United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park. NC 27711
EPA-454/R-92-024
(Revises EPA-450/4-88-009)
December 1992
Air
& EPA
WORKBOOK OF SCREENING
TECHNIQUES FOR ASSESSING
IMPACTS OF
TOXIC AIR POLLUTANTS
(REVISED)
-------
EPA-454/R-92-024
WORKBOOK OF SCREENING
TECHNIQUES FOR ASSESSING
IMPACTS OF
TOXIC AIR POLLUTANTS
(REVISED)
U.S. Environmental Protection Agency
Region 5, Library (PL.-12J)
77 West Jackson Boulevard, 12th Floor
Chicago, IL 60604-3590
Office Of Air Quality Planning And Standards
Office Of Air And Radiation
U. S. Environmental Protection Agency
Research Triangle Paric, NC 27711
•
December 1992
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This report has been reviewed by the Office Of Air Quality Planning And Standards, U. S. Environmental
Protection Agency, and has been approved for publication. Any mention of trade names or commercial
products is not intended to constitute endorsement or recommendation for use.
EPA-454/R-92-024
(Revises EPA-450/4-88-009)
u
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PREFACE
This document supersedes the workbook version dated September
1988. Changes include: development of new methods for estimating
emission rates; revisions to methods for esitmating emission rates
to establish consistency with current guidance; addition of several
new scenarios, especially those related to Superfund/ and the
addition of a new screening method based on the work of Britter and
McQuaid to estimate the impact of aerosols and denser-than-air
gases released from chemical spills. Ambient concentrations are
now illustrated by using the TSCREEN model instead of hand
calculations. Thus, users comparing the predicted maximum ground
level concentrations with those shown in the earlier document will
now find different, and more accurate, estimates.
111
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ACKNOWLEDGEMENTS
This report was prepared by Pacific Environmental Services,
Inc., under EPA Contract No. 68D00124, with Mr. Jawad S. Touma as
the Work Assignment Manager.
IV
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TABLE OF CONTENTS
PREFACE
ACKNOWLEDGEMENTS iv
1.0 INTRODUCTION 1-1
2.0 SELECTION OF SCREENING TECHNIQUES FOR TOXIC AIR
CONTAMINANTS 2-1
2.1 Release Categorization 2-1
2.2 Limitations and Assumptions 2-1
2.3 Scenario Selection 2-3
2 .4 Determining Maximum Short'-Term Ground Level
Concentration 2-17
2.4.1 Dispersion Models used in TSCREEN .... 2-17
2.4.2 Dispersion Model Selection 2-17
2.5 Considerations for Time-Varying and Time-Limited
Releases 2-24
2.6 Denser-Than-Air Materials 2-25
2.7 Dispersion Screening Estimates for Denser-Than-Air
Contaminants 2-26
3.0 SUPPORT DATA FOR SCREENING ESTIMATES .' 3-1
3.1 Meteorological Data 3-1
3.1.1 Wind Speed and Direction 3-1
3.1.2 Stability and Turbulence 3-2
3.1.3 Temperature 3-3
3.1.4 Atmospheric Pressure .., 3-3
3.2 Chemical and Physical Parameters 3-3
4.0 SCENARIOS AND TECHNIQUES FOR RELEASE AND EMISSIONS
ESTIMATES 4-1
4.1 Particulate Matter Release 4-2
4.1.1 Releases from Stacks, Vents 4-2
4.1.2 Continuous Fugitive/Windblown Dust
Emissions 4-11
4.1.3 Ducting/Connector Failures . . - 4-17
4.2 Gaseous Release 4-23
4.2.1 Continuous Flared Stack Emissions -
Gaseous 4-23
4.2.2 Continuous Release from Stacks, Vents,
Conventional Point Sources 4-28
4.2.3 Continuous Gas Leaks from a Reservoir . . 4-34
4.2.4 Instantaneous Gas Leaks from a Reservoir . 4-67
4.2.5 Continuous Gas Leaks from a Pipe Attached
to a Reservoir 4-69
4.2.6 Instantaneous Gas Leaks from a Pipe
Attached to a Reservoir 4-87
4.2.7 Continuous Multiple Fugitive Emissions . . 4-89
4.2.8 Continuous Emissions from Land Treatment
Facilities 4-93
4.2.9 Continuous Emissions from Municipal Solid
Waste Landfills 4-97
v
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4.2.10 Continuous Emissions of Pesticides .... 4-103
4.2.11 Instantaneous Discharges from Equipment
Openings 4-108
4.3 Liquid Release 4-112
4.3.1 Continuous Evaporation from Surface
Impoundments (Lagoons) 4-112
4.3.2 Continuous (Two-Phase) Release Rate
Estimates: Saturated Liquid from
Pressurized Storage 4-116
4.3.3 Instantaneous (Two-Phase) Release Rate
Estimates: Saturated Liquid from
Pressurized Storage 4-124*
4.3.4 Continuous (Two-Phase) Release Rate
Estimates': Subcooled Liquid from
Pressurized Storage 4-126
4.3.5 Instantaneous (Two-Phase) Release Rate
Estimates: Subcooled Liquid from
Pressurized Storage 4-134
4.3.6 Continuous High Volatility Leaks 4-136
4.3.7 Instantaneous High Volatility Leaks . . . 4-144
4.3.8 Continuous Low Volatility Liquids from
Tanks and Pipes 4-146
4.3.9 Instantaneous Low Volatility Liquids from
Tanks and Pipes : 4-155
4.4 Superfund Releases 4-162
4.4.1 Air Strippers 4-162
5.0 ATMOSPHERIC DISPERSION ESTIMATES 5-1
5.1 SCREEN 5-2
5.1.1 Point Sources .• 5-2
5.1.2 Area Sources 5-14
5.2 RVD 5-19
5.2.1 Inputs 5-19
5.2.2 Model Output 5-21
5.3 PUFF 5-26
5.3.1 PUFF Model Discussion 5-26
5.3.2 Model Inputs 5-28
5.3.4 Model Output 5-30
5.4 Britter-McQuaid ' 5-33
5.4.1 Method for Cold Contaminant Releases — Heat
Transfer Effects ". . 5-34
5.4.2 Method for Contaminant Aerosol Releases . 5-34
5.4.3 Continuous (Plume) Releases 5-36
5.4.4 Instantaneous (Puff) Releases 5-41
5.4.5 Assumptions in TSCREEN 5-45
5.4.6 Model Inputs 5-46
5.4.7 Model Output 5-47
REFERENCES R-l
VI
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APPENDIX A EMISSION FACTORS A-l
APPENDIX B ESTIMATING SELECTED PHYSICAL PROPERTIES OF
MIXTURES B-l
APPENDIX C SELECTED CONVERSION FACTORS C-l
APPENDIX D AVERAGING PERIOD CONCENTRATION ESTIMATES . . D-l
VII
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1.0 INTRODUCTION
This workbook provides a logical approach to the selection
of appropriate screening techniques for estimating ambient
concentrations due to various toxic/hazardous pollutant releases.
Methods used in the workbook apply to situations where a release
can be fairly well-defined, a condition typically associated with
non-accidental toxic releases. The format of this workbook is
built around a series of release scenarios which may be
considered typical and representative of the means by which toxic
chemicals become airborne. This document supersedes the earlier
workbook (EPA, 1988a).
Screening techniques are simplified calculational procedures
designed with sufficient conservatism to allow a determination of
whether a source: 1) is clearly not an air quality threat or 2)
poses a potential threat which should be examined with more
sophisticated estimation techniques or measurements. Screening
estimates obtained using this workbqok represent maximum short-
term ground level concentration estimates from a meteorological
perspective. If the screening estimates demonstrate that during
these conditions the ground level concentrations are not likely
to be considered objectionable, further analysis of the source
impact would not be necessary as part of the air quality review
of the source. However, if screening demonstrates that a source
may have an objectionable impact, more detailed analysis would be
required using refined emissions and air quality models.
For each release scenario, the workbook describes the
procedure to be used and provides an example illustration using
the TSCREEN model. TSCREEN, a model for screening toxic air
pollutant concentrations, is an IBM PC-based interactive model
that implements the release scenarios and methods described in
this workbook. TSCREEN allows the user to select a scenario,
determine an emission rate, and then apply the appropriate
dispersion model in a logical problem solving approach. The
model consists of a front-end control program with many
interactive menus and data entry screens. As much information as
is logically and legibly possible is assembled onto unique data
entry screens. All requests for input are written in clear text.
Extensive help screens are provided to minimize numeric data
entry errors, and default values are provided for some
parameters. The user is able to return to previous screens and
edit data previously entered. A chemical look-up database and an
on-line calculator are also available. Once the nature of the
release is determined, the user must specify the emission rate.
For some scenarios, extensive references to EPA methods are
provided, while for others, a specific method for calculating the
emission rate is given. Density checks for the release are
performed to determine which dispersion model is selected. Data
necessary to execute that particular model is then requested in a
logical format. Once the model is executed, the concentrations
are calculated and then tabulated in a clear and legible manner,
1-1
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and an- easy to read graph of concentration versus distance is
provided. The printed text and graphical output can be sent to a
variety of printers and plotters through built-in software;
minimum user interface is required.
The front-end program in TSCREEN is written in the FoxPro™
programming language, a superset of the dBASE language family
suitable for PC's running MS-DOS™. The primary purpose of a
dBASE language is database manipulation, but is can also be used
for general purpose programming. The reasons for using this
system are: 1) a user interface which facilitates the debugging
process, and as a result, reduces the development cost/ 2) pull-
down menus and windows which require minimal programming effort
to create,- 3) built-in functions for database manipulation, and
as a result, much less code is required to create the chemical
database in TSCREEN; 4) memory management capabilities that allow
TSCREEN to run on machines with less random access memory (RAM);
and 5) the ability to release most of the TSCREEN front-end
program from memory before it executes the dispersion models.
The main disadvantage of th'is system is the size of the files
that a user needs to run. The system is distributed with two
run-time libraries. These are files that contain the
implementation of functions that are called by the program. One
of these libraries is over 300 kilobytes (K) and the other is
close to 1 megabyte (MB). TSCREEN is distributed through the
EPA's Technology Transfer Network, SCRAM Bulletin Board System.
The workbook is organized into five sections and six
supporting appendices. Section 2 discusses selection of
screening techniques and the general approach to using the
workbook. Users are advised to consult this section both for
releases explicitly presented in the workbook and for less
typical releases. This section also considers assumptions,
limitations and conservatism of estimates. Section 3 describes
the support data (i.e., meteorological data and chemical and
physical parameters) needed for making estimates. Section 4
presents the inputs required for each scenario and the applicable
methods for determining release (emission) rates. This section
also includes an example showing the data entry screening and
sample calculations for each scenario as used in TSCREEN. (Note:
the values that TSCREEN produces may be slightly different than
the values in the examples due to differences in rounding.) In
this workbook 24 release scenarios have been selected to
represent situations likely to be encountered. Section 5
describes the dispersion models that are referenced in this
workbook and are embedded in TSCREEN.
Appendix A discusses currently available sources for
obtaining emission factors that can be used for some of the
scenarios. Appendix B provides a method for estimating selected
physical properties for mixtures. Appendix C provides some
useful unit conversion factors applicable to the workbook.
1-2
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Appendix D provides some techniques for converting concentrations
calculated by the models to different averaging times.
Methods used in this workbook should be applied with
caution. Techniques for estimating emissions are evaluated and
revised on a continuing basis by EPA. Thus the user should
consult with EPA on the most recent emission models and emission
factors. Meteorological methods presented in this workbook
reflect guidance published elsewhere, and in particular the
Guideline on Air Quality Models (Revised) (EPA, 1986) and its
supplements. The Regional Modeling Contact should be consulted
as to the present status of guidance on air quality modeling.
•1-3
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2.0 SELECTION OF SCREENING TECHNIQUES FOR TOXIC AIR CONTAMINANTS
This workbook attempts to account for many of the scenarios
expected to produce toxic chemical releases to the atmosphere.
2. 1 Release Categorization
Selection of appropriate technique for screening estimates
requires categorization of the toxic chemical release of .
interest. There are three overlapping categories which should be
considered when defining problems for screening:
1) Physical State - Gaseous releases to the atmosphere can,
in general, be simulated using techniques developed for
criteria air pollutants unless the gas is dense, is
highly reactive, or rapidly deposits on surfaces.
Additional source modeling must be performed if the
release is liquid, aerosol or multi-phased to determine
the state of the material as it disperses in air.
2) Process/Release Conditions - Knowledge of the
circumstances under which chemicals are released helps to
determine both state and dispersive characteristics. For
example, location of a leak in a pressurized liquefied
gas storage tank will determine if a release is liquid or
gas and if source modeling is required prior to
dispersion estimates.
3) Dispersive Characteristics - Techniques for pollutant
dispersion estimates are categorized by terms such as
instantaneous versus continuous, or point versus area, or
volume releases. To complete dispersion estimates, this
final characterization is required at some point in
concentration calculations.
The primary emphasis of this workbook is to serve as an
accompanying guide to the TSCREEN program which implements
screening techniques for estimating short-term, ground level
concentrations of toxic chemicals released to the atmosphere.
However, in order to do this, the workbook also provides
assistance to the user in formulating the release conditions.
2.2 Limitations and Assumptions
Methods included in TSCREEN are intended to provide
simplified screening estimates for situations which-may represent
extremely complex release scenarios. As such, the methods are
limited in their applicability. Some of these limitations are as
follows:
• Screening techniques provided are intended for use on
small to mid-scale non-accidental releases.
2-1
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All techniques assume that the toxic air contaminant is
non- reactive and non-depositing. Thus these screening
methods are not applicable for reactive gases and
particle depositions. For two-phase flows, all released
liquid is assumed to travel downwind as an aerosol with
insignificant (liquid) rain out near the source.
Denser-than-air contaminant behavior is a consequence not
only of the initial (depressurized) contaminant density
but also of the contaminant release rate and the ambient
wind speed; if denser-than-air contaminant behavior is
not expected to be important, passive atmospheric
dispersion modeling techniques should be applied. In
TSCREEN Version 3.0, the determination of denser-than-air
behavior is done based on the initial contaminant density
comparison to ambient air.
Conditions resulting in worst case concentrations cannot
be uniquely defined where meteorological conditions
affect source estimates. For example, in the case of
evaporation, the highest emission rates are related to
high wind speeds, which, however, result in more dilution
and lower ambient concentrations.
Time dependent emissions cannot be simulated with these
simple screening technique. Techniques provided assume
steady releases for a specified period.
All release calculations assume ideal conditions for gas
and liquid flows.
B •
The influence of obstructions such as buildings and
topography on denser-than-air releases and releases close
to the ground are not included.
Complicated post-release thermodynamic behavior for
denser-than-air releases is not accounted for in these
screening techniques.
Because of the simplifying assumptions inherent in these
screening methods, which are specifically aimed at decreasing the
amount of information required from the user and decreasing the
computation time and sophistication, more refined assessment
techniques should be applied to a release scenario which"is
identified by these screening procedures as violating ambient air
quality standards or other specified levels of concern. Refined
techniques involve both refined release (emission) rate estimates
as well as more refined atmospheric dispersion models. (See for
example, "Guidance on the Application of Refined Dispersion
Models for Air Toxics Releases" (EPA, 1991a).) As with any air
quality assessment, the screening methods described here should
be applied with due caution.
2-2
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2.3 Scenario Selection
Release scenarios are grouped according to four categories:
particulate matter, gases, liquids, and releases from Superfund
sites as shown in Table 2-1. For some of'the categories, there
are additional subcategories. Figure 2-1 provides a graphical
illustration of each release scenario. Descriptions on similar
release scenarios are provided to help guide the user in
selecting the correct release category. Once the correct release
category has been selected, the user should proceed to the
relevant section where further information on the release
scenario is given. For each release scenario, methods for
determining emission estimates are provided and then the
appropriate dispersion model is selected to determine ambient
concentrations.
2-3
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TABLE 2-1
RELEASE SCENARIOS
Initial Form of Release
Release Type
Scenario Modeling
Nunber Category*
Particulate Matter
Gases
Liquid
Continuous Particulate Release from Stack, Vents
Fugitive/Windblown Dust Emissions
Ducting/Connector Failures
Flared Stack Emissions
Continuous Releases from Stacks, Vents, Point Sources
Continuous Leaks from Reservoir
Instantaneous Leak from Reservoir
Continuous Leaks from Pipe Attached to Reservoir
Instantaneous Leak from Pipe Attached to Reservoir
Gaseous Emissions from Multiple Fugitive Sources
Gaseous Emissions from Land Treatment Facilities
Emissions from Municipal Solid Waste Landfills
Emissions from Pesticides/Herbicide Applications
Discharges from Equipment Openings
Evaporation from Surface Impoundments (Lagoons)
Continuous 2-Phase Saturated Liquid from Pressurized Storage
Instantaneous 2-Phase Saturated Liquid from Pressurized Storage
Continuous 2-Phase Subcooled Liquid from Pressurized Storage
Instantaneous 2-Phase Subcooled Liquid from Pressurized Storage
Continuous High Volatility Liquid Leaks
Instantaneous High Volatility Liquid Leaks
Continuous Lou Volatility Liquid Leaks
Instantaneous Low Volatility Liquid Leaks
1.1
1.2
1.3
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
CP
CA
IP
CP
CP
CP
IP
CP
IP
CA
CA
CA
CA
IP
CA
CP
IP
CP
IP
CP
IP
CA
IP
Superfund Sites
Air Stripper
4.1
CP
* c - Continuous
P - Point
A - Area
I - Instantaneous
Table 2-1 shows that, for example, a continuous gaseous release
from stacks, vents and point sources is given Scenario number 2.2.
Figure 2-1 provides a graphical illustration and a brief description
of this scenario. Figure 2-2 (Section 2.4) shows that this scenario
is discussed in detail in Section 4.2.2 and that the SCREEN dispersion
model is selected within TSCREEN to estimate ambient ground level
concentrations for this scenario.
2-4
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Figure 2-,l. Schematic Illustrations of Scenarios
Continuous Releases of Particulate Matter from Stacks, Vents -1.1
Similar Releases: Continuous emissions of particulate matter
from vertical stacks and pipes or conventional point sources and
some process vents when emission flow rates and temperature are
known. Combustion sources and chemical reactors are typical
emission sources that may emit such pollutants through stacks.
These releases may also be due to a process failure such as a
rupture disk release or failure of control equipment.
Continuous Fugitive/Windblown Dust Emissions - 1.2
Fugitive Dust
Similar Releases: Any fugitive dust from process losses,
generated by mechanical action in material handling or windblown
dust. Such emissions tend to originate from a surface or a
collection of small poorly defined point sources.
2-5
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Particulate Releases from Ducting/Connector Failures - 1.3
Fugitive
Dust —*
Similar Releases; Instantaneous bursts of particulates due to
duct failure (e.g., pneumatic conveyor line failures), line
disconnection, isolation joint failure, or other types of
equipment openings.
Continuous Flared Stack Emissions - 2.1
Emissions
Flare
Similar Releases: Flares are used as a control device for a
variety of sources. As such flares must comply with requirements
specified in 40 CFR 60.18.
2-6
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Continuous Release from Stacks, Vents, Conventional
Point Sources - 2.2
Similar Releases: Continuous emissions of a gas from vertical
stacks and pipes or conventional point sources and some process
vents when emission flow rates and temperature are known.
Combustion sources and chemical reactors are typical emission
sources that may emit such pollutants through stacks. These
releases may also be due to a process failure such as a rupture
disk release or failure of control equipment.
Continuous Gaseous Leaks from Reservoir - 2.3
Emissions
Leaking flange
Similar Releases: Continuous release of a gas (at constant
pressure and temperature) from a containment (reservoir) through
a hole or opening. Possible applications include a gas leak from
a tank, a (small) gas leak from a pipe, or gas discharge from a
pressure relief valve mounted on a tank.
2-7
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Instantaneous Gaseous Leak from Reservoir - 2.4
Instantaneous
Gaseous Emission
Blown Rupture Disk
Similar Releases: Instantaneous release of a gas (at constant
pressure and temperature) from a containment (reservoir) through
a hole or opening. Possible applications include a gas leak from
a tank, a (small) gas leak from a pipe, or gas discharge from a
pressure relief valve mounted on a tank.
Continuous Leaks from a Pipe Attached to a. Reservoir - 2.5
Similar Release: Continuous release of a gas
pressure and temperature} from a containment
a long pipe.
(at constant
reservoir) through
2-8
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Instantaneous Leaks from a Pipe Attached to a Reservoir - 2.6
Similar Release: . Instantaneous release of a gas (at constant
pressure and temperature) from a containment (reservoir) through
a long pipe.
Continuous Multiple Fugitive Emissions - 2.7
Range Leaks
Hand Valve Stem
Pump Seals
Open Ditches
Similar Releases: Releases from any continuous area or volume
source where the emissions are uniformly released over the area
or the area represents a collection of small sources poorly
defined in terms of location (e.g., multiple vents on large
manufacturing buildings, fugitive VOC sources in refineries or
chemical process manufacturing plants).
2-9
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Continuous Emissions from Land Treatment Facilities - 2.8
Emissions
Organic Sludge
SoiJ Treatment
Similar Releases: Landfarms; ground level application of sludge
(containing volatile organic material in oil) to soil surface.
Continuous Emissions from Municipal Solid Waste Landfills - 2.9
Emissions
Similar Releases: None. Emission rates applicable, to municipal
solid waste landfills only.
2-10
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Continuous Emissions from Pesticides/Herbicide Applications
2.10
Emissions
Similar Releases: Emissions resulting from the volatilization of
pesticides or herbicides applied to open fields.
Instantaneous Discharges from Equipment Openings - 2.11
• Chemical
Reactor
Emissions
Coke Oven
Similar Releases: 'Any puff or burst type release with short
duration emissions resulting from the opening of equipment after
processing (e.g., coke ovens or chemical reactors), from routine
sampling of product processing or gaseous emissions from
disconnected lines.
2-11
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Continuous Evaporation from Surface Impoundments (Lagoons) - 3.1
Similar Releases ; Waste lagoons and other impoundments with
emissions resulting from the evaporation of volatile chemicals
from liquid mixtures with biological activity.
Continuous 2-Phase Saturated Liquid from Pressurized Storage -
3.2
Liquid Phase ontad in Qts Phaa»
Emissions /
Similar Releases: Continuous-release of a pressurized liquid
stored under saturated conditions. The release occurs (at
constant pressure and temperature) from the containment
(reservoir) through a hole or opening; a provision is made for
the effect of a pressure drop (piping) between the tank and the
hole or opening. Possible applications include a saturated
liquid leak from a pressurized tank or a saturated liquid leak
from a pipe.
-------
Instantaneous 2-Phase Saturated Liquid from Pressurized Storage
3.3
Emissions UquM Phase canted In Gas Phase
Similar Releases; Instantaneous release of a pressurized liquid
stored under saturated conditions. The release occurs (at
constant pressure and temperature) from the containment
(reservoir) through a hole or opening; a provision is made for
the effect of a pressure drop (piping) between the tank and the
hole or opening. Possible applications include a saturated
liquid leak from a pressurized tank or a saturated liquid leak
from a pipe.
Continuous Subcooled Liquid from Pressurized Storage - 3.4
Relief
Valve
Liquid Phase canted In Gas Phase
Emissions /
Similar Releases: Continuous release of pressurized liquid
stored below its saturation pressure. The release occurs (at
constant pressure and temperature) from a containment (reservoir)
through a hole or opening; a provision is made for the effect of
a pressure drop (piping) between the tank and the hole or
opening. Possible applications include a subcooled liquid leak
from a pressurized tank or a subcooled leak from a pipe.
2-13
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Instantaneous Subcooled Liquid from Pressurized Storage - 1.5
Emissions
Similar Releases: Instantaneous release of pressurized liquid
stored below its saturation pressure. The release occurs (at
constant pressure and temperature) from a containment (reservoir)
through a hole or opening; a provision is made for the effect of
a pressure drop (piping) between the tank and the hole or
opening. Possible applications include a subcooled liquid leak
from a pressurized tank or a subcooled leak from a pipe.
Continuous High Volatility Liquid Leaks
Emissions M|f|!®8,
- 3.6
Pipe
Emissions
Hole
Tank
Similar Releases: Continuous release of high volatility liauid
(at constant temperature and pressure) from a containment
(reservoir) through a hole or opening. Possible applications
include a (high volatility) liquid leak from a tank or a liquid
leak from a pipe (when the ratio of the hole diameter to the pipe
diameter is less than 0.2).
2-14
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Instantaneous High Volatility Liquid Leaks - 3.7
Emissions
T^ \jl QWIV
Pipe
Emissions
Tank
Hole
A.
Similar Releases: Instantaneous release of high, volatility
liquid (at constant temperature and pressure) from a containment
(reservoir) through a hole or opening. Possible applications
include a (high volatility) liquid leak from a tank or a liquid
leak from a pipe (when the ratio of the hole diameter to the pipe
diameter is less than 0.2).
Continuous Low Volatility Liquid Leaks - 3.8
Tanks
Pipe
Leaking Pipe Range
Similar Releases; Continuous release of liquid whose normal
boiling point is above ambient temperature. A low volatility
material stored at moderate to low pressure (and where the
boiling point is above storage temperature) will typically be
released as a liquid and form a pool or puddle on the ground.
The (conservative) assumption is that the liquid evaporates at
the same rate it is spilled (except when the liquid is confined
by a bund dike from which liquid does not overflow). Possible
applications include a (low volatility) liquid leak from a tank
or a pipe.
2-15
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Instantaneous Low Volatility Liquid .Leaks - 3.9
Tanks
Pipe
Similar Releases: Instantaneous release of liquid whose normal
boiling point is above ambient temperature. A low volatility
material stored at moderate to low pressure (and where the
boiling point is above storage temperature) will typically be
released as a liquid and form a pool or puddle on the ground.
The (conservative) assumption is that the liquid evaporates at
the same rate it is spilled (except when- the liquid is confined
by a bund dike from which liquid does not overflow). Possible
applications include a (low volatility) liquid leak from a tank
or a pipe.
4.1 Air Strippers
"Clean"
Air
Air
Contaminated
Water
Clean" Air
Pump
•Clean' Water
Similar Releases: None.
2-16
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2.4 Determining Maximum Short-Term Ground Level Concentration
2.4.1 Dispersion Models used in TSCREEN
Maximum short-term ground level concentrations in TSCREEN
are based on three current EPA screening models (SCREEN, RVD, and
PUFF) and the Britter-McQuaid screening model. All four models
are embedded in the TSCREEN model. SCREEN is a Gaussian
dispersion model applicable to continuous releases of particulate
matter and non-reactive, non-dense gases that are emitted from
point, area, and flared sources. The SCREEN model implements
most of the single source short-term procedures contained in the
EPA screening procedures document (EPA, 1988c.) This includes
providing -estimated maximum ground-level concentrations and
distances to the maximum based on a pre-selected range of
meteorological conditions. In addition, SCREEN has the option of
incorporating the effects of building downwash. The RVD model
(EPA, 1989) provides short-term ambient concentration estimates
for screening pollutant sources emitting denser-than-air gases
and aerosols through vertically-directed jet releases. The model
is based on empirical equations derived from wind tunnel tests
and estimates the maximum ground level concentration at plume
touchdown at up to 30 downwind receptor locations. The PUFF
model (EPA, 1982) is used where the release is finite but smaller
than the travel time (i.e., an instantaneous release.) This
model is based on the Gaussian instantaneous puff equation and is
applicable for neutrally buoyant non-reactive toxic air releases.
The Britter-McQuaid model (1988) provides an estimate of
dispersion of denser-than-air gases from area sources for
continuous (plume) and instantaneous (puff) releases. Further
discussion on model assumptions'is given in Chapter 5.0.
2.4.2 Dispersion Model Selection
Figure 2-2 shows which screening model is associated with
each scenario. In TSCREEN, ambient impacts of releases from
pressurized storage vessels (and pipes) or liquid releases are
evaluated using the following test. The release density p2
(kg/m3) is compared with ambient density, pair (kg/m3) . If the
release density is more than ambient density (i.e., j02//oair > 1),
then the release is considered denser-than-air. For denser-than-
air releases (both continuous and instantaneous), TSCREEN uses
the RVD model if the release is a^ vertically-directed jet and the
Britter-McQuaid model for all other releases. For releases that
are considered passive (i.e., p2/p3il <_ 1) , TSCREEN uses the SCREEN
model for a continuous release and the PUFF model for an
instantaneous release.
If the release density is greater than ambient density
(i.e., P2/P& > 1), a further determination of the importance of
denser-than-air behavior based on contaminant release rate and
the ambient wind speed is made after calculating the Richardson
number (see below). Since for many applications (e.g., planning
2-17
-------
analyses) the actual wind speed is not known, this method is not
used in TSCREEN (version 3.0). The following shows how the user
may approach the problem.
2-18
-------
Figure 2-2. Model Selection
Paniculate Hitter
Release Type
TSCREEN
Gaseous
Release Type
Liquid
Release Type
Superfund
Release Type
Stacks, Vants
4.1.1
PARTICULATE MATTER
RELEASE TYPE
Fugitive/Windblown
Oust Emissions
4.1.2
SCREEN
Area
Ducting/Connector
Failures
4.1.3
SUPERFUND RELEASE TYPE
Air Stripper
4.4.1
SCREEN
Point
2-19
-------
GASEOUS RELEASE TYPE
Flared Stack Emissions
4.2.1
Land Treatment Facilities
Stacks. Vent*. Conventional
Point Sources
4.2.2
Multiple Fugitive Sources
4.2.7
Pesticide/Herbicide Applications
4.2.10
Leaks from Reservoir
Discharges from Equipment
Openings
4.2.11
Leaks from Pipe
Attached To Reservoir
2-20
-------
LIQUID RELEASE TYPE
2-Phase Saturated Liquid
From Pressurized Storage
Surfacs
Impoundment*
4.3.1
Z-Phase Subcooled Liquid
From Pressurized Storage
Contln- .
uous
4.3.2
Instan-
taneous
4.3.3
YES
YES
2-21
-------
2.4.2.1 Continuous Release
1. Perform buoyancy check as a first check.
A. Calculate the density of air using the following:
(2.4-1!
where R = 8314 (J/kg-mole-°K). The molecular weight of
air is assumed equal to 28.9 (kg/kmol), and atmospheric
pressure is 101325 (Pa).
B. If p2/Pair > !/ then the buoyancy is negative; go to steps
2 or 3. Otherwise, buoyancy is neutral or positive and
the SCREEN model for a point source should-be used.
2. For a vertically directed jet release, the release
Richardson number, Ri, is calculated using the following
equation:
Ri = g Ui-1 Qm/u D0 p2 U20 (U./ulo)2 (2.4-2)
where g is the acceleration of gravity (m/s2) , p2 is the
plume density (kg/m3) , p^ is the ambient density (kg/m3) , Qm
is the exhaust gas mass flow rate (kg/s), u is the wind
velocity at the.top of the stack (m/sec), D0 is the stack
diameter (m) , u10 is the wind velocity at 10m above the
ground, U./UIQ is the ratio of friction velocity (m/s) to the
wind speed at 10m (m/s). In version 2.0 of the RVD model,
this ratio is assumed to equal 0.06 for all atmospheric
stability classes. The value of u is calculated via the
equation:
u = u,0 (hs/10)P (2.4-3)
where h, is the stack height (m) and p is the wind speed
profile exponent, which varies as a function of atmospheric
stability. By using g = 9.81 m/s2, u = 1 m/sec, u,/uto =
0.06, u!0 = 1 m/s, the Richardson number is reduced to:
(p.
Ri = 2,725 —i-1
(2.4-4!
2-22
-------
U = 1 m/sec was chosen as a screening method for determining
denser-than-air effects. However, denser-than-air effects
do not always correspond to largest hazard extent.
3. For other denser-than-air releases, Britter-McQuaid
recommend that denser-than-air effects be ignored if:
<0.005 (2.4-5)
where g is the acceleration of gravity (m/s2) , E is the
release rate in kg/s, D is the (low-momentum) horiaontal
dimension of the source(m), Ur is the wind speed at 10 m
(m/s), p2 is the discharge (depressurized) density of air
(kg/m3) . See Section 5.0 for additional explanation.
Thus, if the wind speed during the release is known, then it
can be inserted in the equation and a determination can be
made whether a dense gas model should be used. Selections
are summarized in the table below:
TABLE 2-2
MODEL SELECTION FOR CONTINUOUS RELEASE
Continuous
1. Buoyancy Check
2. Vertically Directed Jet
3. Other
Criteria
Pj/P«r < 1
Pz/P- > 1
Yes - Ri > 30
Ri < 30
No - (Go to '3. Other')
Ri < (1/6)3
Ri > (1/6)3
Passive
(Go to '2. or 3.')
Dense
Nondense
Dense
Passive
Models
SCREEN
RVD
SCREEN
B-M
SCREEN
4.2.2 Instantaneous Release
1. Perform buoyancy check as a first check.
A. Calculate the density of air using equation 2.4-1.
B. If PI/p^ > I/ then the buoyancy is negative; go to step 2
or 3. Otherwise, buoyancy is positive and the PUFF model
will be used.
2. For a vertically directed jet release, calculate the release
Richardson number as shown in equation 2.4-4.
3. For other denser-than-air releases, Britter-McQuaid
recommend .that denser-than-air effects be ignored if.:
2-23
-------
- Pa
g (E,/p2)
Tl/2
s 0.2
(2.4-7)
where g is the acceleration of gravity (m/s2) , p2 is the
discharge density (kg/ra3) , p^ is the ambient density
(kg/m3) , E, is the total amount of material released (kg) ,
and Ur is the wind speed at 10 m (m/s).
If denser-than-air effects are determined to be important,
then the Britter-McQuaid model is used. Otherwise, the
release is considered non-dense (passive) and the PUFF model
applies. Selections are summarized in the.table below:
TABLE 2-3
MODEL SELECTION FOR INSTANTANEOUS RELEASE
Continuous
Criteria
Models
1. Buoyancy Check
Pl/P«r i
P2/P* >
Passive
(Go to '2. or 3.')
PUFF
2. Vertically Directed Jet
3. Other
Yes - Ri.> 30
Ri < 30
No - (Go to '3. Other')
BH Criteria > 0.2
BM Criteria < 0.2
Dense
Nondense
Dense
Passive
RVD
PUFF .
B-M
PUFF
2.5 Considerations for Time-Varying and Time-Limited Releases
A release is considered time-varying if the release rate
varies with time. Typically, this behavior might be expected
because the reservoir pressure and temperature vary with time.
As discussed in Chapter 4, reservoir pressure and temperature
would be expected to vary with time if the release rate was very
large in comparison with the reservoir volume. For these
conditions, the release rate decreases with time so that the
maximum release rate can be determined from initial reservoir
(stagnation) conditions. Therefore, a screening method which
uses the initial reservoir conditions would be expected to
overestimate the release rate; this overestimation could be quite
large depending on the situation.
A release is considered (only) time-limited if the release
rate is constant over the duration of the r-alease, but the
release duration is short in comparison with other important time
scales (e.g., the averaging time used to assess the toxicity, or
the cloud travel time to a downwind position of interest).
Typically, this behavior might be expected if, for example, an
automatic shutoff system is assumed to stop the release after a
specified (generally short) time period. The release rate for
time-limited releases can still be estimated using the screening
2-24
-------
methods outlined in Chapter 4; the total amount of material
released Q could then be estimated by Qm Td where Qm is the
release rate and Td is the release duration. (i.e., Q = Qm Td)
Finally, a release may be both time-varying and
time-limited. As in the time-varying case, a screening method
which uses the initial reservoir conditions can be used to (over)
estimate the release rate, and the total amount released Q could
again be estimated by Qm Td where Qm is the release rate and Td is
the release duration. Of course, the (estimated) total amount
released can not exceed the amount of material on hand before the
release.
2.6 Denser-Than-Air Materials
In this workbook, the discussion of gas leaks are for
materials stored as a gas which remains entirely in the gas phase
throughout the depressurization process. Two-phase leaks can
result for materials which are stored under pressure and will
depressurize when released to the atmosphere. This
depressurization will then result in the formation of two
contaminant phases (saturated liquid and vapor). Two-phase leaks
occur for gases which cool so that condensation occurs during the
depressurization process, and for high volatility liquids
(liquids whose normal boiling point is below the ambient
temperature) which are stored typically above ambient pressure.
For screening purposes, a release from the liquid space is
considered to form an aerosol when the liquid is stored at a
temperature above its boiling point (and ambient pressure); this
assumption becomes more unrealistic as the storage pressure
approaches ambient pressure (or equivalently as the storage
temperature approaches its boiling point).
A high volatility liquid is considered to be a material
whose boiling point is below the ambient temperature; a high
volatility material will be released as a liquid if the storage
pressure is near ambient pressure whereas release from high
pressure storage will result in aerosol formation; aerosol
formation is assumed when the liquid is stored at a temperature
above its (depressurized) boiling point. In contrast, a low
volatility liquid is considered to be a material whose boiling
point is above the ambient temperature; a low volatility material
stored at moderate to low pressure (and where the boiling point
is above the storage temperature) will typically be released as a
liquid and form a pool or puddle on the ground. Releases of low
volatility materials typically do not exhibit denser-than-air
effects. Table 2-4 summarizes this information.
2-25
-------
TABLE 2-4
(DEPRESSURIZED) RELEASE PHASE FOR SCREENING PURPOSES*
Storage Phase (Depressurized) Release Phase
Gas Gas
Aerosol possible (when T2 < Tb)
High Volatility Liquid Liquid (TB > T,)
-------
been extensively compared to the large number of recent field
test programs aimed at studying denser-than-air contaminants;
some similarity models (e.g., DEGADIS) have been found to
reproduce the range of the field results quite well.
Unfortunately, this success comes at the (modest) cost of
preparation time and user sophistication which may not entirely
fit the mold of a screening program, but in fact, this "state-of-
the-art" implies that proven similarity models should be the next
tool applied if a screening program identifies a release scenario
as a potential problem.
3. Correlation models are based on a dimensional analysis of
the important parameters which influence the important dependent
variables (e.g., distance to a given concentration level and area
covered by a plume or puff) and on information gathered from
field test results, laboratory results, and other mathematical
models. The stated objective of a correlation-based model is to
fit the observed data (on which it is based) within a certain
factor (typically two). Because of the nature of a simple
correlation, this approach is well suited for use in a screening
program. The RVD and the Britter-McQuaid models are derived from
correlations based on different wind tunnel experiments.
The screening techniques presented here are designed to
identify release scenarios which may violate safety or health
criteria. The simplifying assumptions inherent in these
screening methods are specifically aimed at decreasing the amount
of information required from the user and decreasing the
computation time and sophistication. More refined assessment
techniques should be applied to a release scenario which is
identified by these screening procedures as violating safety or
health criteria. As with any hazard assessment, these screening
techniques should be applied with due caution.
Refined release rate estimates may involve more detailed
analysis of the specifics of the release as well as application
of more refined engineering methods (e.g., Lees (1980) and Perry
et al. (1984)). Refined atmospheric dispersion models which
account for denser-than-air contaminant.behavior (such as
DEGADIS; Spicer and Havens (1989)) can be applied. It should be
noted that the screening assumptions inherent in the methods
suggested by Britter and McQuaid (1989) and the RVD model (EPA,
1989) may become less justifiable for contaminants with more
complicated thermodynamic behavior after release to the
atmosphere -- particularly ammonia (NH3) , liquefied natural gas
(LNG) , and hydrogen fluoride (HF) ,• more sophisticated atmospheric
dispersion models may be used to account for such circumstances.
2-27
-------
3.0 SUPPORT DATA FOR SCREENING ESTIMATES
Simulations of air toxic releases require information on the
meteorological conditions at the time of release as well as
physical and chemical parameters describing the materials being
released.
3.1 Meteorological Data
Computational procedures for estimating concentrations
require data on wind speed and direction, temperature and
atmospheric pressure. These data are normally collected at
National Weather Service stations and some military installations
on an hourly basis. Stability and turbulence parameters can be
estimated from cloud data as described below. A record of these
is available from the National Climatic Data Center, Asheville,
North Carolina and also from the EPA's SCRAM BBS. On-site
meteorological data are sometimes recorded at air quality
monitoring sites. Use of the on-site data with proper quality
assurance procedures as described in On-site Meteorological
Program Guidance for Regulatory Modeling Applications (EPA,
1987c) is preferred.
3.1.1 Wind Speed and Direction
Wind speed and direction data are required to estimate
short-term peak concentrations. Wind speed is used to determine
(1) plume dilution, (2) plume rise and (3) mass transfer in
evaporation models. These factors, in turn, affect the magnitude
of, and distance to, the maximum ground-level concentration.
•
Most wind data are collected near ground level. The wind
speed at release height can be estimated by using the following
power law equation:
u =
where: u = the wind speed (m/s) at release height h (m),
ut = - the wind speed at the anemometer height z
(m),
p = the stability-related exponent from Table 3-1.
3-1
-------
TABLE 3-1
WIND PROFILE EXPONENT AS A FUNCTION OF ATMOSPHERIC STABILITY
Stability Class
A
a
c
0
E
F
Rural Exponent
0.07
0.07
0.10
0.15
0.35
0.55
Urban Exponent
0.15
0.15
0.20
0.25
• 0.30
0.30
The wind direction is an approximation for the direction of
transport of the plume. The variability of the direction of
transport over a period of time is a major factor in estimating
ground-level concentrations averaged over that time period.
3.1.2 Stability and Turbulence
Stability categories, as depicted in Tables 3-1 and 3-2,
are indicators of atmospheric turbulence. The stability category
at any given time depends upon thermal turbulence (caused by
heating of the air at ground level) and mechanical turbulence (a
function of wind speed and surface roughness). Stability is
generally estimated by a method given by Turner (1970), which
requires information on solar elevation angle, cloud cover, cloud
ceiling height, and wind speed (see Table 3-2).
TABLE 3-2
KEY TO STABILITY CATEGORIES
Surface Wind *~
Speed at Height
of 10m (m/sec)
<2
2-3
3-5
5-6.
>6
Day
Incoming Solar Radiation"
Strong
A
A-B
B
C
C
(Insolation)
Moderate
A-B
B
B-C
C-0
0
Slight
B
C
C
0
D
Might"
Thinly Overcast or £
4/8 Low Cloud Cover
F
E
D
0
0
5 3/8
Cloud
Cover
F
F
E
D
D
The neutral class (D) should be assumed for all overcast conditions during day or night.
Night is defined as the period from one hour before sunset to one hour after sunrise.
Appropriate insolation categories may be determined through the use of sky cover and solar elevation
information as follows:
3-2
-------
Sky Cover (Opaque or Total)
4/8 or Less or Any Amount of
High Thin Clouds
5/8 to 7/8 Middle Clauds
(7000 feet to 16,000 foot
base)
Solar Elevation
Angle > 60"
Strong
Moderate
Solar Elevation
Angle < 60"
But > 35°
Moderate
Slight
Solar Elevation
Angle < 35"
But > 15°
Slight
Slight
5/8 to 7/8 Low Clouds (less
than 7000 foot base) Slight Slight Slight
The solar elevation angle is a function of the time of year
and the time of day, and is presented in charts in the
Smithsonian Meteorological Tables (List, 1968). The hourly
weather observations of the National Weather Service include
cloud cover, cloud ceiling height, and wind speed. Methods for
estimating atmospheric stability categories from on-site data are
provided in EPA modeling guidelines.
Friction velocity (u.) represents mechanical turbulence due
to wind flow over the surface and is used in calculating the
release Richardson number. Friction velocity is a function of
stability, decreasing with increasing stability. An
approximation of friction velocity under neutral stability
conditions and assuming a roughness length of 1 cm is:
u. = 0.0 6u
where u is the wind speed (m/s) at a height of 10 m.
3.1.3 Temperature
Ambient air temperature must be known in order to calculate
the amount of rise of a buoyant plume and to calculate
evaporation rates.
3.1.4 Atmospheric Pressure
. Atmospheric pressure data are used in calculating gas and
liquid release rates from storage and process vessels and pipes.
3.2 Chemical and Physical Parameters
Numerous chemical and physical properties of contaminants
are required to perform some of the emission estimation
techniques presented. TSCREEN includes a chemical database which
contains values that can be automatically returned to data entry
fields. For information on the use of the Chemical Database see
Appendix D - Running TSCREEN. A list of the chemical properties
from TSCREEN's Chemical Database is shown.in Figure 3-1.
3-3
-------
Figure 3-1. TSGREEN's Chemical Database
Chemical Data
Chemical Name % r /' ; - '
Boiling Point at Ambient Pressure.
Specific Heat of Liquid
at Constant Pressure
at Constant Volume
Specific Heat of Vapor
at Constant Pressure
at Constant Volume
Molecular Weight
Latent Heat of Vaporization
Liquid Density
Critical Temperature
J/kg "K
/ J/kg °K
-" J/kg °K
J/kg '<
kg/kmol
J/kg
kg/cubic m
Edit
Delete
Exit View. Screen
The complexity and diversity of chemical and physical behavior of
many air toxic substances make it critical that the correct input
parameters are obtained. These parameters can be found in
compendiums of physical and chemical characteristics. Three of
the more comprehensive sources of information are listed in the
reference section.
The user should be cautioned that a characteristic "constant"
used in modeling may have different values depending on the
reference from which the parameter was obtained.
3-4
-------
4.0 SCENARIOS AND TECHNIQUES FOR RELEASE AND EMISSIONS ESTIMATES
Techniques for estimating air toxics emissions must be
capable of treating a large variety of potential release
scenarios. This section is intended to help the user identify
the applicable release scenario, determine release and emission
rates, and to guide the user through the scenario inputs into
TSCREEN. Scenarios addressing various types of particulate,
gaseous, and liquid releases are presented in this workbook. In
addition there are scenarios typically found at Superfund sites.
If the appropriate scenario choice is not obvious, consult the
descriptions of similar releases that accompanies the graphical
illustrations shown in Section 2.3 or the EPA Regional Modeling
Contacts.
Since many various processes and sources have the potential
for toxic chemical releases, the scenarios do not cover all
possible release, emission, and dispersion combinations. In all
applications, the characterization of emissions is a critical
step which is best met through a complete and accurate
measurement program. In practical applications, measured data
are seldom available and the user is left to techniques such as
those presented in this section, data from existing inventories,
emission factors, or process specific material balance estimates.
Some of the numerous sources of existing data are permits
and files, technical literature, and SARA Title III reporting
forms. A new data source summarizing regulatory data is the
National Air Toxics Information Clearinghouse (NATICH) and Data
Base. Information on NATICH is available through the EPA
Regional Air Toxics Contacts, Air/Superfund Coordinators and :'
Pollution Assessment Branch (MD-12)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
(919) 541-0850
For some sources, mass balances are used to estimate
releases when conservative assumptions concerning quantities of
input and output streams are made. The amounts entering and/or
leaving a process can be measured or estimated. A mass balance
can then be performed on the process as a whole or on the
subprocess. For processes where material 'reacts to form a
product or is significantly changed, use of mass balance may be
too difficult for estimating emissions and the use of emission
factors may be more appropriate.
When measured or plant specific data are unavailable, the
user is advised to review emission factors developed for specific
processes. Appendix A provides a description of sources of
emission factors. Emission factors represent average conditions
and do not necessarily provide a conservative estimate of total
emission rate.
4-1
-------
4.1 Particulate Matter Release
A particulate matter release is a release of any solid
material such as particulates, dust, or ash.
4.1.1 Releases from Stacks. Vents
Similar Releases: Continuous emissions of particulate matter
from vertical stacks and pipes or conventional point sources and
some process vents when emission flow rates and temperature are
known. Combustion sources and chemical reactors are typical
emission sources that may emit such pollutants through stacks.
These releases may also be due to a process failure such as a
rupture disk release or failure of control equipment.
Discussion:
Emission rates from such sources can be determined through
source testing using EPA. Reference Methods (40 CFR Part 60
Appendix A) or "Screening Methods for the Development of Air
Toxics Emission Factors", EPA-450/4-91-021 or process
calculations. If source-specific emissions are not available,
representative emission factors can be substituted. Emission
factors are available for individual toxic compounds (Appendix
A). Otherwise, factors determined by compiling extensive source
test results using EPA Reference Methods are reported in AP-42.
Since the input is source specific, there is'no input
section for this scenario. If this scenario is selected, TSCREEN
directly accesses the SCREEN model input section for a point.
source. See Section 5.1.1 for a complete list of inputs.
4-2
-------
Limitations and Assumptions:
For screening, particulate deposition is assumed to be
ins igni f i cant.
Input Information:
D diameter at release point (m)
V volumetric flow rate (m3/s)
4.1.1.1 Procedure:.
1. Exit Velocity. Calculate the exit velocity Vs (m/s) through
a stack as follows:
V, = _LY_ (4.1.1-1)
7T D2
4.1,1.2 Example: Cadmium emission
Discussion:
A facility .emits 0.0029 tons per year of cadmium through a
stack that is 16 meters above ground. The stack inside diameter
is 0.1 meters, the stack exit temperature is 298 °K, and the
volumetric flow rate is 0.14 m3/s. The stack is adjacent to a
square building with height and building dimensions equal to
19 m. The site is classified as rural, with complex terrain
being present. Concentrations at'a receptor located 25 meters
from the stack is required.
The following information will be required to use the SCREEN
model (see Section 5.1.1):
B,,^ building maximum horizontal dimension (19 m)
BJHU, building minimum horizontal dimension (19 m)
D diameter at release point (0.1 m)
H, release height above ground (16 m)
Hb building height (19 m)
Qm emission rate (0.0029 tons per year is equal to 9.3x-iO"*
g/s)
T, temperature of the material released (298 °K)
Ta ambient temperature (298 °K)
V volumetric flow rate (0.14 m3/s)
Procedure;
1. Exit Velocity. Calculate the stack gas exit velocity from
Equation (4.1.1-1):
4-3
-------
4 . 0.14mVs =17>8m/s
3.14 (.l)2m2
Data entry in the TSCREEN model for this example is shown below:
— Continuous Participate Releases from Stacks, Vents - Scenario 1.1
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 7
Enter a unique title for "this data's model run:
''' ......... """ ...... """" ........ '""
RELEASE PARAMETERS
Emission Rate (Qm) -> ?,3S?-4 g/s
Exit Velocity (Vs)-> If.tt m/s
Release Height above Ground 14 m
Diameter at Release Point (D) -> .1 • m
Temperature of the Material Released (Ts) -> 298 °K
AMBIENT PARAMETER
Ambient Temperature (Ta) -> 298
— Continuous Participate Releases from Stacks, Vents - Scenario 1.1
SCREEN MODEL INPUTS - Page 2 of 7
BUILDING PARAMETERS
Building Height (enter 0 if no building) -> t9 m
Minimum Horizontal Building Dimension -> 1^ m
Maximum Horizontal Building Dimension -> T9 m
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural -> B
FENCELINE DISTANCE
Enter the distance from the base of the stack
to the plant fenceline ->
"'-'8aft " t»r«*i f.
SIMPLE TERRAIN
Are receptors above stack-base T
SIMPLE NON-FLAT TERRAIN
You have terrain between stack base and stack top.
Do you have receptors above ground level
(i.e. Flag Pole Receptors) (Y/N) -> K
screen
$*»««•
4-4
-------
2. In this example, there are receptors at or below stack top,-
therefore, "Y" is entered for the "terrain type" question.
3. In this example, there are receptors above stack base;
therefore, "Y" is entered, for the "simple terrain"
question.
Since "Y" was entered, proceed to step 5.
The question "Do you have specific locations where you would
like pollution concentrations calculated (Y/N)" will be
skipped at this point, but it will be asked after the user
has finished entering terrain elevations on page 4 of 7.
In this example, receptors are at ground level/ therefore,
"N" is entered for the "flag pole receptor" question.
Since "Y" was entered in Step 3, proceed to Step 7.
The prompt "You have completed simple terrain inputs. Do
you want to continue with complex terrain (Y/N)" will be
skipped at this point but will appear later.
Continuous Particulate Releases from Stacks, Vents - Scenario 1.1
SCREEN MODEL INPUTS/SIMPLE TERRAIN STAIRSTEP SEARCH - Page 4 of 7
Enter distance and terrain elevation for "stair-step search".
Enter a blank Maximum Distance to stop input.
Distance (meters)
Minimum Maximum Height (meters)
100 fence
200
400
800
1200
Last Maximum Distance will be extended to 50000 m
IB,,,
^i'-^ '
In this example, the terrain elevations for four distance
ranges are shown above. After entries are complete a window
will appear with the prompt listed in Step 4.
In this example, there are specific locations of interest;
therefore, proceed to Step 8.
4-5
-------
— Continuous Particulate Releases from Stacks, Vents - Scenario 1.1-
SCREEN MODEL INPUTS DISCRETE RECEPTORS - Page 5 of 7
Enter a height and distance(s) from the source to terrain feature(s)
at which a specific receptor Mill be located.
Enter a blank after the distance to stop inputs for that height.
Enter a blank height to stop input.
Height (m)
**; :"
Distances (m)
Height..(m)
Distances (m)
188 ••
Height (m)
Height (m) Height (m)
Distances (m) Distances (m) Distances (m)
In this example, the specific locations of interest are at
distances associated with terrain heights shown in the
figure above.
— — uoniinuous ranicuiaie neieases Tram abacus, vents • scenario i . i
SCREEN MODEL INPUTS COMPLEX TERRAIN - Page 7 of 7
Enter height and distance for receptor location.
Enter a blank Distance to stop input. '
Plume Height -> 18.1 m
Distance to Final Plume Rise -> 152.6 m
Height (m) Distance (m) Height (m) Distance (m)
1 IT ttJB
2 2» 155
3 25 ZOO
4 4? fOQa
5
6
7
a
9 - :
10 : : -:-
11
12
13
14
15
16 •
17
18
19
20 .
s^^.;i^i^^^^^^
In this example, terrain height for receptors above stack
top and distances to those heights are shown in the figure
above. The figure above shows that final plume height is
18.1 m and the distance to final plume rise is 152.6 m.
This information is useful in determining at what elevation
the plume will impact terrain and the user may wish to add
other receptor heights at this elevation to ensure
calculating the maximum concentration.
After the complex terrain inputs have been entered, TSCREEN
4-6
-------
runs the SCREEN model for a point source.
The SCREEN model output is displayed below:
*** SCREEN-1.2 MODEL RUM ***
*** VERSION DATED 90XXX ***
Participate Stack Release
COMPLEX TERRAIN INPUTS:
SOURCE TYPE = POINT
EMISSION RATE (G/S) = .9300E-03
STACK HT (M) = 16.00
STACK DIAMETER (M) = .10
STACK VELOCITY (M/S)= 17.80
STACK GAS TEMP (K) = 298.00
AMBIENT AIR TEMP (IC)= 298.00
RECEPTOR HEIGHT (M) = .00
IOPT (1=URB,2=RUR) a 2
1
*** SCREEN-1.2 MODEL RUN ***
*** VERSION DATED 91/10 **«
Participate Stack Release
SIMPLE TERRAIN INPUTS:
SOURCE TYPE = POINT
EMISSION RATE (G/S) - .9300E-03
STACK HEIGHT (M) = 16.00
STK INSIDE D1AM (M) = .10
STK EXIT VELOCITY (M/S)= 17.8000
STK GAS EXIT TEMP (K) = 298.00
AMBIENT AIR TEMP (K) = 298.00
RECEPTOR HEIGHT (M) = .00
IOPT (1=URB,2=RUR) = 2
BUILDING HEIGHT (M) = 19.00
MIN HORIZ BLDG DIM (M) = 19.00
MAX HORIZ BLDG DIM (M) - 19.00
***************************************
*** SUMMARY OF SCREEN MODEL RESULTS ***
11-30-92
15:05:25
11-30-92
15:05:25
CALCULATION
PROCEDURE
SIMPLE TERRAIN
COMPLEX TERRAIN
BUILDING CAVITY- 1
BUILDING CAV1TY-2
MAX CONC
(UG/M**3)
1.396
3.204
1.717
1.717
DIST TO 1
MAX (M)
105.
100.
28.
28.
rERRAIN
HT (M)
16.
17. (24-HR CONC)
-- (DIST = CAVITY LENGTH)
-- (DIST = CAVITY LENGTH)
***************************************************
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
***************************************************
BUOY. FLUX
.00 M**4/S**3; MOW. FLUX = .79 M**4/S**2.
4-7
-------
FINAL STABLE PLUME HEIGHT (N) = T8.1
DISTANCE TO FINAL RISE (M) = 152.6
TERR
HT '
(M)
MAX 24* HR PLUME HT PLUME HT
DIST CONC CONC ABOVE STIC CONC ABOVE STK U10M UST
(M) (UG/M**3) (UG/M**3) BASE (M) (UG/M**3) HOT (M) SC (M/S)
17. 100. 3.204 .1377E
20. 155. .4536E-02 .4536E
25. 200. .1232E-01 .1232E
47. 1000. .1047E-01 .1047E
BUOY. FLUX = .00 M**4/S**3;
*** FULL METEOROLOGY ***
*** SCREEN AUTOMATED DISTANCES *"
*** TERRAIN HEIGHT OF 1
DIST
STAB (M/S) (M/S) (M) HT (M) Y (M) Z (M) DWASH
400. .3688
500. .3214
600. .2840
700. .2537
300. .2289
6
6
6
6
6
MAXIMUM 1-HR CONCENTRATION
400. .3688
*** SCREEN AUTOMATED
***«****************<
6
1.0
1.0
1.0
1.0
1.0
AT OR
1.0
1.3
1.3
1.3
1.3
1.3
BEYOND
1.3
5000
5000
5000
5000
5000
400
5000
.0
.0
.0
.0
.0
. M:
.0
6.0
6.0
6.0
6.0
6.0
6.0
25
28
32
35
38
25
.7
.9
.0
.1
.2
.7
23
23
24
24
25
23
.3
.9
.4
.9
.4
.3
SS
SS
SS
SS
SS
SS
DISTANCES ***
*** TERRAIN HEIGHT OF 15. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES **
4-8
-------
DIST CONC U10M USTK MIX HT PLUME SIGMA SIGMA
(M) ++<&+++ * * *^*^^**^^ ^ ^^^^
25.4
6=F)
SS
4-9
-------
** TERRAIN HEIGHT OF 10. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES **
DIST CONC U10M USTK NIX HT PLUME SIGMA SIGMA
(UG/N**3) STAB (M/S) (M/S) (M) HT (M) Y (M) Z (M) DUASH
111.
222.
333.
*** SCREEN
1.230
.5581
.4084
DISCRETE
4
4
6
DISTANCES
«•«*«*•«««
1
1
1
*
.0
.0
.0
***
***
1.1
1.1
1.3
320
320
5000
.0
.0
.0
'6.0
6.0
6.0
13.0
21.2
23.6
16.0
22.5
22.9
SS
SS
SS
** TERRAIN HEIGHT OF 16. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES **
DIST CONC U10M USTK MIX HT PLUME SIGMA SIGMA
(M) (UG/M**3) STAB (M/S) (M/S) (M) HT (M) Y (M) Z (M) DWASH
105.
188.
299.
315.
1.396
.7250
.4471
.4353
4
4
6
6
1.0
1.0
1.0
1.0
1.1
1.1
1.3
1.3
320.0
320.0
5000.0
5000.0
.0
.0
.0
.0
12.6
18.2
22.5
23.0
15.7
20.9
22.7
22.8
SS
SS
SS
SS
DWASH" MEANS NO CALC MADE (CONC = 0.0)
DUASH=NO MEANS NO BUILDING DOWNWASH USED
DWASH-HS MEANS HUBER-SNYDER DOWNWASH USED
DWASH-SS MEANS SCHULMAN-SC1RE DOWNUASH USED
DWASH-NA MEANS DOWNWASH NOT APPLICABLE, X<3*IB
wmr www www www www wwwwwwwww»w w www ww w w w w www wwww w
* SUMMARY OF TERRAIN HEIGHTS ENTERED FOR *
* SIMPLE ELEVATED TERRAIN PROCEDURE *
TERRAIN DISTANCE RANGE (M)
HT (M) MINIMUM MAXIMUM
1.
5.
10.
15.
10.
10.
10.
16.
16.
16.
16.
100. 200.
200. 400.
400. 800.
800. 50000.
111.
222.
333.
105.
188.
299.
315.
*** CAVITY CALCULATION - 1 *** *** CAVITY CALCULATION -
CONC (UG/M**3) =
CRIT WS 310M (M/S) =
• CRIT US a HS (M/S) =
DILUTION US (M/S) =
CAVITY HT (M) =
CAVITY LENGTH (M) -
1.717 CONC (UG/M**3) =
1.00 CRIT US 310M (M/S) =
1.10 CRIT US 3 HS (M/S) =
1.00 DILUTION WS (M/S) =
27.28 CAVITY HT (M) =
27.97 CAVITY LENGTH (M) =
ALONGUIND DIM (M) = 19.00 ALONGUIND DIM (M) =
2 ***
1.717
1.00
1.10
1.00
27.28
27.97
19.00
*** END OF SCREEN MODEL OUTPUT ***
At 25 m from the stack, the receptor is in the cavity region and
the maximum concentration is 1.72 ^g/m3. The maximum
concentration, however, is 2.21 ptg/ra3 at a distance of 105 m from
the source in complex terrain 16 m above "stack base.
4-10
-------
4.1.2
ussions
FugtttoDust
Similar Releases: Any fugitive dust from process losses,
generated by mechanical action in material handling or windblown
dust. Such emissions tend to originate from a surface or a
collection of small poorly defined point sources.
Discussion:
These fugitive dust releases are generalized area emissions
originating from a surface or collection of small, poorly
quantified point sources. Emissions are either user-specified or
calculated with representative emission factors. Emission
factors for fugitive dust emissions are typically found in AP-42
and are assumed to be independent of wind speed for this
workbook. Toxic components can be determined using the methods
described in Appendix A, item 4. This example demonstrates
calculation of particulate emissions from storage piles and use
of particulate matter profiles to study a specific chemical.
Limitations and Assumptions:
'Worst case emission estimates are wind speed dependent.
For screening, particle desposition is assumed to be
insignificant.
Input Information:
s
P
w
m
D
percent silt content (%)
number of days per year with more than 25 mm of
precipitation (dimensionless)
percent of time wind speed exceeds 5.4 m/s (%)
pollutant percent of total mass (%)
diameter of storage pile (m)
4-11
-------
4.1.2.1 Procedure :
l. Emission Rate. Calculate emission rate for wind blown dust
(QJ (g/s) :
A. Emission Factor. Calculate the aggregate storage
emission factor for wind blown dust:
E (kg/dy /hectare) =1.9 (s/1.5) ~ (w/15) (4.1.2-1)
B. Area. Calculate the area (A) (m2) of the storage pile:
A(m2) ="-2 (4.1.2-2)
C. Convert. Convert the emission factor (E) in
kg/dy /hectare to g/s-m2:
E (g/s-m2) = E(kg/dy/hectare) 1000 (g/kg)
86400 (s/dy) 1000 (m2/hectare)
D. Emission Rate. Calculation of emission rate (Qm) in
g/s.
Qm (g/s) = E (g/s-m2) JJL A (m2) (4.1.2-3)
2. Run the SCREEN model for an area source. For an explanation
of inputs for the SCREEN model for an area source, see
Section 5.1.2.
4.1.2.2 Example: Emission from Pile of Flyash
Discussion:
Concentration estimates at the fenceline (100 m) are
required for arsenic emissions resulting from wind erosion from a
circular pile of flyash (3 m high, and 10 m in diameter) at a
secondary lead smelter blast furnace. Since the emissions factor
is not directly applicable, conservative assumptions are made
that the silt content is 50 percent, no days have precipitation
in excess of 25 mm and that 20 percent of wind exceeds 5.4 m/s.
The following information will be required:
s percent silt content (50 %)
p number of days per year with more than 25 mm of
precipitation (0)
w percent of time wind speed exceeds 5.4 m/s (20 %)
m percent of pollutant in total mass (.3 %)
D diameter of storage pile (10 m)
4-12
-------
Procedure ;
1. Emission Rate. Emissions factors for aggregate storage are
available in AP-42 as are particulate matter profiles
(Appendix A) . For this example, the profiles indicate that
arsenic makes up 0.3 percent of fine particles (less than
2.5 microns) emissions mass.
A. Emission Factor. Calculate the aggregate storage
emission factor for wind blown dust from Equation
(4.1.2-1) :
E (kg/dy /hectare) =1.9 (50/1.5) (3^"0) (20/15) =131.2
£* O J
B. Area. Calculate area (A) (m2) of the storage pile from
Equation (4.1.2-2) :
A = 3 . 14159 \ =78.5 (m2)
C. Convert. Convert emission factor (E) in kg/dy/hectare
to g/s-m2:
E = 131-5 (kg/dy/hectare) 1000 (g/kg) = Q Q0015 ( /S_m2)
86400 (s/dy) 1000 (m2/hectare)
D. Emission Rate. Since 0.3 % of this mass is arsenic,
calculate emission rate (Qm) in g/s from Equation
(4.1.2-3).
Qm = 0.00015 (g/s-m2) • °'3(%) • 78.5 (m2) = 0 .000036 (g/s)
2. TSCREEN will run the SCREEN model for an area source.
Data entry in the TSCREEN model for this example is shown below:
4-13
-------
Release of Fugitive/Windblown Oust Emissions - Scenario 1.2
SOURCE PARAMETERS - Page 1 of 1
Enter a unique title for this data's model run:
-!''
SOURCE TYPE
Enter S if source is a storage pile - 0 if other -> |
EMISSION RATE
Enter the Emission Rate (Qm), if unknown enter
the boxed variables belou to calculate -> HM18BB& g/s
Percent Silt Content (s) -> 56
Number of Days per Year the Precipitation
exceeds 25 mm (p) -> $
Percent Time Wind Speed exceeds 5.4 m/s (w) -> Z8
Percent of Pollutant in Total Mass (m) •> ,3
Diameter of Storage Pile (D) -> t &!:$;?£ m
•
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural -> R
FENCELINE DISTANCE
Enter the distance from the nearest edge of the
source to the plant fenceline -> 138 m
FLAG POLE RECEPTORS
Enter Receptor Height above Ground (Zr) -> 6 m
RECEPTOR LOCATIONS
Do you have specific locations where you would like
pollutant concentrations to be calculated (Y/N> -> Y
Edtt: Abort-
4-14
-------
SCREEN MODEL INPUTS
RECEPTOR LOCATIONS:
the source at which
Enter a blank after
Distance from
source (meters)
1 100 fence
2 ft? '
3 333
4 1609
5
6
7
8
9
10 - < _
- Page 2 of 2
Enter (up to 30) distances from
concentrations should be calculated.
the last distance to stop
Distance from
source (meters)
11
12
13 ;
14
15 ;
16
17
18
19
20
input.
Distance from
source (meters)
21 •"
22 .
23
24
25
26
27
28
29
30
,«a>«ftt -
-------
of the SCREEN model's data contains only points for the automated
distance array used by the model.
Oi
i
40
36
32
28
Em t salons fVom a P f I« oF F I
iFenceline
2 24
^^
X
220
2 16
h
h-
Z
UJ
O
Z 4
O
O
0,00 0.50
3.00 3.50 4.
4,50 5,!
DISTANCE (Km)
Maximum concentration 3.677E-001 ug/cubic ra at 0,100 Km (Automated Distances)
Press any key to continue
4-16
-------
4.1.3 Ducting/Connector Failures
Fugitive
Dust —*••
Similar Releases: Instantaneous bursts of particulate matter due
to duct failure (e.g., pneumatic conveyor line failures), line
disconnection, isolation joint failure, or other types of
equipment openings.
Discussion:
Limited information on powder releases from duct failures is
available in the technical literature. Crude estimates of
release amounts can be-made based on-transfer line rates and time
for equipment shutdown and equipment capacity. If possible, the
user should attempt to estimate the initial cloud dimension
resulting from dilution due to the mechanical action of the
release.' If initial dilution cannot be estimated by the user,
conservative concentration estimates can be obtained using an
instantaneous point source simulation with the PUFF model. There
is no release rate input section for this scenario. For this
scenario, TSCREEN goes directly to the PUFF model input section.
See Section 5.3 for a complete list of inputs.
Limitations and Assumptions:
For screening, particle deposition is assumed to be
insignificant.
Input Information^
Q total amount of material released (g)
H, release height above ground (m)
0y initial laterial dispersion (m)
-------
4.1.3 Ducting/Connector Failures
Fugitive
Dust —»•
Similar Releases: Instantaneous bursts of particulate matter due
to duct failure (e.g., pneumatic conveyor line failures), line
disconnection, isolation joint failure, or other types of
equipment openings.
Discussion:
Limited information on powder releases from duct failures is
available in the technical literature. Crude estimates of
release amounts can be made-based on transfer line rates and time
for equipment shutdown and equipment capacity. If possible, the
user should attempt to estimate the initial cloud dimension
resulting from dilution due to the mechanical action of the
release. If initial dilution cannot be estimated by the user,
conservative concentration estimates can be obtained using an
instantaneous point source simulation with the PUFF model. There
is no release rate input section for this scenario. For this
scenario, TSCREEN goes directly to the PUFF model input section.
See Section 5.3 for a complete list of inputs.
Limitations and Assumptions:
For screening, particle deposition is assumed to be
insignificant.
Input Information:
Q total amount of material released (g)
Hs release height above ground (m)
-------
4.1.3.1 Example: Failure of a Pneumatic Conveyor System
Discussion:
A failure of a pneumatic conveyor system carrying 3,3-
dichlorobenzidine powder from a spray dryer lasted 5 minutes.
Estimates are required for 15-minute average concentrations at
receptors downwind at or beyond the 100 m fenceline. The release
height is 10 m, the conveyance rate is 2 kg/s and the duct
diameter is 0.305 m.
The example represents a class of possible releases from
various types of gas-solid conveyance systems or reactor
failures. Common causes of this type of release are duct failure
due to abrasion or failure of flexible connectors. Short.
duration events can be simulated as instantaneous passively
dispersing puffs (i.e., all mass was released instantaneously
(within a few minutes)). The effect of this assumption is a
conservative estimate of the ambient concentration. In general,
powders emitted by this type of release will consist of
relatively large particles (greater than 10 /z) which would be
subject to gravitational fallout.
Procedure:
1. The release scenario would result in an initially high rate
of emissions which decreases rapidly as line pressure
decreases, as in a pipeline blowdown. A point source is
assumed because there was no indication of initial dilution
dimensions in the problem. The total emissions (Q) is:
Q = 5(min) 60(s/min) 2(kg/s) 1000(g/kg)= 600,000(g)
2. The release height is 10 m above ground, the initial lateral
and vertical dispersion parameters are 0 m, and the
fenceline distance is 100 m.
Data entry in the TSCREEN model for this example is shown below.-
4-18
-------
Ducting/Connector Failures - Scenario 1.3
Based on use input, PUFF model has been selected.
PUFF MODEL INPUTS - Page 1 of 2
Enter a unique title for this data's model run:
i^iS*^sbi^B«Si«^:.' s "::./. •:•„••
RELEASE PARAMETERS
Total Amount of Material Released (Q) ->
Release Height above Ground (Hs) -> t(
Initial Lateral Dispersion (.ay) -> ft
Initial Vertical Dispersion (oz) -> $•'
FENCELINE
Enter the distance from the nearest edge of the
source to the plant fenceline -> tf
9
m
m
JJBjct Scrwan <6E.c> fibcrt
Ducting/Connector Failures - Scenario 1.3
PUFF MODEL INPUTS - Page 2 of 2
AVERAGING TIME
Select Desired Averaging Time from menu below for graphic output:
Instantaneous (1 second)
1 minute (60 second)
5 minutes (300 seconds)
1 hour (&0fii seconds)
Selected Averaging Time: 15 minutes (900 seconds)
&di€ J>r*viOos Screen «F1S> (ton Model <£so Abort
The PUFF model's output is shown below:
Release from Puff Source
TOTAL AMOUNT OF MATERIAL RELEASED (G): .6000E+06
RELEASE HEIGHT ABOVE GROUND (M): 10.00
INITIAL LATERAL DISPERSION SIGMA (Y) (M): .0000
INITIAL VERTICAL DISPERSION SIGMA (Z) (M): .0000
*********************************
*** SUMMARY OF PUFF MODEL RESULTS ***
«*•«»*•«*«*«•«**««»•«««•««•««•«*•«•••**»**«««*»«*«««*••*
THE MAXIMUM CONCENTRATION AND THE DISTANCE TO MAXIMUM
CONCENTRATION FOR DISTANCES BEYOND FENCELINE .100 (KM).
FOR NEAR SURFACE RELEASE MAXIMUM CONCENTRATION WILL OCCUR AT
THE FENCELINE.
AVERAGING
TIME (MIN)
INSTANTANEOUS
1
5
15
60
**********»**»<
MAXIMUM
CONCENTRATION (G/M**3)
5.734E+01
1.764E+01
3.530E+00
1.177E+00
2.941E-01
i «»«»*••« »•«•••«•«•« «««•***«
DISTANCE TO
MAX. CONC. (KM)
.161
.221
.221
.221
.221
'•!»••««••<»««•
STABILITY
CLASS
N
N
N
N
N
4-19
-------
REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
noil «««««»•«« ««•««•«•<> «««i>«**<>«i>i»>i>*i> •••**•*••«••«
«««««««*«« »«>«»«> **«**«***•«•*•»
*** PUFF DISTANCES ***
«««r«»«l»l>««*«« «««««>«•«>*****•****
THE MAXIMUM CONCENTRATION AS A FUNCTION Of DOWNWIND DISTANCE
AND THE CONDITIONS THAT PRODUCED THE MAXIMUM AT THAT DISTANCE.
MIXING HEIGHT (M) 320.
WIND SPEED (M/SEC) 1.0
AVERAGING DOWNWIND DISTANCE (KM)
TIME (MIN) MAXIMUM CONCENTRATION (G/M**3) AT VARIOUS DOWNWIND DISTANCES.
STABILITY CLASS THAT PRODUCED THE MAX. LISTED BELOW
0.01 0.03 0.05 ' 0.07 0.1 0.5
====3Z======r=======X==3==33S=============================================
INST. 3.997E-I-01 3.376E+02 1.748E+02 9.261E+01 4.288E+01 1.359E+01
U U U U U N
1 2.005E+00 4.531E+01 3.745E+01 2.701E+01 1.732E+01 9.327E+00
U U U U U N
5 4.009E-01 9.062E+00 7.490E+00 5.403E+00 3.472E+00 2.073E+00
U U U U U N
•15 1.336E-01 3.021E+00 2.497E+00 1.801E+00 1.157E+00 6.910E-01
U U U U U N
60 3.341E-02 7.551E-01 6.242E-01 4.502E-01 2.893E-01 1.728E-01
U U U U U N
AVERAGING DOWNWIND DISTANCE (KM)
TIME (MIN) MAXIMUM CONCENTRATION (G/M**3) AT VARIOUS DOWNWIND DISTANCES.
STABILITY CLASS THAT PRODUCED THE MAX. LISTED BELOW
1.0 3.0 5.0 7.0 10.0 30.0
=========================r====================3======3r=r==================
INST. 3.239E+00 5.931E+00 2.976E+00 1.637E+00 8.060E-01 7.088E-02
S S S S S S
1 ' 2.610E+00 4.759E+00 2.709E+00 1.554E+00 7.837E-01 7.061E-02
N S S S S S
5 8.487E-01 1.232E+00 9.742E-01 7.200E-01 4.701E-01 6.436E-02
N S S S S S
*15 2.829E-01 4.108E-01 3.248E-01 2.411E-01 1.630E-01 3.736E-02
N S S .S S S
60 7.072E-02 1.027E-01 8.119E-02 6.027E-02 4.076E-02 9.529E-03
N S S S S S
STABILITY CLASSES
U = UNSTABLE
N = NEUTRAL
S = STABLE
* INDICATES AVERAGING TIME THAT WAS SELECTED FOR PLOTTING
********************************
*** END OF PUFF MODEL OUTPUT ***
********************************
The following is a graph of the PUFF model output. The data
that are plotted are for the averaging time that the user
selected from the second page of the PUFF model inputs. These
data are marked with an asterisk (*) above.
4-20
-------
20
R 16
u
3
2 12
^^
X
z18
2 8
t-
Z
U
o
o
0
Ipencaline
I
J
I
I
1
a 00 i.i
2.00 3.00 4.00 5.00 6.1
7.1
a 00 9.00 10.00
DISTANCE (Km)
Maximum concentration 1.177EH306 mlcrograras/abic meter at 0.221 Km
Press any key to continue
This is a plot of maximum concentration regardless of
meterological conditions. For example close to the source
unstable conditions produce the maximum concentrations. Beyond 3
km stable conditions produce the maximum concentration.
The output of the PUFF model consists of four parts. Part 1
summarizes the input parameters by the user. These values shoud
be checked to insure accurate entry. Part 2 of the model output
is a table that provides the maximum concentration and the
distance to maximum concentration for different averaging times.
In this table the minimum distance for concentration calculations
is the fenceline. For near surface releases, highest
concentrations will always occur at the fenceline. Part 3 of the
output is an extended table showing the maximum concentration
versus downwind distance (beyond fenceline) for four averaging
times and the atmospheric stability conditions that produced the
maximum. For a surface release, stable atmospheric conditions
produce maximum concentrations for all downwind distances and
averaging times. With increasing puff release height the
atmospheric stability conditions which produce the maximum
surface concentrations change. In this example, where the
release hiehgt is 10 m, unstable atmospheric conditions produce
4-21
-------
the maximum concentrations near the source. It is the values
from this table that are used to produce the plot of maximum
concentration versus downwind distance shown in the fourth part
of the output of the PUFF model. The plot, however, only
displays the averaging time selected by the user. : -
4-22
-------
4.2 Gaseous Release
A gaseous release is a release of any matter in vapor form
such as sulfur dioxide, volatile organics, etc.
4.2.1 Continuous Flared Stack Emissions - Gaseous
Emissions
Flare
Similar Releases: Flares are used as control devices for a
variety of sources. As such, flares must comply with
requirements specified in 40 CFR 60.18. Once emissions are
vented through the flare, a minimum 98% reduction of all
combus-tible components of the original emission must be achieved.
Discussion:
Flare problems are done in two parts, an emission
calculation and dispersion modeling. Toxic emissions for
permitted flares are reduced to 2% of the potential emissions
based on a required control efficiency of 98%. Flare problems
are similar to stack examples except that there are buoyancy flux
reductions associated with radiative heat losses and a need to
account for flame length in estimating plume height.
Flares are used as a control device for a variety of
sources. As such, flares must comply with requirements specified
in 40 CFR 60.18 if the flare is subject to the requirements of
Part 60 (New Source Performance Standards) or Part 61 (National
Emission Standards for Hazardous Air Pollutants). Not all flares
are subject to these requirements. Properly designed and
operated flares should be able to meet a 98% control requirement,
however, the actual control efficiency will depend on .whether the
flare is steam or air assisted,, whether the gases are combusted,
whether an auxiliary fuel is used for combustion of low heat
4-23
-------
content gases, etc. Refer to AP-42 (EPA, 1985) Section 11.5,
"Industrial Flares", when estimates of flare emissions are
needed. There is no release rate input section for this
scenario. For this scenario, TSCREEN goes immediately to the
SCREEN model input section for a flare source. See Section 5.1.1
for a complete list of SCREEN model inputs.
Limitations and Assumptions:
Approximately 45% of the total heat release is assumed
to be radiated as sensible heat.
Input Information:
Hj total heat release rate (J/s)
H, physical stack height above ground (m)
Hsl effective release height before plume rise (m)
M,,, molecular weight of material released (g/g-mole)
V volumetric flow rate to the flare (m3/s)
vol volume fraction of pollutant (%)
fj volume fraction of each component of the flare input
gas
Hj net heating value of each component (J/g-mole)
4.2.1.1 Procedure :
1. Emission Rate (Qm) . Calculate the emission rate in g/s:
V(mVs) Mw(g/g-mole) 0.02
Q (g/s)
m
0.0224(m3/g-mole)
Total Heat Release Rate (H,) (m) . Calculate the total heat
release rate from the flare gas combustion (Lahey & Davis,
1984) :
n
Hr = 44.64 V £ fj Hj (4.2.1-2)
i-l
where the value 44.6 is derived for air as:
pair(g/m3) _ 1292.
Mw (g/g-mole) 28.97
=44.6(g-mole/m3)
and the summation is over the n components of the flare
input gas stream.
3. Effective Release Height above Ground (H^). Calculate the
effective release height by adding the flare height to the
stack height, as follows (Beychok, 1979) :
4-24
-------
Hsl = Hs + 4.56xlO-3( ..b)a478 (4.2.1-3)
where 4.1868 is a conversion factor (Joules to calories) .
Plume rise for the combusted gas is calculated in the SCREEN
model for this effective release height (EPA, 1988c).
4.2.1.2 Example: Flare Emission
Discussion;
A gas is sent to an elevated flare to be burned. For,
simplicity, it is assumed that the flare is a permitted one. The
gas is a mixture with one toxic component. The gas stream is
made up of 50% methane, 9.8% ethane, and 40% carbon dioxide and
.2% benzene. Maximum one-hour concentrations are required for
benzene assuming 98% reduction efficiency of the flare. There is
a cubical building, 19 m in height, next to this flare. The
fenceline is 100 m from the flare.
The following input information will be required:
HT total heat release rate (3.84xl07 J/s)
H, physical stack height above ground (32 m)
Hsl effective release height (m)
M,, molecular weight of material (78.1 g/g-mole)
V volumetric flow rate (6.58 m3/s)
vol volume fraction of pollutant in feed gas (0.2 %)
Procedure:
1. Emission Rate (Qm) . Calculate the emission rate in g/s.
Determine the emission rate of benzene from the volume
fraction, molar volume, flow rate, and molecular weight.
The volume of benzene is the volume fraction of pollutant
(vol) times material flow rate (V). Mass emission rate (Qm)
after controls is given by determining the number of moles
in the benzene fraction and multiplying by the molecular
weight (the gas is assumed to be at standard conditions
considering the control efficiency) from Equation (4.2.1-1) :
Q (g/s) = -002 • 6.58(m3/s) • 78.1 (g/g-mole) -0.02 = Q 918 (g/s)
0.0224(m3/g-mole)
2. Total Heat Release Rate (HT) (m) . The user calculates che
total heat release (Hr) from the flare from Equation
(4.2.1-2). In this example, carbon dioxide is not
combustible and is assumed not to affect flame heat. Total
heat generated by the flame is determined using mole
fractions, molar flow rate, and heats of combustion for
4-25
-------
methane, ethane, and benzene (see references for physical
constants).
H^J/s)- (44.64 g-mole/m3) 6.58 m3/s [0 .5 (8 .0286xl05 J/g-
mole) + 0.098 (1.4288xl06 J/g-mole) + 0.002
(3.2696xl06 J/g-mole)]
1.61 x 108 (J/s) (or 3.84X107 (cal/s))
Effective Release Height above Ground (H^). The effective
release height is calculated from Equation (4.2.1-3):-
32 + 4.56x10
-3 • (1.61X108)-478 = 51.26 m
4.1868
Dispersion calculations for this scenario are made using the
SCREEN model for a flare.
Data entry in the TSCREEN model for this example is shown below.-
- Flared Stack Emissions - Scenario 2.1
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 7 •
Enter a unique title for this data's model run:
* •:>''v':''x'^':: ........
RELEASE PARAMETERS
Enter the Emission Rate (Qm), if unknown enter
the boxed variables below to calculate ->
g/s
Volume Fraction of Pollutant £:fJC?: %
Volumetric Feed Gas Flow Rate (V) -> &i.5&.;':H; cubic m/s
Molecular Weight of Feed Gas (Mw) -> 7g£&;:W g/9 mole
Total Heat Release Rate -> f,{&&''?• J/s
Release Height above Ground -> 3Z;v ' : m
?«MG>:-*lext:.Scr«e«-
Flared Stack Emissions - Scenario 2.1
SCREEN MODEL INPUTS - Page 2 of 7
BUILDING PARAMETERS
Building Height (enter 0 if no building) -> 19? r::;
Building Minimun Horizontal Dimension -> tSt""^-..
Building Maxinun Horizontal Dimension -> T5'
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural -> 8
FENCELINE DISTANCE
Enter the distance from the base of the stack
to the plant fenceline -> 1:SO;::::.::,
m
m
m
4-26
-------
A summary of the SCREEN model's output for this example is shown
below.
*** SCREEN-1.2 MODEL RUN ***
*** VERSION DATED 90XXX ***
Release from Flare Source
SIMPLE TERRAIN INPUTS:
SOURCE TYPE = FLARE
EMISSION RATE (G/S) = .9177
FLARE STACK HEIGHT (M) = 32.00
TOT HEAT RLS (CAL/S) = .3840E+08
RECEPTOR HEIGHT (M) = .00
IOPT (1=URB,2=RUR) = 2
EFF RELEASE HEIGHT ««««««***•«»•«••*«*
*** SUMMARY OF SCREEN MODEL RESULTS ***
CALCULATION
PROCEDURE
MAX CONC
(UG/M**3)
DIST TO
MAX (M)
TERRAIN
HT (M)
SIMPLE TERRAIN
.5505
1243.
15.
***************«*•**••**«*•**•*«>••••****»•**•*****
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
«**«««««*»*»*******««*i>*i>««i>*««i>**«« >««<•*«>••**««*
4-?7
-------
4.2.2 Continuous Release from Stacks. Vents. Conventional
Point Sources
Similar Releases: Continuous emissions of gases from building
vents, vertical stacks and pipes or conventional point sources
when emission flow rates and temperature are known. These "
results may also be due to a process failure such as a rupture
disk release or failure of control equipment. .
Discussion:
Continuous emissions of gases from stacks are analyzed in
this scenario. Emission factors are "available for individual
toxic compounds for some processes (Appendix A, items 1, 2, and
3). In other cases, total VOC emission rates can be obtained
from AP-42. To determine toxic components of these emissions,
see Appendix A item 4.
Limitations and Assumptions:
Release behaves as an ideal gas
Release is neutrally buoyant
Input Information:
D0 diameter at release point (m)
M3 mean molecular weight (g/g-mole)
R gas constant (8314 Pa-m3/kg-mole-'°K or
8314 J/kg-mole-°K)
Qm total material emission rate (g/s)
Ta . ambient temperature (°K)
T, temperature of material released (°K)
V volumetric flow rate (m3/s)
H, release height above ground (m)
•
4-28
-------
4.2.2.1 Procedure;
1. Density Check. The user should choose to perform a density
check if the release material is thought to be denser-than-
air. TSCREEN will help the user determine if the release is
buoyant (passive gas) or denser-than-air. If the release is
thought to be buoyant (e.g., a very hot plume from an
incinerator, power plant, furnace, etc.), then a density
check need not be performed. To perform a density check,
proceed to step 2. Otherwise, proceed to step 4.
2. Buoyancy Check.
A. Mean Molecular Weight (M,) . Determine the mean
molecular weight of the gas stream using the method
described in Appendix B:
M
i-1
-1
(4.2.2-1)
where: n^ = mass fraction of each component
Mj = molecular weight of each component
(g/g-mole)
B. Discharge Density. Calculate the discharge density p2
(g/m3) using the ideal gas law:
(4.2.2-2)
where P, is the ambient pressure (assumed to equal
101325Pa) .
C. Density of Air . Calculate the density of air pair
(kg/m3) using the ideal gas law:
where P, is the ambient pressure (assumed to equal
101325Pa) , and Ma is the molecular weight of air
(assumed to equal 28.9 kg/kg-mole) .
D. Perform Buoyancy Check
If -Li
P«r
4-29
-------
buoyancy is negative and the release is denser-than-
air. If buoyancy is negative proceed to step 3.
Otherwise, buoyancy is positive and the release is
assumed to be passive (i.e., not denser-than-air). If
buoyancy is positive proceed to step 4.
3. Richardson Number. Perform release Richardson number (Ri)
check:
Ri = 2725 I, " - 1 - (4.2.2-4)
1000 -D
0
where 1000 is used to convert the densities from kg/m3 to
g/m3. Emission rates (Qm) must be calculated from process
parameters or determined from representative emission
factors. If there are emission factors, then convert to
emission rate by multiplying by production rate:
AP-42 f Ib ] production f 1000ft2] _ emission/ lb\
emission factor 1000 ft2 rate [ 5r J~ rate \hr/
emission rate (g/s) = emission rate (Ib/hr) • conversion factor
See Section 2.4 for a discussion of the Richardson number.
If Ri is a 30 then the release is passive. Otherwise, the
release is dense.
Exit Velocity. Determine stack gas exit velocity (Vs)
(m/s) -.
(4.2.2-5)
where: V = volumetric flow rate (mVs)
5. If the release is passive, then TSCREEN runs the SCREEN
model for a point source. If the release is dense, use
Scenario 2.3 - Continuous Gaseous Leaks from Holes in Tanks,
Pipes, Relief Valves.
4.2.2.2 Example: Hydrogen Cyanide (HCN) release
Discussion:
Hydrogen Cyanide (HCN) is released from a vent stack at a
rate of 0.2 tons/day. The stack is 16 meters above ground, has
an inside diameter of 0.1 meter, the stack exit temperature is
298 °K and the volumetric flow rate is 0.14 m3/s. The stack is
adjacent to a square building with height and width dimensions
4-30
-------
equal to 19 m. The site is classified as rural', non-complex
terrain. Hourly maximum concentration estimates are required.
This example represents a continuous release of a gas with a
specified emission rate through a stack with possible building
downwash due to the influence of an adjacent building. The
fenceline is 100 meters form the vent stack.
The following input information will be required:
D diameter at release point (0.1 m)
1^ building height (19 m)
building minimum horizontal dimension (19 m) -
building maximum horizontal dimension (19 m)
M, mean molecular weight (kg/kg-mole)
Qm total material emission rate (2.13 g/s)
R gas constant (8314 Pa-mVkg-mole- °K or
8314 J/kg-mole-°K)
Tt ambient temperature (298 °K)
T, temperature of material released (298 °K)
V volumetric flow rate of material released (0.14 m3/s)
Procedure :
1. Density Check. A density check will be performed for this
example, therefore, proceed to step 2.
2 . Buoyancy Check .
A. Mean Molecular Weight (M,) . Stack tests show that HCN
(molecular weight 27) is the primary constituent (13%)
besides air in the gas stream. Mean density is
calculated as follows using Equation (4.2.2-1):
Ms = - — i - _ =28.7 kg/kg-mole
. o / . -L-i
28 .9 ~2~T
B. Discharge Density. Calculate the discharge density p2
(kg/m3) using Equation (4.2.2-2):
' H. 2.2-2,
C. Density of Air . Calculate the density of air
(kg/m3) using Equation (4.2.2-3):
D. Perform Buoyancy Check. Since discharge density is
less than air density ( 1.17 (kg/m3) /1. 18 (kg/m3) < 1) ,
the release is positively buoyant . Proceed to step 4
4-31
-------
4. Exit Velocity. Calculate stack gas exit velocity (Vs) (m/s)
using Equation (4.2.2-5):
= 4 • 0.14 = 17>8m/s
' 3.14 (.I)2
5. Since the release is passive, dispersion calculations for
this scenario are made using the SCREEN model for a point
source.
Data entry in the TSCREEN model for this example is shown below:
Continuous Releases from Stacks, Vents, Point Sources - Scenario 2.2 1
SOURCE PARAMETERS - Page 1 of 2
Enter a unique title fijr this data's model run:
GAS DENSITY
BUOYANCY CHECK
Do you want to check for release
gas density (Y/N) -> |
Discharge Density (|?) -> 1.173638 kg/cubic m
Temperature of Material Released (Ts) -> £98 "K
Exhaust Gas Molecular Weight (Mw) -> 2S«7 kg/kg-mole
' Density of Air (fair) -> 1.181817 kg/cubic m
Ambient Temperature (Ta) •> J98(££;::i*i °K
Buoyancy is Positive
•«F2»,fefit <&>> Previous Sfrrsen
Steam* -.-f3iwv.; •
Continuous Releases from Stacks, Vents, Point Sources - Scenario 2.2
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 6
RELEASE PARAMETERS
Emission Rate (Om) -> 2»13;'';: : g/s
Exit Velocity -> 17,8 m/s
Diameter at Release Point -> .1 ; m
Release Height above Ground -> 16 ; m
BUILDING PARAMETERS
Building Height (enter 0 if no building) -> T9 m
Building Minimum Horizontal Dimension -> 19 m
Building Maximum Horizontal Dimension -> 1$ - m
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural -> 8
FENCELINE DISTANCE
Enter the distance from the base of the stack
to the plant fenceline -> 100 . m
ftfaort
A summary of the SCREEN model's output for this example is shown
below.
4-32
-------
*** SUMMARY OF SCREEN MODEL RESULTS
CALCULATION
PROCEDURE
SIMPLE TERRAIN
BUILDING CAVITY- 1
BUILDING CAVITY-2
«««««««>»«««*
MAX CONC
(UG/M**3)
.8543
1.717
1.717
«««««««»«**
DIST TO
MAX (M)
100.
28.
28.
TERRAIN
HT (M)
0.
" (
" (
(DIST a CAVITY LENGTH)
= CAVITY LENGTH)
REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
4-33
-------
•\
4.2.3 Continuous Gas-Leaks from a Reservoir
4.2.3.1 Release Rate Estimates': Gas Leaks from a Reservoir
Emissions
Leaking flange
Similar Releases; A gas leak from a tank, a (small) gas leak
from a pipe, or gas discharge from a pressure relief valve
mounted on a .tank.
Discussion:
This procedure applies to a continuous release of a gas (at
constant pressure and temperature) from a containment (reservoir)
through a hole or opening.
Limitations and Assumptions:
The hole or opening size must be sufficiently small,
otherwise the reservoir temperature and pressure may no longer be
constant. For the case of a leak from a tank, the assumption of
constant reservoir temperature and pressure may be violated if a
significant percentage of the tank contents is released. For the
case of a leak from a pipe, the assumption of constant
temperature and pressure may be violated if /? > 0.2
(approximately) with £ as defined below,- if £ > 0.2, the scenario
described in Section 4.2.5 may be appropriate. If the reservoir
temperature and pressure are not constant, the release race mav
vary with time, but the maximum release rate is generally
obtained for the initial reservoir temperature and pressure
(Spicer, 1992).
_The released material must be an ideal gas at the reservoir
conditions, during the depressurization process, and after
depressurization to the atmosphere. For the case of a tank
4-34
-------
\
containing vapor .and liquid, the hole must be in the vapor .space
of the tank.
Input Information:
AQ area of reservoir hole or opening (ra2)
AI , flow area representing reservoir conditions (m2) (In
case of a leak from a tank, Aj -» » (and /3 = 0) ; in the
case of a leak from a pipe, Aj is the cross-sectional
area of the pipe.)
Cp gas (contaminant) heat capacity at Tt (J/kg-°K) (For
contaminant mixtures, see Appendix B)
D0 (equivalent) diameter of hole or opening (D0 =
2-^Ao/ir ) (m)
^ gas (contaminant) molecular weight (kg/kg-mole) (For
contaminant mixtures, see Appendix B)
Pv vapor pressure as a function of temperature (Pa) -
Pt ambient pressure (Pa)
P! reservoir pressure (Pa)
R gas constant (83*14 J/kg-mole-°K or 8314
Pa -mVkg-mole • °K)
Tb contaminant normal boiling point (°K)
Tc critical temperature (for contaminant mixtures, see
Appendix B)
T! reservoir temperature (°K)
j8 y/Ao/Aj (dimensionless)
7 (Cp/C,,) - 1/(1 - R/(CpM)) at Tt (dimensionless)
\ heat of vaporization at the normal boiling point (J/kg)
P! contaminant density at reservoir conditions (Tt and pv)
(kg/m3)
Procedure:
1. Choked Flow Pressure. Estimate the choked flow pressure P,
to determine if the flow is choked from Perry et al. (1984):
P. / 2 \ T'fr'1)
-1 = —i_ ' (4.2.3-1)
PI IT * I/
If P. * P,, then the flow is choked; go to step 2. If P. <
P., then the flow is subcritical (not choked) ; go to step 3 .
2. Choked Flow. For choked flow, estimate the gas temperature
T, when the pressure is P., the emission rate Qm/ and the
discharge temperature T2.
A. Estimate T*. Estimate T* as follows:
T.
,—^, (4.2.3-2)
Li
4-35
-------
This estimate of T, must be checked to see if Equation
(4.2.3-2) applies. If T. is greater than the (pseudo)
critical temperature Tc, Equation (4.2.3-2) applies; if
not, the following procedure is suggested. For single
component contaminants, evaluate the contaminant vapor
pressure at T, (PV(T.)) using the Clausius-Clapeyron
equation:
IN r *i i
•TT ?• ~ T-
R 1T» T- J J
If PV(T.) s P«, then contaminant condensation occurs
during the process of depressurization, and this
approach is not valid; this release should be
considered a two-phase release. If the release is two-
phase go to step 5 (Section 4.2.3.2).
B. Estimate Emission Rate. Estimate the emission rate Qm
(kg/s) as follows from Perry et al. (1984):
(4.2.3-3)
where C = 0.75 (when P, = P,; when P. > Pa/ C can be
higher).
Estimate Discharge Temperature. Estimate the discharge
temperature T2 (after depressurization). (T2 is
estimated assuming the expansion from reservoir
conditions to choked conditions occurs adiabatically
and reversibly; the expansion from choked conditions to
atmospheric pressure is assumed to occur adiabatically
but not reversibly. After Lewitt (1953), assume this
adiabatical (irreversible) expansion is 85% efficient.)
T2 is estimated using:
/ .. i \ \
(4.2.3-4)
(Note that T2 > T,.) Proceed to Step 4.
Subcritical Flow. For subcritical (not choked) flow,
estimate the emission rate Qm and the discharge temperature
T2.
A. Estimate Emission Hate. Estimate the emission rate Qm
(kg/s) as follows from Perry et al. (1984)':
Qm = KYA0[2Pl- (Pj-P. I]'" (4.2.3-5)
where
K - C / ^ 1 -04
4-36
-------
•\
IP _ p 1
_L !_ (0.41 H- 0.35 04) ,
PI 7 J
where C = 0.62. (Although C can be-larger for Reynolds
numbers less than 104, typical Reynolds numbers for
these applications are larger than 104.)
B. Estimate Discharge Temperature. Estimate the discharge
temperature T2 (after depressurization). T2 is
estimated from energy balance considerations (Lees,
1980):
T2 = 2 T! / [ 1 + ( 1 + 4 a T! ) 1/2 ] (4.2.3-6)
where
~ 2-v c1 I "P" MA"
' S> ^ e» mv **0 J
The estimate of T2 must be checked. If T2 is greater
than the (pseudo) critical temperature Tc, the equation
used to estimate T2 applies; if not, the following
procedure is suggested. For single component
contaminants, evaluate the contaminant vapor pressure
at T2 (PV(T2)) using the Glausius-Clapeyron equation:
Pv = 101325 exp
I I b
If PV(T2) si P., then contaminant condensation occurs
during the process of depressurization, and this
approach is not valid; this release should be
considered a two-phase release. If the release is two
phase go to step 6 (Section 4.2.3.2).
4. Discharge Density. Estimate the discharge density p2 from
the discharge temperature T2 using the ideal gas law: p2 =
P,MW/RT2 where R * 8314 (Pa-mVkg-mole- °K) . (Note that
correct application of a dispersion model may require that
the diameter of the hole or opening be modified to
D0(P.T2/(P.T,))1/2 for choked flow and D0(p1/p2)1/2 for subcritical
flow if the model accounts for intial air dilution due to
jetting or momentum effects using an initial velocity
estimate; if this modification is not applied, the initial
gas velocity is incorrectly over estimated. This correction
is not needed in TSGREEN). Go to step 7 (Section 4.2.3.3).
to select the appropriate dispersion model.
If the screening procedure above indicates that partial
condensation of the released gas occurs, the following section
should be used.
4-37
-------
4.2.3.2 Continuous (Two-Phase) Release Rate Estimate: Gas
Storage which Partially Condenses on Depressurizat ion.
Similar Releases; A gas leak from a tank, a gas leak from a
pipe, or gas discharge from a pressure relief valve mounted on a
tank.
Discussion:
Materials which are stored under pressure will depressurize
when released to the atmosphere. This depressurization can
result in the formation of two contaminant phases (saturated
liquid and vapor) for: gases which cool so that condensation
occurs during the depressurization process/ and high volatility
liquids (liquids whose normal boiling point is below the ambient
temperature) which are stored at above ambient pressure
(typically). (See Section 4.3.2 for more discussion on two-phase
releases.) This scenario considers the release from a tank (or
reservoir) and includes a provision for the effect of a pressure
drop (piping) between the tank and the hole or opening.
This procedure applies to a continuous release of a gas
which partially condenses during depressurization; the screening
procedure for this scenario should only be applied if the
screening procedure above indicated that partial condensation of
the released gas occured. The release occurs (constant pressure
and temperature) from a containment (reservoir) through a hole or
opening; a provision is made for the effect of a pressure drop
(piping) between the tank and the hole or opening.
Limitations and Assumptions:
The pressure and temperature of the tank (or reservoir)
contents are essentially constant. The hole or opening size must
be sufficiently small, otherwise the reservoir temperature and
pressure may no longer be constant. For the case of a leak from
a tank, the assumption of constant reservoir temperature and
pressure may be violated if a significant percentage of the tank
contents is released. -If the reservoir temperature and pressure
are not constant, the release rate may vary with time, but the
maximum release rate is generally obtained for"the initial
reservoir temperature and pressure.
For the case of a leak from a pipe when /3 > 0.2 (as define'd
below), the assumption of constant temperature and pressure in
Che pipe may be violated; for such a case, the reservoir
conditions should be taken from an upstream location (tank or
reservoir) where the temperature and pressure will be
(approximately) constant. For the case of a leak from a pipe
when j3 s 0.2, the assumption of constant temperature and pressure
in the pipe is reasonable, and the reservoir conditions should be
taken to be the conditions within the pipe.
4-38
-------
The vapor phase of the released material must be an ideal
gas at the reservoir conditions, during the depressurization
process, and after depressurization to the atmosphere; for the
case of a tank containing vapor and liquid, the hole must be in
the vapor space of the tank. For two phase flows, all released
liquid is assumed to travel downwind as an aerosol with little
rain out of liquid near the source (Spicer, 1992) .
Input Information:
AO area of reservoir hole or opening (m2)
A! flow area representing reservoir conditions (m2) (In
case of a leak from a tank, At -» » (and 0 =• 0) ; in the
case of a leak from a pipe, Aj is the cross -sectional
area of the pipe . )
Cp gas (contaminant) heat capacity at Tt (J/kg-mole- °K)
(For contaminant mixtures, see Appendix B)
D0 (equivalent) diameter of hole or opening (D0 =
Dp pipe diameter (as appropriate) (m)
Lp pipe length (as appropriate) (m)
M, gas (contaminant) molecular weight (g/g-mole) (For
contaminant mixtures, see Appendix B)
P; ambient pressure (Pa)
Pv vapor pressure as a function of temperature (Pa)
PI reservoir pressure (Pa)
R gas constant (8314 J/kg-mole- °K or 8314
Pa • mVkg-mole • °K)
Tb contaminant normal boiling point (°K)
Tc critical temperature (°K) (For contaminant .mixtures,
see Appendix B)
Tj reservoir temperature (°K)
j8 ^A0/A1 (dimensionless)
7 (Cp/CJ = 1/(1 - R/(CpM)) at Tt (dimensionless) where R =
8314 ( J/kg-mole • °K)
\ heat of vaporization at the normal boiling point
(cal/g-mole)
P! contaminant density at not normal boiling point (kg/m3)
Procedure :
Two-Phase Choked Flow. Estimate the choked flow pressure P,
to determine if the flow is choked using the procedure
described in Section 4.2.3.1. If the flow is not choked,
proceed to Step 6. For choked flow, estimate the discharge
temperature T2, discharge density 02, and the emission rate
Qm.
A. Estimate T.. For pure components, estimate T, (the
temperature which corresponds to P.) from the vapor
pressure (Clausius-Clapeyron) equation:
4-39
-------
P. =101325 - exp - - (4.2.3-7)
Tb
which can be rewritten as:
1
T. =
in I P'
Tb AI^, 101325
B. Estimate Properties at Choked Flow Conditions. Based
on assumed isentropic behavior, estimate the vapor
fraction at choked flow conditions X, as follows:
(4.2.3-8)
Using X, from Equation (4.2.3-8), estimate the enthalpy
change (Ht-H*) and the density p, as follows:
H! - H. = Cp (T! - T.) + X (1 - X.) (4.2.3-9)
Note that values for individual enthalpies Ht and H. are
not required.
C. Estimate Emission Rate. Extending the ideas suggested
by Lees (1950), estimate the emission rate Qm (kg/s) as
follows:
[f H - H 1 "I1/2
2'°-85[l*4fL;/D,jJ (4.2.3-11,
where 0.85 is included to account for irreversibilities
in the flow based on Lewitt (1953) and the term 4fLp/Dp
accounts for (piping) pressure drop between the
reservoir and the hole or opening; as a preliminary
estimate, use f=0.0045 (since typical Reynolds numbers
for these applications are larger than 105) .
D. Estimate Discharge Temperature and Density. Estimate
the discharge temperature T: (after depressuri-aticn) .
If a condensed phase is present, T2 will be given by
the Clausius Clapeyron equation:
P. = 101325 exp \^L [ * - 1 |] (4.2.3-12)
R Tb T2
4-40
-------
\
which can be rewritten as:
In
Tb M 101324
Using this estimate of T2, estimate the vapor fraction
X, as:
(4.2.3-13)
X, - X. * Cp(T. - T2)/X
When X2 (estimated from Equation (4.2.3-13)) satisfies
1 * %2 z 0, the estimate of T2 is valid, and the density
of the discharged material is given by:
-*,
PL
-i
(4.2.3-14]
(Note that for choked flow conditions, correct
application of a dispersion model may require that the
diameter of the hole or opening be modified to
D0(p,/p2)1/2 if the model accounts for initial air
dilution due to jetting or momentum effects; if this
modification is not applied, the initial aerosol
velocity is incorrectly overestimated. This correction
is not needed for TSCREEN.)
However, if Xj < 0 or X2 > 1, the contaminant condensed
phase which was present at P. and T. is no longer
present, and the released contaminant is a gas (without
any condensed phase) ; the discharge temperature and
density are estimated as follows:
T2 = T. + X(l - X.)/Cp (4.2.3-15)
A,- ' (4.2.3-16)
X2 = 0.
E. Go to step 7 (Section 4.2.3.3) to select the dispersion
model .
Two-Phase Subcritical (Nonchoked) Flow. For subcritical
flow, estimate the gas/liquid discharge temperature T2,
discharge density p2, and the emission rate Qm.
A. Estimate T2. For pure components, estimate T2 from the
Glaus ius-Clapeyron equation:
4-41
-------
101325 exp - (4.2.3-17)
R Tb T2
which can be rewritten as:
1
T
1
Tb AT^ [101325
B. Estimate Properties at Discharge Conditions. Based on
assumed isentropic behavior, estimate the vapor
fraction at discharge flow conditions X2 as :
T.
2
fT
M.C.ln U -Rln _1 (4.2.3-18)
Using X2 from Equation (4.2.3-18), estimate the
enthalpy change (Hj - 1^) and the density p2 as :
H, - Hj = C (Tt - T2) + X (1 - Xj) (2.3-19)
-x,
PL
-i
(2.3-20)
Note that values for the individual enthalpies are not
required.
Estimate Emission Rate. Extending the ideas suggested
be Lees (1950), estimate the emission rate Qm as:
Qm = AO p2 2-0.85
HI -H,
Tl/2
4 f Lp / Dp
(2.3-21)
where 0.85 is included to account for irrevesibilities
in the flow based on Lewitt (1953) and the term 4fLp/Dp
accounts for the pressure drop (piping) between the
reservoir and the hole or opening (as appropriate); as
a preliminary estimate, use f = 0.0045 (since typical
Reynolds numbers for these applications are larger than
105) .
D. Go to step 7 to select the dispersion model.
4.2.3.3 Dispersion Model Selection
See Section 2.4 for a complete discussion of the model
selection.
4-42
-------
Input Information;
Tt ambient temperature (°K)
Q total amount of material released (kg)
Procedure :
7. Buoyancy Check. Evaluate release buoyancy as a first check.
A. Calculate the density of air using the following:
P M
^jr (4.2.3-22)
where- M, is the molecular weight of air (assumed to
equal 28.9 kg/kmole) .
B. If p2/P«ir > I/ then the buoyancy is negative. For
negative buoyancy, the RYD model should be used if the
release is from a vertically directed jet; otherwise,
the Britter-McQuaid model should be used/ go to step 8.
If the buoyancy is neutral or positive, the SCREEN
model for a point source should be used. (See Section
2.4 for more information on model selection.)
Release Duration. The release duration is used as an input
into the RVD and Britter-McQuaid models . The release
duration is used to determine if the release should be
modeled as continuous or instantaneous (see Section 2.5) .
Calculate the release duration- Td using the equation below-.
Td (min) = _— - — . , . . . (4.2.3-23)
Qm (kg/s) • 60 (s/min)
4.2.3.4 Examples
4.2.3.4.1 Example 1: Air Leak from Reservoir - Choked
•
Discussion :
In this example, 400 kg of a chemical with the same
properties of (dry) air stored at 1.101x10* Pa and 293.15 °K is
released from a tank through a 5.25 cm hole on the side of the
tank. The nearest distance to the fenceline is 100 meters.
Maximum 15 -minute average concentration is needed. This example
demonstrates the procedure when the flow is choked.
The following information will be required:
AO area of reservoir hole or opening
4-43
-------
(TrD02/4 = 0.002165 m2)
At flow area representing reservoir conditions (At -» « m2)
Cp gas (contaminant) heat capacity at Tt (1004 J/kg-°K)
D0 diameter of hole or opening (D0 = 0.0525 m)
MW gas (contaminant) molecular weight (29 kg/kmole)
P, ambient pressure (101325 Pa)
Tb boiling point temperature (79 °K)
P! reservoir pressure (1.101x10* Pa)
R gas constant (8314 J/kg-mole-°K or 8314
Pa-m3/kg-mole-°K)
Q total amount of material released (400 kg)
T, ambient temperature (293.15 °K)
Tc critical temperature (132 °K)
Tt reservoir temperature (293.15 °K)
0 ^Ag/Aj (0.0)
7 (Cp/C,) « 1/(1 - R/(CpMj) at T! (1.40)
Pi reservoir density (at Tj and Pt) (pt = P^/ (RTt) =
(l.lOlxlO6) (29)/((8314) (293.15)) = 13.10kg/m3)
With this information, the procedure discussed above is used to
determine the release rate, the discharge temperature, and the
discharge density. For dispersion calculations, 15-minute
average concentrations at a fenceline of 100 m are desired.
Procedure:
1. Choked Pressure. Estimate the choked pressure P. to
determine if the flow is choked. From Equation (4.2.3-1):
/ -} \ 1.40/U.40-1)
P. = • l.lOlxlO6 = 5.82xl05 (Pa)
\ -L • fz w ** X /
Since P« > Pa, the flow is choked; go to step 2.
2. Choked Flow. For choked flow, estimate the gas temperature
T. when the pressure is P., the emission rate is Qm/ and the
discharge temperature is T2.
A. Estimate T.. Estimate T» using Equation (4.2.3-2) with
7 = 1.40 and Tt,= 293.15 °K:
2
1.40 -*- 1
293.15 = 244 °K
This estimate of T. must be checked to see if Equation
(4.2.3-2) applies. If T« is greater than the (pseudo)
critical temperature Tc for air, Equation (4.2.3-2)
applies. (The pseudo critical temperature of air is Tc
= 0.79(126.2) + 0.21(154.6) = 132°K where the assumed
composition (mole fraction) of air is 79% N2 and 21% 02,
and the critical temperatures of N2 and 02 are 126.2 °K
and 154.6 °K, respectively.)
4-44
-------
B. Estimate Emission Rate. Estimate the emission rate Qm
using Equation (4.2.3-3) with C = 0.75:
Qm = C-0.002165
L.101xl06-13.10-1.40
1.40
Qm. = 4 .22 kg/s
C. Estimate Discharge Temperature. Estimate the discharge
(after depressurization) temperature T2 with Equation
(4.2.3-4):
T2 = 293.15
1 - 0.85
1.40 - 1
1.40 + 1
252 °K
Note that T2 > T,, so equations used were appropriate.
Since flow is choked, proceed to Step 4.
4. Discharge Density. Estimate the discharge density p2 from
the discharge temperature T2 using the ideal gas law:
(101325) (29)/(8314) (252) = 1.40 kg/m3
(For these choked flow conditions, correct application of a
dispersion model may require that the diameter of the hole
or opening be modified to D0(P.T2/P,T.) l/2 = 0.0525 [(5.82xl05)
(252) /(101325) (244)] 1/2 = 0.128 m if the model accounts for
initial air dilution due to jetting or momentum effects.)
Since no partial condensation was indicated by screening
calculations, proceed to Step 7.
7. Perform Buoyancy Check.
A. Calculate density of air using Equation (4.2.3-22) :
101325 -28.9 -
- 8314 • 293.15 -
•
B- P2/P& > 1 therefore, buoyancy is negative.
/
8. Release Duration. Calculate the release duration Td using
Equation (4.2.3-23) as follows:
=1.58 min
A ^ ,„ , . . ,
4.22 (kg/s) • 60 (s/min)
After this calculation run the Britter-McQuaid model since
the release is not from a vertically directed jet. (See
Section 5.4 for more information on the Britter-McQuaid
model . )
Data entry in the TSCREEN model for this example is shown below
4-45
-------
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS - Page 1 of 4
Enter; a unique.vtitle; for..jtj^s_djita/s_mdel._run:
SOURCE OF LEAK
Area (Ao) of Hole or Opening -> Zl^JS cm*
Enter P for Pipe - T for tank -> t
FLOW CHARACTERISTIC
Critical Pressure (P*) -> 581698.9 Pa
Gas Heat Capacity (Cp) -> TffiJft
Reservoir Pressure (P1) -> f>.i3fE&
Molecular Weight (Mw) -> 23
J/kg °K
Pa
kg/kmol
Flow Characteristic -> Choked
Ambient Pressure (Pa) -> 1S132S
Pa
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS - Page 2 of 4
TEMPERATURES
Gas Temperature (T*) at Critical Pressure •> 244.3249 °K
Reservoir Temperature (T1) -> 208.fj °K
Critical Temperature (Tc) -> T2KJ ' °K
S«Ht *&>?rtm9U8 $cr*en *f11)> ««»t
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS - Page 3 of 4
EMISSION RATE
Emission Rate (dm) -> 4222.151 g/s
Density at Reservoir Conditions (f1) -> 13..18' . kg/cubic m
DISCHARGE CHARACTERISTICS
Discharge Temperature (T2) -> 251.6487 °K
Discharge Density (f2) -> 1.404462 kg/cubic m
Density of Air (fair) -> 1.201474 kg/cubic m
Ambient Temperature (Ta) -> 293.15' °K
Buoyancy is Negative
4-46
-------
SOURCE PARAMETERS - Page
VERTICALLY DIRECTED JET
Does the release
1
riME
Total Amount of
4 of 4
result in a vertically
directed jet (Y/M) -> f
Release Duration (Td) -> 1.578974 min
Material Released (0) -> 40$ kg
**"!*fc V*»ft*t«»;ftfM» ;^^*«*'«WMK «tst>AtoWt
Based on user input, the Britter-McQuaid model has been selected.
BRITTER-McQUAID MODEL INPUTS - Page 1 of 3
MODEL PARAMETERS
Relative Humidity (Rh) -> 58 ,, X
Desired Averaging Time for the Calculation
of Concentrations -> 1$ -. min
Pollutant Boiling
Point Temperature (Tb) -> 79 °K
•<(&• idH «f$v j*B*v?«» Sera*w s ^Ftl^ »«xt $wr«» <6$$* Abort
: Continuous Leaks from Reservoir - Scenario 2.3 —
BRITTER-McQUAID MODEL INPUTS - Page 2 of 3
FENCELINE DISTANCE
Enter the distance from the base of the stack
to the plant fenceline -> tGU; m
RECEPTOR LOCATIONS
Do you have specific locations where you would
like pollutant concentrations calculated (Y/N) -> H
«F$>:
.- Screen:
Rt»* Kocte-fc x£s Abort
The Britter-McQuaid model's output is displayed below:
*** B4M MODEL RUN ***
Air Leak from Reservoir
INPUTS:
AMBIENT PRESSURE (ATM)
AMBIENT TEMP (K)
AVERAGING TIME (MIN)
BOILING PT TEMP (K)
DURATION (S)
EMISSION RATE (KG/S)
EXIT TEMP (K)
MASS (KG)
11-19-92
13:34:04
1.000
293.1
15.00
79.00
94.74
4.222
251.6
400.0
4-47
-------
MOL. WEIGHT (G/G-MOLE) - 29.00
RELATIVE HUMIDITY (%) = 50.00
VAPOR FRACTION - 1.000
*** SUMMARY OF B&M MODEL RESULTS ***
MAX CONC
(UG/M**3)
MAX CONC
(PPM)
DIST TO
MAX (M)
WIND SPEED
(M/S)
.7978E+08 .6617E+05
100.
** REMEMBER TO INCLUDE BACKGROUNDCONCENTRATIONS **
**************«**••*•»«*******•*»«•»»»»»****»****••»•
***********•******»*•«*******«»•«**
*** B&M DISTANCES ***
•I*********************************
DIST
(M)
100.
200.
300.
400.
500.
600.
700.
300.
900.
1000.
1100.
1200.
1300.
1400.
1500.
1600.
1700.
1900.
2100.
2300.
2500.
2700.
2900.
3100.
3300.
3600.
3900.
4200.
4500.
5000.
CONC
(UG/M**3>
.7978E+08
.1323E+08
.7453E+07
.3704E+07
.2371E+07
.1821E+07
.2115E+07
.2861E+07
.2132E+07
.1638E+07
.1291E+07
.1039E+07
.8502E+06
.7064E+06
.5945E+06
.5059E+06
.4348E+06
.3292E+06
.2564E+06
.2042E-CQ6
.1658E*06
.1368E+06
.1144E+06
-9683E+05
-8282E+05
.66635+05
.5455E+05
.4532E+05
.3814E+05
.2931E+05
CONC
(PPM)
.6617E+05
.1098E+05
6182.
3072.
1966.
1510.
1754.
2373.
1768.
1359.
1071.
861.4
705.2
585.9
493.1
419.6
360.6
273.1
212.6
169.4
137.5
113.4
94.88
80.31
68.69
55.26
45.24
37.59
31.63
24.31
WIND SPEED
(M/S)
i.
2.
2.
2.
3.
3.
2.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
CALCULATED VALUES:
DENSITY OF DEPRESSURIZED CONTAMINANT (KG/M*
DENSITY OF AMBIENT AIR (KG/M**3)
MOLE FRACTION
MIN OIST INST (M)
MAX DIST CNST (M)
1.405
1.199
1.000
3158.
757.9
NOTES & DEFINITIONS
(a) "inst" refers to an instantaneous release (Section 3.6 of B-M Workbook)
(b) "enst" refers to a continuous release (Section 3.6 of B-M Workbook)
4-48
-------
(c) "MIN D1ST INST" is the mininun distance downwind at which the release
may be treated as instantaneous
(d) "MAX OIST CNST" is the maximum distance downwind at which the release
may be treated as continuous
END OF B&M OUTPUT
4.2.3.4.2 Example 2: Air Leak from Reservoir - Subcritical (Not
Choked)
Discussion:
In this example, (dry) air stored at 1.82xl05 and 293.15 °K
is released, from a tank through a 5.25 cm hole in the tank; this
example is the same as the previous example except for the
reservoir pressure. This example demonstrates the procedure when
the flow is not choked.
The following information will be required:
AO area of reservoir hole or opening
(7rD02/4 » 0.002165 tn2)
A! flow area representing reservoir conditions (Aj -* « m2)
Cp gas (contaminant) heat capacity at
T! (6.959 cal/g-mole °K)
D0 diameter of hole or opening (D0 = 0.0525 m)
M« gas (contaminant) molecular weight (29 kg/kmole)
Pt ambient pressure (101325 Pa)
Pt reservoir pressure -(1.82xl05 Pa)
R gas constant (8314 J/kg-mole-°K or 8314
Pa-iirVkg-inole-0K)
Q total amount of material released (400 kg)
T, ambient temperature (293.15 °K)
T= critical temperature (132 °K)
TI reservoir temperature (293.15 °K)
13 VV^ (0.0)
7 (Cp/CJ = 1/(1 * R/MCpMJ) at T, (1.40)
Pi reservoir density (at Tt and Pt) (pl = P1MW/(RT1) =
(1.82X103) (29)/( (8314) (293.15) ) = 2.17 kg/m3)
With this information, the procedure discussed above is used to
determine the release rate, the discharge-temperature, and the
discharge density.
Procedure:
1. Choked Pressure. Estimate the choked pressure P. to
determine if the flow is choked. From Equation (4.2.3-1):
4-49
-------
..
•* • 1.82x10* = 9..61X104 (P.)
Since P. < Pt, the flow is not choked; go to step 3.
3. Subcritical Flow. For subcritical (not choked) flow,
estimate the emission rate Qm and the discharge temperature
T2.
A. Estimate Emission Rate, Estimate the emission rate Qm
using Equation (4.2.3-5):
Qm = K-Y-.002165[ 2-2.17(1.82xl05 - 101325 ) ]^ = 0.691 kg/s
where
K = 0.62 / V 1 - 0 • O4 =0.62
Y = 1 - [ 1.82x10' -101325 ] (Q ^ + Q>35 . Q4) . Q
[ 1.82xl05 • 1.40 J
B. Estimate Discharge Temperature. Estimate the discharge
(after depressurization) temperature T2. From Equation
(4.2.3-6):
T2 = 2 • 293.15 / [ 1 + (1 + 4 - a • 293 .15 )1/2 ] = 265 °K
where
a = _i_ ( °-691 ' 8314 Y = 4.06x10-"
2-Cp\ 101325-29-0.002165 /
where
Cp/(J/kg<'K)=6.95889(cal/g-mole "K? • 100Q (g/k,g) / 4 '184 (J/cal) =1004 (J/kg°K)
29(g/g-mole)
Since T2 > Tc, proceed to Step 4.
4. Discharge Density. Estimate the discharge density p2 from
the discharge temperature T2 using the ideal gas law:
(101325) (29)/(8314) (265) = 1.33 kg/m3
(Correct application of a dispersion model may require that
the diameter of the hole or opening be modified to D0(p,/,o~)1/2
= 0.0525 m (2.17/1.33)1'2 = 0.0671 m if the model accounts "
for initial air dilution due to jetting or momentun effects/
if this modification is not applied, the initial gas
velocity is incorrectly overestimated.) Since no
condensation is predicted from the above calculations,
proceed to Step 7.
4-50
-------
Perform Buoyancy Check.
A. Calculate density of air using Equation (4.2.3-22):
. 101325 -28.9
B.
P^lPm
8314 • 293.15 ' >~M **'*
therefore, buoyancy is negative.
Release Duration. Calculate the release duration Td using
Equation (4.2.3-23) as follows:
T, (min) =
400 (kg)
0.691 (kg/s) • 60 (a/rain)
=9.65 min
After this calculation run the Britter-McQuaid model since
the release is not from a vertically directed jet. (See
Section 5.4 for more information on the Britter-McQuaid
model.)
Data entry in the TSCREEN model for this example is shown below:
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS - Page 1 of 4
Enter a unique title for this data's model run:
Sub^lef&rAfr&sic '
SOURCEof LEA* ' ' "
Area (Ao) of Hole or Opening -> 21 .iS '' cm1
Enter P for Pipe - T for tank -> f
FLOW CHARACTERISTIC
Critical Pressure (P*) -> 96157.31 Pa
Gas Heat Capacity (Cp) -> TBS&
Reservoir Pressure (P1) ->
Molecular Weight (Mw) -> 29
J/kg "K
Pa
kg/kmol
Flow Characteristic -> Subcritical
Ambient Pressure (Pa) -> tO$525p. Pa
4-51
-------
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS - Page 2 of 4
EMISSION RATE
Emission Rate (Qn» -> 691.131 g/s
Reservoir Density (f1) -> 1**^ ' kg/cubic m
DISCHARGE TEMPERATURE
Discharge Temperature (T2) -> 264.6861 °K
Reservoir Temperature ^||5jp °K
Sift 1&i;!fe|£: "K
DISCHARGE DENSITY
Discharge Density ((2) -> 1.335283 kg/cubic m
Density of Air (fair) -> 1.201474 kg/cubic m
Ambient Temperature (Ta) -> %j$3$%, °K
Buoyancy is Negative
edit *t9* Previous $nra*n «f t0> »«*t Ser«*n
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS - Page 4 of 4
VERTICALLY DIRECTED JET
Does the release result in a vertically
directed jet (Y/N) -> H
TIME
Release Duration (Td) -> 9.646025 min
Total Amount of Material Released (Q) -> 4(&t?3z£. kg
4-52
-------
Continuous Leaks from Reservoir - Scenario 2.3
Based on user input, the Britter-McQuaid model has been selected.
BRITTER-McQUAID MODEL INPUTS - Page 1 of 3
MODEL PARAMETERS
Relative Humidity (Rh) -> 56 X
Desired Averaging Time for the Calculation
of Concentrations -> 1$° nrin
Pollutant Boiling Point Temperature (Tb) -> 79 °K
Continuous Leaks from Reservoir - Scenario 2.3
BRITTER-McQUAID MODEL INPUTS - Page 2 of 3
FENCELINE DISTANCE
Enter the distance from the base of the stack
'to the plant fenceline ->
j m
RECEPTOR LOCATIONS
Do you have specific locations where you would
like pollutant concentrations calculated (Y/N) -> lit
Eetf tf «F9> Previous $«•«« «F1S> Run «od*L
.3102E+08 .2573E+5
100.
1.
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
»*«*»»**«»**»*•»*«»»*«***«*»*»»**«»«**»*«»*»*»»»****
4.2.3.4.3 Example 3: Chlorine Gas Leak - Choked
Discussion:
In the example, chlorine gas stored at 6.7999 atm and 320 °K
is released through a 2.8 cm hole. This example demonstrates the
procedure when the flow is choked.
The following information will be required:
AO area of reservoir hole or opening (7rD02/4 = 0.0006158
m2)
A! flow area representing reservoir conditions (Aj -» oo m2)
Cp ' gas ('contaminant) heat capacity at Tj (489 J/kg-°K)
4-53
-------
D0 diameter of hole or opening (D0 = 0.028 m)
1^ gas (contaminant) molecular weight (70.9 kg/kmole)
P, ambient pressure (101325 Pa)
Pt reservoir pressure (6.89xl05 Pa)
R gas constant (8314 J/kg-mole-°K or 8314
Q total amount of material released (400 kg)
Ta ambient ' temperature (293 °K)
Tc critical temperature (417.15 °K)
Tr reservoir temperature (320 °K)
j8 ^V^" (0.0)
7 (Cp/CJ - 1/(1 - R/fCpMj) at T\ (1.32)
heat of vaporization at normal boiling point
'(2.879X105 J/kg)
P! contaminant liquid density at the normal boiling point
(18.36 kg/m3)
With this information, the procedure discussed above determines
the release rate, the discharge temperature, and the discharge
density.
Procedure :
1. Choked Pressure. Estimate the choked pressure P, to
determine if the flow is choked. From Equation (4.2.3-1):
..
! 32 + i) ' 6-89xl°5 " 3.74X105 P.
Since P. > P., the flow is choked; go to step 2.
Choked Flow. For choked flow, estimate the gas temperature
T, when the pressure is P., the emission rate Qm, and the
discharge temperature T2.
A. Estimate T.. Estimate T. using Equation (4.2.3-2) with
7 = 1.32 and Tt = 320 °K:
T- = ' 32C • 276 °K
The Clausius-Clapeyron equation can be conveniently
used to estimate the vapor pressure at T. as follows :
P. - 10132S exp
Since PV(T.) > P., no condensation occurs.
B. Estimate Emission Rate. Estimate the emission rate Q
using Equation (4.2.3-3) with C = 0.75:
4-54
-------
Qm = C-0.0006158
'\
1/2
S.89xl05-18.36-1.32
.1.32 + 1
Qm = 1.10 kg/s
C. Estimate Discharge Temperature. Estimate the emission
discharge (after depressurization) temperature T2 with
Equation (4.2.3-4):
T2 = 320
= 283 °K
Since flow is choked, proceed to Step 4.
4. Discharge Density. Estimate the discharge density p2 from
the discharge temperature T2 using the ideal gas law:
(101325) (70.9)7(8314) (283) = 3.05 kg/m3
(For these choked flow conditions, correct application of a
dispersion model may require that the diameter of the hole
or opening be modified to D0(P./P.)1/2 * 0.028 m (3.69/l)1/2 =
0.0538 m if the model accounts for the initial air dilution
due to jetting or momentum effects. Since flow is one-
phase, proceed to Step 7.
7 . Perform Buoyancy Check .
A. Calculate density of air use Equation (4.2.3-22) as
follows :
B- PI/P& > 1 therefore, buoyancy is negative.
8. Release Duration. Calculate the release duration Td using
Equation (4.2.3-23) as follows:
. ,n ,v n , i '
1.10 (kg/s) • 60 (s/min)
After this calculation run the Britter-McQuaid model since
the release is not from a vertically directed jet. (See
Section 5.4 for more information on the Britter-McQuaid
model . )
Data entry in the TSCREEN model for this example is shown below:
4-55
-------
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS - Page 1 of 4
Enter a unique title for this data's model run:
1Si&jiKm'W&'-'WiW1i& ,
SOURCE OF LEAK
Area (Ao) of Hole or Opening -> 6-1*58' cm2
Enter P for Pipe - T for tank -> I"
FLOW CHARACTERISTIC
Critical Pressure (P*)
Gas Heat Capacity (Cp)
Reservoir Pressure (P1)
Molecular Weight (Mu)
Flow Characteristic
Ambient Pressure (Pa)
-> 374093.4
-> 49* *
-> &SB&
-> Choked
-> t8&$&&
Pa
J/kg "K
Pa
kg/kmol
Pa
Edit Previous Screen Next Screen Abort
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS - Page 2 of 4
TEMPERATURES
Gas Temperature (T*) at Critical Pressure -> 276.4043 °K
Reservoir Temperature (T1) -> 58$f,::L.:::;,''' "K
Critical Temperature (Tc) -> 417.15 "K
VAPOR PRESSURE
Vapor Pressure (Pv) at Gas Temperature -> 405986 Pa
Latent Heat of Vaporization (Lvap) at Tb -> Zia75!I J/kg
Boiling Point Temperature (Tb) -> 2$5&9j|::r °K
•«F<> &*lt Previous 4#ew^C:'*?T^^
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS - Page 3 of 4
EMISSION RATE
Emission Rate (Qm) -> 11006.45 g/s
Density at Reservoir Conditions (f1) -> 1&Jf&y< kg/cubic m
DISCHARGE CHARACTERISTICS
Discharge Temperature (T2) -> 282.9437 "K
Discharge Density (f2) -> 3.053886 kg/cubic m
Density of Air (fair) -> 1.20209 kg/cubic m
Ambient Temperature (Ta) -> 2J>S|;:}T:f °<
Buoyancy is Negative
Prepays
4-56
-------
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS • Page 4 of 4
VERTICALLY DIRECTED JET
Does the release result in a vertically
directed jet (Y/N) ->
TIME
Release Duration '(Id) -> 0.6055085 min
Total Amount of Material Released (Q) ->
fitft " '" s
Stfeen
UeXt:
Jffiort '
Continuous Leaks from Reservoir - Scenario 2.3
Based on user input, the Britter-McQuaid model has been selected.
BRITTER-McQUAID MODEL INPUTS - Page 1 of 3
MODEL PARAMETERS
Relative Humidity (Rh) -> SO X
Desired Averaging Time for the Calculation
of Concentrations -> t$ min
- SeMt
Previous Scrserr- Next Screes
Continuous Leaks from Reservoir - Scenario 2.3
BRITTER-MCQUAID MODEL INPUTS - Page 2 of 3
FENCELINE DISTANCE
Enter the distance from the base of the stack
to the plant fenceline ->
RECEPTOR LOCATIONS
Do you have specific locations where you would
like pollutant concentrations calculated (Y/N) -> 8
. <{|2>- Beilr
-------
4.2.3.4.4 Example 4: Saturated Vapor Chlorine Leak
Discussion:
In this example, saturated chlorine vapor is discharged
through a pressure relief valve (10.16 cm diameter) designed to
open at 2.586xl06P4 (375 psia); the chlorine vapor temperature is
estimated to be 349.2 °K using the Clausius-Clapeyron equation
and the normal boiling point of chlorine (239.05 °K) .
Condensation will be present in this release (at the choked flow
conditions). This example demonstrates the procedure when the
flow is choked.
The following information will be required:
AQ area of reservoir hole or opening
(irD02/4 = 0.008107 m2)
AI flow area representing reservoir conditions (At -» o> m2)
Cp gas (contaminant) heat capacity at Tt (489 J/kg-°K)
D0 diameter of hole or opening (D0 = 0.1016 m)
1^ gas (contaminant) molecular weight (70.9 kg/kmol)
P. ambient pressure (101325 Pa)
Pj reservoir pressure (2.586xl06 Pa)
R gas constant (8314 J/kg-mole-°K or 8314
Pa-m3/kg-mole-°K)
Q total amount of material released (400 kg)
Ta ambient temperature (293 °K)
Tb contaminant normal boiling temperature (239.05 °K)
Tc critical temperature (417.15 °K)
Tx reservoir temperature (349.2 °K)
•0 y/Ao/Ai (0.0)
7 (Cp/CJ = 1/(1 - R/tCpMJ) at T, (1.32)
X heat of vaporization at the normal boiling point
(2.879x10* J/kg)
P! contaminant liquid density at the normal boiling point
(1574 kg/m3)
With this information, the procedure discussed above determines
the release rate, the discharge temperature, and the discharge
density. ,
Procedure:
1. Choked Flow Pressure. Estimate the choked flow pressure P*
to determine if the flow is choked. From Ecruation (4.2.3-
1) :
/ <> \ 1.32/(1.32-t)
P. = _—±—~\ • 2.586xl06 = 1.40xl06 (Pa)
Since P. > Pa, the flow is choked; go to step 2.
4-58
-------
Choked Plow. For choked flow, estimate the gas temperature
T, when the pressure is P., the emission rate Qm, and the
discharge temperature T2.
A. Estimate T,. Estimate T« using Equation (4.2.3-2) with
7 = 1.32 and Tt » 349.2 °K:
T' ' 349. 2 =301 oK
This estimate of T* must be checked to see if Equation
(4.2.3-2) applies. T. is not greater than the (pseudo)
critical temperature Tc (417.15 °K) ; therefore, the
contaminant vapor pressure at T. (PV(T.)) must be
calculated using the Clausius-Clapeyron equation:
P, . 10132S exp
The chlorine vapor pressure at 301 °K is less than P,/
so, condensation was predicted; proceed to step 5.
Two- Phase Choked Flow. For choked flow, estimate the
discharge temperature T2, discharge density p2, and the
emission rate Qm.
A. Estimate T«. Estimate T. (the temperature which
corresponds to P.) from Equation (4.2.3-7) :
T, = - - - = 321 °K
1 8314 In2.586xl06]
239.05 2.879xl05-70.9 [ 101325 J
B. Estimate Properties at Choked Flow Conditions. Based
on assumed isentropic behavior, the vapor fraction at
choked flow conditions is estimated from Equation
(4.2.3-8):
r2.586xl06]"
= 1 + . 70.9-439 inl - 8314 in
2.879x102-70.9 [_ * 321 ' [l.40x!06JJ
= .966
Using Equation (4.2.3-9), the enthalpy change is
estimated as:
Ht - H. = 489 (349.2 - 321) + 2.879xl05 (1 - .966) = 2.36xl04 (J/kg)
The density is estimated using Equation (4.2.3-10) :
4-59
-------
p.
c.
n
= 0 966
L I1
Estimate
emission
= 0.00810
8314-321 1 +
.40xl06-70.9J
/ 1 - 0.966 \ "
\ 1574 / _
-i
= 38.5
Emission Rate. Using Equation (4.2.
rate is estimated as:
7-38.5 2-0.85
kg/m3
3-11),
the
A ~\ I1'2
2-36x10* -, ....
D. Estimate Discharge Temperature and Density.
Application of Equation (4.2.3-12) gives the discharge
temperature (T2) as:
T, = _ - - = 239.05 °K
1 8314 / 101325 \
239.05 2.879xl05-70.9 U01325
and Equation (4.2.3-13) gives the vapor fraction (X2)
as:
X, = .966 + 489(321 - 239 . 05) /2 . 879xl05 = 1.11
since X2 > 1, these estimates are not valid. Using
Equation (4.2.3-15) gives T2 as :
T2 = 321 -»• 2.879xl05(l - .966)/489 = 341 °K
and Equation (4.2.3-16) gives the discharge density
(P2) as:
(For these choked flow conditions, correct application
of a dispersion model may require that the diameter of
the hole or opening be modified to D0(p*/p2)1/2 =
0.1016(38.5/2.53)m = 0.396 m if the model accounts for
initial air dilution due to jetting or momentum
effects; if this modification is not applied, the
initial gas velocity is incorrectly overestimated.)
Proceed to Step 7. -
7. Perform Buoyancy Check.
A. Calculate density of air using Equation (4.2.3-22) as
follows:
4-60
-------
B. • p2/Piir > ! therefore, buoyancy is negative.
Release Duration. Calculate the release duration Td using
Equation (4.2.3-23) as follows:
T, (min) =
400 (kg)
62.5 (kg/s) • 60 (s/min)
= 0.107 min
Since the release is from a relief valve, run the RVP model
(See Section 5.2 for more information on the RVD model.)
Data entry in the TSCREEN model for this example is shown below:
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS • Page 1 of 4
Enter a unique title for this data's model run:
$«^irt^vii^" £1.67 " cm1
Enter P for Pipe - T for tank -> |
FLOW CHARACTERISTIC
Critical
Pressure
Gas Heat Capacity
Reservoir Pressure
Molecular Weight
Flow
Ambient
(P*)
->
->
->
->
->
1404072
2.JSB6E&
7&J
Choked
mm
Pa
J/kg °K
Pa
kg/kmol
Pa
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS - Page 2 of 4
TEMPERATURES
Gas Temperature (T*) at Critical Pressure -> 301.6262
Reservoir Temperature (T1)
Critical Temperature (Tc) -> 4;1^||5*;j:j, "K
VAPOR PRESSURE
Vapor Pressure (Pv) at Gas Temperature -> 853262.5 Pa
Latent Heat of Vaporization (Lvap) at Tb ->
Boiling Point Temperature (Tb) ->
J/kg
°K
•. -Edit?-.. t.f
-------
Continuous Leaks from Reservoir - Scenario 2.3
SOURCE PARAMETERS - Page 3 of 4
EMISSION RATE
Emission Rate (Qra) -> 62583.96 g/s
Density at Reservoir Conditions (f1) -> 15?£ kg/cubic in
DISCHARGE CHARACTERISTICS
Discharge Temperature (T2) -> 341.572 °K
Discharge Density (|7) -> 2.529709 kg/cubic m
Vapor Fraction at Discharge Flow Conditions(X2)-> 1.105221
Density of Air (fair) -> 1.20209 kg/cubic m
Ambient Temperature (Ta) -> 293KPC. °IC
Buoyancy is Negative
aftt <&> Previous serasn t
TIME
Release Duration (Td) -> 0.106524 min
Total Amount of Material Released (Q) -> 4&Jf/?!%:; kg
edit «I9> Pf**$«u» Screen :Afebrt
Continuous Leaks from Reservoir - Scenario 2.3
Based on user input, RVO model has been selected.
RVD MODEL INPUTS - Page 1 of 3
RELEASE PARAMETERS
Release Height above Ground -> 1ft' : m
Exhaust Gas Exit Velocity -> TWL8?l m/s
POLLUTANT INFORMATION
Pollutant Concentration (vol) -> tOCfi -v .:•; ? %
Pollutant Molecular Weight -> 7?|%/1:;;. g/g-mole
TIME
Desired Averaging Time for the Calculation
of Concentrations -> t&-: "''*•-.. min
£dit Previous Screen ' Next Screen- <£sc> Abort
4-62
-------
Continuous Leaks from Reservoir - Scenario 2.3
RVD MODEL INPUTS - Page 2 of 3
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural •> f
FENCELINE DISTANCE
Enter the distance from the base of the stack
to the plant fenceline ->
RECEPTOR LOCATIONS
Do you have specific locations where you would
like pollutant concentrations calculated (Y/N) ->
$er«ft
The RVD model's output is displayed below:
Saturated Vapor Chlorine Leak 07-30-1992
Input Data
Pollutant emission rate (kg/sec) = 62.58396
Exit gas velocity (m/sec)= 148.87
Exit Temperature (K)= 341.572
Stack Height (m) = 10 Diameter (m) = .101598
Pollutant Concentration (volune X) * 100
Exhaust Gas Density (kg/m3) = 2.523289
Exhaust Gas Molecular Weight - 70.9
Exhaust Gas Mass Flow Rate (kg/sec) = 62.58396
Pollutant Molecular Weight = 70.9
Release duration (min) = .106524 Av. Time (min) = 15
1.0 2.0 3.0 4.0 5.0
8.0 10.0 15.0 20.0
Distances (m) = 100 200 300 400 500 600 700
. 800 900 1000 1100 1200 1300
1500 1600 1700 1900 2100 2300
2700 2900 3100 3300 3600 3900
4500 5000
Ambient Temperature (K) = 293 293 293 293 293 293
Rural Wind Speed Profile Exponents
Wind Speeds (m/sec) =
1400
2500
4200
*** SUMMARY OF RVD MODEL RESULTS ***
*»*******»**»********»«****«*»**«««****«******»»***•*«»*»****
.Maximum off site concentration is 582952.8 ug/m3
or equivalent ly 201.4435 ppm
occurring at 112.2981 m downwind
when wind speed is 1 m/sec
and stability is A
REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS
4-63
-------
*** RVD DISTANCES
««««»« **««•*
Distance Concentration
(m)
(ug/m3)
Stability Wind
Class Speed
(m/sec)
-------
Release Richardson Numbers
Stability Class
Wind
Speed
1.0
2.0
3.0
4.0
5.0
8.0
10.0
15.0
20.0
A
-
729135.7
91142.0
27005.0
11392.7
5833.1
1424.1
729.1
216.0
91.1
B
729135.7
91142.0
27005.0
11392.7
5833.1
1424.1
729.1
216.0
91.1
C
729135.7
91142.0
27005.0
11392.7
5833.1
1424.1
729.1
216.0
91.1
D
729135.7
91142.0
27005.0
11392.7
5833.1
1424.1
729.1
216.0
91.1
E
729135.7
91142.0
27005.0
11392.7
5833.1
1424.1
729.1
216.0
91.1
F
729135.7
91142.0
27005.0
11392.7
5833.1
1424.1
729.1
216.0
91.1
Dense Plume Trajectory
Stability Wind Plune Touchdown
Class
A
A
A
B
B
B
B
B
C
C
C
C
C
C
C
C
C
D
D
D
D
D
D
0
0
D
E
E
E
E
F
F
F
Speed
(rn/sec)
1.0
2.0
3.0
1.0
2.0
3.0
4.0
5.0
" 1.0
2.0
3.0
4.0
5.0
8.0
10,0
15.0
20.0
1.0
2.0
3.0
4.0
5.0
8.0
10.0
15. Q
20.0
2.0
3.0
4.0
5.0
1.0
2.0
3.0
Rise Distance
(m) (m)
31.8 112.30
25.2 234.32
22.0 361.81
31.8 112.30
25.2 234.32
22.0 361.81
20.0 493.46
18.6 628.57
31.8 112.30
25.2 234.32
22.0 361.81
20.0 493.46
18.6 628.57
15.9 1050.62
14.8 1343.49
12.9 2107.74
11.7 2909.84
31.8 112.30
25.2 234.32
22.0 361.81
20.0 493.46
18.6 628.57
15.9 1050.62
14.8 1343.49
12.9 2107.74
11.7 2909.84
25.2 234.32
22.0 361.81
20.0 493.46
18.6 628.57
31.8 112.30
25.2 234.32
22.0 361.81
Touchdown
Concentration
(ug/m3)
0.58295E+06
0.42725E+06
0.35393E+06
0.58295E+06
0.42725E+06
0.35393E+06
0.30867E+06
0.27705E+06
0.58295E+06
0.42725E+06
0.35393E+06
0.30867E+06
0.27705E+06
0.21933E+06
0.19571E+06
0.15828E+06
0.13557E+06
0.58295E+06
0.42725E+06
0.35393E+06
0.30867E+06
0.27705E+06
Q.21933E+06
0.1 9571 E+06
0.15828E+06
0.13557E+06
0.42725E+06
0.35393E+06
0.30867E+06
0.27705E+06
0.58295E-MJ6
0. 42725 E+06
0.35393E+06
(ppm)
0.20144E+03
0. 14764E+03
0.12230E+03
0.20144E+03
0.14764E+03
0.12230E+03
0.10666E+03
0.95737E+02
0.20144E+03
0.14764E+03
0.12230E+03
0.10666E+03
0.957376*02
0.75791E*02
0.67630E+02
0.54696E+02
0.46846E+02
0.20144E*03
0.14764E+03
0.12230E+03
0.10666E+03
0.95737E+02
0.75791E+02
0.67630E+02
0.54696E+02
. 0.46846E*02
0.14764E+03
0.12230E+03
0.10666E+03
0.95737E+02
0.20144£t'03
0.14764E+03
0.12230E+03
4-65
-------
Concentrations at Specific Receptor Distances
Stability Wind Distance Concentration
Class Speed
A
A
A
A
A
A
F
F
F
F
F
F
*******!
*** END
(m/see)
1.0
1.0
2.0
1.0
2.0
3.0
1.0
2.0
3.0
(m)
200.0
300.0
300.0
400.0
400.0
400.0
4500.0
4500.0
4500.0
0.40060E+06
0.30778E+06
0.36385E+06
0.25529E+06
0.30180E+06
0.33158E+06
0.18137E+05
0.28100E+05
0.35945E+05
1.0 5000.0 0.15163E+05
2.0 5000.0 0.23492E+05
3.0 5000.0 0.30050E+05
(PP">
0.1384E+03
0.1064E+03
0.1257E+03
0.3822E+02
0.1043E+03
0.1146E+03
0.6267E+01
0.9710E+01
0.1242E+02
0.5240E+01
0.8118E+01
0.1038E+02
OF RVD MODEL OUTPUT ***
4.2.3.5 Considerations for Time-Varying and Time-Limited
Releases
See Section 2.5 for a discussion of considerations for time-
varying and time-limited releases.
4-66
-------
4.2.4 Instantaneous Gas Leaks from a Reservoir
Instantaneous
Gaseous Emission
Blown Rupture Disk
Similar Releases: A gas leak from a tank or a (small) gas leak
from a pipe.
Discussion:
This procedure applies to an instantaneous release of a gas
(at constant pressure and temperature) from a containment
(reservoir) through a hole or opening.
Limitations and.Assumptions:
Same as Scenario 4.2.3.
Input Information:
Same as Scenario 4.2.3.
Procedure:
1-6. Same as Scenario 4.2.3
7. Buoyancy Check. Perform buoyancy check as a first check.
A. Calculate the density of air using the following:
R T.
(4.2.4-1!
where. Mt is the molecular weight of air (assumed to
4-67
-------
equal 28.9 kg/kmol).
B. If p^/Pta > 1« then the buoyancy is negative. For
negative buoyancy, the RVD model should be used if the
release is from a vertically directed jet/ otherwise,
the Britter-McQuaid model should be used/ go to step 8.
If the buoyancy is positive, the PUFF model for a point
source should be used. (See Section 2.4 for more
information on model selection.)
8. Same as Section 4.2.3
4.2.4.1 Examples
See the examples in Section 4.2.3.
4-68
-------
4.2.5 Continuous Gas Leaks from a Pipe Attached to a Reservoir
4.2.5.1 Release Rate Estimates: Gas Leaks from a Pipe Attached'
to a Reservoir'
Similar Releases: Continuous release of a gas (at constant
pressure and temperature) from a containment through a long pipe.
Limitations and Assumptions:
The hole or opening size must be sufficiently small,
otherwise the reservoir temperature and pressure may no longer be
constant. For the case of a leak from a tank, the assumption of
constant reservoir temperature and pressure may be violated if a
significant percentage of the tank contents is released. If the
reservoir temperature and pressure are not constant, the release
rate may vary with time, but the maximum release rate is
generally obtained for the initial reservoir temperature and
pressure .
The flow through the pipe is assumed to be adiabatic (i.e.,
the heat transfer to the gas being released is unimportant) ; this
assumption is not very restrictive (Levenspiel (1977) ) .
The released material must be a (ideal) gas at the reservoir
conditions, during the depressurization process, and after
depressurization to the atmosphere, and for the case of a tank
containing vapor and liquid, -the pipe must be attached to the "
vapor space of the tank (Spicer, 1992) .
Input Information:
area of reservoir hole or opening (m2)
(equivalent) diameter of hole or opening (D0 =
4-69
-------
) (m)
Dp pipe diameter (m)
Lp pipe length (m)
MV gas (contaminant) molecular weight (g/g-mole) (For
contaminant mixtures, see Appendix B)
Ne number of pipe elbows (dimensionless)
Pv vapor pressure as a function of temperature (Pa)
P. ambient pressure (Pa)
Pt reservoir pressure (Pa)
R gas constant (8314 J/kg-mole-°K or 8314
P,-m3/kg-mole-°K)
Tc critical temperature (°K)
T! reservoir temperature (°K)
~ 1/(1 - R/tCMJ) at T! (dimensionless)
Procedure:
1. Pipe Friction Loss. Estimate the friction loss in the
piping system. After Perry et-al. (1984), estimate the
frictional loss N as-.
4 f L
N = —_I + 0.5 + 0.75 Ne + [0.5] (4.2.5-1)
In Equation (4.2.5-1), the first term represents the skin
friction losses in the pipe; f=0.0045 (the coefficient of
skin friction) can be used as a preliminary estimate (i.e.,
a tighter estimate of f would probably be less than 0.0045,
and although f can be larger for Reynolds numbers less than
105, typical Reynolds numbers for these applications are
larger than 10s) . The second term provides for the effect
of friction losses in the reservoir-to-pipe connection. The
third term accounts for frictional losses in any pipe
elbows. The fourth term (written in brackets) should only
be included if D0/DP s 0.2, otherwise it should be left off.
2. Discharge for Choked Flow. Estimate the discharge rate as
if the flow is choked (the validity of this assumption will
be checked); in this case, the gas approaches the speed of
sound at the exit. For choked flow, the following equations
must be solved simultaneously for the Mach number at the
pipe entrance Mj and a dimertsionless parameter (at the pipe
entrance) Y2:
tfi
Y, = 1 + /JLlJL) Mj2 (4.2.5-2)
\ 2 /
2Y* 1- f_l -lU7N = 0
*t (^ + 1) j 1M* j (4.2.5-3)
After M2 and Y2 are known, the mass flux G is fixed by:
4-70
-------
^1/2
G = P1M2
1TT7
(4.2.5-4)
The discharge pressure must be checked to determine if the
flow is indeed choked:
P, (Pa)
(4.2.5-5)
If P3Pi, then the flow is not choked, and these
estimates for G, M^ Y2/ and P3 are not valid; proceed to
step 3. If P^P^P,, then the flow is choked, and the
release rate is given by Qm (kg/s) = G AO. The discharge
temperature T3 is given by 2^7(7+1) . Proceed to step 4..
3. Discharge for Subcritical Flow. Estimate the discharge rate
for subcritical flow; in this case, the gas pressure at the
pipe exit approaches ambient pressure (P3=PJ . For
subcritical flow, the following eight equations must be
solved simultaneously for the mass flux G; the Mach number
at the pipe entrance and exit M2 and M3; the pressure at the
pipe entrance P2 (Pa); the temperature at the pipe entrance
and exit T2 and T3; and the dimensionless flow parameters (at
the pipe entrance and exit) Y2 and Y3:
Y = 1 + / T
Y, = 1 + ( T
Y3 1 J
JULi ) in f !i5l ] - f
i «b** i
2 / M2 Y
^ 3 1
IM "v
__!lZ
"D T1
R J-i
M, = -£ [-
K.-*P
' P2 [1
P, f T,
_! = i-l
•**\ 1 I-M
~ 1 \ M| (4.2.5
/
1 1 Ma2 (42^
2IV13 \-X.4.. _<
/
A-jLln-7N = 0
M M 1
^ M3 J (4.2.5
>,l/2
Y('Y'*'1)/(1"— y) 1 / /i o c
2 (4 . 2 . b
J
T 11/2
ill (4.2.5-
» •£ -)l/2
^CT (4.2.5-
MWJ
17/( 7-D
(4.2.6-
-6)
-7)
-8)
-9)
10)
11)
12)
(4.2.5-13)
The solution to these equations must be checked particularly
to ensure that M3<1, Pi>P2, and Tt>T2. If these conditions
are not met, the value of f is probably too low and should
be increased. The release rate is given by Qm (kg/s) = G
4-71
-------
A,,. Proceed to step 4.
4. Check Discharge Temperature T3. The estimate of T3 must be
checked. If T3 is greater than the (pseudo) critical
temperature Tc, the equation used to estimate T3 applies; if
not, the following procedure is suggested. For single
component contaminants, evaluate the contaminant vapor
pressure at T3 (PV(T3)). If PV(T3) a Pa< then contaminant
condensation occurs during the process of depressurization,
and this approach is not valid; this release should be
considered a two-phase release. If this is a two-phase
release proceed to step 6, otherwise proceed to step 5.
5. Discharge Density. Estimate the discharge density from the
discharge temperature T3 using the ideal gas law: p3 =
PjMw/ (RT3) . (Note that for choked flow conditions, correct
application of a dispersion model may require that the
diameter of the hole or opening be modified D0(P3/Pa)U2 if the
model accounts for initial air dilution due to jetting or
momentum effects;-if this modification is not applied, the
initial gas velocity is incorrectly overestimated.) Proceed
to step 9.
4.2.5.2 Continuous (Two-Phase) Release Rate Estimate: Gas
Storage which Partially Condenses on Depressurization
Similar Releases -. A gas leak from a tank, a gas leak from a
pipe.
Discussion:
Materials which are stored under pressure will depressurize
when released to the atmosphere. This depressurization results
in the formation of two contaminant phases (saturated liquid and
vapor) for: gases which cool so that condensation occurs during
the depressurization process; and high volatility liquids
(liquids whose normal boiling point is below the ambient
temperature) which are stored at (typically) above ambient
pressure. (See Section 4.3.2 for more discussion on two-phase
releases.) In this scenario, the terms gas, saturated liquid,
and subcooled liquid all refer to the state of the tank
contents.) This scenario considers the release from a tank (or
reservoir) and includes provision for the effect of a pressure
drop (piping) between the tank and the hole or opening.
This procedure applies to a continuous release of a gas
which partially condenses during depressurization; the screening
procedure for this scenario should only be applied if the
screening procedure above indicated that partial condensation of
the released gas occurs. The release occurs (at constant
pressure and temperature) from a containment (reservoir) through
a hole or opening; a provision is made for the-effect of a
pressure drop (piping) between the tank and the hole or opening.
4-72
-------
Limitations and Assumptions:
The pressure and temperature of the tank (or reservoir)
contents are essentially constant. The hole or opening size must
be sufficiently small, otherwise the reservoir temperature and
pressure may no longer be constant. For the case of a leak from
a tank, the assumption of constant reservoir temperature and
pressure may be violated if a significant percentage of the tank
contents is released. If the reservoir temperature and pressure
are not constant, the release rate may vary with time, but the
maximum release rate is generally obtained for the initial
reservoir temperature and pressure.
For the case of a leak from a pipe when j8 > 0.2 (as defined
below), the assumption of constant temperature and pressure in
the pipe may be violated; for such a case, the reservoir
conditions should be taken from an upstream location (tank or
reservoir) where the temperature and pressure will be
(approximately) constant. For the case of a leak from a pipe
when |8 s 0.2,. -the assumption of constant temperature and pressure
in the pipe is reasonable, and the reservoir conditions should be
taken to be the conditions within the pipe.
The vapor phase of the release material must be an ideal gas
at the reservoir conditions, during the depressurization process,
and after depressurization to the atmosphere; for the case of a
tank containing vapor and liquid, the hole must be in the vapor
space of the tank. For two phase flows, all released liquid is
assumed to travel downwind as an aerosol with little rain out of
liquid near the source (Spicer, 1992).
Input Information:
AQ area of reservoir hole or opening (m2)
A! flow area representing reservoir conditions (m2) (In •
case of a leak from a tank, At -» oo (and /3 = 0) ; in the
case of a leak from a pipe, At is the cross-sectional
area of the pipe.)
Cp gas (contaminant) heat capacity at T! (J/kg-°K) (For
contaminant mixtures, see Appendix B)
D0 (equivalent) diameter of hole or opening (D0 =
2-^Ao/Tr ) (m)
Dp pipe diameter (as appropriate) (m)
Lp pipe length (appropriate) (m)
Mw gas (contaminant) -molecular weight (kg/kmol) (For
contaminant mixtures, see Appendix B)
P. ambient pressure (Pa)
Pv vapor pressure as a function of temperature (Pa)
P! reservoir pressure (Pa)
R gas constant (8314 J/kg-mole-°K or 8314 P.-m3/kg-
mole-°K)
Tb contaminant normal boiling point (°K)
4-73
-------
Tc critical temperature (for contaminant mixtures, see
Appendix B)
T! reservoir temperature (°K)
j8 ^AQ/AJ {dimensionless)
7 (Cp/Cv) » 1/(1 - R/tCpMJ) at Tt (dimensionless)
X heat of vaporization at the normal boiling point (J/kg)
P! contaminant density at reservoir conditions (T: and PL)
(kg/m3)
Procedure:
6. Choked Pressure. Estimate the choked pressure P, to
determine if the flow is choked from Perry et al. (1984).
'ITU
(4.2.5-14)
If P. a P., then the flow is choked; go to step 7. If P. <
P,, then the flow is subcritical (not choked); go to step 8.
7. Two-Phase Choked Flow. For choked flow, estimate the
discharge temperature T2/ discharge density p2, and the
. emission rate Qm.
A. Estimate T.. For pure components, estimate T* (the
temperature which corresponds to P.) from the Glausius-
Clapeyron equation:
P. = 101325 exp f-^.f i -ill (4.2.5-15)
[ R [ Tb T. J J
which can be rewritten as:
1
T. =
R in
Tb XMW 101325
B. Estimate Properties at Choked Flow Conditions. Based
on assumed isentropic behavior, estimate the vapor
fraction at choked flow conditions X, as follows:
T F CTl rDll
X- - 1 f T^r M. C. in Ui -R m -^- i (4.2.5-16;
Using X. from Equation (4.2.5-16), estimate the
enthalpy change (Hj-H,) and the density p, as follows:
H, - H. = Cp (Tt - T.) + \ (1 - X.) (4.2.5-17)
4-74
-------
p. = X. I R T' I + I 1 " X* I (2.5-17)
Note that values for the individual enthalpies H! and H*
are not required.
C. Estimate Emission Rate. Extending the ideas suggested
by Lees (1950), estimate the emission rate Qm (kg/s) as
follows:
P. 2-0.85
- H
4 f
1/2
(4.2.5-19)
where 0.85 is included to account for irrevesibilities
in the flow based" on Lewitt (1953) and the term 4fLp/Dp
accounts for the pressure drop (piping) between the
reservoir and the hole or opening/ as a preliminary
estimate, use f =0.0045 (since typical Reynolds numbers
for these applications are larger than 105) .
D. Estimate Discharge Temperature and Density. Estimate
the discharge temperature T2 (after depressurization) .
If a condensed phase is present, T2 will be given by
the Glaus ius-Clapeyron equation:
P. = 101325 exp i * - * 1 (4.2.5-20)
Tb
which can be rewritten as:
m _ 1
. in
Tb \M; [101325 J
Using this estimate of T2/ estimate the vapor fraction
X2 as:
(4.2.5-21)
X. = X. + Cn(T. - T2)/X
When X2 estimated from Equation (4.2.5-21) satisfies 1
a X, a 0, the estimate of T2 is valid, and the density
of che discharged material is given by:
r
T
2
*
PL
(4.2.5-22)
However, if X2 < 0 or Xj > 1, the contaminant condensed
phase which was present at P. and T. is no longer
»
4-75
-------
present, and the released contaminant is a gas (without
any condensed phase); the discharge temperature and
density are estimated as follows:
T2 = T.
- X.)/C
(4.2.5-23)
(4.2.5-24)
E.
where X, = 0 .
Go to step 9 to select the dispersion model.
8. Two-Phase Subcritical (Nonchoked) Flow. For subcritical
flow, estimate the gas/liquid discharge temperature T2,
discharge density ,o2/ and the emission rate Qm.
A. Estimate T2. For pure components, estimate T2 from the
Glausius-Clapeyron equation:
Pa = 101325 exp
X Mw
~R~
(4.2.5-25)
which can be rewritten as:
1
T =
•"•2
R
i M.
In
101325
B. Estimate Properties at Discharge Conditions. Based on
assumed isentropic behavior, estimate the vapor
fraction Xj at discharge flow conditions as:
X2 = 1
•"•2
"Ml
C ln - B in i
(4.2.5-26}
Using X2 from Equation (4^.2.5-26), estimate the
enthalpy change (K^ - 1^) "and the density p2 .as:
- H,
Cp (Tt - T2) f X (1 - X2)
R T2
PL
-i
(4.2.5-27)
(4.2.5-28)
Estimate Emission Rate. Extending the ideas suggested
be Lees (1950), estimate the emission rate Qm (kg/s)
as:
Q.
Pi
0.85
HI -
4 f LP / DP
(4.2.5-29)
4-76
-------
where 0.85 is included to account for irrevesibilities
in the flow based on Lewitt (1953) and the term 4fLp/Dp
accounts for the pressure drop (piping) between the
reservoir and the hole or opening (as appropriate); as
a preliminary estimate, use f = 0.0045 (since typical
Reynolds numbers for these applications are larger than
10J) .
D. Go to step 9 to determine the dispersion model.
4.2.5.3 Dispersion Model Determination
See Section 2.4 for a complete discussion of the model
determination.
Input Information;
T, ambient temperature (°K)
Q total amount of material released (kg)
Procedure:
9. Buoyancy Check. Evaluate release buoyancy as a first check.
A. Calculate the density of air using the following:
(4.2.5-30)
where M» is the molecular weight of air (assumed to
equal 28.9 kg/kmol ) .
B. If p2//°«ir > !' then the buoyancy is negative. For
negative buoyancy, the RVD model should be used if the
release is from a vertically directed jet; otherwise,
the Britter-McQuaid model should be used; go to step
10. If the buoyancy is positive, the SCREEN model for a
point source should be used. (See Section 2.4 for more
information on model selection.)
x
10. Release Duration. The release duration is used as an input
into the RVD and Britter-McQuaid models . The release
duration can be used to determine if the release is
continuous or instantaneous (see Section 2.5). Calculate
the release duration Td using the equation below:
Td (min) = ____ — , , y . , (4.2.5-31)
Qm (kg/s) • 60 (s/min)
4-77
-------
4.2.5.4 Examples
4.2.5.4.1 Example 1: Air Leak - Choked
Discussion:
In this example (from Perry et al. (1984)), (dry) air stored
at l.lOlxlO6 Pa and 293.15 °K is released from a tank through 10
m of a 5.25 cm (inside diameter) Schedule 40 steel pipe/ there
are three elbows in the line. The diameter of the opening is the
diameter of the pipe. The fenceline is 100 m from the tank.
This example demonstrates the procedure when the flow is choked.
The following information will be required:
AO area of reservoir hole or opening (7rD0/4 = 0.002165 m2)
Cp gas (contaminant) heat capacity at TI (1004 J/kg °K)
D0 diameter of hole or opening (D0 = 0.0525 m)
Lp pipe length (10 m)
MV gas (contaminant) molecular weight (29 kg/kmol)
Ne number of pipe elbows (3)
Pa ambient pressure (101325 Pa)
P! reservoir pressure (l.lOlxlO6 Pa)
R gas constant (8314 J/kg-mole- °K)
Tb normal boiling point (79 °K)
Q total amount of material released (400 kg)
. Ta ambient temperature (293 °K)
Te critical temperature (154.6 °K)
TI reservoir temperature (293.15 °K)
at Tt (1.40)
With this information, the procedure discussed above determines
the release rate, the discharge temperature, and the discharge
density.
1. Pipe Friction Loss. Estimate the friction loss in the
piping system. In Equation (4.2.5-1), the first term is
4 (0.0045) (10) /(O. 0525) = 3.43; the second term is 0.5; the
third term is 0 .76 (3) =2 .25; and the fourth term is not
included:
N = 3.43 + 0.5 + 2.25 = 6.18
2. Discharge for Choked Flow. Estimate the discharge rate as
if the flow is choked (the validity of this assumption will
be checked). For choked flow, Equations (4.2.5-2] and
(4.2.5-3) are solved simultaneously for Mj and Y2/- computer
solution gives Mj = 0.283 and Y2 = 1.016. With R, and Y2
known, the mass flux G is given by Equation (4.2.5-4) as:
4-78
-------
G = l.lOlxlO6 • 0.283 / 2^232 'is 1.016<1;40*l>'<1-1-40>)1/2 = 1210 kg/m2s
The discharge pressure P3 is given by Equation (4.2.5-5) as:
P3 (Pa) =1210 [**£ ; ^°( ^0%-JJ =2.71x10* Pa
Since P3 a P,, the flow is choked, and release rate is given
by Qm=(1210) (0.002165) =2.62 kg/s. (Note that the
estimated release rate for the same reservoir conditions is
reduced from 4220 g/s to 2620 g/s if the piping pressure
drop is included.) The discharge temperature T3 is given by
2Tj/(7+l); T3 = 244 °K/ Go to Step 4.
4. Check Discharge Temperature T3. The estimate of T3 must be
checked. For this example, T3 = 244 °K, and the pseudo
critical temperature of air is 154.6 °K, so no condensation
.occurs for these conditions.
5. Discharge Density. Estimate the discharge density p3 from
the discharge temperature T3 using the ideal gas law:
p3 = (101325) (29)/( (8314H244) ) = 1.45 kg/m3
(For these choked flow conditions, correct application of a
dispersion model may require that the diameter of the hole
or opening be modified to DQ(P3/Pt)in = 0.0525 m
(2.71x!OVl01325)1/2 = 0.0859 m if the model accounts for
initial air dilution due to jetting or momentum effects; if
this modification is not applied, the initial gas velocity
is incorrectly overestimated.) Go to step 9.
9. Perform Buoyancy Check.
A. Calculate density of air.
B. Ps/Pur > 1 therefore, buoyancy is negative.
10. Release Duration. Calculate the release duration Td using
the equation below:
2.54 min
, ^ » , ,
2.62 (kg/s) • 60 (s/min)
Since the release is not from a vertically directed jet, the
Britter-McQuaid model is used. (See Section 5.4 for more
information on the Britter-McQuaid model . )
4-79
-------
Data entry in the TSCREEN model for this example is shown below:
Continuous Leaks from Pipe Attached to Reservoir - Scenario 2.5
SOURCE PARAMETERS - Page 1 of 4
Enter a unique title for this data's model run:
Air Leak from Pipe Attached to a Reservoir
INPUT INFORMATION
Area (Ao) of Hole or Opening -> 21-65' cm1
.Pipe Diameter (Dp) -> 9.0525 m
Pipe Length (Lp) -> 16 m
Molecular Weight (Mw) -> Z9 kg/kmol
Number of Pipe Elbows (Ne) -> 3
Ambient Pressure (Pa) -> 1ST52S Pa
Reservoir Pressure (P1) -> t.ltJlEi- Pa
Reservoir Temperature (T1) -> 253*15 °K
• Gas Heat Capacity (Cp) -> 1084 J/kg °K
Continuous Leaks from Pipe Attached to Reservoir - Scenario 2.5
SOURCE PARAMETERS - Page 2 of 4
CRITICAL TEMPERATURE
Critical Temperature (Tc) ->
EMISSION CHARACTERISTICS
Flow Characteristic •> Choked
Emission Rate (Qm) -> 2625.677 g/s
Exit Temperature (T3) -> 244.3249 "K
Discharge Density (f3) -> 1.446561 kg/cubic m
Pipe Friction Loss (N) -> 6.178571
Exit Pressure (P3) -> 271306.2 Pa
Mass Flux (G) -> 1212.783 kg/m's
- Previous- Street* -Next- Seraet*. i *Ssc> Jtoorr
Continuous Leaks from Pipe Attached to Reservoir - Scenario 2.5 —
SOURCE PARAMETERS - Page 3 of 4
DENSITY
Density of Air (fair) -> 1.20209 kg/cubic m
Ambient Temperature (Ta) -> 293 ::T °<
Buoyancy is negative
4-80
-------
Continuous Leaks from Pipe Attached to Reservoir - Scenario 2.5
SOURCE PARAMETERS • Page 4 of 4
VERTICALLY DIRECTED JET
Does the release result in a vertically
directed jet (Y/N) -> if
TIME
Release Duration (Td) -> 2.539028 min
Total Amount of Material Released (Q) ->
Continuous Leaks from Pipe Attached to Reservoir - Scenario 2.5
Based on user input, the Britter-McQuaid model has been selected.
BRITTER-McQUAID MODEL INPUTS - Page 1 of 3
*
MODEL PARAMETERS
Relative Humidity (Rh) -> 50 %
Desired Averaging Time for the Calculation
of Concentrations ->&-.', min
Pollutant Boiling Point Temperature (Tb) -> 79- °K
£d1r
Previous Screen
RECEPTOR LOCATIONS
Do you have specific locations where you would
like pollutant concentrations calculated (Y/N) -> ti
Abart
A summary of the Britter-McQuaid model's output is displayed
below:
SUMMARY OF B&M MODEL RESULTS
MAX CONC MAX CONC DIST TO WIND SPEED
(UG/K**3) (PPM) MAX (M) (M/S)
.7283E+08 .6037E+05
100.
2.
REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS
4-81
-------
A
4.2.5.4.2 Example 2: Air Leak - Subcritical (Not Choked)
Discussion :
In this example, (dry) air stored at •!. 82xl05 atm and 293.15
°K is released from a tank through 10 m of a 5.25 cm (inside
diameter) Schedule 40 steel pipe; there are three elbows in the
line. The diameter of the opening is the diameter of the pipe.
The fenceline is located 100 m from the tank. This example
demonstrates the procedure when the flow is not choked and is
similar to the last example except for the reservoir pressure.
The following information will be required:
AO area of reservoir hole or opening (7rD0/4 = 0.002165 m2)
Cp gas- (contaminant) heat capacity at T: (1004 J/kg °K)
D0 diameter of hole or opening (D0 = 0.0525 m)
Lp pipe length (10 m)
MT, gas (contaminant) molecular weight (29 kg/kmol)
Ne number of pipe elbows (3)
P. ambient pressure (101325 Pa)
P! reservoir pressure (1.82xl05 Pa)
R gas constant (8314 J/kg-mole- °K)
Tb normal boiling point (79 °K)
Q total amount of material released (400 kg)
T, ambient temperature (293 °K)
Tc critical temperature (154.6 °K)
T! reservoir temperature (293.15 °K)
7 (Cp/C,) = 1/(1 - R/fCpMj) at Tj (1.40)
With this information, the procedure discussed above determines
the release rate, the discharge temperature, and the discharge
density.
Procedure :
1. Pipe Friction Loss. Estimate the friction loss in the
piping system. In Equation (2.5-1), the first term is
4(0.0045) (10)7(0.0525) = 3.43; the second term is 0.5; the
third term is 0.76 (3) =2 .25; and the fourth term is not
included :
N = 3.43 + 0.5 + 2.25 = 6.18
2. Discharge for Choked Flow. Estimate the discharge rate as
if the flow is choked (the validity .of this assumption will
be checked). For choked flow, Equations (4.2.5-2) and
(4.2.5-3) are solved simultaneously for IV^ and Y2; computer
solution gives Mj = 0.283 and Y2 = 1.016. With Mj and Y2
known, the mass flux G is given by Equation (4.2.5-4) as-.
4-82
-------
G = 1.82x10* • 0.283 ' i.oi6<1-*'*«/»-1-*»> » 201 kg/m2s
The discharge pressure P3 is given by Equation (4.2.5-5) as
'' ' 201 29 1 40
Since P.P2, and Tt>T2. The release rate is given be Qm = (184)
(0.002165) - 0.398 kg/s. (Note that the estimated release
rate for the same reservoir conditions is reduced from 693
g/s to 398 g/s if the piping pressure drop is included.) Go
to step 4.
4. Check Discharge Temperature T3. The estimate of T3 must be
checked. For this example, T3 » 282 °K, and the pseudo
critical temperature of air is 154 . 6 °K, so no condensation
occurs for these conditions .
5. Discharge Density. Estimate the discharge density p3 from
the discharge temperature T3 using the ideal gas law:
p3 = (101325) (29)/( (8314) (282) ) = 1.25 kg/m3
Go to step 9 .
9. Perform Buoyancy Check.
A. Calculate density of air. /
_ 101325 • 28.9 _ .
* 8314 . 293
B- Pi/Pair >!• therefore, buoyancy is negative.
10. Release Duration. Calculate the release duration Td using
the equation below:
T' (min) •
0.398 W40 is/mini
4-83
-------
After this calculation run the Britter-McQuaid model since
the release is not from a vertically directed jet. (See
Section 5.4 for more information on the Britter-McQuaid
model.)
Data entry in the TSCREEN model for this example is shown below:
Continuous Leaks from Pipe Attached to Reservoir - Scenario 2.5
SOURCE PARAMETERS - Page 1 of 4
Enter a unique title for this data's model run:
INPUT INFORMATION
Area (Ao) of Hole or Opening -> 21.65 cm1
Pipe Diameter (Dp) -> O.OS2J m
Pipe Length (Lp) -> TO - m
Molecular Weight (Mw) -> 29 kg/kmol
Number of Pipe Elbows (Ne) ->• 3
Ambient Pressure (Pa) -> T3T325 Pa
Reservoir Pressure (P1) -> t»$2&i: Pa
Reservoir Temperature (T1) -> 292S.1* "K
Gas Heat Capacity (Cp) -> TSQ4 J/kg °K
Prevfw*
«e*t fcf«e» •<£«> -Abort'
Continuous Leaks from Pipe Attached to Reservoir - Scenario 2.5
SOURCE PARAMETERS - Page 2 of 4
CRITICAL TEMPERATURE
Critical Temperature (Tc) -> T54i,»f.;{: °K
EMISSION CHARACTERISTICS
Flow Characteristic -> Subcritical
Emission Rate (Om) -> 397.0481 g/s
Exit Temperature (T3) -> 282.4518 °K
Discharge Density (f3) -> 1.251296 kg/cubic m
Pipe Friction Loss (N) -> 6.178571
Exit Pressure (P3> -> 101325.0 Pa
Mass Flux (G) -> 183.3939 kg/m's
Scrowt
Continuous Leaks from Pipe Attached to Reservoir - Scenario 2.5 —
SOURCE PARAMETERS - Page 3 of 4
DEMSITY
Density of Air (fair) -> 1.20209 kg/cubic m
Ambient Temperature (Ta) ->
Buoyancy is Negative
fiflt
Sfefeen
»«5*ae»
4-84
-------
Continuous Leaks from Pipe Attached to Reservoir - Scenario 2.5
SOURCE PARAMETERS - Page 4 of 4
VERTICALLY DIRECTED JET
Does the release result in a vertically
directed jet (Y/N) -> H
TIME
Release Duration (Td) -> 16.79058 min
Total Amount of Material Released (Q) ->
«#£>*• 8«lJt' , "Pr*vf«*»- Screen X
Desired Averaging Time for the Calculation
of Concentrations -> t? •• min
Pollutant Boiling Point Temperature (Tb) -> 79 °K
- Continuous Leaks from Pipe Attached to Reservoir - Scenario 2.5
BRITTER-MCQUAID MODEL INPUTS - Page 2 of 3
FENCELINE DISTANCE
Enter the distance from the base of the stack
to the plant fenceline ->
RECEPTOR LOCATIONS
Do you have specific locations where you would
like pollutant concentrations calculated (Y/N) ->
ltodeC
Abort
A summary of the Britter-McQuaid model's output is displayed
below:
4-85
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SUMMARY OF B&M MODEL RESULTS
MAX CONC MAX CONC DIST TO WIND SPEED
(PPM) MAX (M) (M/S)
.2459E-HJ8 .2038E+05 100. 1.
REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS
4.2.5.5 Considerations for Time-Varying and Time-Limited
Releases
. See Section 2.5 for a discussion of considerations for time-
varying and time-limited releases.
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4.2.6 Instantaneous Gas Leaks front a Pipe Attached to a
Reservoir
Similar Releases-. Instantaneous release of a gas from a
containment (at constant pressure and temperature) through a long
pipe.
Limitations and Assumptions:
Same as for Scenario 4.2.5.
Input Information;
Same as for Scenario 4.2.5.
Procedure:
1-8. Same as for Scenario 4.2.5
9. Buoyancy Check. Evaluate release buoyancy as a first check.
A. Calculate the density of air using the following:
x
P M
Plit = _±_! (4.2.6-1) .
&
where M, is the molecular weight of air (assumed to
equal 28.9 kg/kmol).
B. If p2//°iir > !/ then the buoyancy is negative. For
negative buoyancy, the RVD model should be used if the
release is from a vertically directed jet; otherwise,
the Britter-McQuaid model should be used; go to step
10. If the buoyancy is positive, the PUFF model for a
4-87
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point source should be used. (See Section 2.4 for more
information on model selection.)
10. Same as Section 4.2.5
4.2.6.1 Examples
See the examples in Section 4.2.5.
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4.2.7 Continuous Multiple Fugitive Emissions
Range Leaks
Hand Valve Stern
Pump Seals
Open Ditches
Similar Releases: Releases from any continuous area or volume
'source where the emissions that are uniformly released over the
area or the area represents a collection of small sources poorly
defined in terms of location (e.g., multiple vents on large
manufacturing buildings, fugitive VOC sources in refineries or
chemical process manufacturing plants).
Discussion:
Fugitive gaseous emissions resulting from a collection of
small sources and gaseous area source emissions of different
types (e.g., process equipment, valves, etc.) are modeled in this
section. Often, areas of fugitive emissions can be specified for
elevated releases such as manufacturing facilities where
substantial numbers of hood and vent sources are found on the
roof and fugitive emissions identified in mass balances are
suspected from ventilation sources. In these cases, the area of
release can be considered as a volume source using a
characteristic height such as a building height. Dispersion
calculations can assume area and volume source releases.
However, currently, the TSCREEN model does not include volume
source releases.
" The use of EPA fugitive emission factors for selected
equipment are found in the EPA report Protocol for Generating
Unit-Specific Emission Estimates for Equipment Leaks of VOC and
VHAP. EPA-450/3-8S-010 (Appendix A). For selected air toxic,
fugitive factors are also found in Appendix A (items 1 and 3) .
4-89
-------
Limitations and Assumptions-.
Dispersion calculations assume area source releases
only.
Input Information:
EF emission factor from various fugitive emissions (Mg/yr)
Pd production rate (kg/Mg)
Q.m emission rate (g/s)
4.2.7.1 Procedure
1.^ Emission Rate. Fugitive gaseous emissions resulting from a
collection of small sources and gaseous area source
emissions of different types (e.g., process equipment,
valves, etc.) are modeled using a source specific emission
rate or fugitive emission factors. The document Protocols
for Generating Unit-Specific Emissions Estimates for
Equipment Leaks or VOC. and VHAP. EPA-450/3-88-010 describes
methodologies the EPA considers appropriate for development
of unit specific emission estimates for equipment leaks of
organic compounds: volatile organic compounds (VOC) and
volatile hazardous air pollutants (VHAP). Estimates
generated using this document would be specific to process
units (or groups of sources) for which an estimate was made.
EPA has made provisions for extending such estimates beyond
the limits of that group of sources. Five methods for
estimating emissions from equipment leaks from a specific
chemical processing unit are included in the protocol:
average emission factor method; leak/no-leak emission factor
method; three-strata emission factor method; application of
EPA correlations; and development of new correlations. For
selected air toxics, factors are also found in Appendix A
items 1 and 3.
If the emission rate is not known it can be .calculated as
follows: ,
A. Emission Rate in kg/yr. Calculate emission rate in
kg/yr.
Qm (kg/yr) =Pd (Mg/yr) EF (kg/Mg) (4.2.7-1)
B; Emission Rate in g/s. Convert emission rate from kg/yr
to g/s.
Q (g/s) _ Qm (kg/yr) .1000 (g/kgl
365 (dy/yr) 86400 (s/dy)
4-90
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2. TSCREEN will run the SCREEN model for an area source. See
Section B.I.2 for a complete list of inputs.
4.2.7.2 Example: Ethylene Bichloride Release
Discussion:
The maximum hourly average concentration estimate is
required for ambient ethylene dichloride at a fenceline receptor
100 meters downwind from a production facility. The area of
emissions at the plant is 100 m x 100 m, and production rate is
204,000 Mg/yr in continuous operation over the year.
Normal production of ethylene dichloride in vinyl chloride
plants results in fugitive emissions from storage vents.
Specific sources of emissions cannot be specified. As a result,
simulations make use of emission factors to provide average
emissions plantwide. These emissions are then used in a
continuous ground level area source dispersion model.
Procedure: .
1. Emission Rate. Emissions are obtained from emission factors
published by EPA (1987b). Plant-wide emissions are
calculated from the production rate and an emission factor
from various fugitive sources. 'The emission factor per
production unit is given by:
chIorination vent 0.0216 kg/Mg
column vents 0.06 kg/Mg
• process storage vents 0.0003 kg/Mg
process fugitive 0.265 kg/Mg
Totat 0.3469 kg/Hg
A. Emission Rate in kg/yr. Total emissions (in kg/yr) for
the plant ar.e given by Equation (4.2.7-1) :
Qm (kg/yr) » 204,000 (Pflg/yr) X 0.3469 (icg/Mg). = 70,768 (kg/yr)
B. Emission Rate in g/s. Convert emission rate to g/s:
Q (j/g?- 70,768 (kg/yr) 1000 (g/kg) = 2_24 / }
Wm y/ 365 (dy/yr) 86400 (s/dy) a
2. Run the SCREEN model for an area source. For a complete
explanation of the inputs for the SCREEN model for an area
source, see Section 5.1.2. The default release height (Hs)
for this scenario is 0.
Data entry in the TSCREEN model for this is shown below:
4-91
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— Gaseous Emissions from Multiple Fugitive Sources - Scenario 2.7
SOURCE PARAMETERS - Page 1 of 1
Enter a unique title for this data's model run:
"
9/s
EMISSION RATE
Enter the Emission Rate (dm), if unknown enter
• the boxed variables below to calculate ->
Production Rate (Pd) -> 20*09$ Mg/yr
Emission Factor from various fugitive sources (EF) -> .3469 kg/Mg
id-it
*®s$>f Afeort.-:
Gaseous Emissions from Multiple Fugitive Sources - Scenario 2.7
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 2
RELEASE PARAMETERS
Release Height above Ground (Hs) -> P|i*?C n>
Area of the Emitting Source (A) -> 1€ieoi&C: m'
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural -> R:
FENCELINE DISTANCE
Enter the distance from the nearest edge of the
source to the plant fenceline -> |t98x••• j...' m
FLAG POLE RECEPTORS
Enter Receptor Height above Ground (Zr) -> 0;:;; •-..:',,:-.. m
RECEPTOR LOCATIONS
Do you have specific locations where you would like
pollutant concentrations to be calculated (Y/N) -> (jf
A summary of the SCREEN model's output for this example is shown
below:
*** SUMMARY OF SCREEN MODEL RESULTS ***
***************************************
CALCULATION
PROCEDURE
MAX CONC
(UG/M**3)
OlST TO
MAX (M)
TERRAIN
HT (M)
SIMPLE TERRAIN
1190.
100.
0.
***************************************************
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
4-92
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4.2.8 Continuous Emissions from Land Treatment Facilities
Emissions
Organic Sludge
Soft treatment
Similar Releases: Landfarms; ground level application of sludge
(volatile organic material in oil) to soil surface.
Discussion:
The emissions equation is a simplification of the Thibodeax-
Hwang model, assuming ground-level application of the waste, more
rapid diffusion through the oil layer, and vapor-liquid
equilibrium between the oil layer and pore spaces.
Limitations and Assumptions:
Waste is a sludge consisting of organics in oil.
Methods are a simplification of the Thibodeax-Hwang
emission model (Thibodeax and Hwang, 1982) .
Assumes no subsurface injection, slower diffusion of
organic component through air-filled po&e spaces than
through the oil layer, and vapor-liquid equilibrium
between the air in the pore spaces and the^ oil layer.
Assumes that Raoult's Law applies.
Effective diffusivity is assumed to be 40 % of pure
component diffusivity.
Input Information:
A release area (m2)
LV.P latent heat of vaporization (J/kmol)
Tb boiling point temperature (°K)
M,, molecular weight (kg/kmol)
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pptn grams of organic component per million grams of waste
oil (g/Mg)
Pv vapor pressure as a function of temperature (Pa)
R gas constant (8314 J/kg-mole- °K)
4.2.8.1 Procedure
1. Vapor Pressure. Calculate the vapor pressure (Pv) in Pa.
The vapor pressure of a pure substance is temperature
dependent. The Antoine equation could be used to. estimate
vapor pressure; however, the Glaus ius-Clapeyron equation is
used in TSCREEN because the required input is readily
available for most chemicals in TSCREEN' s chemical database
The Claus ius-Clapeyron equation is:
Pv = 101325 exp2-: - (4.2.8-1)
where T = liquid temperature (°K) , assumed = 298 °K. The
vapor pressure must be greater than 0 .
2. Emission Rate. Calculate Emission Rate (Qm) (g/s) . 'Since
typical applications involve applications of volatile
liquids such as benzene, the Thibodeux- Hwang emission model
has been simplified for screening purposes using default
values .-
Qm « K • ppm (g/Mg) - A (m2) • (Pv)1/2 (Pa) (4.2.8-2)
where: K = 9 .101xlO'10(g/Pa1/2-m2-s)
3 . Run the SCREEN model for an area source . For an explanation
of inputs to the SCREEN model to an area source, see Section
5.1.2.
4.2.8.2 Example: Emission from sludge containing _ benzene
Discussion:
Sludge containing 1000 ppm benzene is applied to a one acre
land treatment site at a rate of 1 lb/ft2 and filled to a depth
of 8 inches. Hourly average concentrations at the fenceline of
200 m are needed.
The following input information will be required:
A release area (one acre or 4046.8 m2)
^ latent heat of vaporization (3.9393xl05 J/kg)
Tb boiling point temperature of benzene (351 °K)
M, molecular weight (78.12 kg/kmol)
ppm. grams of benzene per million grams of waste oil (1000 g
•
4-94
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benzene/Mg oil)
gas constant (8314 J/kg-mole-°K)
Procedure:
1.
Vapor Pressure. The vapor pressure is calculated using
Equation (4.2.8-1) as follows:
P, . Z01325 exp 3.^3x^.73.12 |_1_ .
4 Pa
2. Emission Rate. Calculate the emission rate (Qm) in g/s
using Equation (4.2.8-2):
Qm = S.lOlxlO'10 • (1000) -4046.8 • (1.55xl04) m = 0 .46 g/s
3. Run the SCREEN model for an area source.
Data entry in the TSCREEN model for this example is shown berow:
Gaseous Emissions from Land Treatment Facilities - Scenario 2.8
SOURCE PARAMETERS - Page 1 of 2
Enter a unique title for this data's model run:
EMISSIONS RATE
Is the Emission Rate (Qm) known (Y/N) -> ft
VAPOR PRESSURE
Enter the Vapor Pressure of the Constituent (Pv),if unknown
enter the variables below to calculate -> f$$&$*€9 Pa
Latent Heat of Vaporization (Lvap) -> 3^959365 J/kg
Boiling Point Temperature (Tb) -> 35-t °K
Molecular Weight (Mw) -> 75.15. kg/kmol
<$%>•• £di-t •
Previous Screen-; Next: Senew*-
Abort
Gaseous Emissions from Land Treatment Facilities - Scenario 2.8
SOURCE PARAMETERS - Page 2 of 2
EMISSION RATE
Emission Rate (Qm) -> 0.459121 g/s
Parts of Organic Component in Waste Oil (ppm) -> 1000 g/Mg
Release Area (A) -> t&<>6*&, m1
4-95
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Gaseous Emissions from Land Treatment Facilities - Scenario 2.8
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 2
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural -> B
FENCELINE DISTANCE
Enter the distance from the nearest edge of the
source to the plant fence line -> •&)$. m
FLAG POLE RECEPTORS
Enter Receptor Height above Ground (Zr) -> ft m
RECEPTOR LOCATIONS
Do you have specific locations where you would like
po.Uutant concentrations to be calculated (Y/N) -> It
Run Jtodei.
Abort ]
A summary of the SCREEN model's output for this example is shown
below:
**********»*»*»*******»**«*#***********
*** SUMMARY OF SCREEN MODEL RESULTS ***
**»**•**•«**•***•*•*•»»*»**»**********«*•*»»*
CALCULATION
PROCEDURE
MAX CONC
(UG/M**3)
DIST TO TERRAIN
MAX (M) HT (M)
SIMPLE TERRAIN
3464.
100.
0.
*» REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
#***»*******«**»»**»*****»*»**»»*»**»•*****»*******
4-96
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4.2.9 Continuous Emissions from Municipal Solid Waste Landfills
Similar Releases: None. Emission rates applicable to municipal
solid waste landfills only.
Discussion:
A New Source Performance Standard was proposed on May 30,
1991 for Municipal Solid Waste Landfills (MSWLFs). Air emissions
from MSWLFs contribute to the formation of ambient ozone and
potentially to global warming. The U.S. EPA estimates that
MSWLFs emit about 1% of the national stationary source volatile
organic compound (VOC) emissions. Also, the methane produced
from landfills is between one third and one half of the national
total. Toxics, explosion potential, and odor nuisance are
additional problems related to air emissions from MSWLFs.
Landfill air emissions are controlled through application of
a gas collection system and control device. Three engineering
components comprise the collection and control system.
Extraction wells pull the gas up from the depth of the fill. A
header system links all the wells and collects the gas by vacuum.
A control device either burns the ga"s or uses it for fuel.
s
In the proposed regulation, the U.S. EPA has developed a
system to determine which landfills should be controlled. A non-
methane organic compound (NMOC) emission rate was selected for
determining applicability under this regulation. Each landfill
calculates its annual emissions. If a landfill emits over a
certain amount of NMOC per year, a gas collection and control
system must be installed.
The information in this section is taken from the background
document for proposal of air regulations for municipal solid
waste landfills (EPA, 1991b). This document explains how
emissions can be estimated using either (1) an equation based on
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default values or (2) sampling data (e.g., field measurements of
the gas flow rate and composition) . The equation is based on the
Scholl Canyon model (EMCON Associates, 1982) and uses default or
measured values of methane generation potential and nonmethane
organic compounds (NMOCs) . The total VOC emissions determined by
this procedure can be speciated using a profile as shown in Table
4.2.9-1. There are a number of factors contributing to the
variability in gaseous emissions from municipal solid waste
landfills (e.g., waste composition, landfill moisture content,
age of refuse, pH and alkalinity of landfill, amount of buried
waste, climate, and physical and operating characteristics of the
landfill) . The greatest sources of uncertainty are the type and
amount of waste buried in a landfill. Use of sampling data is
strongly recommended (as described in the EPA background document
for proposed regulations for municipal solid waste landfills) .
However, the use of an equation is considered appropriate as a
simple screening tool, and this approach is described below.
Ambient concentrations resulting from municipal solid waste
landfill emissions are determined using area source techniques in
the SCREEN model.
Limitations and Assumptions:
Emission rates are applicable to municipal solid waste
landfills only.
An average NMOC emission rate is provided. (To obtain
the individual toxic constituent emission rate, the
individual toxic constituent percent of total emissions
is needed. The background document for the proposed
regulations provides the range in the vapor phase
concentration of toxic constituents that has been
measured from landfills nationwide.)
Emission 'rates are assumed to be steady-state, with no
seasonal or diurnal variation.
Output :
MNMOC = Average annual NMOC emission rate, Mg/yr
MNMOC (g/s) = MNMOC (Mg/yr) X 0.0317
Input Information:
*
L0 refuse methane generation potential (mJ/Mg refuse)
R average annual waste acceptance rate (Mg/yr)
k methane generation rate constant (1/yr)
c year since closure (c=0 for new/active landfills)
t age of landfill (yrs)
CNMOC concentration of NMOC (ppmv as hexane)
ConstPer constituent percent of total VOC emissions (%)
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3.595 X 1C)'9 conversion factor
The variables R, c, and t should be known for each landfill.
The average annual acceptance rate, R, can be determined by
dividing the refuse in place by the age of the landfill . If
site-specific values of k, L0, or CNMQC are unknown, default
values of 0.02/yr, 230 mYMg, and 8000 ppmv as hexane may be
used, respectively.
4.2.9.1 Procedure ;
1. Mass Emission Rate of NMOC, Mg/yr. Calculate the average
annual NMOC emission rate. The following equation is best
suited for the purposes of the U.S. EPA to determine the
NMOC emission rate:
MNMOC = 2L0R(e-kc - e*) (CNMOC) (3.595 X 10'9) (4.2.9-1)
2. Mass Emission Rate of NMOC, g/s. Convert Mass Emission Rate
of NMOC from Mg/yr to g/s.
MNMOC (9/s) = MNMOC (Mg/yr) X 0.0317 (4.2.9-2)
Fraction of total NMOC emissions/ Qm (g/s).
Qm (g/s) = MNMOC (g/s) X ConstPer (%)/100 (4.2.9-3)
4 . Dispersion of emissions from a landfill is simulated as an
area source, involving determination of dispersion
parameters based on virtual distances before concentrations
can be calculated at each receptor location. The SCREEN
model for an area source is used for this scenario. For an
explanation of inputs for the SCREEN model for an area
source, see Section 5.1.2.
4.2.9.2 Example •. Municipal Solid Waste Landfill
Discussion:
Hourly concentration estimates are required for emissions of
perchloroethene from a municipal landfill in Ohio. The landfill
area is 3 hectares and the distance to the nearest offsite
receptor is 100 m.
Concentration estimates from landfills are determined
using an emissions model or site-specific measurements. In this
example, measurements are not available and the NMOC emission
model in Section 4.2.9.1 is used. Once NMOC emissions are
calculated, NMOC emission profiles (Table 4.2.9-1) are used to
determine what fraction of the total is perchloroethene. The
example concentrations listed are averages; site- specif ic
4-99
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concentrations are dependent on the type of waste in the
landfill.
The following input information will be required:
L0 refuse methane generation potential (230 m3/Mg refuse)
R average annual waste acceptance rate (13,000 Mg/yr)
k methane generation rate constant (0.02 (1/yr))
c year since closure (0)
t age of landfill (10 yrs)
CNMOC concentration of NMOC (8000 pptnv as hexane)
molecular weight of NMOC (87.00 Ib/mole NMOC)
TABLE 4.2.9-1
SPECIATED VOC EMISSION PROFILE
Air Toxic Chemical Molecular Wt . Concentration (ppmv)
Benzene 78.12 3.52
Carbon Tetrachloride 153.81 1.49
Chloroform 119.38 0.06
Ethylene Bichloride 98.96 1.85
Methylene Chloride 84.93 19.70
Perchloroethene 165.83 6.82
Trichloroethene 131.29 3.80
Vinyl Chloride 62.50 ' 7.04
1, 1-Dichloroethylene 96.94 0.16
Procedure:
1. Mass Emission Rate of NMOC, Mg/yr. From Equation (4.2.9-1),
emissions are calculated as :
MNMOC = 2(230) (13,000) (1 - e^0'02*10') (8,000) (3.595X10'9)
=31.2 Mg/yr
2. Mass Emission Rate of NMOC, g/s. From Equation (4.2.9-2
the emissions in g/s are calculated as:
•
MNMOC "= 31.2 Mg/yr X 0.0317 = .989 g/sec
4-100
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3. Fraction of total NMOC emissions/ Qm (g/s). The fraction of
perchloroethylene to the total NMOC emissions can be
calculated as follows:
6.82(ppmv) X 165.83(Ib/mole) = 0.0016
8000(ppmv) 87.00(Ib/mole NMOC)
(ConstPer = 0.0016 x 100% = 0.16%)
Perchloroethylene emissions Qra can then be calculated as
follows:
Qm = -989 (g/s) X .0016 = .0016 g/s
4. TSCREEN will run the SCREEN model for an area source.
Landfill area = 3 hectares (30,000 m2)
Distance to nearest offsite receptor = 100 m
Data entry in the TSCREEN model for this example is shown below:
Emissions from Municipal Solid Waste Landfills - Scenario 2.9
SOURCE PARAMETERS - Page 1 of 1
Enter a unique title for this data's model run:
» ""
EMISSION RATE
Enter the Emission Rate (Qm), if unknown
enter the boxed variables below to calculate -> Q»0015ST g/s
Average Annual Acceptance Rate (R) ->
Year since Closure (c) -> 8
Age of Landfill (t) -> Iff
Methane Generation Rate Constant (k) -> 5.02
Refuse Methane Generation Potential (Lo) -> 23BS
Concentration of NMOC (Cnmoc) ->
Constituent % of Total VOC Emissions -> .
Mg/yr
yrs
1/yr
cubic m/Mg
ppmv as hexane
- Next. Se««w -- Abort-
4-101
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Emissions from Municipal Solid Waste Landfills - Scenario 2.9
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 2
RELEASE PARAMETERS
Release Height above Ground (Hs) -> ip$fficj m
Area of the Emitting Source (A) -> $&(9^ft m'
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural -> ft
FENCELINE DISTANCE
Enter the distance from the nearest edge of the
source to the plant fence line -> %S;p|./|¥ m
FLAG POLE RECEPTORS
Enter Receptor Height above Ground (Zr) -> ^±?*Q? m
RECEPTOR LOCATIONS
Do you have specific locations where you would like
pollutant concentrations to be calculated (Y/N) -> ft
j||i||f^|fi!i^^ ••_.";
A summary of SCREEN model's output for this example is displayed
below:
***************************************
*** S.UMHARY OF SCREEN rKOEl RESULTS ***
CALCULATION MAX CONC DIST TO TERRAIN
PROCEDURE (UG/M**3) MAX (M) HT (M)
SIMPLE TERRAIN 5.008 100. 0.
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
***************************************************
4-102
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4.2.10 Continuous Emissions of Pesticides
Emissions
Similar Releases: Emissions resulting from the volatilization of
pesticides or herbicides applied to open fields.
Discussion:
Pesticides are classified according to the targeted pest.
The most widely used pesticides, particularly in-agriculture, are
herbicides, insecticides, fungicides, and nematicides. A
pesticide, otherwise known as the active ingredient, is combined
with inert ingredients in formulations such as sprays, dusts,
granules, aerosols, fumigants, and microencapsulation.
There are several factors that influence the extent and rate
of pesticide volatilization, including physical and chemical
properties of the pesticide, method of application, the type of
surface to which the pesticide is applied, and degree of
incorporation into the soil.
Evaporative losses during application and post-application
are proportional to vapor pressure. The vapor pressure of active
ingredients generally range from 10'3 to 10'8 millimeters of
mercury" (mm Hg) . Fumigants usually have higher vapor pressures.
Ethylene bromide, a common fumigant, has a vapor pressure of 0.8
mm Hg at 20°C. Often the inert ingredient -i's an organic solvent
such as xylene, which has a vapor pressure of 8 mm Hg.
For pesticides applied to soils, the soil moisture content
and the depth of the tilling are important factors affecting
volatilization. Pesticides applied to dry soils do not
4-103
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volatilize as rapidly as pesticides applied to moist soils
because of greater adsorption of pesticides on dry soil. The
evaporation rate of pesticides incorporated into the soil is
limited primarily by pesticide movement through the soil to the
surface. The resistance increases with mixing depth.
Ambient concentrations resulting from the volatilization of
applied pesticides are determined by using area source techniques
in the SCREEN model.
Limitations and Assumptions
Maximum evaporation rates of pesticides are estimated
based on the rate of evaporation of a compound such as
water.
The method is based on the principle that loss of a
pure substance into the atmosphere from an inert
surface is proportional to the vapor pressure and the
square root of the molecular weight of the substance.
The water evaporation rate is adjusted for the type of
surface and relative humidity.
References -.
The best sources of information are technical
literature searches and contacts with agricultural research
stations. Information on pesticide formulations, air
emissions potential, and control strategies can be found in
the Alternative Control Technology (ACT) for Application of
Agricultural Pesticides report. The draft report was
released April 1992 for peer review by the Emissions
Standards Division of the Environmental Protection Agency
located in Research Triangle Park, North Carolina. The
reader may also find the following reference to be helpful .-
Spencer, W.P. and Cliath M.M., 1973: "Pesticide
Volatilization as Related to Water Loss from Soil,"
Journal of Environmental Quality.
Input Information:
E evaporation rate of water per acre (inches of water
evaporated X 226,600 pounds per inch on one acre)
(in/day)
aE adjusted water evaporation rate in lb/acre; aE=0.73E,
0.40E, and 0.70E for application to vegetated land,
soil surfaces, and water surfaces, respectively
RH relative humidity (%)
Pw vapor pressure of water at same temperature as PP
(atm)
»
4-104
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PP vapor pressure of pesticide ingredient (atm)
Mw molecular weight of water (18 g/g-mole)
Mp molecular weight of pesticide ingredient (g/g-mole)
A area of application (m2)
4.2.10.1 Procedure
1. Evaporation Rate of Water. Convert the evaporation rate of
water (E) from in/day to g/s.
E(lb/s/acre)= E(in/day)226600(Ib/in/acre)(day/8640Qs)
(4.2.10-1)
E (Ib/s) =E (Ib/s/acre) • A (m2) (4.2.10-2)
3910.3445 (mVacre)
E (g/s) *E (Ib/s) • 493.593 (g/lb) (4.2.10-3)
2. Emission Rate Qm. The following equation developed by
Spencer is used ,to determine the evaporation rate of a
pesticide ingredient per acre:
^= [aE/(l -RH/100)] [P, . 760 • Q (4.2.10.4)
Pw • 760 • M^'2
3. Area source dispersion techniques are used for the emissions
from pesticide application. The SCREEN model for an area
source is used for this scenario. For an explanation of
inputs to the SCREEN model for an area source, see Section
5.1.2
4 .2 .10.. 2 Example: Continuous Emissions from an Herbicide
Discussion:
Bentazon is applied to 14.5 acres (56,700 m2) for
postemergence control of broadleaf weeds. The active ingredient
is sodium bentazon at 40 percent by weight. The molecular weight
of sodium bentazon is 262 grams per mole. The vapor pressure at
25°C is approximately IxlO""' mm Hg (1.32xlO'10 atm) . Rate of
application is one pound of active ingredient per acre. The
evaporation rate of water is 0.20 inches per day. The property
boundary is located 100 meters from the edge of the study field.
Maximum post-application one-hour average concentrations are to
be estimated. The relative humidify is 60 percent.
The following input information will be required:
E evaporation rate of water per acre (Ib/day/acre)
(inches of water evaporated per day X 226,600 pounds
per inch on one acre); 0.20 in/day of water evaporated
*
4-105
-------
aE adjusted water evaporation rate in- lb/acre/ aE=0.73E
for application to vegetated land
RH relative humidity (60 %)
Pw vapor pressure of water at same temperature as PP
(.03158 atm)
PP vapor pressure of pesticide ingredient (1.32xlO~10 atm)
Mw molecular weight of water (18 g/g-mole)
MP
A
Procedure:
1.
molecular weight of pesticide ingredient (262 g/g-mole)
area of application (56,700 m2)
Evaporation Rate of Water. Calculate the evaporation rate
of water using Equations (4.2.10-1), (4.2-10.2), and (4.2-
10.3):
E(Ib/s/acre)=0.20(in/day)226600(Ib/in/acre)(day/86400s)=0.52(Ib/s/acre)
E (Itr/s) = E (Ib/s/acre)
A (m2)
=7.6 (Ib/s)
3910.3445 (m2/acre)
E (g/s) = E (Ib/s) • 493.593 (g/lb) = 3440 (g/s)
2. Emission Rate Qm. Use the evaporation rate of water to
estimate emissions of sodium beritazon from the field with
Equation (4.2.10-4):
Q = t0.73-3440/(l - 60/100)] [1. 32xlQ-10-760 • 2621/23 = 00oi(q/s)
.03158-760-181/2
3. TSCREEN will run the SCREEN model for an area source:
Data entry in the TSCREEN model for this example is shown below:
Emissions from Pesticide/Herbicide Applications - Scenario 2.10
SOURCE PARAMETERS - Page 1 of 1
Enter a unique title for this data's model run:
w '«••+ ..'.; + • • .*.. _. • . •. ••.••. . ••. . . . . • • . ••-,,•.
EMISSION RATE
Enter the Emission Rate (Qm), if unknown enter
the boxed variables below to calculate -> ftiQODf g/s
Evaporation Rate of Water G&2? T: in/day
Enter V for Vegetated Land-S for Soil Surfaces
W for Water Surfaces -> V
Relative Humidity (Rh) -> 6Q 7,
Vapor Pressure of Water (Pw) -> fc,.83:t$i8i:. atm
Vapor Pressure of Pesticide Ingredient (Pp) -> $i32Ei;;K> atm
Molecular Weight of Pesticide Ingredient(Mp) -> 263: ; kg/kmol
Area of Application (A) -> 56?
-------
Emissions from Pesticide/Herbicide Applications - Scenario 2.10
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 2
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural -> R
FENCELINE DISTANCE
Enter the distance from the nearest edge of the
source to the plant fenceline -> 19& m
FLAG POLE RECEPTORS
Enter Receptor Height above Ground (Zr) -> 8 m
RECEPTOR LOCATIONS
Do you have specific locations where you would like
pollutant concentrations to be calculated (Y/N) •> ft
Ran ««tet,
„ -&%> -Hilt . "SPSS" *r«*f«**Se««w "••
A summary of the SCREEN model's output for this example is
displayed below:
*** SUMMARY Of SCREEN MODEL RESULTS ***
•n*************************************
CALCULATION MAX CONC DIST TO TERRAIN
PROCEDURE (UG/M**3) MAX (M) HT (M)
SIMPLE TERRAIN
.2360
100.
0.
REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
4-107
-------
4.2.11 Instantaneous Discharges from Equipment Openings
Emissi
Chemical
Reactor
Emissions
Coke Oven
Similar Releases: Any puff or burst type release with short
duration emissions resulting from the opening of equipment after
processing (e.g., coke ovens or chemical reactors), from routine
sampling of product processing or gaseous emissions from
disconnected lines.
Discussion:
Sources of this type are modeled as instantaneous point-
sources of gaseous emissions due to the momentum of their
release. Emissions can either be estimated on a source-specific
basis by the user or calculated from representative emission
factors. Emissions estimates are available in AP-42 for some
batch operations. VOC profiles are also available to identify
toxic components (Appendix A, item 4). Simple estimates of
emissions from failed or disconnected transfer lines or similar
sources can be calculated from the gas volume between the break
point and nearest shutoff valve. Ambient concentrations
resulting from instantaneous discharges are determined by using
the PUFF model (see Section 5.3).
Limitations and Assumptions:
• • Release is presumed to be neutrally buoyant.
"There is no plume rise algorithm in the current version
of the PUFF model. The height of release should be set
to stack height.
4-108
-------
Input Information:
EF total emission times fraction associated with
particular pollutant (g/kg)
Pd total production of the facility of all emissions (kg)
4.2.11.1 Procedure
1. Total Amount of Material Released. Calculate the total
amount of material released (Q) (g).
Q (g) = Pd (kg) • EF (g/kg) (4.2.11-1)
2. Since the release is neutrally buoyant, dispersion estimates
are determined using the PUFF model. For an explanation of
inputs to the PUFF model, see Section 5.3.
4.2.11.2 Example: Release from equipment opening
Discussion:
A common source of emissions due to equipment openings is
found in the production of coke where the opening of the ovens at
the completion of processing results in a near instantaneous
release. One toxic component of the emission is toluene. A coke
oven battery produces 20,000 kg total emissions. The oven door
is 5 m above ground. An estimate of IS-minute average
concentration at distances beyond 50 m downwind of this source is
needed.
Emissions from coke ovens result primarily from charging and
discharging operations and fugitive losses which occur on a
continuous basis. The example presented is for the near
instantaneous emissions which result from discharge in the
completed coke through the oven doors. Sample simulations are
based on the impact of a single furnace although in real
applications total emissions from a battery of ovens over time
would be more typical. Simulations require determinations of an
emission factor for the oven and total emissions based on oven
capacity. Dispersion estimates are made assuming that the
release is instantaneous with no initial dispersion.
The following input information will be required:
•
EF total emission times fraction associated with
particular pollutant
Pd total production at the facility of all emissions
Hs release height above ground (5m)
Procedure:
1. Total Amount of Material Released. To begin, the emissions
are estimated using emission factors (EPA, 1987b). Assume
4-109
-------
that VOC emissions are approximately 3% of total coke
pushing emissions. (Note, AP-42 suggests 0.2 Ib/ton). The
total VOC production is:
0.03 X 20,000 kg = 600 kg.
Assume that total toluene emissions from coke production are
0.48 Ib/ton of VOC (0.24 g/kg). Coke pushing emissions are
then given by multiplying the emission factor times the
total production using Equation (4.2.11-1):
Q(g) =0.24 (g/kg) • 600 (kg) = 144 (g) toluene
2. Because the release is neutrally buoyant, the cloud is
treated as passive for this example. TSCREEN will run the
PUFF model.
Data entry in the TSCREEN model for this example is shown below:
Discharges from Equipment Openings - Scenario 4.2.9
SOURCE PARAMETERS - Page 1 of 1
Enter a unique title for this data's model run:
'' ................
RELEASE MASS
Enter Total Amount of Material Released (Q), if unknown
enter the boxed variables below to calculate -> 1^|:;?;c g
Total Production (Pd) ->
Emission Factor (EF) ->
P€f kg
jjj&: 9/kg
Discharges from Equipment Openings - Scenario 4.2.9
PUFF MODEL INPUTS - Page 1 of 2
RELEASE PARAMETER
Release Height above Ground -> $
Initial Lateral Dispersion (cry) -> $
Initial Vertical Dispersion ( -> 9
FENCELINE DISTANCE
Enter the distance from the nearest edge of the
source to the plant fenceline -> 5&
m
m
m
4-110
-------
A summary of the PUFF model's output for this:example is shown
below:
SUMMARY OF PUFF MODEL RESULTS
THE MAXIMUM CONCENTRATION AND THE DISTANCE TO MAXIMUM
CONCENTRATION FOR DISTANCES BEYOND FENCELINE .050 (KM).
FOR NEAR SURFACE RELEASE MAXIMUM CONCENTRATION WILL OCCUR AT
THE FENCELINE.
AVERAGING MAXIMUM DISTANCE TO STABILITY
TIME (MIN) CONCENTRATION (G/M**3) MAX. CONC. (KM) CLASS
INSTANTANEOUS 1.693E-01 .060 N
1 2.107E-02 .082 N
5 4.213E-03 .082 N
* 15 1.404E-03 .082 N
60 3.511E-04 .082 N
*«««««•««««>•««*«•»«« ««•»«•«««»•«•««««««««>«< •«*«•«••
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
4-111
-------
4.3 Liquid Release
A liquid release is a release of material that may
immediately evaporate (no pooling results) ort may pool first and
then evaporate.
4.3.1 Continuous Evaporation from Surface Impoundments (Lagoons)
Similar Releases: Waste lagoons and other impoundments with
emissions resulting from the evaporation of volatile chemicals
from liquid mixtures with biological activity.
Discussion:
Emission rates from well-mixed aqueous waste in surface
impoundments are modeled in this scenario. Techniques are
provided for both quiescent and aerated impoundments. Emission
estimates account for volatilization solely, with other removal
mechanisms assumed to be negligible. Ambient concentrations
resulting from continuous evaporation from surface impoundments
are determined by using area source techniques in the SCREEN
model.
Limitations and Assumptions;
Equations are simplifications of EPA methods (EPA,
1987a) for quiescent surface impoundments with and
without flow and for aeration basins.
Equations are simplified by assuming a wind speed of 5
4-112
-------
m/s, a constituent diffusivity in water of 10"3 cm2/s,
and a constituent diffusivity in air of 0.10 cm2/s.
Assumes waste is well mixed in impoundment.
Assumes removal entirely by volatilization, with no
loss due to biodegradation, seepage, or absorption.
Assumes waste is aqueous, with no separate organic
phase.
Input Information:
A area of impoundment (m2)
C0 initial concentration of chemical in the waste (g/m3)
4.3.1.1 Procedure
1. Emission Rate. For VOC emission estimates from waste water
treatment systems, refer to Industrial Waste Water VOC
Emissions -Background from BACT/LAER. EPA-450/3-90-004,
NTIS PB90-194754. This document is available from the EPA
Control Technology Center, (919) 541-0800.
The emission rate can be calculated as follows:
Qm (g/s)" » K(m/s) C^g/m3) A(m2) (4.3.1-1)
where: K = 4 x 10"*(m/s) for the quiescent case
K = 8 x 10"* (m/s) for the aerated case
2. Run the SCREEN dispersion model for an area source.
4.3.1.2 Example: Emission of benzene
Discussion:
One-hour concentration estimates of benzene are desired from
a quiescent impoundment with an area of 1500m2 and a fenceline
200 m from source.
The following input information will be required:
A area of impoundment (1500 m2)
C0 •initial concentration of the chemical in the waste
(1000 g/m3)
4-113
-------
Procedure:
1.
2.
Emission Rate. Calculate the emission rate using Equation
(4.3.1-1):
Qm(g/s) = 4X10-6 (m/s) • 1000 (g/m3) 1500 (m2) = 6 (g/s)
TSCREEN will run the SCREEN model for an area source.
Data entry in the TSCREEN model for this example is shown below;
Evaporation from Surface Impoundments(lagoons) - Scenario 4.3.1
SOURCE PARAMETERS - Page 1 of 1
Enter a unique title for this data's model run:
ftm Surface
IMPOUNDMENT TYPE
Enter Q for Quiescent - A for Aerated -> CJ
EMISSION RATE
Enter the Emission Rate (Qm), if unknown enter
the boxed variables below to calculate -> &••'
g/s
Initial Concentration of Chemical
in-the Waste (Co) -> TW6J.";.'. g/cubic m
Area of Impoundment (A) -> 1588::N m2
»«*t Scr««n «£g«> jsfcort
Evaporation from Surface Impoundments - Scenario 4.3.1
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 2
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural -> ft
FENCELINE DISTANCE
Enter the distance from the nearest edge of the
source to the plant fenceline -> <& 0-
RECEPTOR LOCATIONS
Do you have specific locations where you would like
pollutant concentrations to be calculated (Y/N) •> It
ft
-------
A summary of the SCREEN model's output for this example is shown
below:
*** SUMMARY OF SCREEN MODEL RESULTS ***
*t*******»t******tiit***t***»t»t**t*t**»
CALCULATION MAX CONC DIST TO TERRAIN
PROCEDURE (UG/M**3) MAX (M) HT (M)
SIMPLE TERRAIN .2944E+05 200. 0.
REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS
4-115
-------
4.3.2 Continuous (Two-Phase) Release Rate Estimates
Saturated Liquid from Pressurized Storage
Relief
Valve
Liquid PhaM canted In Gas BUM
Emissions
Similar Releases: Saturated liquid leak from a pressurized tank
(possibly through a relief valve) or a saturated liquid leak from
a pipe.
Digcussipr^:
Materials which are stored under pressure will depressurize
when released to the atmosphere. This depressurization results
in the formation of two contaminant phases (saturated liquid and
vapor) for: gases which cool so that condensation occurs during
the depressurization process; and high volatility liquids
(liquids whose normal boiling point is below the ambient
temperature) which are typically stored at above ambient
pressure. (So called saturated liquids are liquids stored at a
pressure equal to their vapor pressure for the storage
temperature; subcooled liquids are liquids stored at a pressure
above their vapor pressure for the storage temperature,- and
superheated liquids are liquids stored at a pressure below their
vapor pressure for the storage temperature. For a preliminary
estimate, the temperature of superheated liquid releases should
be set to the saturation temperature.) In this scenario, the
terms gas, saturated liquid, and subcooled liquid all refer to
the state of the tank contents. The scenario considers the
release from a tank (or reservoir) and includes a provision for
the effect of a pressure drop (piping) between the tank and the
hole or opening.
This procedure applies to a continuous release of
pressurized liquid stored under saturated conditions. The
release occurs from (constant pressure and temperature)
contaminant (reservoir) through a hole or opening,- a provision is
made for the effect of a pressure drop (piping) between the tank
and the hole or opening. -
4-116
-------
Limitations and Assumptions:
The hole or opening size must be sufficiently small,
otherwise the reservoir temperature and pressure may no longer be
constant.' For the case of a leak from a tank, the assumption of
constant reservoir temperature and pressure may be violated if a
significant percentage of the tank contents is released. If the
reservoir temperature and pressure are not constant, the release
rate may vary with time, but the maximum release rate is
generally obtained from the initial reservoir temperature and
pressure. For the case of a leak from a pipeline, the initial
pipeline conditions can be used to estimate the release rate, but
this may greatly overpredict the actual release rate as the hole
size approaches the pipe diameter.
The vapor phase of the released material must be an ideal
gas at the reservoir conditions, during the depressurization
process, and after depressurization to the atmosphere,- for the
case of a tank containing vapor and liquid, the hole must be in
the liquid space of the tank (Spicer, 1992) .
Input Information;
Ag area of reservoir hole or opening (m2)
Cp gas (contaminant) heat capacity .at Tt (J/kg-°K) (For
contaminant mixtures, see Appendix B)
Cp, liquid (contaminant) heat capacity at Tt (J/kg-°K) (For
contaminant mixtures, see Appendix B)
D0 (equivalent) diameter of hole or opening
(m)
Dp pipe diameter (as appropriate) (m)
Lp pipe length (appropriate) (m)
1^ gas (contaminant) molecular weight (kg/kmol) (For
contaminant mixtures, see Appendix B)
Pa ambient pressure (Pa)
Pt reservoir pressure (Pa)
Q total amount of material released (kg)
T, ambient temperature (°K)
Tb contaminant normal boiling point (°K)
Tt reservoir temperature (°K)
X heat of vaporization at the normal boiling point (J/kg)
Pi contaminant liquid density at the normal boiling point
(kg/m3)
R gas constant (8314 J/kg-mole°K or 3314 Pa.mVkg-
mole.°K)
4-117
-------
4.3.2.1 Procedure:
1. Estimate Discharge Temperature. For pure components,
estimate the discharge temperature T2 from the vapor
pressure (Clausius-Clapeyron) equation:
P. = 101325 exp
1
T
X
(4.3.2-1)
which can be rewritten as:
T-TV-H£1
Tb X Mw [MWJ
Vapor Fraction after Depressurization. Estimate the vapor
mass fraction (or quality) after depressurization X2 as:
X, = Cpl ( T, - T2 ) / X
(4.3.2-2;
If 1 > Xj > 0, then this estimate is valid/ go to step 3.
If X2 s 0 then the release should be modeled like a high
volatility liquid release; the case of X2 a 1 is unlikely on
physical grounds.
Release Rate. As recommended by Pauske and Epstein (1987),
estimate the emission rate Qm (kg/s) depending on the pipe
length Lp as follows: If Lp/Le s 1 (where Le=0.1 m) ,
where
N =
« (kg/s)
R
'A,
X Mw Pt
R Tf
f TI
INC,
(XMWP,)2
1/2
(4.3.2-3)
2 (Pl - P.) Pl C2 (RT,)
(4.3.2-4)
where C is the discharge coefficient (here, C =0.6). (Note
that if Lp/Le = 0, Equations (4.3.2-3) and (4.3.2-4) reduce
to the standard orifice equation for incompressible flow.)
If
Qm (kg/s) = AO F
XM p
R T?
11/2
(4.3.2-5)
where F represents the effect of friction in the pipe (here,
F2 = I/(l+4fLp/Dp) / for a Reynold's number typical of liquid
flow, f=0.0015 can be used as an estimate).
4-118
-------
4. Discharge Density.. Estimate the density after
depressurization p2 as:
ft ftj/W - [«, ££) * [115] J' (4.3.2-6)
5. Buoyancy Check. Estimate release buoyancy as a first check.
A. Calculate the density of air using the following:
(4.3.2-7)
where M, is the molecular weight of air (assumed to
equal 28.9 kg/kmol).
B. If p2/P«r > !/ then the buoyancy is negative. For
negative buoyancy, the RVD model should be used if the
release is from a vertically directed jet; otherwise,
the Britter-McQuaid model should be used; go to step 6.
If the buoyancy is zero or positive, the SCREEN model
for a point source should be used. (See Section 2.4
for more information on model selection.)
6. Release Duration. The release duration is used as an input
into the RVD and Britter-McQuaid models. The release
duration can be used to determine if the release is
continuous or instantaneous (see Section 2.5). Calculate
the release duration Td using the equation below-.
Td (min) = - ,., ? (kfj! , , . . (4.3.2-8)
Qm (kg/s) • 60 (s/min)
4.3.2.2 Example; Saturated Liquid Chlorine Leak
Discussion:
In this example, saturated chlorine liquid is discharged
from a heated pressurized tank through a 10.16 cm diameter hole
well below the liquid level in the tank (the pressure and
temperature were chosen to illustrate that the release rates from
the vapor space are generally much smaller than release rates
from the liquid space); the chlorine vapor temperature is that of
the tank, 349.2 °K. The fenceline is 100 m from the tank
The following information will be required:
AQ area of reservoir hole or opening (0.008107 m2)
Cp, liquid (contaminant) heat capacity at 1l (920 J/kg-°K)
D0 diameter of hole or opening (0.1016 m)
4-119
-------
MV gas (contaminant) molecular weight (70.9 kg/kmol)
Pt ambient pressure (101325 Pa)
Pt reservoir pressure (2.586x10* Pa)
Q total amount of material released (50,000 kg)
Tt ambient temperature (293 °K)
Tb contaminant normal boiling point (239.05 °K)
Tt reservoir temperature (349.2 °K)
X heat of vaporization at the normal boiling point
(2.870X103 J/kg)
P! contaminant density at reservoir conditions (1574
kg/m3)
Procedure:
1. Estimate Discharge Temperature. Estimate the discharge
temperature T2 from Equation (4.3.2-1):
T, = = 239.05 °K
2 1 8314 ,J101325\
239.05 2.879xl05-70.9 U01325/
(This temperature is also the normal boiling point since Pa
= 101325 Pa).
2. Vapor Fraction after Depressurization. Estimate the vapor
fraction after depressurization X2 from Equation (4.3.2-2)
Xj = 920 ( 349.2 - 239.05 ) / 2.879xl05 = 0.352
Since 1 > X2 > 0, then this estimate is valid; go to step 3.
3. Release Rate. Since Lp/Le s 1 (where Lp = 0 and Le = 0.1 m) ,
estimate the release rate from Equation (4.3.2-3):
Qm (kg/s) =0.008107 [2-879x10*.70.9-2.586x10*] / 349.2
m [ (8314) • (349.2)2 j \0.365 • 920
Qm = 430 kg/s
where N is calculated from Equation (4.3.2-4) -.
N = 8314 (2.879x10* • 2.586xl06)2 +0/1 = 0 365
2 (2.586xl06 - 101325) 1574 • 0. 62 (8314 349.2)3 920
(Note that at this rate a "ton" container would be emptied
in 2 to 3 seconds.)
4. Discharge Density. Estimate the density after
.depressurization p2 from Equation (4.3.2-6):
4-120
-------
(kg/m3)
3) = fo.
352
/8314 • 239. 05
\101325 . 70. 9
I - 0.187\
1574 /
= 10.23 kg/m3
5. Buoyancy Check. Estimate release buoyancy as a first check.
A. Calculate the density of air using the following:
'*'^-229839'^°*^
where 28.9 kg/kmol is the molecular weight of air.
B. P2/P«T >:L therefore, buoyancy is negative.
Release Duration. Calculate the release duration Td using
the equation below:
Td (min) =
50,000 (kg)
430 (kg/s) • 60 (s/min)
=1.94 min
After this calculation run the Britter-McQuaid model since
the release is assumed not to be vertically directed jet.
(See Section 5.4 for more information on the Britter-McQuaid
model.)
Data entry in the TSCREEN model for this example is shown below:
— Continuous 2-Phase Saturated Liquid from Pressurized Storage - 3.2
SOURCE PARAMETERS - Page 1 of 4
Enter a unique title for this data's model run:
Saturated tkfujd efclarfn* leak
SOURCE OF LEAK
Area (Ao) of Hole or Opening -> 8-1,87'!' cm2
Enter P for Pipe - T for Tank -> ?
DISCHARGE TEMPERATURE
Discharge Temperature (T2) -> 239.05
°K
Ambient Pressure (Pa) ->
Boiling Point Temperature (Tb) •>
Latent Heat of Vaporization (Lvap) ->
Molecular Weight CHw) ->
Pa
°K
J/kg
kg/kmol
idit/- ' «#9>- Pteyiaus. Street*,;
Abort
4-121
-------
— Continuous 2-Phase Saturated Liquid from Pressurized Storage - 3.2
SOURCE PARAMETERS - Page 2 of 4
VAPOR FRACTION AFTER DEPRESSURIZATION
Vapor Fraction after Depressurization (X2) -> 0.352
Liquid Heat Capacity (Cp) -> 92& J/kg °K
Reservoir Temperature (T1) -> 54^.2. °K
EMISSION RATE
Emission Rate (Qm) -> 430193.2 g/s
Reservoir Pressure (P1) -> i*S&6&t Pa
Liquid Heat Capacity at T1 (Cpl) -> 92fl J/kg °K
Contaminant Liquid Density (fD -> 1£?4 kg/cubic m
fidft
— Continuous 2-Phase Saturated Liquid from Pressurized Storage - 3.2
SOURCE PARAMETERS - Page 3 of 4
DISCHARGE DENSITY
Discharge Density (f2) -> 10.23 kg/cubic m
DENSITY OF AIR
Density of Air (fair) -> 1.20209 kg/cubic m
Ambient Temperature (Ta) -> 2S<3£;f?|£: °K
Buoyancy is Negative
&JU «f$>- Prevfcocfc Sfcre*n Meat
Continuous 2-Phase Saturated Liquid from Pressurized Storage - 3.2
SOURCE PARAMETERS - Page 4 of 4
VERTICALLY DIRECTED JET
Does the release result in a vertically
directed jet (Y/M) -> H
TIME
Release Duration (Td) -> 1.937114 min
Total Amount of Material Released (Q) ->
4-122
-------
— Continuous 2-Phase Saturated Liquid from Pressurized Storage • 3.2
Based on user input, the Britter-McQuaid model has been selected.
BRITTER-McQUAID MODEL INPUTS - Page 1 of 3
MODEL PARAMETERS
Relative Humidity (Rh) -> 5ft>" ' X
ff <
Desired Averaging Time for the Calculation
of Concentrations -> 18- min
— Continuous 2 -Phase Saturated Liquid from Pressurized Storage - 3.2
BRITTER-McQUAID MODEL INPUTS - Page 2 of 3
FENCELINE DISTANCE
Enter the distance from the nearest edge of the
source to the plant fenceline -> t<£): m
RECEPTOR LOCATIONS
Do you have specific locations where you would
like pollutant concentrations calculated (Y/N) -> X
Bdift
Screw*
ttan Itotel.
A summary of the Britter-McQuaid model's output is displayed
below:
**• SUMMARY OF B&M MODEL RESULTS *•*
««l»«l»«>«*lHHt«1»
MAX CONC
MAX CONC
(PPM)
DIST TO
MAX (M)
WIND SPEED
(M/S)
.3535E+09 .1199E+06
200.
1.
>«•*•«»**»•«*»***•»***
REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS
****»*»*»»»*»***»*»*»«
**************
4.3.2.3 Considerations for Time-Varying and Time-Limited
Releases
See Section 2.5 for a discussion of considerations for time-
varying and time-limited releases.
4-123
-------
4.3.3 Instantaneous (Two-Phase) Release Rate Estimates
Saturated Liquid from Pressurized Storage
Emissions
din Gas Phase
Similar Releases: Saturated liquid'leak from a pressurized tank
or a saturated liquid leak from a pipe.
Discussion:
This procedure applies to an instantaneous release of
pressurized liquid stored under saturated conditions. The
release occurs (at constant pressure and temperature) from a
containment (reservoir) through a hole or opening,- a provision is
made for the effect of a pressure drop (piping) between the tank
and the hole or opening. See Section 4.3.2 for further
discussion.
Limitations and Assumptions:
Same as Section 4.3.2.
Input Information:
Same as Section 4.3.2.
4.3.3.1 Procedure:
1-4. Same as Section 4.3.2.
4-124
-------
5. Buoyancy Check. Perform buoyancy check as a first check.
A. Calculate the density of air using the following:
'••TX <*-3-*-»
where M, is the molecular weight of air (assumed to
equal 28.9 g/g-mole).
B. If Pj/Pair > 1, then the buoyancy is negative. For
negative buoyancy, the RVD model should be used if the
release is' from a vertically directed jet; otherwise,
the Britter-McQuaid model should be used; go to step 6.
If the buoyancy is positive, the PUFF model for a point
source should be used. (See Section 2.4 for more
information on model selection.)
6. Same as Section 4.3.2.
4.3.3.2 Examples
See the examples in Section 4.3.2.
4-125
-------
4.3.4 Continuous (Two-Phase) Release Rate Estimates
Subcooled Liquid from Pressurized Storage
Relief
Valve
Uquld PtaM canted In Gas Phaaa
Emissions
Similar Releases.- Subcooled liquid leak from a pressurized tank
(possibly through a relief valve) or a subcooled liquid leak from
a pipe.
Discussion:
Materials which are stored under pressure will depressurize
when released to the atmosphere. This depressurization results
in the formation of two contaminant phases (saturated liquid and
vapor) for: gases which cool so that condensation occurs during
the depressurization process; and high volatility liquids
(liquids whose normal boiling point is below the ambient
temperature) which are typically stored at above ambient
pressure. (So called saturated liquids are liquids stored at a
pressure equal to their vapor pressure for the storage
temperature; subcooled liquids are liquids stored at a pressure
above their vapor pressure for the storage temperature; and
superheated liquids are liquids stored at a pressure below their
vapor pressure for the storage temperature. For a preliminary
estimate, the temperature of superheated liquid releases should
be set to the saturation temperature.) In this scenario, the
terms gas, saturated liquid, and subcooled liquid all refer to
the state of the tank contents. The scenario considers the
release from a tank (or reservoir) and includes provision for the
effect of a pressure drop (piping) between the tank and the hole
or opening.
This procedure applies to a continuous release of a
pressurized liquid stored above its saturation pressure. This
release occurs (at constant pressure and temperature) from a
containment (reservoir) through a hole or opening; a provision is
made for the effect of pressure drop (piping) between the tank
and the hole or opening.
4-126
-------
Limitations and Assumptions:
The hole or opening size must be sufficiently small,
otherwise the reservoir temperature and pressure may no longer be
constant. For the case of a leak from a tank, the assumption of
constant reservoir temperature and pressure may be violated if a
significant percentage of the tank contents is released. If the
reservoir temperature and pressure are not constant, the release
rate may vary with time, but the maximum release rate is
generally obtained from the initial reservoir temperature and
pressure. For the case of a leak from a pipeline, the initial
pipeline .conditions can be used to estimate the release rate, but
this may greatly overpredict the actual release rate as the hole
size approaches the pipe diameter.
The vapor phase of the released material must be an ideal
gas at the reservoir conditions, during the depressurization
process, and after depressurization to the atmosphere; for the
case of a tank containing vapor and liquid, the hole must be in.
the liquid space of the tank (Spicer, 1992).
Input Information:
AO area of reservoir hole or opening (m2)
Cp gas (contaminant) heat capacity at Tt (J/kg-°K) (For
contaminant mixtures, see Appendix B)
Cpj liquid (contaminant) heat capacity at T! (J/kg-°K) (For
contaminant mixtures, see Appendix B)
D0 (equivalent) diameter of hole or opening (D0=2-yA0/7r )
(m)
Dp pipe diameter (as appropriate) (m)
Lp pipe length (appropriate) (m)
Mw gas (contaminant) molecular weight (kg/kmol) (For
contaminant mixtures, see Appendix B)
P, ambient pressure (Pa)
PI reservoir pressure (Pa)
R gas constant (8314 J/kg-mole-°K or 8314
Pa-m3/kg-mole-°K)
Q total amount of material released (kg)
Tt ambient temperature (°K)
Tb contaminant normal boiling point (°K)
Tt reservoir temperature (°K)
X heat of vaporization at the normal boiling point (J/kg)
pl contaminant density at the normal boiling point (kg/m3)
4-127
-------
4.3.4.1 Procedure:
1. Estimate Discharge Temperature. For pure components,
estimate the discharge temperature T2 from the Clausius-
Clapeyron equation:
P. = 101325 exp - -1 - * (4.3.4-1)
K M-b i2
which can be rewritten as:
Tb XM, [101325 J
Vapor Fraction after Depressurization. Estimate the vapor
mass fraction (or quality) after depressurization X2 as:
X, = Cpl ( Tt - T2 ) / X (4.3.4-2)
If 1 > X2 > 0, then this estimate is valid,- go to step 3.
If X2 s 0 then the release should be modeled like a high
volatility liquid release; the case of X2 a 1 is unlikely on
physical grounds.
Release Rate. As recommended by Fauske and Epstein (1987),
estimate the emission rate Qm (kg/s) as follows:
1/2
T72 f X M P- I2
2 C2 (P -P ) n + e v
* *- 1*1 *V Pi* r< rp | pTrT-
K11
(4.3.4-3)
where
lv
(Pa) = 101325 exp \—l .£ - _i (4.3.4-4)
where C is the discharge coefficient (here, C =0.6) and F
represents the effect of friction in the pipe (here, F2 =
l/(l+4fLp/Dp) ; for a Reynold's number typical 'of liquid flow,
f=0.00l5 can be used as an estimate) .
Discharge Density. Estimate the density after
depressurization p2 as :
(kg/m3
(4.3.4-5)
L'lp-N I >> J
5. Buoyancy Check. Perform buoyancy check as a first check.
A. Calculate the density of air using the following:
4-128
-------
(4.3.4-6)
where M, is the molecular weight of air (assumed to
equal 28.9 kg/kmol) .
B. If Pa/Pa* > 1, then the buoyancy is negative. For
negative buoyancy, the RVD model should be used if the
release is from a vertically directed jet; otherwise,
the Britter-McQuaid model should be used; go 'to step 6.
If the buoyancy is positive, the SCREEN model for a
point source should be used. (See Section 2.4 for more
information on model selection.)
Release Duration. The release duration is used as an input
into the RYD and Britter-McQuaid models. The release
duration can be used to determine if the release is
continuous or instantaneous (see Section 2.5). Calculate
the release duration Td using the equation below:
T' ""in) •
Q. (fcg/s) o is/mini -'
4.3.4.2 Example: Subcooled Liquid Chlorine Leak
Discussion:
In this example, subcooled chlorine liquid is discharged
through a 10.16 cm diameter hole in a tank (the pressure and
temperature were chosen to illustrate that the release rates from
the vapor space are generally much smaller than release rates
from the liquid space) ; the chlorine vapor temperature is
estimated to be 349.2 °K using the Clausius-Clapeyron equation
and the normal boiling point of chlorine (239.05 °K) . The
fenceline is 100 m from the tank.
The following information will be required:
AO area of reservoir hole or opening (0.008107 m2)
Cp gas (contaminant) heat capacity at Tt (489 J/kg-°K)
Cp, liquid (contaminant) heat capacity at TI (920 J/kg-°K)
D0 diameter of hole or opening (0.1016 m)
Mw gas (contaminant) molecular weight (70.9 kg/kmol)
P, ambient pressure (101325 Pa)
Pj reservoir pressure (2.586xl06 Pa)
Q total amount of material released (50,000 kg)
Tt ambient temperature (293 °K)
Tb contaminant normal boiling point (239.05 °K)
Tj reservoir temperature (298.15 °K)
\ heat of vaporization at the normal boiling point
(2.879xl05 J/kg)
Pi contaminant density at reservoir conditions (1574
4-129
-------
kg/m3)
Procedure:
1. Estimate Discharge Temperature. Estimate the discharge
temperature T2 from Equation (4.3.4-1):
T, - = 239.05 °K
2 1 _ 8314 . ,J101325\
J -ml.
3-70. 9 \
239.05 2.879xl03-70.9 U01325/
(This temperature is also the normal boiling point since Pa
= 101325 Pa).
Vapor Fraction after Depressurization. Estimate the vapor
fraction after depressurization X2 from Equation (4.3.4-2)
Xj = 920 ( 298.15 - 239.05 ) /.2.879xl05 = 0.1888
Since 1 > X2 > 0, then this estimate is valid; go to step 3.
Release Rate. Using Lp=0 (and F = 1) , estimate the release
rate from Equation (4.3.4-3):
Qm(kg/s)=.008107
2C2(2.586xl06-Plv)1574
p2|2.879xlQ5-70.9-2 .586xl06
8314 298.15
920-298.15
Qm (kg/s) = 493 (kg/s)
where C = 0.6 and
239.05 298.15
= 7.76xl05 Pa
Plv (Pa) = 101325 exp 2.879x10^70.9 (
4. Discharge Density. Estimate the density after
depressurization p2 from Equation (4.3.4-5):
p, (Kg/.-, - [0.1.8. (;%35»^) * (i-^) }' = 18'9S k3/I"3
5. Buoyancy Check. Perform buoyancy check as a first check.
A. Calculate the density of air using the following:
B- P2/P«r > I/ therefore, buoyancy is negative
•
4-130
-------
6. Release Duration. Calculate the release duration Td using
the equation below:
TV, (min)
50,000 (kg)
493 (kg/s) • 60 (s/min)
= 1.69 min
After this calculation run the Britter-McQuaid model since
the release is not from a vertically directed jet. (See
Section 5.4 for more information on the Britter-McQuaid
model.)
Data entry in the TSCREEN model for this example is shown below:
Continuous 2-Phase Subcooled Liquid from Pressurized Storage - 3.4
SOURCE PARAMETERS • Page 1 of 4
Enter a unique title for this data's model run:
Sobc^B^'tiqiM'Btitdi^ie^Ba^'' i'
SOURCE OF LEAK
Area (Ao) of Hole or Opening -> S-1.67" cm'
Enter P for Pipe - T for Tank -> t
DISCHARGE TEMPERATURE
Discharge Temperature (T2) -> 239.05
Ambient Pressure (Pa) -> t&faSJ Pa
Boiling Point Temperature (Tb) -> 23$,-8£ "K
Latent Heat of Vaporization (Lvap) -> Z.879ES J/kg
Molecular Weight (MM) -> ?&.? kg/kmol
continuous i-pnase suocooiea Liquid Trom Pt
SOURCE PARAMETERS - Page 2 of 4
VAPOR FRACTION AFTER DEPRESSURIZATION
Vapor Fraction after Depressurization (X2)
Vapor Heat Capacity (Cp)
Reservoir Temperature (T1)
EM I SSI OH RATE
Emission Rate (dm)
Reservoir Pressure (P1)
Liquid Heat Capacity at T1 (Cpl)
Contaminant Liquid Density (f1)
•essurized si
-> 0.1888
-> 485
-> 493423.2
-> 2.5S6E6
rorage - 5.4
J/kg °K
"K
9/s
Pa
J/kg °K
kg/cubic m
ll^^'lii&i^^
4-131
-------
— Continuous 2-Phase Subcooled Liquid from Pressurized Storage - 3.4
SOURCE PARAMETERS - Page 3 of 4
DISCHARGE DENSITY
Discharge Density (f2) -> 18.96 kg/cubic m
DENSITY OF AIR
Density of Air (fair) -> 1.20209 kg/cubic m
Ambient Temperature (Ta) -> 295
Buoyancy is Negative
rfffrwt
— Continuous 2-Phase Subcooled Liquid from Pressurized Storage - 3.4
SOURCE PARAMETERS - Page 4 of 4
VERTICALLY DIRECTED JET
Does the release result in a vertically
directed jet (Y/N) -> tl
TIME
Release Duration (Td) -> 1.688882 min
Total Amount of Material Released (Q) -> Sj&DCp" kg
— Continuous 2-Phase Subcooled Liquid from Pressurized Storage - 3.4
Based on user input, the Britter-HcQuaid model has been selected.
BRITTER-McQUAID MODEL INPUTS - Page 1 of 3
MODEL PARAMETERS
Relative Humidity (Rh) -> 5&? J: : %
Desired Averaging Time for the Calculation
of Concentrations •> 15 min
;'^
Continuous 2-Phase Subcooled Liquid from Pressurized Storage - 3.4
BRITTER-McQUAID MODEL INPUTS - Page 2 of 3
FENCELINE DISTANCE
Enter the distance from the nearest edge of the source
to the plant fenceline -> 1SQ
RECEPTOR LOCATIONS
Do you have specific locations where you Mould
like pollutant concentrations calculated (Y/N) -> »
Edit «F9> frftWidtlS Stl*e*&
-------
A summary of the Britter-McQuaid model's output is displayed
below:
*** SUMMARY OF B&M MODEL RESULTS
««««««««»«m>«««««i>«> *«««««««««•«•«•
MAX COHC MAX CONC DIST TO WIND SPEED
«««l»***l>l>«l»««l>«>*«»«««« »««*««««•«*• «•*«»•*•
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
4.3.4.3 Considerations for Tinie-Varying and Time-Limited
Releases
See Section 2.5 for a discussion of considerations for time-
varying and time-limited releases.
4-133
-------
4.3.5 Instantaneous (Two-Phase) Release Rate Estimates
Subcooled Licmid from Pressurized Storacre
Emissions
UquU RUM canted In Gas Ptww
Similar Releases: Subcooled liquid leak from a pressurized tank
or a subcooled liquid leak from a pipe.
Discussion:
This procedure applies to an instantaneous release of a
pressurized liquid stored above its saturation pressure. This
release occurs (at constant pressure and temperature) from a
containment (reservoir) through a hole or opening; a provision is
made for the effect of pressure drop (piping) between the tank
and the hole or opening. See Section 4.3.4 for further
discussion.
Limitations and Assumptions.-
Same as Section 4.3.4.
Input Information:
Same as Section 4.3.4.
4.3.5.1 Procedure •.
1-4. Same as Section'4.3.4
•
5. Buoyancy Check. Perform buoyancy check as a first check.
A. Calculate the density of air using the following:
P, M,
0.-- (4.3.5-1)
4-134
-------
where Ma is the molecular weight of air (assumed to
equal 28.9 kg/kmol).
B. If p^/Pta > I/ then the buoyancy is negative. For
negative buoyancy, the RVD model should be used if the
release is from a vertically directed jet; otherwise,
the Britter-McQuaid model should be used; go to step 8.
If the buoyancy is positive, the PUFF model for a point
source should be used. (See Section 2.4 for more
information on model selection.)
6. Same as Section 4.3.4.
4.3.5.2 Examples
See the examples in Section 5.4.4.
4-135
-------
4.3.6 Continuous High Volatility Leaks
Emissions
Pipe
Crack
Emissions
Tank
Similar Releases: High-volatility liquid leak from a tank or a
high volatility liquid leak from a pipe (when the ratio of the
hole diameter to the pipe diameter is less than 0.2).
Discussion:
A high-volatility liquid is considered to be a material
(liquid) whose normal boiling point is below the ambient
temperature; a high-volatility material will be released as a
liquid if the storage pressure is near ambient pressure whereas
release from high pressure storage will result in aerosol
formation. The following considers the problem of estimating the
release rate of a high-volatility liquid when the diameter of the
hole or opening is less than the diameter of the containment
(e.g., a pipe or a reservoir). (When considering hole sizes
which approach the pipe diameter, the release rate should be
taken as the maximum, of the pipe flow rate and the estimated
release rate.) For high-volatility liquid releases, the
(conservative) assumption is that the liquid boils off
instantaneously so that the liquid release rate is equal to the
(gas) evolution rate.
This procedure applies to a continuous release of a high
volatility liquid (at constant temperature and pressure) from a
containment (reservoir) through a hole or opening.
4-136
-------
Limitations and Assumptions:
For this screening procedure, the following assumptions are
applied:
The pressure and temperature of the liquid in the
reservoir are essentially constant.
The hole or opening is located in the liquid space (as
opposed to the vapor space).
The gas evolution rate is assumed to be equal to the
liquid release rate (i.e., vaporization is
instantaneous).
The hole or opening size must be sufficiently small,
otherwise considerations other than those outlined below may
determine the release rate. For the case of a leak from a. pipe,
/3 (defined below) should be less than 0.2; if j8>0.2, the release
rate should be taken to be the normal flow rate in the pipe. In
either case, the gas evolution rate is assumed to be equal to the
liquid release rate (i.e., vaporization is instantaneous). If
the reservoir temperature, pressure, and liquid level are not
constant, the release rate may vary with time, but the maximum
release rate is generally obtained for the initial reservoir'
conditions (Spicer, 1992).
Input Information:
AO area of hole or opening (m2)
AI flow area representing reservoir conditions (m2) (In
the case of a leak from a tank, A!-*» (and j3=0) ; in the
case of a leak from a pipe, At is the cross-sectional
area of the pipe.)
D0 (equivalent) diameter of hole or opening (D0=2 -^AQ/TT )
(m)
g acceleration due to gravity (9.81 m2/s)
HL distance between the hole or opening and the top of the
liquid level (m) (In the case of a leak from a pipe,
Hr»0.)
M» contaminant molecular weight (kg/kmol)
P, ambient pressure (Pa)
Pv vapor pressure as a function of temperature (Pa)
Pt reservoir pressure (Pa)
R gas constant (8314 J/kg-mole-°K or 8314
Pa-m3/kg-mole-°K)
Q total amount of material released (kg)
Ta ambient temperature (°K)
Tb contaminant normal boiling point (°K)
T! reservoir temperature (°K)
/3 ^/AO/AJ (dimensionless)
7 heat of vaporization at the normal boiling point (J/kg)
4-137
-------
P! contaminant (liquid) density at reservoir conditions
(Tt and Pt) (kg/m3)
4.3.6.1 Procedure:
1. Pressure at the Hole or Opening. Estimate the liquid
pressure at the hole or opening P, as:
P. = max(Pt< Pt) + pt g HL (4.3.6-1)
where P^P,,^) which is estimated using-the Clausius-
Clapeyron Equation:
Pv = 101325 exp \^L f * - * |] (4.3.6-2)
[ R [ Tb T! J J
2. Emission Rate. Estimate the emission rate Qm (kg/s) as
follows from Perry et al. (1984):
r 11/2
Qm (kq/s) = KAgf 2 Pl(P. - P. ) J (4.3.6-3)
where
K = C / 1 - /34
where C = 0.65 (although C can be larger if j8>0.2)
Discharge Density. Calculate the discharge density as
follows:
P M
_ » w
K ^ ' (4.3.6-4)
Buoyancy Check. Perform buoyancy check as a first check.
A. Calculate the density of air using the following:
P M,
P. = iV (4.3.6-5)
1
where M, is the molecular weight of air (assumed to
equal 28.9 kg/kmol).
B. If PI/P& > 1, then the buoyancy is negative. For
negative buoyancy, the RVD model should be used if the
release is from a vertically directed jet; otherwise,
the Britter-McQuaid model should be used; go to step 5.
If the buoyancy is positive, the SCREEN model for a
point source should be used. (See Section 2.4 for more
information on model selection.)
Release Duration. The release duration is used as an input
into the RVD and Britter-McQuaid models. The release
4-138
-------
duration can be used to determine if the release is
continuous or instantaneous (see Section 2.5). Calculate
the release duration Td using the equation below:
T (min) '
< Q. gs o
-------
Procedure •.
1. Pressure at the Hole or Opening. Estimate the liquid
pressure. P, at the hole or opening from Equation (4.3.6-1) .
In this case, liquid chlorine is being released as a
saturated liquid at ambient pressure, so Pa=P1=101325 Pa, and
P, is estimated as:
P. =max(101325, 101325) + 1574 • 9.81 • 0.4 = 1.075xl05 Pa
which is greater than Pv calculated from Equation (4.3.6-2) :
P, . 10X325 exp -' - • "»25 Pa
2. Emission Rate. Estimate the emission rate Qm from Equation
(4.3.6-3) as follows:
f / \ \m
Qm = K 0.0005067 [ 2 • 1574 ( 1.075xl05 - 101325 ) j = 1.45 kg/s
where
K = 0.65 / J 1 - 0 . 04 = 0.65
At this (maximum) rate, the tank will be emptied in 436 s;
the actual time would be longer since Qm will decrease with
time (because HL decreases with time) . (Note that this
situation can be compared to the earlier two-phase chlorine
.examples if the hole diameter is changed to agree with the.
earlier examples; if the hole diameter is changed to 10.16
cm, the emission rate' for this case would be 23.2 kg/s.
This liquid release rate is even smaller than the example
pressurized vapor release rate of Section 2.3.)
3. Discharge Density. Calculate the discharge density using
Equation (4.3.6-4) as follows:
. _ 101325 -70.9 _ , -n v«/n,3
P> " 8314 • 239.05 ~ 3'61 kg/m
4. Buoyancy Check. Perform buoyancy check as a first check.
A. Calculate the density of air using Equation (4.3.6-5):
where 28.9 kg/kmol is the molecular weight of air.
B. Since p2/ ' p& > 1, the buoyancy is negative.
4-140
-------
Release Duration. Calculate the release duration Td using
the equation below:
TV, (min)
200 (kg)
1.45 (kg/s) • 60 (s/minT
=2.30 min
After this calculation run the Britter-McQuaid model since
the release is not from a vertically directed jet. (See
Section 5.4 for more information on the Britter-McQuaid
model.)
Data entry in the TSCREEN model for this example is shown below:
Continuous High Volatility Liquid Leaks - 3.6
SOURCE PARAMETERS - Page 1 of 4
Enter a'unique title for this data's model run:
CMorin* Lea*.. '
SOURCE OF LEAK
Area (Ao) of Hole or Opening ->
Enter P for Pipe - T for Tank -> |
cm»
VAPOR PRESSURE
Vapor Pressure (Pv) -> 101325 Pa
Latent Heat of Vaporization (Lvap} -> Z.879E5 J/kg
Boiling Point Temperature -> 3&JB& "K
Reservoir Temperature (T1) -> 2$M£ °K
Molecular Weight (Mw) -> 78*9< kg/kmol
Sdit
Mext S6r«e»
Jttwft
Continuous High Volatility Liquid Leaks - 3.6
SOURCE PARAMETERS - Page 2 of 4
PRESSURE
Liquid Pressure at Hole or Opening (P*) -> 107501.4 Pa
Ambient Pressure (Pa) -> 101325 Pa
Reservoir Pressure (P1) -> 101325 Pa
Contaminant Density (f1) at Reservoir Conditions -> |574;;v.5.;::::; kg/cubic m
Distance between the Hole or Opening
and Top of Liquid Level (Hi) -> fti%,7%. m
EMISSION
Emission Rate (Qm) -> 1453.136 g/s
£d1t Abort
4-141
-------
Continuous High Volatility Liquid Leaks - 3.6
SOURCE PARAMETERS - Page 3 of 4
DISCHARGE DENSITY
Discharge Density ((7) -> 3.614632 kg/cubic m
DENSITY OF AIR
Density of Air (fair) -> 1.20209 kg/cubic m
Ambient Temperature (Ta) -> 295
Buoyancy is Negative
Continuous High Volatility Liquid
SOURCE PARAMETERS - Page 4 of 4
VERTICALLY DIRECTED JET
Does the release result in a vertically
directed jet (Y/N) -> »
TIME
Release Duration (Td) -> 2.293889 min
Total Amount of Material Released (Q) -> 200".%" kg
Continuous High Volatility Liquid Leaks - 3.6
Based on user input, the Britter-McQuaid model has been selected.
BRITTER-McQUAID MODEL INPUTS - Page 1 of 3
MODEL PARAMETERS
Relative Humidity (Rh) -> 58- /I:..- %
Desired Averaging Time for the Calculation
of Concentrations -> 15 ' min
-£dit ... <*9> Previous Screen . &1Q* Hejtt Sere«t=. . ;*$&<&• <8»rt
Continuous High Volatility Liquid Leaks - 3.6
BRITTER-McQUAID MODEL INPUTS - Page 2 of 3
FENCELINE DISTANCE
Enter the distance from the nearest edge of the source
to the plant fenceline -> HXJ' '
RECEPTOR LOCATIONS
Do you have specific locations where you would
like pollutant concentrations calculated (Y/N) -> H
xl*?*:*^
4-142
-------
A summary of the Britter-McQuaid model's results is displayed
below:
*** SUMMARY OF B&M MODEL RESULTS ***
MAX CONC MAX CONC OIST TO WIND SPEED
(UG/M**3) (PPM) MAX (M) (M/S)
.2865E+08 9716. 100. 3.
REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
4.3.6.3 Considerations for Time-Varying and Time-Limited Releases
See Section 2.5 for a discussion of considerations for time-
varying and time-limited releases.
4-143
-------
4.3.7 Instantaneous High Volatility Leaks
Emissions
Pipe
Emissions
Hole
Tank
Similar Releases: (High volatility) liquid leak from a tank or a
liquid leak from a pipe (when the ratio of the hole diameter to
the pipe diameter is less than 0.2).
Discussion:
This procedure applies to an instantaneous release of a high
volatility liquid'(at constant temperature and pressure) from a
ment (reservoir) through a hole or opening. See Section 4.3.6
for further discussion.
Limitations and Assumptions:
Same as Section 4.3.6.
Input Information:
Same as Section 4.3.6.
4.3.7.1 Procedure:
1-3. Same as Section 4.3.6
4. Buoyancy Check. Perform buoyancy check as a first check.
A. Calculate the density of air using the following:
P. M.
Pair =
~R~T
(4.3.7-1)
4-144
-------
where Ma is the molecular weight of air (assumed to
equal 28.9 k/kmol).
B. If PI/Pat > !/ then the buoyancy is negative. For
negative buoyancy, the RVD model should be used if the
release is from a vertically directed jet; otherwise,
the Britter-McQuaid model should be used; go to step 8.
If the buoyancy is positive, the PUFF model for a point
source should be used. (See Section 2.4 for more
information on model selection.)
5. Same as Section 4.3.6.
4.3.7.2 Examples
See the examples in Section 4.3.6.
4-145
-------
4.3.8 Continuous Low Volatility Liquids from Tanks and Pipes
Tanks
Pipe
Leaking Pipe Range
Similar Releases: Possible applications include a (low
volatility) liquid leak from a. tank or a pipe.
Discussion:
Low volatility liquid is considered to be a material whose
normal boiling point is above the ambient temperature,- a low
volatility material stored at moderate to low pressure (and so
that the boiling point is above the storage temperature) will
typically be released as a liquid and form a pool or puddle on
the ground. For low-volatility liquid releases, the
(conservative) assumption is that the liquid evaporates at the
same rate it is spilled (except when the puddle is confined by a
bund or dike from which liquid does not overflow).
Limitations and Assumptions:
The liquid level, pressure, and temperature in the
reservoir are essentially constant. If these
parameters are not constant, the release rate may vary
with time, but-the maximum release rate is generally
obtained for the initial reservoir conditions.
The hole or opening is located in the liquid space (as
opposed to the vapor space).
The gas evolution (evaporation) rate is assumed to be
equal to the liquid release rate (except when the
puddle is confined by a dike or bund from which liquid
does not overflow). See Spicer, 1992.
Input Information:
AQ area of hole or opening (m2)
Ap puddle area (m2) (For unbounded puddles, \ is to be
determined; for releases within dikes or bunds, Ap is
the dike or bund area from which liquid would
4-146
-------
evaporate.)
At flow area representing reservoir conditions (m2) (In
the case of a leak from a tank, Aj-wn (and /3=0) ; in the
case of a leak from a pipe, Aj is the cross-sectional
area of the pipe.)
D0 (equivalent) diameter of hole or opening (D0=2-,/AO/TT )
(m)
g acceleration due to gravity (9.81 m2/s)
HL distance between the hole or opening and the top of the
liquid level (where the pressure is PJ (m) (In the
case of a leak from a pipe, HL=0.)
M, contaminant molecular weight (kg/kmol)
P, ambient pressure (Pa)
Pv vapor pressure as a function of temperature (Pa)
P! reservoir pressure (Pa)
R gas constant (8314 J/kg-mole-°K or 8314
Pa-m3/kg-mole- °K)
Q total amount of material released (kg)
T. ambient temperature (°K)
Tb contaminant'normal boiling point (°K)
Tt liquid storage temperature (°K)
Ur ambient windspeed (typically considered to be at 10 m
elevation) (m/s)
/3 Y/AQ/A! (dimensionless)
X heat of vaporization at the normal boiling point (J/kg)
P! contaminant density at reservoir conditions (Tt and Pj)
(kg/m3)
4.3.8.1 Procedure:
1. Pressure at the Hole or Opening. Estimate the liquid
pressure at the hole or opening P. as:
P. = max(P4, Pt) + Pl g HL (4.3.8-1)
2. Emission Rate. Estimate the emission rate Qm (kg/s) as
follows from Perry et al. (1984):
•
r , > il/2
Qm (kg/s) = K Ao[2 Pl ( P. - P, ) j (4.3.8-2)
where K = C / \l 1 - P*
where C = 0.65 (although C can be larger if j3>0.2)
Puddle Area. For unconfined puddles, estimate the puddle
area Ap required for the emission rate Qm as follows from
Clewell (1983) -.
Qm (kg/s) =6 . 94xl(T7(l+0 . 0043[T2-273 . ls]'2)tf-7
4-147
-------
(4.3.8-3)
where T3 = maxCT^T,) and [T2-273.15]* is taken to be zero if
T2 - 273.15 < 0; Pv (in Pa) is evaluated at T2 using the
Clausius-Cl apeyr on Equation:
Pv = 101325 exp _= hi- - •£ (4.3.8-4)
where Pvh is the vapor pressure (in Pa) of hydrazine
evaluated at T2 as follows :
Pvh = exp I 76. 8580 - 7245'2 - 8.22 ln(T2) + 0.0061557 T2 J
I T* J
For (potentially) confined puddles where Ap is known a
priori. Equation (4.3.8-3) must be solved for Qm using the
known value to Ap. -If Qm from Equation (4.3.8-3) is less
than Qm from Equation (4.3.8-2), the estimate of Qm from
Equation (4.3.8-3) and the a priori value of Ap best
represent the release conditions. However if Qm from
Equation (4.3.8-3) is greater than Qm from Equation (4.3.8-
2), the estimate of Qm from Equation (4.3.8-2) and Ap
estimated from Equation (4.3.8-3) best represent the release
conditions. (Ap is so estimated in this case because the
puddle size from Equation (4.3.8-3) is smaller than the
confining area for the release conditions . )
4. Discharge Density. Calculate the discharge density as
follows :
P M
— 1 W
R T
2 (4.3.8-5)
5. Buoyancy Check. Perform buoyancy check as a first check.
A. Calculate the density of air using the following:
(4.3.8-6)
where M, is the molecular weight of air (assumed to
equal 28.9 kg/kmol).
B. If PI/Pfr > 1, then the buoyancy is negative. For
negative buoyancy, the Britter-McQuaid model should be
used; go to step 6. If the buoyancy is positive, the
SCREEN model for an area source should be used. (See
Section 2.4 for more information on model selection.)
4-148
-------
6. Release Duration. The release duration is used as an input
into the Britter-McQuaid model. Calculate the release
duration Td using the equation below:
T, (min) = 9 (kg) ' (4.3.8-7)
d Qm (kg/s) • 60 "(s/min)
4.3.8.2 Example: Continuous Leak of Liquid Unsymmetrical
Dimethlhydrazine (UDMH)
Discussion:
For this example, consider a liquid UDMH (101325 Pa and 283
°K) leak from a 3.2 cm diameter hole in a tank; the hole is 1.0 m
below the liquid surface. The tank is located in a bund with a
floor area of 2500 m2. The distance to the fenceline is 100 m.
The following information will be required:
AO area of hole or opening (-jfD0V4 = 0.0008042 m2)
Ap (maximum) puddle area (2500 m2)
A! flow area representing reservoir conditions (A!-*« m2)
D0 (equivalent) diameter of hole or opening (0.032 m)
g acceleration due to gravity (9.81 m2/s)
HL distance between the hole or opening and the top of the
liquid level (where the pressure is PJ (1.0 m)
N^ contaminant molecular weight (60.1 kg/kmol)
P, ambient pressure (101325 Pa)
Pv vapor pressure as a function of temperature (Pa)
P! reservoir pressure (101325 Pa)
R gas constant (8314 J/kg-mole-°K or 8314
Pa-m3/kg-mole- °K)
Q total amount of material released (500 kg)
T, ambient temperature (283 °K)
Tb contaminant normal boiling point (335.5 °K)
T, liquid storage temperature (283 °K)
Ur ambient windspeed (typically considered to be at a 10 m
elevation) (2.0 m/s)
j8 J5J&T (0.0)
X heat of vaporization at the normal boiling point
(5.44X105 J/kg)
pl contaminant density at reservoir conditions (Tt and Pt)
(800 kg/m3)
With this information, the procedure discussed 'above determines
the release rate and puddle area.
Procedure:
1. Pressure at the Bole or Opening. Estimate the liquid
pressure P* at the hole or opening using Equation (4.3.8-1) .
4-149 :
-------
In this case, the UDMH is released as a liquid at the -
ambient pressure and temperature, so P.=P1=101325 Pa:
P. = max(101325, 101325) + 800-9.81-1.0 = 1.09xl05 Pa
2. Emission Rate. Estimate the emission rate Qm using Equation
(4.3.8-2) with C = 0.65 as follows:
f / \ 11/2
Qm(kg/s) = K-0.0008042-[ 2-800-( 1.09xl05 - 101325 )] =1.83 kg/s
where
K = 0.65 / ^1 - O.O4 =0.65
3. Puddle Area. Since this puddle could be bounded, use the
known Ap = 2500 m2 in Equation (4.3.8-3) to determine Qm as
follows:
Qm = 6. 94xlO'7 (l +' 0.0043 [283 - 273 . 15 f) 2 . 0°-75- 2500 • 60 . 1 • Pv/Pvb
Qm = 3.9 kg/s
where T2 = min(283 °K,283 °K) = 283 °K and Pv (in Pa) is
evaluated at T2 using the Glaus ius-Clapeyron Equation
(4.3.8-4) :
- ,0X3,5 exp - - - I.15xl0. Pa
where Pvh is the vapor pressure (in Pa) of hydrazine
evaluated at T2 as follows:
Pvh = exp ( 76.8580 - 7245'2 - 8.22 • ln(2S3) + 0.0061557 - 283 \ = 730 Pa
\ 283 /
So Qm (3.9 kg/s) from Equation (4.3.8-3) is greater than Qm
(1.83 kg/s) from Equation (4.3.8-2), and the estimate of Qm
(1.83 kg/s) from Equation (4.3.8-2) is accepted. Using 1.83
kg/s in Equation (4.3.8-3) A^ is calculated as follows-.
A = 1.83 • 730
p
6.94xlQ-7 (l + 0.0043[283 - 273 .15 ])2 . 0°'75 • 60.1 • i.iSxlO4
Ap = 1170 m2
4. Discharge Density. Calculate the discharge density using
Equation (4.3.8-5) as follows:
4-150
-------
5.
*-iJ££^i-•*•»*/*
Buoyancy Check. Perform buoyancy check as a first check.
A. Calculate the density of air using Equation (4.3.8-6)
6.
where 28.9 kg/kmol is the molecular weight o£ air.
B. Since p2/'p& > 1.02, then the buoyancy is negative.
Release Duration. Calculate the release duration Td using
the equation below:
Td (min) =
500 (kg)
1.83 (kg/s) • 60 (s/min)
= 4 .55 min
After this calculation run the Britter-McQuaid model. (See
Section 5.4 for more information on the Britter-McQuaid
model.)
Data entry in the TSCREEN model for this example is shown below:
Continuous Low Volatility Liquid Leaks - 3.8
SOURCE PARAMETERS - Page 1 of 4
Enter a unique title for this data's model run:
SOURCE OF LEAK
TEMPERATURE
Area (Ao) of Hole or Opening ->
Enter P for Pipe - T for Tank -> f
Discharge Temperature (T2) -> 283
cm2
Storage Temperature (T1) -> 28$ ..;. °K
Ambient Temperature (Ta) -> ZfcSrv^:.. ..:•"; °K
PUDDLE AREA
Is Maximum Puddle Area (Ap) Known (Y/N) ->
Maximum Puddle Area (Ap) ->
tn>
i;:;:g^
4-151
-------
Continuous Low Volatility Liquid Leaks - 3.8
SOURCE PARAMETERS - Page 2 of 4
PRESSURE
Liquid Pressure 109173 Pa
Ambient Pressure (Pa) -> 161325 Pa
Reservoir Pressure CP1) -> 101325 Pa
Contaminant Liquid Density (f1) -> tt& - kg/cubic m
Distance between Hole or Opening
and Top of the Liquid Level (HI) -> 1 m
VAPOR PRESSURE
Vapor Pressure (Pv) -> 11518.01 Pa
Molecular Weight (Mw) -> 60,1 kg/kmol
Latent Heat of Vaporization (Lvap) -> 5«*4€5: J/kg
Boiling Point Temperature (Tb) -> 335?ȣ "K
idtt «&* PfevfcKW. SKtt&ft ftttKX S«te*ft
Continuous Low Volatility Liquid Leaks - 3.8
SOURCE PARAMETERS - Page 3 of 4
EMISSION RATE
Emission Rate (Qm) -> 1851.863 g/s
Uind Speed (Ur) -> 2 m/s
AREA
Area -> 1180.678 m»
DISCHARGE DENSITY
Discharge Density (|7) -> 2.588181 kg/cubic m
DENSITY OF AIR
Density of Air (fair) -> 1.244566 kg/cubic m
Buoyancy is Negative
Edit Previous Screen *PtO> M«*t ScreaB' <6So>-Afaor
Continuous Lou Volatility Liquid Leaks - 3.8
SOURCE PARAMETERS - Page 4- of 4
TIME
Release Duration (Td) -> 4.499973 min
Total Amount of Material Released (Q) -> 50$ kg
Edit Jlext Screen Abort
4-152
-------
Continuous Low Volatility Liquid Leaks - 3.8
Based on user input, the Britter-McQuaid model has been selected.
BRITTER-McQUAID MODEL INPUTS - Page 1 of 3
MODEL PARAMETERS
Relative Humidity (Rh) -> 56 %
Desired Averaging Time for the Calculation
of Concentrations -> 1$ min
Afeart
Continuous Low Volatility Liquid Leaks - 3.8
BRITTER-McQUAID MODEL INPUTS - Page 2 of 3
FENCELINE DISTANCE
Enter the distance from the nearest edge of the source
to the plant fenceline -> Ij^S^'
RECEPTOR LOCATIONS
Do you have specific locations where you would
like pollutant concentrations calculated (Y/N) -> M
A summary of the Britter-McQuaid model's output is displayed
below:
SUMMARY OF B&M MODEL RESULTS
MAX CONC
-------
A release is considered (only) time limited if the liquid
release rate is constant over the duration of the release, but,
the release duration is short in comparison with other important
time scales (e.g., the averaging, time used to assess the
toxicity, the cloud travel time to a downwind position of
interest, or the time required to evaporate the released liquid
puddle). For liquid releases of short duration.(including
instantaneous liquid releases), the procedure outlined above can
be used to estimate the vapor evolution rate Qm if the puddle
area for screening purposes, the puddle area can be estimated if
a liquid depth of, say 1 cm is assumed. (While an equilibrium
depth, of 1 cm may be justified strictly on the grounds it is a
reasonable estimate for screening purposes, more extensive
modeling efforts have used a 1 cm equilibrium depth to fit
experimental data e.g., Moorehouse and Carpenter (1986) and
Webber and Jones (1987).) With this assumption, an unconfined
puddle size can be determined. Finally, the (vapor) release
duration Td can be calculated as Td = Q/Qm where Q is the total
mass of liquid released. (Note that Td may be sufficiently large
enough to consider the vapor release as being continuous even for
an instantaneous liquid release.)
4-154
-------
4.3.9 Instantaneous Low Volatility Liquids from Tanks and Pines
Tanks
Pipe
Leaking Pfpa Range
Similar Releases: Possible applications include a (low-
volatility) liquid leak from a tank or a pipe.
Discussion:
Low-volatility liquid is considered to be a material whose
normal boiling point is above the ambient temperature; a. low-
volatility material stored at moderate to low pressure (and so
that the boiling point is above the storage temperature) will
typically be released as a liquid and form a pool or puddle on
the ground. For low-volatility liquid releases, the
(conservative) assumption is that the liquid evaporates at the
same rate it is spilled (except when the puddle is confined by a
bund or dike from which liquid does not overflow). Possible
applications include a (low-volatility) liquid leak from a tank
or a pipe.
In contrast to scenario 4.3.8, pressure at the hole or
opening is not applicable to an instantaneous liquid release.
Although determination of the liquid release rate is not
applicable to an instantaneous liquid release, determination of
whether the liquid puddle will be confined or not is necessary to
know how to proceed.
Limitations and Assumptions-.
The liquid level, pressure, and temperature in the
reservoir are essentially constant. If these
parameters are not constant, the release rate may vary
with time, but the maximum release rate is generally
obtained for the initial reservoir conditions.
The hole or opening is located in the liquid space (as
opposed to the vapor space).
4-155
-------
The gas evolution (evaporation) rate is assumed to be
equal to the liquid release rate (except when the
puddle is confined by a dike or bund from which liquid
does not overflow). See Spicer, 1992.
Input Information:
Ap puddle area (m2) (For unbounded puddles, Ap is to be
determined; for releases within dikes or bunds, Ap is
the dike or bund area from which liquid would
evaporate.)
Mw contaminant molecular weight (kg/kmol)
R gas constant (8314 J/kg-mole-°K or 8314
Pa -mYkg-mole • °K)
Q total amount of material released (kg)
T. ambient temperature (°K)
Tb contaminant normal boiling point (°K)
T! liquid storage temperature (°K)
Ur ambient windspeed (typically considered to be at 10 m
elevation) (m/s)
V volume of liquid spilled (m3)
X heat of vaporization at the normal boiling point (J/kg)
pl contaminant density at reservoir conditions (T{ and PJ
(kg/m3)
4.3.9.1 Procedure:
1. Puddle Area. Calculate the area of liquid spilled based on
volume of liquid spilled assuming a 1 cm puddle depth.
T 0.01 (m)
If the area from Equation (4.3.9-1) is smaller than the bund
area (which is the maximum possible puddle area), then the
area from Equation (4.3.9-1) is used as the puddle area
(Ap). Otherwise, if the bund size is smaller than the area
calculated in Equation (4.3.9-1), then the bund area is used
as the puddle size
2. Emission Rate. The puddle area is used'to calculate the
emission rate Qm (kg/s)'as follows:
Qm = 6.94xlO'7 (l + 0.0043 [T2 - 273.15J*2) Ur°-75ApMwPv/P.
vh
4.3 .9-2)
where T2 = max(Tt,Tt) and [T2-273.15]* is taken to be zero if
T2 - 273.15 < 0; Pv (in atm) is evaluated at T2 using the
Clausius-Clapeyron Equation:
(4.3.9-3)
Pv = 101325 exp
4-156
-------
where Pvh is the vapor pressure {in Pa) of hydrazine
evaluated at T2 as follows:
Pvh = exp 76.8580 - ,' - 8.22 ln(T2) + 0.0061557 T
2
3. Discharge Density. Calculate the discharge density as
follows:
P2 = „
2 (4.3.9-4)
4. Buoyancy Check. Perform buoyancy check as a first check.
A. Calculate the density of air using the following:
P. M.
'-•TTT: (4.3.9-5)
where M, is the molecular weight of air (assumed to
equal 28.9 kg/kmol).
B. If p2/pair > 1, then the buoyancy is negative. For
negative buoyancy, the Britter-McQuaid model should be
used. If the buoyancy is positive, the PUFF should be
used. (See Section 2.4 for more information on model
selection.)
5. Release Duration. The release duration is used as an input
into the PUFF and Britter-McQuaid models. Calculate the
release duration Td using the equation below:
_ ^_^__
d ' Qm (kg/s) • 60 (s/min)
4 . 3.. 9 . 2 Example: Instantaneous Liquid UDMH Leak
Discussion:
For this example, consider an instantaneous spill of 20 m3
liquid UDMH from storage at 1 atm and 283 °K. The spill occurs
in a bund with a floor area of 2500 m2. The fenceline is 100 m
away.
The following information will be required:
Ap maximum puddle area (2500 m2)
M^ contaminant molecular weight (60.1 g/g-mole)
R gas constant
Q total amount of material released (16,000 kg)
T, ambient temperature (283 °K)
4-157
-------
Tb contaminant normal boiling point (335.5 °K)
T! liquid storage temperature (283 °K)
Ur ambient windspeed (typically considered to be at 10 m
elevation) (2.0 m/s)
V volume of liquid spilled (20 m3)
X heat of vaporization at the normal boiling point
(5.44x105 J/kg)
Pi contaminant density at reservoir conditions (Tt and Pt)
(800 kg/m3)
Procedure:
1. Puddle Axea. Calculate-the area of liquid spilled based on
the volume of liquid spilled assuming a 1 cm puddle depth
from Equation (4.3.9-1) as follows:
a (m2) = 20 m3 = 2000 m2
f n ni m
0.01 m
The area from Equation (4.3.9-1) is smaller than the bund
area (which is the maximum possible puddle area) ,- therefore,
the- area from Equation (4.3.9-1) is used as the puddle area
(A,).
Emission Rate. The puddle area is used to calculate the
emission rate (Qm) from Equation (4.3.9-2) as follows:
Qm=6 . 94xlO'7(l+0 . 0043 [283-273 . 15 ]2) 2 . 0°-75 • 2000 • 60 . 1 • Pv/Pvh
Qm = 3.13 kg/s
where T2 = min(283 °K,283 °K) = 283 °K and Pv (in atm) is
evaluated at T2 using the Glaus ius-Clapeyron Equation
(4.3.9-3) :
P, = 101325 exp - - - • 1-lSxlo<
where Pvh is the vapor pressure (in Pa) of hydrazine
evaluated at T2 as follows:
•
Pvh = exp ( 76.8580 - 7245'2 - 8.22 ln(283) + 0.0061557 • 283 ) = 730 Pa
\ 283 /
3. Discharge Density. Calculate the discharge density using
Equation (4.3.9-4) as follows:
n - 101325 -60.1 n c
P2 " 8314 • 283 = 2'5
4-158
-------
4. Buoyancy Check. Perform buoyancy check as a first check.
A. Calculate the density of air using Equation (4.3.9-:
where 28.9 kg/kmol is the molecular weight of air.
B. Since p2/p& > 1, the buoyancy is negative.
Release Duration. Calculate the release duration Td using
the equation below:
Td (min) =
16,000 (kg)
3.13 (kg/s) • 60 (s/min)
= 85 min
After this calculation run the Britter-McQuaid. (See
Section 5.4 for more information on the Britter-McQuaid
model.)
Data entry in the TSCREEN model for this example is shown below:
Instantaneous Low Volatility Liquid Leaks - 3.9
SOURCE PARAMETERS.- Page 1 of 4
Enter a unique title for this data's model run:
Volume of Liquid Spilled (V) -> 20:...f: :..- cubic m
Discharge Temperature (T2) -> 283 "K
VOLUME
TEMPERATURE
Storage Temperature (T1) ->
Ambient Temperature (Ta) ->
"K
PUDDLE AREA
Is Maximum Puddle Area (Ap) Known (Y/N) -> T
Maximum Puddle Area (Ap) ->
«F2> Edit ~"&9>e Prevlbua Screen; . '• •"••
*:<£w£*-: Abort!
Instantaneous Low Volatility Liquid Leaks - 3.9
SOURCE PARAMETERS - Page 2 of 4
VAPOR PRESSURE
Vapor Pressure (Pv) -> 11518.01 Pa
Molecular Weight (Mw) ->
Latent Heat of Vaporization (Lvap) ->
Boiling Point Temperature (Tb) ->
•: kg/kmol
J/kg
4-159
-------
Instantaneous Low Volatility Liquid Leaks - 3.9
SOURCE PARAMETERS - Page 3 of 4
EMISSION RATE
Emission Rate (dm) -> 3136.949 g/s
Wind Speed (Ur) -> 2 m/s
AREA
Area -> 2000 m'
DISCHARGE DENSITY
Discharge Density (f2) -> 2.588181 kg/cubic m
DENSITY OF AIR
Density of Air (fair) -> 1.244566 kg/cubic m
Buoyancy is Negative
8dit 85.00829 min
Total Amount of Material Released (Q) -> 16000: kg
Instantaneous Low Volatility Liquid Leaks - 3.9
Based on user input, the Britter-McQuaid model has been selected.
BRlTTER-McQUAID MODEL INPUTS - Page 1 of 3
MODEL PARAMETERS
Relative Humidity (Rh) -> 56 .! %
Desired Averaging Time for the Calculation
of Concentrations -> 15- min
Afcort
Instantaneous Lou Volatility Liquid Leaks - 3.9
BRITTER-McQUAID MODEL INPUTS - Page 2 of 3
FENCELINE DISTANCE
Enter the distance from the nearest edge of the source
to the plant fenceline -> 100
RECEPTOR LOCATIONS
Do you have specific locations where you would
like pollutant concentrations calculated (Y/N) -> H
Sewer*
-------
A summary of the Britter-McQuaid model's output is displayed
below:
<««««>«>«««»«»««>«»««*« ««•«««»««>•*»«
*** SUNMARY OF B£M MODEL RESULTS ***
««««•«» »••>•««««««*«««««>
MAX COHC MAX CONC DIST TO WIND SPEED
(Ua/M**3> (PPM) MAX (M) (M/S)
.4904E+08 .1895E+05 100. 4.
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
«««<••»«*«««>«« >«»>«««•««•«•««««t«m»««« «««•«•«>«««
4.3.9.3 Considerations for Time-Varying and Time Limited
Releases
See Section 4.3.8.3 for a discussion of considerations of
time-varying and time-limited releases.
4-161
-------
4.4 Superfund Releases
4.4.1 Air Strippers
Contaminated
Wafer
"Clean" i
Air
Air
Discussion:
Air stripping is a widely used technique for removing
volatile organic compounds (VOC) from contaminated water.
Procedures are given to evaluate the effect of the concentration
of contaminants in water and the effect of the stripping rate on
the emission rates and on the ambient air concentrations at
distances from, the air stripper'.
Limitations and Assumptions L
None.
References:
For further information see: Air/Superfund National
Technical Guidance Study Series - Air Stripper Design Manual.
EPA-450/1-90-003, U.S. Environmental Protection Agency, Research
Triangle Park, NC, May 1990, NTIS PB91-125997, pp 51-52.
Input Information:
In addition to the SCREEN model input (see Secicn 5.1.1).
the following is needed-.
C concentration of contaminant (mg/L)
Q incoming water flow rate (L/'min)
4.4.1.1 Procedure
4-162
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1. Emission Rate. Calculate emission rate (Qm) (g/s) using the
concentration of the contaminant (C) and the incoming water
flow rate (Q). VOC concentrations in ground water typically
range from 0.1 to 1 ppmw. Typical values for an air
stripper are shown in Table 4.4.1-1.
Qm(g/s) = C(mg/L) Q(L/minute) 1.67xKT5 (4.4.1-1)
TABLE 4.4.1-1
TYPICAL VALUES FOR AN AIR STRIPPER
Parameter
Incoming Water Flow
Stack Height
Stack Diameter
Structure Dimensions
Exit Gas Velocity
Exit Gas Temperature
Ambient Temperature
Units
L/min
m
m
m
m/sec
°K
°K
Small
570
7.6
0.31
7.6x1.2x1.2
6.4
293
293
Typical Value
Medium
2840
9
0.61
9x3.6x3.6
8.0
293
293
Large
5700
14
0.91
•13x3.6x3.6
7.3
293
293
2. TSCREEN will run the SCREEN model for a point source.
4.4.1.2 Example: Air stripper example
Discussion:
This example uses the default values provided by TSCREEN for
a large air stripper. The fenceline is 100 m from the air
stripper.
The following input information will be required:
C
Q
Procedure;
1.
concentration of contaminant 0.5 (mg/L)
incoming water flow (L/min) 4700 (default)
Emission Rate. Calculate emission rate (Qm) (g/s) using
Equation (4.4.1-1):
= -5 (mg/L) 5700 (L/minute) l.SVxlO'5 = 0.048 (g/s)
TSCREEN will run the SCREEN model for a point source . For
an explanation of inputs- for the SCREEN model see Section
5.1.1.
4-163
-------
Data entry in the TSCREEN model for this example is shown below:
Air Strippers - Scenario 4.4.1
SOURCE PARAMETERS * Page 1 of 1
Enter a unique title for this data's model run:
EMISSION RATE
Enter the Emission Rate (Qm), if unknown enter
the boxed variables below to calculate -> IM&?5$$ g/s
Concentration of Contaminate (C) -> ,5 mg/L
Incoming Water Flow (Q) -> 5-TfflJ L/min
sdft.
p^:p$^^
Air Strippers - Scenario 4.4.1
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 7
RELEASE PARAMETERS
Exit Velocity -> 7*3
Release Height above Ground -> 14
Diameter at Release Point -> .91
Temperature of the Material Released -> 293
AMBIENT PARAMETER
Ambient Temperature -> 293
m/s
m
m
"K
> Abort
Air Strippers - Scenario 4.4.1
SCREEN MODEL INPUTS - Page 2 of 7
BUILDING PARAMETERS
Building Height (enter 0 if no building) -> 13 ; m
Building Minimum Horizontal Dimension -> &$• ;*,};. m
Building Maximum Horizontal Dimension -> &&}.;.:/' m
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural -> ft
FENCELINE DISTANCE
Enter the distance from the base of the stack
to the plant fenceline -> 100 ' : m
idtt • *f9*: f*r««tt .«w«.t,$«f«en,:. ;,,,,.
-------
•It*************************************
*** SUMMARY OF SCREEN MODEL RESULTS ***
CALCULATION
PROCEDURE
MAX CONC
(UG/M**3)
DIST TO
MAX (M)
TERRAIN
HT (M)
SIMPLE TERRAIN 7.276
BUILDING CAVITY-1 678.0
BUILDING CAVITY-2 678.0
104.
12.
12.
0.
(DIST
(DIST
•• CAVITY LENGTH)
'.CAVITY LENGTH)
it**************************************************
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
***************************************************
4-165
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5.0 ATMOSPHERIC DISPERSION ESTIMATES
Maximum short-term ground level concentrations in TSCREEN
are based on current EPA screening models (SCREEN, RVD, and PUFF)
which are embedded in the TSCREEN model. In addition, TSCREEN
implements the Britter-McQuaid method for estimating maximum
concentration from denser-than-air continuous (plume) and
instantaneous (puff) releases. This section lists the TSCREEN
model inputs needed. Sources of additional information about the
models are referenced, where appropriate.
5-1
-------
5.1 SCREEN
The SCREEN model implements most of the single source, short
term procedures contained in the revised EPA screening procedure
document (EPA, 1988c). This includes providing estimated maximum
ground-level concentrations and distances to the maximum based on
a pre-selected range of meteorological conditions. SCREEN is a
Gaussian dispersion model applicable to continuous releases of
particulate matter and non-reactive, non-dense gases that are
emitted from point, area, and flared sources. In addition,
SCREEN has the option of incorporating the effects of building
downwash, as described in the Industrial Source Complex (ISC2)
model user's guide (EPA, 1992) . Refer to the document referenced
above for more information about the implementation of the SCREEN
model.
5.1.1 Point Sources
5.1.1.1 Model Inputs
This section contains a complete listing of the inputs
TSCREEN will request for the SCREEN point source. Some of these
inputs may have already been entered from the scenario input
section.
SCENARIO NAME & NUMBER
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 7
Enter a unique title for this data's model run:
RELEASE PARAMETERS
Emission Rate (Qm) ->
Exit Velocity (Exitv)->
Release Height above Ground (Hs) ->
Diameter at Release Point (0) ->
Temperature of the Material Released (Ts) ->
AMBIENT PARAMETER
Ambient Temperature (Ta) -> 293
g/s
m/s
m
m
Help Calculator Previous Screen Abort
RELEASE PARAMETERS
- Emission Rate (Om) (g/s) -
Enter the source specific emission rate. EPA recommends that
emission rates from sources be determined through source
testing using EPA References Methods (40 CFR Part 60 Appendix
A) or process calculations. If source specific emissions are
not available, representative emission factors can be
substituted. Emission factors are available for individual
toxic compounds. For some sources of applicable emissions
5-2
-------
factors for individual toxic compounds see Appendix A items
1-4 of this workbook.
2 Exit Velocity (Exitv) (m/s) -
This value can be calculated from the following equation:
Exitv = 4 V/(7rD2)
where:
D = inside diameter of stack (m)
V = volumetric flow rate (m3/s)
3 Release Height above Ground (H;) (m) -
Enter the height of the stack or of the release point above
the ground.
4 Diameter at Release Point (D) (m) -
Enter the inside diameter of the stack or release point in
meters.
5 Temperature of the Material Released (T.) (K) -
Enter the temperature of the material released in degrees
Kelvin.
AMBIENT PARAMETER
6 Ambient Temperature (Tj (K) -
The default if 293 °K.
SCENARIO NAME & NUMBER
SCREEN MODEL INPUTS - Page 2 of 7
BUILDING PARAMETERS
Building Height (enter 0 if no building) -> : ; . m
Building Minimum Horizontal Dimension -> m
Building Maximum Horizontal Dimension -> m
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural ->
FENCELINE DISTANCE
Enter the distance from the base of the stack
to the plant fenceline -> . ; m
Help -Calculator Previous Screen Abort
5-3
-------
BUILDING PARAMETERS
7 Building Height (m) -
Enter the buildings maximum height above ground in meters.
Building parameters are needed for calculating downwash for a
stack due to a "nearby" building. "Nearby" includes
structures within a distance of five times the lesser of the
height or width of the structure, but not greater than 0.8 km
(0.5 mile). If more than one building is involved, each
building/stack configuration must be modeled separately. -For
information about complex structures, refer to the Guideline
for Determination of Good Engineering Practice Stack Height
(Technical Support Document for Stack Height Regulations).
Revised. EPA 450/4-80-023R. For these complex
configurations, a refined model such as the Industrial Source
Complex (ISC) model is recommended. Wake effects are
included. Cavity calculations are made for two building
dimensions alongwind. The cavity calculations are summarized
in the SCREEN model output at the distance-dependent
calculations. Building downwash effects are not considered
in the SCREEN model in either the VALLEY or simple terrain
component of the complex terrain screening procedures (see
description Terrain Type below), even if the building
downwash option is selected by entering a building height.
*• If the building height is 0 the next two parameters are
not requested and the user will proceed to step 10.
8 Building Minimum Horizontal Dimension (m) -
Enter the alongwind minimum .horizontal dimension of the
"nearby" structure in meters. A simple rectangular building
is assumed. (See the description of Building Height above.)
9 Building Maximum Horizontal Dimension (m) -
Enter the alongwind maximum horizontal dimension of the
"nearby" structure in meters. A simple rectangular building
is assumed. (See the description of Building Height.)
URBAN/RURAL CLASSIFICATION
10 Enter U for Urban - R for Rural -
The classification of a site as urban or rural is based on
the procedures described in Section 8.2.8 of the Guideline on
Air Quality Models (Revised). EPA-450/2-78-027R.
FENCELINE DISTANCE
11 Enter the distance from the base of the stack to the plant
fenceline (m) -
Enter the distance from the base of the stack to the plant
fenceline in meters. SCREEN calculates the maximum
concentrations across a range of meteorological conditions
for the minimum distance given (> 1 m) and then for each
5-4
-------
distance in a built-in array of distances. Thus, the user
can input the minimum fenceline distance as the minimum
distance for calculation and obtain a concentration at the
site boundary and beyond. Distances less than the fenceline
are ignored. Receptors beyond the fenceline are defined as
ambient air.
SCENARIO NAME & NUMBER
SCREEN MODEL INPUTS - Page 3 of 7
TERRAIN TYPE
Is this a FLAT or SIMPLE TERRAIN evaluation (Y/N) ->
SIMPLE TERRAIN
Are receptors above stack-base (Y/N) ->
SIMPLE FLAT TERRAIN
Do you have specific locations where you would like •
pollutant concentrations to be calculated (Y/N) ->
Do you have receptors above ground level
(i.e. Flag Pole Receptors) (Y/N) ->
You have completed simple terrain inputs. Do you
want to continue with complex terrain (Y/N) ->
Help Calculator Previous Screen Abort
TERRAIN TYPE
12 Is this a FLAT or SIMPLE TERRAIN elevation (Y/N) -
Terrain type is determined according to whether it is above
or below stack-top. Simple terrain is an area where terrain
features are all lower in elevation than the top of the stack
of the source. Complex terrain is defined as terrain
exceeding the height of the stack being modeled. In TSCREEN,
the user is given the option of modeling simple elevated
terrain heights where terrain heights exceed stack base but
are below stack height, or simple flat terrain, where terrain
heights are assumed not to exceed stack base elevation.
Answer "N" if there are no flat or simple terrain receptors;
- a "N" answer will bring up the COMPLEX TERRAIN screen.
Answer "Y" if one or more receptors are located in terrain
which is below stack-top. Answer "Y" if your evaluation
involves both simple and complex terrain receptors. You will
have another opportunity following completion of the simple
terrain inputs to evaluate the complex terrain receptor. In
summary:
"Y" selects FLAT or SIMPLE TERRAIN
"N" selects COMPLEX TERRAIN
* If "Y" was entered above, TSCREEN proceeds to step 13.
5-5
-------
+ If "N" was entered above, TSCREEN proceeds to step 15.
SIMPLE TERRAIN
13 Are receptors above stack-base (Y/N) -
Simple terrain is an area where terrain features are all
lower in elevation than the top of the stack of the source.
Answer "Y" if one or more receptors are located in simple
terrain. "N" if all receptors are in FLAT terrain. In
summary:
"Y" selects SIMPLE TERRAIN
"N" selects FLAT TERRAIN
+ If "Y" was entered, TSCREEN proceeds to step 15.
•
* If "N" was entered, TSCREEN proceeds to step 14.
SIMPLE FLAT TERRAIN
14 Do you have specific locations where you would like pollutant
concentrations to be calculated (Y/N) -
The entry of "Y" will allow the user to input any number of
specific distances (>1 m) and the maximum concentration for
each distance will be calculated. Note that SCREEN has an
automated distance array which calculates maximum
concentrations at a pre-selected array of 50 distances
ranging from 100 m to 50 km. Increments of 100 m are used
out to 3 km, increments of 500 m are used from 3 km to 10 km,
increments of 5 km from 10 km to 30 km, and increments of 10
km are used out to 50 km. For example, a specific_location
of interest may be a school 117 m from the source.
15 Do you have receptors above ground level (i.e. Flag Pole
Receptors) (Y/N) -
A flag pole receptor is any receptor which is located above
local ground level, e.g., on the roof of a building. Flag
pole receptors are useful for estimating concentrations on
rooftops or similar exposed locations and are most often used
in urban modeling evaluations. Note, flag pole receptors
should NOT be used to evaluate impacts on hilltops or on
other exposed terrain features; the latter should be
evaluated using the TSCREEN options for simple or complex
terrain. Answer "Y" if you want to use flag pole receptors.
A "Y" response will invoke a request for the receptor (i.e.,
flag pole) height. Answer "N" if you do not want to use flag
pole receptors. The receptor height defaults to zero for a
"N" response.
5-6
-------
16
* If there is Simple terrain (response of "Y" at step 13)
then, TSCREEN proceeds to step 17.
> If there is no Simple or Flat terrain (response of "N"
at step 12) then, TSCREEN assumes that there is Complex
terrain and proceeds to step 19.'
* If there is Flat terrain and specific locations of
interest (response of "N" at step 13 and response of
"Y" at step 14) then, TSCREEN proceeds to step 18.
*• If there is Flat terrain but no specific locations of
interest (response of "N" at step 13 and response of
"N" at step 14) then, TSCREEN proceeds to step 16.
You have completed simple terrain inputs. Do you want to
continue with complex terrain (Y/N) -
Complex terrain is terrain exceeding the height of the stack
being modeled. Enter "Y". to model complex terrain. SCREEN
has no automated distance array for Complex Terrain.
Distances must be specified by the user.
* If "Y" was entered, TSCREEN proceeds to step 19.
+ If "N" was entered, TSCREEN runs the SCREEN model.
SCENARIO NAME & NUMBER
SCREEN MODEL INPUTS/SIMPLE TERRAIN STAIRSTEP SEARCH-- Page 4 of 7
Enter distance and terrain elevation for "stair-step'search".
Enter a blank Maximum Distance to stop input.
Distance (meters)
Minimum Maximum Height (meters)
100 fence
200
400
800
1200
Last Maximum Distance will be extended to 50000 m
Help
Calculator
Previous Screen
Abort
SIMPLE TERRAIN STAIR-STEP SEARCH
17 Enter distance and terrain elevation for "stair-step search"-
The SCREEN model assumes that terrain elevation either
remains the same or increases with distance from the source,
i.e., incremental steps, as in an ascending staircase or on a
5-7
-------
terraced hillside. "Stair-step search" describes how the
SCREEN model searches for the maximum concentration in simple
terrain. The user should enter the distance to and the
elevation (above stack-base) of each stair-tread or terrace.
SCREEN assumes that the first stair-tread begins at the ;
fenceline. Thus, the user must begin by entering the
elevation and the distance to the end of the first stair-
tread. This is repeated for each succeeding stair-tread.
The distance to the end of the last stair-tread defaults to
50 km.
After finishing inputs for this section, TSCREEN will ask if
there are specific locations of interest (See step 13).
* If "Y", TSCREEN proceeds to step 18.
> If "N", TSCREEN will ask the. if there is Complex
terrain (See step 16).
*• If there is Complex terrain, TSCREEN proceeds to step
19.
* If there is no Complex terrain, TSCREEN runs the SCREEN
model.
SCENARIO NAME & NUMBER
SCREEN MODEL INPUTS DISCRETE RECEPTORS - Page 5 of 7
Enter a height and distance(s) from the source to terrain feature(s)
at which a specific receptor will be located.
Enter a blank after the distance to stop inputs for that height.
Enter a blank height to stop input.
Height (m)
Height (m)
Height (m)
Height (m)
Height (m)
Distances (m) Distances (m) Distances (m) Distances (m) Distances (m)
Help
Calculator
Previous Screen <£sc> Abort
DISCRETE RECEPTORS
18 Enter a height and distance(s) from the source to terrain
feature(s) at which a specific receptor will be located -
The program will calculate concentrations at receptors for a
specified distance from their release. In the case of simple
terrain, a terrain height can be specified from these
receptors. This height must be s the stack height. For the
case of flat terrain, a terrain height is not requested.
5-8
-------
*• If 5 heights are entered, TSCREEN will ask if the user
wants to enter more discrete receptors. If the
response is "Y" a Page 6 of 7, which looks the same as
Page 5 of 7, will appear.
After finishing inputs for DISCRETE RECEPTOR section, TSCREEN
will ask if the user wants to proceed with complex terrain
(See step 17).
*• If response is "Y" then TSCREEN proceeds to step 19.
+ If" response in "N" then, TSCREEN runs the SCREEN model.
SCENARIO NAME & NUMBER
SCREEN MODEL INPUTS COMPLEX TERRAIN - Page 7 of 7
Enter height and distance for receptor location.
Enter a blank Distance to stop input.
Plume Height -> m
Distance to Final Plume Rise -> m
Height (m) Distance (m)
2
3
4
5
6
7
8
9
Height (m) Distance (m)
11 ""'•;•..
12 :' •""-, '- . ;':V
13 •;:/:'-?:-,.:;. ::;4 •••••;•' '•'
15 -v>. •:."-"i. /":S-"v
16 . ••• -*,:•; .-•-.• . "•-
17 ••'fi.:"" .-. :•••
18 "^ .•:•-. ; -. ';-•
20 ...'•'•:'::... •' ':-."'. •••""•'•
Help
Calculator
Previous Screen
Abort
COMPLEX TERRAIN
19 Enter height and distance from receptor locations -
Enter the terrain height and distance in meters for the
receptor of interest. The terrain height must be greater
than the stack height.
> After finishing inputs for this section, TSCREEN runs
the SCREEN model.
5.1.1.2 Model Output
For a complete example of the SCREEN model for a point
source, see Section 4.1.1. See Appendix E - Running TSCREEN fcr
output options after model is run.' The following shows the
format of the output file that SCREEN would generate for a point
source if the user has chosen to show the maximum concentration
in parts per million (PPM) in addition to ^g/m3 and shows the
maximum concentration for additional averaging times.
5-9
-------
1 02-05-92
09:50:06
*** SCREEN-1.2 MODEL RUN ***
*** VERSIOH DATED 90XXX ***
Paniculate Stack Release
COMPLEX TERRAIN INPUTS:
SOURCE TYPE = POINT
EMISSION RATE (G/S) =
STACK HT (M) -
STACK DIAMETER (M) -
STACK VELOCITY (M/S)=
STACK GAS TEMP (K) =
AMBIENT AIR TEMP (K)=
RECEPTOR HEIGHT (M) =
IOPT (1=URB,2=RUR) =
1 ' 02-05-92
09:50:06
* *** SCREEN-1.2 MODEL RUN ***
*** VERSION DATED 91/10 •**
SIMPLE TERRAIN INPUTS:
SOURCE TYPE = POINT
EMISSION RATE (G/S) =
STACK HEIGHT (M) =
STK INSIDE DIAM (M) =
STK EXIT VELOCITY (M/S)=
STK GAS EXIT TEMP (K) =
AMBIENT AIR TEMP (K) =
RECEPTOR HEIGHT (M) =
IOPT (1=URB,2=RUR) =
BUILDING HEIGHT (M) -
MIN HORIZ BLDG DIM (M) =
MAX HORIZ BLDG DIM (M) =
IF*********************
SUMMARY OF SCREEN MODEL RESULTS *»
CALCULATION
PROCEDURE
MAX CONC
(UG/M**3)
MAX CONC
(PPM)
DIST TO
MAX (M)
TERRAIN
HT (M)
SIMPLE TERRAIN
COMPLEX TERRAIN (24-HR CONC)
BUILDING CAVITY-1 -- (DIST = CAVITY LENGTH)
BUILDING CAVITY-2 -- (DIST = CAVITY LENGTH)
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
««•««««««««•««««»*««««•««»**«• «•*««««»«
BUOY. FLUX = M«*4/S»*3; MOM. FLUX = M«*4/S**2.
FINAL STABLE PLUME HEIGHT (M) =
DISTANCE TO FINAL RISE (M) =
•VALLEY 24-HR CALCS* "SIMPLE TERRAIN 24-HR CALCS**
TERR MAX 24 -HR PLUME HT PLUME HT
HT DIST CONC CONC ABOVE STK CONC ABOVE STK U10M UST
5-10
-------
(M) (M) (UG/M**3) (UG/M**3) BASE CM) (UG/M**2) HGT (M) SC
BUOY. FLUX = M**4/S**3; MOM. FLUX = M**4/S**2.
*** FULL METEOROLOGY ***
**»*•***•************1
*** SCREEN AUTOMATED DISTANCES ***
********************************** •
*** TERRAIN HEIGHT OF M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES **
DIST CONC U10M USTK MIX HT PLUME SIGMA SIGMA
(M) (UG/M**3) STAB (M/S) (M/S) (M) HT (M) Y CM) Z (M) DWASH
100.
200.
MAXIMUM 1-HR CONCENTRATION AT OR BEYOND M:
************
*** SCREEN AUTOMATED DISTANCES ***
**********************************
*** TERRAIN HEIGHT OF M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES **
DIST CONC U10M USTK MIX HT, PLUME SIGMA SIGMA
(M) (UG/M**3) STAB (M/S) (M/S) (M) HT (M) Y (M) Z (M) DUASH
200.
300.
400.
MAXIMUM 1-HR CONCENTRATION AT OR BEYOND M:
**********************************
*** SCREEN AUTOMATED DISTANCES ***
**********************************
*** TERRAIN HEIGHT OF M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES **
DIST CONC U10M USTK MIX HT PLUME SIGMA SIGMA
(M) (UG/M»*3) STAB (M/S) (M/S) (M) HT (M) Y (M) Z (M) DWASH
MAXIMUM 1-HR CONCENTRATION AT OR BEYOND M:
*** SCREEN AUTOMATED DISTANCES **«
**********************************
*** TERRAIN HEIGHT OF M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES **
DIST CONC U10M USTK MIX HT PLUME SIGMA SIGMA
" (M) (UG/M**3) STAB (M/S) (M/S) (M) HT (M) Y (M) Z (M) OWASH
900. 1000.
5-11
-------
1100.
1200.
1300.
1400.
1500.
1600.
1700.
1800.
1900.
2000.
2100.
2200.
2300.
2400.
2500.
2600.
2700.
2800.
2900.
3000.
3500.
4000.
4500.
5000.
5500.
6000.
6500.
7000.
7500.
8000.
8500.
9000.
' 9500.
10000.
15000.
20000.
25000.
30000.
40000.
50000.
MAXIMUM 1-HR CONCENTRATION AT OR BEYOND
OIST = DISTANCE FROM THE SOURCE
CONC = MAXIMUM GROUND LEVEL CONCENTRATION
STAB = ATMOSPHERIC STABILITY CLASS (1=A, 2=8, 3=C, 4=0, 5=E, 6=F)
U10M = WIND SPEED AT THE 10-M LEVEL
USTK = WIND SPEED AT STACK HEIGHT
MIX HT = MIXING HEIGHT
PLUME HT= PLUME CENTERLINE HEIGHT
SIGMA Y = LATERAL DISPERSION PARAMETER
SIGMA Z = VERTICAL DISPERSION PARAMETER
OWASH = BUILDING DOUNWASH:
DUASH= MEANS NO CALC MADE (CONC = 0.0)
DUASH=NO MEANS NO BUILDING DOUNWASH USED
DUASH=HS MEANS HUBER-SNYDER OOUNUASH USED
DWASH=SS MEANS SCHULMAN-SCIRE DOUNUASH USED
DWASH=NA MEANS DOUNUASH NOT APPLICABLE, X<3*LB
*** SCREEN DISCRETE DISTANCES *»*
*********************************
•* TERRAIN HEIGHT OF M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES **
DIST CONC U10M USTK MIX HT PLUME SIGMA SIGMA
(M) (UG/M**3) STAB (M/S) (M/S) (M) HT (M) Y (M) Z (M) DUASH
5-12
-------
*** SCREEN DISCRETE DISTANCES **•
»««n>*«i»« «••««»•**•*<"»«*••****•*«
TERRAIN HEIGHT OF
N ABOVE STACK BASE USED FOR FOLLOWING DISTANCES
DIST CONC U10M USTK NIX HT PLUME SIGMA SIGMA
(M) (UG/M*»J) STAB (M/S) (M/S) (M) HT (M) Y ««I>«««II«I»I> «««•«•*«••»•«**•*
* SUMMARY OF TERRAIN HEIGHTS ENTERED FOR *
* SIMPLE ELEVATED TERRAIN PROCEDURE *
*»«««*<>IH>«««lr*«*««*«****««*«*«***«**<><>««*****
TERRAIN DISTANCE RANGE (M)
HT (M) MINIMUM MAXIMUM
*** CAVITY CALCULATION
CONC (UG/M**3) =
CRIT US 310M (M/S) =
CRIT US 3 HS (M/S) =
DILUTION US (M/S) =
CAVITY HT (M) =
CAVITY LENGTH (M) =
ALONGUIND DIM (M) =
*** CAVITY CALCULATION - 2
CONC (UG/M**3) =
CRIT US aiOM (M/S) =
CRIT US 3 HS (M/S) =
DILUTION US (M/S) =
CAVITY HT (M)
CAVITY LENGTH (M) =
ALONGUIND DIM (M) =
******************
*** USER SPECIFIED AVERAGING TIMES ***
*****************************
ESTIMATED MAXIMUM
UG/M**3
ESTIMATED MAXIMUM
UG/M**3
CONCENTRATION FOR 15 MIN AVERAGING TIME:
PPM
CONCENTRATION FOR 30 MIN AVERAGING TIME:
PPM
ESTIMATED MAXIMUM
(*/- )
CONCENTRATION FOR 3 HR AVERAGING TIME:
UG/M**3 (+/- ) PPM
ESTIMATED MAXIMUM CONCENTRATION FOR 8 HR AVERAGING TIME:
(+/- ) UG/M**3 (+/- ) PPM
ESTIMATED MAXIMUM CONCENTRATION FOR 24 HR AVERAGING TIME:
(+/- ) UG/M**3 . («•/- ) PPM
5-13
-------
*>««>«>l» «*«**•«**« *»««»•« «»•**«*•*•
*** END OF SCREEN MODEL OUTPUT ***
*«>««*«••» ««I>«>««<««<»»«*«*
5.1.2 Area Sources
5.1.2.1 Inputs
This section contains a listing of the inputs TSCREEN will
request that are unique for the SCREEN area source. Some of
these inputs may have already been entered from the scenario
input section.
SCENARIO NAME & NUMBER
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 2
RELEASE PARAMETERS
Release Height above Ground (Hs) ->
Area of the Emitting Source (A) ->
m
m*
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural ->
FENCELINE DISTANCE
Enter the distance from the nearest edge of the
source to the plant fencetine ->
FLAG POLE RECEPTORS
Enter Receptor Height above Ground (Zr> -> <^;-V':;- m
RECEPTOR LOCATIONS
Do you have specific locations where you would like
pollutant concentrations to be calculated (Y/N) -> :
Help Calculator Previous Screen Abort
RELEASE PARAMETERS
1 Release Height above Ground (H.) -
Enter the height of the release area above the ground in
meters. If the height is < 10 m, then the model assumes a
ground level release. If the height is > 10 m, the release
are is probably a volume source and SCREEN cannot handle this
case.
f
2 Area of the Emitting Source (A) -
Enter the release area in square meters.
URBAN/RURAL CLASSIFICATION
3 Enter U for Urban - R for Rural -
The classification of a site as urban or rural is based on
the procedures described in Section 8.2.8 of the Guideline on
Air Quality Models (Revised). EPA-450/2-78-027R.
5-14
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FENCELINE DISTANCE
4 Enter the distance from the nearest edge of the source to the
plant fenceline -
Enter the distance from the base of the stack to the plant
fenceline in meters. SCREEN calculates the maximum
concentrations across a range of meteorological conditions
for the minimum distance given (> 1 m) and then for each
distance in the array. Thus, the user can input the minimum
fenceline distance as the minimum distance for calculation
and obtain a concentration at the site boundary and beyond.
Distances less than the fenceline distance are ignored.
Receptors beyond the fenceline are defined as ambient air.
FLAG POLE RECEPTORS
5 " Enter Receptor Height above Ground (Zr) -
Flag pole receptors are receptors at heights (meters) above
local terrain elevation, e.g., on the roof of a building.
Enter 0 if receptor heights are at ground level. Flag pole
receptors are useful for estimating concentrations on
rooftops or similar exposed locations and are most often used
in urban modeling evaluations. The default is 0.
RECEPTOR LOCATIONS
Since area sources are ground level releases, there is no
impact on "complex terrain"; only receptors classified as "simple
terrain."
6 Do you have specific locations where you would like pollutant
concentrations to be calculated (Y/N) -
The entry of "Y" will allow the user to input any number of
specific distances (>1 m) and the maximum concentration for
each distance will be calculated. Note that SCREEN has an
automated distance array which calculates maximum
concentrations at a pre-selected array of 50 distances
ranging from 100 m to 50 km. For example, a specific
location of interest may be a school 117 m from the source.
With the automated distance array, the SCREEN model uses an
iteration routine to determine the maximum value and
associated distance to the nearest meter. Note: SCREEN
assumes that the overall maximum concentration occurs for the
same stability class that is associated with the maximum
concentration from the automated distance array, and begins
iterating from that value, examining a range of wind speeds
for that stability.
* If response is "Y" then TSCREEN proceeds to step 7.
»• If response is "N" then TSCREEN runs -the SCREEN model.
5-15
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SCREEN MODEL INPUTS
RECEPTOR LOCATIONS:
the source at which
Enter a blank after
Distance from
source (meters)
— awcnnitiw nfwic tt nunDCK ~~~
- Page 2 of 2
Enter (up to 30) distances
from
concentrations should be calculated.
the last distance to stop input.
Distance from
source (meters)
1 fence 11 " -'
2 V" :
3
4
5
6
7
8
9
10
Help
12
13 !
14
15
16 ,
17
18
19
20
Calculator Previous
Distance from
source (meters)
21
22
23
24
25 ,
26 :
27
28
29
30 ;
Screen Abort
DISCRETE RECEPTORS
7 Enter (up to 30) distances from the source at which
concentrations should be calculated -
Enter the Distance in meters from the release for calculating
the maximum ground level concentrations.
> After all of the desired distances have been entered,
TSCREEN will run the SCREEN model for an area source.
5.1.2.2 Model Output
For a complete example of the SCREEN model for a area source,
see Section 4.1.2. (See Appendix E-Running TSCREEN for output
options after the model is run.) The following shows the format
of the output file that SCREEN would generate for a area source
if the user has chosen to show the maximum concentration in part
per million (PPM) in addition to /zg/m3.
SCREEN-1.2 MODEL RUN
VERSION DATED 90XXX
03-03-92
10:04:59
SIMPLE TERRAIN INPUTS:
SOURCE TYPE
EMISSION RATE (G/S)
SOURCE HEIGHT (M)
LENGTH OF SIDE (M)
RECEPTOR HEIGHT (M)
IOPT (1=URB,2=RUR)
AREA
SUMMARY OF SCREEN MODEL RESULTS
5-16
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«««««• ««•«•«> ««•*•••• ««««W»1
CALCULATION MAX CONC
PROCEDURE
MAX CONC
(PPM)
DIST TO
MAX (M)
TERRAIN
HT (M>
SIMPLE TERRAIN
««»«»»*in>*»«>ii»»in»««*»«***««**««««*«««««««*«**««
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
*«««««««»>« »•*«««*««**•«•« ******* «««•««••«•«««««•««
BUOY. FLUX = M**4/S**3; MOM. FLUX a M**4/S**2.
*** FULL METEOROLOGY ***
*** SCREEN AUTOMATED DISTANCES ***
««»»«•«»»«••««««*«•««««««•*«*****«
*** TERRAIN HEIGHT OF 0. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES **
DIST CONC U10M USTK MIX HT PLUME SIGMA SIGMA
(M) (UG/M**3) STAB (M/S) (M/S) DUASH
100.
200.
300.
400.
500.
600.
700.
800.
900.
1000.
1100.
1200.
1300.
1400.
1500.
1600,
1700.
1800.
1900.
2000.
2100.
2200.
2300.
2400.
2500.
2600.
2700.
2800.
2900.
3000.
3500.
4000.
4500.
5000.
5500.
6000.
6500.
7000.
7500.
8000.
8500.
9000.
9500.
10000.
15000.
5-17
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20000.
25000.
30000.
40000.
50000.
MAXIMUM 1-HR CONCENTRATION AT OR BEYOND M:
OIST - DISTANCE FROM THE SOURCE
CONC - MAXIMUM GROUND LEVEL CONCENTRATION
STAB = ATMOSPHERIC STABILITY CLASS (1=A, 2=8, 3=C, 4=0, 5=£, 6=F)
U10M * WIND SPEED AT THE 10-M LEVEL
USTK = WIND SPEED AT STACK HEIGHT
MIX HT = MIXING HEIGHT
PLUME HT= PLUME CENTERLINE HEIGHT
SIGMA Y = LATERAL DISPERSION PARAMETER
SIGMA Z = VERTICAL DISPERSION PARAMETER
DUASH = BUILDING DOWNUASH:
OUASH= MEANS NO CALC MADE (CONC = 0.0)
DUASH=NO MEANS NO BUILDING OOWNWASH USED
DWASH=HS MEANS HUBER-SNYDER DOUNUASH USED
DWASH=SS MEANS SCHULMAN-SCIRE DOUNUASH USED
DUASH=NA MEANS DOUNUASH NOT APPLICABLE, X<3*LB
****»**********<
SCREEN DISCRETE DISTANCES
** TERRAIN HEIGHT OF 0. M ABOVE STACK BASE USED FOR FOLLOU1NG DISTANCES **
DIST CONC U10M USTK MIX HT PLUME SIGMA SIGMA
(M) (UG/M**3) STAB (M/S) (M/S) (M) HT (M) Y (M) Z (M) DUASH
QUASH- MEANS NO CALC MADE (CONC =0.0)
DUASH=NO MEANS NO BUILDING OOUNUASH USED
OUASH-HS MEANS HUBER-SNYDER DOUNUASH USED
DUASH=SS MEANS SCHULMAN-SCIRE DOUNUASH USED
DUASH-NA MEANS DOUNUASH NOT APPLICABLE, X<3*LB
»»»**•»»»»»»*»»»***••*»»****
*** END OF SCREEN MODEL OUTPUT
***********»*********»**•*'
5-18
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5.2 RVD
The RVD model provides short-term ambient concentration
estimates for screening pollutant sources emitting denser-than-
air gases and aerosols through vertically-directed releases.
The model is based on empirical equations derived from wind
tunnel tests and estimates the maximum ground level concentration
at plume touchdown at downwind receptor locations. For more
information refer to User's Guide for RVD2.0J A Relief Valve
Discharge Screening Model EPA-450/4-88-024.
5.2.1 Inputs
SCENARIO NAME & NUMBER
Based on user input, RVD model has been selected.
RVD MODEL INPUTS - Page 1 of 3
RELEASE PARAMETERS
Release Height above Ground -> ':'•;%..'':
Exhaust Gas Exit Velocity -> 4..;.'^
POLLUTANT INFORMATION
Pollutant Concentration (vol) ->
Pollutant Molecular Weight -> .
TIME
Desired Averaging Time for the Calculation
of Concentrations ->
' v?',:' x
':';. •'.•"'• g/g-mole
min
Help Calculator
Previous Screen Abort
RELEASE PARAMETERS
1 Release Height above Ground (m) -
Enter the height of the stack or of the release point above
the ground in meters.
2 Exhaust Gas Exit Velocity (m/s) -
The exit velocity (m/s) for a two-phase mixture may be
calculated from the equation:
Exitv(m/s) =
Q«(g/s)
A(m2) /o,(g/m3)
where:
A
Pi
emission rate (g/s)
area (trr)
liquid density of released material
(g/m3)
5-19
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POLLUTANT INFORMATION
3 Pollutant Concentration (%) -
Enter the volume percent of the pollutant in the release
material.
4 Pollutant Molecular Weight (g/q-mole) -
This is the individual pollutant's molecular weight, not the
molecular weight of the exhaust material.
TIME
Desired Averaging Time for the Calculation of Concentration
(min) -
Enter the desired time span for calculating concentrations in
minutes. If the release duration is less than the averaging
time of interest, or if the averaging time of interest is
less than 60 minutes, a correction factor is calculated
within RVD.
SCENARIO NAME & NUMBER
RVD MODEL INPUTS - Page 2 of 3
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural ->
FENCELINE DISTANCE
Enter the distance from the base of the stack
to the plant fenceline ->
RECEPTOR LOCATIONS
Do you have specific locations where you would
like pollutant concentrations calculated (Y/N) ->
Help Calculator Previous Screen Abort
URBAN/RURAL CLASSIFICATION
6 Enter U for Urban - R for Rural -
The classification of a site as urban or rural is based on
the procedures described in Section 8.2.8 of the Guideline on
Air Quality Models (Revised). EPA-450/2-78-927R.
FENCELINE DISTANCE
7 Enter the distance from the base of the stack to the giant
fenceline (m) -
Enter the distance from the closest edge of the source to the
fenceline in meters. The model calculates concentrations
only at receptors beyond the fenceline in ambient air.
5-20
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RECEPTOR LOCATIONS
8 Do vou have specific location where you would like pollutant
concentrations calculated (Y/N) -
The entry of SPECIFIC LOCATIONS allows for calculating the
maximum ground level concentrations.at discrete,
user-specified distances from the release. TSCREEN will
automatically give you maximum ground level concentrations at
30 distances starting at the fenceline. The first 16
distances are in 100 m increments. The next 8 distances are
in 200 m increments, and the remaining 5 distances are in 300
m increments.
+ If "Y" is entered, proceed to step 9.
+ If "N" is entered, TSCREEN runs the RVD model.
RVD MODEL INPUTS -
RECEPTOR LOCATIONS:
the source at which
Enter a blank after
Distance from
source (meters)
Page 3 of 3
Enter (up to 30) distances
from
concentrations should be calculated.
the last distance to stop input.
Distance from
source (meters)
1 fence 11 "-""^ -t
2 ir :V::ci.U
3 <::-V-x,:.;
4 •-.'•"•• •'" '
5 •"-.- '-.
6 v.:.:;;>:x;:
7 ." ""•*: '•"-
8 'rf *:*...
9 *; •••'•-.;. •'
10 ,,..:......'.
Help
12 •;>:.•:,•.• "'*'
13 ;.'..:-:V:U-
14
15 ."-- ., .'
16 .;:jf '". ' :
17 ; :•=•:.-
18 . ''"••<•'*' '•
19 ': : '•"••
20 ;,;. ,.-;:,:.
Calculator Previous
Distance from
source (meters)
21 '• '.-. "••' "
22 v'v .-'
23 .":::->-
24 "..'; '-,-.
25 ::
26 . •
27 ""'.-.,
28 :- ;V- /
29 : .
30 , ^v_ ' -
Screen Abort
RECEPTOR LOCATIONS
9 Enter (up to 30) distances from the source at which
concentrations should be calculated -
Enter the distance in meters from the rel'ease for calculating
the maximum ground level concentrations.
*• After the user finishes entering distances, TSCREEN
runs the RVD model.
5.2.2 Model Output
For a complete example of the RVD model, see Section 4.2.3.
(See Appendix E - Running TSCREEN for output options after model
is run.) The following shows the format of the output file that
RVD would generate. The output begins with a listing of model
inputs. The second portion of the output identifies the maximum
5-21
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concentration and the distance at which it occurred, and the
meteorological conditions associated with the maximum
concentration. The next section lists the maximum concentration
at each of the distances along with the meteorological
conditions. The next portion of the output identifies those
cases in which the model is applicable. In this section, a "0"
indicates that the release is passive and the model is
inapplicable, a "1" indicates that the gas is influenced by
gravitational effects and a "2" indicates that the meteorological
condition identified is not. likely to occur. The determination
of whether the gas is affected by gravitational effects is based
initially on the Richardson number for which a table is
presented. Next, the model results are presented in two forms,
a table showing plume rise, touchdown distance, and touchdown
concentration for each meteorological condition and a table of
concentrations at specified receptors.
Input Data
Pollutant emission rate (kg/sec) =
Exit gas velocity (m/sec)=
Exit Temperature (K)=
Stack Height Cm) = Diameter (m) =
Pollutant Concentration (volume X) =
Exhaust Gas Density (kg/m3) =
Exhaust Gas Molecular Weight =
Exhaust Gas Mass Flow Rate (kg/sec) =
Pollutant Molecular Weight =
Release duration (min) = Av. Time (min) =
Wind Speeds (in/see) = 1.0 2.0 3.0 4.0 5.0
8.0 10.0 15.0 20.0
Distances (m) - 100 200 300 400 500 600 700
800 900 1000 1100 1200 1300 1400
1500 1600 1800 2000 2200 2400 2600
2800 3000 3200 3500 3800 4100 4400
4700 5000
Ambient Temperature (K) =
Rural Wind Speed Profile Exponents
*** SUMMARY OF RVD MODEL RESULTS • ***
*************************************************************
Maximum offsite concentration is ug/m3
or equivalently ppm
occurring at m downwind
when wind speed is m/sec
and stability is
*** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS *»»
***********************
*** RVD DISTANCES ***
***********************
Distance Concentration Stability Wind
Class Speed
5-22
-------
(m) (ug/m3) (m/sec) (ppm)
100.0
200.0
300.0
400.0
500.0
600.0
700.0
800.0
900.0
1000.0
1100.0
1200.0
1300.0
1400.0
1500.0
1600.0
1800.0
2000.0
2200.0
2400.0
2600.0
2800.0
3000.0
3200.0
3500.0
3800.0
4100.0
4400.0
4700.0
5000.0
Dense Gas Behavior
Stability Class
Wind A B C D E F
Speed
1.0
2.0
3.0
4.0
5.0
8.0
10.0
15.0
20.0
(0=Non-Dense Behavior 1=0ense Gas Behavior
2=Combinations that cannot occur)
Release Richardson Numbers
Stability Class
Wind A B C D
Speed
1.0
2.0
3.0
4.0
5.0
8.0
10.0
15.0
20.0
5-23
-------
Dense Plume Trajectocy
Stability Wind Plume Touchdown Touchdown
Class Speed Rise Distance Concentration
(rn/sec) (m) (m) (ug/m3) (ppm)
A
A
A
B
B
B
B
B
C
C
C
C
C
C
C
D
D
D
D
D
D
D
E
E
E
E
F
F
F
Concentrations at Specific Receptor Distances
Stability Wind Distance Concentration
Class Speed
(m/sec) (m) (ug/m3) (ppm)
5-24
-------
END OF RVD MODEL OUTPUT ***
5-25
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5.3 PUFF
The PUFF dispersion model provides an estimate of peak
downwind concentrations for the case where the release time is
finite but smaller than the travel time (i.e., an instantaneous
release) . The PUFF model is based on the Gaussian instantaneous
puff equation and is applicable for neutrally buoyant non-
reactive releases. For more information on PUFF refer to
(Petersen, W. , 1982: Estimating Concentrations Downwind from an
Instantaneous Puff Release EPA 600/3-82-078) . The following is
brief summary of the model assumptions.
5.3.1 PUFF Model Discussion
The generalized puff equation is given as :
(5.3-1)
Following the puff, and assuming <7X = ayl the puff equation can be.
written as follows:
(5.3-2)
The peak concentration at distances beyond the point where crz is
greater than 0.8L (mixing height) can be expressed as:
Xu.o.o.0) = —^T- f or az >0 . 8L (5.3-3)
TKe concentration at the ground from an elevated release at a
radical distance y from the puff center is given by Equation
5.3-4:
Equations 5.3-3 and 5.3-4 account for reflection from the top of
the mixed depth layer and are appropriate for surface level
5-26
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releases during neutral and unstable conditions. However, if the
effective release height is small compared to the mixing height,
Equations 5.3-3 and 5.3-4 are still good approximations.
Frequently, instantaneous releases are large enough in the
horizontal and vertical dimensions that the initial size cannot
be ignored in the concentration estimates. One approach to
assessing the impact of the initial size on downwind
concentrations is to introduce an initial horizontal dispersion
parameter, ay , and an initial vertical dispersion parameter,
az . For a ground level release, ay can be approximated by
dividing the total initial width (W) of the puff by 4.3, CTV
•>o
W/4.3. The second parameter, az , can be approximated by
dividing the initial vertical extent of the puff (h) by 2.15,
az = h/2.15. For an elevated release, ay can be approximated
by dividing the total initial diameter (D) of the puff by 4.3,
ay = az = D/4.3. The total horizontal and vertical
dispersion parameters are then given by:
ay = (a2 * a/)1'2 (5.3-5)
Jf J Ja
a = (az2 + az2)I/2 (5.3-6)
Stability Parameters
The stability parameters used in the instantaneous puff model
are those recommended by Slade (1968). Slade classified the data
according to the broad categories of unstable, neutral, and very
stable. A review of the data reveals two pertinent points: (I)
There was very little data upon which to base the azs during
unstable conditions; (2) Much of the dispersion data during
stable conditions lie closer to the Pasquill-Gifford F curve than-
to the curve recommended by Slade.
Model Applicability
Estimating concentrations at point locations is very
difficult because of the deficiencies in determining the
trajectory of the puff. Puff trajectory is most important if
concentration estimates are to be made at specific points.
However, the .modeling effort is significantly simplified if the
magnitudes of the concentrations are needed without regard to
exactly where the concentrations will occur. Releases are seldom
point sources, but are more typically small area sources. Small
area source releases can be modeled to some extent by using
initial dispersion parameters. The initial horizontal dispersion
5-27
-------
is typically calculated by dividing the initial horizontal
dimension of the area source by 4.3. This method will give
reasonable concentration estimates at downwind distances greater
than about five times the horizontal dimension of the source.
The initial vertical dispersion parameter is typically evaluated
by dividing the initial vertical extent of the surface release by
2.15.
Many sources are not truly instantaneous. However, if the
travel time is long compared to- the release time, then the puff
model can be used to estimate concentrations. If the travel time
to a receptor is on the same order or smaller than the release
time, the Gaussian plume model can be used (see Turner, 1970) .
For the case where the release time is finite but smaller than
the travel time, the instantaneous puff model will provide a
worst-case estimate of peak concentrations for the same total
release. It is difficult to evaluate the effect on average
concentrations over a given sampling time for a finite release
using simple models, since the puff is distorted in the downwind
direction. Finally, the modeling procedures are simple
approaches to very complex problems. In general, these
techniques will yield worst-case concentration estimates. The
proper modeling of any sudden release requires the skills of an
air.quality specialist and a thorough understanding of the
physical and chemical properties of the release.
5.3.2 Model Inputs
This section contains a complete listing of the inputs
TSCREEN will request to run the PUFF model.
SCENARIO NAME & NUMBER
Based on use input, PUFF model has been selected.
PUFF MODEL INPUTS - Page 1 of 2
Enter a unique title for this data's model run:
RELEASE PARAMETERS
Total Amount of Material Released (Q) -> g
Release Height above Ground (Hs) -> m
Initial Lateral Dispersion (ay) -> S^vV;.;.,;::.; m
Initial Vertical Dispersion in) -> 0*j ':':,:.»?:. "»
FENCELINE
Enter the distance from the nearest edge of the
source to the plant fenceline -> ":""••{: •'•':.: m
Help
Calculator Previous Screen Abort
RELEASE PARAMETERS
1 Total Amount of Material Released (0) (a) -
Calculate total amount of material released during the
duration of the release. If limited information is available
5-28
-------
in the technical literature. Conservative estimates of
release amounts can be made based on transfer line rates and
time from equipment shutdown and equipment capacity. A point
source is assumed because no indication of initial dilution
dimensions are provided in the problem.
Release Height above Ground (H.) (m)
Enter the height of the stack for the release point above the
ground in meters. If the puff has positive buoyancy the
effective height of release is release height plus the rise
of the puff due to buoyancy. Screening methods are not
available for estimating plume rise for a PUFF release.
Initial Lateral Dispersion (jy) (m) -
Frequently, instantaneous releases are large enough in the
horizontal dimension that the initial size cannot be ignored-
in the concentration estimates. One approach is to introduce
the impact of the initial horizontal dispersion parameter,
ay. For a ground level release, ay can be approximated by
dividing the total initial width (W) of the'puff by 4.3, ay =
W/4.3. For an elevated release, ay can be approximated by
dividing the total initial diameter (D) of the puff by 4.3,
ay = D/4.3. The default in TSCREEN is 0 m.
Initial Vertical Dispersion (aT] (m) -
Frequently, instantaneous releases are large enough in the
vertical dimension that the initial size cannot be ignored in
the concentration estimates. One approach is to introduce
the impact of the initial vertical dispersion parameter, az.
For a ground level release, az can be approximated by
dividing the total initial vertical extent of the puff (h) by
2.15, az - h/2.15. For an elevated release, az can be
approximated by dividing the total initial diameter (D) of
the puff by 4.3, az = D/4.3. The default in TSCREEN is 0 m.
FENCELINE
Enter the distance from the nearest edge of the source to the
plant fenceline (m) -
Enter the Distance from the edge of the source to the plant
fenceline in meters. The fenceline distance is used only to
set the minimum distance for concentration calculations.
5-29
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SCENARIO NAME & NUMBER
PUFF MODEL INPUTS - Page 2 of 2
AVERAGING TIME
Select Desired Averaging Time from menu below:
iftstantawous. ft s*c«nd?
1 minute ''(60 seconds) •
5 minutes (300 seconds)
15 minutes (900 seconds)
1 hour (3600 seconds)
Selected Averaging Time: Instantaneous (1 second)
Help Calculator Previous Screen Abort
AVERAGING TIME
6. Select Desired Averaging Time from menu below:
Instantaneous(1 second)
1 minute (60 seconds)
5 minutes (300 seconds)
15 minutes (900 seconds)
1 hour (3600 seconds)
The PUFF model will calculate averaging times according, to
the procedure described in Appendix D. The PUFF model will
calculate concentrations at all five averaging times, but
only the concentrations at the selected averaging time will
be plotted if the user chooses to graph the data (See
Appendix E - RUNNING TSCREEN). The averaging time would
normally be based on some health related standards. See
Appendix D in the Technical Guidance for Hazards Analysis.
Emergency Planning for Extremely Hazardous Substances as an
example. From this document, threshold limiting values
(TLV's) for averaging times and concentrations can be
obtained for certain chemicals. The user can then use the
model output to locate the distance or the distance range
where this TLV occurs.
> After the user makes this selection, TSCREEN runs the
PUFF model.
5.3.4 Model Output
For a complece example of che PUFF model, see Section 4.1.3.
(Also see Appendix E - Running TSCREEN for output options after
model is run). The following shows the format of the output file
that PUFF would generate. This output is useful in determining:
1) sensitivity of the concentrations to the averaging time; and
2) distances to important concentrations (e.g., TLV's). The PUFF
model uses three stability categories: labeled U for unstable, N
for neutral, and S for stable. Unstable corresponds to stability
5-30
-------
categories 1 through 3 (for stabilities A - C) used by the SCREEN
model, neutral corresponds to 4 (for D), and stable corresponds
to 5 and 6 (for E and F).
TOTAL AMOUNT OF MATERIAL RELEASED (G):
RELEASE HEIGHT ABOVE GROUND (M):
INITIAL LATERAL DISPERSION (SIGMA Y) (M):
INITIAL VERTICAL DISPERSION (SIGMA Z) (M):
•
a*************************************** ««••*•*•***«••
*** SUMMARY OF PUFF MODEL RESULTS ***
«*««»»**«********1>|>«>>I>«*««*<>**«>«**««*«««**«>«I>«1><>*««
THE MAXIMUM CONCENTRATION AND THE DISTANCE TO MAXIMUM
CONCENTRATION FOR DISTANCES BEYOND FENCELINE (KM).
FOR -NEAR SURFACE RELEASE MAXIMUM CONCENTRATION WILL OCCUR AT
THE FENCELINE.
AVERAGING
TIME (MIN)
•INSTANTANEOUS
1
5
15
60
MAXIMUM
CONCENTRATION (G/M**3)
DISTANCE TO
MAX. CONC. (KM)
STABILITY
CLASS
********************************
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
***************************************** *************
*********************************
*** PUFF DISTANCES ***
*********************************
THE MAXIMUM CONCENTRATION AS A FUNCTION OF DOWNWIND DISTANCE
AND THE CONDITIONS THAT PRODUCED THE MAXIMUM AT THAT DISTANCE.
MIXING HEIGHT (M)
WIND SPEED (M/SEC)
DOWNWIND DISTANCE (KM)
MAXIMUM CONCENTRATION (G/M*»3) AT VARIOUS DOWNWIND DISTANCES.
STABILITY CLASS THAT PRODUCED THE MAX. LISTED BELOW
0.01 0.03 0.05 0.07 0.1 0.5
AVERAGING
TIME (MIN)
*INST.
1
5
15
60
AVERAGING DOWNWIND DISTANCE (KM)
TIME (MIN) MAXIMUM CONCENTRATION (G/M**3) AT VARIOUS DOWNWIND DISTANCES.
STABILITY CLASS THAT PRODUCED THE MAX. LISTED BELOW
1.0 3.0 5.0 7.0 10.0 30.0
5-31
-------
•INST.
1
5
15
60
STABILITY CLASSES
U = UNSTABLE
N = NEUTRAL
S = STABLE
* INDICATES AVERAGING TIME THAT WAS SELECTED FOR PLOTTING
«»««««««>«I>««»IHI»1>«««*« »•««•!»•*
*** END OF PUFF MODEL OUTPUT ***
5-32
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5.4 Britter-McQuaid
Britter and McQuaid (1988) report work which provides a
correlation for estimating the dispersion of denser-than-air
gases from area sources for continuous (plume) and instantaneous
(puff) release. The objective was to produce correlations which
predicted the dependent variables (distance to a given
concentration level and area covered by a plume or puff) to
within a factor of two. The analysis identified the dominant
independent variables as: volumetric rate (or total) contaminant
released; density of released material; windspeed at a standard
height (taken to be 10 m); and a characteristic source dimension.
Based (at least in part) on the fact that presently available
field-test data for denser-than-air gases do not clearly indicate
such, independent variables of lesser- importance were identified
as: surface roughness; atmospheric stability; atmospheric
turbulence; and exact source dimension. Other effects not
included in Britter and McQuaid's analysis are: source momentum;
condensation of ambient humidity; and non-ideal gas behavior.
(It should be. noted that the e'ffects which were not indluded may
be of crucial importance for contaminants whose molecular weight
is less than air including, for example, liquefied natural gas
(LNG), ammonia, and hydrogen fluoride; some similarity models
(such as DEGADIS) can take these effects into account.)
For screening purposes, the original procedure set forth by
Britter and McQuaid will be simplified in two important ways:
Other established (passive) screening methods are
recommended if the release is determined to be passive
from the source (i.e., the denser-than-air effects are
not expected to be important).
The influence of buildings, topography, and releases
not close to the ground are not included.
In addition, the effect of initial dilution due to jetting is
beyond the scope of this effort. At present, the RVD model (U.S.
EPA, 1989) is used for such cases as pressure relief valve
discharge where source jetting will bring about air entrainment
(and resulting dilution) for the hypothesized release. For cases
where the jet orientation is unknown or is not directed
vertically upward, the most conservative assumption (i.e., the
assumption which results in the maximum downwind distance to a
given concentration level under otherwise identical
circumstances) is'to discount the initial dilution due to
]etcing; the correlations of Britter and McQuaid do noc include
the effects of source jetting.
5-33
-------
5.4.1 Method for Cold Contaminant Releases — Heat Transfer -
Effects
Heat transfer effects are not included in Britter and
McQuaid's correlation; two ways suggested at looking at the
limiting effects associated with heat transfer:
Assume that heat transfer is unimportant and perform
the calculations using the originally estimated
temperature and density (T2 and p2, respectively).
Assume that the heat transfer is important and (for the
sake of maximizing its importance) assume that all of
the heat transfer occurs at the source.
The (real) effect of heat transfer should lie somewhere between
these two extremes (limiting cases). So, an estimate of the
downwind distance to the desired concentration level should be
made for each of the limiting cases, and the greatest of the two
estimates of x (distance to a given concentration level) should
be reported. For the first case, the input parameters will be
the same as calculated in the earlier sections. For the second
case though, the initial density and temperature are modified as
follows:
- i>2 "- P2 (T2/Ta) (5.4-la)
T2«-Ta (5.4-lb)
where the A represents the "adjusted" initial values; for this
case then, these "adjusted" values should be used whenever p2 and
T2 are required.
5.4.2 Method for Contaminant Aerosol Releases
Since Britter and McQuaid' s correlations are based on the
analysis of dispersing gases, the complex thermodynamic effects
of an aerosol must be considered using an ad hoc argument that,
near the source, sufficient air will be entrained to evaporate
all of the condensed aerosol phase and raise the temperature of
the air/contaminant (gas) mixture to a temperature where the
contaminant vapor pressure is eqaal to the ambient pressure (for
an aerosol release, T;) . For such a process, the resulting Ticle
fractions of contaminant and air are:
(T-T) (5.4-2a)
^ J-a L2'
5-34
-------
Za = 1-ZC (5.4-2b)
where (as discussed above) the effects of humidity have been
ignored. This air entrainment process will also change the
temperature and density of the air/contaminant mixture.
Furthermore, since for most release scenarios, T2 5* Ta, the effect
of heat transfer may also be important. Therefore, two cases are
considered:
Case 1; Air dilution neglecting heat transfer. The initial
density is modified as follows:
P2- Ji (ZCMW + zaMa) (5.4-3)
K12
where as before the * represents the "adjusted" initial values-;
Ma is the molecular weight of air (28.96 kg/kmol). In addition,
the. initial volume of the release is modified. For continuous
releases, Qm is modified as:
Qm«-Q»
-------
5.4.3 Continuous (Plume) Releases
To estimate the importance of denser-than-air- effects on
continuous releases, Britter and McQuaid recommend that denser-
than-air effects be ignored if:
>6 (5.4-7)
where D is the (low-momentum) horizontal dimension of the source
(m) , Qm is the release rate (kg/s), Ur is the windspeed at 10 m
(m/s) , pa is the ambient air density (kg/m3) . If the value of D
is not otherwise known (such as the diameter of a liquid pool), a
(screening) estimate of D can be made assuming that the ratio of
the vertical source dimension to the horizontal source dimension
is approximately 1/2 and the momentum of the release is
inconsequential. Using this assumption,
. D = v/2 (Qm/p2) /Ur (5.4-8)
(Note that D is not necessarily the same as the hole or opening
diameter and may be much larger.) If denser-than-air effects are
determined to be unimportant, standard passive atmospheric
dispersion techniques should be applied. Finally, note that
Equation 5.4-7 can be rewritten as:
< 1/63
where the left-hand side is a Richardson number; therefore, the
criteria in Equation 5.4-7 is comparable to other Richardson
number-based criteria suggested, for example, by Spicer and
Havens (1989) and that Ur/U. = 20 to 30 for typical atmospheric
flow fields (where U. is the friction velocity.)
However, if denser-than-air effects are determined to be
important, the method of Britter and McQuaid can be used to
determine the downwind extent of a given concentration level
(Cm/C0) by use of Figure 5.4-1. For simplicity, the abscissa and
ordinate are given as:
ur5
5-36
-------
in
i
ui
Range of full-scale data
n>
U1
i
H
W
H
H-
ft
ft
0>
H
4
it
P>
0
H
0
ft
H-
§
M>
O
O
O
p
ft
H-
8
O
-------
X2
respectively where x is the estimated downwind distance to the
concentration level Cm/C0. The choice of Cm should reflect the
source temperature correction and the averaging time effect
discussed below. Once Cm/C0 is set, Figure 5.4-1 can be used to
determine the downwind distance to that ratio; interpolation for
intermediate values of Cm/C0 should be done using log-log
interpolation (at a fixed fc) . For fc > 3, £c should be
determined by (linear) extrapolation on the log-log plot in the
absence of other information since no field test data exists for
fc > c. If the desired Cm/C0 < 0.002, the following equation can
be used:
[C 1-1/2 .„
-£\ Ic'"2 (5.4-10)
*-o J
(based on extrapolation and fitting of Britter and McQuaid's
Figure 9) . If the desired Cm/C0 < 0.002 and 1 a £c a 0.2, no data
exists for this region so Britter and McQuaid make no
recommendation. .However, the following equation can be used:
= 22.6 - $; (5.4-11)
based on simply forcing Equation (5-10) to agree with the passive
limit .
Once the distance x is determined, the release duration Td
should be checked to see if steady-state conditions are expected
at this distance. If UrTd/x > 2.5, then the estimate based on a
continuous release is valid as recommended by Britter and
McQuaid. If 0.6 < UrTd/x < 2.5, then an estimate assuming the
release to be instantaneous should also be made, and the greatest
estimate for x should be reported. If UrTd/x < 0.6, then the
release should be assumed to be instantaneous .
•
The effect of averaging time should be taken into account
before using Figure 5.4-1 if the desired averaging time is not: a
long-term average (taken to be 10 minutes) . Britter and McQuaid
mention that shorter averaging times will produce larger
concentrations with factors ranging from 1.4 (based on field-
scale data) to 1 . 6 (based on laboratory data) over the long time-
averaged concentrations. If the ratio of 1.4 is used along with
a short averaging time of about one second, the following
5-38
-------
(approximate) power-law relationship would hold:
C,(10minn F iOminj-0.05
C.(tJ J I tw J
where Cm(10 min) would represent the value of Cm to be used in
Figure 5.4-1, and Cm(tav) is the value of Cm based on the desired
averaging time t^ (Britter, 1992).
The effect of temperature should be taken into account before
using Figure 5.4-1 if the discharge (depressurized) contaminant
temperature is different from ambient; Britter and McQuaid
recommend using a value for Cm which reflects the nonisothermal
effects as follows:
C" ^ C + T fl-C ) /T (5.4-13)
uni * xa ^ Sii' ' i2
where C^ is the nonisothermal concentration (mole fraction), Ta
is the ambient temperature (K) , and T2 is the discharge
(depressurized) contaminant temperature (K).
In summary, the following procedure should be used for
continuous (plume) releases:
A. For aerosol releases, two cases must be considered for
each release as outlined in Section 5.4.2. Initial
conditions for the dispersion calculation for each case
are based on Equations 5.4-2 through 5.4-6. Go to Step
C.
B. For cold gas releases, two cases must be considered for
each release as outlined in Section 5.4.1. Original
initial conditions based on release calculations and
modified initial conditions from Equation 5.4-1 are
used in the dispersion calculation for each case.
C. For each continuous release case:
a. Check to see if denser-than-air effects are
important with Equation 5.4-7. If denser-than-air
effects are unimportant, use a passive atmospheric
dispersion model.
b. .Modify the desired concentration Cm for averaging
time using Equation 5.4.11.
c. Modify Gm from (b) for source cemperacure erfeons
using Equation 5.4-12.
d. With Cm from (c), determine the downwind distance
x using Figure 5.4-1 or Equation 5.4-10.
e. Determine whether the release duration is of
sufficient length to establish a steady-state
plume at the distance x. As discussed earlier,
5-39
-------
depending on UrTd/x, a dispersion calculation for
an instantaneous release may also be required.
Example: Chlorine Gas Leak
Consider the example chlorine gas leak discussed in Section
4.2.3. Based on the earlier example, the gas evolution rate Qm
was 1.10 kg/s and discharged at a temperature T2 of 282.5°K; the
discharge density p2 was 3.059 kg/m3. For a release in 2 m/s
winds (at 10 m), determine the downwind distance to 1 ppm based
on a 15-minute time average. The ambient temperature and
pressure are 293.15°K and 101325 Pa, respectively.
A. Since this is not an aerosol release, Step A is
ignored.
B. The discharge temperature T2 is >282»5°K, so heat
transfer is probably unimportant since T, - T2 is not
large. For the sake of illustration, though,* consider
two cases: (1) p2 and T2 unchanged/ and»(2) ^2 = 3.059
kg/m3 (282.5/293.15 = 2.948 kg/m3 and T2 = 293.15°K.
C. For case 1 (p2 = 3.059 kg/m3 and T2 = 282.5°K) :
a. The left side of Equation 5.4-7 is 0.959 (with pa
= 1.204 kg/m3/ D = 0.600 m, using Equation 5.4-8)
so denser-than-air effects are expected to be
important.
b. Using tw = 15 min in Equation 5.4-11, C^ = 1.020
(1 ppm) = 1 ppm.
c. Using C^ = 1 ppm = 1 x 10"6 mole fraction in
Equation 5.4-12, C,,, = 1 ppm.
d. Since C^/C,, = 1 x 10"6 « 0.002, Equation 5.4-10 is
used to determine x = 8710 m £c = 1.21; fc =
20540) .
e. For this release to be considered as a steady-
state release, UrT,pc > 2.5,- so, if Td > 10900 s
(182 min) then the release is a continuous plume.
C. For case 2 (p2 = 2.948 kg/m3 and T2 = 293.15°K) :
a. The left side of Equation 5.4-7 is 1.04 (with D =
0.611 m, using Equation 5.4-8) so denser-than-air
effects are expected to be important.
b. As in case 1, using t^ = 15 min in Equation 5.4-
11, Qa = 1.020 (1 ppm) = 1 ppm.
c. Also in case 1, using C* = 1 ppm = 1 x 10"6 mole
fraction in Equation 5.4-12, C,,, = 1 ppm.
d. Since C^/C,, = 1 x 10"* « 0.002, Equation 5.4-10 is
5-40
-------
used to determine x = 8950 m (£c = 1.19; ¥c =
20720).
e. For this release to be considered as a steady-
state release, UrTd/x > 2.5; so, if Td > 11200 s
(186 min), then the release is a continuous plume.
Therefore, the reported distance to the 15 minute averaged
chlorine concentration is 8950 m (provided the release is of
sufficient duration.)
5.4.4 Instantaneous (Puff) Releases
To estimate the importance of denser-than-air effects on
instantaneous releases, Britter and McQuaid recommend that
denser-than-air effects be ignored if:
g"' f*-P.lP/» S0.2 (5.4.14)
where Q is the total amount of material released, Ur is the
windspeed at 10 m, p2 is the discharge (depressurized) density,
and pa is the ambient air density. If denser-than-air effects
are determined to be unimportant, standard passive atmospheric
dispersion techniques should be applied.
However, if denser-than-air effects are determined to be
important, the method of Britter and McQuaid can be used to
determine the downwind extent of a given concentration level
(Cm/C0) by use of Figure 5.4-2. For simplicity, the abscissa and
ordinate are given as:-
g «,/„,» [P2-P,, » (5_4_i5a)
ur-
and
tfi = x/(Q/p2)"3 (5.4-15b)
respectively where x is the estimated downwind distance to the
concentration level Cm/C0. The effect of temperature should be
taken into account before using Figure 5.4-2 if the discharge
(depressurized) contaminant temperature is different from ambient:
using Equation 5.4-12. Because Figure 5.4-2 uses concenLranicn
data based on (ensemble) short-term averaged concentrations,
taking longer averaging times into account would simply shorten
predicted distances to a given concentration level; in the
absence' of further information, the predicted concentrations will
be assumed to apply regardless of averaging time (which,- for
screening purposes, is a conservative assumption). Once the
»
5-41
-------
ratio Cm/C0 is set, Figure 5.4-2 can be used to determine the
downwind distance to that ratio; interpolation for intermediate
values of Cm/C0 should be done using log-log interpolation (at a
fixed £i) . For £s > 10, ^ should be assigned the value of
¥j(£i=10) . If the desired Cm/C0 < 0.001, the following equation
can be used:
r cj
•k
-o.4
(5.4-16)
(based on extrapolation and fitting of Britter and McQuaid's
Figure 12) ; note that for £•, > 10, a value of £; = 10 should be
used in Equation 5.4-16. If the desired Cm/C0 < 0.001 and l a
£i * 0.2, no data exists for this region so Britter and McQuaid
make no recommendation. However, the following equation can be
used:
-0.4
(5.4-17)
based on simply forcing Equation (5-16) to agree with the passive
limit.
5-42
-------
Figure 5.4-2.
Britter and McQuaid (1989) Correlation
Instantaneous (Puff) Releases
- o
5-43
-------
In summary, the following procedure should be used'for :
instantaneous (puff) releases:
A.• For aerosol releases, two cases must be considered for
each release as outlined in Section 5.4.2. Initial
conditions for the dispersion calculation for each case
are based on Equations 5.4-2 through 5.4-6. Go to Step
C.
B. For cold gas releases, two cases must be considered for
each release as outlined in Section 5.4.1. Original
initial conditions based on release calculations and
modified initial conditions from Equation 5.4-1 are
used in the dispersion calculation for each case.
C. For each, instantaneous release case:
a. Check to see if denser-than-air effects are
important with Equation 5.4-13. If denser-than-
air effects are unimportant, use a passive
atmospheric dispersion model.
b. Modify Cm for source temperature effects using
Equation 5.4-12.
c. With Cm from (b) , determine the downwind distance
x using Figure 5.4-2 or Equation 5.4-15.
Example: Saturated Liquid Chlorine Leak(Reservoir Pressure of
2.586 x 106 Pa.- 10.16 cm hole)
Consider the example chlorine leak discussed in Section 3.2.
Based on the earlier example, the evolution rate Qm was 430 kg/s
and the discharge temperature T2 was 239.05°K; the discharge
density pz was 19.13 kg/m3. For this example, assume the release
came from a "ton" cylinder which was initially half full
(approximately 500 kg); in this case, the release duration Td
would be small and the release can be assumed to occur
instantaneously (with Q = 500 kg). For a release in 2 m/s winds
(at 10 m), determine the downwind distance to 1 ppm based on a
15-minute time average. The ambient temperature and pressure are
293.15°K and 101325 Pa, respectively. •
A. Because this is an aerosol release, an initial amount
if air is assumed to mix with the contaminant aerosol
so that the liquid phase is evaporated and the mixture
temperature is raised to the contaminant vapor pressure
(239.05°K in this case). First, zc and za are estimated
using Equation 5.4-2 as 0.188 and 0.812, respectively
(using Cpa = 1006 J/kgK) . Two cases must be
considered: (1) •
5-44
-------
P2 = (101325) (36.8) / ((8314) (239.05)) =1.876kg/m3 7 and
Q = (500) (36.8) / ( (0.188) (70^9) ) = 1380 kg; and (2)
P2 = (101325) (36.8) / ((8314) (239..15)) =1.530kg/m3 ; and
T2 = 293.15°K. Q will be the same for both
cases. Go to Step C.
C. For case 1 (p2 = 1.876 kg/m3; T2 = 239.05°K; Q = 1380
kg) :
a. The left side of Equation 5.4-13 is 3.52 (with pa
= 1.204 kg/m3) so denser-than-air effects are
expected to be important.
b. Using C^ = 1 ppm = 1 x 10"* mole fraction in
Equation 5.4-12, Cm = 1 ppm.
c. Since Cm/C0 « 1 x KrVo.188 = 5 x lO"6 < 0.001,
Equation 5.4-15 is used to determine x = 6480 m
(£i = 3.52; *i = 717) .
C. For case 2 (p2 = 1:530 kg/m3; T2 = 293.15°K; Q = 1380
kg) :
a. The left side of Equation 5.4-13 is 2.53, so
denser-than-air effects are expected to be
important.
b. As in case 1, using Cni = 1 ppm = 1 x 10"6 mole
fraction in Equation 5.4-12, Cm = 1 ppm.
c. Since Cm/C0 = 1 x IQ^/O.ISS = 5 x 10"6 < 0.001,
Equation 5.4-15 is used to determine x = 7550 m
(£i = 2.97; ¥; = 781) .
Therefore, the reported distance to the 15-minute averaged
chlorine concentration is 7550 m.
5.4.5 Assumptions in TSCREEN
In the implementation of the Britter-McQuaid model used in
TSCREEN, the model calculates concentrations for an array of 9
windspeeds, for the D stability class, at each distance. Then,
the model output displays the maximum concentration for each
distance and the windspeed at which that concentration occurred.
5-45
-------
5.4.6 Model Inputs
SCENARIO NAME & NUMBER
Based on user input, the Britter-McQuaid model has been selected.
BRITTER-MCQUAID MODEL INPUTS - Page 1 of'3
MODEL PARAMETERS
Relative Humidity (Rh) -> " •• X
Desired Averaging Time for the Calculation
of Concentrations ->
Pollutant Boiling Point Temperature (Tb) ->
mm
Help Calculator Previous Screen Abort
MODEL PARAMETERS
1 Relative Humidity (Rh) -
Enter the relative humidity (%) .
2 Desired Averaging Time for the Calculation of Concentration
(min) -
The averaging "time is used by the Britter and McQuaid model
to correct for averaging times different from 10 min.
Pgllutant Boiling Point Temperature (Tfr) -
Enter the boiling point temperature. This value can be
obtained from TSCREEN's chemical database.
SCENARIO NAME & NUMBER
BRITTER-McOUAID MODEL INPUTS - Page 2 of 3
FENCELINE DISTANCE
Enter the distance from the base of the stack
to the plant fenceline ->
RECEPTOR LOCATIONS
Do you have specific locations where you would
like pollutant concentrations calculated (Y/N) -> ;J
Help Calculator Previous Screen Abort
FENCELINE DISTANCE
4 Enter the distance from the base of the stack to the plant
fenceline (m) -
Enter the distance from the closest edge of the source to the
fenceline in meters. The model calculates concentrations
only at receptors beyond the fenceline in ambient air.
5-46
-------
RECEPTOR LOCATIONS
Do you have specific location where you would like pollutant
concentrations calculated (Y/N) -
The entry of SPECIFIC LOCATIONS allows for calculating the
maximum ground level concentrations at discrete,
user-specified distances from the release. TSCREEN will
automatically give you maximum ground level concentrations at
30 distances starting at the fenceline. The first 16
distances are in 100 m increments. The next 8 distances are
in 200 m increments, and the remaining 5 distances are in 300
m increments.
> If "Y" is entered, proceed to step 8
* If "N" is entered, TSCREEN runs the Britter-McQuaid
model.
BRITTER-McQUAID MODEL INPUTS - Page 3 of 3
RECEPTOR LOCATIONS:
the source at which
Enter a blank after
Distance from
source (meters)
1 fence
2
3
4
5
6
7
8
9
10 ,
Help
Enter (up to 30) distances from
concentrations should be
the last distance to stop
Distance from
source (meters)
11
12
13
14 '
15
16
17
18
19
20
calculated.
input.
Distance from
source (meters)
21
22
23
24 '
25
26
27
28
29
30
Calculator Previous Screen Abort
RECEPTOR LOCATIONS
*
6 Enter (UP to 30) distances from the source at which
concentrations should be calculated -
Enter the distance in meters from the release for calculating
the maximum ground level concentrations.
> After the user finishes entering distances, TSCREEN
runs the Britter-McQuaid model.
5.4.7 Model Output
For a complete example of the Britter-McQuaid model ,see
Section 4.2.3. (See Appendix E-Running TSCREEN for output
options after the model is run.) The following shows the format
of the output file that Britter-McQuaid would generate.
5-47
-------
- -92
*** B&M MODEL RUN ***
INPUTS:
AMBIENT PRESSURE (ATM)
AMBIENT TEMP (K)
AVERAGING TIME (MIN)
BOILING PT TEMP (K)
DURATION (S)
EMISSION RATE (KG/S)
EXIT TEMP (K)
MASS (KG)
MOL. WEIGHT (G/G-MOLE)
RELATIVE HUMIDITY (X)
VAPOR FRACTION
««i» «««««««
*** SUMMARY OF B&M MODEL RESULTS ***
MAX CONC
(UG/M**3)
MAX CONC
(PPM)
DIST TO
MAX (M)
WIND SPEED
(M/S)
I***************************************************
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
****«*»*»*»»•*•»**•*»**•»*«**•****•»*****»•»»»»»*•*•
**********************************
*** B&M DISTANCES ***
••««««*•««««««••«•««•«»•***•««««••
DIST CONC CONC WIND SPEED
(M) (UG/M**3) (PPM) (M/S)
100.
200.
300.
400.
500.
600.
700.
800.
900.
1000. .
1100.
1200.
1300.
1400.
1500.
1600.
1700.
1900.
2100.
2300.
2500.
2700.
2900.
3100.
3300.
3600.
3900.
4200.
5-48
-------
4500.
5000.
CALCULATED VALUES:
DENSITY OF DEPRESSURIZED CONTAMINANT (KG/M**3) =
DENSITY OF AMBIENT AIR (KG/M**3) =
MOLE FRACTION =•
' MIN DIST INST (M) =
MAX DIST CNST (M) a
NOTES & DEFINITIONS
(a) "inst" refers to an instantaneous release (Section 3.6 of B-M Workbook)
(b) "cost" refers to a continuous release (Section 3.6 of B-M Workbook)
(c) "MIN DIST INST" is the minimum distance downwind at which the release
may be treated as instantaneous
(d) "MAX DIST CNST1" is the maximum distance downwind at which the release
may be treated as continuous
END OF B&M OUTPUT
5-49
-------
REFERENCES
Beilstein, 1987: Handbook of Organic Chemistry. Springer-Verlag,
New York.
Beychok, M., 1979: Fundamentals of Stack Gas Dispersion. Irvine,
CA.
Britter R.E. and J. McQuaid, 1989: Workbook on the Dispersion of
Dense Gases, U.K. Health and Safety Executive Contract
Research Report No. 17/1988.
Britter, R.E., personal communication, 1992.
Clancey, V.J., 1984: The Evaporation and Dispersion of Flammable
Liquid Spillages, in Chemical Process Hazards with Special
Reference to Plant Design; Proceedings of the 5th Symposium
held at the University of manchester, 1974. Institution of
chemical Engineers, London.
•
Clewell, H.J., 1983: A Simple Formula for Estimating Source
Strengths from Spills of Toxic Liquids, U.S. Air Force
Report ESL-TR-83-03.
Cox, A. and R. Carpenter, 1980: Further Development of a Dense
Vapor Dispersion Model for Hazardous Analysis. Heavy Gas
and Risk Assessment, S Hartwig (ed.) D. Reidel Publishing,
Dordrecht, Holland.
EMCON Associates, 1982: Methane Generation and Recovery from
Landfills. Ann Arbor Science, Ann Arbor, MI.
Environmental Protection Service, 1985: Introduction Manual,
Technical Information for Problem Spills (TIPS), Technical
Services Branch. Ottawa, Canada
Fauske, H.K. and M. Epstein, 1987: Source Term Considerations in
Connection with Chemical Accidents and Vapor Cloud Modeling.
Presented at the International Conference on Vapor Cloud
Modeling, Center for Chemical Process Safety. New York, NY.
Fingas, M., I. Buist, R. Belore, D. Mackay, and P. Kawamura,
1986: The Input of Spilled Chemicals into the Environment.
Hazardous Materials Spills Conference, St. Louis.
Havens, J. and T. Spicer, 1985: Development of an Atmospheric
Dispersion Model for Heavier-than-Air Gas Mixtures, U.S.
Dept. of Transportation CG-D-23-85.
Hoot, T., R. Meroney, and J. Peterka, 1973: Wind Tunnel Tests of
Negatively Buoyant Plumes, EPA 650/3-74-003. U.S.
Environmental Protection Agency, Research Triangle Park, NC.
R-l
-------
Hunsaker, J. and B. Rightmire, 1947: Engineering Applications of
Fluid Mechanics. McGraw-Hill, New York.
Leahey, D. and M. Davies, 1984: Observations of Plume Rise from
Sour Gas Flares, Atm. Envir.. 18:917-922.
Lees, P.P., 1980: Loss Prevention in the Process Industries.
Butterworths, London.
Levenspiel, 0., 1977: The Discharge of Gases from a Reservoir
through a Pipe, AIChE Journel, 23. 3, pg 402.
Lewitt, E.H., 1953: Thermodynamics Applied to Heat Engines. 5th
ed, Sir Isaac Pitman and Sons, London.
List, R., 1968: Smithsonian Meteorological Tables. Smithsonian
Institute, Washington, B.C.
Moorehouse, J., and R.J. Carpenter, 1986: Factors Affecting
Vapour Evolution Rates from Liquefied Gas Spills,
Proceedings I. Chem. E. (N.W.Branch) conference on
Refinement of Estimates of the Consequences of Heavy Toxic
Vapor Releases.
National Oceanographic and Atmospheric Administration, 1988:
ALOHA-Areal Locations of Hazardous Atmosperes, Technical
Appendix, Hazardous Materials Response Branch, Seattle, WA.
Pasquill, P., 1976: Atmospheric Dif f usi on (2nd ed.). John Wiley &
Sons, New York.
Perry, R.H., D.W. Green, and J.O. Maloney, 1984: Perry's Chemical
Engineer's Handbook. 6th Ed, McGraw-Hill, New York, pp. 5-
12 through 5-15.
Petersen, W., 1982-. Estimating Concentrations Downwind from an
Instantaneous Puff Release, EPA 600/3-82-078. U.S.
Environmental Protection Agency, Research Triangle Park, NC.
Sandier, S.I., 1989: Chemical and Engineering Thermodynamics. 2nd
ed., John Wiley and Sons, New York.
Spicer, T.O. and J. Havens, 1989: User's Guide for the DEGADIS
2.1 Dense Gas Model, EPA-450/4-89-019. U.S. Environmental
Protection Agency, Research Triangle Park, NC.
Spicer, T.O., 1992: Personal communication.
Slade, D., 1968: Meteorology and Atomic Energy. U.S. Atomic
Energy Commission (T10-24190).
R-2
-------
Thibodeaux, L. and S. Hwang, 1982: Landfarming of Petroleum
Wastes - The Modeling Problem, Environmental Progress, 1
(46) .
Turner, D., 1970: Workbook of Atmospheric Dispersion Estimates,
Office of Air Programs Publication AP-26, U.S.
Environmental Protection Agency.
U.S. Environmental Protection Agency, 1985: Compilation of Air
Pollutant Emission Factors, Fourth Edition. AP-42,
September 1985. And Supplement A, 1986; Supplement B, 1988;
Supplement C, 1990; Supplement D, 1991.
U.S. Environmental Protection Agency, 1986: Guideline on Air
Quality Models (Revised), EPA-450/2-78-027R. U.S.
Environmental Protection Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1987a: Hazardous Waste
Treatment, Storage, and Disposal Facilities , (TSDF) - Air
Emissions Models, Draft Report, U.S. Environmental
Protection Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1987b: Emission Factors for
Equipment Leaks of VOC and HAP, EPA-450/3-86-002. U.S.
Environmental Protection Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1987c: On-site
Meteorological Program Guidance for Regulatory Modeling
Applications, EPA-450/4-87-013. U.S. Environmental
Protection Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1988a: A Workbook of
Screening Techniques for Assessing Impacts of Toxic Air
Pollutants, EPA-450/4-88-009. U.S. Environmental Protection
Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, I988b: Air Emissions from
Municipal Solid Waste Landfills - Background Information for
Proposed Standardous and Guidelines', Office of Air Quality
Planning and Standards (Preliminary Draft). U.S.
Environmental Protection Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1988C: Screening Procedures
for Estimating the Air Quality Impact of Stationary Sources,
EPA-450/4-88-010. U.S. Environmental Protection Agency,
Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1989: User's Guide for RVD
2.0 - A Relief Valve Discharge Screening Model, EPA-
450/4-88-024. U.S. Environmental Protection Agency,
Research Triangle Park, NC.
R-3
-------
U.S. Environmental Protection Agency, 1990: User's Guide to
TSCREEN, A Model for Screening Toxic Air Pollutant
Concentrations, EPA-450/4-90-013. U.S. Environmental
Protection Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1991a: Guidance on the
Application of Refined Dispersion Models for Air Toxics
Releases, EPA-450/4-91-007. U.S. Environmental Protection
Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1991b: Air Emissions from
Municipal Solid Waste Landfills - Background.Information for
Proposed Standards and Guidelines, EPA-450/3-90-lla. U.S.
Environmental Protection Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1992: User's Guide for the
Industrial Source Complex (ISC2) Dispersion Models, Volume
II - Description of Algorithms, EPA-450/4-92-008b. U.S.
Environmental Protection Agency,tResearch Triangle Park, NC.
•
Van Ulden, A. 1974: On Spreading of a Heavy Gas Released Near the
Ground, 1st International Loss Prevention Symposium, The
Hague/Delft.
Verschueren, K., 1983: Handbook of Environmental Dataon Organic
Chemicals. Van Nostrand Reinhold Company, New York.
Wallis, G. 1969: One Dimensj-Qnal Two-Phase Flow. McGraw-Hill, New
York.
Webber, D.M., and S.J. Jones, 1987-. A Model of Spreading
Vaporising Pools, in International Conference on Vapor Cloud
Modeling. John Woodward, ed., American Institute of Chemical
Engineers, New York.
R-4
-------
APPENDIX A
EMISSION FACTORS
-------
APPENDIX A
EMISSION FACTORS
One alternative for estimating air toxic emissions from
sources is through the use of emission factors. Emission
factors have been developed for a number of processes and
pollutants. Emission factors provide an estimate of
emissions as a function of source activity such as process
rate or some other operating parameter. Emission factors
are intended to been used for making preliminary estimates
of toxic air emissions. As such, they represent generic
factors whose applicability to a specific source may be
questionable. These factors will not likely provide exact
estimates of emissions from any particular source. The
source of an emission factor must be carefully evaluated to
determine whether it is applicable to a particular facility.
Emission factors are available for both area and point
sources. Some sources of emission factors applicable to air
toxics emissions are presented below.
1} U.S. Environmental Protection Agency. Locating
and Estimating Air Emissions from (or of) (Source
Category or Substance). EPA 450/4-84-007a-q. EPA
450/4-88-004, 450/2-89-001, 450/2-89-002, •
450/2-89-006, 450/2-89-013, 450/2-89-021,
450/2-90-009, 450/4-91-029. .
EPA has underway a program to compile and publish
emission factors for various air toxics. To date,
twenty-four reports have been published as part of this
program. The substances covered by this series include:
acrylonitrile, carbon tetrachloride, chloroform, ethylene
dichloride, formaldehyde (revised), nickel, chromium,
manganese, phosgene, epichlorohydrin, vinylidene chloride,
ethylene oxide, chlorobenzenes, PCBs, POM, benzene, organic
liquid storage tanks, coal and oil combustion sources,
municipal waste combustors, perchloroethylene and
trichloroethylene, 1,3-batadiene, and sewage sludge
incinerators and styrene.
2) U.S. Environmental Protection Agency. Survey of
(Substance) Emission Sources.
A second series of reports on specific air toxics has
been developed by EPA as part of the National Emissions
Standards for Hazardous Air Pollutants (NESHAPS) program.
The substances covered by this series include:
trichloroethylene (EPA 450/3-85-021), perchloroethylene (EPA
450/3-85-017), ethylene oxide (EPA 450/3-014), chloroform
(EPA 450/3-85-026), ethylene dichloride (EPA 450/3-84-018),
methylene -chloride ^EPA 450/3-85-015) , and -carbon
tetrachloride (EPA 450/3-85-018).•
A-l
-------
3) U.S. Environmental Protection Agency.
XATEF-Crosswalk/Air Toxic Emission Factors
Database.
The database is available from the EPA Office of Air
Quality Planning and Standards, Technology Transfer Network
(TTN). Files may be downloaded by dialing (919) 541-5742.
[There is no charge for access.] This database management
system presents emission factors of air toxic pollutants for
a variety of sources with varying activity levels. , This
database management system is updated and expanded
periodically. The factors are associated with pollutant
names and CAS numbers, process descriptions and SIC codes,
emission source descriptions and SCC codes, notes on the
derivation of the factors and on control measures associated
with the factors, and references. The emission factors can
be used to obtain.quick, rough estimates of air toxic
emissions. More detailed data on the emission sources can
be obtained from the Notes and References Sections listed in
the emission factors tables. The primary limitation of
using just the emissions factors listed in this compilation
is that their accuracy in application to a given source is
not known. More accurate emissions estimates may require
evaluation of the application of available test data to
specific s.ource characteristics. Otherwise, factors
determined by compiling extensive source test results using
EPA Reference Methods are reported in AP-42. Toxic
components of emissions can be determined using SPECIATE
database management system (see above).
4) U.S. Environmental Protection Agency. Compilation
of Air Pollutant Emission Factors. Fourth Edition.
AP-42, September 1985. And Supplement A 1986,
Supplement B 1988; Supplement C, 1990; Supplement
D, 1991.
Another tool for estimating air toxic emissions
involves the use of VOC/PM factors presented in AP-42 and
species profiles in SPECIATE database management system.
AP-42 contains emission factors for total VOC and PM rather
than for a single chemical compound. These factors can be
used with profiles contained in SPECIATE to estimate the
releases of specific toxic compounds based on the total
amount of VOC or PM released from a source. SPECIATE shows
the percent by weight and percent by volume of specific
chemicals in emissions from specific chemicals in emissions
from specific processes. "Speciation factors are used to
estimate emissions of air toxics from emission factors or
estimates of total VOC or PM. Both volumes are similarly
organized with speciation data presented by source category
and by Source Classification Codes (SCO . Species profiles
for VOCs and PM are for generic sources and -may not be
representative of emissions from an individual facility. .
A-2
-------
SPECIATE is updated periodically.
5) U.S. Environmental Protection Agency. Fugitive
Emission Sources of Organic Compounds - Additional
Information on Emissions. Emission Reductions, and
Costs. EPA-450/3-82-010, 1982.
This document contains the data and methodologies which
EPA believes most accurately characterize average synthetic,
organic chemical manufacturing industry equipment leak
emission rates of VOC, effectiveness of.control techniques,
and control costs for selected equipment used in the
processing of organic chemicals. The emission factors (on
Page 1-4) can be used tb estimate VOC emissions from any
industrial plant which has the selected equipment and
handles organic chemicals.
A-3
-------
APPENDIX B
ESTIMATING SELECTED PHYSICAL PROPERTIES OF MIXTURES
-------
APPENDIX B
ESTIMATING SELECTED PHYSICAL PROPERTIES OF MIXTURES
This appendix describes methods to estimate selected
physical properties of mixtures using pure component
physical properties. These mixture properties include:
Cp gas (contaminant) heat capacity (J/kg °K)
Cp, liquid (contaminant) heat capacity (J/kg °K)
M contaminant molecular weight (g/g-mole)
T.c pseudo-critical .temperature (°K)
X contaminant latent heat of vaporization (J/kg)
For each of these mixture fluid properties, the
corresponding fluid property for each of the mixture
constituents is required. In addition, the mixture
composition is required; for some calculations, the mixture
composition expressed as mole fractions is required, while
for other calculations, the mixture composition expressed as
mass fractions is required. Because the mixture molecular
weight is required when converting from mass to mole
fractions, this calculation is outlined first. The
calculation of mixture heat capacity and latent heat of
vaporization is discussed together because these
calculations all require that the mixture composition be
specified as mass fractions.
Mixture Molecular Weight
The mixture molecular weight M (g/g-mole) is calculated
using mixture mass fractions as:
(B-l)
where ^ is the mass fraction of species i, M, is the
molecular weight of species i (g/g-mole) , and the summation
is over all C components.
Using mixture mole fractions, the equation for mixture
molecular weight is:
Z-, M, (B-2)
where z( is the mole fraction of species i . Conversions
between mass and mole fractions can be made using:
(B-3)
B-l
-------
for each of the i components. So, if mass fractions are .
known and mole fractions are desired, Equation (B-l) can be
used to calculate the molecular weight, and Equation (B-3)
can be used to calculate the mole fractions for each
component. And, if mole fractions are known and mass
fractions desired, Equation (B-2) can be used to calculate
the molecular weight, and Equation (B-3) can be used to
calculate the mass fractions for each component.
Pseudo-Critical Temperature
Tc is:
The equation-to determine pseudo-critical temperature
(?
ZiTA (B-4!
where Zj is the mole fraction of species i and TCii is the
temperature of species i.
Mixture Heat Capacity and Latent Heat of Vaporization
The equations to determine mixture (gas and liquid)
heat capacities (Cp and Cp,) and latent heat of vaporization
(X) are based on a mass-fraction weighted contribution of
each pure component property. So, the equation to determine
the (mixture) gas-phase contaminant heat capacity Cp is:
C = IXc* Cj (B-5)
•(£-
\c
where
-------
APPENDIX C
SELECTED CONVERSION FACTORS
-------
APPENDIX C
SELECTED CONVERSION FACTORS
Area
1 m2
1 ft2
1 hectare
1 acre
= 104 cm2
= 0.0929 m2
= 104 m2
- 4046.86 m2
IN = 1 kg • m/sec2
= 105 dynes
- 0.2248 lbf
1 dyne = 1 g • cm/sec2
= 10'5 N
= 2.248 x ID"6 lbp
1 lbf » 4.448 N
= 4.448 x 10s dynes
Concentration
conversions with ppm by volume:
Gas Constant
mg
mg
24.04
=ppm by vol (20°C)
0.8347 x 10-*= ppm by wt
^1 • 62.43 x 10-9= lbm 1 ft3
m
mg
m~
for ideal gases
vol
vol % x 10
fraction x 106
= ppm by vol
= ppm by vol
Energy or Work
1 J = N
= 107
= 107
= 0
= 0
m
ergs
dyne
cm
23891 g-cal
7373 ft-lbf
= 9.486 x ID"4 BTU
ft-lbf =
1 cal(g)
1 BTU
0.0012861 BTU
1.3562 J
1.3562 x 107 ergs
0.32396 g-cal
3.9685 x
1.0543 x 1010 ergs
1054 Joules •(N-m)
10'3 BTU
Flow
1 m3/h = 3600 m3/s
Force
• PV
Mwair
8314.0
0.08314
0.08206
0.08206
62.36
0.7302
10.73
= nRT
* 29(79% N2/ 21% 02)
m3-Pa/kg-mole- °K
bar•liters/g-mole•°K
m3- atm/kg-mole • °K
liter-atm/g-mole•°K
1-mm Hg/g-mole-°K
ft3-atm/lb-mole- °R
ft3-psia/lb-mole-°R
8.314 x 10-3J/kg-mole-°K
8.314 J/g-mole-°K
1.987 cal/g-mole-°K
1.987 BTU/lb-mole-0R
5.467 gal-atm/lb-mole °R
1 gmole gas occupies 22.41 at
0°C
1 Ib-mole gas occupies 359 ft3
at 0°C
1 Ib-mole gas occupies 380 ft3
at 60°F
Heat Rate
1 cal/s « 1.102 x ID"6 BTU/h
Length
1m = 100 ^m
= 1000 mm
= 39.37 in
= 3.2808 ft
= 1.0936 yards
= 0.0006214 mils
= 106 microns (jn)
= 1010 angstroms (A)
C-l
-------
1 ft
1 in
12 -in
% yd
0.3048 ra
30.48 cm
2.540 cm
°F + 460
°C + 273.6
°R
°K
Mass
1kg = lOOOg
= 0.001 metric tons
= 2.20462 Ibm
= 35.27392 oz
.llbm = 16 oz
= 5 x 1Q-4 tons
= 453.593 g
= .453593 kg
Mass Release Rate
i g/s =
1 t/yr =
1 t/dy =
7.9367 Ib/hr
3.16'x ID'2 g/s
11.57 g/s
Power
1 w = l J/sec
= 14.34 g-cal/min
- 1.341 x 10"3 hp
= 0.7376 ft-lbf/sec
Pressure
1 atm = 1.1325 x 10s N/M2
= 1.01325 x 105 Pa
= 1.01325 x bars
= 1.01325 dynes/cm2
= 760 mm Hg
= 29.9212 in Hg
= 10.33 m H20
= 33.9 ft H20
= 14.696 psi
1 millibar = 1000 dynes/cm2
1 mm Hg = 1333.224 dynes/cm2
1 Ib/irr = 58,947.6 dynes/cm2
1 in Hg = 33,863.9 dynes/cm2
1 Pascal = 10 dynes/cm2
Volume
1 m3
1 ft3
1 bbl =
1 liter =
1 gallon =
1000 liters
106 cm3
106 m 1
35.3145 ft2
61, 023 in3
220.8 imperial gal
264.17 gallons
1056.68 quarts
1728 in3
0.028317 m3
28.317 liters
28,317 cm3
7.4805 gallons
42 gallons
158.99 liters
103 cm3
3.785 cm3
Temperature
9/5°C +32 - °F
C-2
-------
Conversion Calculations
1. To convert from ^g/m3 to parts per million (ppm), use the
following:
IT 1
-£ 0.0245/MW (C-l)
aJ
where:
TO = 273.15 (°K)
Ta = ambient temperature (°K)
MV = molecular weight (g/g-mole)
Equation (C-l) is simplified in TSCREEN by assuming T0/Ta=l.
2. To convert J/kg to cal/g-mole use the following:
J/kg (1^/4184) = cal/g-mole (C-2)
C-3
-------
APPENDIX D
AVERAGING PERIOD CONCENTRATION ESTIMATES
-------
APPENDIX D
AVERAGING PERIOD CONCENTRATION ESTIMATES
The purpose of this appendix is to provide some simplified
techniques for converting concentrations calculated by the models
to different averaging times. Methods presented are applicable to
ground-level and elevated emissions of passive gases and
particulate matter.
Instantaneous Estimates
For computing ground level concentrations from an
instantaneous surface release for a given stability class and
sampling time, the average concentration over sampling time r can
be expressed as some fraction of the-peak concentration.
Xr = Xf * F ' (D-l)
where: XT is tne average concentration for a given sampling
time T,
T is the sampling time, i.e. 5 min., 1 hour etc.,
(expressed in seconds)
Xp is the instantaneous peak concentration.
F is the correction factor for sampling time, which
always has a value less than or equal to one.
The correction factor F can be computed using the procedure given
by Petersen, 1982 for the averaging times not provided in TSCREEN.
The concentration at a given receptor location ranges from
zero to a peak value as the puff moves towards trie receptor. The
peak instantaneous concentration is always assumed to occur at time
t when the center of the puff is at the receptor location. If the
growth of the puff is small as the puff passes over the receptor,
then the peak average concentration for sampling time T at a
particular location occurs during the time period t - r/2 to t +
T/2.
Continuous Estimates
•
To obtain the estimate of the maximum concentration for a
longer averaging time, multiply the 1-hour maximum concentration by
the given factor:
Averaging Time Multiplying Factor
3 hours 0.9 (±0.1)
8 hours 0.7 (±0.2)
24 hours 0.4 (±0.2)
annual 0.08 (±0.2)
The numbers in parentheses are recommended limits to which one may
diverge form the multiplying factors representing the general case.
D-l
-------
For example, if aerodynamic downwash or terrain is a problem at the
facility, or if the release height is very low, it may be
appropriate to increase the factors up to the limits specified in
parentheses. Conversely, if the stack is relatively tall and there
are no terrain or downwash problems, it may be appropriate to
decrease the factors . For averaging times in between the values
listed above, use the multiplying factor for the shorter averaging
time. For example, if a 4 -hour average concentration is needed,
use the multiplying factor for the 3 -hour averaging time (0.9) .
To obtain the estimated maximum concentration for a shorter
averaging times between 30 and 60 minutes, use the 1-hour maximum
concentration. For averaging times less than 30 minutes use the
following equation:
(D-2)
where: t s 30 minutes
TSCREEN will present a menu containing these averaging times and
the 15 and 30 minute averaging times after the SCREEN model has
been run. The user may select one or more of these maximum
concentrations calculated by the model. The new concentrations
will appear at the end of the SCREEN model output.
D-2
-------
APPENDIX E
RUNNING TSCREEN
-------
APPENDIX E
RUNNING TSCREEN
E.1 Introduction
To correctly analyze toxic emissions and their subsequent
dispersion from one of many different types of possible releases,
the computer program TSCREEN, A Model for Screening Toxic Air
Pollutant Concentrations, should be used in conjunction with this
workbook. With the use of these tools one can determine the type
of release and the steps to followed to simulate the release via
an applicable computer model. Then, the dispersion
characteristics and pollutant concentrations of the resulting
plume can be calculated. The air toxics dispersion screening
models imbedded in TSCREEN that are used for the various
scenarios are SCREEN, RVD, PUFF, and the Britter-McQuaid model.
Using TSCREEN, a particular release scenario is selected via
input parameters, and TSCREEN automatically selects and executes
the appropriate dispersion model to simulate that scenario. The
model to be used and the worst case meteorological conditions are
automatically selected based on criteria given in those in this
workbook. TSCREEN has a front-end control program to the models
that also provides, by use of interactive menus and data entry
screen, the same steps as the workbook. The correct release
scenario and associated characteristics of a toxic emissions
release are selected with the help of on-screen text and graphics
and data input is performed in a full-screen edit mode. TSCREEN
saves the input data for each release scenario to a file that can
be retrieved and later edited or executed. TSCREEN also provided
a. method of easily viewing and saving the modeling results for
each modeled scenario.
E.2 Getting Started
Hardware Requirements
TSCREEN is an IBM PC-based software application written and
compiled in FoxPro™, a software application development system,
and Microsoft™ C Version 5.1. The program requires 500
kilobytes (KB) of free Random Access Memory (RAM). Although
TSGREEN may operate with certain memory resident programs
installed, no attempt has been made to test its operation against
all memory resident programs available today. If problems occur
while TSCREEN and memory resident programs are running
simultaneously, try removing the memory resident programs from
memory and re-executing TSCREEN. The TSCREEN program files
occupy about 2.2 megabytes (MB) of disk space. As data from
scenario runs are saved, the hard disk space needed will
increase. To install TSCREEN on hard disk systems, make sure
there is at least 2.5 MB of free disk space available to load and
execute the program. The time required to run the dispersion
models will be greatly reduced if the computer has a math co-
processor.
E-l
-------
The computer running TSCREEN must be booted with the CONFIG.SYS
file in the root directory of the boot up disk containing the
following parameters:
Files » 30
Buffers = 22
If the CONFIG.SYS file already has these statements with higher
values assigned, then no modification is necessary, otherwise
either add -the needed statements or increase their value to that
of the example and reboot the computer.
Software requirements
The files required to run TSCREEN are as follows:
BMTS.EXE - The Britter & McQuaid model
CHEMBASE.DBF - The chemical database
CHEMBASE.IDX - The chemical database index-file
DISPLAY.DBF - File used to display file lists
ERHANDLE.EXE - The error handling program
ERMSG.DAT - Error message file
FOXSWAP.COM - FoxPro memory management program
FOXUSER.DBF - FoxPro database
FOXPRO.ESL - FoxPro run-time library
FOXPRO.ESO - FoxPro run-time library
FOXUSER.FPT - FoxPro database
GRAPH.EXE - The graphics generation program
PIPERES.EXE - Program-that performs calculations for the
scenarios involving gas leaks from a pipe attached to a reservoir
PUFFTS.EXE - The PUFF model
OLDRUNS.DBF - Database that contains previously entered data
OUTPUT.DBF - File used to display model output
RVDTS.EXE - The RVD model
SCREENTS.EXE - The SCREEN model
TSCREEN.EXE - The main program
TSHELP.DBF - The help database
TSHELP.FPT - File containing help text
VFONT101.FNT - The graph font file
TSMACRO.FKY - FoxPro macro file
First Time Installation
Installing TSCREEN
Because of the size of the TSCREEN program, TSCREEN is separated
into four separate zipped (compressed) files:
E-2
-------
File Size(K)
TSCREEN1.ZIP 568
TSCREEN2.ZIP 193
TSCREEN3.ZIP 344
TSCREEN4.ZIP 227
TSCREEN1.ZIP contains the FoxPro runtime program, FOXPRO.ESO, and
TSCREEN2.ZIP contains the FoxPro runtime program, FOXPRO.ESL, and
the FoxPro memory manager FOXSWAP.COM. If you already have these
files for TSCREEN version 3.0, July 1992, then you do not need to
download TSCREEN1.ZIP and TSCREEN2.ZIP. Make sure though to
include these files in the same sub-directory of the updated
TSCREEN version 3.0, November 1992, before running the updated
program.
To unzip (decompress) the files, you will need to have a copy of
PKUNZIP.EXE file. PKUNZIP.EXE is availible on most Bulletin Board
Systems (BBS).
Please refer to your DOS manual for the relevant commands for
creating sub-directories and copying files if the following
instructions are unclear.
TSCREEN must be installed on a hard disk in order to run. To
install TSCREEN on a hard disk, check the available disk space
by running the DOS program CHKDSK. To check to see if the DOS
programs are accessible from the PATH setting simply type:
PATH
If the DOS sub-directory or sub-directories containing the DOS
files is listed the type:
CHKDSK
at the hard disk prompt where TSCREEN is to be installed. If
not, read your DOS manual to understand what you have to do to
run CHKDSK. Check to make sure there is at least 2.5 MB of
available disk space. Ifm there is enough free disk space, then
create a /TSCREEN sub-directory -from the root directory of the
hard drive on which TSCREEN will be installed. The command to
create a TSCREEN sub-directory off the main or root directory is:
CD\
MD TSCREEN
Once the sub-directory is created, insert the first TSCREEN
diskette in the high-density drive of the computer (usually the A
drive on IBM AT-type machines) and copy the files from the
diskette to the sub-directory by typing the command:
E-3
-------
COPY A:*.* X:\TSCREEN
where X is the letter designation of the drive which TSCREEN is
to be installed (where the sub-directory was created). Repeat
the command above for the other diskettes. Also, copy the
PKUNZIP.EXE file to your TSCREEN sub-directory. While in the
TSCREEN sub-directory,decompress the TSCREEN zip files by typing
following command:
PKUNZIP TSCREEN1.ZIP
Repeat the command for the other three TSCREEN zip files
replacing TSCREEN1.ZIP with the other file names: TSCREEN2.ZIP,
TSCREEN3.ZIP, TSCREEN4.ZIP. Once the files are unzipped
(decompessed), the installation is complete. Type the following
command :
TSCREEN
to start the program.
E.3 Example Scenario
An example TSCREEN session is demonstrated in this section.
For more information on the scenarios in TSCREEN, see Sections 4
and 5 of this workbook.
Title Screen
Upon starting the program a title screen will appear as shown
in Figure E-l.
Figure E-l. Title Screen
TSCREEN
A"ModeI for Screening Air Toxic Pollutant Concentrations
Version 3.0 (Dated 92182) August 1992
for Questions Contact:
Developed by:
Jawad S. Touna, Project Officer
US EPA, OAQPS, TSO CMO - 14)
Source Receptor Analysis Branch
Research Triangle Park, NC 27711
(919) 541-5381
Pacific Environmental Services, Inc
5001 So. Miami 3lvd, Suite 300
P.O. Box 12077
Research Triangle Park, NC 27709
(919) 941-0333
E-4
-------
Selection Windows
After the reference pages, the main menu bar appears across
the top of the screen, and a list available keys appears across
the bottom of the screen as shown in Figure E-2. From this menu
the user can select:
File - to retrieve previously entered data, previously
saved model printed output, or previously saved model
graphic output
Initial Form of Release - to select a form of release and
enter a new scenario
Chemical Database - to view or edit the Chemical Database
• Quit - to exit TSCREEN.
Figure E-2. Main Menu
Initial Form of Release
Chemical Database Quit
Help <1>/Scroll Vertical Menus <«»->/<-».>ScrolI Horizontal Menu
<£nter>/Letter=Select Menu Item Exit Current Menu Exit All Menus
Menu selections in TSCREEN can be made by clicking a mouse,
by moving the highlight bar with the arrow keys and pressing
, or by pressing the letter of a menu item that is a
different color. To enter data for this scenario, select
'Initial Form of Release' from the menu bar. The pull-down menu
shown in Figure E-3 will appear.
Figure E-3. Initial Form of Release
File
Jnitfal
Initial Form of Release
Pwilcutatfii'Hatter Bet ess* Typ<*
Gaseous Release Type
Liquid Release Type
Superfund Release Type
Chemical Database
Quit
Help /Scroll Vertical Menus <-«->/<-»>ScroU Horizontal Menu
/Letter=Select Menu Item Exit Current Menu EXit All Menus
TSCREEN has help available at each point in the system,
activated by pressing the key. Even the selection windows
have help pages associated with them. An example of pressing the
key from the first menu item in the 'Initial Form of
E-5
-------
Release' menu is shown in Figure E-4. (See Section E.7 for a
detailed discussion on the use of the help system.)
Figure E-4. Help Window
File tn*ti*t ftw«:-fl*
Chemical Database Quit
« Topics »
" < Next >
< Previous >
< Look Up >
I Paniculate Natter Release Type I
A Particulate Matter type release is a release of any solid
material such as particulates, dust, or ash.
See Also: Release Definition
Help /Scroll Vertical Menus <*->/<-»>ScrolI Horizontal Menu
/Letter=Select Menu Item Exit Current Menu Exit All Menus
Next select 'Particulate Matter Release Type' from the
'Initial Form of Release' menu. Then the menu in Figure E-5 will
appear.
Figure E-5. Particulate Matter Release Type Menu
File
Irtit1[*l;fwin:<>ftRelease Chemical Database Quit
— Initial Form of Release
Part(cutate Matter Release Type
Workbook Scenario
Fugitive/Windblown Dust Emissions - 4.1.2
Ducting/Connector Failures - 4.1.3
Help /<4>ScrolI Vertical Menus <-«->/<-»>ScrolI Horizontal Menu
/Letter=Select Menu Item Exit Current Menu Exit All Menus
The second menu of release types that appears lists only the
scenarios specific to the Initial Form of Release selected from
the first selection menu (See Section E.4 for a complete list of
the scenario selection menus). The user can return to previous
menus or data entry windows by pressing the key. Pressing
from a menu item or from the data entry windows that follow
will cause the user to return to the main menu bar.
E-6
-------
Data Entry Screens
Once the scenario has been selected, unique data entry
screens will appear for that scenario. These screens will guide
the user through calculations that will select the appropriate
dispersion model based on the data entered. For example, some of
the screens calculate gas densities and others help calculate
emission rates. Data entry screens for this example are shown in
Figures E-6 through E-8. Note that in this example there is no
scenario input section since the scenario has already been
determined. Thus, the user is taken directly to the model input
section.
Figure E-6. Data Entry Screen
— Continuous Participate Matter Releases from Stacks - Scenario 4.1.1-
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 7
Enter a unique title for this data's model run:
................................
g/s
m/s
m
m
"K
<£stV Abort
RELEASE PARAMETERS
Emission Rate (dm) ->
Exit Velocity (ExitV)->
Release Height above Ground (Hs) -> 1&d
Diameter at Release Point (0) -> ;.1S: :
Temperature of the Material Released (Ts) -> J9 2Mt,;
iSftreefti:
Sa:ilx':". \
Figure E-7. Data Entry Screen
— Continuous Particulate Matter Releases from Stacks - Scenario 4.1.1
SCREEN MODEL INPUTS - Page 2 of 7
BUILDING PARAMETERS
Building Height (enter 0 if no building) -> 19 m
Building Minimum Horizontal Dimension -> 19- : m
Building Maximum Horizontal Dimension -> 1?" .!. : m
URBAN/RURAL CLASSIFICATION
Enter U for Urban - R for Rural -> R
FENCELINE DISTANCE
Enter the distance from the base of the stack
to the plant fenceline -> 1 Help Calculator previous Screen Abort
E-7
-------
Figure E-8. Data Entry Screen
— Continuous Participate Natter Releases from Stacks - Scenario 4.1.1
SCREEN MODEL INPUTS - Page 3 of 7
TERRAIN TYPE
Is this a FLAT or SIMPLE TERRAIN evaluation (Y/N) -> V.
SIMPLE TERRAIN
Are receptors above stack-base (Y/N) -> jf
FLAT TERRAIN
Do you have specific locations where you would like
pollutant concentrations to be calculated (Y/N) -> T
Oo you have receptors above ground level
(i.e. Flag Pole Receptors) (Y/N) -> H
edit?
«6f««-
Based on user input, the SCREEN model has been selected with
Flat terrain only. Note that the program automatically
calculates concentrations for many receptors. If the user
selects "Y" to enter discrete receptors, pressing will
advance TSCREEN to the next page (see Figure E-9) and allow the
user to enter specified distances of interest that will be added
to the automatic receptors.
If the user enters "N" for discrete receptors, SCREEN is
executed with only the automatic number of receptors.
Figure E-9. Data Entry Screen for Discrete Receptors
toniinuous parrici
SCREEN MODEL INPUTS
RECEPTOR LOCATIONS:
the source at which
Enter a blank after
Distance from
source (meters)
1 100 fenci
2 " ' .
3 <..^,.:
4 >^:;rt
5 "• - •••":?1 .
6 ft;>$^
7 •:•:;%;.•<*><
8 ;:-.. '"'"> :
9 '":••"'>•-..: '
10 ' •"H*'":X
. Edit. ... *F9>
jiaie natter Releases iron
- Page 4 of 7
Enter (up to 30) distant
concentrations should be
the last distance to sto|
Distance from
source (meters)
5 11
12 ••:.!'• •
13 .•««: '.":?•*
14 .•„:.••'?%«.;,:
15 ::";'-: - •:'•'
16 '-:••; *i
17 .k,;.*' .:-H
is .;::::v-s ::;
19 :>•„, "i
. 20 ••:-x::':/; H-
ffevfous Screen.
> siacics - scenario <».i.i
:es from
calculated.
> input.
Distance from
source (meters)
21
22
23
24
• 25
26
27
28
29
30
Ran ftodel:.: : <£so- Abort ...
In Figure E-9, the first distance is the fenceline distance
specified on the previous page. It will appear automatically.
All subsequent distances entered must be greater than the
fenceline. will execute the SCREEN model. As the program
E-8
-------
executes the user is shown what percent of the program is
complete.
Parts Per Million
After the SCREEN model has run, the data entry window in
Figure E-10 appears. The user can choose to have the maximum
concentrations displayed in parts per million (ppm) in addition
to /zg/m3. "N" is entered in this example. If "Y" had been
entered the user would then be required to enter the appropriate
molecular weight and the concentration in ppm would be calculated
using the following formula:
concentration (ppm) = concent rat ion (pig/m3) —'— '
1 '\v
where: Mw = molecular weight (g/g-mole)
Figure E-10. Parts Per Million
Do you want maximum concentrations
in parts per million (ppm) (Y/N) -> It
Help Up <;>Down Exit/No ppm calculation
Averaging Times
The default averaging time in the'SCREEN model is 1 hour.
If the SCREEN model is used, the maximum concentration can be
calculated for additional averaging times selected from the menu
shown in Figure E-ll. Since we are only interested in 1-hour
averages for this example, we will not select any of the
additional averaging periods.
Figure E-ll. Averaging Times
Averaging Time
The default averaging time is 1 hour
select one or more from below. . .
30 Minutes
3 Hours
8 Hours
24 Hours
Annual
Up 0own
/ Mark/Unmark Time
Select Marked Times
Abort Without Selection
E-9
-------
Averaging times can be selected by pressing the key
or the Space bar to mark the averaging time with an asterisk.
After all of the desired averaging times have been selected,
press to proceed. If additional averaging times were
selected, the estimated concentrations for the new averaging
times would appear at the end of the model output.
Model Output
When the model has completed execution, the output will be
presented on the screen. A portion of the model's output as it
would appear on the screen is shown in Figure E-12. A complete
listing of the model's output is shown in Figure E-13. The user
can scroll through the output with the / or /
keys. A complete list of the SCREEN model output -is shown in
Figure E-13. The user can scroll through the output using the
various keys shown. The user can also graph, print or save the
entire output to a file. The instructions for the keys used in
viewing the model output are explained in Section E.6 of this
appendix.
The SCREEN model output begins with the time and date that
the model was run. Next, there is the model name and version
number. Following the model name is the run's title and the user
input. Next, the output contains a summary of results showing
the maximum concentration and the distance to the maximum. Next,
there is a list of concentrations for SCREEN's automated
distances. Finally, there is a listing of the cavity
concentrations since the effects of building downwash are being
considered. If additional averaging times had been selected,
these results would at the end of the model output.
E-10
-------
Figure E-12. Model Output on the Screen
Continuous Particulate Hatter Releases from Stacks - Scenario 4.1.1
*** SCREEN-1.2 MODEL RUN ***
•*** VERSION DATED 91/10 ***
Particulate Stack Release
SIMPLE TERRAIN INPUTS:
SOURCE TYPE = POINT
EMISSION RATE (G/S) = .9300E-03
STACK HEIGHT (M) = 16.00
STK INSIDE DIAM (M) = .10
STIC EXIT VELOCITY Graph
Alt,
Print
, , ,
Save to File Exit
Figure E-13. Complete Model Output
*** SCREEN-1.2 MODEL RUN ***
*** VERSION DATED 91/10 ***
Particulate Stack Release
SIMPLE TERRAIN INPUTS:
SOURCE TYPE = POINT
EMISSION RATE (G/S) = .9300E-03
STACK HEIGHT (M) = 16.00
STK INSIDE DIAM (M) = .10
STK EXIT VELOCITY (M/S)= 17.8000
STK GAS EXIT TEMP (K) = 298.00
AMBIENT AIR TEMP (K) = 298.00
RECEPTOR HEIGHT (M) = .00
IOPT (1=URB,2=RUR) = 2
BUILDING HEIGHT (M) . = 19.00
MIN HORIZ BLDG DIM (M) = 19.00
MAX HORIZ BLDG DIM (M) = 19.00
05-02-92
13:16:50
**********************************
* SUMMARY OF SCREEN MODEL RESULTS
CALCULATION
PROCEDURE
MAX CONC
(UG/M**3)
DIST TO
MAX (M)
TERRAIN
HT (M)
SIMPLE TERRAIN .8543
BUILDING CAVITY-1 1.717
BUILDING CAVITY-2 1.717
100.
28.
28.
0.
(DIST
(DIST
CAVITY LENGTH)
CAVITY LENGTH)
r*W************W
REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
E-ll
-------
BUOY. FLUX = .00 M**4/S**3; MOM. FLUX = .79 M**4/S**2.
*** FULL METEOROLOGY ***
*** SCREEN AUTOMATED DISTANCES ***
*** TERRAIN HEIGHT OF 0. M ABOVE STACK BASE USED FOR
DIST COHC U10M USTK MIX HT PLUME
(M) (UG/M**3) STAB (M/S) (M/S) (M) HT (M)
100.
200.
300.
400.
500.
600.
700.
800.
900.
1000.
1100.
1200.
1300.
1400.
1500.
1600.
1700.
1800.
1900.
2000.
2100.
2200.
2300.
2400.
2500.
2600.
2700.
2800.
2900.
3000.
3500.
4000.
4500.
5000.
5500.
6000.
6500.
7000.
7500.
8000.
8500.
9000.
9500.
10000.
15000.
20000.
25000.
30000.
40000.
50000.
MAXIMUM
100.
.8543 3
.4906 4
.3483 6
.3011 6
.2648 6
.2360 6
.2125 6
.1930 6
.1766 6
.1626 6
.1505 6
. 1420 6
.1327 6
.1245 6
.1172 6
.1107 6
.1048 6
.9939E-01 6
.9450E-01 6
.9003E-01 6
.8592E-01 6
.8214E-01 6
.7865E-01 6
.7542E-01 6
.7242E-01 6
.6963E-01 6
.6702E-01 6
.6458E-01 6
.6230E-01 6
.6015E-01 6
.5115E-01 6
.4429E-01 6
.3891E-01 6
.3458E-01 6
.3151E-01 6
.2857E-01 6
•-2609E-01 6
.2397E-01 6
.22;4E-01 6
.2054E-01 6
.1914E-01 6
.1790E-01 6
.1679E-01 6
.1581E-01 6
.9929E-02 6
.7119E-02 6
.5491E-02 6
.4461E-02 6
.3229E-02 6
.2512E-02 6
1-HR CONCENTRATION AT
.8543 3
1.0 1.0 320.
1.0 1.1 320.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
t.O 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
I.O 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1 .3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
1.0 1.3 5000.
I.O 1.3 5000.
1.0 1.3 5000.
I.O 1.3 5000.
1.0 1.3 5000.
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
I.O 1.3 5000.0
1.0 1.3 5000.
1.0 1.3 5000.
.0 1.3 5000.
.0 1.3 5000.
.0 1.3 .5000.
.0 1.3 5000.
.0 1.3 5000.
.0 1.3 5000.
.0 1.3 5000.
.0 1.3 5000.
.0 1.3 5000.
.0 1.3 5000.
.0 1.3 5000.
.0 1.3 5000.
.0 1,3 5000.
.0 1.3 5000.
.0 1.3 5000.
OR BEYOND 100.
.0 1.0 320.
0
0
0
0
0
0 •
0
0
0
0
0
0
0
0
0
0
0
N:
0
16.1
16.0
16.
16
16
•
•
16.
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
.
.
.
„
.
.
•
B
B
.
.
.
m
,
m
.
•
m
f
f
m
•
m
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
16.0
16
16
16
.
,
„
0
0
0
16.0
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
f
.
,
B
.
,
•
m
.
a
.
.
.
.
B
•
.
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
FOLLOUING DISTANCES **
SIGMA SIGMA
Y (M) Z (M) DUASH
12.5
19.6
22
25
28
32
35
38
41
44
47
50
53
56
59
.
•
•
•
a
•
B
•
^
.
m
5
7
9
0
1
2
2
2
2
2
2
1
0
61.9
64
67
70
73
76
79
81
84
87
90
93
95
98
101
114
m
n
m
.
,
m
9
m
.
m
f
m
0
B
B
8
7
5
4
2
1
9
7
5
2
0
8
5
3
8
128.2
141
154
167
180
192
205
218
230
242
254
„
m
m
^
m
m
m
m
B
B
5
5
5
3
9
5
0
4
7
9
267.0
279
396
508
617
722
927
1124
12
.
.
1
2
.4
B
.
B
•
a
0
7
0
0
5
15.3
21.9
22.8
23.3
23.9
24.4
24.9
25.4
26.0
26.5 •
27.0
26.8
27.3
27.7
28.1
28.5
28.9
29.2
29.6
30.0
30.4
30.7
31.1
31.4
31 .8
32.1
32.5
32.8
33.1
33.5
35.0
36.6
38.0
39.4
40.0
41.1
42.3
43.3
44.4
45.4
46.4
47.3
48.2
49.1
55.8
61.0
65.5
69.0
74.6
79.3
15.3
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
SS
OIST
- DISTANCE FROM THE SOURCE
E-12
-------
CONC
STAB
U10N
USTK
NIX HT
PLUME HT
SIGMA Y
SIGMA Z
QUASH
MAXIMUM GROUND LEVEL CONCENTRATION
ATMOSPHERIC STABILITY CLASS (1=A, 2=8, 3=C, 4=0, 5=E, 6=F)
WIND SPEED AT THE 10-M LEVEL
WIND SPEED AT STACK HEIGHT
MIXING HEIGHT
PLUME CENTERLINE HEIGHT
LATERAL DISPERSION PARAMETER
VERTICAL DISPERSION PARAMETER
BUILDING DOUNUASH:
DWASH= MEANS NO CALC MADE (CONC =0.0)
DWASH=NO MEANS NO BUILDING DOUNUASH USED
DWASH=HS MEANS HUBER-SNYDER DOUNUASH USED
DUASH=SS MEANS SCHULMAN-SCIRE DOUNUASH USED
DUASH=NA MEANS DOUNUASH NOT APPLICABLE, X<3*LB
*** CAVITY CALCULATION - 1 ***
CONC (UG/M**3) 1.717
CRIT US 310M (M/S) 1.00
CRIT US 3 HS (M/S) 1.10
DILUTION US (M/S) 1.00
CAVITY HT (M) 27.28
CAVITY LENGTH (M) 27.97
ALONGUIND DIM (M) 19.00
«««•«!>««» ««««•*•••••*«««•«*•«•«•«•
*** END OF SCREEN MODEL OUTPUT **•
*** CAVITY CALCULATION - 2 ***
CONC (UG/M**3) = 1.717
CRIT US 31OM (M/S) = 1.00
CRIT US 3 HS (M/S) = 1.10
DILUTION US (M/S) = 1.00
CAVITY HT (M) = 27.28
CAVITY LENGTH (M) = 27.97
ALONGUIND DIM (M) = 19.00
Save to File
If the 'Save to File' option is selected, the user will be
asked to enter a file name of no more than eight characters in
the data entry window shown in Figure E-13. To view previously
saved model output at a later time, select 'File' from the main
menu bar. Then select 'Access Model Printer Output' and a list
of files containing previously saved model output will appear as
shown in Figure E-14. The. menu in Figure E-14 also contains
'Access Data from Previous Scenario' which allows the user to
retrieve data from previously run scenarios by selecting the
scenario's title from a list. The other menu item is 'Access
Model Graphic Output' which allows the user the retrieve a graph
from a list of files containing previously saved graphs.
E-13
-------
Figure E-13. Save to File
1
*** SCREEN- 1.2 MODEL RUN
*** VERSION DATED 91/10
Particulate Stack Release
03-04-9
15:47:0
***
*•*
SIN
Enter a unique file name for this model output -> .RPT
Exit/ No Save
STK &»• EXIT tEWMK>
AMBIENT AIR TEMP ( 1C )
RECEPTOR HEIGHT (M)
I OPT "(1=URB,2=RUR)
BUILDING HEIGHT (M)
*s 298*80
= 298.00
.00
= 2
* 19.00
:-x "'•
:'3$.
.}:•;:.
?£.'
, , «->, <-»>, Alt, Alt, , , ,
Graph Print Save to File Exit
Figure E-14. Retrieve Model Output
Initial Form of Release
— File
Chemical Database Quit
Access Data from Previous Scenario •.£
Accei'"" ""'—"""'""''""'"•"" ''"'""''' ''''"'"Hode"l""Printed Output
RVD4S RPT
S411ALL RPT
SCRNALL RPT
Select Highlighted Run Exit/No Select
Up Down Up One Screen Down One Screen
Bottom <0el> Delete File
Press any other key to find a file beginning with that character
Graph
If the 'Graph' option in Figure E-12 is selected, a plot of
the concentrations vs distances will be drawn. The following
window will appear first as shown in Figure E-15.
E-14
-------
Figure E-15. Distance for Graph
Graphics - Distance
Enter Maxinun Distance for Graph •> 5 Km
Graph is for Simple terrain only.
Use 50.00 Km
In this example 5 km has been selected. JIf the key
had been pressed, the graph would be plotted from 100 m to 50.00
km downwind. Once a distance has been specified, the following
menu will appear as shown in Figure E-16 from which you can
select an output device for the graph'.
Figure E-16. Graphic Output Menu
Graphics - Main Menu
•••*: :-.•:•:••. • :-: • ••: • ••».>:; . •:•• * :•••:•••:. _• • .•:•: :•••
. .
EPSOM FX, MX-Draft Quality
EPSON FX, MX - High Quality
EPSON LQ - Draft Quality
EPSON LQ - High Quality
NEC Pinuriter - Draft Quality
NEC Pinwriter - High Quality
OKIDATA - Draft Quality
OKIDATA - High Quality
HP LaserJet/DeskJet - Draft Quality
HP LaserJet/DeskJet - High Quality
Hewlett-Packard plotter
Houston Instruments plotter
Change Distance for Graph
Save Graph to File
Exit Graphics
From this menu the output device is selected.
example, the user should select 'Screen'.
For this
Note that if your computer does not have the ability to
display graphics, the option 'Screen' will not be on this menu.
If a printer is selected then the output device is assumed to be
LPT1. If a plotter if selected then the output device is assumed
to be COM1. For more information on redirection of output, the
user should consult the DOS manual. Before printing the graph,
be sure that the printer is connected and on-line. After
exiting from che Graphics menu the user is returned no che model
output. Consult your printer's user's manual to determine which
of the above printers is compatible with your printer.
If 'Save Graph to File' is chosen from the bottom of the menu
shown in Figure E-16, then the data entry window in Figure E-17
will appear. Enter a filename of not more than eight characters.
E-15
-------
If you choose to save the graph's .data, then the graph can be -
generated at a later time. To view a previously saved graph at a
later time, select 'File' from the main menu bar. Then select
'Access Model Graphic Output' and a list of previously saved
graphs will appear as shown in Figure E-18.
Figure E-17. Save Graph
Graphics - Save
Enter a unique file name for this graphic output ->
.GRF
Exit/ No Save
Figure E-18. Retrieve Graph
£ili Initial Form of Release Chemical Database Quit
"•'•'"•'•'•• cue - • — - ,
Access Data from Previous Scenario
Access Model Printer Output
fe*ES*?«wtei;?^fi«1:itir:::QtitpiJt
— — — — — — — — — — noae i urapnic uuipui — — — ^ —
si»*^r:rG*i
PUFFT GRF
SCRNP1 GRF
SCRNP6 GRF
Select Highlighted Run Exit/No Select
Up Down Up One Screen Down One Screen
Top Bottom <0el> Delete File
Press any other key to find a file beginning with that character
If you are using a plotter, the DOS MODE command should be
used to configure your computer's communications port to
correctly match the communications settings of the plotter.
Otherwise, you will probably not get any output from the plotter.
For example, the Hewlett-Packard 7475A plotter has a set of
switches located"on the back of the plotter which allows you to
set the communications parameters. A common setting for these
switches is shown in Figure E-19.
Figure E-19. Switch Configuration
S2 S1 Y US A3 B4 B3 82 81
1
0
E-16
-------
The DOS MODE command which should be used to correspond to these
settings is:
MODE COM1:96,E,7,1
This command sets serial port 1 (COM1) to 9600 baud with even
parity, seven data bits, and I stop bit.
Each plotter has unique methods of setting the
communications parameters. You should use the plotter's manual
for the plotter configuration in conjunction with your DOS
manual's explanation on the use of the MODE command to be certain
that your computer and plotter are configured correctly.
An example of the graph whose descriptive title was saved as
"Particulate Stack Release" in the Data Entry Screen depicted in
Figure E-6 is shown in Figure E-20.
Figure E-20.. Graphic of Concentration vs Distance
Par—t f cu 1 ate Stack Re t ease
DISTANCE (Km)
Moxinun concentration 1.240E+000 ug/cubic r» at 0.100 Km (Automated Distances)
Press any key to continue
Exiting TSCREEN
After exiting the graph, the user returns to the model
output viewing window shown in Figure E-13. After pressing
from this window the user 'will return to the main menu bar shown
in Figure E-2. At this point the user can exit TSCREEN by
E-17
-------
selecting 'Quit' from the main menu bar as shown in Figure .E-21
Figure E-21. Quit Menu
File Initial Form of Release Chemical Database
r " "Quit TSCREEN ? -,
, ; **
* h
Help /Scroll Vertical Menus <•«->/<-»>ScrolI Horizontal Menu
/Letter=Select Menu Item Exit Current Menu Exit All Menus
E.4 Scenario Selection
Twenty-four of most prevalent release scenarios were
selected for TSCREEN and are grouped according to four
categories:'particulate matter, gases, liquids, and releases from
Superfund sites.
To select a scenario in TSCREEN, first select 'Initial Form
of Release' from the menu bar across the top of the screen. The
'Initial Form of Release' Menu as shown in Figure E-22 will then
appear.
Figure E-22. Initial Form of Release Menu
File 5n:lt;i:at/fi(5FW:^|RHelp /ScroU Vertical Menus <<->/<-»>Scroll Horizontal Menu
/letter=Select Menu Item Exit Current Menu Exit All Menus
If the release is any solid material such as particulates,
dust, of ash, then 'Particulate Matter Release Type' should be
selected. The menu in Figure E-23 will appear listing
particulate scenarios.
E-18
-------
Figure E-23. Particulate Matter Release Type Menu
File I&ttfet FftOft Of R«t«J«i Chemical Database
Initial Form of Release
Quit
Particuiate Matter Release Type
Workbook Scenario
Fugitive/Windblown Dust Emissions - 4.1.2
Ducting/Connector Failures - 4.1.3
Help /ScrolI Vertical Henus <-«->/<-»>Scroll Horizontal Menu
/Letter=Select Menu Item Exit Current Menu Exit All Menus
If the release is any matter in vapor from such as sulfur
dioxide, volatile organics, etc, then the user should select
'Gaseous Release Type'. The menu in Figure E-24 will appear
listing gaseous scenarios. Two scenario numbers for one menu
choice indicates that there is both a continuous (first number)
and instantaneous (second number) scenario.
Figure E-24. Gaseous Release Type Menu
File intf
Pai
Gat
Li
Su
Help
/Lei
t-1at:.form::o;f-; Release Chemical Database
- Initial Form of Release .
•ticulate Matter Release Type :f
«M^:';R>l'«8«e--'Typ*'-.,7-...''- ..•?•''„} "'--..
Stack's, 'Vents, Conventional Point Sources'
Leaks from Reservoir
Leaks from a Pipe Attached to Reservoir
Multiple Fugitive Sources
Land Treatment Facilities
Municipal Solid \/Scroll Vertical Menus <<->/<-*>ScroU Horizontal Menu
tter=Select Menu Item Exit Current Menu Exit All Menus
If the release is material that may immediately evaporate
(no pooling results) or may pool first and then evaporate, then
the user should select 'Liquid Release Type'. The menu in Figure
S-25 will appear listing liquid scenarios. Two scenario numoers
for one menu choice indicates that there is both a continuous
(first number) and instantaneous (second number) scenario.
E-19
-------
Figure E-25. Liquid Release Type
File
.Tv.*:*^^"*:^:™-:^*:-:*?:*:*?: ~" .1:7:7: ~
i - Initial Form of Release
Participate Matter Release
Gaseous Release Type
Chemical Database Quit
ease \
ease Type ';
- ' " ' -
*<-.••• <-v_'
, , , ,,
Liquid Release Type
Workbook Scenario
v ™"-:->."v:-:;:-XvT-.T5EvT.^':-.TT::".vrv:.-7 :*7:~.~.'''^—**•• 2*" u
2-Phase Saturated Liquid from Pressurized Storage - 3.2,3.3
2-Phase Subcooled Liquid from Pressurized Storage - 3.4,3.5
High Volatility Liquid Leaks - 3.6,3.7
Lou Volatility Liquid Leaks - 3.8,3.9
Help /Scroll Vertical Menus <<->/<-»>Scroll Horizontal Menu
/Letter»Select Menu Item Exit Current Menu Exit All Menus
If 'Superfund Release Type' is selected then the menu in
Figure E-26 will appear listing Superfund scenarios.
Figure E-26. Superfund Release Type
File
Chemical Database
r— initial Form of Release
Particulate Matter Release Type
Gaseous Release Type
Liquid Release Type
Quit
Superfund Release type
Workbook Scenario
Help /Scroll Vertical Menus <-«->/<-».>ScroU Horizontal Menu
/Uetter=Select Menu Item Exit Current Menu Exit All Menus
E.5 Determining Maximum Short-Term Ground Level Concentration
Maximum short-term ground level concentrations in TSCREEN
are based on three current EPA screening models (SCREEN, RVD, and
PUFF) that are imbedded in the TSCREEN model and an
implementation of the Britter-McQuaid model. SCREEN is a
Gaussian dispersion model applicable to continuous releases of
particulate matter and non-reactive, non-dense gases that are
emitted from point, area, and flared sources. The SCREEN model
implements all of the single source short-term procedures
contained in the EPA screening procedures document (EPA, 1988a).
This includes providing estimated maximum ground-level
concentrations and distances to the maximum based on a pre-
selected range of meteorological conditions. In addition, SCREEN
has the option of incorporating the effects of building downwash.
The RVD model (EPA, 1989) provides short-term ambient
concentration estimates for screening pollutant sources emitting
E-20
-------
denser-than-air gases and aerosols through vertically-directed
releases. The model is based on empirical equations derived from
wind tunnel tests and estimates the maximum ground level
concentration at plume touchdown at up to 30 downwind receptor
locations. The PUFF model (Petersen, 1982) is used where the
release finite but smaller than the travel time (i.e., an
instantaneous release.) This model is based on the Gaussian
instantaneous puff equation and is applicable for neutrally
buoyant non-reactive toxic air releases. The Britter-McQuaid
model is used for continuous and instantaneous denser-than-air
scenarios.
E.6 Enter/Edit Scenario Data
This section provides a description of the use of the
various keys and data entry procedures.
Data Fields
Data for each scenario is entered in two sections. There is
the scenario input section which contains a unique set of inputs
for each scenario. The user enters this section first and inputs
data. Based-on user data, one of the four models is selected by
TSCREEN, and the user proceeds to the model input section. The
inputs for this section are unique for each model although they
are not unique for each scenario. For certain scenarios there is
no unique scenario input section, and the user proceeds directly
to the model input section. Each input section starts with 'Page
1 of. . . '. A typical data entry window for a scenario input
section is shown in Figure E-27.
Figure E-27. Typical Data Entry Window
Flared Stack Emissions - Scenario 2.1
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 7
Enter a unique title for this data's model run:
RELEASE PARAMETERS
Enter the Emission Rate (Qm), if unknown enter
the boxed variables below to calculate ->
Volume Fraction of Pollutant (Vol) -> ;
Material Flow Rate (V) ->
Molecular Weight of Material Released (Mw) ->
ip X
; : cubic m/s
: g/g-mole
Total Heat Release Rate (Hr) •>
Release Heignt above Ground (Us) ->
,,,?;' g/s
••ip *
; : cubic m/s
: g/g-mole
Help Calculator
Previous Screen Abort
Commands active while editing data fields include:
- Help on current field
E-21
-------
- Calculator
- Return to previous screen
- Abort entry and return to the main menu bar
The keys that can be used for editing while in the highlighted
data entry fields are as follows:
or - toggle insert/overwrite mode (cursor changes
size)
or - delete character at cursor position
<•*-> (left arrow) - move cursor left one character
<-» (right arrow) - move cursor right one character
<*-> (Control key and left arrow) - move cursor left one
word
<-*•> (Control key and right arrow) - move cursor right one
word
- move cursor back one character and delete character
- move cursor to 'beginning of data in field
- move cursor to end of data in field
Valid entry into numeric fields are numbers, minus signs(-), plus
signs(+), a decimal(.), and the letter E or e to stand for
scientific notation (6.02E026 = 6.02e026 = 6.02E+26 = 6.02e+26 =
6.02 x 1026) .
Titles
. An important data field in TSCREEN for rerunning old
scenarios is the Scenario Title field. This field should contain
a unique title for each run. Several ways to make the title
unique are to give the facility name or add example 1, example 2,
etc, or the date and time to the title. This is helpful when the
user wants to retrieve data from a previously entered scenario
run by selecting 'File' from the main menu bar then selecting
'Access Data from Previous Scenario'. The selection window will
appear allowing the user to view the titles of all previously run
scenarios. A previous scenario may be selected to either run
again or update the data for another run. This window is shown
in Figure E-28. The last scenario entered appears at the bottom
of the list.
E-22
-------
Figure E-28. Previously Entered Scenarios
Initial Form of Release
File 1
Chemical Database
Quit
Acce
Acce
Previous Scenario
Johnson WJdset Cowpany RanOOt
Oust E ject i oh Number 21720/92
Cont. Part. Stack Release-Power Plant-1/20/92
Particulate Stack Release
Select Highlighted Run Exit/Mo Select
Up <1> Down Up One Screen Down One Screen
Top Bottom <0el> Delete Run
Press any other key to find a title beginning with that character
From this window a previous scenario's data can be reloaded
by highlighting that scenario's title and pressing the
key or clicking with the mouse. The 'Initial Form of Release'
menu will appear with the highlighted bar on the form of release
of the selected scenario. By selecting the highlighted bar on
the preselected release type, a second menu will appear with the
appropriate scenario name and number highlighted. By selecting
this scenario, the data entry windows of the scenario are
displayed with the data fields filled with the loaded scenario's
data. Menu selections can be changed at any point, but changing
the selections will cause the loaded data to be lost, and the
user will have to retrieve that scenario's data again from the
menu in Figure E-28.
Calculated Fields
Some of the data entry screens have fields that can be input
directly or calculated automatically from certain other
parameters. The alternative parameters will be located inside a
box directly below the unknown parameter. In Figure E-29, the
user did not know the emission rate; therefore, the data fields
in the box were entered. Once all of the boxed variables were
entered, the emission rate was calculated and displayed. If the
screen is reedited and the calculated field is changed then the
other parameter fields making up the calculated value will be
blanked out. If the emission rate is known it can be entered
directly and the program will automatically skip over the
parameter fields in the box.
E-23
-------
Figure E-29. Calculated Field Illustration
- Flared Stack Emissions • Scenario 2.1
Based on user input, SCREEN model has been selected.
SCREEN MODEL INPUTS - Page 1 of 7
Enter a unique title for this data's model run: .
' -
RELEASE PARAMETERS
Enter the Emission Rate (dm), if unknown enter
the boxed variables below to calculate -> &v0t}3S?5 g/s
Volume Fraction of Pollutant (Vol) -> .2 " X
Material Flow Rate (V) -> 4*58 " cubic m/s
Molecular Weight of Material Released (Mw> -> 78,1 g/g mole
«F2>- ?dft
Total Heat Release Rate (Hr) -> 3.346? cal/s
Release Height above Ground (Hs) -> 32 m
Streert A&ort
End of Screen Action
Once data entry on the screen has been completed, the
program presents the user with a chance to visually review the
data entered on the current screen as shown in Figure E-29. The
only active keyboard commands are highlighted at the bottom of
the screen:
- Edit the current screen
- Return to previous screen
- Proceed to next screen
- Abort current scenario and return to main menu bar
Field Sensitive Help
The help facility (see Section E.7.) can be accessed by
pressing the key from any of the selection menus or data
entry fields. After pressing the key a window with help
text will appear to further define or clarify the current data
entry field. The user can then scroll up or down through the
help text or view help for other data fields using the buttons on
the left side of the help window. An example of a help screen is
shown in Figure E-30.
E-24
-------
Figure E-30. Sample Help Screen
Evaporation from Surface Impoundments (Lagoons) - Scenario 3.1
T Emission Rate • Scenarioi 3.1j
« Topics »
Next >
Previous >
Look Up >
See Also
Emission rates from well-mixed aqueous waste in surface
impoundments are described in section 4.3.1 in the
workbook. The following is a simplified screening emission
rate estimate based on parameters described in the
workbook:
E = KCoA
where:
E * emission rate
Co - initial concentration of
waste (g/cubic m)
A = area of impoundment (m1 )
K - equilibrium constant
the chemical in the
Help Calculator Previous Screen Abort
Chemical Look-up Database
The chemical look-up database is a table of chemicals and
their associated parameters that are applicable to TSCREEN.
TSCREEN is initially distributed with only two chemicals. Any
desired chemical and its associated parameters may be added to
suite the specific needs of the user. The chemical database can
be accessed in two ways. First, the chemical database can
selecting 'Chemical Database' from the main menu bar. If this
selection is made the menu shown in Figure E-31 will appear.
Figure E-31. Chemical Database Menu
File
Initial Form of Release
Chemical totafas8« Quit
I Chemical Database
S«srct> ttw Database
Add a Chemical to Database
Help /Scroll Vertical Menus <-«->/<-»>Scrol I Horizontal Menu
/Letter=Select Menu Item Exit Current Menu Exit All Menus
To search the chemical database for a specific chemical,
select 'Search the Database' and a scrollable window appears with
a list of the available chemical names as shown in Figure E-32.
E-25
-------
Figure E-32. Chemical Name List
Chemical Name
CHLORINE
Select Highlighted Chemical Exit/No Select
Up Down Up One Screen Down One Screen
Top Bottom
Press key to find a chemical beginning with that character
The chemical names contained in the database will be
displayed in alphabetic order. The highlighted bar can be moved
directly to first chemical name starting with a certain letter
just by pressing that letter key. The 'Chemical Name' window
will size itself proportionally to the number of chemical names
contained in the database up to the number of chemical names that
can fit on the screen. After a chemical is selected, the
chemical parameters will be displayed.
If 'Search Chemical Database' was selected from the menu in
Figure E-31, the Chemical Database parameter window in Figure E-
33 will appear. If is pressed, the user can edit the data
in any of the fields except the Chemical Name. If is
pressed, the user can delete the chemical that is currently in
the window. If is pressed, the user will return to the
chemical list.
Figure E-33. Chemical Database Parameters
Chemical Data
Chemical Name 86K2ENE
Boiling Point at Ambient Pressure 351 °K
Specific Heat of Liquid
at Constant Pressure '":::: ''V' J/kg "K
at Constant Volume . i J/kg °K
Specific Heat of Vapor
at Constant Pressure ; j/kg °K
at Constant Volume J/kg "K
Molecular Weight 7B..1H^"'; kg/kmol
Latent Heat of Vaporization 5.93865? J/kg
Liquid Density J5787E-5 g cubic m
Critical Temperature SS&ifSH °K
Edit
<0el> Delete
Exit View Screen
If 'Add a Chemical to Database' was selected from the menu
in Figure E-31, the Chemical Data window in Figure E-33 will
appear. A chemical list will not appear. A chemical name must
be entered before any of the other parameters can be entered. If
is pressed, TSCREEN will ask if the new chemical is to be
saved. Then the user will return to the menu in Figure E-35.
E-26
-------
Figure E-35. Chemical Database Parameters for Adding
Chemical Data
Chemical Name " . .. '
Boiling Point at Ambient Pressure.
Specific Heat of Liquid
at Constant Pressure
at Constant Volume
Specific Heat of Vapor
at Constant Pressure
at Constant Volume
Molecular Weight
Latent Heat of Vaporization
Liquid Density
Critical Temperature
J/kg "K
J/kg "1C
J/kg "K
J/kg °K
kg/kmol
J/kg
g cubic m
"K
Up
Down
Exit Add Screen
The second way to enter the chemical database is by
accessing help for a data entry field that is a chemical
parameter. If the user enters the chemical database from a data
entry field, a value from the database can be returned to that
field.. A pointer '*' will appear beside the value that will be
returned. For example, if the user, were in a molecular weight
input field, the user could press , and help for that field
would appear. After pressing to exit the help window, the
chemical list shown in Figure E-32 would appear. The menu shown
in Figure E-31 does not appear if the chemical database is •
accessed through a data entry field. After the user chooses the
desired chemical, the chemical look-up screen would appear as in
Figure E-33. The , , and keys work as described
above when 'Search Chemical Database' was selected from the menu
in Figure E-31. Pressing will exit the chemical database
and return the marked value to the data entry field.
Figure E-36. Chemical Database Accessed from Data Entry Field
Chemical Data
Chemical Name BENZENE
Boiling Point at Ambient Pressure JSt, : °K
Specific Heat of Liquid
at Constant Pressure :: :: J/kg "1C
at Constant Volume J/kg "1C
Specific Heat of Vapor
at Constant Pressure -: :L- J/kg °K
at Constant Volume : ""• : J/kg °K
Molecular Weight »78*12 kg/kmol
Latent Heat of Vaporization 3»953ES J/kg
Liquid Density .SToTE-S g cubic m
Critical Temperature 562..Q9 "K
Edit <0el>0elete Exit/Select Data Exit/No Select
E-27
-------
Calculator
When entering data, a calculator is available on-line to
perform any heeded calculations. The calculator is accessed by
pressing the key from any data entry field. The results of
a calculation can be passed directly from the calculator to the
entry field by pressing the equals <=> key. While in the
calculator a help screen on the calculator's functions can be
accessed by pressing the key. The calculator has several
built-in functions that include memory clear, memory store,
memory recall, square, square root and it. An example of the
calculator is shown below in Figure E-37.
Figure E-37. Calculator
— Evaporation from Surface Impouncknents (Lagoons) - Scenario 3.1
SOURCE PARAMET5
Enter a unique
IMPOUNDMENT TYP
Enter
EMISSION RATE
Enter the Emiss
the box
In
Help
F1
HELP
F2
MC
F3
MS
Ft,
MR
"
•
7
4
1
0
F5
SO
8
5
2
•
F6
SR
9
6
3
S
F7
PI
+
-
*
/
E
g/s
g/cubic m
ra»
n::: Ahnrr
Model Output
Upon completing the last screen of data entry for the
scenario, the command is 'Run Model' and not 'Next Screen'
When the key is pressed, the entered data is saved. The
dispersion model then executes. For computers without math co-
processors, the SCREEN model will execute for 3 to 10 minutes,
the RVD model for 1 to 5 minutes and the PUFF model for 1 to 5
minutes depending on the data and the computer setup on which
TSCREEN is running. The model output will appear on the screen
in a window as shown in Figure E-38.
E-28
-------
Figure E-38. Output Window
Continuous Paniculate Matter Releases from Stacks - Scenario 4.1.1
03-04-9
15:47:0
•** SCREEM-1.2 MODEL RUM ***
*** VERSION DATED 91/10 ***
Continuous Participate Stack Release from Power Plant
SIMPLE TERRAIN INPUTS:
SOURCE TYPE = POINT
EMISSION RATE (G/S) = 1200.
STACK HEIGHT (M) = 20.00
STK INSIDE DIAM (M) = 1.50
STIC EXIT VELOCITY (M/S)= 5.00
STK GAS EXIT TEMP (K) = 400.00
AMBIENT AIR TEMP (K) = 293.00
RECEPTOR HEIGHT (M) = .00
IOPT (1=URB,2=RUR) = 2
BUILDING HEIGHT (M) = 25.00
MIN HORIZ BLDG DIM (M) = 20.00
MAX HORIZ BLDG DIM (M) = 45.00
Alt,
Print
Graph
, , ,
Save to File Exit
The model output can be scrolled line by line up or down by
pressing the up or down arrow keys. The output can be put into a
continuous scroll up or down by pressing the Alt - up or down
arrow key combinations and stopped by pressing any key. The
output can be scrolled a full screen at a time by pressing the
or keys. By pressing the key the output
display will show the top of .the output listing and by pressing
the key the display will show the end of the output
listing.
To get a listing of the output on a printer press the
key. To avoid some common printing problems, before selecting
printed output, make sure that a printer is connected to the
computer, that the printer's power is on, that the printer is on-
line and that there is plenty of paper loaded in the printer. To
save the output data to a file press the key and give a
filename for the output. To get a graph of the concentrations vs
distances press the key.
E.7 Help System
The help system included with TSCREEN is field sensitive.
As a result, when the key is pressed from a data entry field
or from a menu item, help for that field or menu item will appear
in a help window like the one shown in Figure E-39.
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Figure E-39. Example Help Window
Liquid Release Type
A Liquid type release is a release of material that may
immediately evaporate (no pooling results) or may pool
first and then evaporate.
See Also: Release Definition, Pool Definition, Evaporation
Definition
After the entering the help system, the user can access help
for any data entry field or menu item in TSCREEN pressing the
"buttons" on the panel on the left side of the help window.
These buttons can be pressed in three ways:
The user can click on the button with a mouse.
The user can highlight a button and then press to
select that button. To highlight a button, press the
key to first highlight the « Topics » button.
Press again to move to each succeeding active
button on the panel. If a button is not active, its
feature will not be available, and it will be a different
color than the other buttons.
Each button has a letter that is a different color (i.e.,
a "hot-key"). Press that key to select that button.
Each button's function is described below:
« Topics »
If this button is pressed, the table of contents of the help
system will appear in the help window. A portion of the
table of contents is shown in Figure E-40 as it would appear
if « Topics » where pressed from the help window in
Figure E-39. From the table of contents, the user can
scroll to and select any definition in the help system. The
table of contents is organized as follows: 1) help for the
menu items 2) help for the model inputs (SCREEN, PUFF, RVD,
and Britter-McQuaid) 3) help for the scenario inputs in the
order they appear in the workbook and 4) a Glossary of
terms.
Once the topic of interest has been highlighted, press
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or select the « HELP » button by the methods listed
above.
Figure E-40. Help System Table of Contents
File
Access Data From Previous Scenario
Access Model Print Output
Access Model Graphic Output
Quit
Initial Form of Release .
Particulate Matter Release Type
Gaseous Release Type
Release type '
« Help »
Next
If this button is pressed, the next help definition as
listed in the table of contents will appear.
< Previous >
If this button is pressed, the previous help definition as
listed in the table of contents will appear.
< Look Up >
This button is not active when the help window first
appears. To make this button active, mark (i.e., highlight)
a portion of text in the'help window. Text can be marked by
holding the mouse button and dragging the mouse or by
holding down the key and moving the arrow keys.
Once text has been marked, press this button to bring up
help if the marked text is an item in the table of contents.
If the marked text is not in the table of contents, another -
window appears as shown in Figure E-41 that contains a list
of the topics in the table of contents. In this example
"Retrieve" was marked and < Look Up > was pressed. Since
this was not found in the table of contents, a second window
opens and 'Richardson Number Definition' is highlighted
because it is the closest topic alphabetically to
"Retrieve".
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Figure E-41. Look Up Window when Topic Is Not Found
4
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t ropics »
E Next >
: Previous >
: Look Up >
See Also
No help found for Retrieve
Available Help Topics:
Molecular Weight Definition
Neutral Definition
Passive Release Definition
Pool Definition
Reactive Definition
Release Definition
tffiMi*}&Mifiii&miffi&ffi&
i
« Select »
< Cancel >
Slumping Definition «
Temperature of Release Mater|
Two-phase Release Definition!
Scenario
This button is only active if there is a "See Also" list of
topics in the help window. If this button is active and is
pressed a window will appear as shown in Figure E-42 that lists
the topics to cross-reference. Making a selection from this menu
will bring up the help definition for the selected item.
Figure E-42. See Also Example
« Topi cs »
< Next >
< Previous >
< Look Up >
Liquid Release Type
A Liquid type release is a release of material that may
immediately evaporate (no pooling results) or may pool
first and then-evaporate.
Release
Pool' Definition"
Evaporation Definition
lease Definition, Pool Definition, Evaporation :
When a topic is selected from the See Also menu and help for
that topic appears in the help window, the first item of the new
topic's See Also menu contains a reference to the topic from
which the new topic was called. Using the See Also menu from the
new topic, the user can then return to the original topic. For
example, if "Release Definition" was selected from the menu in
Figure E-42, the help definition in Figure E-43 will appear. The
E-32
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first item in the See Also menu for "Release" is "Liquid Release
Type" which the user can select to return to the help definition
for "Liquid Release Type".
Figure E-43. Cross-Referenced Help Item
» Kelp *
::j « Topics » | Release
*-";:
i; < Next >
:* < PrCVIOUS >
?• < Look Up >
Chemicals or pollutants leaving containment, stacks, or
vents.
E.8 Error Handling
If an error occurs while TSCREEN is running a window like
the one shown in Figure E-44 will appear. This window contains
an error message, the FoxPro™ error number, the procedure in
which the error occurred, and the line number in the code at
which the error occurred.
Figure E-44. Error Message Window
WARNING:
Error Number
In Procedure
At line number
The error information above are saved in: ERROR.OUT
Please save this file for use in error diagnosis.
Press any key to continue ...
If an error occurs, data entered up to the point at which
the error occur will be saved. The data can be retrieved by
selecting 'File' from the main menu bar then selecting ''Access
Data from Previous Scenario'. The data will be the last item on
the list with appears. In addition, the error information from
the window in Figure E-44 will be saved in the file "ERROR.OUT".
This file should be saved for error diagnosis. After the user
exits the window shown in Figure E-44, the user will exit
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TSCREEN.
If an error occurs while a Model is running, the ERROR.OUT
file will contain the data that was sent to the Model and the
error message which will appear in the error window that is
displayed. After the user exits the error window that is
displayed when an error in a model occurs, the user will return
to the main menu bar.
E.9 Backing Up Data
The file BACKUP.COM that comes with DOS must be in the DOS
PATH as explained in 2.0 GETTING STARTED. To backup the data
enter the command:
BACKUP X:\TSCREEN\*.* A: /S
where X is the drive letter where the TSCREEN system resides.
Note that it is important .to back up every time data is edited or
added in case of a hard disk failure.
The number of backup disks needed depends upon the amount of
data entered into the system. As more data is entered, more
backup disks will be required to store the data. These disks
must be formatted prior to backing up the data files. Backup
disks should be labeled accordingly and stored in a safe place.
To ward off data corruption, rotating back up disks is
recommended. Rotating backup diskettes consists of 2 or 3 sets
of backup diskettes that are rotated when the backup procedure is
called. " In using a rotating backup procedure you can minimize
the possibility of backing up bad data and having corrupt files
on the system and on the backup disks.
The BACKUP.COM program fits as much data on one disk as it
is'physically capable of storing. If the program is in the
middle of backing up a file it will split it and store the
remaining part of the file on another disk(s). These backed up
files are not DOS compatible files, DO NOT copy them to another
disk, especially NOT to the hard disk. The only way these files
can be used is to first restore them with the DOS RESTORE.COM
program (discussed below). These diskettes are created for
backup purposes only and are to be restored only when the data
files on the hard disk have become damaged beyond repair.
The command to restore the data files is:
RESTORE A: X: /S
where X is the drive letter where the TSCREEN system resides.
Note that the RESTORE.COM file must be in the DOS PATH in order
to execute this program from any prompt. This command should be
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used only when there has been damage done to the data files on
the hard disk!
E.10 Notes on Compiling the Source Code
The procedure described on this page is only for those who wish
to make changes in the source code and recompile it. Only
someone with experience using computers and preferably with
compilers should attempt this procedure.
TSCREEN is written in and compiled with FoxPro™ Version 2 and
Microsoft™ C Version 5.1. One C library was used: INGRAF™
Version 2.10 by Sutrasoft. The program source code is available
from the SCRAM Bulletin Board phone (919) 541-5742. Technical
questions should be directed to Jawad S. Touma; Office of Air
Quality Planning and Standards; Technical Support Division/
Source Receptor Analysis Branch (MD-14)/ Research Triangle Park,
NC 27711, phone (919) 541-5381.
FoxPro™ Version 2.0 or later, C Version 5.1 or later, and
INGRAF™ Version 2.10 or later are necessary to compile the
source code. All of the .PRG (FoxPro™) files and .C (C) files
should be on a hard disk with the following files:
C
CL.EXE
LINK.EXE
MLIBCE.LIB
SLIBCE.LIB
[STRING.H]
[STDIO.H]
-[STDLIB.H]
[PROCESS.H]
[MATH. H]
[DOS.H]
[10.H]
The files in brackets are included with the Microsoft C
compiler
INGRAF
INGRAF.LIB
IGEXTERN.H
Note that you may have to change the path specifications in these
files as well as in the C files. The compilation process will
create: TSCREEN.EXE, GRAPH.EXE
E-35
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TECHNICAL REPORT DATA
(Please read Instructions on reverse before completing)
1. REPORT NO.
EPA-454/R-92-024
3. RECIPIENT'S ACCESSION MO.
4. TITLE AND SUBTITLE
5. REPORT DATE
December 1992
Workbook of Screening Techniques for Assessing
Impacts of Toxic Air Pollutants
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
». PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
Pacific Environmental Services
5001 South Miami Blvd.
Research Triangle Park, NC 27709-2077
11. CONTRACT/GRANT NO.
EPA Contract No. 68-D00124
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards, TSD
Research Triangle Park, NC 27711
Final Report
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
This document revises EPA-450/4-88-009
Technical Representative: Jawad S. Touma
16. ABSTRACT
This workbook provides a logical approach to the selection of appropriate
screening techniques for estimating ambient concentrations due to various
toxic/hazardous pollutant releases. Methods used in the workbook apply to situations
where a release can be fairly well-defined, a condition typically associated with non-
accidental toxic releases. The format of this workbook is built around a series of
release scenarios which may be considered typical and representative of the means by
which toxic chemicals become airborne. For each release scenario, the workbook
describes the procedure to be used and provides an example illustration using the
TSCREEN model. TSCREEN, a model for screening toxic air pollutant concentrations is an
IBM PC-based interactive model, that provides screening techniques for estimating
impact from various air pollutant releases. TSCREEN allows the user to select a
scenario, determine an emission rate, and then apply the appropriate dispersion model
in a logical problem solving approach.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/GrouD
Air Pollution
Hazardous Waste Assessment
Toxic Air Pollutants
Dense Gas
Air Quality Dispersion Model
TSCREEN Model
Dispersion Modeling
Meteorology
Air Pollution Control
123
18. DISTRIBUTION STATEMENT
Release Unlimited
1*. SECURITY CLASS IKtport I
Unclassified
21. NO. OF PAGES
315
20. SECURITY CLASS IPig*)
Unclassified
1PA form 22ZO-1 (Rwr. 4-77)
PREVIOUS EDITIOH IS OBSOLETE
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