Phast Manual

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Contents

Chapter 1

Chapter 1 Introduction

Introduction

For Users of PHAST Micro and PHAST Professional

PHAST is available in two forms: the fully-featured PHAST Professional, and the simpler PHAST Micro. This manual covers both forms.

All of the features of PHAST Micro are included in PHAST Professional, and Chapters 2 to 4 are fully applicable to both.

If you are following the early chapters of the manual while working with PHAST Professional, you will see features in the program that do not appear in the

illustrations in the manual. These are features that are unique to PHAST Professional, and you should ignore them at this stage, since they will be covered

in Chapters 5 to 7, which are applicable to PHAST Professional only.

For New Users and Existing Users

This manual is aimed at all users of PHAST , whether or not you have experience of previous versions.

Existing User Existing User

If you have used PHAST before, you may decide not to work through the tutorials, but simply to read the chapters that give you a quick tour of the features, i.e. Chapter 2 for users of PHAST Micro, and Chapters 2 and 5 for users of PHAST Professional. This may be sufficient to show you how the functions that you know

from previous versions have been implemented in this version, and to introduce you to new functions.

New User of PHAST Micro New User of PHAST Micro

If you have not used PHAST before, you should work through the first two tutorials before starting on your own work. Tutorial 1 deals with essential techniques and shows you how to get results quickly, and Tutorial 2 looks at the inputs and results in more detail, with explanations that may save you time in defining your own releases and in interpreting the results. The tutorials are quick to perform—about

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Getting Started with PHAST

New User of PHAST Professional New User of PHAST Professional

If you are using PHAST Professional for the first time, you must complete Tutorials 1 and 2 (as for the new user of PHAST Micro), but you may not need to work through Tutorials 3 and 4 immediately, since the simpler features may be sufficient for the first work that you do with PHAST . However, you should complete the tutorials before you use any of the additional features in your work since they include advice that may be very useful.

After completing Tutorials 1 and 2, read Chapter 5 for an introduction to the additional features, and then put the manual aside while you gain experience in using PHAST . You can return to the manual to complete the tutorials when you think that the additional features might be useful in a particular hazard analysis problem.

Use the Online Help to Learn More

This manual does not describe each feature in detail, and you should refer to the online Help (or “Help system”) for more information, and for guidance in setting values and interpreting results.

The Help system includes context-sensitive Help, which can give you information on the various input fields while you are working in a dialog. You will probably find this the most useful aspect of the Help system when you are first learning to use PHAST , and it is described further in Chapter 2.

When you are more familiar with PHAST , you may find the Search (or “Index”) function in the Help system useful. You may know that a feature exists, but not be sure where to find it, and the Help system can save you the effort of looking through every menu or input dialog. For example, if you want to change the Toxic Averaging Time (introduced in Chapter 3) but can t remember where the value is set, move to the Index tab in the Help Window, type “toxic” or “average”, and you will soon locate it in the Toxic Parameters.

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Chapter 2: Tour of the Main Features

Chapter 2

Chapter 2 A Quick Tour of the Main Features

A Quick Tour of the Main Features

All Examples are from PHAST Micro

There are two versions of PHAST , and this manual covers both of them. PHAST Micro is the simpler version, containing DNV s sophisticated dispersion modeling

in full, but with some limitations to the options in other areas of the modeling. PHAST Professional is the fully-featured version, offering control over most aspects of the modeling, and including stand-alone versions of the fire, explosion and pool vaporization models that are built into the integrated dispersion modeling. All of the examples in this chapter are based on PHAST Micro and are fully applicable to that version. If you are using PHAST Professional, you will see some features in your program that do not appear in the illustrations and are not described in the text. At this stage you should simply ignore these features, but they will be described in the later chapters in this manual (from Chapter 5 onwards), which deal with the features that are unique to the Professional version.

Starting PHAST

When you install PHAST , the installation routine places aDnv folder underPrograms in your Start menu, and you can start PHAST running by selecting the icon from the folder.

The installation routine also offers the option to place a PHAST icon on the desktop, and if you chose this option, then you can also start PHAST running by clicking on the desktop icon.

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The PHAST Window

When you start PHAST running, the PHAST Window will open, as shown.

The window opens with no Study Folder loaded—where a “Study Folder” is a file that contains the definition of a collection of consequence modeling calculations—and you must open or create a Study Folder file before you can perform any modeling work with PHAST .

At the end of the Message Log, the program reports on the security checks, with either “Security OK” or “Security failed”. There are two security methods available with PHAST . The default method is the Security Chip which attaches to the parallel port on the computer; this method is described further in the online Help. The second method is Software Security, which involves obtaining a unique license code from DNV and then entering the code into the computer; you select the method using the Software License Utility, which is available from DNV on special request. If the security has failed, you will not be able to save any changes to input data or run any of the calculations, although you will be able to view the features of the program that do not involve calculations. In this manual, it is assumed that the security has already been set up correctly.

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Opening an Example Study Folder

In this chapter, you will open one of the Example Study Folders that are supplied with the program for a quick introduction to the terminology and approach used in PHAST . In the next chapter you will create a new Study Folder and perform a

simple “worst case” analysis. To open an Example Study Folder, choose Open Example from the File menu. A dialog will appear as shown, listing the Example Study Folders supplied, each of which has the file extension PSU. Choose the Study Folder called Example, which is one of the simplest supplied.

When you click onOpen, you will be returned to the PHAST window. Some messages will appear in the Message tab section in the “Log

Window” pane along the bottom of the window, reporting on the process of opening and checking the Study Folder, and then the “Study Tree” pane will open along the left side of the window, showing the structure of the Example Study Folder, as in the illustration below.

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The Study Tree Pane

The Study Tree Pane allows you to organize and edit the values that are used in the calculations. It appears along the left side of the window whenever you have a Study Folder open, as shown in the illustration on the previous page. If you close the Study Folder, the pane will disappear.

The pane contains a number of tab sections, each of which covers a different type of input data:

Models Tab Section Models Tab Section

You use this tab section to add “Models” to the Study Folder, where each Model_{represents a different hazardous release for processing through the consequence} modeling. The illustration on the previous page shows the eight models in the Example Study Folder; the first four represent different release scenarios for a chlorine vessel, and the last four represent the equivalent scenarios for a butadiene vessel.

This tab section contains a tree with several levels. The top level represents the entire Study Folder, with the nameExample. If you click on the icon for the Study Folder, you will see that the red “Study” icon becomes enabled in the Toolbar:

You can use this icon to add a Study to the tree, and this can be useful if your Study Folder contains hundreds of models and you want to organize them in different groups. For a simple Study Folder such as the Example Study Folder, a single Study—also named Example—is sufficient.

The Study is the second level of the tree, and each new Study Folder is always created with one Study already defined, since each model must be assigned to a Study. If you click on the icon for a Study, you will see that the Folder icon and the blue Vessel and Pipe Source Model icon become enabled in the Toolbar:

You can use the Folder icon to organize models within a Study, and you can have multiple levels of Folders; the simple Example Study Folder does not use any folders.

You use the Model icon to add a new Model to the Study Folder, placing it inside the current Study, or the current Folder. It is probably the most important tool in PHAST , and you will use it in Tutorial 1, in the next chapter.

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Weather Tab Section Weather Tab Section

Click on the Weather tab to move to the Weather tab section. This tab section shows the weather conditions that have been defined and can be used in the consequence modeling. You can define any number of weather conditions and then select between them for a particu-lar run of the consequence calculations. The tree in the Weather tab section shares

the top levels of its structure with the tree in the Models tab section, so that if you add a Study to the Study Folder in either section then it will appear in the tree in the other section. However, the lower levels are not shared, and you can have different structures of Folders in each tab section.

If you click on the icon for a Study, you will see that the Folder icon and the yellow-and-blue Weather icon become enabled in the Toolbar:

You use the Weather icon to add a new definition of weather conditions to the Study Folder, placing it inside the current Study, or the current Folder. However, each new Study Folder is created with three default weathers already defined, and for most work it may be sufficient to edit these, rather than creating any additional weathers.

Parameters Tab Section Parameters Tab Section

Click on the Parameters tab to move to the Parameters tab sec-tion.

The parameters system in PHAST is based around a

three-level hierarchy, although only two levels of the hierarchy are evident in the Parameters tab section. You may, in fact, never

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The top level is the System level, which is the central store for all PHAST Parameters data supplied with the program, and is not visible in the tab section. If your copy of PHAST is installed on a network, then the System values will also be on the network, and will be shared between all people using PHAST network data. In PHAST Micro, you can not change the values at the System level, and must use the values that are supplied with the program. In PHAST Professional, the values can be changed, but only by an Administrator using the special administration options, which are described in the online Help.

The next level is the Global level, which applies to an entire Study Folder and is visible in the tab section. Each new Study Folder is created with a full set of parameters at Global level, represented by the eleven icons in the Global Parameters folder. The Global Parameters take their default values from the System Param-eters, but you can edit them to set the appropriate values for the Study Folder. The lowest level in the hierarchy is the Local level, and PHAST creates a Local Parameters folder for each Study in the Study Folder. If you want the Models in a particular Study to use different values for, say, the Pool Vaporization Parameters, select the Local Parameters folder for that Study, then select Pool Vaporization from the Parameters cascade in the Insert menu. The Models in this Study will use the Local values for the Pool Vaporization Parameters, but Models in all other Studies will use the Global values (or their own Local values).

The Local group of a particular group of Parameters (e.g. the Pool Vaporization Parameters) will take its default values from the Global Parameters, but you can edit the group to set the appropriate values for the Study. The program knows which items in the group have been changed, so if you later edit the Pool Vaporization Parameters in the Global Parameters, the program will

automati-cally update any items in the Local Parameters that have not been edited.

Materials Tab Section Materials Tab Section

Click on the Materials tab to move to the Materials tab section. As wi th th e Pa ram et er s, th e

Materials Property system in PHAST is based around a

three-level hierarchy, with only the bottom two levels of the hierarchy visible in the Materials tab section.

Materials Tab Section

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The top level is the System level, which is the central store for all PHAST Property data supplied with the program, and which is not visible in the Materials tab section. If your copy of PHAST is installed on a network, then the System values will also be on the network, and will be shared between all people using PHAST network data. The System values can only be changed by an Administrator using the special administration options, which are descibed in the online Help. The next level is the Global level, which applies to an entire Study Folder. When you add a material to Global Materials folder in the Materials tab section, PHAST creates a copy of the material inside that Study Folder, using the values from the System level as defaults. PHAST will add a material to the Global list the first time you use it in a Study Folder, but you can also add materials yourself, using the two Materials icons that appear in the Toolbar when you have the Global Materials folder selected in the Materials tab section:

The Example Study Folder only uses two materials in its models—chlorine and butadiene—but you can see that there are many more in the Global list, and these were added using the icons in the Toolbar.

You can edit the values for the Global version of the material, as described later in this chapter, and these edits will be used throughout the Study Folder. The lowest level in the hierarchy is the Local level. PHAST creates a Local Materials folder for each Study in the Study Folder, and you use these if you want to create a version of a particular material that will be used only by that Study, while all other Studies use the Global version. You can add a material to the Local Materials folder either by copying and pasting from the Global list using the Edit menu, or by using the Materials icons that appear in the Toolbar when you select theLocal Materials folder.

PHAST knows which fields for the Local material have not been edited and therefore still have the default values taken from the Global level. If you edit a field for a Global material, PHAST will update the field for any Local versions that are still using the Global default.

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Map Tab Section Map Tab Section

Click on the Map tab to move to the Map tab section. This tab section shows the maps that have been de-fined and on which you can superim-pose consequence results. You can define any number of maps and then select between them when viewing a particular set of consequence results.

The tree in the Map tab section shares the top levels of its structure with the trees in the Models and Weather tab sections, so that if you add a Study to the Study Folder in any section then it will appear in the tree in the other sections. However, the lower levels are not shared, and you can have different structures of Folders in each tab section.

If you click on the icon for a Study, you will see that the Folder icon and the Map icon become enabled in the Toolbar:

You use the Map icon to add a new Map to the Study Folder, placing it inside the current Study, or the current Folder. Each new Study Folder is created without any Map defined, so you must create a new Map if you want to view any map-based results.

Viewing Input Data

The section above described the organization of the different types of input data, and this section describes how to open the dialogs for the input data and view the values that are set for the Example Study Folder. In the next chapter, you will set values when working on a tutorial analysis.

Setting the Default Units Setting the Default Units

Before you start viewing the input data, you should set the default units for PHAST to your preferred system of units. As you will see later, you can change the units for a given item of data from inside the input dialogs, but it is much easier to set a default system that will be used throughout PHAST , including any dialogs and results.

To set the default system, choose Select Another System from the Units cascade in the Options menu. A dialog will appear, as shown in the illustration on the next page.

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PHAST is supplied with four pre-defined systems of units, but you can also edit these to create your own. At this stage, simply choose the pre-defined system that is closest to your preferences, and click on Make selected system current to set this as the default system throughout PHA ST . The examples in this

chapter use the BRITISH system, which is mostly English Imperial units.

Getting Help on the Input Data Getting Help on the Input Data

PHAST has a large set of input data. This gives it the flexibility to model a wide range of releases and situations, but can be confusing at first. If you are unsure of the purpose of a particular dialog or field, you can use the context-sensitive online Help to get a description.

Most dialogs have a Help button at the bottom right. When you click on this, the Help window will appear, with the Help topic for that dialog displayed in the right-hand pane, as shown:

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A What’s This Help button in a Title Bar

Most dialogs also have a “What s This Help” button in the form of a question mark at the right of the title bar:

If you click on this button, the cursor will change to a question mark, showing that you are in “What s This Help” mode, and if you then click on a field in the dialog, a popup window will appear over the field, describing the field and giving advice on values, as shown below. The popup window will disappear the next time you click with the mouse.

You will see both of these features in the dialogs that are described below. You can also bring up the What s This Help for a field by pressing the F1 key while

the cursor is on that field. In addition, if you press theF1 key again while the What s This Help is being displayed, the Help window will appear, displaying the Help topic for the dialog, as described on the previous page. You may find theF1 key more convenient than the buttons for accessing the Help system.

Input Data for a Model Input Data for a Model

In the Models tab section, double-click on the icon for theCL2 RUPTURE model. The Model Data dialog will open, as shown in the illustration on the next page. The full set of input data is large, and is divided over many tab sections. The illustration shows the tab section for Material data, where you set the material that is released, the amount released, and the process or storage conditions at the time of the accidental event which leads to the release.

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Although the full set of data is large, you do not have to decide on and enter a value for every item of data in order to model a release; PHAST is supplied with default values for many of the items, and if you accept these default values, then you can define a release easily and quickly.

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Input Data for Weather Input Data for Weather

In the Weather tab section, double-click on the icon forWeather 1, and the dialog will open as shown.

The set of input data is much smaller than for a model, and the most important items are in the Weather Data tab section. All of the items in the Atmospheric Parameters tab section take their initial values from the defaults system, so you can either accept the default value, or enter your own.

You can tell that the Atmospheric Parameters tab section takes all of its values from the default system without even moving to it, because PHAST usesitalic lettering for the headings of all such tabs. When a tab has italic lettering , you know that there are no fields on that tab section that youhave to complete before you can use the Weather (or Model, or Material) in a calculation; however, if the heading of a tab section uses bold letteringbold lettering—such as the Weather Data tab section—then this tells you that there are fields in the tab section that are initially blank, and that you must complete. This system of lettering can be useful when you want to obtain preliminary results quickly.

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Input Data for Materials Input Data for Materials

In the Material tab section, double-click on the icon forCHLORINE.

The set of input data for Chlorine is very large, and some of it is very specialized and technical. If you want to add a new material to the properties system in PHAST , you will have to gather and enter a lot of information before you can use

the material in the calculations. However, since PHAST is supplied with full data for a large number of materials, it is unlikely that you will ever need to define a completely new material, and, indeed, you may use PHAST for years without ever making any changes to any materials data.

You are most likely to use the Materials tab section for defining a Mixture—made up of existing Pure materials—and for looking up property data. You can refer to the input dialog to obtain the values of constant properties (i.e. those that are not a function of conditions), and you can use the options in theMaterial cascade in the Run menu to calculate properties at a given pressure and temperature (e.g. vapor density, saturation conditions, etc.).

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Input Data for Maps Input Data for Maps

When you double-click on the icon forMap of region around plant in the Maps tab section, a separate window will open in the region to the right of the Study Tree pane.

The main data that you have to define for a new map are the location of the bitmap file on the system, the location of the srcin on the map, and the scale for the map. You define these using the Graph menu, which is added to the main menu bar whenever the Graph window is open. You will define a new map in the next chapter, which

gives details of these operations.

The Map Window

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Running the Calculations

The Example Study Folder does not have any modeling results at the moment, and you must run all of the calculations before you can view the results. There are two ways of running the calculations:

Batch Run Batch Run

The Batch Run allows you to run any combination of models, from any Studies and Folders in the Study Folder. Before you can start the calculations, you must select Batch/Weather Setup from the Run menu to open the Run Batch dialog and choose the models and weathers that you want to process in the next Batch Run.

To make a selection in the Batch Setup window, check the box beside the element that you want to run. In the illustration, only two of the Models in theExample Study are selected; if you want to run all of the Models in the Study, then you can simply check the Study itself, and all Models inside the Study will become selected; if you have more than one Study, you can check the Study Folder to select all Models in all Studies.

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After you have selected the Models, move to the Weather tab section and select the Weathers that you want to model in the dispersion and effects calculations. The program will process each selected Weather for each selected Model, giving a separate set of results for each Weather.

To start the calculations running, selectBatch Run from the Run menu. A progress bar shows the proportion of the combination of Models and Weathers that have been processed, and also allows you to stop the calculations at any point. The calculations for a given combination of Model and Weather are normally very quick, taking only a few seconds.

When the calculations are complete, you will see that the color of the text for the Models that have been processed has changed from black to blue. This gives you an easy way of identifying the models that have been run successfully and that have results that you can view. The process of viewing results is described later in this chapter.

Direct Run of a Single Model, Folder or Study Direct Run of a Single Model, Folder or Study

To run a single Model, or to run all Models in a single Folder or Study, select that Model (or Folder or Study) in the Models tab section and then chooseRun Model(s) from the right-click menu orModel(s) from the Run menu, or pressCtrl+M.

The Run Model(s) command processes all of the calculations, from discharge through dispersion to flammable and toxic effects. If you want to run the discharge calculations alone, without proceeding to the dispersion and effects calculations, select the Run Discharge(s) command instead, or press Ctrl+D.

When you are running a single item in this way, the program performs the calculations for the Weather conditions that are currently selected for the Batch Run.

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Viewing the Results

If the Study Folder contains Models that have been processed successfully through the calculations—shown by the use of blue text for the names of the Models—then you can view the results.

To view the results, select the Model in the Models tab section, and then selectReport or Graph from the View menu, or pressCtrl+R for the Report, or Ctrl+G for the Graph. A single Report or Graph can display the results for more than one Model, but the options for selecting the multiple Models are different for each, and described separately below.

Viewing the Reports Viewing the Reports

Reports are displayed in the Report Window, which appears in the free space inside the PHAST Window—i.e. in the space not occupied by the Study Tree and the Log Window—which is normally to the right of the Study Tree.

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You can generate a Report that contains the results for more than one Model if the Models are in the same folder or Study. Select the folder or Study and then use the option to view the Report, and the program will generate a Report with the results for all of the relevant Models.

The window will contain several Reports, depending on the Model and the type of results that are relevant to the Model. By default, the program will display all available reports, but you can use Preferences... in the Options menu to exclude Reports that are not of interest in the current analysis. The Reports and the options for displaying them are described in more detail in the next chapter.

You use the tabs to move between the Reports.

Some Reports are long, and cover many pages. You can move between the pages of a Report using the navigation buttons at the left of the Toolbar for the Report Window.

You can also move to a particular part of the Report by using the Report Tree at the left of the window. When you expand the tree, it shows the structure of the Report, with the sections that cover the different Models (if the Report covers more than one Model), the sections that cover each Weather that was processed for the Model, and the sections that cover the different release segments for each Weather, shown as 1, 2, 3, etc. in the illustration.

Most Models have a single release segment, but a Model may have more than one segment if you used time-varying discharge modeling (which is an option in the Vessel tab section of the input data), or if the release contains liquid that rains out to form a pool, and the pool then evaporates, since the evaporation is treated as a form of time-varying discharge.

To move to a particular part of the Report, click on that part in the Tree (e.g. segment 4 for Weather 1 in the illustration), and the program will move to the page that contains the beginning of that part of the Report.

The other main features of the Report Window are the Print button and the Export button in the Toolbar. Use the Print button to send all or part of the current report to the printer, and use the Export button to export the contents of the Report to an external file of a given format (e.g. Excel, HTML, text).

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If the initial size of the window is small, you may find it difficult to view the Reports clearly, and in this case you should chooseFull Screen from the Window menu or from the Toolbar, since this option expands the window to fill the entire screen. To return from Full Screen to Normal mode, pressCtrl+W, or click on theRestore button that is always visible when you are in Full Screen mode.

You can have more than one Report Window open at any time. Use the Window menu to switch between multiple Report Windows, or to arrange the windows so they are all visible at the same time.

Viewing the Graphs Viewing the Graphs

When you select Graph from the View menu, the Plot Setup dialog will appear, prompting you to choose between the Weather conditions that have been modeled, and to choose a Map on which to superimpose the footprint results.

The Window Menu

Choosing the Results to Plot The Restore Button

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You can also choose the option to view a Graph from the Weather tab section of the Study Tree. In this case, the Plot Setup dialog will contain a Model tab section instead of a Weather tab section, and you can select multiple Models to plot for the Weather that is currently selected in the Study Tree.

When you have chosen the items that you want to plot, the Graph Window will open in the area to the right of the Study Tree. The Graph Window contains many Graphs, and you move between them using the tabs. The Graphs and the options for displaying them are described in more detail in the next chapter.

As with with Report Window, you can have more than one Graph Window open at a time, and you use the Window menu to arrange the Graph Windows, and to switch to Full Screen mode.

If you choose a single Weather and Model, the graphs will show the results for different concentrations, distances and overpressures, as appropriate for the typw of graph. If you choose more than one Weather or Model, the graphs will show the results for a single concentration, distance or overpressure for each Weather or Model.

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Saving the Example Study Folder

Although you have not made any changes to the input data for the Example Study Folder, you have run the calculations. If you save the results with the rest of the Study Folder data, then the next time you open the Example Study Folder, you will be able to view the results immediately, without having to rerun the calculations. You should leave the Example.PSU file from the Examples folder unchanged, so that

other users will be able to explore it in its srcinal state. This means that you should not use theSave option from the File menu, since this would overwrite the file in the Examples folder. Instead, you should use the Save As... option from the File menu, so that you can save the Study Folder to a different location, creating your own copy of it.

When you install PHAST , the installation program creates a folder to be the preferred location for Study Folder data. The default name and location for this folder are c:\DNVuser (if PHAST is installed on thec: drive), but you can set any name and location during the installation. If you have access to this folder, you should use it for your copy of the Example Study Folder.

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Before clicking onSave, you should ensure that theSave resultsSave results check box is ticked, as shown in the illustration on the previous page. By default, PHAST does not save results for theExample Study Folder or for any new Study Folder, and you must use Save As... if you want to change this option.

The results can make the Study Folder files very large. Since the calculations usually run very quickly, you may prefer to save your Study Folder files without the results, and then rerun the calculations every time you open the files.

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Chapter 3: Tutorial 1

Chapter 3

Chapter 3 Tutorial 1: Performing a Worst-Case Analysis

Tutorial 1: Performing a Worst-Case Analysis

All Examples are from PHAST Micro

There are two versions of PHAST , and this manual covers both of them. PHAST Micro is the simpler version, containing DNV s sophisticated dispersion modeling

in full, but with some limitations to the options in other areas of the modeling. PHAST Professional is the fully-featured version, offering control over most aspects of the modeling, and including stand-alone versions of the fire, explosion and pool vaporization models that are built into the integrated dispersion mod-eling.

As with the previous chapter, all of the examples in this chapter are based on PHAST Micro and are fully applicable to that version. If you are using PHAST Professional, you will see some features in your program that do not appear in the

illustrations and are not described in the text. At this stage you should simply ignore these features, but they will be described in the later chapters in this manual (Chapter 5 onwards) which deal with the features that are unique to the Professional version.

Do Not Expect Identical Results

The results given in this manual were obtained with a pre-release version of PHAST , and are likely to be different from those that you obtain when you are

working on the tutorials. The results that you obtain are also likely to change between versions of PHAST , as the consequence modeling is progressively im-proved and refined. The differences in the results may even reverse some of the assumptions and conclusions given in this manual. For instance, the manual may find that Release A gives greater effects than Release B, and then proceed to investigate Release A in more detail—whereas your results may show that Release B gives greater effects.

Please do not be concerned about these differences, and please do persist with the tutorial even if a “reversal” of the conclusions means that the later stages of the tutorial are no longer very relevant. The purpose of this manual is not to help you reproduce particular results, but to introduce the main techniques for working with

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Introduction to the Analysis

In this chapter, you will perform a simple worst-case analysis for the Anysite chemical installation, to determine whether releases on the site have the potential to reach populated areas beyond the site boundary.

Hazardous Materials Hazardous Materials

There are four hazardous materials present on the site in significant quantities:

Storage Conditions Storage Conditions

The ethylene is stored under supercritical conditions, and the three other materials are stored under saturation conditions. For the worst-case analysis, the materials will be modeled at the maximum temperature experienced at the facility over the last five years, which is 90°F (32°C). At this temperature, the storage pressures for the materials are as follows:

Hazardous Inventory for Anysite Facility

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Release Scenarios Release Scenarios

Different scenarios will be modeled for the toxic and the flammable materials, since different types of release cause the worst long-range effects.

For the two toxic materials, the release scenario will be a release of the entire inventory over ten minutes, and for the two flammable materials, the scenario will be an instantaneous release of the entire inventory.

For toxic releases, the duration and concentration profile at the populated areas are more important than the total mass in the cloud at any given time. A large continuous release will give a greater duration of exposure than the equivalent instantaneous release. It may also take longer to disperse to harmless concentra-tions, since air is mixed into the cloud from the sides only, whereas air is mixed into an instantaneous release across all exposed surfaces.

For flammable releases, the greatest effect distances are usually produced by vapor cloud explosions, and the size of these explosions depends on the flammable mass in the cloud at the time of the explosion—which will be greater for an instantaneous release than for a continuous release.

Critical Effect Zones Critical Effect Zones

For the toxic materials, the calculations will obtain the dispersion distances to the Emergency Response and Planning Guidelines (ERPG) Level 2 concentration, which is the concentration that nearly all individuals can be exposed to for up to an hour without experiencing any irreversible adverse health effects or symptoms which could impair the ability to take protective action. For ammonia, this concentration is set at 200 ppm, and for hydrogen cyanide, it is set at 10 ppm.

For the flammable materials, the calculations will obtain the explosion distances to an overpressure of 1 psig, which is an overpressure that may cause injuries as a result of minor structural damage (e.g. broken windows), but is unlikely to cause fatalities.

Weather Conditions Weather Conditions

The calculations will use a windspeed of 5 ft/s (1.5 m/s) and an atmospheric stability of F, which are common night-time conditions for the location. These conditions give low levels of atmospheric turbulence, and the release may travel long distances before being diluted to a harmless concentration.

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Town Town

Commercial and light Commercial and light

industrial area industrial area Everychem's Everychem's Anysite facility Anysite facility

beach, used for beach, used for

recreation recreation miles km 0.5 1 1.5 2 1 2 3 ocean ocean N

The calculations require a value for surface roughness, which is a measure of the turbulence induced in the air as it moves over the ground, and will be set conservatively to 0.06, a value for sea or for flat, treeless land. This assumes that the wind is blowing towards the town, and that the surface conditions upwind of the release determine the surface roughness.

Location of the Anysite Facility Location of the Anysite Facility

As shown in the map, Anysite is a large, ocean-side facility, located in an industrial area, and nearly two miles from the nearest residential area.

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Creating the Anysite Study

Creating the Anysite Study Folder

Folder

First, you must create a new Study Folder to store all of your work on the Anysite facility. Close any Study Folder that is currently open in PHAST , and then select New from the File menu.

The program will create a new Study Folder called Untitled with an empty Study called New Study.

Saving the Study Folder Saving the Study Folder

You cannot save a Study Folder with the name Untitled. Use either the Save or the Save As... options in the File menu to save the new

Study Folder to the DNVuser directory with the name Anysite.PSU.

Renaming the Study Renaming the Study

Click on the Study to select it, and then chooseRename from either the Edit menu or the right-click menu. An insertion point will appear in the name of the Study, and you should edit this to change it toWorst Case.

Using Program Preferences to Open the Study Folder Automatically Using Program Preferences to Open the Study Folder Automatically

All of the tutorials in this manual use the Anysite Study Folder. If you do not perform the tutorials in a single session, you will be returning to the Study Folder several times. The list of recently-used Study Folders at the bottom of the File menu makes it easy to re-open a Study Folder that you have been working on, but you can also use the Preferences for the program to make this even easier.

Select Preferences... from the Options menu. The Preferences dialog will appear, and you should set the option in the Startup tab section toTry to open most recently used file, as shown in the illustration on the next page. If the file has been deleted or moved, the program will display a File Open dialog instead, so you can locate the file yourself.

The New Study Folder in the Study Pane

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Setting the Materials Input Data

In the database of System Materials supplied with the program, ammonia and hydrogen cyanide are defined as being both flammable and toxic. However, for the worst case analysis, you are only interested in the toxic effects, and you can simplify the input data and the results if you define them as toxic only for this analysis. You do this by creating local copies of the materials, and editing the property data. If you wish, you can omit this stage, since it is not essential. However, you may find it useful as a quick and straightforward introduction to the properties system.

Creating Local Versions of the Toxic Materials Creating Local Versions of the Toxic Materials

Move to the Materials tab section of the Study Tree, select the Local Materials folder under the Worst Case Study, and select Material... from the Insert menu. The Insert Material dialog will appear, as shown in the illustration on the next page. The dialog offers three ways of inserting a material. The NewNew option allows you to create a completely new material, with no pre-defined properties data. The Existing

Existing and CopyCopy options both allow you to create a copy of a material that is already in the materials database at a higher level (i.e. at the System or Global level): the ExistingExisting option keeps a link to the srcinal material, and if the values for the srcinal material are changed, the program will automatically update the values for any fields that are still using the srcinal, default values; theCopyCopy option does not keep a link, and the local version will not be affected by any changes to the srcinal material.

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Select the ExistingExisting option, locate and select AMMONIA in the list of materials, and then click on OK to add the material to the Local Materials folder.

Next, repeat the process, selecting HYDROGEN CYANIDE as the material.

Editing the Materials Data for the Local Materials Editing the Materials Data for the Local Materials

When you expand the Study Tree below the Local Materials folder, you will see the icons for the two materials. Double-click on the icon for AMMONIA to open the input dialog, and set the Flammable/ToxicFlammable/Toxic field in the General tab section from the default value of Both to Toxic only, as shown in the illustration on the next page.

Click on OK to save the changed data, and then repeat the process with the local version of HYDROGEN CYANIDE.

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Setting the Weather Input Data

Before defining any of the worst-case releases, you will define the other aspects of the input data, which will be the same for all four releases: the Weather data, and the Map data.

Each new Study Folder is created with a set of default Weather conditions defined for the default Study, as shown in the illustration. These default Weathers are representative of the range of com-mon conditions, and they enable you to obtain results for a new Study Folder very quickly. For this Worst Case analysis, you are only going to model one condition—1.5 m/s with F stability —which is one of the default conditions.

The Changed Data for Ammonia

The Default Weather Conditions for a New Study Folder

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Delete the Unwanted Conditions Delete the Unwanted Conditions

First, delete the other default conditions. You delete an icon from the tree by clicking on it to select it, and then using theDelete (Del) key or the Delete option in the Edit menu or the right-click menu. You could leave the conditions in the tree, but it will make the design of the analysis clearer if you delete them.

Set the Detailed Weather Data Set the Detailed Weather Data

Next, double-click on theWeather 1.5/F icon to open the dialog for input data, and set the following values in the Atmospheric Parameters tab section:

All of the fields in the Atmospheric Parameters tab section take their initial values from the defaults system, which is shown by the green border around each field. When you change the values to those required for this analysis, you will see that the border disappears—the color-coded borders mean that you can see at a glance which fields in a dialog are using the default values directly, and which have been changed.

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Setting the Map Data

In the Map tab section of the Study Tree, select the Worst Case Plant, and then insert a new Map using the icon in the Toolbar, the Insert menu, or the right-click menu. Give the map the name Anysite surroundings, and then double-click on the map icon to open it in the Map Window.

Selecting the Bitmap Image Selecting the Bitmap Image

The Map Window will be blank, since you have not yet selected an image for the new map. A bitmap image of the Anysite facility and its surroundings is supplied with PHAST , and should be installed in theProgram Files/Dnv/Phast/Examples folder, which

is the folder that contains theExample Study Folder covered in the previous chapter. To load the image into the window, selectBitmap... from the right-click menu or from the Graph menu. A Open File dialog will appear, and you must locate the Examples folder, and then select theanysite.bmp file.

When you return to the Map Window, you will see the map displayed in it.

Changing the Proportions of the Map Window Changing the Proportions of the Map Window

At first, you will probably not be able to see all of the map image in the Map Window, and will have to use the vertical scroll bar to view the lower part of the map. If you want to make the whole map visible, you must resize the window, reducing the width until the window has same tall, thin proportions as the map image. As you are resizing the window, you will see PHAST rescaling the map to fit the new size of the window, and this makes it easy to know when the proportions are correct for the image.

You do not have to have the whole map visible in order to work with the map, and you can change the window to any size and shape while you are setting the map input data. However, you may save time if you know how the dynamic rescaling behaves, and it is worth spending some moments experimenting with the window.

Setting the Scale Setting the Scale

You set the scale by giving the width of the map image, which is 3.1 miles for the Anysite surroundings map. The program sets a default scale for each new map, so the scale that you see when you first load the bitmap will not be the correct scale.

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To set the scale, select Set Scale... from the Graph menu or the right-click menu, and then enter the width in the dialog which appears, as shown. When you return to the Map Window, you will see that the horizontal and vertical axes have been rescaled for the new value.

Setting the Origin Setting the Origin

The program sets the default srcin for each new map in the middle of the blank, default map, where it appears as a red shape. For this map, you must set the srcin in the middle of the Anysite facility. You will set the coordinates of the releases to (0, 0), which will place them at this srcin.

To set the srcin, select Set Origin from the Graph menu or the right-click menu. The cursor will change to a cross-wire, and you simply click on a point on the map to set that point as the srcin. For this worst case analysis, you do not have to place the srcin with great precision, and any location near the middle of the site will be suitable.

You have now finished defining the Map, which should appear as shown in the illustration. In the illustration, the dimensions on the scale are in feet, which is the default unit for distance. The srcin on the scale appears to be at the bottom left corner, and does not reflect the location that you have just given for the srcin, but when you come to view the results on the Map you will see that program is using the correct srcin.

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The New Model in the Study Tree

Defining the Ammonia Release

The first worst-case release is the 40,000 lb (18.1 tonne) ammonia release.

Inserting the Model Inserting the Model

Select the Study, and then insert a Vessel or Pipe Source Model, either by clicking on the icon in the toolbar, or by selectingVessel or Pipe Source from the Insert menu. The new Model will be given the nameNew Vessel/Pipe Source, and you should rename it immedi-ately to Ammonia, as shown.

When you insert the new Model, you will find that red boxes appear around all of the icons in the Models tab section of the Study Tree. The box appears around the new Model to show that it does not have a

complete set of input data, and you will therefore not be able to process it through the calculations; when you have completed the data input for the Model, the box will disappear. The box appears around the Worst Case Study to show that a Model inside the Study has incomplete data, and similarly for the Study Folder; this effect on the higher levels of the tree can be useful in a large analysis with many Studies.

Setting ppm as Unit for Concentration Setting ppm as Unit for Concentration

Before starting work on the input data, you should set ppm as the default unit for cloud concentration. The previous chapter described how to choose a system of units from the four that are supplied with the program, and this is the next level of refinement—changing the selection of units for a particular system.

To change the system of units, chooseEdit Current System... from the Units cascade in the Options menu, and the Edit dialog will appear. The concentrations use the “SmallFraction” unit-type, so you must selectSmallFraction in the main list at the left of the dialog, then selectppm in the drop-down list as shown in the illustration on the next page. Next, click on the Replace Unit button, and you will see the unit for SmallFraction change in the main list, and you can then click onOK to implement the change.

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The Edit Dialog for Units

Selecting a Material Setting the Material Data

Setting the Material Data

Double-click on the Ammonia icon to open the dialog for the input data, and set values in the Material tab section as shown in the illustration on the next page. To set the Discharge MaterialDischarge Material,

click on the button with three dots at the far right of the dialog, and select AMMONIA from the list which appears, as shown. You will see that the list contains many materials, and not just the two materials that you inserted in the Local Materials folder. The Scope column shows these two materials as Local, whereas all of the other materials are shown asSystem. If the Scope is System, then there is currently no Global or Local version of the material. If you selected one of these System materials (e.g. BENZENE ), the program would automatically create a version of

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The Input Values for Material Data

When you select the material, the program automatically sets the Material toMaterial to Track

Track to AMMONIA. You only have to choose a material to track if the DischargeDischarge Material

Material is a mixture.

Note that you can use scientific notation when entering values, so you can enter the inventory as “40e3”.

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Setting the Scenario Data Setting the Scenario Data

Move to the Scenario tab and set the following: Scenario

Scenario 10 Minute Release Release Phase

Release Phase Vapor

For most other types of Scenario, you have to give additional data that will enable the discharge calculations to calculate the release rate. However, for the 10 Minute Release, the release rate is given by (inventory/600 seconds) and not by any discharge calculations, and the Scenario input data are very simple.

Setting the Location Data Setting the Location Data

Move to the Location tab, skipping the Vessel tab, and set the values shown in the illustration:

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The ElevationElevation has a default value which is greater than zero, and you should leave it with this default value. If a release is located at ground level (i.e. theElevationElevation is zero), the program omits the detailed modeling of liquid droplets and their evaporation and possible rainout, and simply assumes that all of the liquid in the release rains out immediately; this is a reasonable assumption, since liquid droplets will have no opportunity to evaporate during the fall to the ground if they are released directly onto the ground. However, most releases will be at some elevation above ground level, and the program is supplied with a defaultElevationElevation that will give a treatment of the liquid droplets that is more typical of a real release. This worst case ammonia release is a vapor-only release, so the elevation is not as important as for a liquid or two-phase release, but it is still more realistic to place the release at some distance above the ground.

Leave the NorthNorth and EastEast coordinates with the default coordinates of zero, which will place the release at the srcin for the Map, which is in the middle of the Anysite facility.

You can leave the bund data unset, since they are not relevant to this vapor release. For a liquid release, however, the presence and size of the bund can have a very large effect on the results: if there is no bund, then the pool from any liquid rainout can spread to cover a very wide area, giving a high evaporation rate from the surface of the pool; whereas if there is a bund, then it limits the area of the pool and the evaporation rate, as you will see in the next chapter.

Leave the three DistancesDistances blank. You can set a distance if you are interested in the effect levels at a particular location, but for this analysis you are interested in the maximum dispersion distance to a concentration of 200 ppm.

Check the box for Concentration of interestConcentration of interest, set a value of 200 ppm, and set UsesUses averaging time

averaging time to Toxic. The significance of the Averaging time is described in detail below.

Averaging Times in PHAST: an

Averaging Times in PHAST: an IntroductionIntroduction

The averaging time is important in PHAST , and is more prominent now than in previous versions. It is used to take into account the effects of changes in the wind direction over the course of the release, and the way that the changes cause the plume to meander from side to side. In order to interpret concentration results correctly, you must know the averaging time that was used in calculating the concentration, and the program allows you to specify different averaging times for different types of concentration results.

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The wind does not blow steadily in a straight line; its direction varies with time, which causes a cloud plume to meander from side to side. If you are standing downwind, at one moment you are in the centre of cloud, experiencing the peak concentration, and the next moment the peak has moved away to the side, and you are experiencing a much lower concentration—and in the moment after that, the peak comes back over you and off to the other side, and so on.

The average concentration you receive over, say, 5 minutes will be much less than the peak concentration; if you stood at the location for 30 minutes, the average would be lower still. This factoring down of the peak concentration is carried out by the Averaging Averaging Time Time AdjustmentAdjustment—the longer the time window, or Averaging Averaging Time

Time, the lower the calculated average concentration will be.

For the Concentration of InterestConcentration of Interest, you can choose between several averaging times, depending on the type of release. For a toxic-only material, there are five choices: aUser-Defined time that you set in theUser-definedUser-defined field at the bottom left of the dialog. group below; a Toxic time that is set in the Toxic Parameters; and the ERPG, IDLH and STEL times that are set as part of the definitions of these measures of toxicity, and cannot be changed. When you select a type of averaging time from the list, the value of the averaging time will be displayed in the field to the right of the list; the default toxic averaging time is 600 seconds, which is also the duration of this release.

Setting the Indoor/Outdoor Data Setting the Indoor/Outdoor Data

Next, move to the Indoor/Outdoor tab and set the Release DirectionRelease Direction to Horizontal. You can model a release as out of doors, where the only obstruction is the ground,

or as inside a building, where the size and ventilation of the building affects the initial stages of dispersion.

Ignoring the Other Tab Sections Ignoring the Other Tab Sections

You skipped the Vessel tab section, and you can ignore all of the remaining tab sections and clickOK to save the changes you have made.

For a vapor release, the Vessel tab section is only relevant if you want to perform time-dependent discharge modeling, in which case you must give information about the dimensions of the vessel and the liquid level. Such modeling is not applicable to the 10 Minute Release scenario, which requires only the simplest

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Defining the Hydrogen Cyanide Release

The ammonia and the hydrogen cyanide releases have the same data for the Scenario and Indoor/Outdoor tab sections, and differ only in the Material and Location data. To take advantage of this, you will create the Hydrogen cyanide model as a copy of the Ammonia model, and then edit the Material and Location data.

Copying the Ammonia Model Copying the Ammonia Model

Select the Ammonia icon, and then selectCopy from the Edit menu or from the right-click menu. Then select the Worst Case Study, and selectPaste from either menu. The program will give the copy the name Ammonia(1), and you must rename it to Hydrogen cyanide.

Setting the Material Data Setting the Material Data

Double-click on the Hydrogen Cyanide icon to open the dialog, and change the values in the Material tab section to the following values:

Discharge Material

Discharge Material HYDROGEN CYANIDE Inventory

Inventory 5,000 lb (2.3 tonnes)

Move to the Location tab section and change the values to the following: Concentration of interest

Concentration of interest 10 ppm

These changes complete the data for the release, and you can click on OK to save the edited data.

Defining the Ethylene Release

The input data for the flammable releases are significantly different from those for the toxic releases, and there is nothing to be gained from copying one of the existing releases. Create the ethylene release by inserting a new Vessel or Pipe Source Model, and give it the nameEthylene.

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Setting the Material Data Setting the Material Data

Double-click on theEthylene icon to open the dialog, and set the values in the Material tab section as follows:

Discharge Material

Discharge Material ETHYLENE Inventory

Inventory 50,000 lb (22.7 tonnes) Process Conditions

Process Conditions Temperature Pressure Temperature

Temperature 90 F (32o_C)

Pressure

Pressure 700 psig (48.3 barg)

The ethylene is stored under supercritical conditions, and you must specify both the temperature and the pressure.

After you have set the temperature and pressure, you will see that the program gives the Vessel Typ Vessel Typee and PhasePhase as Unknown. At this point, the program has not checked the state of the material at these conditions, and does not know that it is supercritical.

Setting the Scenario Data Setting the Scenario Data

Set the following data: Scenario

Scenario Catastrophic Rupture Release Phase

Release Phase Vapor

When youfirst move to the tab section, you will see that there is a choice between Vapor and Liquid for the phase. However, if you move back to the Material tab section and then back to the Scenario tab section again, you will find that the tab section has changed, and Vapor is the only choice.

This happens because the program does not check the state of the material until you moveback to the Material tab section. At this point the program determines that the material is supercritical—which the program models as vapor—and it then updates the choice of phase throughout the input data.

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Move to the Location tab section and set the values shown in the illustration:

Unlike the toxic cases, you do not need to set aConcentration of interestConcentration of interest or choose or set an associated Averagin Averaging g TimeTime. For flammable releases, the program automatically performs the dispersion to a fraction of the lower flammable limit (where the fraction is set in the Flammable Parameters), using the Flammable Averaging Time (also set in the Flammable Parameters). If you are interested in the details of the concentration results for a flammable material, you might set an additional concentration of interest and a user-defined averaging time, but for this analysis the effects from an immediate explosion are likely to be more significant than any later cloud dispersion.

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Checking the Flammable Data Checking the Flammable Data

Move to the Flammable tab section and check that the Explosion MethodExplosion Method is set to TNT. PHAST now has three explosion models available.

Leave the Early Explosion Mass Early Explosion Mass Modification FactorModification Factor with its default value of 3. This factor is used in calculating the mass involved in an early explosion. The program calculates the mass of vapor in the cloud after it has expanded to atmospheric pressure, and then multiplies this mass by theModification FactorModification Factor to obtain the explosion mass, with an upper limit set by the flammable mass released.

Setting the TNT Data Setting the TNT Data

Move to the TNT tab section. The tab section is to the right of the Flammable tab section and may not be immediately visible when the dialog first opens. If you cannot see the tab section, use the navigation button at the far right of the tabs to reveal the other tabs in the dialog.

Leave the TNT Explosion EfficiencyTNT Explosion Efficiency with its default value of0.1. This determines the fraction of the combustion energy in the explosion mass that is converted into explosion energy.

Set Air Air / / Ground Ground BurstBurst to Ground Burst, which means that the explosion occurs near the ground, i.e. at the same elevation as the release. For this type of explosion, the effects of reflection from the ground are assumed to double the amount of energy involved in an explosion, so this type will give the worst case results.

These changes complete the data for the release, and you can click on OK to save the edited data.

Defining the Propylene Release

The propylene release differs from the ethylene release only in the Material data, so you can create it as a copy of the Ethylene model, using the method described for creating the hydrogen cyanide release. Give the copied model the name Propylene.

Phast Manual

Contents

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