~?~?~iiiii~iiiiiiiii i! ~ i ~! i ~ i ~
P-NITROCHLOROBENZENE 100-00-5 METHYL CHLORIDE 74-87-3
4-NITRODIPHENYL 92-93-3 ?~iiiiiiiiii?iii?i!!iiii!i:iiiiiiiiii~iiii~ili!iiii!iiiii!!iiiiii!il METHYL CHLOROFORM 71-55-6
NITROETHANE 79-24-3 METHYLCYC LOHEXANE 108-87-2
NITROGEN DIOXIDE 10102-44-0 METHYLCYCLOHEXANOL 25639-42-3
C NITROGEN TRIFLUORIDE 7783-54-2 O-M ETHYLCYC LOH EXANONE 583-60-8
· NITROGLYCERIN 55-63-0 2-M ETHYLCYCLOPENTADIENYL
NITRO METHANE 75-52-5 MANGANESE TRICARBONYL 12108- 13-3
1-NITROPROPANE 108-03-2 METHYL DEMETON 8022-00-2
2-NITROPROPANE 79-46-9 METHYL N-BUTYL KETONE 591-78-6
N-NITROSODIMETHYLAMI NE 62-75-9 METHYLENE BIS(4-CYCLOHEXYLISO-
NITROTOLUENE 99-08-1 CYANATE) 5124-30-1
NONANE 111-84-2 METHYLENE BISPHENYL ISOCYANATE 101-68-8
Chemical Name CAS number Chemical Name CAS number
PROPARGYL ALCOHOL 107-19-7 OCTACHLORONAPHTHALENE 2234- 13-1
' BETA-PROPIOLACTONE 57-57-8 OCTANE 111-65-9
PROPIONIC ACID 79-09-4 OIL MIST, MINERAL 8012-95-1
PROPOXUR 114-26-1 OSMIUM TETROXIDE 20816-12-0
PROPYL ALCOHOL 71-23-8 OXALIC ACID" 144-62-7
N-PROPYL ACETATE 109-60-4 OXYGEN DIFLUORIDE 7783-41-7
PROPYLENE 115-07-1 OZONE 10028- 15-6
PROPYLENE DICHLORIDE 78-87-5
PROPYLENE GLYCOL DINITRATE 6423-43-4
PROPYLENE GLYCOL MONOMETHYL ETHER 107-98-2 PARAFFIN WAX FUME 8002-74-2
PROPYLENE IMINE 75-55-8 PARAQUAT 4685-14-7
PROPYLENE OXIDE 75-56-9 PARATHION 56-38-2
N-PROPYL NITRATE 627-13-4 PENTABORANE 19624-22-7
PYRETHRUM 8003-34-7 PENTACH LORONAPHTHALENE 1321-64-8
PYRIDINE 110-86-1 PENTACHLOROPHENOL 87-86-5
PENTAERY"HtRITOL I 15-77-5
P ENTAN E 109 -66 -0
QUINONE 106-51-4 PERCH LOROETHYLENE 127-18-4
PERCH LOROM ETh'YL MERCAPTAN 594-42-3
PERCItI.ORYL FLUORIDE 7616-94-6
· ~.. RESORCINOL 108-46-3 PHENOL 108-95-2
t RHODIUM 7440- 16-6 PHENOTHIAZINE 92-84-2
RONNEL 299-84-3 P-PHENYLENE DIAMINE 106-50-3
ROTENONE 83-79-4 N- PH ENYL-B ETA- NAPHTHYLAMI NE 135-88-6
RUBBER SOLVENT PHENYL ETHER 101-84-8
PHENYL GLYCIDYL ETHER 122-60-1
PH ENYLHYDRAZI NE 100-63-0
SELENIUM COMPOUNDS 7782-49-2 PHENYL MERCAPTAN 108-98-5
SELENIUM HEXAFLUORIDE 7783-79-1 PHENYLPHOSPHINE 638-21 - 1
SESONE 136-78-7 PHOIOkTE 298-02-2
SILICON 7440-21-3 PHOSGENE 75-44-5
SILICON CARBIDE 409-21-2 PHOSPHINE 7803-51-2
SILICON TETRAHYDRIDE 7803-62-5 PHOSPHORIC ACID 7664-38-2
SILVER 7440-22-4 iiiiiii~iiiii]::::::::::::::::::::::::~:::::::::::::::::::::::::: PHOSPHORUS (YELLOW) 7723-14-0
SODIUM AZIDE 26628-22-8 PHOSPHORUS OXYCHLORIDE 10025-87-3
SODIUM BISULFITE 7631-90-5
i~iiii!~ii ii~i!iiiii~::iii~! PHOSPHORUS PENTACHLORIDE 10026- 13-8
SODIUM FLUOROACETATE 62-74-8 ! ~iiiet.'..i!i ~iii~ii~iiiii! PHOSPHORUS PENTASULFIDE 1314-80-3
SODIUM HYDROXIDE 1310-73-2 ~?~!~!~i~ii~ii!~]~?~i~i~i~?~iii~i~?~PHOSPHORUS TRICHLORIDE 7719-12-2
SODIUM METABISULFITE 7681-57-4 ................ iii:i:::::iiii~ii!ii!i!ii! PHTHALIC ANHYDRIDE 85-44-9
STARCH 9005-25-8 M-PHTHALODINITRILE 626- 17-5
STIBINE 7803-52-3 PICLORAM 1918-02-1
.. STODDARD SOLVENT 8052-41-3 PICRIC ACID 88-89-1
( STRYCHNINE 57-24-9 PINDONE 83-26-1
STYRENE, MONOMER 100-42-5 PIPERAZINE DIHYDROCHLORIDE 142-64-3
SUBTILISINS 1395-21-7 PLATINUM 7440-06-4
SUCROSE 57-50-1 PORTLAND CEMENT 65997-15-1
SULFOTEP 3689-24-5 POTASSIUM HYDROXIDE 1310-58-3
SULFUR DIOXIDE 7446-09-5 PROPANE 74-98-6
SULFUR HEXAFLUORIDE 2551-62-4 PROPANE SULTONE 1120-71-4
Chemical Name CAS number Chemical Name CAS number
(~ TRICHLORONAPHTHALENE 132 1-65-9 SULFURIC ACID 7664-93-9
- 1,2,3-TRICHLOROPROPANE 96- 18-4 SULFUR MONOCHI.ORIDE 10025-67-9
TRIE'. ri tYLAMINE 121-44-8 SULFUI~. PENTAFLUOI,IIDE 5714-22-7
Tied FLUOI.IOBROMOMET! lANE 75-63-8 SULFUR. TET~FLUOI~II)E 7783-60-0
TRIMELLITIC ANHYDRIDE 552-30-7 SULFURYL FI~UORIDE 2699-79-8
TRI METHYI.AMINE 75-50-3 SULPROFOS 35400-43-2
TRIMETHYL BENZENE 25551 - 13-7
TRIMETHYL PHOSPHITE 121-45-9 93-76-5
2,4,6-TRIN1TROTOLUENE 118-96-7 2,4,5-T
'I'RIOI~I'I IOCRESYL PI IOSPI lATE 78-30-8 TALC 14807-96-6
TRIPHENYL AMINE 603-34-9 TANTALUM 7440-25-7
TRIPHENYL PHOSPHATE 115-86-6 TELLURIUM & COMPOUNDS 13494-80-9
TELLURIUM H EXAFLUORIDE 7783-80-4
TUNGSTEN 7440-33-7 TEMEPHOS 3383-96-8
TU RPE NTI N E 8006- 64- 2 TEPP 107-49 -3
TERPH ENYLS 26140-60-3
URANIUM 7440-61 - 1 1,1,2,2-TETRACHLOROETHANE 79-34-5
1,1,1,2-TETRACHLORO-2,2-DIFLUORO-
ETHANE 76-11-9
N-VALERALDEI IYDE 110-62-3 TETRACHLORONAPHTHALENE 1335-88-2
VANADIUM 1314-62-1 TETRAETHYL LEAD 78-00-2
.... VINYL ACETATE 108-05-4 TETRAHYDROFU RAN 109-99-9
- VINYL BROMIDE 593-60-2 TETRAMETHYI. LEAD 75-74-1
VINYL CHLORIDE 75-01-4 TETRAMETHYL SUCCINONITRILE 3333-52-6
VINYL CYCLOHEXENE DIOXIDE 106-87-6 TETRANITROMETHANE 509-14-8
VINYLIDENE CHLORIDE 75-35-4 TETRA, SODIUM PYROPHOSPHATE 7722-88-5
VINYl. TOLUENE 25013- 15-4 1,1,2,2-TETROCHLORO- 1,2-DIFLUORO-
ETHANE 76-12-0
VM & P NAPHTI'[A 8030-30-6 TETRYL 479-45-8
THALLIUM 7440-28-0
WARFARIN 81-81-2 4,4'-THIOBIS(6-TERT- BUTYL-M-CRESOL) 96-69-5
WELDING FUMES THIOGLYCOLIC ACID 68-11-1
........................... : ........................... THIONYL CHLORIDE 7719-09-7
THIRAM 137-26-8
XYLENE 1330-20-7 TIN 7440-31-5
M-XYLENE ALPHA, ALPHA'-DIAM1NE 1477-55-0 TITANIUM DIOXIDE 13463-67-7
XYLIDINE 1300-73-8 O-TOLIDINE 119-93-7
TOLUENE 108-88-3
TOLUENE-2,4-DIIS.OCYANATE 584-84-9
I~ YTI'RIUM 7440-65-5 O-TOLUIDINE 95-53-4
M-TOLUIDINE 108-44- 1
P-TOLU1DINE 106-49-0
t ZINC CHITDR1DE 7646-85-7 TRIBUTYL PHOSPHATE 126-73-8
ZINC CHROMATE 13530-65-9 1,2,4-TRICHLOROBENZENE 120-82-1
ZINC OXIDE 13 14-13-2 1,1,2-TRICHLORO- 1,2,2-TRIFLUOROETHANE 76-13- 1
ZINC STEARATE 557-05-1 TRICHLOROACETIC ACID 76-03-9
ZIRCONIUM COMPOUNDS 7440-67-2 1,~I,2-TRICHLOROETHANE 79-00-5
TRICHLOROETHYLENE 79-01-6
TRICH LORO FLUORO METHANE 75-69-4
REFERENCES
American Conference of Governmental Industrial Hygien-
ists, Threshold Limit Values and Biological Exposure Indices
for 1987-88, American Conference of Governmental Indus-
'REFERENCES
trial Hygienists, Cincinnati, OH (1987).
Blewitt, D.N., J.F. Yohn, and D.L. Ermak, "An Evaluation of
SLAB and DEGADIS Heavy Gas Dispersion Models Using
the HF Spill Test Data," (AICHE International Conference
on Vapor Cloud Modeling, Boston, MA, Nov. 2-4, 1987).
Blewitt, D.N., J.F. Yohn, R.P. Koopman, and T.C. Brown,
'Conduct of Anhydrous Hydrofluoric Acid Spill Experi-
ments," (AICHE International Conference on Vapor Cloud
Modeling, Boston, MA, Nov. 2-4, 1987).
(
Briggs, G. A., Diffusion Estimates for Small Emissions, At-
mospheric Turbulence and Diffusion Laboratory, ATDL
Contribution File No. 79 (19731'.
Briggs, G.A., Plume Rise (U.S.' Atomic Energy Commission,
Division of Technical Information, 1969), pp. 57-60.
Briggs, G. A., "Plume Rise Predictions," in Lectures on Air
Pollution and Environmental Impact Analyses, Workshop
Proceedings (American Meteorology Society, Boston, MA,
Oct. 3, 1975), pp. 59-111.
Environmental Protection Agency, Guideline on Air Quality
Models, Office of Air Quality Planning and Standards,
Research Triangle Park, NC, OAQPS Guideline Series No.
1.2-080, Report EPA-45012-78-027 (1978).
National Institute for Occupational Safety and Health, Ermak, D.L. and S.T~ Chan, A Study of Heavy Gas Effects
NIOSH Pocket Guide to Chemical Hazards, U.S. Department on the Atmospheric Dispersion of Dense Gases, Lawrence
of Health and Human Services, Public Health Service, Livermore National Laboratory, Livermore, CA, UCRL-
Centers for Disease Control, Washington, DC, DHEW
92494 (1985).
(NIOSH) Publication No. 78-210 (1985).
Gifford, F.A., Jr., 'Use of Routine Meteorological Observa-
Pasquill, F., 'The Estimation of the Dispersion of Wind- tions for Estimatin~ Atmospheric Dispersion," Nuclear
borne Material," Meteorology Magazine, 90, pp. 33-49 Safety, 2:4, pp. 45-57 (1961).
(1961).
Gifford, F.A., Jr., 'An Outline of Theories of Diffusion in the
Pasquill, F., Atmospheric Diffusion, 2nd. ed. (New York, Lower Layers of the Atmosphere,' in Meteorology and
John Wiley & Sons, 1974). Atomic Energy--1968, D. H. Slade, Ed. (U.S. Atomic Energy
Commission, Report TID-24190, National Technical Infor-
Sutton, O.G., 'A Theory of Eddy Diffusion in the mation Service), pp. 66-116 (1968).
Atmosphere, Proceedings of the Royal Society (London),
Series A, 135, p. 143 (1932). Gifford, F.A., Jr., 'Turbulent Diffusion Typing Schemes--A
Review," Nuclear Safety, 17, pp. 68-86 (1976).
Turner, D. B., Workbook of Atmospheric Dispersion Esti-
mates, U.S. Department of Health, Education, and Welfare, Goldwire, H.C., Jr., T.G. McRae, G.W. Johnson, D.L.
Public Health Service, National Air Pollution Control Ad- Hipple, R.P. Koopman, J.W. McClure, L.K. Morris, and
ministration, Cincinnati, OH (revised, 1969). RiT. Cederwall, Desert Tortoise Series Data Report, 1983
Pressurized Ammonia Spills, Lawrence Livermore National
Laboratory, Livermore, CA, UCID-20562 (1985).
Van der Hoven, I., "Deposition of Particles and Gases," in
Meteorology and Atomic Energy--1968, D.H. Slade, Ed.
(U.S. Atomic Energy Commission, Report TID-24190, Havens, J.A. and T.O. Spicer, Development ofanAtmos-
National Technical Information Service), pp. 202-207 pheric Dispersion Model for Heavier-Than-Air Gas Mixtures,
1968). U.S. Coast Guard Report CG-D-22-85 (1985).
Irwin, J. S., "A Theoretical Variation of the Wind Profile
Power Law Exponent as a Function of Surface Roughness
and Stability,' Atmos. Environ. 13, pp. 191-194 (1979).
National Fire Protection Association, Fire Protection Guide
on Hazardous Materials, Code 704M, 4th ed., National Fire
Protection Association, Boston, MA (1972).
HOMANN Associates, Inc.
Software and Safety Engineering
39831 San Moreno Court
Fremont, California 94539
(415) 490-6379 · FAX (415) 967-4823
Dan Cox September 12, 1990
The FPE Group
3687 Mt. Diablo Blvd. Ste. 200
Lafayette, CA 94549
Dear Dr.~ox,
Enclosed is the information you requested, including a copy of a
document from the Planning and Management Division of the U.S.
Environmental Protection Agency entitled "A Perspective on the
Prevention, Prediction and Response Aspects of Major Chemical
Accidents", which references EPIcode and reproduces the EPIcode
algorithms in the appendix. This recently published document was
written by Norman A. Beddows, CIH, CSP, Regional Health and
Safety Manager, EPA Region 1. Additional copies of this document
are available upon request by contacting Norman Beddows at
(617) 565-3388, or writing to Region 1, J.F. Kennedy Federal
Building, Boston, Massachusetts 02203-2211.
If you require additional information, please give us a call.
Steven G. Homann, President
Certified Health Physicist
Homann Associates
39831 San Moreno Court
Fremont, CA 94539
(415) 490-6379 FAX (415) 967-4823
BHOPAh MIC 9 O, 000 lb in 90 rain, E Stab ]
h=40 rm u(2)=2 m/s, crrY Terrain
100
0.1 1 10
Downwind Centerline Distance (km)
Bhopal Gas Tragedy
MOLECULAR WEIGHT : 57.06 gram/mole
TERM RELEASE : 90,000 pounds in 90 minutes
SURFACE ROUGHNESS : CITY
STABILITY CLASS : E
EFFECTIVE RELEASE HEIGHT : 40 meters
WIND SPEED @ 10 meters : 3 meters/sec (= 2 m/s @ 2 m)
SAMPLE TIME : 10 minutes
The Rao model is a dispersion model which was found to be
qualitatively correlated to the human fatalities and
injuries, and the observed damage effects on trees and
vegetation in the affected areas surrounding Bhopal.
REFERENCE: Rao, K. Shankar, National Oceanic and Atmospheric
Administration Atmospheric Turbulence & Diffusion Division,
Oak Ridge, TN., Singh, M.P., Ghosh, S., Center for
Atmospheric Sciences Indian Institute of Technology, New
Delhi, India. "The Bhopal Gas Tragedy", Determination of
Atmospheric Dilution for Emergency Preparedness, A Joint
EPA-DOE Technical Workshop,pp. 17-24, Appendix A, pp. Al-A24,
October 15-17, 1986.
Scenario 1.: .Butane. 15 kg/s, F Stability
h=5 rn, u(h)=2 m/s, Ta=lO s, R=0.3 mi
1000000
00000
00O13
O.01 0.1 1 10
Downwind Centerline Distance (lan)
~MERICAN INSTITUTE OF CHEMICAL ENGINEERS - WORKBOOK TEST CASE
FOR A RELEASE OF NORNAL BUTANE
MOLECULAR WEIGHT : 58.12 gram/mole
RELEASE RATE : 15 kg/s (CONTINUOUS RELEASE)
SURFACE ROUGHNESS : 0.3 meters (CITY in EPIcode)
STABILITY CLASS : F
RELEASE HEIGHT : 5 meters
WIND SPEED @ RELEASE HEIGHT : 2 meters/sec (=1.2 m/s @ 2 m)
SAMPLE TIME : 0.167 minutes (10 seconds)
AMBIENT METEOROLOGY
TEMPERATURE : 30 degrees C
PRESSURE : 1.013 x 10A5 N/m^2
Relative Humidity : 50%
The standard Gaussian assumes sample averaging times of about
10 minutes. In this scenario, the instantaneous
concentrations are assumed to be given by a 10 second
sampling averaging time.
SLAB and DEGADIS are two dense gas models. The DEGADIS model
was developed by the U.S. Coast Guard (Havens and Spicer,
1985), and the SLAB model is similar in range of application
to the DEGADIS model (Ermak and Chan, 1985).
REFERENCE: Hanna, S., Strimaitis, D., Workbook of Test Cases
for Vapor Cloud Source Dispersion Models, Center
for Chemical Process Safety, American Institute
of Chemical Engineers. New York, 1989, pp 18-25.
Scenario 2: Ammonia 5.42 kg/s, F Stab
h=O m, u(h)=2 m/s, Ta=15 mm, R=0.3 tn
c 1
o
0.01 0.1 -' 1 10
Downwind ~nterline Distance (km)
~MER~CAN INSTITUTE OF CHEHIC~L ENGINEERS - WORKBOOK TEST C~SE
FOR ~ PRESSURIZED L~U~D .AI~ONI~ L~NE RUPTURE
MOLECULAR WEIGHT : 17.03 gram/mole
RELEASE RATE : 5.42 kg/s .(CONTINUOUS RELEASE)
SURFACE ROUGHNESS : 0.3 meters (CITY in EPIcode)
STABILITY CLASS : F
RELEASE HEIGHT : 0 meters
WIND SPEED @ RELEASE HEIGHT : 2 meters/second
SAMPLE TIME : 15 minutes ~
AMBIENT METEOROLOGY
TEMPERATURE : 25 degrees C
PRESSURE : 8.9 x 10~5 N/m^2
Relative Humidity : 80%
The standard Gaussian assumes sample averaging times of about
10 minutes. In this scenario, the concentrations are assumed
to be given by a 15 minute sample averaging time.
DEGADIS is a dense gas model, developed by the U.S. Coast
Guard (Havens and Spicer, 1985).
REFERENCE: Hanna, S., Strimaitis, D., Workbook of Test Cases
for Vapor Cloud Source Dispersion Models, Center
for Chemical Process Safety, American Institute
of Chemical Engineers. New York, 1989, pp 29-35.
Y4MERICAN
JOURNAL Septernbe,. 1989
INDUSTRIAL
HYGIENE'
ASSOCIATION
EPlcode [Emergency Prediction informa- Other information provided includes com- limit. For color monitors this is shown in
lion Codel, Version 3.3 Homann Associates, mon synonyms and the National Fire Pro- red. yellow, and white. For monochrome
Inc. 39831 San Moreno Ct.. Fremont, CA tection Association (NFPA} hazard class(fi- monitors this is shown as the values 1,2. and
94539. 1989. S495.00. cation rating for that selection. From this 3 within the plume graphic.
Reviewedb.c S.Z. Mansdo~L Ph.D., (_'IH: £'u3ahoga point, the user is prompted for the physical
The manual for the program is straight-
I-~lls. Ohio state of the substance (solid, liquid, gas,
EPIcode is an MS-DOS software program unknown). The next screen is one from forward, easily followed, 'and includes a
which provides plume and "puff"dispersion which the user selects the type of release of number of excellent examples (similar to
modeling. The developer states in the lntro- the substance. The choices are continuous or case studies) for using the model. The man-
duct(on to the user's guide that the" .. pro- term releases (plume versus pufl') on a point ual also includes three appendixes. One of
gram was developed to provide emergency source or area basis. Based on this response, the appendixes is a brief but valuable de-
response personnel and emergency planners other data input requests or menu options script(on of the algorithms used and the the-
with a software tool to help evaluate the appear. These specific branches of the pro- ory of Gauss(an dispersions. This would be
atmospheric release of toxic substances." gram are too numerous to list completely in especially useful for any users who are not
The program is provided on two standard this review. In summary, the remaining familiarwiththebasisfordispersionmodeling.
five-and-one-quarter-inch floppy disks (360K screens are queries as to the particulars of the Strengths of the program include the eas-
format) but can be transferred easily to other instantaneous or source release, ily followed manual, menu driven queries
media such asa three-and-one-half-inch floppy For stacks the user inputs the normal which make it very user friendly, and numer-
of 720 or 1.44 megabyte format since it is not Gauss(an dispersion information, such as ous input options which allow for the "what
copy protected, source rate, stack height, stack gas velocity if." Most experienced personal computer
The program works best on a hard drive and temperature, wind velocity, meteorolog-, users will find they can be up and running
system and with color or monochrome mon- (cai conditions, etc. For the puff model, 'within less than 20 minutes usmg the manual
itors, includinglaptops, it is very simple and input data includes the effective radius of the only for reference.
painless to install with an installation routine release, meteorological conditions, terrain, The weaknesses of the program are rain-
on the first "boot-up." etc. In both cases, unit selection is based on (mai. The values given for the concentrations
The program is entirely user friendly and what the user selects initially (metric or can beinengineering notation(e.g.. 1.0E-02).
is menu driven. This reviewer has installed American units), which may be difficult for some persons to
the program without difficulty on everything EPlcode has a number of unique options comprehend, although not for the majority
from a Tandy 1200 laptop with hard drive to which allow the user to evaluate both modeled of users. "Escaping" is not possible on every
an IBM PS2 Model 70. values based on actual field data and to con- screen (although it can be done from most).
sider the "what if." These options include a Inclusion of printer (especially laser printers}
The program initially starts with a user
worst-case selection option within the mete- and plotter drivers would greatly enhance
warning and copyright notice. The warning
orological stability choices, ~_~n ~9v~gr3~{-iS~n the graphics output capability o~' the pro-
is the typical disclaimer concerning the use of ';o~pti-on5} user variable off axis (x coordinate) gram. Finally, the output to disk cannot be
models l`or safety and health decisions, and receptor (z coordinate) heights, plume recalled by the program. Hopefully, these en-
The program starts with the selection of rise values, and other options, hancements will bentxlded in future upgrades.
the emission. Thc menu choices are chemical The output options are to the screen, print- In conclusion, I would recommend this
name, chemical abstract number (with or er, disk file (for use in a spreadsheet), and to program highly to industrial hygienists, emer-
without dashes), Department of Transporta- a screen or printer plot. These options can be gency responders, emergency management
tion (DOT) hazard guide number, or a utilized with default or user-provided down- planners, air pollution engineers, and others
"browse" function which allows the user to wind (x coordinate) and crosswind (y cool involved with the estimation or modeling of
go through the chemical library of over 600 dina~e) distances. The plot options can be chemical dispersions in air. It should be
substances or develop his or her own per- prin~ed utilizing "print screen" from the PC especially valuable for developing spill con-
sonal library of substances. Once the chemi- keyboard, tingency plans. It is one of the few modeling
cai being emitted is selected, the user is pro- .The plots include both concentration vet- programs available which offers a fairly high
vided with a screen displaying information sus downwind distance (x coordinate) and a level of sophistication and options while
about the substance. This includes such data plume contour (y coordinate) versus down- remaining entirely user friendly.
as molecular weight, the time-weighted aver- wind distance. The plume contbur is a bird's
age (TWA)limit, short-term exposure limit eye v ew show(riga two-dimensional x and y S ft R i
(STEL). immediately dangerous to life or plot on the screen. In, both cases the plots O w~.r~ ~Y ~w$
health (IDLH) values and DOT number, show the concentration in the dispersion as Z~lgk Mansdorf, Ph.D., CIH
The exposure limit values {given in both ppm greater than IDLH (or I0 times the TWA Department Editor
and mg/ma units} appear to be from the limit if no IDLH value}, greater than the
NlOSH Pocket Guide to ChemicaI Hazards. TWA limit, and less than 0. l times the TWA
Emergency Prediction Information
Norman A. Beddows, CIH, CSP
Regional Health and Safety Manager and Industrial Hygienist
United States Environmental Protection Agency
Region 1, ~ohn F. Kennedy Federal Building, Room 2211
Boston, MA 02203
Presented at the Joint Regional U. S. Department of Labor, Occupational
Safety and Health Administration, and U.S. Environmental Protection
Agency Seminar, "OccuPational and Public Health and Safety," June 27, 1989.
Imagine that you are an emergency coordinator in a large city. On a hot,
calm summer day you receive a call about a semi truck that has crashed
through a side wall of an overpass downtown. The back of the truck is
hanging over the overpass. It is carrying three 250-gallon tanks of chlorine.
· You have just called for an evacuation. What area will you evacuate?
The quality of your decision in coordinating or planning for an
emergency involving a release or threat of release of an extremely hazardous
substance depends in large part 'on the emergency prediction information that
is immediately available.
This presentation provides a background to understanding how such
information is structured, and how commercially available PC-software
systems can be used in the decision-making process. This process involves
the planning and risk management associated with a release of an'·axtremely
hazardous 'substance. Solving the chlorine-release question mentioned above
will illustrate a typical process.
"Background Information
Developing information on an emergency involving a chemical release
is no longer the pursuit of a few public safety officers and first-responders to
accidents. It is now a vital part of planning for handling emergencies, and it
is a practical necessity for some people in state and local government and the
chemical industry, under the Emergency Planning and Community Right-to-
Know Act of 1986: SARA, Title III.
-1-
Members of community planning committees, including industry
representatives and plant safety and health specialists, need to have access--
sometimes immediate access--to information on extremely hazardous
chemicals so that they can assess risks in accidents and release scenarios.
Being able to provide predictive information within a few minutes on
demand is essential to establishing a high-quality emergency response plan.
This is a skill that safety specialists, industrial hygienists, and emergency
coordinators will find invaluable.
Risk Analysis and Priority Sett-ing
In considering risks with the many hundreds of toxic chemicals in
common use, the myriad of uses, and the storage and transportation of such
chemicals, one soon realizes the necessity of setting priorities in establishing
emergency prediction information.
Setting priorities is done by assessing risks in terms of (a) the likelihood
of a release of a toxic substance occurring in a particular situation, and (b) the
severity of the adverse effects of acute exposure of people from the release.
Each of these two elements of risk assessment can be grouped into "high",
"medium", and "low" classes. Certain combinations of these two-groupings
are viewed as "situations of major concern." For example a combination of
(a) medium likelihood and (b) medium severity (of acute exposure) is a major
concern. Situations of major concern and plausible worst-case scenarios are
always first to be evaluated in planning for emergencies following a risk-
based scheme. In planning, one must be primarily concerned with the
severity of effects from acute (one hour or less) exposures. This includes all
life-threatening and serious health risks, including explosion and impair-
ment of function. Likely mild, transient, reversible effects are not critical in
developing emergency prediction information. However, such effec~t_$ from a
release can be major public nuisances and issues. For example, if the concen-
tration exceeds the odor threshold, the public could perceive the hazard as
very high, especially if the odor is foul.
Classification of Substances
Issues that arise in planning for emergencies are: What is an extremely
hazardous substance? And with such substances, what concentrations in air
constitute imminently dangerous to life or health (IDLH) exposures?
Guidance on these two matters is provided by regulatory authorities and
standards-setting institutions.1
-2-
The U.S. Environmental Protection Agency has published a list of
extremely hazardous substances (and their corresponding threshold planning
quantities) in Appendices A and B of Part 355 ("Emergency Planning and
Notification") of the 1986 Superfund Amendments and Reauthorization
ActmSAKA. An unlisted, extremely hazardous substance may be considered
to be one which, when tested on animals, exhibits certain acute toxicity
characteristics2 expressed in toxicological terms: inhalational, dermal, or oral
median lethal doses or concentration--LCs0. Figure 1 shows criteria for
classifying a substance as "extremely hazardous" (EHS).
Median Lethal Concentration in Air (LCso)--Inhalation
Less than or equal to 0.5 milligrams per liter of air for exposure time of an hour
or less.
Median Lethal Dose (LD50)--Dermal
Less than or equal to 50 milligrams per kilogram of body weight.
Median Lethal Dose (LD5o)--Oral
Less than or equal to 25 milligrams per kilogram of body weight.
Figure 1. EHS classification system.
Level of Concern--LOC
Identifying some situations as major concerns requires professional
judgement. It involves deciding upon a "level of concern" for a particular
substance in a given situation. Judgement is also needed during an ongoing
emergency to make sure that. no serious, irreversible effects arise from any
short-term exposure of the first-responders.
One basis for establishing a level of concern is to use a fractional level of
the relevant IDLH concentration. Frequently, one tenth of the IDLH is used.
At this level and above, an emergency coordinator may require evacuation of
-3-
any populated area that may potentially be affected by the release. This area is
usually called the "vulnerable zone." In some instances, IDLH values are not
reported or known. Usually, however, threshold level values (TLVs)--short-
term exposures, and eight-hour weighted average exposures, or toxicological
data, such as the lethal concentration-lowest response value, LClow, for
animal tests, are known. Data for these types of information can be used--
with professional judgement--to establish appropriate levels of concern for
extremely toxic substances. As an example, a tenfold TLV level might be used
in a particular case as the level of concern, absent IDLH data (but only with
professional judgement). It is noted that TLVs (a trademark of the American
Conference of Governmental IndUstrial Hygienists--ACGIH) are intended for
use only in the practice of industrial hygiene. Their use as described above is
neither recommended nor opposed by the ACGIH at this time. The
constraints that apply to a TLV must be known before use.
Another type of level of concern, associated only with a release of
flammable gas or vapor, is a fractional value of the lower explosive limit
(LEL). Frequently, one tenth of the LEL is used as the limit at or above which
a level of concern exists. In spills of gases or volatile organic compounds, a
potential exists for the gas or vapor to ignite and form a fireball or explosion~
However, for any flammable, extremely hazardous substance, the lower
explosive limit is about two orders of magnitude greater than the
corresponding IDLH level. A leak of an explosive gas or vapor is a matter
that must be regarded as posing a serious risk to public safety. On this point,
any visible cloud should be regarded initially as posing an IDLFI risk.
Severity of Concern
Only when there is virtually no exposure (when concentrations are
hazardous) may one regard a release or threat of release as a low concern.
Whenever any public exposure exists to a release of a substance th_at is, or
reasonably could be, present at a concentration that causes concern, then this
concern is severe. Plans to isolate the public from the risk must be made in
these situations. Also, special plans will need to be developed, and
evacuation arrangements made, when nurseries and homes for the aged exist
in a vulnerable zone.
Downwind Movement of a Release
A plume---developed from the release of a toxic gas, vapor, or fine
particulate in airmmoves in the same direction as the incident wind ar~cl, in
doing so, tends to become larger and less concentrated as it moves. The
degree of dilution that occurs depends partly on atmospheric factors and
-4-
terrain. Turbulence and air entrainment affect plume size, shape, and
concentrations. Concentrations within the plume are also affected by
deposition rate3 and physical factors.
Establishing a "Vulnerable Zone"
A host of factors--many of which are interrelated---influence the size of
a vulnerable zone. These factors include: the type of release (whether the
release is a term release or a continuous one, or a small source release or a
release involving a diffuse area); the effective height of the release and the
plume rise associated with the release; meteorologic conditions; the type of
terrain (city terrain or open terrain); the atmospheric stability; and the
physical and chemical properties of the substance that is released.
The radius of an initial zone will be reduced by (a) a smaller amount and
a smaller rate of release; (b) greater wind speeds and less atmospheric stability;
and (c) selecting a higher value for the level of concern, e.g., setting .the level
at one fifth the IDLH level.4
Classification of Releases
For the purpose of emergency prediction, releases can be classified con-
veniently in four general classes:
· Continuous Release--a prolonged, small-area release, e.g., emis-
sions of sulfur dioxide from a chemical process stack.
· Term Release--the type of release described in the accident
mentioned at the beginning of this paper. When the duration of release is
less than about one tenth of a minute, the release is considere'cl-to be a
spontaneous release, or "puff."
· Area Term Release--The type of release one encounters in the
relatively fast evaporation of a spilled pool of liquid. To characterize an Area
Term release one needs to know the area size and the approximate duration
of the release (one assumes that all or some fraction of the release evaporates
over a limited time).
· Area Continuous Release--A release associated with a continuous
evaporation process, e.g., a waste pond release.
In addition to classifying the release for use in predicting emergency
information, one needs to characterize it in terms of the quantities and
-5-
durations involved, as well as the effective release height. (Ground-level
releases may actually have significant effective release heights, which can
materially alter ground concentrations at downwind and crosswind points.)
In cases of releases from stacks or reactor vessels, the effective height
may be the stack or vessel height, or greater, depending on the momentum
and buoyancy of the particular effluent. These releases can result in a major
increase in the effective release height and a corresponding significant
decrease in ground-level concentrations'~at downwind and crosswind points,
other factors being equal. Elevated releases tend to result in maximum
concentrations at ground level at a point downwind from the release point.
However, this concentration decrease diminishes over distance.
Environmental Factors
The concentrations at ground level from a plume depend on the
physical properties and reactivity of the chemical itself, the type of release, the
duration of release, the effective height of the release, and environmental
factors such as terrain and meteorological conditions.
In large urban areas, increased dispersion of a release occurs, relative to
open terrain, because of the thermals that arise from the heatzretaining
concrete and asphalt, and because of turbulence from buildings. In general,
the open or standard terrain scenario will yield the more conservative
estimate of ground-level concentrations, and this should be used in making
estimates if there is any doubt about the type of terrain.
Meteorological conditionsmthe height of the sun in the sky (the degree
of insolation); the degree of cloudiness, daytime and nighttime; and wind
speed--all affect the atmospheric stability and concentrations. Classes of
meteorological stability have been established in terms of stable, neutral, and
unstable atmosphere. This is useful for the purpose of evaluating'potential
distributions and exposures. It should-be mentioned that even in seemingly
calm conditions, some surface and elevation winds exist. These are sufficient
to cause some drifting of any plume. Also, the worst situation does not
automatically arise from one set of conditions or stability. Evaluations using
appropriate models must be made to determine the "worst case."
Meteorological conditions are classified according to a variety of
schemes; one popular and simple scheme, Which is especially useful for pre-
dicting emergency information, is the Pasquill-type classification. Classes of
stability--which are often factored into models that are appropriate for eval-
uating releases according to type are defined in terms of sun (insolation);
time (daytime, nighttime); cloud conditions; and surface wind speed. In this
scheme, letters are used to classify conditions. Thus, A = extremely unstable
and F = moderately stable. Either a Pasquill class or stability data will be
needed as input to the program.
Figure 2 shows the Pasquill classes of atmospheric stability.
Daytime sunlight
Wind speed Night or thin
(m/s) Strong Moderate Slight . overcast < 3/8 cloud
<2 A A~B B
2-3 A-B B C E F
3-4 B B-C C D E
4-6 C C-D D D D
>6 C D D D D
A: Extremely unstable D: Neutral
B: Moderately unstable E: Slightly stable
C: Slightly unstable F: Moderately stable
Figure 2. Pasquill classes of atmospheric stability.
Models and Software
Several commercial PC-software products are available for providing
emergency-response personnel, emergency planners, and health and safety
professionals with a fast assessment of the concentrations in air resulting
from releases of toxic substances. Such software packages are capable of
providing first-order, on-the-spot determinations of the concentrations
expected from the atmospheric release. Mostly, they are based on t.h.~ widely
used Gaussian Plume Model,5 which reportedly produces results in good
agreement with experimental data.6
A system of defining coordinates, which places the source of origin at a
point beneath the release site, is used as the basis for modeling releases.
Figure 3 illustrates this coordinate system.
Atmospheric concentrations (C)--expressed in parts per million or
milligrams per cubic meter can be estimated using basic equations included
in the Gaussian model. This model was developed in the early 1930s and was
subsequently enlarged upon in the last twenty years or so by various workers
for the purpose of determining gas or vapor concentrations of aerosols
(suspensions of particles less than about ten microns in aerodynamic
diameter).
-7-
ir/ e~c.(x'y) x
axis
Figure 3. System coordinates.
Without describing the equations used for either a "puff" phase or a
continuous phase in relevant Gaussian models, it is noted that atmospheric
concentration depends on: the rate of release; the effective height of the
release; the coordinates involved (downwind distance, crosswind distance,
and vertical axis distance); the average wind speed at the effective release
height; the height of any inversion layer that is present; and the standard
deviations of the concentration distributions in the coordinate directions
involved.
The available software products for use in predicting emerge~-cy infor-
mation are compatible with most of the commonly available PC hardware.
These products employ programs that characterize releases, calculate release
heights, and use classes of meteorological conditions and terrain in a way that
is very similar to one another. What separates software--in terms of
usefulness for predicting emergency information--is the straightforwardness
of the codes used and the rapidity of generating estimates. How well the
software is developed to ensure that is it easy to use, reliable for on-the-spot
application, and how well it graphically provides the needed information are
important criteria for selecting software. Emergency response personnel and
emergency planners need to be able to quickly evaluate atmospheric releases
of toxic substances. The preceding criteria (together with appropriate
application of factor-weights) should be employed before any software is
purchased.
-8-
Every relevant program in one way or another will prompt the user to
provide input. This input will identify the substance, classify the type of
release, provide release-rate and/or release-duration information, provide an
estimate of the effective release height, and classify the meteorological
conditions, atmospheric stability, and terrain. Other prompts will follow for
output options. Figure 4 shows some of the basic inputs and steps.
Rate Duration Radius of Release Rad us ol Release
I I 1
[ Enter Total Quan,~y Enter Release or I I Enter Release I
of Material Released Evaporation rate Duration
I
I Enter Tolal Quantily I Enter Total Quant~y
of Material Released I of Malerat Released
ENTER EFFECTIVE I
RELEASE HEIGHT
I
Figure 4. Some key inputs for emergency prediction software.
-9-
A good program will make such input activities easy, and will provide a
rapid first-order check of the situation against complex, more extensive
(mainframe) models. Also, it will yield a reasonable level of accuracy for
making a timely initial assessment, and it will include an extensive and
enlargeable library of chemical substances. This library will contain current
exposure limits and other data that are acceptable to industrial hygienists and
public-safety specialists. The "graphics" part of the program will be com-
patible with color and monochrome monitors, and it will not require addi-
tional "special" graphics hardware, etcetera. The graphics package should
provide plots of plume contours in terms of (a) an IDLH contour and other
exposure limit criteria, (b) a target value contour (e.g., odor threshold, etc.),
and (c) concentration versus distance, expressed in units of parts per million
or milligrams per cubic meter of airborne substance. This provision may be
done with "autoscaling" (which fully displays the entire plume), or with
"zooming" to achieve a desired resolution.
Worked Example: The Chlorine Release Case
Perhaps the best way of showing the processes involved in emergency
prediction information is to address the question we started with--the case of
the potential release of chlorine.
Typically, we would run the required MS-DOS operating system, and
follow by loading the program in the A drive and the "library" in the B drive.
Alternatively, we could load both the program and the library on a hard disk.
This done, we would proceed to respond to the prompts as they occur. In the
example at hand, we woutd assume the worst--that the release will occur and
become life-threatening. Some of the principle inputs to prompts are
illustrated below.
1. Enter "CHLORINE," "CL," or "CL2" at the main men~ for the
substance. (Immediately, key properties and toxicological data for chlorine
will be displayed.)
2. Enter, say, "15 minutes" for your estimate of the duration of the
release.
3. Enter "250 gallons" for the quantity.
4. Enter "0" for the release height--it is a ground-level spill.
5. Enter "CITY" for the terrain factor.
-10-
6. Enter "sun high" in response to the prompt for meteorological
conditions (alternatively, use a Pasquill stability term).
7. Enter "1 mph" for wind speed (it is a calm day).
After completing this characterization of the release, proceed to define
the output options that you require, following the relevant prompts. This
latter step deals with what you want to see on the screen and what you want
to print. Under "output," in this case, you may want to obtain graphical
representations of the chlorine IDLH (25 parts per million) contours and
concentration versus distance, expressed in parts per million. Very likely,
you will also want a contour of some target value of concentration that you
will use to define the size of the vulnerable zone or to determine the odor
boundary. In this regard, perhaps you have made the judgement to use 5
ppm (one fifth of the chlorine IDLH value) on which to set a radius of
evacuation. Depending on the value of the level of concern you employ,
evacuation of a zone of about one-half mile in radius evidently will be
needed in this particular case, assuming dispersion will be uniformly radial.
Alternatively, a downwind and crosswind setting may be used as the
boundary for the vulnerable zone.
Another output of vital importance will deal with the time it takes for a
plume with potentially lethal concentrations of substance to be radially
transported, and how long such a plume will remain present in any
vulnerable zone under the stated prevailing circumstances.
Concluding Remarks
The preceding background material and example illustrate how the
widely accepted "workhorse" Gaussian Plume Model and programs based on
such a model can be rapidly used to establish emergency prediction
information. This capability is invaluable in resolving and planning for
emergencies. With a good program one can quickly evaluate an atmospheric
release of a toxic substance in either actual conditions or in "what if?" type
scenarios considered as part of chemical emergency preparedness planning.
Before closing, we should answer the inevitable question: how realistic is
such modeling compared to actual data obtained in tests of releases?
Comparative data are not plentiful. However, a sufficient number of tests
have been conducted by government agencies and private organizations to
support the contention that there is generally good agreement between actual
and predicted data. Agreement is, reportedly, well within an order of
magnitude, by about 3x to 5x, according to some suppliers of modeling
software. Reportedly, agreement is optimal when the region of concern is (a)
-11-
not in the very immediate zone of the release (i.e., within 250 feet), and (b)
not in complex terrain.
Certainly, using emergency prediction information software products
can provide release data that are sufficiently accurate to evaluate the impact of
a release in reasonably complex situations. Makers of such products have
reported that agreement within a factor of about three can be reasonably
expected in many cases. They can provide information on the performance
and reliability of their products. In some instances, specific performance and
comparative test data are available.
Figure 5 shows comparative data reported by one maker--Homann
Associates, for its trademarked product, EPIcode.7
U.S. Department of Energy
1986 Test
I Total liquid
HF release (gal) 980
· EPI code
o Actual data
Spill duration
(rain) 2.1
-
Wind speed
2-m height
(m/s) 5.6
Stability
classification D
Release
height (m) 0
10 :~ 10 Terrain ~ Standard
0istance (m)
Figure 5. Comparative data from emergency prediction software and
actual test results.
In Figures 6, 7, and 8, respectively, we see downwind location concen-
trations, downwind and crosswind concentrations, and downwind maximum
concentration arrival times for the case in point, using the characteristic form
of output provided by the EPIcode® software. The information provided is
fairly typical of the outputs that may be obtained using any of the superior
software products.
-12-
CHLORINE Stability: A
1000 --
TERM : 2.5E+02 gallons
Release Duration : 1.LE+O1 MiL
100 '111 SURFACE WIND SPEED : 1.0 Miles/hour
11111 DEPOSITION VELOCITY: 0. 100 cz/second
HEIGHT-EFFECTIVE : 0 Feet
11111111
1111111112 STABILITY CLASS : A
10 -1111111112222 TERRAIN : CITY
11111111122222 RECZPTOR HEIGHT : 0 Feet
PPM 1111111112222222
111111111222222222.,
1 -11111111122222222223 --
11111111122222222223
I/1~11 II ~x~
1.0~.-01 I1-111~ II< o.o6 ,~i 33 -
111111 ii> 4.6E+02 PPM 333
I~1111 ,' 33333
1.0E-02 I/1111111112222222222333333333333' ' ' ' ' ' '
· 1 .3 .6 1 3 6 10 30 60 100
DOWNWIND DISTANCE - Miles
3 : Less than TWA 2 : Greater than TWA 1 : Greater than IDLH
Figure 6. Downwind location concentrations·
CHLORINE Stability: A
R 3600 -- I I --
O 3200 -- --
S 2800 --
TERM : 2.5E+02 gallons
S 2400 -- 3333 Release Duration : 1.SE+01 MiL
W 2000 3333333333 SURFACE WIND SPEED : 1.0 Miles/hour
I 1600 -- 33333333333333 DEPOSITION VE~CITY: 0.100 cz/second
N 1200 -- 333322222223333333 HEIGHT-EFFE~IVE : 0 Feet
D 800 -- 3332222222222222333333 STABILITY CLASS : a
400 '2222222222222222223333333 TERRAIN : CITY
Feet 0.0 1111111122222222223333333 RECE~OR HEIGHT : 0 Feet
-400 ~2222222222222222223333333
D -800 -- 3332222222222222333333 --
I -1200 -- 333322222223333333 --
S -1600 -- 33333333333333 --
T -2000 3333333333
A -2400 -- 3333 --
N -2800 --
C -3200 --
.1 .3 .6 1 3 6 10 30 60 100
IDLH: 2.5E+01 ppm DOWNWIND DISTANCE - Miles
3 : Greater than 0.1 TWA 2 : Greater than TWA 1 : Greater than IDLH
Figure 7. Downwind and crosswind concentrations.
-13-
TERM : 2.5E+02 gallons
Release Duration : 1.5E+01 Min
SURFACE WIND SPEED : 1.0 Miles/hour
DEPOSITION VELOCITY: 0.100 cm/second
HEIGHT-EFFECTIVE : 0 Feet
STABILITY CLASS : A
TERRAIN : CITY
RECEPTOR HEIGHT : 0 Feet
DOWNWIND CONCENTRATION ARRIVAL TIME
Distance-Mi ppm hours:minutes
0.10 170 : 6
0.20 42 :12
0.30 18 :18
0.40 10 :24
0.50 5.9 :30
0.60 3.7 :36
0.70 2.3 :42
0.80 1.5 :48
0.90 0.93 :54
1.00 0.56 1:0
2.00 0.077 2: 0
4.00 0.011 4:0
6.00 0.0038 6:0
8.00 0.0018 8:0
10.0 0.0010 10:0
Figure 8. Downwind maximum concentration arrival times.
This paper has intentionally dealt with imminent major risks to people
exclusively. Releases may pose environmental risks. Nothing herein
diminishes the need to safeguard the environment and comply with all
relevant regulations and standards.
-14-
End Notes
1. IDLH is not consistently defined in the regulations of the various
agencies. Herein, it means a situation that will cause serious harm within a
matter of a few minutes of continuing exposure.
2. LC50 and similar bio-terms are not constants. The test and conditions
involved can cause an order-of-magnitude difference in values.
3. Deposition rate depends on aerodynamic diameter. For default, use 0.1
cm/s for gases, 1 cm/s for solids less than 10 micron a.dia.
4. The selection of the divisor is arbitrary; 1/10 is common. Selection is
influenced by the anticipated degree of agreement of actual-to-predicted
values of concentration.
5. The Gaussian Plume Model is described in EPA Guide, OAQPS
Guideline on Air-Quality Models, EPA Report 45012-78-027 (1978).
6. H.C. Goldwire, et al., Lawrence Livermore National Laboratory Report
UCID-20562, Lawrence Livermore National Laboratory, Livermore, CA (1985).
7. EPIcode® is a software product of Homann Associates, Inc., 39831 San
Moreno Ct., Fremont, CA 94539; (415) 490-6379, FAX (415) 967-4823.
-15-
q( ,,,~.c, J.F. KENNEDY FEDERAL BUILDING, SOSTON, MAlBACHUB~
AN OUTREACH PROGRAM of the
PLANNING AND MANAGEMENT DIVISION of the
U.S. ENVIRONMENTAL PROTECTION AGENCY, REGION 1.
A Perspective on the
Prevention, Prediction and Response
Aspects of Major Chemical Accidents
J~n~l' 7, 1990
This document provides basic inform°-tion for use by the
p.blic, emergency planners, fire chiefs, plant managers and
process operators, and state and local government
~employees. Additional copies, and a companion four-hour,
audio-visual module for presentation to interested public
groups are available from Region I on request.
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION I
J.F. KENNEDY FEDERAL BUILDING, BOSTON, MASSACHUSETTS 02203-2211
January 7, 1990
Dear Reader:
Attached is a guidance document on the three key points of major chemical
accident concerns - Prevention, Prediction, and Response.
The information which is presented is believed by the w_~_thor to be consistent
with the teachings of the agencies and organizations which have jurisdiction or
special competency in the subject area. It is intended to be of help to people irt
enhancing public safety. However, it is not presented as a statement of
~ndatory safety engineering. And no assurance is made that a particular
action or control, if implemented, will prevent a future chemical accident.
The U.S. Environmental Protection Agency, and the U.S. department of Labor -
OSHA have primary jurisdiction respectively for community and occupational
safety. The U.S. Coast Guard has jurisdiction in matters involving navigable
waters. And, it provides support services to federal, state and local authorities.
If you have questions, members of these agencies will be pleased to be of service
to you. Key EPA and OSHA personnel in Region I (New England States) whom
you can contact directly for particular information are:
The U.S. Environmental Protection Agency (EPA}
SARA Title 111: Repo.rtinq, Inventories, and Technical Pro~ram Information -
Thomas D' Avanzo (61 7) 565-4502
Chemical Safet~l A~_~ditinq - Ray Dinardo (617) 860-4385 -.~-~
The U.S.D.O.L- OSHA
Technical and Compliance - Oco_~pational Health and Safer!i_ Standards -
Dr. Ronald Ratney (617) 565-7164. Fred Mallaby, CIH (617) 565-7164
The U.S. Coast Guard Strike Team, Atlantic Area, COmmanding Officer:
LCDR. G. A. Wiltshire has a 24-hour emergency service: (205) 694-6601.
If you need additional information, or have questions about this document, please
contact Norman Beddows, Regional Industrial Hygienist and Safety Manager,
EPA-Region I, Planning and Management Division (617) 565-3388.
i
ACKNOWLEDG~NT
Some of the presented information is drawn from The 1987 Proceedings of the International
Symposium on Preventing Major Chemical Accidents (Editor, J.L. Woodward). This symposium
was Jointly sponsored by the American Institute of Chemical Engineers, The U.S. Environmental
Protection Agency, The World Bank, and The Center for Chemical Process Safety. Other
information is drawn from publications and guidance documents issued by the National
Response Team (Chairman: J.L. Makris, U.S. EPA, Washington, D.C. (202) 475-8600)
The permission of the American Institute Of Chemical Engineers to use information and
physical data relating to preventing major chemical accidents, obtained from the referenced
1987 proceedings, is acknowledged with gratitude.
I am indebted to Mr. Steven Homann. Homann Associates, Fremont, California for his critique
of the parts on industrial hygiene, and area exposure modeling using the Gaussian model
EPICODE - which is used herein to illustrate the principles of vapor dispersion modeling.
Reference to this user-friendly product, however, is not an official Agency endorsement.
I gratefully acknowledge the review and comments on the chemical safety engineering and
methodology parts, by Mr. William Early, .Corporate Safety Manager, Chemical Engineering
Division, Stone and Webster Company, Houston, Texas.
The perspective which is presented is believed to be consistent with the teachings of the
relevant regulatory authorities. However, in the final analysis, it is a personal one. It does not
necessarily reflect the views or rules of any of the organizations mentioned.
Norm Beddows
- A Perspective on the
Prevention, Prediction and Response
Aspects of Major Chemical Accidents
Norman A. Beddows CIH, CSP.
Abstract
This document is presented in support of an outreach program of the U.S. Environmental
Protection Agency, Region 1, under the 1986 Right To Know Act (EPRA).
It provides basic information for use by local emergency planners, fire chiefs, chemical plant
managers and personnel, chemical safety auditors, state and local government employees and
the public. This information will serve as a basis for discussion between the public and
chemical facility managers to promote harmony in potentially contentious, situations. And, it
will serve as a basis for developing protocols for chemical safety auditing of many of the
operations which comprise the highly variable chemical industry.
A background is provided tn standards, regulations, motivation and policies. This complements
information provided by the federal National Response Team, chaired by the U.S. Envtt~ental
Protection Agency. Chemical hazards are discussed. Aspects of prevention, prediction and
response for major chemical accidents are presented.
For prevention: hazard analysis techniques are described, and matters of experience and
guidance are discussed, especially in context with information provided in the 1989 U.S.
Environmental Protection Agency's publication "CHEMICAL ACCIDENT PREVENTION
BULLETIN." Also, certain engineering and administrative controls for safety are identified and
described. /
For prediction: hazard identification is described, and an explanation is given of how potential
exposures and health and safety risks can be evaluated. Also, explanations and examples of
the use of computer software for developing emergency prediction information are provided.
For emergency response: acute exposure risks are identified. Means of personal protection are
discussed. Also, certain suppression and containment techniques are explained.
INTRODUCTION
Concern over the safety of manufacturing, transporting and using extremely
hazardous chemicals is worldwide. Bhopal~, Seveso2, the Rhine River Spill3, and
other environmental catastrophes have made this so. Nationally, there is an
increased awareness and concern. A great many people in the United States
think that a major chemical accident will happen domestically in the next fifty
years4. At the local level, many communities in which explosive or toxic
chemicals are made or handled are fearful. Large residential areas and
institutions have been established in some communities around chemical plants
and tanks, which preceded them.
The U.S. Environmental Protection Agency (EPA} has been one of the principle
agencies to date in developing policies and programs for preventing and
mitigating major chemical accidents (involving either (l) extremely hazardous
substances or (ii) hazardous sustances, as defined at Parts 101 (14) and 355
of Title 40, and section 1910.1200(c) of Title 29, of the Code of Federal
Regulations). Other agencies who have primary responsibilities are the
Department of Transportation, the Department of Labor - OSHA, and the U.S.
Coastguard. In 1985, the U.S. Environmental Protection Agency introduced
comprehensive accident prevention and emergency preparedness programs for
use in the private and public sectors to protect the public. And the Superfund
Amendment Reauthorization Act (SARA) of 1986 provided for community
involvement in accident prevention, and prescribed programs for emergency
planning and notification. The relevant SARA programs are rather technical.
However. dialogue between all the parties which EPA and OSHA promotes will
off-set this.
The American Institute of Chemical Engineers, the Center for Chemical Process
Safety, The World Bank, the chemical industry itself, and numerous technical
.societies5 also support the private and public sectors in their efforts for
chemical safety. Even so, some of the public believe that not enough is being
done to protect them against potentially catastrophic effects from major
chemical accidents. Evidently some of the public believe that some involuntary
risks are substantially greater than levels reported by the governments' or the
industrys' experts. Most peoPle understand that there are inherent hazards in
producing, using or transporting chemicals. Most people agree that the public's
safety must be fully maintained.. Few would agree, however, on a level of
balance needed to achieve both optimal safety and economic viability in a
chemical industry. Also, some people want the government to regulate the
design and operation of chemical plants, in the same way that the' Nuclear
Regulatory Commission regulates design, construction, quality assurance and
operation in the nuclear power generation industry~. The chemical industries
resist this viewpoint. The U.S. Environmental Protection Agency evidently is
not intent on regulating the design or operation of chemical plants and
processes7. Rather, it seeks to have industries comply voluntarily with the
highest standards for safety.
Federal and state agencies promote the use of the best practical technology,
compliance with stringent standards and recommendations8, and mutual
cooperation of plant managers, emergency planners and the public. They
ensure that local officials, fire fighters, and citizens have access to detailed
information on chemical hazards. They have provided the risk-bearers and the
local officials, a real role in emergency prevention. Specifically, the U.S.
Environmental Protection Agency requires facilities to undertake emergency
planning, and be involved with state and local officials in emergency planning
when an extremely hazardous substance equal to or in excess of its
threshold planning q~Rntity is present [40 CFR 355.30(a)]. The agency itself
has broad police powers aimed at preventing and mitigating accidents.
The U.S. DOL OSHA exerts an influence on chemical plant design and
operation by enforcing specific standards and regulations, and, in the £mal
analysis, by requiring the employer to provide work and workplaces for the
employees which are free of recognizable hazards.
Complete regulation of the design of chemical processes would be very difficult.
The industry is highly diversified in the chemicals which it uses and
manufactures, and in the kinds of processes and equipment which It employs.
No one set of safety criteria applies to even a single operation, and no sets of
criteria apply as a basis for identifying all of the chemicals and processes which
could be of concem. There are literally hundreds of relevant, mostly
specification-oriented safety standards, codes and guidelines for the industry.
4
Performance-oriented standards also exist. The latter type has special value
for highly variable process operations. Several national technical societies
provide research support for safety. Some st_~ndards and groups are shown in
Table 1.
STANDARDS. CODES, GtrlDELINF~ & ORaANIZATIONS ·
National Fire Protection Association (NFPA)
NFPA 30 - Flammable & Combustible Liquids
NFPA 58/59/59A - Liquid petroleum: new designs
American Petroleum Institute (APl)
APl 650 - tanks welded steel
APl 520/521 - design, construction, Systems
APl 526 - flanges, safety/relief valves
APl Guidelines publication # 7580: Lessons learnt
APl Recommended Practice # 1112: DOT response; emergencies.
APl 2000 - venting low pressure storage tanks
American National Standards Institute (ANSI)
ANSI-B 31.3 - piping, chemical plant
ANSI.B 16.9 - overpressure design/piping
American Society Mechanical Engineers - Guidelines and Standards
American Institute of Chemical Engineers - Guidelines and Standards.
The Occupational Safety and Health Administration (OSHA) - The General Duty
Clause: employers to provide safe workplaces, at 29 CFR. 1910.5(a)(1).
The Emergency response rule, at 29 CFR Part 1910.120.
Table 1. Some Stsnd~.rds, Codes, Guidelines And Org~tions
Motivation and Policies
Most managers in the domestic chemical industries are very committed to
providing the highest achievable level of safety. They are morally motivated.
The industries themselves are strongly motivated to provide maximal safety.
They are so persuaded by the potential for crtmtr~! citation, the possible
lmpostUon of J~tl sentences on executives, and the great financial liability which
5
exists with a major chemical accident. However. to some extent, some plants
are de-motivated-by the low economic viability of some processes, and by
frequent turn-over in executive management. In some plants, an emphasis on
minimizing costs of investment and operations without due regard to the
required level of engineered safety is evident.
Optimal safety in the chemical process industry may not be achieved through
regulation alone. The highest level of chemical safety is likely to be attained
only by industry, government and the public working openly together. Much
can be achieved. Government could provide consultative services to the
industry. Chemical safety audits, separate from enforcement actions, could be
offered without plant managers fearing a threat of a first-instance sanction.
The public could become more informed on chemical safety matters and more
generally re~lJ?e that great economic loss can arise by unwarranted pressure
on chemical manufacturers, users or transporters. The industries might more
openly advocate their programs for public safety, and ensure that their
management systems are appropriate. Companies must make sure that efforts
to minimize costs of investment and operations are not translated into
implementing only minimal safety programs. Requiring only minimal
safeguards, and minimal investment in equipment, real estate, and labor.
without regard to the potential for a catastrophic accident, because a process
or plant is mature or has a poor profitability, is quite unacceptable. The total
resources of a company - not merely the short-term cash flow picture of a profit
and loss center - must be available when first needed to achieve safety.
The managers of chemical industry and the heads of the agencies which are
primarily involved should ensure that their senior staffs include experts in plant
layout for safety; process and unit operations safety; and safety engineering.
And, persons will be needed who will deal authentically with the concerns of,
the public.
Chemical Hazards
Airborne concentration and exposure duration are the key factors of potential
acute health hazard with most chemical exposures. The most common concern
of route of exposure is inhalation. Dermal exposure is another important
concern - about a quarter of the known extremely hazardous substances show
dermal toxicity. Airborne concentration is the primary factor of fire or explosion
hazard with a flammable gas, vapor or mist. Pressure and temperature, of
course, greatly affect both the potential for detonation with any given system,
and the destructive energy of a gaseous release in an accident.
For toxicity, the relationship of concentration and duration of expos~ure, and the
potential for toxic lethality are not the same for all extremely hazardous
chemicals. As an example, the impact of methyl isocyanate (MIC) increases
rapidly as the exposure time increases, even when the initial, short-term
exposure is without apparent effect; whereas the .toxicity of chlorine or
ammonia does not disproportionately increase with increasing duration of
exposure. For these two chemicals, the initial dose is the significant
determinant of severity of effect. The influence of duration of (inhalation)
exposure on response, regarding a serious hazard with a gas or vapor, may be
evaluated using the ratio of the 10 minute and the 30 minute median lethe
concentrations (LC50s) from animal studies, when these data are known. As
an example. MIC exhibits a 10 minute. LC50. and a 30 minute LC50.
respectively, of approximately 600 and 100 parts per million (ppm) - a 6:1
ratio. However. chlorine exhibits a 10 minute LC50, and 30 minute LCS0.
respectively, of approximately 450 ppm. and 250 ppm a 2:1 ratio.
Comparisons can be made in other ways. Table 2 provides data.
CHEMICAl, IDLH LCS0/10' LC50/30' BPt Ht.¥AP'
[Extreme Hazard] [ppm] [ppm] [ppm] *C KJ/KG
~OSGE~ 2 72 24 8 253
BROMI~ 10 651 376 59 194
~ROGEN ~UO~DE 20 992 331 19 1562
C~~ 25 433 250 -34 288
~ROGEN CYmE 60 597 277 26 935
~ROGEN SU~HIDE 300 SS0 44~ -62 SS0
SULPHUR DIODE ~00 ~882 627 -~0 ~882
~ROGEN C~~E X00 5SSS ~850 -84 443
~0~ 500 20;000 XXS40 L0 L374
~/10' = ~ ~al Con~n~on. 10 ~u~cs. ~ stunts.
~uFCC: PR~EED~GS: 1987 S~POSIUM ON P~~G ~OR CHEMI~ ACCIDE~.
~cnc~ Ins~tute of Ch~c~
Table 2. Some To~colo~c~ ~d ~ysic~ ~ope~F Dm~.
8
ASPECTS OF PREVENTION
Hazard Analysis and Chemical Safety Auditing
The diversity and complexity of the chemical industry and its processes are so
great that even the use of the most comprehensive line-by-line check lists (such
as the thousands-of-line sized lists used in the petroleum Industry in
conjunction with other analytical schemes) is not fully adequate for hazard
analysis. Systematic evaluations involving consideration of potential inter-
related, contributing events are also needed. These types of evaluations should
be conducted by a team of special:sts, for the maximum benefit. People with
experience in the particular chemical plant or process in case should be part
of every team. A systems-approach coupled with specific expertise is the
preferred basis for making a chemical safety audit. In California and New
Jersey, this is mandatory and .analytical methods are prescribed. At times,
chemical safety auditing calls for the skills of a safety consultant or the prime
contractor who has special knowledge of the particular process. They will work
with the in-house engineers and specialists.
Formal analytical techniques are now used throughout the chemical and
petroleum industries to prevent losses and solve problems. No one technique
is the universal method of choice. A hazard analysis technique which is very
beneficial when used at the conceptual stage of a project, might not provide the
information necessary to identify and correct an existing problem. The
technique to use in a particular situation needs to be carefully selected.
Safety engineering techniques - Hazard Inventory, Risk Analysis. Fault Tree
Analysis, Event Tree Analysis, Hazard and Operability Studies (HAZOPS), and
Failure Modes And Effects Analysis (FMEA) are described briefly here.
Hazard Inventory. This technique8 is applicable to both the design and
operation of a chemical plant. It involves identifying and classifying risks in
terms of (a) the types and qualities of toxic and hazardous chemicals which are
stored or used, (b) the storage and handling conditions or practices employed,
and (c) the engineering and management systems involved. The recording of
physical spacing is important. Distances should be set aside for safety
assurance. Typically, a 200 foot spacing around hazardous operations is used
to enhance safety and make mitigation of liquid releases easier. Dikes are used
to contain liquid spills and subsequent dispersion when either flammable
materials are stored in any way in the plant, or potentially interactive factors
of hazard exist -such as a spill of flammable liquid spreading under a storage
tank of hydrogen cyanide.
No special format for record-keeping is required or specified for hazard
inventory. The technique is useful for making improvements in plant lay-out,
process control, and risk management. It is a requirement for conducting a
comprehensive safety audit. Lastly, an inventory of extremely hazardous
substances in reportable quantities (RQ) is mandatory under SARA Title 111.
Risk Analysis. This is a technique9 for characterizing risks which is especially
useful in designing plants; siting plants; and changing processes. It helps
coordinators to plan for emergencies. It is used throughout the chemical and
petroleum industries. Risk analysis involves three basic steps: (a) identifying
failure cases and modes; (b) assessing the respective consequences of the
identified failures (in the case of a detonation risk with a chemical
accident, the destructive energy and impact effects at distances may be
expressed as an equivalent amount of TNT explosive); and (c) estimating the
respective probabilities of the failures. These factors are considered together for
each event in assessing impact. Identifying failure cases involves knowing the
inventories of toxic or hazardous chemicals, and carefully considering process
flows, piping, control instrumentation, and modes of operation. Check-lists and
"vVhat If' evaluations are used for this purpose. After characterizing events, a
grid of risk classes {low, medium, high) is made, as a record of the analysis.
Assessing the consequences of a failure in the above scheme involves classifying
the possible outcome of an accident in terms of human health and safety (and
ecology and community welfare). For this, modeling releases for toxic or
fire/explosive impacts is very useful. In modeling, assessment is based on
plausible worst-case scenarios. Also, potential exposures are assumed, and the
issue is whether or not the concentrations and the durations of exposure at
various locations would be sufficient to cause serious, acute (or chronic) health
hazards. Also, fire risks are assessed. In making a risk analysis for a
chemical plant, information on frequency of failure is needed. Histories of
11
physical plant equipment, system and operator failures are useful for this
purpose. In many chemical plants, a data base already exists in the
maintenance department, which may be used for this purpose. The technique
is limited in usefulness when data of failure or accident rates are scant or
incomplete, or when the models used for evaluating exposures are inaccurate
of otherwise limited. Risk analysis can be of great value in designing and
siting new plants, and in operating existing ones. As a yardstick of risk, one
."standard" for acceptable (major accident) risk is one in a million/year - -
10'6/year. Systems reliability studies of complex processes are especially
important to designers. Several techniques exist for use in design work and
safety management, and may have preferred applications. These include Fault
Tree analysis, and Event Tree Analysis. These techniques are used extensively
in the chemical industry, and are briefly described here.
Fault Tree Analysis. This technique~°, involves identifying and defining modes
of failure called "top events." Two examples of top events are the release of
a toxic gas from a rupture in a pressure vessel; and the thermal rtmaway of a
chemical reaction in a vessel.
For each top event, precedent events and combinations of precedents which
lead directly to the failure are identified. A "tree" diagram of causes and effect
is developed. The diagram shows (a) causation, and (b) estimates of the
associated frequencies of occurrences. In this way, the contributory causes and
the direct cause of a failure or accident are found, and required preventative
actions are identified. A feature of fault tree analysis is the use of AND and
OR gates to express logical cause and effect relationships. Rules for
construction exist. A safety analyst and individuals who have knowledge and
experience of the type of plant and process involved are needed to perform the
analysis.
Event Tree Analysis. This is another systems reliability technique~'. The "event
tree" is similar in format to the "fault tree", except that 'bottom events" are
first identified. Thereafter, the possible outcomes from these bottom events are
stated, and a series of "gate" questions, with YES and NO strings (with assigned
probabilities) are employed. This technique allows human error and other
factors to be shown in relationship to consequences.
Figures la and lb illustrate typical' branches of the "Fault Tree", and the "Event
Tree", respectively (without the estimates).
Figure la: Fault Tree Fo~m Figure lb: Event Tree Form
Hazard and Operability Studies - HAZOPS. This is a technique~2 which
involves the systematic identification and evaluation of possible routes to failure
in a system. It provides a basis for conducting a thorough safety evaluation
of a new plant design, making recommendations for major improvements to
proposed or existing processes, and developing reliability and risk analyses. It
is used extensively in the chemical and petrole~_]m industries at the design stage
for risk iden.flcation and problem resolution. HAZOPS uses a study-team
approach to address sets of potential problems and produce alternative
solutions. The technique is labor-intensive. Typically, several hundreds of
man-days will be expended in studying piping and instrumentation for a new
plant, before anything is ordered.
The basic procedure in a HAZOPS is to ask certain guide-words during the
course of scrutinizing many possible operating conditions and deviations. This
identifies possible causes of potential accidents. What if questions using guide-
words are asked. For example, "what ff more temperature occurred"; "what if
reverse flow occurred"; "what ff more pressure arose"; "what ff more time
elapsed in a self-heat situation." The words more, reverse and similar
descriptors are used in this way to explore potential upsets whose
consequences are to be evaluated.
Failure Modes and Effects Analysis (FMEA). This is a simple, widely-used
technique~3, similar to HAZOPS. It is used to systematically identify possible
failure modes and inter-related factors. It involves the use of first-principles
and engineering experience in looking at components separately, an~[ identifying
possible ways of failure.
Info.axation on Experience and Guidance
Personal experience in chemical processing, knowledge of the proximate and
contributory causes of past accidentS and near-misses, and knowledge of design
and the principles of hazard analysis are indispensable for managing an
accident prevention program. A historical perspective is also indispensable.
Some points on these matters are discussed here. And findings are reported
from a 1989 study by the U.S. Environmental Protection Agency of why
chemical accidents happen.
Chemical Accident and Release Tr~formation'
The U.S. Environmental Protection Agency's Chemical Accident Prevention
Bulletin (July 1989, OSWER-89~008- 1) provides Information on why chemical
accidents occur. The bulletin focuses on' reports of accidents, and a database,
developed under Title III requirements. This information is intended to provide
local emergency planning committees with the means of holding useful dialogs
with local facilities on accident prevention and investigation. The Accidental
Release Information Program (ARIP) findings are:
· "the most frequently released chemicals in the ARIP database have been
chlorine, methyl chloride, ammonia, sulfuric acid, and sodium hydroxide--all
large-volume industrial chemicals.
· Most of the releases occurred at facilities that manufacture chemicals or other
products.
· Although accidents commonly have more than one cause, the most commonly
cited causes are equipment failure and operator error.
· About a quarter of the releases were from storage vessels, and a similar
number from piping and process vessels. Valves and other equipment
contributed to a smaller fraction of releases.
· Most releases occurred during routine processing of chemicals; loading,
unloading, and maintenance played a lesser, but significant role."
Remarks On Storage Tank Accidents
Storage vessel accidents feature in about a quarter of the (SARA) reported
accidental releases; releases of one hundred to one thousand or more gallons
are most often involved. Some of the more common causes of failure involved
are mechanical impact; embrittlement; delamination; and internal development
of a vacumm - "sucking in." Incorrect selection or fabrication of construction'
material can lead to failure. Plasticized polymers continuously exposed in use
to leaching agents, such as sodium hydroxide, are prime candidates for impact
or cyclical stress failure. A blockage of a vent at the time of emptying can
cause an internal vacumm, and lead to collapse.
Safety Design and Operation Criteria for Tanks and Storage re: Extremely
Hazardous Substances.
Criteria for evaluating storage tank and related activities include the following:
· a roof over a tank and bunded area (weather protection)
· impervious, sloping, non-reactive, low heat-tranfer base support
· vertical concrete (higher than flood plain height} walls for containment
· strong barriers to guard against impact from trucks
· a drainless, insulated sump tank (200 gallon ?) for lesser spill containment,
equipped with: a pump or air lift for rainwater; a non-return flap valve; and a
vent leading to an absorption or a destruction unit
· tank pipework connections and pumps above the tank top
· remote-operated, Teflon seat-b~ll valves, and internal plug valves.
NOTE: IN SOME SAFETY DESIGNS, A BO'I'I~M VALVE IS PRECLUDED.
e pressure and temperature, multiple sensors
e a piping flow control system to prevent the simultaneous feeding and
discharge of the tank
· no sharing of vent pipes for any system component
· no dead volume space in valve, loop, vent or pipe places
, mimimal inventory, balanced against risks involved in material loading and
transfer
~ wind-indicators (windsock), strategically placed
· physical separation from potential harm (such as from a fire from a spill,
affecting another vessel), and from critical plant structures and boundaries
· dedicated fire fighting equipment, dedicated personal protective equipment,
and means of access for accident mitigation
· formal standard operating procedures covering such points as {i) material-
handling, (ii) trained personnel' only allowed as operators, (iii) the correct
selection, use, and maintenance and storage of personal protective equipment,
and (iv) the proper handling and storage of transfer lines and equipment -
transfer lines must never be left on the ground, dirt will get on the_. connection
surfaces. A raised open-grid metal trough should should be used for storage.
Other general aspects of safeguarding tanks and associated equipment are
mentioned elsewhere. As a final comment here, the use of rail-cars as a
permanent in-process inventory storage facility for an extremely hazardous
substance without the safeguards mentioned is not prudent.
18
Figure 2 shows some possible features of construction for storage tank safety.
R~I)t~OANT LEVEL GAS vrdtT.--~(ABSOi~BEIt)
D~ECTOK/CONTROt. L~
II4*ACT R,E$ISTANT MALL- ~ VALvr:,s AUTO WALL ABOV~ FLOOO PLAIIt
(IF VALES
·
LOM HEAT TRANS~R HATERIAL ,. ...
· 'f (-~ C' . NON REll/RN FI.AP RAINI~TER Pt.~P
o
Figure 2. Safety Design features for Storage Tanks
Remarks On Pressure Vessel Accidents
Pressure vessels are extensively used in chemical processing: they are involved
in many major accidents. Over-pressurization and inadequate pressure relief
capability are causes. However, these are not the dominant ones. More
common causes involve failure of the non-pressurized parts of the system
because of corrosion, wear, impact, or human error in the design or operational
stages. Other common causes include exotherms in stagnant pools of reactive
material In dead spaces, and loss of coolant In a reactor self-heat failure (the
latter poInt Is Illustrated In Figure Ia). Some general aspects of safeguarding
reactor vessels and associated equipment are mentioned later.
Controls For Process Safety
Potential areas of future accidents In existing plants are aging facilities, reduced
Investments In equipment and maintenance, a reduction In the availability of
skilled operators and maintenance personnel, and a thin-spreadIng of the
available cadre of skilled process operators and chemical safety engineers. At
the time of start-up of a new plant or process, experienced or skilled personnel
may be In short supply, limitations can be severe. This ts a vulnerable time
when the value of Incorporated engineered control is often demonstrated.
Safety depends on the use of engineered controls as least as much as on
operator-skill.
To ensure that plants operate at the lowest risk, comprehensive engIneering
plans, together with safety programs, are needed. Both types of con~trol must
be considered In the design phase and the plant operation phase. At the
conceptual engineering and design time, major efforts In process hazard
analysis must be made. This Includes studying any alternative chemistries and
processes to make sure that the least hazardous reactants and conditions are
used. On this point, the toxicity of a chemical may be greatly changed by a
minor change to the molecule. Also, the vapor hazard with a process may be
decreased by IncreasIng reactant molecular weight. As an example, In a series
20
of (moderately) exothermic Friedel Craft/Schotten-Baumann reactions, the
substitution of extremely hazardous phosgene (boiling point:8°C) by benzoyl
chloride (boiling point: 140°C) is sometimes possible, while still making the same
desired product:
~osoEm~! COCk + CH, -[iiCI,l-> CJ~,COCt + C~ - t~aO~ -:
[BENZOYI, CHLORIDE] C~COCI + CsHsNI~ ~[Na0H]-->C,HsCONHC,HS<-~
Other examples of risk reduction with chemistry-process changes are:
· mercury free dyemaking (replacing mercury catalysed AQ sulphonation, CIBA-
GEIGY process)
· continuous polymerization of styrene in a closed system (rather than batch-
proceSSing in a vented pressure vessel, MONSANTO process)
· the use of a condenser on a vent on a pressure vessel charged with toxic
reactants.
It must be said, however, that the oportunlty to use alternative chemistries and
processes is generally quite limited. Nevertheless, the point is worth reiterating
that a formal procedure should be established to ensure that the senior
managers are given information on options, so that they can properly manage
the risks.
To minimize risks of fire and explosion, the design of new or modified chemical
plants should require certain critical processes and facilities to be remote and
physically isolated from both each other and the plant boundary. Guidance on
such safeguarding is provided in various API and NFPA codes. Also, local and
state codes are useful (and .applicable). Providing safety by distance is an
effective way to control explosion risk. And physical isolation can be very
effective in limiting the potential damage from spills of flammable or corrosive
liquids. Invariably, using distance as a safety control entails greater first-costs
for real estate, compared to using a close-packed (less safe) layout. Safety and
net economy may have to be strongly argued during the cost-benefit reviews.
'\
The point which may need making is that the cost of a major accident, however
infrequent,' is always very great. The Bhopal settlement cost a reported $470
millions!
Passive (Intrinsic) and Active (Extrinsic) Safeguards
To incorporate safety in new and existing facilities, one needs to employ both
passive and active principles. ~--
Passive principles are policies and plans, essentially. These include such
matters as:
· requiring each plant to have Standard Review Plans, and Standard Safety
Operating Plans. These plans would cover evaluation of potential accidents;
dispersion prediction information; groundwater protection; safety assurance in
new or changed processes, facilities or operations; mandatory periodic meetings
with local planners, interested citizens and media personnel who may be
involved 'in public safety: safe working practices, including the "buddy" system
with high hazard activities; and other points.
· requiring critical facilities to be located in remote locations and safeguarded
by distance and diking, when appropriate.
· requiring design for mitigation of accidents.
· requiring experts to participate in the selection and sizing of pressure relief
equipment and flame arrestors; in vessel and piping construction and material
selection; and in decision-making on process automation-versus-manual control
· requiring a human factors engineer to participate in the concept and design
stages of planned new construction
· requiring pre-processing system leak checks, and periodic, non-destructive
testing of vessels and parts involved in any high hazard process
· requiring regular formal inspections of all process piping, flanges and gaskets,
and instrumentation when they are part of, or service any high hazard process
· requiring the use of hard wired back-up for critical interlocks, and alarms on
hazardous processes .~-_
· requiring multiple, and different types of, controls on hazardous processes
(control redundancy)
· requiring electrical, coolant and other critical services, and tanks and
equipment for extremely hazardous chemicals, to be physically protected against
accidental impact or abrasion, and "backed - up" by emergency services.
· emphasizing that flash point and auto-ignition point are not constants, and
that the dynamics (e.g., agitation) of the process can create risks
· requiring studies of potential rates of reaction and self-heat rates (in some
studies of upsets, 1000°C/minute plus, instantaneous rates have been reported)
· requiring pilot plant scale-up studies for safety in new processes, and safety
rules for each pilot plant
· requiring the preferential selection of reactants, processes and conditions
which pose the least impact on the community in an 'accidental release.
· requiring feasible pressure relief systems to match plausible worst-case
overpressurization/self-heat conditions
· requiring reactor vessels to be operated at the lowest feasible pressures and
temperatures (a cubic foot of gas at 2000 psi and 20°C has about as much
potential energy to do some harm as has a pound of TNT, even if the release
modes are different!)
· having a firm policy of physically protecting tanks, gas lines, and critical
valves and lines against impact by fork-lift and other types of trucks
· prohibiting any physical change or procedural change to any. process and
procedure, regardless of any percieved inutility, without the express permission
of both the Manager of Engineering and the Manager of Safety. This
prohibition would be conspicuously posted on the equipment.
Active principles are related to operatin~ or using! engineering and
administrative controls. Such active safeguarding includes using:
· pressure relief devices. Most importantly, such devices need to be sized to
match the pressure generated in a maximal self-heat case, when this is
physically feasible
· rupture discs. The associated pipes and support-structure must be strong
enough to absorb the potential rupture thrust force
· automated detector systems for critical process parameters
· back-up storage/liquid spill containment capacity (flexible tanks are available
with capacities up to 100,000 gallons)
· a separator and a containment vessel. These would be installed in-line, after
a rupture disc or relief valve
· inerting and explosion-venting of low pressure tanks used for storing
flammable liquids at or above their respective flash points
· periodic acoustical-testing of critical fiberglass and metal tanks, vessels and
parts
· dedicated fire-fighting, and personal protection equipment
· a multi-channel automated monitor/alarm system for leak detection, with all
extremely hazardous chemical processes
· a back-up containment pressure vessel (properly-sized, larger than the
primary reactOr) for highly poisonous chemicals, such as phosgene or hydrogen
cyanide
· positive-pressurization of (i) an on-site command center, and (ii) electrical
controllers and devices in hazardous {DIVISIONS I and 2) locations
· a TFE-fluorocarbon valve seat with a valve in a high hazard system, to assure
full closure of the valve
® a public communication procedure and system for emergency action,
including public evacuation (on which the public must be well-informed before
any accident occurs).
In using active safeguards, the design and equipment employed should be in
accordance with the most recent and stringent regulations and standards.
They should also meet the standards of the relevant guidance from competent
authorities, such as insurers. It is noted that some consensual safety standards
do not address or meet ail of the needs for safety in some situations. And
design should accommodate the plausible worst-case regarding self-heat,
corrosion and wear, not the average cases. On the point of effective codes,
safety standardization has made considerable progress in recent years. This
has come from newer engineering design guidelines and process simulation with
computerization. The American Institute of Chemical Engineers, the chemical
safety design institutes, the American Society of Mechanical Engine. ers and the
larger engineering companies have made major contributions in these areas.
Controlling Contributory Human Error
Many major chemical accident reports point to human error - error in operation
or maintenance as the proximate cause. Accidents are often attributed to an
operator's error, without due regard to the existence of other contributors, such
as inadequate design or poor administration.
Controlling all contributory human error is important for safety. This involves
such matters as:
· removing repetitive tasks from the operator's direct control. This involves
automation using reliable appropriate sensors and controllers
· making a process tolerant of an operator error. For example, use max/mum
or minimum liquid level controllers; maximum temperature shut-offs; flow rate
controllers, and (high-high/low-low) limit controllers
· simplifying vessel construction, piping, and operating features
· using valves and equipment with the better rating for use in severe chemical
environments, whenever extremely hazardous substances are involved
· color-coding and labelling pipes, and labelling valves
· operating vent pipes to scrubbers under a slight negative pressure, with
appropriate sensing and interlocking of critical functions, to control accidental
releases (as might occur in starting up a process with an open vent valve)
· automating infrequent process-termination steps
· holding safety talks which include stressing the point that automation does
not reduce the need for safety training. If anything, it makes the_ training of
operators and maintenance personnel even more critical to safe operations.
· providing specific instruction and training to operators and maintenance
personnel
· providing refresher training at least annually to operators and maintenance
personnel, and flrst-responders - to whom standard 29 CFR 1910.120 applies
· not assuming that a trained and instructed operator will perform a task
consistently and will not deviate from a standard operating procedure.
· involving operators and workers in chemical safety audits
· giving the operator control of a critical service. For example, the operator
would have lock-out control of a (normally open) water-line on a process chiller.
· conducting mock exercises to assure a satisfactory response to an accidental
spill, and test the (mandatory) spill prevention and counter measure plan.
Management, and Management Systems
Most managers throughout the chemical process industry are highly committed
to the cause of safety and environmental protection. Many of them undergo
continuing education, and participate in relevant technical meetings. However,
some of the systems and practices that some managers employ do not indicate
or reflect a high level of commitment.
Safety management systems, methods for assessing plans, and procedures for
evaluating risks and auditing practices are an integral part of every successful
management program for accident prevention. The importance that the
management places on safety must be seen in the actions of the m._anagers and
staff. The general manager, the senior managers and their staffs need to be
involved personally in meetings with employees, local officials, interested
citizens, and local media personnel at appropriate times. The safety committee
must meet at least monthly. Also, all process operations should be observed
regularly to make sure that "short-cuts" have not been introduced. And
managers must guard against accident risks from a decline in an operator's
ability or fitness. Operators and shop stewards must appreciate this need.
ASPECTS OF PREDICTION
Hazard identlflcatlon and modeling of atmospheric dispersion of extremely
hazardous chemical releases underlie developing emergency predict_ion
information. The acute health risk is determined from the acute eXPosure data,
the kinds of end-points result, lng from the exposures, and the probabilities of
the exposures occurring.
Hazard Identification, and Hazard Determinants
Toxicity and physical properties are major determinants of acute health hazard.
And boiling point, density and latent heat of vaporization underlie the vapor
hazard from a release. Terrain and meteorology influence dispersion. Also,
dispersion depends on the type of release, and the nature of the chemical itself.
As an example of how a chemical property can influence dispersion, look at a
denser-than-air gas release. Chlorine gas, which is about twice as dense as air,
tends to follow the line of least resistance to travel, when it is undiluted. In
reported cases of a major chlorine release, one frequently reads about chlorine
moving down a valley. ~--
Another example of the effect of a physical property on dispersion, is that of a
liquid which has a specific heat lower that another liquid with a similar boiling
point vaporizing relatively faster, with a similar heat input. On the preceding
point, compare chlorine and ammonia:
CHLORINE: B.Pt: -34°C. Ht.Vap'.: 288 kJ/kg.
AMMONIA: B.Pt: -33°C. Ht.Vap'.: 1374 kJ/kg.
29
With other factors being equal, in some spill situations, anm~onia will evaporate
relatively slower ~h. an chlorine because of its greater heat of vaporization.
Regarding terrain and meteorology, examples of relevant effects are:
· the sun immediately heating the ground-level air, causing turbulence and
enhanced dispersion
· nighttime cooling and stratification of ground-level air, causing reduced
turbulence and dispersion (nighttime releases frequently pose potentially serious
impacts)
· structures and obstacles, such as tall buildings in city centers and trees in
urban areas, creating a degree of meteorological ground roughness which
provides enhanced air turbulence and relatively greater dispersion.
Methodology Underlying Prediction Information Software
Software products are commercially available~4 for modeling air releases for
acute health risk analysis. At this time, there are about 40 models available
for evaluating vapor cloud dispersions (the Center for Chemical Process Safety
of the American Institute of Chemical Engineers published a guideline review
of such models in 1987).
Underlying the methodology used with many such models is classification and
quantification of:
· the release - as a continuous release; term release; area-term release, or area-
continuous release
· the atmospheric stability - in terms of wind-speed, daytime sunlight, and
nighttime clouds
· the terrain: city-terrain or standard-terrain.
Deposition rates and other factors also apply.
Commercial software products are usually based on the Gaussian Plume
model'5. This model is widely accepted and it is the work-horse for emergency
prediction purposes. In some instances, sophisticated versions of the model are
used which can factor into the dispersion estimate the effects of complex
terrain, buoyancy, and the thermodynamic factors with the chemical release.
In other cases, different dispersion models which are quite complex are used.
Ex_~mples of such models are those used for modeling dispersion of isotopes,
prescribed in the NRC Regulatory Guide #1.1 1 1.
Figure 3 shows typical (minimal) input for a simple and very useful model for
predicting emergency information, with a generally accePtable level of precision,
bearing in mind the limited accuracy ex/sting for the dose-respon~ picture for
most of the chemicals of concern.
COKTINUOU$ TERlll RELEASE AREA COlfrINUOU$ ARF...A TEI~I
RELEASE DURATIOI~ - ? EFF. AREA ' ? EFF. AREA - ?
I~TE- ?
QUAI~r~TY - ? EVAP. RATE - ? RELEASE DURATI~ -
TOTAL- ? TOTAL - ?
#ETEOROLOGICAL
REL. HEIGi'fl' - ? CO#DITI~S
STANDARD TERRAIN CITY TERRAIN STABILITY
CLASS
OUTPUT/OPTI~#$
Figure 3. Input for Emergency Prediction Info,~tton
Typical Output of A Simple Model
The typical output of a simple emergency prediction information includes:
· optional monochrome or color screen display
· print-outs of concentrations at down-wind and cross-wind locations and
distances (in units of miles or kilometers)
· receptor-height concentrations {in units of part per rml]ton-ppm, or r~illigr~arl
per cubic meter-mg/m~)
· arrival times, in minutes or hours, of ~trbome concentrations distributions
(plumes), downwind and cross-wind of the release,
CONTINUOUS TERIq RELEASE AREA COI~TI#UOU$ AIF. A
RELEASE DURATIOtt - ? EFT. AREA ' ? EFF. /LRf..A - ?
~TE- ?
QUANTTTY - ? EVAP. RATE
TOTAL- ? TOTAL - ?
i i, -J O,.~S '
OOTPUT/OPTIOIIS
Figure 3. Input for Emergency Prediction Infoimation
Typical Output of A Simple Model
The typical output of a simple emergency prediction information includes:
· optional monochrome or color screen display
· print-outs of concentrations at down-wind and cross-wind locations and
distances (in units of miles or kilometers)
· receptor-height concentrations (in units of part per wtllton-ppm, or wtlligram
per cubic meter-mg/m~)
· arrival times, in minutes or hours, of airborne concentrations distributions
(plumes), downwind and cross-wind of the release,
33
PHOSGENE CAS Number: [75-44-5]
TWA : 0.10 DDm T~A : 0.40 mg/m'3
IDLH : 2 DDm
DOWNWIND MAXIMUM CONCENTRATION ARRIVAL T[ME
Distance-Mi mg/m^3 DDm hours:mtnu~es
0.10 120000 30000 : 6
0.20 30000 7300 :12
0.30 13000 3200 :18
0.40 7100 1700 :24
0.50 4400 1100 :30
0.60 3000 740 :36
0.70 2200 530 :42
0.80 1600 400 :48
0.$0 1300 310 :54
1.00 1000 250 1:0
2,00 170 42 2:0
4,00 16 3.g 4:0
6.00 6.6 1.6 6:0
8.00 3.4 0.83 8:0
10.0 2.0 0.50 10:0
20.0 0.42 0.10 20:0
Figure 5. Arrival Times, Distances, and (~oncentrations
Precision of Predictive data
The predictive information obtained from current models is only approximate,
but it ts usually good enough to be very useful tn dectsion~-maktng for
emergencies. ~_Wl~th stmple models, when dense g~es are involved, over- ~
prediction of airborne levels may occur because of the non-neutral buoyancy
c~onditions. However. reportedly, for low levels below about five percent, the
effect is usually minor and it conservatively Influences the output. Comparative
test data for establishing precision are not plentiful. A s-fficient number of
tests have been conducted by the federal govenament (tn particular, the U.S.
Department of EnergY. tn the mtd-80's) and private organizations whose
34
reported results_can be used to evaluate a simple model (which actually can be
more useful in a real emergency than a less user-friendly, more sophisticated
one because of a stop occurring with the use of the latter type model when
data are unknown). As a general comment on precision, software vendors claim
that agreement between actual and predicted data for releases of extremely
hazardous chemicals is often about x3 - x5, either way. Reportedly, agreement
is optimal when the region of concern is (i) outside of the immediate zone of the
release, that is the area of concern is more than 250 feet away from the site
of release, and (ii) lies in level, open terrain.
Specific performance and comparative test data for the commercially available
products are available from the suppliers.
Using Predictive Information, and Exposure Guidelines
When emergency data and prediction information on a release have been
obtained, the next step is to compare them to the known or assessed, relevant
immediately dangerous to life or health (IDLH) leveP?. This is done. to establish
the zone of vulnerability.
In practice, the zone will be set-up using either a fractional value of one-fifth
or one-tenth of the IDLH, depending of the Judgment of the responsible
coordinator. When an IDLH value is unknown, ten times (or somewhat greater)
the threshold limit value~8 (TLV) for the chemical, ff it is known, may be useful
(and conservative) as an approximation of the IDLH level (others have proposed
using a x500 factor, this could be too great in some cases, in the view of the ~,
writer). The selection of such a factor requtres in.formed Judgment.
ASPECTS OF RES~NSE TO RELEASES
Despite the best of preventative planning, major chemical accidents happen,
and mitigation plans must be developed beforehand. In the plan must be
requirements for well-trained response personnel and appropriate equipment
being immediately available, and procedures for in-plant and community
communications being in place. Specific federal (OSHA and EPA) regulations
apply to each one of these points.
In planning for mitigation, one needs to identify potential hazards, and evaluate
potential exposures and durations of exposures. A plausible worst-case
scenario is to be used when accurate information is missing. With regard to
hazards, when a flammable liquid or gas is released, a fire may result within
a matter of minutes when the vapor or mist concentration is above the relevant
lower flammable limit (LFL) [the more familiar concern in this regard is a major
accidental release of light hydrocarbons or LPG, which is to be dreaded]. Static
electricity and other sources for initiating a fire must be presumed to exist in
all such releases. The primary safeguard in such a case is rapid evacuation.
Apart from the risk of fire, exposures involving inhalation of toxic substances
and dermal uptake of such substances must be presumed to arise, unless
36
information to t~e contrary is known. Initially, in responding to a release of a
toxic chemical, maximal risk is to be presumed to exist, and maximal personal
protection is presumed to be needed. Thus, a se.If contained breathing
apparatus, in the pressure demand mode, together with a fully encapsulating
suit. will be used by each responder. Only after hazards have been properly
assessed can any lower level of protection be employed.
Large-scale releases of many chemicals can present serious health hazards
through inhalation at distances which are several miles downwind of the site
of the release, even though there is no accompanying fire hazard. This could
require either rapid evacuation or the public staying indoors with the windows
closed, depending on the risk.
When a ground-level release of a volatile, toxic chemical occurs, the responders
who are close to the release are the ones who first face imminent danger.
regardless of their compass location. In the case of a ground-level release of
a denser-than-air liquid, the spill can move initially against the wind direct_ion.
First-responders must be thoroughly trained and instructed in handling
releases. People at the work site can be exposed within minutes of the start
of the release. And the local community - people who are down-wind by several
miles may become seriously exposed within the hour or thereabouts,' depending
on the wind speed, the magnitude of the release, and other factors.
Communities farther away may be exposed to serious or non-serious conditions
within a few hours. The point is that dangerous exposures can confront
employees, workers and people in the nearby communities within minutes of
the start of a major chemical accident. Everyone must be instantly alerted and
told what to do. They must be informed in advance what the public alarm is,
and what they must do when the alarm is given (that is, evacuate, stay indoors,
listen to a radio station, obey officials, et cetera). It must be realized that in
some grave accidents, people who are more than ten miles from the release may
experience a serious harm or a major nuisance within a few hours of the start
of the release.
To safeguard people who might be affected tn a major chemical accident, a
contingency plan must be in place. The plan must be thoroughly understood
·nd practiced by those who are required to take corrective action, and by the
people who will be affected. It must cover or require, amongst other things:
· a company-fire department-citizens plan for emergency alert, evacuation, and
other safety needs
· engineered containment, and provision of needed equipment, such as a pump
and a flexible (instant) storage tank ....
· assurance of the immediate availability of trained personnel
· assurance of the immediate availability of personal protection. At least six
sets of either Level A or Level B protection will be required, depending on the
hazards involved
· administrative procedures to inform the public, to be in place.
38
Personal Protection
Personal protection for flrst-responders and those involved in cleanup efforts
must be selected on the basis of the route of entry, and the toxicity of the
chemical of concern. Protection against a chemical which poses potentially
serious inhalation and dermal (including eye) hazards, such as liquid chlorine
(first degree hazard), would require the use of a self-contained breathing
apparatus (SCBA), and a fully encapsulating suit: Level A in U.S. EPA
terminology~9. In the case of a serious inhalation hazard only, a self-contained
breathing apparatus, with suitable body covering (Level B protection) would be
required. .
NOTE: A distinction may be made between going into a normally safe area
and undert_sking a potentially hazardous activity, such as transfering
hydrogen cyanide from a rail car, and entering a site wherein a release of
an extremely hazardous substance has occurred, with respect to
respiratory protection prcedures and equipment for use. This topic, and
the requirements for a respiratory protection program are too extensive
to be discussed here. Specific reg, l~tions ~mder OSHA and EPA must be
consulted, and the provisions applied, before a first response is
implemented. Detailed information on respiratory protection and related
matters is given in the Niosh Publication, //85.115; the OSHA standards
at 29 CFR. 1910.134, and 1910.120; and the EPA standard at 40 CFR 311
which extends application of the OSHA standard to state and local
agencies.
Containment, and Suppression of Vaporization
Physical containment and reduction of vaporization of liquid are needed to
mitigate a release. A concrete bern and catchments need to be constructed.
Other requirements include:
· reduction of the spill surface area (to control vaporization)
· reduction of heat transfer to any pool of a liquid of low specific heat (for
vaporization control). Use lightweight or thermally Insulated concrete.
· provision of sunshade (for controlling temperature and pressure Increases in
containers, and to reduce vaporization rate)
· assurance that the floor of the containment structure does not dangerously
absorb or react with the spilled material. VAs~phalt-sh0-dl~l~-~6.tT.b~ us~-d~b~l~ow a
-ta~k~---c o n.~g-_a~s~t~b-fig-~xid an t
· assurance that drainage is provided for collection (via a sump), and that
storm and sewer drains are not contaminated
· physical shielding of structures against wind, to reduce dispersion
· the use of reactive materials to absorb or neutrmlt?e a chemical, provided that
this can be done without excessive, rapid energy (heat) liberation. For
example, sand might be used Under a hydrofluoric acid tmnk, for neutralization
of minor spills. The stoichiometry is favorable:
6HF + SiO~ ---> I-I~StF, + 2I~0
4O
Foam For Vapor_Containment and Fire Hazard Control
The vaporization rate of a pool of flammable and nOn-flammable liquid can be
reduced in some situations using foam. Fire risks from petroleum spills are
commonly controlled using foam. This basically involves keeping air away from
the liquid surface.
Foam application to an outdoor pool of a toxic chemical can be effective in
reducing the effects of insolation and air flow on the dispersion rate. Also,
foam can be useful in some cases in controlling the movement of the associated
air plume. However, the application of foam to a spill can also cause
dispersion, especially when the liquid has a low specific heat, relative to the
foam. Using foam to control exposures or conta_tn' a spill with an extremely
toxic, highly volatile liquid is of questionable value. Using a foam for an indoor
release of an extremely hazardous, very volatile liquid -as might occur in a
laboratory accident - is not correct. Blanketing the spill with foam would make
the problem worse. Foam application, collapse and reapplication would add
heat to the pool, and increase the pool area. This would increase the
vaporization rate and cause the indoor concentration to increase.
When foam is planned to be used in a response to a major chemical accident,
consideration must be given to:
· the compatibility of the foam with the chemical
. the foam expansion factor [EF] - the volume of foam divided by the volume
of water used to make the foam.
[Note foam characteristics, by EF, are:
EF=10, heavy and wet; EF=100, firm; and EF--200, light and mobile].
~ the dr~tuage of the foam (the amount of water from the collapse of a volume
of foam). More water can add heat to the pool.
Most importantly, the advantages of using a foam - suppression of the
concentration immediately above the pool of the spill, and reduction in the
effects of insolation and wind dispersion - must be weighed against providing
a heat gain to the pool being covered, thus increasing the vaporization rate.
Water Used For Dispersion or Con~_~tnment
Reducing acute hazards from a release of a water-soluble, toxic liquid or a toxic
chemical which readily hydrolyses, such as titanium tetrachloride, can be
achieved with water. A water spray can be effective in dispersing a release of
a combustible or flammable liquid, and in holding concentrations._below the
lower flammable limit [for most flammable liquids, this limit lies in the range
of about 0.7 (7000 ppm) to about 5 percent (50,000 parts per million)].
Spraying is usually done using a high flow/fine (fog) spray nozzle. Application
is made from downstream, when this can be achieved without risk. When
envelopment in a cloud of a flammable vapor or a toxic chemical is likely,
application is made from upstream.
Containment of a plume of a low solubility, denser-than-air vapor or gas, such
as chlorine, can be effectively achieved using a water spray. Also, the
movement of a toxic plume can be controlled in this way.
A water spray should not be applied to any large mass of an alkaline earth
carbide or an alkali metal. In the latter cases, acetylene and hydrogen,
respectively, would evolve and create a fire hazard. However, water can be
sprayed on a reactive, toxic, inorganic halide, such as boron trifluoride,
phosphurous trichloride, tin tetrachloride, and titanium tetrachloride, to reduce
dispersion; acid vapors which are themselves toxic will of course be created.
A pool of immiscible, non-reactive liquid which is denser than water can be
contained using a water blanket. This effectively controls vaporization and
facilitates recovery or neutralization. Spills of carbon disulfide and liquid
bromine can be handled in this manner.
Other Containment, and Control Measures ......
Sand, sulphate powder, granular powder, and certain polymeric powders can
be used to contain spills. The underlying principle of using a solid sorbent is
to reduce the liquid surface area, and, consequently, the rate of vaporization.
The density of the bulk of the solid material which is to be used should be less
than the density of the spilled liquid. The powder must not react violently
with the liquid. It must be fine enough to provide a thick cover.
43
Chemical neutralization, physical barriers, the use of fans, the use of plugs and
patches and ignitio~t are other containment and control measures. These are
mentioned briefly here:
· neutralization of an acid spill can be achieved using soda ash
· neutrali?ation and solidification of some acid or caustic spills can be achieved
using commercially available products
· an impervious cover placed over a volatile liquid spill can effectively reduce
vaporization
· fans can be used to disperse vapors from a flammable liquid spill so that the
lower flammable level is not reached. Use totally enclosed, fan cooled (TEFC)
motors with the proper NFPA 30 class-division-group rating
· a plug or a patch can be used to stop a leak from a vessel (these remedies
have been pioneered by the Chlorine Institute)
· a quick-setting adhesive, or magnetic clamps, with a gasket and cover
arrangement can be used to contain some leaks
· ignition may be used to minimize the escape of a release of a flammable
vapor or toxic gas, such as hydrogen cyanide or hydrogen sulphide. However,
ignition (as distinct from high temperature incineration) is not useful for
controlling a toxic gas release when its concentration is lower than its lower
flammability limit, at which time the concentrations could still be potentially
lethal. Also, the use of, '. ignition is counter-indicated for chemicals whose
oxidation products are toxic. For example, chlorine-containing hydrocarbons
produce phosgene when they are burned in the open.
44
Administrative E~fforts For Safety and Public Assure_rice
An ounce of prevention is worth a pound of cure. This is especially true in
safety management. Managers need to make sure that new plant or projects
involving major changes are bid to exacting safety specifications. The bidder
will offer generally sound safety engineering, but some bidders do not always
have all of the expertise needed for safety assurance. Also, they will offer
whatever is deemed competitive.
Training and instruction of personnel needs to be ongoing. Refresher safety
training in specific operations and standard safety operation procedures {SSOPs)
are essential for safety. Automation is not a substitute for trained workers;
equipment is only as good as the people who use it.
Responses to emergencies must Usually be made within minutes to avert a
catastrophe. In some situations, it is unrealistic to expect a timely response
from a local organization; the distances might be too great, for example. In
these situations, the only practical thing to do is to use specially trained plant
personnel as first-responders. If this is undertaken, the management must
assure the safety of the responders. They must comply with the relevant
provisions of the OSHA Emergency Response rule, at 29 CFR Part 1910.120.
An important but uncommon aspect of risk management is the (radical?) policy
of assuming cert_~_in reactors, vessels and components to be potentially unsafe,
rather than safe, at a certain point (3/4 ?) in their currently expected maximal
45
useful life, and requiring reliability assurance from a designated manager. As
an example, in ~the case of a reflux condenser which has operated in a
chemically and physically hostile environment for, say, 12 years, one would
assume it to be potentially unsafe, because of internal corrosion and stress
cracks, and require it to be thoroughly examined and tested, regardless of any
code test done a few years earlier.
A comprehensive (but easily read) plan for alerting the community and starting
an evacuation, when necessary, must be in place and well-understood by the
employees, the fire department officers, and the public. Such a plan should be
developed with input from local safety officials, and neighbors.
As a parting comment, for a facility or chemical plant to be, and be seen as,
a good neighbor, the plant administrators must make sure that they promptly
and authentically respond to all of. the concerns of the community.
NAB
J~uary7,1~0.
References and End Notes
1. Bhopal, India. 1984 methyl lsocyanate released, due to water ingress, uncontrolled self-heat, and tank
rupture. More than 2000 deaths initially reported.
2. Seveso, Italy. 1976 toxic gas release forced major evacuation. Long term effect of major dioxin release,
major concern.
3. 1987 release of many chemicals from Sandoz company. Major contamination of the Rhine with
mercury and organics. No fatalities; chronic health effects major concern.
4. A poll taken in 1986 by Roper Associates.
5. The American Institute of Chemical Engineers,the American Society of Mechanical Engineers are
dominant in this area.
6. Regulations at Title 10, the Code of Federal Regulations.
7. Statement of Mr. Lee Thomas, former EPA Administrator. February 3, 1987, Washington, Int.
Symposium on Preventing Major Chemical Accidents.
8. Standards and recommendations from the National Consensus standards groups and technical societies
listed (5).
9. Risk analysis, for more description see [SGRA, Risk Analysis in the Process Industries, 1985 Report.
Institution of Chemical Engineers, London.
10/ll/13 - Techniques. There is extensive descriptive material on these topics. For literature and
reprints, consult the National Safety Council, Chicago, Illinois 93120, 527.4800.
12. Hazops key words: see The (1977) Guide, same topic, of the Chemical Industries Association.
London, Eng.
13. The Center of Chemical Process Safety is particularly active in this area. It is group within the
American Institute of Chemical Engineers.
14. Many products are offered. A review of (40} vapor cloud dispersion models is available from the Center
for Chem/cal Process Safety -{212-705-7657). The EpiCode software from Homann Associates, Fremont,
CA, and the Cameo 2 Software from the National safety Council are two easy-to-use products for Public
Hygiene work.
15. The model is described in EPA Guide, OAQPS Guideline on Air Quality MODELS, EPA REPORT 450-
78-028 ....
16. Epicode and (extensive) library. Homann Associates, 39831 San Moreno, CT. Fremont, CA 94539 (415)
490-6379.
17. IDLH is not consistently defined in the regulations of the relevant agencies. Herein, it means the
concentration at which a serious harm is likely to arise within a matter of minutes with a continuing
exposure. The official definition given in the Mine Safety and Health Administration Standard at 30 CFR.
Part 11.3 is preferred by the writer for the purpose of response, discribed herein.
18. 'I~V - trademark term for threshold limit values established by the American Conference of
Governmental Industrial Hygienists.
19. See "EPA - OCCUPATIONAL HEALTH AND SAFETY MANUAL, #1440."
APPENDIX
EPIcode ALGORITHMS
COORDINATE SYSTEM
In the EPIcode system, we have placed the coordinate
origin (x = 0, y = 0, z = 0) at ground level, beneath the point
at which the chemical substance is released. The x axis is
the downwind axis, extending horizontally with the ground
in the average wind direction. The y axis is the crosswind
axis, perpendicular to the downwind axis, also extending
horizontally. The altitude axis (z axis) extends vertically. A
plume travels along, or parallel to, the downwind axis. The
figure below illustrates the EPIcode coordinate system.
Z ~ k~
c(x,y)
X
Y
Crosswincl _y
BASIC EQUATION
The origin of the Gausst-n model is found in work by
Sutton (1932), Pasqufll (1961, 1974), and Glftord (1961,
1968). Additional background and supplemental informa-
tion on the Gaussian model can be found in Turner (1969)
and Hanna et al. (1982).
We use the following Gausst~n model equations to deter-
mine the concentration for a gas or an aerosol (particles
less than approximately 20 pm in diameter).
Continuous Phase:
Q _.1 y__ ex:p- +
C (x,y~.H) = 2~OyOzt~ exp - 2 Oy Oz
2 z+H~l~
Puff Phase:
C (x,y,z,H) = (2~c) 3/2OxOyO~' exp - -~ Oz'"
The 'pulp equation is used for an instantaneous term
release, and the 'continuous" equation is used for a con-
tinuous release, For a non-instantaneous term release
(e.g., 0.5 mm.. 120 mm., etc.) EPIcode automatically
selects the appropriate equation. This selection process is
based upon the plume length (release duration x wind
speed) relative to the ox at the specific downwind, location
being considered. We assume that ox = o. For a term
plume length is les: ox, the
release when the ~ tha~ plume
diffusion process is more accurately characterized by the
Puff' equation. The Continuous equation is used whenever
the plume length is greater than or equal to 2ox. For
plume lengths between ox and 2~x, a combination of both
equations is used.
If the Inversion Layer option is in effect, and Oz exceeds the
inversion height L, the following equations are used.
Continuous Phase, os > L:
C (x.y~,H) = Q exp - ~-
Puff Phase, ~z > L:
C (x.y~,H) = 2~Ox~ylJ exp - ~' ~Y
where C = atmospheric concentration (ppm, mg/m3)
Q = source term (g/s, m3/s, etc.),
-or for a term release
?= Qr/release duration (g/s, etc.)
total release (g, m3, etc.)
H = effective height of chemical substance release
x = downwind distance (m)
y = crosswtnd distance (m)
z = vertical axis distance (m)
= standard deviation of the concentration
distribution in the downwind axis direction
(x axis, meters) o~ =
~y = standard deviation of the concentration
distribution in the crosswind direction
(y axis, meters}
c~z = standard deviation of the concentration
distribution in the vertical direction
(z axis, meters)
u = average wind speed at the effective release
height (m/s, mph)
L = inversion layer height (m).
An upwind virtual point source, which results in an initial
~ equal to the effective radius of the area source, is used to
model an area release.
The values of cry and ct, are representative of a sampling
time of ten minutes. Concentrations directly downwind
from ~ source decrease with sampling time primarily
because of a larger ~ydue to increased meander of wind
direction. For sampling times greater than ten minutes.
and less than the total release time for term releases, the
following equation can be used to predict the sampling
results (Turner, 1969):
10
where C, = the concentration averaged over t, minutes.
For example, you run an air sampler for one hour (60 nmIn)
at a particular downwind location. The EPXcode estimate
at this location ls 25 mg/m3. However. the one-hour aver-
age concentration expected from the pre~ous equation is:
[ 10gin)°'2
Cs = 25mg/m3 ~ = 17mg/m3
EFFECTIVE RELEASE HEIGHT
The actual plume height may not be the physical release
height, e.g., the stack height. Plume rise can occur be-
cause of the velocity of a stack emission, and the tempera-
ture differential between the stack effluent and the sur-
rounding _~ir. The rise of the plume results in an increase
in the release height, as shown in the figure at the top of
the next page.
This effective increase in release height leads to lower
concentrations at the ground level. If you are not able to
visually estimate or calculate the effective release height.
we recommend you use the actual physical release height
{i.e.. the height of the stack)--or use zero height for a
ground-level release. This will always yield conservative
estimates.
Z
H
If the release is from a stack, and you know additional
information on the stack discharge velocity, temperature,
and stack diameter (i.e., if you are designing a new stack
for a building), EPIcode can automatically calculate the
effective release height. This can also be applied to an area
release if the effective release radius is less than fifty
meters.
Select Calculate PLUME' B. ISE by typing PP, from the
release height prompt. EPIcode calculates both the
momentum plume rise (Brlggs, 1969) and the buoyant
plume rise (Briggs, 1975) and chooses the greater of the
two results. The recommended methodologies in the above
two references are strictly followed. ....
STABILITY CLASSIFICATION
Meteorologists distinguish several states of the atmospheric
surface layer: unstable, neutral, and stable. These catego-
ries refer to how a parcel of _~ir would react when It ls
displaced adiabattc_~!1y in the vertical direction. The
EPIcode model offers two ways to select the atmospheric
stability category.
For users who are not familiar with the different stability
classifications commonly used in meteorology, EPIcode will
select the jappropriate stability classification with informa-
tion you provide from direct observations. Or. a user can
directly select and force a particular stability classification.
The simplified method requires selection of the solar insola-
tion factor and ground wind speed {at a 2 meter height).
EPIcode then automatically determines the atmospheric
stability category from the matrix given in Table 1. This
table contains criteria for the six stability classes, which
are based on five categories of surface wind speeds and
four categories of solar insolation. This scheme is widely
used in meteorology and is accepted for stability class
estimation.
Table 1. Meteorological conditions used to define the
Atmospheric Stability Categories, A-F, used in EPIcode.
Sun conditions
Low in
Ground wind High in sky or
speed (m/s) sky cloudy Nighttime
<2 A B F
2-3 A C E
3-4 B C D
4-6 C D D
>6 C D D
Pasquill Stability Types:
A: Extremely Unstable D: Neutral
B: Moderately Unstable E:Sllghtly Stable
C: Slightly Unstable F: Moderately Stable
The user may also select the stability class, A-F, directly
from the table. In addition to these six stability classes,
EPIcode also allows you to enter w for the worst-case
scenario. If w is selected, EPIcode uses a// stability classes
to determine the downwind concentration, then chooses
only the class resulting in the highest contaminant concen-
tration for the particular ground-level location. For
documentation purposes the displayed output indicates
which stability class gave rise to the worst case at each
downw4nd location.
DETERMINATION OF AND
¥ z
The standard deviations of the crosswind and vertical
concentrations from the basic equation are o, and {~,,
respectively.
Once the atmospheric stability category has been deter-
med, EPIcode uses the equations given in Table 2 to es-
timate o and o for two terrain types--Standard and City.
The City terrain factor accounts for the increased plume
dispersion from crowded structures and the heat retention
characteristics of urban surfaces, such as asphalt and. con-
crete. The City terrain factor will estimate lower concentra-
tions than the Standard factor, due to the increased disper-
sion from large urban structures and materials. Choosing
Standard terrain will give the most conservative estimates.
Table 2. Equations used to determine c~ and ~,. This
methodology is derived from Briggs, 1973.
Pasquill Oy Oz
ttpe (mi (mi
Open Country
A 0.22x (1 + O.0001x)-1/2 0.20x
B 0.16x (1 + 0.0001x)-1/2 0.12x -1/2
C 0.11x(l + 0.000Ix)-1/2 0.08x(1 + 0.0002x) 1/2
D 0.08x (1 + O.0001x)-1/2 0.06x[1 + 0.0015X)~l-
E 0.06x (l + 0.000Ix)-1/2 0.03x (1 + 0.0003x)_1
F 0.04x (l + O.0001x)-1/2 0.016x(1 + 0.0003x)
City
A-B 0.32x {1 + 0.0004x)-1/2 0.24x {1 + 0.001x)1/2
C 0.22x (l + O.O004x)-1/2 0.20x
-112 -ti2
D 0.16x (1 + 0.0004x) ..~ 0.14x (1 + 0.0003x) -1/2
E-F 0.11x (1 + 0.0004x)-l/z 0.08x (1 + 0.00015x)
x = downwind distance, m
For brief (puffl releases of less than ten minutes, the ex-
perimental data Indicate that that cry and o, are smaller by
about a:factor of two ($1ade, 1968). EPIcode automatically
uses the following algorithms to determine the short-term
standard deviations, cry' and o,'. These values replace the
cry and o, in the basic Gausstan equation.
The new oy' and o,' are a factor of two smaller than cry and
oz for release durations less than or equal to one minute.
For durations between one and ten minutes, the factor is
linearly interpolated, as shown below.
Release Duration, t
(rnin) o,' ~.'
t> 10 C~ ~.
l<t<_10 c~,/(-0.11t + 2.1 1) ~./(-0.11t + 2.11)
t < 1 C~,/2 ~./2
In a term release and for plume travel times [dtstance/u(H)]
longer than 10,000 seconds, the "continuous' plume os are
more characteristic of the observed diffusion process. For
long plume travel times, °nly continuous-plume os are
used. The transition between puff and continuous os
begins at plume travel times of 1000 seconds and is com-
plete by 10,000 seconds.
Wincl Sl~eecl Variation with Height
The wind speed a user inputs to EPIcode is the estimate for
a height of two meters. However, the Gaussian plume
equation requires the wind speed at height H, the effective
release height. EPIcode automatically uses the following
power-law formula to determine the wind speed for all
effective heights greater than two meters.
u(H) = u(2) [ ~----]P
where u(2) = surface wind speed (m/s) at 2 meters height. H = effective release height (m).
P = factor from Table 3.
Table 3. Exponential factor used by EPIcode for calcu-
latin~ wind speed variation with height (from Irwin
(1979).
Stabmty Clu.
A B C D E F
City 0.15 "0.15 0.20 0.25 0.40 0.60
standsrd
terrain 0.07 0.07 0.10 0.15 0.35 0.55
PLUME DEPLETION
Very small particles and gases or vapors are deposited on
surfaces as a result of turbulent diffusion and Brownlan
motion. Chemical reactions, lmpaction, and other bio-
logical, chemical, and physical processes combine to keep
the released substance at ground level. As this material
deposits on the ground, the plume above becomes depleted.
EPIcode uses a source-depletion algorithm to adjust the air
concentration in the plume to account for this removal of
material.
The source term in EPIcode is allowed to decrease W/th
downwind distance. The code accomplishes this by multi-
plying the original source term by a source-depletion factor,
DF(x). The evaluation of this depletion factor has been
described by Van der Hoven (in Slade. 1968).
The equation used in EPIcode is: v ;-~-
DF(x) = exp 1 H 2 dx
o,_ (x) exp [~. oz (x"~'-~
A-il
where:
DF(x) = Depletion factor.
x = Downwind distance.
v = Deposition velocity. The deposition velocity
is empirically defined as the ratio of the ob-
served deposition rate (e.g., mg/m2 · s) and
the observed air concentration near the
ground surface (e.g., mg/m3}.
u = Average ground level {2 m) wind speed.
H = Effective release height of chemical.
o, (x) = Standard deviation of the air concentration
distribution in the vertical direction (z axis)
for either Standard or City terrain, as
applicable.
The default values for the deposition velocities used in
EPIcode are:
Physical form
of substance v (cra/s)
Solid 1
Gas/vapor O. 1
Unknown O. 1
These default values can be changed by the user if more.
applicable information is available (e.g.. increased deposi-
tion due to chemical reactivity, etc.).
ACCURACY
The many uncertainties associated with the variables in the
Gaussian model, such as fluctuations in the meteorological
conditions, or type of terrain, result in a degree of impreci-
sion in the calculated ground level concentrations. If
inappropriate meteorological data. source term assump-
tions, effective stack height, etc.. are input into the pro-
gram. large errors are possible in the EPIcode estimates.
Given accurate input assumptions, the standard deviation
of the ground concentration as calculated by EPIcode is
thought to be approximately a factor of five. In other
words, 68% of the time (i.e.. the percentage of observations
within + 1 standard deviation, assuming a Gaussian distri-
bution) the calculated ground-level concentration will be
within a factor of 5.
Other percentages can be inferred from the Gaussian
distribution. If C is the calculated ground-level concen-
tration, this means that 50% of the time the true concen-
tration should lie between C/3 and 3C; and 80% of the
time between C/8 and 8C. For example, ff the calculated
value were 300 ppm. at least haft of the time you would
expect the true value to lie between 100 ppm and 900 ppm.
BAKERSFIELD CITY FIRE DEPARTMENT
~ FORM 4A-1 Page 1 of 1
NON--TRADE SECRETS
HAZARDOUS MATERI ALS I NVENTORY
SINESS NAME: San doaquin Community Hospital OWNER NAME: San doaquin Comm. Hospital Corp. FACILITY UNIT #:
DRESS: 2615 Eye Street ADDRESS: 2615 Eye Street FACILITY UNIT NAME:
TV, ZIP: Bakersfi'eld California CITY,ZIP: Bakersfield California
ONE ~: 805-327-1711 PHONE ~: 805-327-1711 IOFFIClAL USE CFIRS CODE
{
ONLY
2 3 4 5 6 ? 8 9 1 0
E MAX ANNUAL CONT USE [,OCATION IN THIS ,~ BY HAZARD D.O.T
E AMOUNT AMOUNT UNIT CODE CODE FACILITY UNIT WT. CHEMICAL OR COMMON NAME CODE GUIDE
M,, 1020 LBS 4080 LBI:LBS 04 36 BASEMENT NW CORNER 100% ETH LENE OXIDE (SEE ATTACHED MSDM) NFLG ....
M 192.5FT3 840 FT3 FT3 04 27 2ND FLOOR SW CORNER 100% HELIUM (SEE ATTACHED MSDS) NFLG
M 322FT3 2760FT3 FT3 04 27 2ND FLOOR SW CORNER, 100% OXYGEN (SEE ATTACHED MSDS) NFLG
M 560FT3 2016FT3 FT3 04 27 2ND FI OOR SW CORNFR lnn% NlT~nl[q n~fn~ (SEE ATTACHED MSDS) NFLG,,
M 3600FT3 10,800 FT3 04 27 2ND FLOOR SW CORNER 100% NITROGEN fSEE ATTA~ZHED MSDS~ NFl C~
W 5 GAL. 200 GAL.GAL. 06 TEST. NW CORNER HISTOLOGY 100% XYLENE {SEE ATTACHED MSDS) ORME
W 5 GAL. 188 GAL,GAL. 07 40 SE CORNER PHARMACY 100% ANTINEOPLASTIC DRUGS fSEF MSDS) ~RMF
M 700GAL. 350 GAL.iSAL. 01 19 NE CORNER BEHIND O,B, 100% UNDERGROUND DIESEL {SC~ M8DS) 2 FLGS
~ .m100GAL. 50 GAL. GAL. 01 19 NE CORNER BEHIND O.B. 100% GASOLINE (UNDERGROUND TANK) (MSDS) FLGS
M 3000GAL. IO00GAL. GAL. O1 19 NW CORNER BY GENiERATO 100% UNDERGROUND DIESEL 2ND TANK (MSDS) FLGS
M 60 GAL. 500 GAL.SAL. O1 29 S~ STORAGE BUILDING 100% ?AINT (SEE MSDS) ORMA
M 55 GAL. 55 GAL. GAL. O1 29 SE STORAGE BUILDING 100% PAINT TMINNFR (Mgn~ ORMA
BILL MARTIN TITLE: DIR. of SECURITY SIGNATURE:~/z~,~'7~~i ~ DATE:
~NCY CONTACT: BILL MARTIN TITLE: DIR. of SECURITY ' PHONE ~ BUS HOURS: 327-1711
AFTER BUS HRS: 872-529!
V CONTACT: KEVIN FISHER TITLE: ASSIST. ADMIN. of FINANCB~HONE * BUS HOURS: 327-1711
nUSINESS ACT~VIT-Y: MEDICAL FACILITY AFTER BUS. HRS: 871,-2607
BAKERSFIELD CITY FIRE DEPARTMENT ~
~ FORM 4A- 1 Page 1 o f 1
NON--TRADE SECRETS
HAZARDOUS MATERI ALS INVENTORY
SINESS NAME: San doaquin Community Hospital OWNER NAME: San Joaquin Conm. Hospital Corp. FACILITY UNIT #:
DRESS: 2615 Eye Street ADDRESS: 2615 Eye Street FACILITY UNIT NAME:
TV ziP: B'akersfield California CITY ZIP: Bakersfiel-d California
ONE ~': 805-327-1711 PHONE ~: 805-327-1711 OFFICIAL USE CFIRS CODE
I
ONLY
2 3 4 5 6 7 8 9 1 0
E MAX ANNUAL CONT USE LOCATION IN THIS % BY HAZARD D.O.T
.E,. AMOUNT AM0,UNT UNIT CODE CODE FACILITY UNIT WT, CHEMICAL OR COMMON NAME CODE GUIDE
M 1020 LBS 4080 LB~;LBS 04 36 BASEMENT NW CORNER 100% ETHYLENE OXIDE (SEE ATTACHED MSDbl) NFLG
M 192.5FT3 840 FT3 FT3 04 27 2ND FLOOR SW CORNER. 100% HELIUM (SEE ATTACHED MSDS) NFLG
M 322FT3 2760FT3 FT3 04 27 2ND FLOOR SW CORNER 100% OXYGEN (SEE ATTACHED MSDS) NFLG
M 560FT3 2016FT3 FT3 04 27 2ND FLOOR SW CORNFR lOn~ NrTl~n~ n~Tn~ (SEE ATTACHED MSDS) NFLG
M 3600FT3 10,800 FT3 04 27 2ND FLOOR SW CORNER 100% NITROGEN (SEE ATTA~ZHED MSDS~ NFl G
W 5 GAL. 200 GAL GAL. 06 TEST. NW CORNER HISTOLOGY 100% XYLENE (SEE ATTACHED MSDS) ORME
W 5 GAL. 188 GAL GAL. 07 40 SE CORNER PHARMACY 100% ANTINEOPLASTIC DRUGS (SEE MSDS) ORME
M 700GAL. 350 GAL.GAL. 01 19 NE CORNER BEHIND O,B, 100% UNDERGROUND DIESEL (SEE MSDS) 2 FLGS
_M 100 GAL, 50 GAL. GAL. 01 19 NE CORNER BEHIND O.B. 100% GASOLINE (UNDERGROUND TANK) (MSDS) FLGS
M 30.OOGAL. iO00GAL. GAL. O1 19 NW CORNER BY GENERATOI 100% UNDERGROUND DIESEL 2ND TANK {MSDS) FLGS
M 60 GAL. 500 GAL.GAL. 01 29 SE STORAGE BUILDING 100% PAINT (SEE MSDS) ORMA
M 55 GAL. 55 GAL. GAL. 01 29 SE STORAGE*BUILDING 100% PAINT TMTNNFR (M%~l.q) ORMA
BILL MARTIN T~TLE: DIR. of SECURITY SIGNATURE: DATE:
7NCY CONTACT: BILL MARTIN T~TI, E: DIR. of SECURITY ' PHONE ~ BUS HOURS: 327-1711
AFTER BUS HRS: 872-5291
V CONTACT: KEVIN FISHER TrTLE.' ASSIST. ADMIN. of FINANCEPHONE , BUS HOURS: 327-1711
~t)StNESS ACTIV~T-¥ :__MEDICAL FACILITY AFTER BUS. HRS: 871-2007
(GI-I~ O1~) G~I'E D~.zRAM _ FAGI~ D~ ','"
..... ~F.OL~ND PLOOF. l='L-.,,kH '~
( Impegta~ Gonmmnl~ ):