
                        DETAILED DOCUMENTATION

                                 FOR

                  USAF TOXIC CHEMICAL DISPERSION MODEL
                          AFTOX VERSION 4.1


                 Capt Clifton E. Dungey, HQ AWS/XTX

                               5 Jan 93


   A.  PROGRAM DESCRIPTION

       1.  Purpose:  The USAF Toxic Chemical Dispersion Model 
(AFTOX) will determine toxic chemical concentrations and give the 
user the option of calculating a toxic corridor, the concentration 
at a specific location, or the maximum concentration and its 
location.

        2.  Application:  AFTOX was developed for real time 
analysis of non-buoyant, toxic chemical releases.  Use of AFTOX is 
governed by AFR 355-1.  AFTOX is written so that Air Weather 
Service (AWS) base weather stations can apply AFTOX to continuous 
or instantaneous, gas or liquid releases from either ground or 
elevated sources.  It can also be applied to heated plumes from 
smokestacks.  AFTOX contains 130 chemicals on file and is able to 
accept additional chemicals.

       3.  Structure:  A detailed explanation of AFTOX is 
contained in AFGL-TR-88-0009 and PL-TR-91-2119.  AFTOX is composed 
of several executable main program files (.EXE files) which are 
chained together for execution purposes.  The program files are 
DSP1.EXE, DSP2.EXE, DSPHP.EXE, and DSP3.EXE.  The file  structure 
and calculations performed by each file are as follows:

           a.  DSP1:  This executable program file determines the 
chemical  properties and meteorological conditions.  Schematic 
representation is  shown in Figure 1.

   Figure 1.  DSP1 Flow Diagram

                           <Station Data>
                                 |
                           <Date and Time>
                                 |
                          <Type of Release> ----- buoyant plume
                                 |                         |
                    instantaneous or continuous            |
                                 |                         |
                          <Chemical Data>                  |
                          _______|_______                  |
                          |  CALCULATE  |                  |
                          | Solar Angle |------------------|
                                 |
                 <Temperature, Wind, Cloud Amount>
           ______________________|__________________________
          DAY                                            NIGHT
           |                                               |
     <Cloud Type>                                          |
   ________|_________                                      |
   |   CALCULATE    |                                      |
   |Solar Insolation|                                      |
           |                                               |
      snow cover? ------yes----->|                         |
           |                     |                         |
           no                    |                         |
           |                     |                         |
    <Ground Moisture> ---------->|<------------------------|
                            _____|_____
                            |CALCULATE|
                            |Heat Flux|
                                 |
                        <Inversion Height>
                _________________|__________________
                |            CALCULATE             |
                |Friction Velocity, 10-m Wind Speed|
                |      Monin-Obukhov Length        |
                       __________|__________
                       |     CALCULATE     |
                       |Stability Parameter| ---->buoyant plume
                                 |                       |
                 <Roughness Length at Spill Site>       EXIT
                        _________|_________          to DSPHP
                        |    CALCULATE    |
                        |Properties of Air|
                                 |
                    chemical properties on file? ------->no
                                 |                       |
                                yes ------gas ---------->|
                                 |                       |
                              liquid                     |
                       __________|__________             |
                       |     CALCULATE     |             |
                       |Chemical Properties| ---->EXIT to DSP2

   Major computations of DSP1 are described as follows:

               (1)  Solar elevation angle:  Determined using date, 
time,  latitude, and longitude.

               (2)  Sensible heat flux:  Determined by one of two 
methods,  dependent on daytime or nighttime conditions.

                     (a)  Daytime:  Cloud amount, temperature, 
ground  moisture, and solar insolation (from solar angle, cloud 
amount, and  cloud type) are used.

                     (b)  Nighttime:  Cloud amount only is used.

               (3)  Turbulence parameters:  Friction velocity, 10-
meter wind  speed, and Monin-Obukhov length are interrelated and 
are determined iteratively from initial estimates based on the 
wind speed, heat flux,  surface pressure, and surface roughness.

               (4)  Stability parameter:  One of two methods of 
computation  are used.

                     (a)  Method 1:  Turbulence parameters 
described in (3)  above are used.

                     (b)  Method 2:  Wind speed and standard 
deviation of the  wind direction are used.

               (5)  Air properties:  Density and viscosity are 
computed from  temperature and pressure.

               (6)  Chemical properties:  For a liquid chemical 
which is in  the data file, the vapor pressure, liquid density, 
and vapor density are  computed from the chemical data, the air 
temperature, and pressure.

           b.  DSP2:  This executable program file determines the 
source  conditions (e.g., emission rate, duration of spill, area 
of spill, and  source strength).  Processing through DSP2 is 
dependent on type of  release.  The air temperature is compared to 
the chemical's boiling point   to determine if it is a gaseous or 
liquid spill.  If the chemical of  interest is not on file, 
default settings may be used or user may input  molecular weight, 
vapor pressure, and whether release is a liquid or gas  to 
determine source strength.  Schematic representation of DSP2 is  
shown in Figure 2.

   Figure 2.  DSP2 Flow Diagram

                                  DSP1
                                    |
                         Source strength known?----no---->|
                                    |                     |
                                    |               AFR 355-1,
                                    |                AWSSUP 1
                                    |                     |
                                    |                 pause for
                                   yes<--------------information
                                    |
                  __________________|_____________
                  |                              |
                 GAS                           LIQUID
           <Height of Leak>                      |
         _________|_________               ______|________
         |                 |              |              |
   continuous     instantaneous     continuous     instantaneous
         |                 |              |              |
<Emission Rate> <Amount Spilled> <Emission Rate> <Amount Spilled>
         |           ______|___           |              |
 <Spill Duration>   |CALCULATE|   <Spill Duration>       |
  _____|_____       |   Area  |      _____|_____         |
  |CALCULATE|       _____|_____      |CALCULATE|      <Area>
  |  Amount |       |CALCULATE|      |  Amount |         |
  | Spilled |       |  Source |      | Spilled |         |
       |            | Strength|           |              |
       |                              <-------->         |
       |                 |       _____|____    |         |
       |                 |      |CALCULATE|  <Area>      |
       |                 |      |  AREA   |    |         |
       |                 |           |         |         |
       |                 |           |      <Pool Temp>->|
       |                 |           |                   |
       |                 |   Evaporation rate=           |
       |                 |       spill rate              |
       |                 |           |                   |
       |                 |  Evaporation time=            |
       |                 |      spill time               |
       |                 |           |                   |
       |                 |    Change area?-yes->|        |
       |                 |       |              |        |
       |                 |      no           <Area>      |
       |                 |       |              |  ______|______
       |                 |       |              |->| CALCULATE |
       |                 |       |                 |Evaporation|
       |                 |       |                 |    Rate   |
       |                 |       |                 ______|______
       |                 |       |                 | CALCULATE |
       |                 |       |                 |Evaporation|
       |                 |       |                 |    Time   |
       |                 |       |                       |
       |---------------->|------>|-->|<------------------|
                                     |
                               EXIT to DSP3

               (1)  Continuous gas release:  Uses the emission 
rate and the  total time of the spill to compute the total amount 
spilled.  The source  strength is the evaporation rate.

               (2)  Instantaneous gas release:  Uses the amount 
spilled and  air density to determine the initial volume of the 
spill.

               (3)  Continuous liquid release:  The evaporation 
rate into the atmosphere is the source strength.  If the area of 
the spill is known, it is used to determine the evaporation rate.  
If the area is unknown, an area is calculated assuming a pool 
depth of 1/4 inch.  For example, 1 cubic foot of liquid will cover 
a 48 square foot area if allowed to spread out to a depth of 1/4 
inch over a flat surface.  Then the emission rate is set equal to 
the evaporation rate based on the  calculated area.  If this 
calculated area appears unreasonably large as compared with the 
observed spill, the user may input a smaller area  which will give 
a new evaporation rate.  An alternate method exist for  chemicals 
without full data information.  Evaporation rate is determined 
using spill area, pool temperature, chemical molecular weight, and 
vapor pressure.  If variables are unknown, the model assumes the 
worst case and the evaporation rate is set equal to the emission 
rate.

               (4)  Instantaneous liquid release:  Uses the amount 
spilled, area covered, chemical, and air properties to compute the 
evaporation rate.  The source strength is set equal to the 
evaporation rate.  The amount spilled and the evaporation rate 
determine the total evaporation time.  The alternate method listed 
in (3) above is used if chemical data is not available.

           c.  DSPHP:  This executable program file determines the 
source conditions for a buoyant plume from a stack (e.g., emission 
rate, duration of spill, height of spill).  Source strength is set 
equal to the emission rate.  As shown in Figure 3, atmospheric 
conditions determine processing through the module.

   Figure 3.  DSPHP Flow Diagram

                              DSP1
                                |
                        <Molecular Weight>
                                |
                         <Emission Rate>
                                |
                   effluent still being emitted?----no--->|
                                |                         |
                               yes                 <Elapsed time
                                |                   of emission>
                                |                         |
                         <Stack Height>----------<--------|
                                |
                   Stack height above inversion?---yes--->|
                                |                         |
                               no                         |
                                |                        END
                      <Gas Stack Temperature>
                                |
                        <Volume Flow Rate>
                                |
                         _______|_______
                         |  CALCULATE  |
                         |Buoyancy Flux|
                         _______|_______
                         |  CALCULATE  |
                         | Equilibrium |
                         |  Distance   |
                         _______|_______
                         |  CALCULATE  |
                         | Equilibrium |
                         |   Height    |
                                |
                    ____________|___________
                    |       CALCULATE      |
                    |Effective Plume Height|
                                |
                     effective height greater
                      than inversion height? ---no-->|
                                |                    |
                               yes                   |
                      __________|___________         |
                      |Set Effective Height|         |
                      |to Inversion Height |         |
                                |                    |
                            EXIT TO DSP3 <-----------|

               (1)  If the stack height is above the inversion, 
then the program terminates since surface input meteorological 
conditions most likely do not apply above the inversion.

               (2)  Buoyancy flux:  It is determined using the air 
temperature, gas stack temperature, volume flow rate, and 
gravitational acceleration.

               (3)  Unstable or neutral conditions:  The buoyancy 
flux is used to compute the distance downstream where the 
equilibrium height is reached.  This distance, the buoyancy flux, 
and wind speed determine the equilibrium height.

               (4)  Stable conditions:  The buoyancy flux, wind 
speed, and potential temperature lapse rate (based on the degree 
of stability) are used to compute the equilibrium height.  
Downwind distance where equilibrium height occurs is not needed.

               (5)  Effective plume height:  This is equal to the 
sum of the equilibrium height and stack height above ground.  
Model assumes gas is released at the effective height for 
dispersion calculations.  If the effective height is above the 
inversion height, it is set equal to the inversion height.  This 
is a conservative approach for calculating ground concentrations.

           d.  DSP3:  This executable program file computes the 
toxic corridor (determined by concentration), concentration at a 
given location and time, or maximum concentration and location, 
and outputs the results.  The type of output determines the 
processing through the file, as shown in the flow diagram of 
Figure 4.

   Figure 4.  DSP3 Flow Diagram

                          DSP2 or DSPHP
                               |
                 <Concentration averaging time>
                               |
               <Elapsed time since start of spill>
        _______________________|________________________
        |                      |                        |
     OPTION 1               OPTION 2                 OPTION 3
(toxic corridor)     (point concentration)   max concentration)
        |                      |                        |
 <Concentration             <Height>                 <Height>
   of Interest>                |                        |
        |             <Downwind Distance>               |
     <Height>        <Crosswind Distance>               |
        |                      |                        |
 |----->|--------X=X+DX------->|<--------X=X+DX---------|<-|
 |                      _______|_______                    |
 |                      |  CALCULATE  |                    |
 |                      | Dispersion  |                    |
 |   |--Y=Y+DY--------->|Coefficients |                   no
 |   |                  |     and     |                    |
 |   |                  |Concentration|                    |
 |   |        |<-----------|   |   |----------------> maximum?
 |  no        |                |                           |
 |   |  equals contour         |                           |
 |   |<-concentration?         |                          yes
 |            |                |                           |
 |           yes               |                           |
 |            |                |                           |
 |    plot concentration       |                           |
 |            |                |                           |
 |<--no--plot complete?        |                           |
              |                |                           |
             yes               |                           |
              |                |                           |
           OUTPUT           OUTPUT                      OUTPUT
        contour plot     concentration             concentration
      max distance for         |                   and distance
        each contour           |                           |
              |                |                           |
           CHANGE?          CHANGE?                    CHANGE?
      met conditions    spill duration            spill duration
     source conditions      location                   height
           height            option                    option
          contours             |                           |
       spill duration          |                           |
concentration averaging time   |                           |
           option              |                           |
            scale              |                           |
            time               |                           |
              |                |                           |
              |--------------->-<--------------------------|
                               |
                             EXIT

               (1)  Chemical concentration computations are 
identical for each output option.  Dispersion coefficients are 
determined using the stability parameter and the surface roughness 
length.  Concentration is then determined using the dispersion 
coefficients, elapsed time of the spill, wind speed, source 
strength, source height, and inversion height.  Locations are 
determined using an X-Y coordinate system with the origin at the 
source site and oriented so the X-axis is in the downwind 
direction and the Y-axis is perpendicular in the crosswind 
direction.

               (2)  Option 1:  This contours user-specified 
concentration (up to 3 contours) and plots the toxic corridor for 
the lowest concentration requested.  At each distance along the X 
axis, the model computes the concentration and checks to see if it 
exceeds the user specified concentration.  If so, concentrations 
are computed for increasing values of Y until the position of the 
user specified concentration is located.  This location is plotted 
and the procedure is repeated at the next incremental value of X.  
When the plot is complete, the maximum distance for the 
concentration of interest is displayed.  The entire process is 
then repeated for the next specified concentration.

               (3)  Option 2:  This outputs the concentration at a 
user specified location (defined by the height, downwind and 
crosswind distances).

               (4)  Option 3:  This outputs the maximum 
concentration and its distance from the source for a user 
specified height.  Due to model assumptions that the maximum 
concentration will be along the X-axis, concentrations are 
calculated for increasing values of X until the maximum is 
located.

               (5)  At the completion of each option, the user may 
change the following input data:

                     (a)  Option 1:  time, meteorological 
conditions, source conditions, scale, concentration averaging 
time, elapsed time since the start of the spill, contours, height 
of interest, and output option.

                     (b)  Option 2:  elapsed time, location, and 
option.

                     (c)  Option 3:  elapsed time, height, and 
option.

   If the scale on option 1 is changed, the plume is replotted.  
For all other input changes, AFTOX recycles to the point where the 
data is input while holding all other data constant and 
reaccomplishes all computations which require the changed data.

       4.  Files Used:  The files used and their functions are 
listed in Tables 1.  Multiple files are used due to storage 
limitations of the GW-BASIC(tm) compiler.  CHAIN statements are 
used to link the files.

             Table 1.  Files and functions for AFTOX Version 4.1
   -------------------------------------------------------------
   Program Files:
     AFTOX.EXE     3 Nov 92     Introduction
     DSP1.EXE      2 Nov 92     Defines chemical properties and
                                meteorological conditions
     DSP2.EXE      2 Nov 92     Defines source conditions
     DSPHP.EXE    27 Oct 92     Defines buoyant plume source
                                conditions
     DSP3.EXE      2 Nov 92     Computes hazard area, concentra-
                                tions, and outputs results

   Data Files:
     SD.DAT                     Station data
     CH.DAT                     Chemical data
     AFT.DAT                    Stores all input and output data
     CONCXY.DAY                 File for storing x and y positions
                                of concentration contour
     DEVICE.DAT                 Contains information on computer 
                                and screen type.

   Ancillary Files:
     SETUP.EXE    26 Dec 90     Established computer and screen
                                type
     SDFIL.EXE     1 Aug 92     Changes data in station data file
     CHFIL.EXE    31 May 91     Changes data in chemical data
                                files

   Supporting Files:
     BRUN20G.EXE                GW-BASIC(tm) Compiler Run-time 

   Library
     PSCMPI.COM                 Utility for MPI printer
     PSCMX80.COM                Utility for MX-80 printer
     PSCOKI.COM                 Utility for OKIDATA printer



   B.  GENERAL INFORMATION

       1.  Version:

           a.  This detailed documentation describes Version 4.1.

           b.  AFTOX Version 4.1 is designed to run on a Zenith Z-
248 microcomputer, equipped with EGA video, running the Microsoft 
MS-DOS(tm) 3 operating system.  It may operate on other true IBM-
PC compatibles using EGA video and MS-DOS(tm) 3.

           c.  AFTOX Version 4.1 also runs on the Zenith Z-180-
series laptop microcomputers, equipped with CGA video, running the 
Microsoft MS-DOS(tm) 3 operating system.  Version 4.1 may operate 
on other true IBM-PC compatibles using CGA video and MS-DOS(tm) 3, 
such as the Zenith Z-150 series.  Version 4.1 will not run on the 
Zenith Z-100 microcomputers, which are not true IBM compatibles.

       2.  Language Used:  Microsoft GW-BASIC(tm) programming 
language.  The Microsoft GW-BASIC(tm) compiler has been used to 
prepare the executable program files (.EXE files) from BASIC 
source code files (.BAS files), and the executable files are 
provided to the user, so no BASIC compilation or interpretation is 
needed to run AFTOX.  The version of AFTOX described here is the 
version dated Jan 1993.  File creation dates of the executable 
files directly related to AFTOX are given in Table 1 above.

       3.  Number of lines of code in Version 4.1:  There are a 
total of 3257 lines of source code, subdivided among the program 
files as follows:

                          Lines of
           Module     BASIC Source Code     Executable Code

           AFTOX           115                 AFTOX.EXE
           DSP1            889                 DSP1.EXE
           DSP2            728                 DSP2.EXE
           DSPHP           163                 DSPHP.EXE
           DSP3           1449                 DSP3.EXE

       4.  Memory and Disk Storage Requirements:  Executable code 
and documentation files are contained on one 5 1/4" double-sided, 
double-density floppy diskette.

       5.  Peripheral Requirements:  One 5 1/4" floppy disk drive 
and a dot matrix printer if hardcopy contour plot is desired.

   C.  TECHNICAL BACKGROUND

       1.  Scientific Theory:  The basic equation used by AFTOX 
for dispersion is the Gaussian puff equation.  The equation 
assumes that the material is conserved during transport and 
diffusion, and further assumes that the distribution of 
concentration within the puff is Gaussian.  Horizontal and 
vertical dispersion parameters are contained within the Gaussian 
puff equation and are used to statistically estimate the 
dispersion of the plume.  Determination of the stability and the 
chemical source strength are based on accepted scientific 
theories.  Refer to AFGL-TR-88-0009 or PL-TR-91-2119 for a 
detailed description of the scientific theory used by the model.

       2.  Equations and Algorithms:  All equations, with 
variables and constants, are listed and defined in AFGL-TR-88-
0009.

       3.  Accuracy and Limitations:  AFTOX has wide 
applicability.  Unlike many methods developed for specific 
situations, AFTOX can be used equally for all atmospheric 
stability conditions and release scenarios.  However, caution must 
be used in interpreting the results.  Although experience has 
shown that Gaussian equation models are best suited for most 
applications, one of their limitations is that calculated 
distances for concentration values are average values.  In order 
to alleviate this potential problem, 90 percent confidence level 
contour (i.e., the toxic corridor) is given.  The toxic corridor 
is plotted for all types of releases and represents, to the 90% 
confidence level, the furthest extent of the chemical 
concentration requested by the user.

   D.  PROGRAM MAINTENANCE

       1.  Conventions:  AFTOX is a fully interactive, user-
friendly program.  Default responses to AFTOX prompts and 
questions are displayed to the user in brackets.  No input other 
than <RETURN> (the <ENTER> or <RETURN> key on the microcomputer 
keyboard) is required to accept these responses.  All other input 
is done by typing in a response, followed by <RETURN>, to 
questions asked interactively by the program.

       2.  Variable Names:

 Variable      Definition

 A         area of spill (m2 or ft2)
 AD        liquid density coefficient
 ALB       albedo
 AMW       molecular weight of stack affluent
 ANGMAT    wind direction adjustment for plot
 AO        flag for (1) print or (2) save/print
 ASP       aspect ratio for plot
 AT        concentration averaging time (min)
 BD        liquid density constant
 BR        vapor pressure constant
 CC        cloud category (1-high 2-middle 3-low)
 CHM$      chemical name
 CLOUD     cloud amount in eighths
 CMIN      smallest concentration of interest (mg m-3)
 CMTC      convective mass transfer coefficient (m/s)
 CONC      concentration at a given point (mg m-3)
 CONCEN    concentration at a given point (ppm)
 CONCI(I)  array of concentrations to plot (mg m-3)
 CONCP(I)  array of concentrations to plot (ppm)
 CONCMI    minimum concentration (mg m-3)
 CONCMX    maximum concentration (mg m-3)
 CONCON    concentration conversion factor
 CR        vapor pressure constant
 CSA       cosine of ANGMAT
 CT1       lag that allows user to back up to inversion height
           input
 DFT       difference between Greenwich and local standard time
 DIFUS     diffusion coefficient (cm2/s)
 DLIQ      chemical liquid density (g cm-3)
 DTE$      date
 DVAP      chemical vapor density (g cm-3)
 DW        ground moisture (1-dry 2-wet)
 DX        downwind distance increment (km)
 DZ        buoyant plume height above stack (m)
 EOK       energy of molecular interaction (J)
 F         buoyancy flux (m4 s-3)
 FAK       DX factor
 G         soil heat flux (W m-2)
 H         height of leak or effective emission height (m)
 HET       station elevation (m)
 HF        sensible heat flux (W m-2)
 HIFT      height of inversion base (ft)
 HINV      height of inversion base (m)
 HS        stack height (m or ft)
 HTCONV    convective heat transfer rate (W/min)
 HYGFAC    hydrazine factor used in alternate evaporation formula
 ISTAT     spill type
 IUCON     code for concentration units (1-mg m-3 2-ppm)
 IUNCO     flag for chemical mol.  wt.  (0-known 1-unknown)
 IUNIT     flag for units used (1-metric 2-English)
 K         total no.  of overlapping puffs for given location
 LA        station latitude
 LO        station longitude
 LX        natural log of X
 MP        mass of pollutant per puff (g)
 MU        dynamic viscosity (g/cm-s)
 MW        molecular weight of chemical
 MWA       molecular weight of dry air
 N         station number in SD.DAT
 NN        chemical number in CHEM.DAT and CH.DAT
 NNNN      number of contour plots
 NP        number of puffs/min
 NS        flag for new scale
 NU        index number for spilled chemical
 NUM       station number of interest
 OPT       option number for output
 OPTN      sigma theta flag (1-unknown 2-known)
 PC        critical pressure (atm)
 PRES      atmospheric pressure (mb)
 PRT       flag for printing contour plot (1-printout requested)
 Q         net radiation at surface (W m-2)
 QPIPE     emission rate for continuous spill (g/min)
 QSPO      evaporation rate for instantaneous liquid spill (g/min)
 QSS       source strength (g/min)
 RATE      the kernal to be integrated to find concentration
 RCONS     gas constant for dry air (erg/mol K)
 RENL      Reynolds number for instantaneous liquid spill
 RENNL     Reynolds number for laminar flow
 RENNT     Reynolds number for turbulent flow
 RHO       air density (g m-3)
 SAN       angle of safety zone (deg)
 SCALE     scale of contour plot (km or mi)
 SCN       Schmidt number
 SHNL      Sherwood number
 SIG       effective diameter of molecule (A)
 SIGTH     sigma theta (standard deviation of wind direction)
 SIGZ      vertical diffusion coefficient before roughness
           correction
 SN$       station name
 SOLAL     solar angle (deg)
 SR        solar radiation factor
 STB       stability parameter
 STBV      vertical stability parameter
 SX        horizontal diffusion coefficient = SY
 SY        horizontal diffusion coefficient
 SZ        vertical diffusion coefficient
 T         elapsed time since start of spill (min)
 TA        air temperature (C)
 TAK       air temperature (K)
 TB        chemical boiling point (K)
 TC        chemical critical temp (C)
 THETA     angle of tic mark (deg)
 TMSP      total mass spilled (g)
 TNU       total number of chemicals listed in CHEM.DAT and CH.DAT
 TP        pool temperature (C)
 TPUFF     total number of puffs
 TRAVT     travel time to X+4SX (s)
 TRAVTI    travel time to X-4SX (s)
 TS        gas stack temperature (C or F)
 TTSP      total time of spill (min)
 TTT       flag in DSP3 for changing parameter
 TW(1)     time weighted average exposure limit (ppm)
 TW(2)     time weighted average exposure limit (mg m-3)
 TW(3)     short term exposure limit (ppm)
 TW(4)     short term exposure limit (mg m-3)
 U         wind speed at 10 m height (m/s)
 UU        wind speed at height ZW (m/s)
 U9        flag indicating new met conditions have been entered
 VC        chemical critical volume (cm3/g-mole)
 VF        stack volume flow rate (m3/min or ft3/min)
 VISCK     kinematic viscosity of air (cm3/s)
 VP        chemical vapor pressure (atm)
 WAT       wind averaging time (min)
 WD        wind direction (deg)
 WDTHL     width of spill assuming laminar flow (m)
 WDTHT     width of spill assuming turbulent flow (m)
 WWIDTH    width of spill (m)
 X         downwind distance (km)
 XMX       maximum distance for a given concentration (km)
 XO        initial downwind distance (0.1 km)
 XS(I)     X position of current concentration contour
 XS1(I)    X position of contour 1
 XS2(I)    X position of contour 2
 XS3(I)    X position of contour 3
 XST       equilibrium downwind distance for buoyant plume (m)
 XY        X + virtual distance
 Y         crosswind distance (m)
 YO        initial crosswind distance (m)
 YS(I)     Y position of current concentration contour
 YS1(I)    Y position of contour 1
 YS2(I)    Y position of contour 2
 YS3(I)    Y position of contour 3
 YSM(I)    = -YS(I)
 Z         receptor height (m)
 ZO        spill site roughness length (cm)
 ZOO       wind site roughness length (cm)
 ZW        height of wind measurement (m)

       3.  Guidelines to Assist Validation:  AFTOX has been 
through several revisions based upon technical evaluations and 
user comments from field testing.  HQ AWS/XTX has reviewed the 
software and has found the versions described in this document 
technically sound.

       4.  Error Handling:  During revisions and field testing, 
errors and possible problem areas were identified and corrected.  
All problems identifiable at this level of testing have been 
accounted for.  It is not possible to test all possible 
paths/options in programs as complicated as this one; instead, the 
operationally most common paths/options are tested and asymptotic 
input values are submitted.  Some errors may have gotten through 
our testing.  If errors are detected during operational use, they 
should be brought through channels to the attention of:

           HQ AWS/XTX
           102 W. Losey Street, Room 105
           Scott AFB IL 62225-5206
           (DSN 576-4598)

       5.  Pseudocode and File Structure:  See schematic 
representation in section A.3 for illustration of structure and 
processing sequence.

       6.  Special Maintenance Considerations:  none

   E.  OTHER INFORMATION

       1.  Security Requirements:  none

       2.  Privacy Act Considerations:  none

       3.  Copyright Information:  AFTOX is written in compiled 
Microsoft GW-BASIC(tm).  The executable (filename.EXE) program 
files result from compilations of GW-BASIC(tm) source code and 
hence require the GW-BASIC(tm) Compiler Run-time Library 
(BRUN20G.EXE) to execute.  Under special agreement with Microsoft, 
the GW-BASIC(tm) Compiler Run-time Library is distributed with 
AFTOX.  The resulting distribution diskette carries external 
markings, and the executable code displays a message to the effect 
that "Portions (C) Copyrighted Microsoft Corp (1986)."  The 
"portions" referred to are, of course, the GW-BASIC(tm) Run-time 
Library (BRUN20G.EXE), which cannot be further distributed except 
as a member of the AFTOX distribution software.

   F.  ADMINISTRATIVE DETAILS

       1.  POC:  HQ AWS/XTX
                 102 W. Losey Street, Room 105
                 Scott AFB IL 62225-5206
                 (DSN 576-4721)

       2.  Configuration Manager:  AWS/SCR

   This program has been validated and satisfactorily performs the 
function for which it was designed.  It is approved for release to 
all government agencies and supported contractors.

APPROVAL AUTHORITY___________________________DATE__________________
