Program description

Dispersion of heavy gas emissions by accidental releases
according to the guidelines VDI 3783 part 1 and 2

Program description


1. Overview
2. Introduction

2.1 Installation
2.2 Files
2.3 Integrated help and manual

3. Input data

3.1 List of pollutants
3.2 Course of emission
3.3 Parameter part 2
3.4 Parameter part 1
3.5 List of receptor points
3.6 Coupling of the models

4. Computation and results

4.1 Calculation of the ambient air concentrations
4.2 Computation log
4.3 Report output
4.4 Graphic output of the ambient air concentration course

5. Operation

5.1 Within the forms
5.2 Within the tables
5.3 Within the graphics

6. Problem solving and compatibility
7. Glossary


Dispersion areas types I - XXV

See Document List

1. Overview

This program is an integrated implementation of the guidelines VDI 3783 part 2 (dispersion of heavy gases in surrounding areas of the source) and VDI 3783 part 1 (dispersion of light gases as well as heavy gases in greater distance from the source).

Therefore, in a simple way, ambient air concentrations (including the temporal courses), even for heavy gases for receptor points in any distance to the source can be calculated. In the close range of the source before the coupling point, it will be calculated according to the guideline VDI 3783 part 2; in the range beyond the minimal permissible receptor point distance, according to VDI 3782 part 1. The section between the coupling point and the minimal receptor point distance will be interpolated logarithmically (part 2, chapter 3.7).

Calculations for numerous materials and receptor points can be executed in one course.

The results of the calculation can be printed as report text or processed in other programs.

A graphic with the curve family of the ambient air concentration courses can be printed or transferred to other programs.

If the related input form has been modified, the calculation results will be deleted.

The demo is protected by several blocked entry fields for source data.

2. Introduction

2.1 Installation

Just start the installation program and follow instructions.

If desired, change the language in the menu Options.

The program can be started by executing pk_3783.exe. For simplification, a link to a user defined program group has been produced during the installation.

2.2 Files

The parameter settings of an project are stored in one project file. The selection of a set of data (Files) or the input of appropriate data is required to access further program functions.

Functions for all necessary file handlings are available in the file manager:

New Creates a new project with the name NONAME in which data can be entered. It can be saved under a new project name. (File/ Save As)
Open In this form, projects can be opened.
Save Saves all files associated with a project. Overwrites without prompting, except when no name is given.
Save as Saves all files associated with a project. The project name can be chosen or entered in a form. If one of the files already exists, the form will ask you if you want to overwrite.

From Version 6 on only projects are stored in a single project file with the extension 3783. Below stated old format can be read still.

Before Version 6. For each project, a set of files with different extensions and the same name (the project) will be put into the current data path by the file manager and administered from there:

*.STI Input data
*.STO Log
*.STS List of the pollutants
*.STA Receptor point list
*.STE Emission course
*.STP Some Results

These files (except *.STP) are simple ASCII-format text files.

The samples of the appendix B of the guideline VDI 3783 part 2 are offered with the project name BSP_1_1 to BSP_3, as well as a sample with a number of materials and receptor points with the name BEISPIEL.

2.3 Integrated help and manual

A context-sensitive help is integrated inside the program. It can be pulled up at any location in the form by pressing the function key "F1". In the help screen, if necessary, highlighted cross references (links) are interspersed, which, by clicking on them, provide more detailed information.

Under App-Config one can override the default Browser with a line like Browser=c:\....\firefox.exe. This is e.g. useful for Wine under Linux.

3. Input data

3.1 List of the pollutants

In the cases in which the exhaust volume rate and the material concentration are known, a complete list of maximal 30 materials can be processed in one calculation course. For each material, the mass flux is calculated from exhaust volume rate and concentration.

If only the mass flux (and the heat tinting) is known, it doesn't make sense to execute the calculation for several materials. These parameters are defined in the course of the emission and are, as a rule, only valid for one material.

Rows can be inserted or deleted in the table with the function keys of the editor.

The following inputs are to be inserted in the columns of the material table:

  • Name of a pollutant
    It can be selected from a list which is stored under the name set on top of the form.
  • Norm density (1013 hPa, 273.15 K) of the gas in kg/m3.
  • For heavy gases the density defines the connecting of the heavy gas model
    For gases lighter than air, a mechanical lift can occur (if it exceeds the thermal lift) which enters the effective source (VDI 3783 part 1 chapter 5). For air, 1.295 kg/m3 is valid.
  • Boiling point (at 1013 hPa) of the gas in °C.
    The boiling point determines the process for liquefied gases (VDI 3783 part 2 chapter 3.3).
  • Lower flammability limit (UZG) of the gas in Vol.%.
  • The material concentration in g/m3. This input is evaluated only if the mass flux is to be calculated from concentration and exhaust volume rate (checkbox for emission course in the form).

The following derived quantities are also indicated:

  • Information for the connecting of the heavy gas model with the values:
    "not required" for: heavy gas model not required
    "spontaneous" for: heavy gas model with instantaneous emission
    "continuous" for: heavy gas model with continuous emission
  • Flammability distance for mean and worst dispersions in meters. For a material concentration of 1 Vol.% on the ambient air concentration location (UZG = 1%), these distances correspond to the coupling distances for the models according to part 1 and 2.
  • Characteristic length in meters.

The list of the pollutants is stored as ASCII files with the extension STS

For materials which are selected from the list, the first three parameters are set to default values.

The selection list must be an ASCII table with a maximum of 50 rows and the following line by line structure:

Material alpha numerical characters
Norm density in kg/m3 numerical
Boiling point in °C numerical
Lower flammability limit(UZG) in Vol.% numerical

The numerical inputs are unformatted, must use the dot as the decimal character and may contain only the characters '0'-'9' and '-' and must be separated by a blank.

The file STOFFE.utf8.DAT comes with the program and contains the material list from the guideline VDI 3783 part 2.

see Form List of the pollutants

3.2 Emission course

The emission course includes a list of maximal 20 emission sections with the parameters: duration, exhaust volume rate, temperature, heat emission and, if necessary, mass flux.

Rows can be inserted or deleted in the table with the function keys of the editor.

The following columns define the emission course:

  • The duration of an emission course in seconds.
  • The exhaust volume rate in m3/s. A newly defined exhaust volume rate changes the heat emission.
  • The temperature of the emitted gas (process temperature) in °C. For heavy gases the temperature determines the specific weight of the gas. A newly defined temperature changes the heat emission.
  • Heat emission in MW. Calculations according to part 1 (if enabled in the appropriate form) use the heat emission to determine the effective source.
  • By modifying the inputs in the columns, exhaust volume rate or temperature, the heat emission will be calculated again. This can be overwritten in the appropriate column.
  • Mass flux in g/s. Depending on the switch setting in the top section of the emission table, the mass flux will be defined by exhaust volume rate and concentration (the columns mass flux will be blocked) or set explicitly.

For calculations according to VDI 3783 part 1, the heat tinting determines the lift of the gas plume. For each emission section (light gases), it will be checked if the temperature equivalent, derived from the density (VDI 3783 part 1 equations 18a and 18b), results in a higher heat emission. The essential lift effect will be used for the calculation of the plume height.

The emission course is stored as an ASCII file with the extension STE

see Form Emission course

3.3 Parameter part 2

For the definition of a calculation according to part 2, the following data is to be entered in a form:

  • With a button, a calculation according to part 2 can be inserted before a dispersion calculation according to VDI 3783 part 1, if the criterions, formulated in part 2, require it.
    The output of the results are influenced by this button.
  • Information for the type of releases and dispersion areas can be selected from a list.

C. f. Form Parameter of the calculation according to Part 2 and dispersion areas.

3.4 Parameter part 1

For the definition of a calculation according to part 1, the following data is to be entered in a form:

  • Any text can be entered, it will appear on the print-out (Report) of the ambient air concentration calculation.
  • The height of the source's top edge above the ground in meters.
    The source height (according to VDI 3783 part 1) must not exceed ground roughness z0
  • The expansion of the source in dispersion direction in meters.
  • The horizontal expansion of the source right-angled to the dispersion direction in meters.
  • The vertical expansion of the source in meters.

For dispersion calculation with connected heavy gas calculation, the source height and expansion are meaningless. On the coupling point these values are always 0 meters.

  • The average vicinity building in meters.
    In cases where calculated with an inversion barrier layer, it must not stay below the value of the vicinity building.
  • Select a type of terrain from a list.
    The type of terrain determines the effective roughness length according to VDI 3783 part 1 chapter 4.1.
  • Button for consideration of the waste gas plume rise, if the heat tinting of the gas doesn't exceed the set threshold value.
    For dispersion calculations with set heavy gas calculation, the plume rise always should be switched off. Otherwise it is assumed that the emission temperature still exists at the coupling point.
  • Threshold value for the heat tinting of the waste gas plume (in MW), from the moment that a rise is to be considered, if the switch was set.
    If the emission is not constant, the section with the highest heat tinting determines the handling of the entire emission course.
  • Switch to consider the inversion barrier layer for the calculation of the concentration under mean dispersion conditions.
  • Select the dispersion category for mean dispersion condition from a list.
  • Wind velocity under mean dispersion conditions in m/s in a height of 10 m.
  • Puff resolution in % as abort criterion.
  • The emissions of an emission section (according to the model VDI 3783 part 1) are released in a form of temporal successive instantaneous missions (puffs). The time distance between the puffs will be gradually decreased, until the variation in the result (ambient air concentration) or the three-dimensional density of the puffs falls below a threshold value.
    The abort criterion indicates at how many percent of the result variation or of the puff distance regarding to 10*sigma_y, the iterative calculation should be finished.
    In the guideline VDI 3783 part 1, only the first criterion (result variation) is known and therefore a threshold of 5% is set. This might be too high, which can be noticed by the irregularities in the ambient air concentration course.
    The second abort criterion was presented to keep the calculation time in an acceptable scale.
  • Number of steps:
    A lower and an upper limit of the admission time is defined for a receptor point (according to chapter 1 of the guideline VDI 3783 part 1).
    In this interval for the calculation and illustration of the ambient air concentration course, equidistant steps are set.
    By the number of steps, the calculation accuracy increases at the expense of the calculation time. The calculation time is proportionally dependent to the number of steps.
  • A calculation for mean dispersion conditions always will be executed.
    With this switch, the clearly more time-consuming calculation for the most extreme dispersion situations can be enabled here.
  • Switch for output of the ambient air concentration course to the calculation log.
    When this switch is set, a graphic illustration of the ambient air concentration course is possible.

see Form Parameter of the calculation according to Part 1

3.5 Receptor point list

Coordinates of maximal 20 receptor points can be set in a table.

Rows can be inserted or deleted in the table with the function keys of the editor.

The receptor point data is stored as an ASCII file with the extension STA.

see Form Receptor point list

3.6 Coupling of the models

The coupling of the models (part 2 for heavy gases and part 1 for light gases) is described in the guideline part 2 .

In the range between the coupling point and the closest permissible receptor point for the light gas dispersion will be interpolated logarithmically (according to chapter 3.7, part 2).

To determine the maximum concentration of a receptor point in the coupling range, the concentration will be interpolated between the maximum value at the coupling point and the closest receptor point.

The interpolation of the ambient air concentration course in the guidelines is not regulated explicitly. A linear temporal interpolation between the ambient air concentration interval at the coupling point (equals, chronologically staggered, the duration of the emission) and the admission time (according to part 1, chapter 1) on the closest receptor point is implemented. Both time intervals are set with the number of equidistant steps; the ambient air concentrations are interpolated between these steps.

The emission course on the coupling point equals, chronological staggered, the emission course on the source. This is provided for in the guideline for continuous and temporally variable emissions (part 2, chapter 3.7).

4. Computation and results

4.1 Calculation of the ambient air concentration

For the list of pollutants and receptor points, ambient air concentrations are calculated. The necessary number of ambient air concentration calculations is time critical in the first place.

The mean dispersion situation requires one calculation step which is always executed.

The determination of the worst dispersion situation requires, without rise, 3 calculation steps (for all dispersion categories with 1 m/s wind velocity), and, with rise, 23 calculation steps (the winds 1 m/s to 6 m/s in stable dispersion, 1 m/s to 10 m/s in neutral dispersion and 1 m/s to 7 m/s in unstable dispersion).

The calculation time is not considerably affected by the number of steps of the ambient air concentration calculation.

4.2 Computation log

The log of the ambient air concentration calculation is a text file with the extension STO which can be displayed under the menu item Log.

The relevant input data, the dose and the maximum concentration are shown for each calculated dispersion situation. The ambient air concentration courses are tabulated in the set content.

4.3 Report output

A prepared form of input data and the calculation results can be found under the menu items Report - "Source data" and Report - "Result" and can be printed.

The form and the content of the report output are controlled by the inputs in the form Report - "Parameter".

An element can be selected from the receptor point list and/or the list of sources. The following inputs can be set in the result report:

  • maximum concentration under mean dispersion conditions
  • maximum concentration under worst dispersion conditions
  • dose under mean dispersion conditions
  • dose under worst dispersion conditions

The results can be summarized to blocks with one receptor point or one material at the time.

The reports are produced in HTML-format and and stored in the temporary directory. The report files then have the name of the project with the extension HTML. To save it elsewhere use your browser's file menu. Of course, these documents can be modified with almost every text processing program, though you should be aware that this documents can be overwritten by the program easily by mistake. The structure of the report can be modified in the form Options/Preferences.

see Form Output parameter

4.4 Graphic output of the ambient air concentration course

Under the menu item Results / Graphic and under Results / Report - "Graphic" (old Version) , ambient air concentration courses can be graphically illustrated in form of a curve family, provided that they have been calculated and stored in the log.

The selection of receptor points and materials are controlled for Results / Report - "Graphic" in the form Report / Parameter.

The following characteristic courses can be illustrated by selecting:

  • Course under mean dispersion conditions
  • Course under conditions resulting in a maximum for the dose
  • Course under conditions resulting in a maximum for the concentration maximum

In Results / Graphic an additional illustration over distance is avlailable.

See also: Graphical Course and Graphic illustration of the course

5.0 Operation

5.1 Within the forms

In den Bildschirmformularen erfolgen die Eingaben in Formularfeldern. Mit den Tasten Cursor rauf, Cursor runter, Tab und Shift Tab oder mit der Maus kann der Cursor über die Felder bewegt werden. Cursor links und Cursor rechts bewegen den Cursor zeichenweise innerhalb eines Feldes.

Reelle Zahlen können mit Punkt oder Komma oder auch als 1e-6 für 10-6 eingegeben werden. Der Fehlerton kann bei der Eingabe ignoriert werden, er wird nur als Warnung ausgelöst, weil 1e oder 1e- keine gültige Zahl ist.

Gegebenenfalls (wenn im Formular gekennzeichnet) kann eine Auswahlliste von diskreten Eingabewerten geöffnet werden.

Mit F1 wird zu einem Formularfeld oder zum ganzen Formular eine kontextbezogene Hilfe angeboten und das integrierte Handbuch zugreifbar.

Mit OK oder ABBRECHEN wird das aktuelle Formular verlassen.

Siehe auch: Calculator

5.2 Within the tables

The order and the width of all columns can be changed by clicking into a column header or between column headers and dragging as desired. This is practical if values are in a particular order, because Tab has to be pressed just once in order to reach the next column.

If the data in the columns are too wide to be displayed, then the symbols (in brackets) will be hidden in the column titles (e.g. Temperature (T0) ). Widening of the column will show that particular symbol.

The buttons "+" and "-" are used to insert or delete data sets. With the button "Dup" the current data set can be duplicated. The new row will become the last row in the table. This is useful if a data set is to be generated with minor difference to the current one. To insert a row, select the lower gray row before pressing the "+" button.

Individual fields, in which a selection is possible, are marked yellow. To activate the selection click once in a cell in order to select this; click a second time in order to activate the selection (no doubleclick).

With the cursor or Tab key, the focus can be moved between individual fields.

The illustrated section can be scrolled one row up or down by moving the cursor across the upper or lower edge of the table form.

Some tables can be sorted. With a right mouse button click into the considerable column, a Pull-Down Menu will be opened, and Sort Ascending or Sort Descending can be selected.

In some tables, a Row-Editor can be invoked. The Row-Editor shows one dataset only and can have more or less features then the grid dialog.

Sometimes single Columns can be imported via the Popup Menu. From the selected file, the values are taken and written to the position, from which the dialog was invoked. One value will be read per line from an ASCII file (includes CSV format) .

Some tables feature a search function. See Find in table

See: Calculator and Alter Column Values.


This feature allows to filter out a column with its value. Only rows with this value in the filtered column and not this column will be shown. The filter can be set to most of the columns (except when they are declared unique). All available column names are shown in the selector next to "Filter:". Once a column is selected, a corresponding value out of this column can be selected in the selector to the right of the equal sign. Filtering is accomplished on a text basis rather than on a value basis (e.g. 1.0 doesn't equal 1).

Using the filter feature will reorder the rows. Only columns, which are not defined as unique, can be selected. Some table can be sorted (Right Mouse Button Click into the column of regard.)

A filter might be active during import / export to exclude or include rows of data.

Table Import and Export

In most tables, data can be imported or exported with the buttons in the tool bar. The sequence of the columns and which columns are used, depends on the current column order and the current filter setting. With a button in the tool bar, a form can be opened which gives information about the current settings.

Single Columns can be imported via the Popup Menu. From the selected file, the values are taken and written to the position, from which the dialog was invoked. One value will be read per line from an ASCII file (includes CSV format) .

Available formats for import and export

CSVColumns are separate by commas (Comma Separated Values). If a text contains commas, it must be written in " " (Quotation marks). The decimal character is the point. Values can optionally contain an exponent (e.g.: 6.E-9), however no additional separators are allowed.
TXTColumns are separated by spaces. If a text contains spaces, it must be written in ' ' (Apostrophe). The decimal character is the point. Values can optionally contain an exponent (e.g.: 6.E-9), however no additional separators are allowed.
Current Project ExtensionIndividual tables can be loaded from project files. The loaded table must fit logically into the project.
The export creates a new project file, which contains only the exported table.
*On selection of the file type [With Options (*.*)], the form Table Import Options will be opened, in which further parameters are available.

The formats can be selected in the appropriate dialogs under the type of file. The filter function is switched off for other formats than CSV, TXT and *!


The tables can be viewed appealingly as an HTML-file by using the preview function. see Report function.

5.3 Within the graphics

Most of the graphics can be zoomed; therefore a rectangle has to be opened with the mouse from the upper left corner to the lower right corner. To reset the zoom, a rectangle from the lower right corner to the upper left corner has to be opened with the mouse. Also the graphic can be moved; therefore the graphic is to be dragged with the right mouse button pressed.

Some dialogs can also be opened by clicking onto the axis, the legend, the title or double clicking the drawing area.

The button has to be down for all functions, which are activated by clicking into the drawing area.

Graphical illustrations on the screen can be printed with File/Print or the button .

The Export of Images can be done with . Images can also be copied to the clipboard with .

Setup (Layout, Export and Format)

A form in which more graphic parameters can be set. Functions for export and graphics formats are also in this form.

Alterations made in will not be saved automatically. In some illustrations it might be possible to save and load configuration changes under the file menu, but it might cause strange effects, because the configuration might not fit to the current illustration. Series, which are not needed in the current illustration and which are not automatically destroyed can be made inactive. Data are managed in so called Series. The configuration can be saved with or without data. The data are normally replaced with the current ones, despite this, sometimes it might still be important to save the data along with the configuration.

Modifications and settings in other forms or of the calculated data can overwrite made changes in Setup!

It is recommended to set the graphic type to the configuration to be loaded.


With the button MAX the scale settings are maximized.


The graphic can be illustrated isometrically by using the button ISO. This has to be repeated after changing the size of the graphic.

6.0 Problem solving and compatibility

Compatibility to previous versions
The program can read the files from previous versions, but files produced by this program can only be partially processed by the predecessors.

7.0 Glossary

UZG Untere Zündgrenze (Lower flammability limit)
VDI Verein Deutscher Ingenieure (The Association of German Engineers)
TA Luft Technische Anleitung zur Reinhaltung der Luft (Technical instructions for air quality management)

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