326494495-Phast-Manual.pdf

Contents

Contents Chapter 1 Introduction

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What is included in the manual, and how and when to use it.

Chapter 2 A Quick Tour of the Main Features

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Using an Example Study Folder supplied with the program, you examine the main types of input data, run calculations, and view reports and graphs of the results.

Chapter 3 Tutorial 1: Performing a Worst Case Analysis

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For two toxic and two flammable materials materials on the Anysite facility, you define worst case releases, and identify the material with the greatest offsite effects.

Chapte Chapterr 4 Tutoria utoriall 2: 2: Inve Investi stigat gating ing the Hydrog Hydrogen en Cyanid Cyanide e Rele Release ase

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For the hydrogen cyanide inventory considere d in Chapter 3, you define a range of releases that are more realistic than the orignal worst case scenario.

The remaining chapters are only applicable to users of PHAST Professional: Professional :

Chapter 5 Introduction to PHAST Professional

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Using an Example Study Folder, you view and investigate the additional features in PHAST in PHAST Professional. Professional .

Chapter 6 Tutorial 3: Full-Bore Pipeline Rupture

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You use the Case List tool and the User-Defined Source Model to model a fullbore release from an ammonia pipeline.

Chapter 7 Tutorial 4: Near-Field Flammable Effects

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You use the stand-alone Jet Fire model to calculate radiation levels at a range of locations at the Anysite facility, to determine the need for shielding on the paths to critical safety equipment.

Index

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Chapter 1: Introduction

Chapter 1 Introduction For Users of PHAST Micro and PHAST Professional PHAST is 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 If you have used PHAST before, 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 versio ns have been implemented in this version, and to introduce you to new functions.

New User of PHAST Micro If you have not used PHAST before, 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, quick ly, and Tutorial 2 looks at the inputs input s 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 ten minutes for each—but some of the details in Tutorial 2 may require time and concentration to absorb.

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Chapter 1: Introduction

Chapter 1 Introduction For Users of PHAST Micro and PHAST Professional PHAST is 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 If you have used PHAST before, 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 versio ns have been implemented in this version, and to introduce you to new functions.

New User of PHAST Micro If you have not used PHAST before, 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, quick ly, and Tutorial 2 looks at the inputs input s 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 ten minutes for each—but some of the details in Tutorial 2 may require time and concentration to absorb.

1

Getting Started with PHAST

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 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 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 a Dnv folder under Programs 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 PHAST Window on Startup

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 on Open, you will be returned to the PHAST window. Some messages will appear in the Choosing the Example Study Folder 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.

The PHAST Window with a Study Folder Open 5


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 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 name Example. 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 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 particular run of the consequence calculations. Weather Tab Section 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 yellowand-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 Click on the Parameters tab to move to the Parameters tab section. The parameters system in PHAST is based around a threelevel hierarchy, although only two levels of the hierarchy are evident in the Parameters tab section. You may, in fact, never make use of this hierarchy, but there are references to it in many places in PHAST , and these may puzzle you at first. Parameters Tab Section 7


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 Parameters, 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 automatically update any items in the Local Parameters that have not been edited.

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 threelevel hierarchy, with only the bottom two levels of the hierarchy visible in the Materials tab section. Materials Tab Section 8


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

Map Tab Section

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. Howe ver, 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 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 predefined 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. Setting Default Units

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:

Online Help on a Dialog

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

What’s This Help on an Input Field

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 the F1 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 In the Models tab section, double-click on the icon for the CL2 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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Input Data for the CL2 RUPTURE Model

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

Input Data for the Weather 1 Weather Condition

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 uses uses italic for the headings of all such tabs. When a tab has italic lettering , you know lettering for that there are no fields on that tab section that you have 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 lettering—such 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 syste m of lettering can be useful when you want to obtain preliminary results quickly.

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Input Data for Materials CHLORINE. In the Material tab section, double-click on the icon for CHLORINE. 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 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 for years without ever making any changes to any materials data.

Input Data for Chlorine

You are most likely likely to to use the Materials Materials tab section section for defining a Mixture—made 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 Material cascade in the a function of conditions), and you can use the options in the Material cascade 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 When you double-click on the icon for Map 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 Map Window

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 origin 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 Graph Menu

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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 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.

Setting the Models for a 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 the Example 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, select Batch 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 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 choose Run Model(s) from the right-click menu or Model(s) from the Run menu, or press Ctrl+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 select Report or Graph from the View menu, or press Ctrl+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 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.

The Report Window

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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.

The Expanded Report Tree

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 choose Full 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, press Ctrl+W, or click on the Restore button that is always visible when you are in Full Screen mode.

The Window Menu The Restore Button

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 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.

Choosing the Results to Plot

The list of Weathers will include all of the Weathers that have been defined for each Study, and not just the Weathers that have been processed for the current Model. If you select a Weather that has not been processed, an error message will appear when you click on OK.

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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.

The Graph Window

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 original state. This means that you should not use the Save 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 the c: 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.

Saving the Example Study Folder

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Before clicking on Save, you should ensure that the Save results check box is ticked, as shown in the illustration on the previous page. By default, PHAST does not save results for the Example 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 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 modeling. 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 improved 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 PHAST , and to show you features that you may find useful in your own work. If you omit parts of the tutorial because of differences in the results, you may miss a feature or a discussion that would save you time or make you much more confident in modeling releases and interpreting results.

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

Type of Hazard

Mass Present lb

tonne

Anhydrous ammonia

Toxic

40,000

18.1

Hydrogen cyanide

Toxic

5,000

2.3

Ethylene

Flammable

50,000

22.7

Propylene

Flammable

75,000

34.0

Hazardous Inventory for Anysite Facility

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: Material

Conditions

psig

barg

Anhydrous ammonia

Saturation

180.1

12.4

Hydrogen cyanide

Saturation

18.7

1.3

Ethylene

Supercritical

700.0

48.3

Propylene

Saturation

201.1

13.8

Storage Conditions

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Storage Pressure


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 concentrations, 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 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 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. The average humidity for the location is 70%, which is typical for a temperate, maritime location.

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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 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. miles km

0.5 1

1

1.5 2

2 3

Town N

Commercial and light industrial area

Everychem's Anysite facility

beach, used for recreation ocean

The Location of the Anysite Facility

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Creating the Anysite Study 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 New from the File menu. The program will create a new Study Folder Untitled with an empty Study called New called Untitled with Study. Study.

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

Renaming the Study

The New Study Folder in the Study Pane

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

Using Program Preferences to Open the Study Folder Automatically All of the tutorials in this manual use the Anysite the Anysite Study 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 recently -used Study Folders Folder s 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. Preferences... from the Options menu. The Preferences dialog will appear, Select Preferences... from appear , and file, you should set the option in the Startup tab section to Try 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.

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Setting the Preferences for Opening a Study Folder Automatically

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 interes ted in the toxic effects, and you can simplify the input data and the results if you define them as toxic tox ic 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, Howeve r, you may find it useful as a quick and straightforward introduction to the properties system.

Creating Local Versions of the Toxic Materials Materials folder Move to the Materials tab section of the Study Tree, select the Local Materials folder Case Study, and select Material... from Material... from the Insert menu. The Insert under the Worst Case Study, Material dialog will appear, as shown in the illustration on the next page. The dialog offers three ways of inserting a material. The New option New option allows you to create a completely new material, with no pre-defined properties data. The Existing and Copy options Copy 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 Existing option Existing option keeps a link to the original material, and if the values for the original material are changed, the program will automatically update the values for any fields that are still using the original, default values; the Copy option Copy option does not keep a link, and the local version ver sion will not be affected by any changes chang es to the original material.

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Inserting a Local Version of Ammonia

AMMONIA in the list of materials, and Select the Existing option, Existing option, locate and select AMMONIA in OK to add the material to the Local Materials folder. Materials folder. then click on OK to CYANIDE as the material. Next, repeat the process, selecting HYDROGEN CYANIDE as

Editing the Materials Data for the Local Materials Materials folder, you will see the icons When you expand the Study Tree below theLocal the Local Materials folder, for the two materials. Double-click Double-clic k on the icon for AMMONIA for AMMONIA to to open the input dialog, and set the Flammable/Toxic field Flammable/Toxic field in the General tab section from the default Both to Toxic only, only, as shown in the illustration on the next page. value of Both to OK to save the changed data, and then repeat the process with the local Click on OK to CYANIDE . version of HYDROGEN CYANIDE.

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The Changed Data for Ammonia

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 common 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 Default Weather Conditions for a New Study Folder

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

Weather Input Values

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 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 the Program Files/Dnv/Phast/Examples folder, which is the folder that contains the Example Study Folder covered in the previous chapter. To load the image into the window, select Bitmap... 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 the anysite.bmp file. When you return to the Map Window, you will see the map displayed in it.

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 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 Scale

The program sets the default origin 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 origin in the middle of the Anysite facility. You will set the coordinates of the releases to (0, 0), which will place them at this origin. To set the origin, 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 origin. For this worst case analysis, you do not have to place the origin 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 origin on the scale appears to be at the bottom left corner, and does not reflect the location that you have just given for the origin, but when you come to view the results on the Map you will see that program is using the correct origin.

The Completed Map

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

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 selecting Vessel or Pipe Source from the Insert menu. The new Model will be given the name New Vessel/Pipe Source, and you should rename it immediately 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 The New Model in the Study Tree 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 theWorst 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 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, choose Edit 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 select SmallFraction in the main list at the left of the dialog, then select ppm 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 on OK to implement the change.

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The Edit Dialog for Units

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 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 as System. 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 Selecting a Material automatically create a version of the material in the Global Materials folder for the Study Folder, and the next time you opened the Select Material dialog, you would see that the Scope for the material had changed from System to Global; you will see this later, when you are defining Models for the two flammable materials.

37


The Input Values for Material Data

When you select the material, the program automatically sets the Material to Track to AMMONIA. You only have to choose a material to track if the Discharge Material is a mixture. Note that you can use scientific notation when entering values, so you can enter the inventory as “40e3”.

38


Setting the Scenario Data Move to the Scenario tab and set the following: Scenario

10 Minute Release

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

Location Input Data 39


The Elevation 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. the Elevation 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 default Elevation 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 North and East coordinates with the default coordinates of zero, which will place the release at the origin 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 Distances 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 interest, set a value of 200 ppm, and set Uses averaging time to Toxic. The significance of the Averaging time is described in detail below.

Averaging Times in PHAST: an Introduction 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 Time Adjustment—the longer the time window, or Averaging Time, the lower the calculated average concentration will be. For the Concentration of Interest, you can choose between several averaging times, depending on the type of release. For a toxic-only material, there are five choices: a User-Defined time that you set in the User-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 Next, move to the Indoor/Outdoor tab and set the Release 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 You skipped the Vessel tab section, and you can ignore all of the remaining tab sections and click OK 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 discharge modeling. The remaining tab sections allow you to change the default settings for explosion, fire and discharge modeling. For a 10 Minute Release of a toxic-only material, these tab sections are not relevant. 41


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 Select the Ammonia icon, and then select Copy from the Edit menu or from the rightclick menu. Then select the Worst Case Study, and select Paste 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 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

HYDROGEN CYANIDE

Inventory

5,000 lb (2.3 tonnes)

Setting the Location Data Move to the Location tab section and change the values to the following: 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 name Ethylene.

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

ETHYLENE

Inventory

50,000 lb (22.7 tonnes)

Process Conditions

Temperature Pressure

Temperature

90 F (32 oC)

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 Type and Phase 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 Set the following data: Scenario

Catastrophic Rupture

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 move back 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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Setting the Location Data Move to the Location tab section and set the values shown in the illustration:

The Location Input Data for the Ethylene Model

Unlike the toxic cases, you do not need to set a Concentration of interest or choose or set an associated Averaging Time. 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 Move to the Flammable tab section and check that the Explosion Method is set to TNT. PHAST now has three explosion models available. Leave the Early Explosion Mass Modification 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 the Modification Factor to obtain the explosion mass, with an upper limit set by the flammable mass released.

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 Efficiency with its default value of 0.1. This determines the fraction of the combustion energy in the explosion mass that is converted into explosion energy. Set Air / Ground Burst 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 onOK 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.

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Setting the Material Data Double-click on the Butane icon to open the dialog, and change the values in the Material tab section to the following values: Discharge Material

PROPYLENE

Inventory

75,000 lb (34.0 tonnes)

Process Conditions

Temperature Saturated Liquid

Temperature

90 F (32 oC)

When you change the material from ETHYLENE to PROPYLENE, a warning message may appear as shown. When you change the material, the program performs flash calculations to check the current process conditions. At 90oF and 700 psig, ethylene is a supercritical vapor but propylene is a liquid, and this message is telling you that the current settings The Warning about for Vessel Type and Phase are incorrect. As soon Process Conditions as you change the conditions from Pressureto Saturated Liquid, the program will update the Vessel Type and Phase, and you should not see the warning message again during your work on the Propylene Model.

Checking the Scenario Data Move to the Scenario tab section, and you will see that the only choice is Liquid. The presence and design of a bund or dike can have a significant effect on liquid release s, but you should leave the bund data in the Location tab section unset, as with the vapor releases, since this will allow the liquid pool to spread indefinitely, giving a larger evaporation rate than with a bund. This completes the release data, and you can click on OK to save the edited values.

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Viewing the List of Global Materials Move to the Materials tab section, and expand the tree under the Global Materials folder. You will see that icons for ETHYLENE and PROPYLENE have been added to the folder; each was added as a copy of the System version when you selected the material in the input dialog. The Ethylene and Propylene Models obtain their materials data from these Global versions. If you add Models for further ethylene or propylene releases, these Models will also use these versions.

Running the Calculations First, select Batch/Weather Setup... from the Run menu, move to the Weather tab section, and check that the Weather 1.5/F condition is selected. Although you will be running the four Models directly, and not in a Batch Run, the run will use the Weathers that are selected in the Batch Setup dialog. If you add other Weathers to the Study Folder, you will have to return to the dialog to select them before the program will process the calculations for the additional Weathers. To run the calculations for all of the Models, select the icon for the Worst Case Study, and then start the run. There are three ways of starting a run: you can select Model(s) from the Run menu or Run Model(s) from the right-click menu, or you can press Ctrl+M. You can follow the progress of the run in the Progress Meter, and also in the Message Log tab section of the Log Window.

Viewing the Results The Graphs give the most direct way of viewing the results. To view the Graphs for a Model, select that Model, then click Ctrl+G, or choose the Graph option from the View menu or the right-click menu. The Plot Setup dialog will appear, prompting you for the Weather and Map to use, and when you click on OK, the program will generate the Graphs, and display them in the Graph Window.

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The Results for Ammonia There are seven Graphs which show concentration results. For this analysis, the most important Graph is the Map. When you first move to the Map tab section, there will be two concentration contours shown on the Map, for around 200 ppm (the concentration of interest) and around 400 ppm, as shown in the illustration. These contours are some distance from the site, and show that the cloud has become detached from the release point because the time taken for the cloud to disperse to 200 ppm was much longer than the ten minute duration of the release.

The Concentration Contours on the Map

This aspect of the release makes the results quite complex, and you may find them difficult to interpret at first, especially as the program gives much more detail in the results than in previous versions and provides many more options. The first thing to notice in Graphs of this type is the Time displayed in the legend. In the Map in the illustration, the time is given as 2297.76 s, and this is the time after the start of the release at which the area covered by the 200 ppm contour (the contour for the concentration of interest) was largest.

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To see the contours for other times, select Dynamic from the Graph menu or the rightclick menu, and the Cloud Dynamics Control will appear. You use this Control to view an animation of the cloud dispersion.

The Cloud Dynamics Control

Click on the rewind button at the left of the control to set the animation time to the beginning of the release, and then click on the play button at the right of the control to start the animation. You will see the development of the cloud displayed on the Map, and when the time reaches about 600 seconds (as shown in the legend), you will see the cloud become detached from the release point. If you run the animation to the end of the release, you will see the 200 ppm contour reach the town, and disappear off the map. This shows that the worst case ammonia release does have the potential to reach populated areas offsite. The effect of the cloud will depend on the time that it takes to pass over the town, and you can see this in the Time tab section. The Time Graph shows the timedependent concentration profile at a particular distance from the release source. When you first move to the tab section, the distance will be set as the mid-point of the cloud at the time that the contour covers the largest area (i.e. as in the first view of the Map Graph), but you can change this distance. The distance from the release to the middle of the town is approximately 14,000 ft (4.3 km). To set this as the distance for the Time Graph, select Properties from the Graph menu or the right-click menu, and set the value as shown:

Setting the Distance for the Time Graph 49


When you click on OK and return to the Time Graph, the Graph will change, and you can see the concentration profile at the town. The Graph shows that a person at that point would only be exposed to the cloud for about ten minutes, but the concentration during this time would be over 400 ppm. The 200 ppm concentration of interest is based on an exposure of an hour, so the effects from this cloud should be small, but could still be unpleasant.

The Concentration Profile at the Outskirts of the Town

The Results for Hydrogen Cyanide As with the ammonia release, the hydrogen cyanide release becomes detached from the source. The 10 ppm contour does not reach its largest area until it is has passed over the town, so the cloud will not be visible in the Map Graph when you first move to the Graph. If you use the Properties... option to set the distance of interest to 14,000 ft and move to the Time Graph, you will see that the duration of exposure at the town is ten minutes, as for the ammonia release. However, for most of this time, the concentration is over five times the concentration of interest (i.e. over 50 ppm), whereas for the ammonia release, the concentration is twice the concentration of interest.

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The Concentration Profile for Hydrogen Cyanide

The difference in the values for concentration of interest makes it difficult to compare the concentration results for ammonia and hydrogen cyanide using the Map and Time Graphs. However, the Lethality Graph allows you to compare the toxic effects directly, and you can also plot the results for the two Models on the same Graph. In order to plot the combined results, you must open a third Graph window. Move to the Weather tab section of the Study Tree, select the 1.5/F Weather, and then press Ctrl+G to generate the Graph. The Plot Setup dialog will open, with a Model tab section instead of a Weather tab section, and you can select the two toxic Models, as shown: Plotting a Graph for more than one Model

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The Lethality Graph shows the results for both Models, and it shows that the toxic effects of the Hydrogen cyanide Model are worse than those for the Ammonia Model. At the town, the ammonia release gives zero probability of death, whereas the hydrogen cyanide release gives a significant probability, of about 10%.

Comparing the Toxic Models in the Lethality Graph

If you look at the Graphs for concentration, you will find that they are plotting the results for 200 ppm, i.e. the concentration of interest for ammonia. The program cannot plot a comparison of the results for 10 ppm, because the calculations for ammonia stopped at 200 ppm, so it can only compare the results for 200 ppm. This comparison at 200 ppm may be misleading, because the inventory for the Hydrogen cyanide Model is much smaller than for the Ammonia Model, and the cloud is diluted to 200 ppm much more quickly. This emphasizes that some Graphs are useful for some purposes (e.g. getting the details of the results for a single Model, or for comparing Models that involve the same material) whereas other Graphs are useful for other purposes (e.g. comparing Models that involve different materials).

The Results for Ethylene and Propylene The two flammable Models have the same critical effect-level, i.e. 1 psig, and their results can be compared directly. Move to the Weather tab section, select the 1.5/F Weather, press Ctrl+G, and then select the two flammable Models in the Models tab section of the Plot Setup dialog, and make sure that the Anysite surroundings Map is selected in the Map tab section.

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When you first move to the Map Graph, it will be displaying the concentration contours for the two Models. This is the default option for the results displayed on the Map, but you can use the Properties... option to change this. In the Display tab section,change the Display Option for Map from Cloud Footprint to Early Explosion Overpressure, as shown. You should also move to the Overpressures tab section, and set the Primary Overpressure to 1 psig, as shown.

Setting the Graph Properties for Viewing the Overpressures on the Map

When you have clicked on OK and the program has redrawn the Map Graph, you will see that the overpressure radii to 1 psig do not extend outside the boundary of the site, and pose no threat to the town, as shown in the illustration.

The Explosion Results for the Flammable Models

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Summary of Worst Case Analysis The Worst Case analysis shows that the hydrogen cyanide inventory poses the greatest offsite risk, and is the only inventory capable of causing fatalities at the town. In Tutorial 2, in the next chapter, you will investigate hydrogen cyanide releases on the site in more detail, finding how the results of realistic release scenarios compare with the worst case.

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Chapter 4 Tutorial 2: Investigating the Hydrogen Cyanide Release 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. 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 improved 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 PHAST , and to show you features that you may find useful in your own work. If you omit parts of the tutorial because of differences in the results, you may miss a feature or a discussion that would save you time or make you much more confident in modeling releases and interpreting results. 55


Stage 1: Instantaneous Release The previous chapter described a simple worst case analysis for the Anysite chemical installation. This analysis considered releases of four materials held on the site in significant quantities, and determined that the hydrogen cyanide releas e had the greatest potential to reach beyond the site boundary. The scenario modeled in the worst case analysis for hydrogen cyanide was a release of the entire inventory as vapor over a period of ten minutes. These investigations will determine whether this is a realistic scenario, and examine the effects of several variables in the modeling.

In the first stage of the investigations, you will model the release of the entire inventory as an instantaneous release. The worst-case scenario was devised assuming that the ten-minute continuous release would give the greater dispersion distances and the greatest toxic effect, and this stage is intended to confirm that assumption, so that the other stages can concentrate on the factors affecting continuous releases.

Create a Separate Study for the Investigations Before you can model the instantaneous release, you must make some preparations in the Anysite Study Folder. Open the Study Folder, select the Study Folder in the Study Tree, and insert a new Study using the icon in the Toolbar or the option in the Insert menu. Give the new Study the name HCN Investigation. You will be placing all of the Models for this tutorial in this Study.

Create a Special “Global” Study for Shared Weathers and Maps When you start to divide a Study Folder into multiple Studies, you have to make some adjustments in the design philosophy for the Study Folder. Some of these adjustments are essential, and you must make them to ensure that the Models in the various Studies are processed as you intended. Other adjustments are optional, but will make the purpose and design of the analysis clearer to another user. This section describes how to create and use a “global” Study as a location for Weathers and Maps that are shared between the Worst Case Study and the HCN Investigation Study. This is an optional adjustment, but strongly recommended.

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Insert another Study, and give it the name Global Weathers and Maps. The program inserts each new Study at the bottom of the list of Studies. However, it will make the design of the analysis clearer if the Global Study is at the top of the list of Studies, especially if you are going to add more Studies to the list. PHAST does not allow you to simply drag the Global Study to the top of the list, and you must take the following steps in order to obtain the order that you require: Drag the icon for the Worst Case Study up to the icon for the Anysite Study Folder The program acts as if you have just “inserted” the Study into the Study Folder, and places it at the bottom of the list. Drag the icon for the HCN Investigation Study up to the icon for the Anysite Study Folder Again, the program places the Study at the bottom of the list. The Studies will now be in the more-natural order shown in the illustration. Next, move to the Weather tab section of the Study Tree, select the 1.5/F Weather, and drag it to the Global Study. Then move to the Map tab section of the Study Tree and do the same with the Anysite surroundings Map. Finally, select Batch/ Weather Setup... from the Options menu, and select the 1.5/F Weather under the Global Study.

The Rearranged Studies

The Global Study makes use of the fact that the program can run a Model in a given Study with a Weather in any other Study, and can display the results on a Map from any other Study. This means that you could have left the Weather and Map in the Worst Case Study, and the Models in the HCN Investigation Study would have been able to use them; however, it would not be obvious to another user that the Weather and Map were supposed to be shared, and this user might find it difficult to duplicate your results. When you use a Global Study, it is clearer which Weathers and Maps are intended to be shared, and which are specific to particular Studies.

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Move the Local Version of Hydrogen Cyanide to t he Global Materials In this second tutorial, you are still only interested in the toxic effects of hydrogen cyanide, and not in the flammable effects. If you ran a Model in the new Study now, the program would not find a version of HYDROGEN CYANIDE in the Local Materials folder for the new Study, and would create a version in the Global Materials folder as a copy of the System Materials version, which is both toxic and flammable. To ensure that the HCN Investigations Study uses the toxic-only version of HYDROGEN CYANIDE, you can either copy the local version from the Worst Case Study to the HCN Investigations Study, or you can move the local version from the Worst Case Study to the Global Materials folder. The second approach is simplest, and is recommended here. To move the material, you can drag it from one folder to the other. Making the toxic-only version into the Global version involves a slight shift in the design philosophy for the analysis. As a Local material, the toxic-only version was the exception, but as a Global material it is now the rule. If you want to investigate the flammable effects of hydrogen cyanide, you will have to create a further Study, insert a Local version of hydrogen cyanide into that Study, and then edit the input data to make the Local version both flammable and toxic. This is another example of the shifts in design philosophy that occur when you start to divide a Study Folder into multiple Studies.

Rerun the Worst Case Study As you saw in the previous chapter, you can only compare the results of Models if they have been processed with the same Weather. In this tutorial, you will be comparing the worst case results for hydrogen cyanide with the results for the various investigations. Since you will be running the investigations with the Weather in the Global Study, this means that you must also run the worst case releases with this Weather. Select the Study (or just the Hydrogen cyanide Model), and press Ctrl+M to rerun. You do not need to view the results at this stage. This may seem like a duplication of effort, since you previously ran the worst case releases with exactly this Weather when it was in the Worst Case Study. However, the program identifies Weathers by their location only, and does not know that the two Weathers are identical and that the results from the Worst Case Weather would be entirely valid for the Global Weather.

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Create and Run the Catastrophic Rupture Model Select the Hydrogen cyanide Model from the Worst Case Study, copy it, and paste it into the HCN Investigation Study. Rename the copy Instantaneous. Double-click on the Instantaneous Model to open the dialog, move to the Scenario tab section, and change the Scenario from 10 Minute Release to Catastrophic Rupture. This is the only change you need to make, and you can click on OK to close the dialog and save the change. Select the Instantaneous Model and press Ctrl+M to run the calculations for the Weather in the Global Study.

View the Results To compare the results for the two Models, move to the Weather tab section of the Study Tree and select the 1.5/F Weather from the Global Study. In the Plot Setup dialog, select the Worst Case/Hydrogen cyanide Model and the HCN Investigation/Instantaneous Model; don t forget to select the Map as well. The Time and the Lethality Graphs give the best comparison. The instantaneous cloud does reach the town, and its peak concentration at the town is similar to that for the worst case release. However, the duration of exposure is much shorter, and the lethality is therefore much lower, as shown in the graph on the next page.

Comparing the Results using the Time Graph

The instantaneous release is diluted more quickly because air is able to mix in over a larger area.

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Comparing the Results using the Lethality Graph

Stage 2: Discharge from Largest Connection on Vapor Side The Instantaneous Model shows smaller toxic effects than the continuous Worst Case Model, but the worst case scenario modeled in the previous chapter may not be realistic for this facility. The worst case scenario was a vapor release, which meant that all of the released material remained in the cloud, and the mass in the cloud was not reduced by rainout of liquid droplets. Assuming that a vapor release will give larger toxic effects than a liquid release, the next stage is to determine the maximum size of a realistic vapor release from the hydrogen cyanide process, and to model the release of the inventory at this release rate. This requires information about the design of the equipment, and the HCN tank and its fittings are shown in the illustration on the next page. The largest vapor release would be caused by the full-bore failure of the vapor pipework, which has a diameter of four inches. A hole with a diameter larger than four inches could occur in the body of the tank, but such a hole would not be stable and would propagate immediately to a catastrophic rupture. Therefore, the fourinch pipework failure is the realistic scenario for the largest continuous vapor release.

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vapor line Diameter: 4"

Tank Length: 12' (3.66 m)

Tank Diameter: 6' (1.83 m)

liquid line Diameter: 1.5" The Hydrogen Cyanide Tank

Create the Model for the Scenario Create a copy of the Instantaneous model, and name it 4 inch vapor .

Edit the Input Data for the 4 Inch Vapor Model Set the following values in the Scenario tab section: Scenario

Leak

Phase to be released Vapor Hole diameter

4 inch (10.2 cm)

You do not need to make any changes in any other tab section, and can click onOK to save the values. Although the incident that you are modeling is the rupture of a pipe, you should choose the Leak scenario at this stage instead of the Line Rupture scenario. The Leak scenario does not take friction into account, and gives more conservative discharge results. If the rupture is close to the tank, then the effects of friction will be negligible, so this conservative approach is still realistic.

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Run the Model and View the Results Use the Run option from the right-click menu to run the model. First, you should compare the discharge results for the worst case Model and the 4 inch vapor Model. The discharge results are shown in the Discharge Report, and you open the Report for each Model by selecting the Model, and then clicking Ctrl+R. The Models are in different Studies, so you cannot generate a single Report that would cover both of them (unlike the Graph), and this means that you must open a separate Report window for each Model. The discharge results are as follows:

Worst Case

4 inch Vapor

30,000 lb/hr (3.78 kg/s)

10,299 lb/hr (1.3 kg/s)

Duration

600 s

1,747 s

Liquid Fraction

0.02

0.02

Mass Release Rate

Comparison of Discharge Reports

The release rate of the largest realistic vapor release is therefore about one third of the release rate for the ten minute release modeled as the worst case. The dispersion distances for this release should be much shorter than the worst case, but the increased duration will increase the toxic effects for a given concentration. Next, view the combined Graphs for the two Models:

The Time Graph 62

The Lethality Graph


The Time Graph shows that the 4 inch vapor model gives a concentration at a distance of 14,000 ft (the middle of town) that is only 50% higher than the lowest concentration of interest (10 ppm), whereas the concentration for the Worst Case Model is more than three times the concentration of interest. The Lethality Graph shows that the reduction in concentration has a greater effect on the lethality than the increase in duration.

Stage 3: Time-Varying Vapor Release The continuous releases that you have modeled so far have all assumed that the release maintains the full initial rate until the inventory is exhausted. In reality, the discharge will change the conditions inside the tank, and as the conditions change, the discharge rate will also change.

Create and Edit the Model Copy the 4 inch Vapor model and name the copy 4 inch Vapor - time-varying. Set the values in the Vessel tab section as shown.

Defining a Time-Varying Release

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The Rates versus time options give you different ways of choosing representative release rates for use in the dispersion modeling. You can model the time-varying discharge profile as a sequence of up to ten “segments”—where each segment has a constant rate over a given duration—or you can model it as a single segment, using one of three methods of choosing the representative conditions for the segment. For this model, you are using the Average rates method, which sets the representative rate by dividing the inventory by the duration of the time-varying release. Refer to the online Help for a full description of each method. The Dimensions are taken from the illustration earlier in the chapter. The ruptured pipe is assumed to be attached to the top of the tank, although the exact location of the leak is less important for a vapor leak than for a liquid leak. When you give the dimensions, the program calculates the volume of the tank and compares this with the volume of the inventory; you will get an error message if the tank is too small to contain the inventory, but in this case the tank has about twice the volume of the liquid inventory.

Run the Discharge Calculations and View the Results Select the model, and then select Run Discharge from the right-click menu or press Ctrl+D. This will run the discharge calculations on their own, without proceeding to the dispersion calculations. Press Ctrl+R to view the Reports. The Discharge Report gives the summary, with the discharge results that will be passed to the dispersion calculations, and the main results in this Report are as follows: Mass Flowrate

5,405 lb/hr (0.681 kg/s)

Release Duration

65.8 s

The average mass flowrate is about half of the initial rate, and the duration is a fraction of the duration calculated by the “initial rate” calculations. The “initial rate” calculations assume that the full inventory is immediately available as vapor, whereas the time-varying calculations consider the separate masses of liquid and vapor in the vessel. The vessel has a volume of about 300 ft3, and the liquid occupies about a third of the volume. At 90°F and saturation conditions, the density of the vapor is 0.09 lb/ft3, so the mass in the vapor space is about 18 lb—a small fraction of the total inventory. As the gas is released and the pressure drops, some of the liquid in the vessel will vaporize and will be available for release, but this vaporization reduces the temperature of the liquid, and so the vaporization rate usually drops quickly to a low value. The program stops the calculations when the vapor inventory drops below a minimum value, and for this Model, that inventory is reached after 65 seconds.

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The TV Discharge Report gives the details of the time-dependent discharge results. With such a short release, the details of the discharge profile will not affect the results significantly, and it is not necessary to examine this Report very thoroughly. For this Model, the single, average rate will be sufficient to represent the discharge behavior in the dispersion calculations.

Run the Dispersion Calculations and View the Results Run the full calculations, and then view the Graphs for the two 4 inch vapor Models. The effect distance for the time-varying Model is less than 2000 ft, which means that effects are not felt beyond the boundary of the site.

Stage 4: Discharge from Largest Connection on Liquid Side You now have a good picture of the hazardous potential of vapor releases, and will move on to investigate realistic releases from the liquid side, starting with a fullbore rupture of the largest pipework connection, which is two inches in diameter.

Create the Model and Set the Input Values Copy the 4 inch vapour model and name the copy 2 inch liquid. Set the following values in the Scenario tab section: Phase to be released Liquid Hole diameter

2 inch (5.1 cm)

and the following value in the Vessel tab section: Tank Head

2 feet (0.6 m)

The Tank Head is a compulsory field for liquid leaks, which means that you must enter a value before you can run the Model. Before closing the dialog, check the Location tab section. You will see that the box by Dike with Bund Area is unchecked, which means you are modeling this as an unbunded release. An unbunded liquid pool is assumed to spread until it reaches a minimum thickness, and this may give a very large pool, with a large evaporation rate. This is a conservative approach, and for the next stage you will model the same case with a bund, and see the effect.

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Run the Calculations and View the Results Select the Model, and press Ctrl+M to run the full calculations. When the calculations are complete, press Ctrl+R to view the Report. As you will see, this release involves rainout and evaporation. The dispersion results for such releases are not always easy to interpret, and some of the simplifying assumptions that are used can produce effects that may initially be disconcerting. For these reasons, the results for this Model are discussed in some detail.

The Discharge Report First, view the Discharge Report, which shows that the maximum liquid discharge rate is twice the rate in the Worst Case Model, and that the release has a very high liquid fraction of 98%. This gives very different dispersion behavior. The Discharge Report for the Liquid Model

The Pool Vaporization Report The Report window contains a Pool Vap. tab section, which gives the Spill Rate (or amount of rainout) as 55,692 lb/hr, which means that the remaining vapor portion of the cloud has a mass rate of 6,922 lb/hr (from the initial release rate of 62,614 lb/ hr). The Report also gives a summary of the pool vaporization results, as shown:

The Pool Vaporization Summary Results

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The program has represented the full time-dependent vaporization behavior with a sequence of seven Average Rates, where each Average Rates has a constant vaporization rate over a given duration; to see the full results that these Rates represent, you can refer to the Pool Details Report. The largest Average Rate (17,119 lb/hr), is about 25% of the liquid release rate, but this vaporization rate is only maintained for just over a minute. For most of the duration of the vaporization, the rate is less than 10% of the initial release rate (5,324 lb/hr).

Setting Options for the Dispersion Report Before you start to look at the Dispersion Report, there are some settings you may need to change in order to make the results easier to read. You should close the Report before you make these changes because the program does not update the Report window dynamically (unlike the Graph window), so you will have to re-open the window after you have made the changes in order to see the effect. First, you must edit the units system (using the Options menu) and change the units for concentration (“SmallFraction") from “fraction” to “ppm”. You may already have done this at the beginning of the previous tutorial, but the choice of unit is particular important when you are looking as the Dispersion Report. The Reports use a maximum of three places of decimals, and therefore all concentrations below 1000 ppm will appear as 0.000 when presented as a fraction, and you will not be able to interpret most of the results. For the second change in the settings, you must change the selection of fields (or columns) that appear in the Dispersion Report. To do this, choose Preferences... from the Options menu, and move to the Dispersion tab section of the Preferences dialog, which is shown in the illustration on the next page. There are more than twenty fields that you can include in the Report, but each Report can show a maximum of eleven columns, so some have to be excluded from the Report. By default, the program selects the first eleven fields—as they appear in the list in the dialog. For this analysis, you are not interested in the more technical measures of plume width and height (Items 8 to 11 in the list), but you are interested in the Mass Flowrate and the Liquid Fraction, since they give useful information about the rainout.

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Select the first seven fields, the Mass Flowrate, and the Liquid Fraction, as shown in the illustration. You can use standard Windows selection techniques with the list, using Shift+click to select a continuous set of items (i.e. the first seven fields), and using Ctrl+click to add further items to an existing selection (i.e. to add the Mass Flowrate and the Liquid Fraction. When you have made the selection, click on OK to save it. You do not need to re-run the calculations, because the program always calculates all of these fields; the setting affects the display of results, only.

Changing the Preferences for the Dispersion Report

You can now use Ctrl+R to open the Report again.

The Dispersion Report The following information appears at the beginning of the Dispersion Report:

Averaging Time Information at the Beginning of the Dispersion Report

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The averaging time used in calculating the centerline concentration in the Dispersion Report is known as the Core Averaging Time, which is set in the Dispersion Parameters. The Report uses a different averaging time when calculating the Plume Height and Plume Width. These are calculated to a concentration of 10 ppm, using the averaging time set in the Location tab section for the Model, which was set as the Toxic Averaging Time (600s by default) with the original worst case Model for hydrogen cyanide, and has been copied to all of the other hydrogen cyanide Models. The longer averaging time for the Plume Height and Plume Width gives lower concentrations than the core averaging time—as you will see later in the Averaging Times Report—and this gives effects in the Dispersion Report that may puzzle you at first. Towards the end of the dispersion, the Height and Width to 10 ppm will be zero, while the Centerline Concentration will be above 10 ppm, and this apparent discrepancy is caused by the difference in averaging times. The details of the dispersion results begin after the statement of averaging times, and they appear in the first page of the Dispersion Report as follows:

The Beginning of the Dispersion Results

There are in fact nine segments reported in the Report, and you can see this if you expand the Report Tree at the left of the Report to its lowest level, as shown. The definition of the various segments can seem complicated at first, and is described below in some detail. You will not have to examine the Report for each Model in this level of detail in order to understand and use the results—indeed, for most Models, the Graphs will give you all the information you need very quickly. However, you may need to refer to the Dispersion Report if you want to know more about the dispersion behavior, and you will find the Report much easier to read if you already know how the program defines segments and reports their results.

The Segments shown in the Report Tree 69


Segment 1 always represents the full initial release, with its mixture of vapor and liquid. The liquid droplets rain out after 0.46 s, at a distance of 12.8 ft from the release point, as you can see from the end of Segment 1 on the next page of the dispersion results:

The End of Segment 1 in the Dispersion Results

Some of the liquid evaporates in this short time while the drops are falling to the ground, as you can see from the drop in the liquid fraction from 0.98 at the beginning of the segment to 0.89 at the end. For this Model, the next few segments (2 to 4) represent a combination of the remaining vapor from the original cloud (with its rate of 6,922 lb/hr), with the vapor that evaporates while the release is continuing. The release has a duration of 287s after rainout, and this covers Average Rate 1 (186 s duration, from the Pool Vap. Report), Average Rate 2 (80 s duration) and the first 21 s of Average Rate 3. Segment 5 is the first segment of vaporization after the release has stopped, and it covers the last 40 s of Average Rate 3. The remaining segments (6 to 9) cover the rest of the vaporization, and correspond exactly with the remaining Average Rates (4 to 7). In the Report, the time-history for each segment is measured from the start of that segment, so the initial time is given as 0.00 s, as you can see in the results for Segment 2, on the previous page. To relate this to the time from the start of the release, you must add the timings for rainout and the durations of the preceding segments. The segments that occur after rainout all start at 12.8 ft from the release location, which is the rainout location and the center of the pool. Next, move through the Report to find the end of Segment 2 and the beginning of Segment 3, which is shown in the illustration on the next page. The Report Tree gives the quickest way of moving to the results for a particular segment—click on the segment in the tree, and the program will move to the beginning of that segment in the Report.

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The Next Segment in the Dispersion Report

Segment 3 is the second segment that occurs after rainout and you can see that, like Segment 2, the time starts at zero, and the position starts at 12.7 ft from the release location. The results for the end of Segment 2 show that this segment takes over an hour and nearly 29,000 ft to dilute to a centerline concentration of 10 ppm (calculated with the core averaging time). For an averaging time of 600 s, the centerline concentration at this distance is much lower, and you can see that the Plume Width and Plume Height, measured to 10 ppm and calculated with an averaging time of 600 s, are both zero. If you go further back in the results, you will see that the Width and Height become zero at about 18,000 ft, which shows that the averaging time can have a large effect of the results. If you look through the results for Segment 2, you will find that the Report does not reflect the duration of the segment. The segment ends after 186 s, but there is no recognition of this in the report, or of any effects from the plume becoming detached from the release location (i.e. the pool). This reflects one of the main simplifying assumptions in the modeling of multi-segment clouds, which is that the calculations treat the release as if it had sufficient duration to give a fully-developed plume. When a plume is fully developed, the material at a given section through the plume is moving forward into the next section of the plume, which is already in motion and mixed with air, and in this state, air is entrained into the plume through the sides only, and not through the leading or trailing edges. For the dispersion results, this is a conservative assumption, since it reduces the total entrainment rate.

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When the program needs to obtain the state of a segment at a given time—e.g. to display on a Graph—it takes a slice from the fully-developed plume which is described in the Dispersion Report. For instance, at 4,514 s, the leading edge of the plume is at 28,960 ft. The trailing edge will be 186 s behind the leading edge (given by the duration), and at 4,328 s (4,514 s less 186 s), the leading edge was at about 27,320 ft. Therefore, at 4,514 s, the leading edge is at 28,960 ft, and the trailing edge is at 27,320 ft. This approach of taking slices through the plume is illustrated much more clearly in the Graphs, as you will see later, but the Dispersion Report is the only form of results that presents the fully-developed plume that is the foundation for the Graphs, and if you can visualize this plume, you should find the Graphs easier to interpret.

The Averaging Times Report The centerline concentrations in the main Dispersion Report are calculated using the Core Averaging Time, but the Averaging Times Report (or Avg Times Report) shows centerline concentrations calculated with different averaging times, and this can be a useful supplement to the results in the Dispersion Report. The Report is similar to the Dispersion Report in that it shows results for each segment, and at the same distance steps. It is simpler in that it only shows the centerline concentration, but it shows the concentration calculated with up to six averaging times, depending on the type of release, and on the averaging times that you selected in the Location tab section of the input dialog. The beginning of the Report appears as follows:

The Averaging Times Report 72


The Report always has values for the Flammable Averaging Time or the Toxic Averaging Time as appropriate for the type of material; the times are set in the Flammable Parameters and the Toxic Parameters. Here, hydrogen cyanide is being modeled as toxic only, so the results for the Flammable time are blank. The Report also always has values for the User-Defined Averaging Time. If you chose User-Defined as the method of setting the time in the Location tab section for the Model, then the User column will contain values for the time that you entered; otherwise, the User column will contain values for the Core Averaging Time, which is set in the Dispersion Parameters. For this Model, you did not set a UserDefined Averaging Time, but selected the Toxic Averaging Time instead. The beginning of the Report shows identical concentrations for the Toxic and User Averaging Times, and if you move to the next page of the Report, you will see that the concentrations remain the same in the two columns until the cloud has reached about 350 ft—and this is the same for all segments. The use of the averaging time applies only to passive dispersion, when the cloud momentum is low enough that the wind is able to move the cloud from side to side, and this release does not start to become passive until about 350 ft. If you look for the distance at which the concentration for Segment 2 falls to 10 ppm for the Toxic Averaging, you will see that this is about 18,000 ft, which is the distance in the Dispersion Report at which the Plume Height and Plume Width—which were calculated using the Toxic Averaging Time—dropped to zero.

The Map Graph You have now seen the most important Reports, and can move on to the Graphs. The Map Graph gives the clearest presentation of the multi-segment results, especially if you use the Dynamic option in the Graph menu or right-click menu to view the animated development of the cloud. The illustration on the next page shows the cloud at a time about half-way through the total dispersion. The cloud looks strange, with many discontinuities that would not be present in reality. These discontinuities occur because of the simplifications that are needed in order to represent the complex time-dependent behavior within sensible limits for the volume of calculations and results. The first simplification is the use of a limited number of Average Rates to represent the time-dependent evaporation rate (which you can see in the Pool Evapn Graph). The mass rate changes abruptly between Average Rates, and therefore between release segments, and this produces abrupt changes in the behavior of the cloud.

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The Multi-Segment Results on the Map

The second simplification is the approach of representing each cloud segment with a slice taken from the corresponding fully-developed cloud, without corrections for the effects of entrainment at the leading or trailing edge. This is a reasonable assumption given that, in reality, the evaporation rate changes smoothly, but in presenting the results for the segments, it has the effect of emphasizing the discontinuities. If you are visualizing the release as a sequence of segments, you may also be visualizing the real-life situations in which a release rate can change abruptly—for instance, the situation when the last of the liquid is discharged from a two-phase vessel, and the release changes from a liquid to a gas release—and in real life you would expect this change to introduce a new leading edge or trailing edge, and to see air entrainment at this edge giving a smoothed concentration profile inside the cloud. If you can bear in mind these simplifications and their effect on each other, you should find these discontinuities less disconcerting, and you should find it easier to visualize the “smoothed” form of the results.

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The aspects of the results that should show the least effect of the discontinuities are the centerline concentration and the plume height and width for the mid-point of each segment. If you concentrate of these measures, you will be able to read the essential data from the results with the same confidence as with a single-segment release.

Comparing Graphs with the Worst Case Model You have now looked at all of the most important aspects of the results for this type of release—i.e. a liquid release with rainout and evaporation—and can now step back from the details, and compare the Model with the Worst Case Model, as you did with the other Models in the Study. Close the Graph and the Report, and then move to the Weather tab section of the Study Tree and open a new Graph with the Worst Case Model and this 4 inch Liquid Model. As you can see in the illustrations, although the initial release rate was larger than the release rate for the Worst Case Model, the rainout and the relatively slow evaporation give a much lower vapor release rate into the cloud, and reduce the size of the cloud and its effects.

Summarized Results for the Model

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Stage 5: Largest Liquid Release with a Bund The two inch liquid release that you have just modeled used conservative assumptions in that it had no bund, so that the pool could spread to the largest possible size, giving the maximum evaporation rate from its surface. In this stage, you will model the same release with a bund, to investigate the effect on the evaporation rate. The hydrogen cyanide tank has a bund 15 feet long by 10 feet wide, which will give a pool about four inches deep with the entire inventory released into the bund.

Create the Model and Set the Input Values Copy the 2 inch Liquid model and name the copy 2 inch Liquid - bunded. Set the values as shown for the bund data in the Location tab section:

Concrete is the default Bund Surface Type.

Run the Calculations and View the Results You will see that the results are identical to those for the unbunded release. The Pool Vap Report states that the bund is not hit, and shows a maximum pool radius of more than 38 ft, which means a pool area of over 4500 ft2—much larger than the 150 ft2 area that you specified in the input data. This is occurring because the rainout position, at 12.77 ft, is outside the bund. The program models the bund as a circle with the area given in the input data, and this equivalent circle has a radius of 6.9 ft, so the rainout position is well beyond the bund. This behavior may puzzle you the first time you see it in the results, since the Report does not emphasize the fact that the rainout takes place outside the bund, and you may think that the program is ignoring the bund completely. This aspect of the modeling is realistic in that rainout is not likely to occur exactly at the release point, and may well be delayed until after the cloud has passed over the bund wall, in which case the bund will not be effective. However, the approach is also simplified in that it treats rainout as occurring at a single point, whereas in reality it would occur at a range of locations, and some of the rainout might be inside the bund, and some outside.

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There are several input variables that affect this aspect of bund modeling, and that you can use for control and investigation. The use of each of these variables is described below.

Variables that Affect Rainout: Release Direction and Elevation You set the release direction in the Indoor/Outdoor tab section, and it is currently set as Horizontal, which was the value that you set for the worst case ammonia release at the beginning of Tutorial 1, and have copied to subsequent toxic Models. If you change this setting to Down - impinging on the ground, as shown in the illustration, the program will ignore the Elevation that is set in the Location tab section, and will model the release as starting at ground level, and with reduced momentum.

Changing the Release Direction

In this situation, the liquid droplets do not have a “fall time” or “fall trajectory” as they do when released from a height, so they do not have the opportunity to evaporate before reaching the ground, or to travel any distance from the release location—and the program models this by assuming that all of the liquid rains out immediately, and at the release location. This is a realistic setting to make for a liquid release, since many releases will be from the bottom of the equipment, and will therefore be directed towards the ground. If you make this setting for the 2 inch liquid - bunded Model, then you will ensure that the rainout does occur inside the 150 ft2 bund. The mass that rains out will be larger than for the unbunded Model because the droplets do not evaporate before raining out, and that will also change the vaporization results. With this setting, the program represents the pool vaporization with a single Average Rate, as shown in the illustration of the Pool Vap Report for the Model:

Pool Vaporization Results

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Compare this with the Average Rates for the unbunded release, where the smallest rate was 3,377 lb/hr, and the rate with the longest duration was 5,324 lb/hr. This shows that a bund can have a significant effect on the results for a liquid release. You can achieve a similar effect by setting the Release Elevation to zero in the Location tab section. In this case, the release will be modeled with no reduction in momentum, because it does not impinge on the ground.

Variables that Affect Rainout: Bund Area Not all liquid releases will be directed downwards, and sometimes you will want to model a release as horizontal (or at some other angle). In this case, if you want to see the effect of the bund, you will have to set the bund area such that the radius of the equivalent circular bund is greater than the distance to rainout; for the 2 inch liquid Model, this requires a bund area of 512 ft 2 or greater, giving a radius greater than 12.7 ft. With this larger bund area, the program models the evaporation using two Average Rates, as shown in the illustration of the Pool Vap Report.

Pool Vaporization Results

Average Rate 1 represents the stage during which the pool is spreading, and Average Rate 2 represents the stage after the pool has reached the edge of the bund. Even with the larger pool size, the evaporation rates are still much lower than those for the unbunded Model.

Variables that Affect Rainout: Dispersion Parameter Note—Applies to Instantaneous Releases only The third method for controlling the modeling of rainout cannot currently be used with the 2 inch liquid release, because the method is only applicable to instantaneous releases. However, the method is discussed here because you may find it useful when you encounter an instantaneous release that is raining out beyond the bund. The method involves the parameter called Cloud rainout at source, which is located on the Liquid tab section of the input dialog for Dispersion Parameters, as shown in the illustration on the next page.

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The Parameter for Controlling the Rainout Position

To open this dialog in order to change this parameter, move to the Parameters section of the Study Tree and double-click on the Dispersion icon in the Global Parameters folder. The parameter has the default value Do not set rainout position, which means that the program will model the rainout at the location predicted by the droplet modeling (e.g. at 12.8 ft for the 2 inch liquid release). If you change the parameter to Do reset rainout position, then the program will perform the droplet modeling in order to calculate the evaporation before rainout, but will ignore the calculated rainout position and will place the rainout at the release location instead. This parameter is provided principally to give you the ability to control this aspect of rainout modeling, so that you can compare results for different Weathers and Models without the additional variable of rainout location. However, you should use it carefully, checking the rainout location for all liquid releases.

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If the rainout is close to the edge of the bund, then it is valid to model both situations, since both are likely to occur in reality; if the rainout is far beyond the edge of the bund, then it is less valid—and also non-conservative—to reset the rainout position to the release location. In principle, this approach could also be applied to continuous releases. The parameter is currently only available for instantaneous releases because of differences in the way that the program devises release segments for the two types of release; it is easy to reset the position for an instantaneous release, but for a continuous release it would introduce problems in the time-sequencing of segments. However, you should not find this a serious limitation, since you can achieve a similar effect for a continuous release by setting the Direction to Down or the Elevation to zero, as described earlier.

Stage 6: Releases Towards the Beach In all of the modeling so far, you have been concentrating on dispersion in the direction of the town, and for this the surface roughness factor in the Weather data was based on the conditions to the south of the facility, i.e. upwind of a release directed towards the town. This upwind area is very flat, with few obstacles to induce turbulence. However, if you are considering a release towards the beach, then you should base the surface roughness factor on the conditions to the north of the facility, and this area is urban and industrial, and will have a much higher surface roughness factor.

Copying and Editing the Weather Data Move to the Weather tab section, create a copy of the 1.5/F Weather in the HCN Investigations Plant, and name this copy 1.5/F Urban. Edit the data for the new Weather, and set the following value in the Atmospheric Parameters tab section: Surface Roughness Parameter

0.33

This is a high value, at the opposite end of the range to the value for the other Weather, as you will see if you click on the Help button in the Weather data dialog and check the list of suggested values for different situations.

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Setting up a Batch Run with the Urban Weather You will run all of the models with the new Weather, and the Batch Runner gives the simplest way of doing this. Choose Batch/Weather Setup... from the Run menu, and make the selections as shown in the illustration.

Batch Setup to Run All Models in the Study with the Urban Weather

Next, choose Batch Run from the Run menu to start the run.

Viewing the Results Of the realistic release scenarios, the 4 inch Vapor Model gives the greatest toxic effects, as seen in the Lethality Graph, and will give the most useful results for comparison. View the Graph for the Model from the Models tab section of the Study Tree, and select both Weathers in the Plot Setup dialog to include the results for both Weathers in the same Graph window.

Comparing the Results for the Different Weathers

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Looking at the Time Graph and the Lethality Graph, you can see that the Urban weather only just reaches 10 ppm at the town (calculated using the Toxic Averaging Time), and that the probability of death is much lower. For the Map, the default wind direction is towards the north, so both contours will initially be directed towards the town. To change the direction and confirm that the smaller contour reaches the beach, select Wind Direction from the Graph menu or the right-click menu; the Wind Direction dialog will appear, and you can slide the control to 180 degrees to turn the release towards the beach. When you click on OK, the program will redraw the contours with the new direction.

Changing the Wind Direction Towards the Beach

The Concentration Contours Redirected Towards the Beach

These results show clearly that the surface roughness has a significant effect on the dispersion. The use of a rural value for dispersion towards the town is certainly conservative, since there is a large industrial area between the facility and the town, and this would introduce some turbulence into the still air that had come from the south of the site. 82


Stage 7: Daytime Weather Conditions As the final stage, you will model a third Weather condition, with a rural surface roughness factor, but with values for windspeed and atmospheric stability that are more appropriate for daytime conditions than the 1.5 m/s and F stability that you have modeled so far. Daytime conditions are less stable and more turbulent than night-time conditions, and will give more rapid dispersion.

Copy and Edit the New Weather Create a copy of the 1.5/F Weather, and name it 6/C. Set the following values in the Weather tab section: Windspeed Stability

19.7 ft/s (6 m/s) C

These are moderately unstable conditions, associated with sun and a medium windspeed—i.e. a typical ocean breeze on a hot day.

Run the Calculations and View the Results Select the new Weather in the Batch/Weather Setup dialog, and run the 4 inch Vapor Model for the new Weather, and then generate the Graph window for both the 1.5/ F Weather and the 6/C Weather.

The Results for the Day and Night Weathers

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The dispersion distances for the 6/C Weather are much shorter than for the 1.5/F Weather, and the plume does not reach the 14,000 ft distance that you have been using in the Time Graph to compare Models. The Map Graph gives the clearest comparison of the dispersion distances, as shown in the illustration on the previous page. With the 6/C Weather, the plume reaches its maximum dispersion distance of about 4,000 ft after 180s. This is much less than the release duration of nearly half an hour, and means that this plume does not become detached from the source, unlike the plume for the 1.5/F Weather.

Summary of Investigation This investigation has showed that the largest realistic release from the Anysite facility, modeled at the most conservative weather conditions, can produce a plume which gives concentrations at the town that are higher than the critical concentration of 10 ppm. However, the exposure duration is less than half an hour, while the critical exposure duration for this concentration is over an hour, and the Lethality Graph confirms that the release does not produce any lethal effect at the town.

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Chapter 5: Introduction to PHAST Professional

Chapter 5 Introduction to PHAST Professional This chapter gives a brief introduction to the features which appear in PHAST Professional but not in PHAST Micro , and which the previous chapters have ignored. Some of these features are used in tutorials in the next chapters. The Example Study Folder that you examined in Chapter 2 uses some of the Professional features. If you have a Study Folder open in PHAST , save it, and use Open Example... from the File menu to open the simpleExample Study Folder.

Additional Types of Model PHAST Professional is The most obvious difference between PHAST Micro and that Micro contains only one type of Model the Vessel and Pipe Source Model whereas Professional contains eight additional types of Model. You can see these additional Models in the Model toolbar, and also in the Models tab section of the Example Study Folder, since this Study Folder uses most of the additional Models.

The Additional Models in the Toolbar

Reading from left to right across the Model toolbar, the additional models are:

User-Defined Source Model This is similar to the Vessel and Pipe Source in that it describes a release of material which will then be processed through the dispersion calculations. The difference is that the inputs for the Vessel and Pipe Source Model include the storage conditions and the release scenario, and the program performs discharge calculations to obtain the state of the material after it has been released from containment and has expanded down to atmospheric pressure; whereas with the User Defined Source Model, you give the state of the material directly, bypassing the discharge calculations.

The Additional Models in the Example Study Folder

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You might use the User-Defined Source Model for a particular release if it had some unusual features that would not be modeled well by the discharge calculations in PHAST . In this case, you might use an external discharge model, and then use the User-Defined Source Model to enter the results from this model into PHAST for processing with the dispersion calculations. For some releases, you might not want to use external discharge calculations, but might want to adjust the results of the built-in discharge calculations before proceeding with the dispersion calculations. For instance, you might want to reduce the discharge velocity, or change the size of the liquid droplets. To do this, you must use a User-Defined Source Model, but PHAST Professional provides a quick method of setting up the Source: 1. Define a Vessel and Pipe Source Model for the release you want to model 2. Run the discharge calculations for the Source Model 3. Select the Source and then select Create Source from the Edit menu The Vessel and Pipe Source Model will have a separate set of discharge result s for each Weather condition that is defined for its Study, and if there is more than one set, the program prompts you to choose one of these sets for the UserDefined source, as shown:

Choosing the Weather

When you click on OK, the program will create a User-Defined Source Model with the name Calculated Discharge, and add it at the bottom of the Study. 4. Give the new Source Model a more informative name 5. Edit the User-Defined Source Model to edit the discharge results 6. Run the User-Defined Source Model through the full modeling 86


Pool Fire Model Jet Fire Model Bleve Model The dispersion calculations include fire modeling, and will calculate the distances to three radiation levels for all of the types of fire that are relevant to a particular release. However, the inputs to this fire modeling are not under your direct control since they depend on the discharge and dispersion modeling. If you want to investigate in detail the hazard produced by a particular fire, then you can use the Pool Fire, Jet Fire or Bleve Models, since these allow you to define the fire directly, and can produce a wide range of radiation results.

Pool Vaporization Model The dispersion calculations include modeling of pool vaporization for all releases which produce a liquid pool. As with the fire modeling, the inputs to this evaporation modeling are not under your direct control, and the Pool Vaporization Model is included so that you can investigate particular cases in detail.

TNT Explosion Model TNO Multi-Energy Explosion Model Baker-Strehlow Explosion Model The dispersion calculations in PHAST Professional include three types of explosion modeling for gas clouds which is another difference from PHAST Micro and these will calculate various measures of explosion effects using the type of explosion model that you selected for the release. However, as with the fire modeling, the inputs to the explosion modeling are not under your direct control. If you want to investigate in detail the hazard produced by the explosion of a particular cloud, then you can use the TNT, Multi-Energy and Baker-Strehlow Explosion Models, which allow you to define the cloud and explosion directly, and can produce detailed overpressure results.

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Case List for Easy Sensitivity Analysis The Case List is a tool that is included in Professional to make it easy to run a sensitivity analysis on a release, or model other variations. If you select any model in the Models tab section, you will see that the blue, table-like Case List icon becomes enabled in the toolbar:

When you click on this icon, PHAST will insert a Case List underneath the selected Model. If you expand the tree underneath the Case List, you will see a single Case icon, called Base Case:

A Model with a New Case List

The Base Case contains the values that you set in the dialog for the main Model (the Pool Fire Example, in the illustration), and the icon includes a padlock to show that you cannot change the values for this Case through the Case List, but only through the main dialog. To work on the Case List, double-click on the icon, and the Case List editor will appear, as shown in the illustration on the next page. The features of the editor are described below:

List of Input Fields The drop-down list at the top of the editor contains all of the numerical input fields for the main Model for the illustration, the main Model is a Pool Fire Model. To include a field in the sensitivity analysis, select it from the list, click on Add Variable, and a column for that variable will be added to the table in the main part of the Pool Diameter editor. In the illustration, Elevation of Release has already been added, and has been selected from the list, ready to be added.

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The Case List Editor

Table of Cases The main part of the editor window contains a table of the Cases for modeling. When you first open the editor for a new Case List, this will contain a single row, for the Base Case. To add a Case, click either on the Add button to the left of the table or on the Add Case button at the top of the first column in the table, and a new row will be added at the bottom of the table, with a default name of the form Case 2, Case 3, etc. The Base Case row shows the value that has been set for each selected variable in the input dialog. You cannot edit this value in the table, and must return to the input dialog for the model if you want to change it. Each new Case will initially be given the values from the row above, and you can edit these values and also the name of the Case. In the illustration, the second Case has been given the name 3 Feet, while the third Case still has its default name. When you close the editor and return to the Study Tree, you will see that a separate icon has been added for each Case underneath the Case List. You can reopen the editor by double-clicking on any of these icons. A Model with Several Cases

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Import and Export Options PHAST Professional allows you to export selected parts of the Study Folder to an *.PDB file), and to import data from other *.PSU or *.PDB files external file (a *.PSU or Export options under into the current Study Folder. You do this using the Import and the File menu.

Exporting Data You can export an entire Study, or a single Model, Weather, group of Parameters, Material or Map, depending on the icon that is selected when you choose the Export option. If you export a Study, then PHAST will export all of the Models, Weathers, Local Parameters, Local Materials and Maps for that Study. You cannot export the entire Study Folder, since this function is already performed by the more common Save andSave As... commands.

Importing Data You can import any PSU or PDB file into the current Study Folder, whether the file contains an entire Study Folder, or a Study, Model, Weather, etc. that had previously been exported. PHAST is very flexible about importing individual items. For instance, you do not have to be in the Weather tab section when you import a Weather, since PHAST will automatically import the Weather to the Study that is selected in the current tab section. However, you will not see the imported Weather until you move to the Weather tab section, so you may find the import easier to check if you do not take advantage of this flexibility.

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Chapter 6 Tutorial 3: Full-Bore Pipeline Rupture This tutorial uses some of the features of PHAST Professional to devise and model a full-bore rupture of an 8 inch ammonia pipeline.

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 improved 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 PHAST , and to show you features that you may find useful in your own work. If you omit parts of the tutorial because of differences in the results, you may miss a feature or a discussion that would save you time or make you much more confident in modeling releases and interpreting results.

The Need for Special Modeling for Pipeline Rupture The lists of available scenarios for a Vessel or Pipe Source Model includes a Line Rupture scenario, but this has many simplifications and excludes some of the effects that are experienced in a full-bore rupture. The Line Rupture scenario considers the rupture of a horizontal pipeline that is attached to a pressure reservoir (i.e. a vessel), where the rupture is a given distance from the reservoir. The material flows along the pipeline from the reservoir to the point of rupture, and the effects of friction during this flow reduce the pressure along the pipe so that the pressure at the point of rupture is less than the pressure in the reservoir. This pressure drop means that the release rate from the pipeline rupture is lower than the release rate from a leak of the same size from the body of the vessel (the Leak scenario), and the effect increases as the pipe length increases. 91


At the beginning of the release there is assumed to be no flow in the system, and the pressure throughout is assumed to be equal to the reservoir pressure. After the rupture occurs, there will be a period of development in which more and more material is removed from the pipeline, and the pressure drop is felt further and further along the pipeline from the point of rupture. Eventually, after a length of time that depends on the length of the pipeline, a steady state is achieved, and this is the state that is modeled in the Line Rupture scenario. Pressure Pv

Pc Pa

Distance Atmospheric Pressure, Pa

Vessel Pipe Length, L Pressure, Pv

Rupture Point Choke Pressure, Pc

The Steady State Pressure Profile for the Line Rupture Scenario

The assumption of steady state conditions is non-conservative, since it does not represent the highest release rates that will be experienced in the event of pipe rupture. When the rupture occurs, the pressure at the point of rupture is equal to the reservoir pressure, and the length of pipe between this pressure and atmospheric pressure is zero. This means that there are no frictional losses and the discharge rate will be the same as the discharge rate for the Leak scenario. The discharge rate will drop from this value during the period of development, and the first stage in this tutorial is to estimate the speed of this drop. In this tutorial, the pressure drop is assumed to move along the pipeline as a wave”, taking a finite time to reach the reservoir. At a given intermediate time, when the pressure wave has moved a distance d from the point of rupture, the pressure profile inside the system will be same as the steady state profile for a Line Rupture scenario of a pipe of length d, as shown in the illustration on the next page, and this means that you can use the Line Rupture scenario to investigate the intermediate behavior.

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time, t = t 1

time, t = 0 Pv

Pressure

Pv

Distance d1 Steady State: time, t = t s

time, t = t 2 Pv

Pv

d2

pipe length, L

The Pressure Profile During the Period of Development

Starting the Ammonia Pipeline Study First, move to the Materials tab section, and drag the version of ammonia in the Local Materials folder of the Worst Case Study to the Global Materials folder. As with the previous tutorials, you are only interested in the toxic effects of the ammonia release, and this version of ammonia is toxic only. Next, add a new Study to the Anysite Study Folder, and give it the name Ammonia Pipeline. Add a Vessel and Pipe Source Model to the new Study, and give it the name Vessel Leak. You will use this to define a Leak scenario, to calculate the dischargerate at the start of the rupture. You can also calculate this rate by defining a Line Rupture scenario with a line length of zero, and you will do this next, for the sake of comparison.

Set Input Data for the Vessel Leak Model Set the following in the Material tab section: Material

AMMONIA

Inventory

40,000 lb

Process Conditions

Temperature Saturated Liquid

Temperature

90 F (32.2 C) 93


then set the following in the Scenario tab section: Scenario

Leak

Phase to be Released

Vapor

Hole Diameter

8 inches

The release is from the vapor side of the vessel. Next, set the following in the Indoor/Outdoor tab section: Direction

Horizontal

and the following in the Location tab section: Concentration of Interest 200 ppm Averaging Time

Toxic

You can leave all of the other tab sections with their default values.

Set Input Data for the Pipeline Rupture Model Create a copy of the Vessel Leak Model with the name Pipeline Rupture, and set the following values in the Scenario tab section: Scenario

Line Rupture

Phase to be Released

Vapor

Line Length

0.1 feet

Pipe Exit Diameter

8 inches

The input field for Line Length does not allow you to enter a length of zero, so you must set some small value for the length. You can leave all of the other tab section with the same values as the Vessel Leak Model.

Run the Discharge Calculations and View the Results Make sure that the Global 1.5/F Weather is the only weather selected in the Batch Setup, then select the Ammonia Pipeline Study and press Ctrl+D to run the discharge calculations only.

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When the calculations have finished, select the Ammonia Pipeline Study and press Ctrl+R to generate a Report that contains the results for both Models. Use the Report Tree at the left of the Report Window for the quickest way of moving between the results for the two Models. The results are shown below:

Results for Vessel Leak

Results for Pipeline Rupture

The slight difference between the results is caused by the 0.1 ft pipeline length. The Vessel Leak rate will be used to model the instant of rupture.

Stage 1: Using a Case List to Model a Range of Pipe Lengths As the next stage—which is the real start of the discharge calculations—you will use the Pipeline Rupture Model as a Base Case” and add a Case List below the Model to define a range of Pipe Lengths. This will allow you to model the different positions of the pressure front with a minimum of input effort.

Adding the Case List Select the Pipeline Rupture Model and then add a Case List using the CaseList option in the Insert menu or the icon in the Toolbar. Give the Case List the name Pipe Lengths.

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Defining the Cases Double-click on the Pipe Lengths Case List icon to open the Case List dialog. When you first open the dialog, the table of Cases will contain only one column and row, as shown:

The Blank Table of Cases

Select Default line length from the list of variables, and click on Add Variable to add the variable to the table. The table will now appear as shown:

The Line Length Added to the Table

The Base Case row represents the Pipeline Rupture Model, and you cannot change any of the values for this row from the Case List dialog.

Adding Cases to the Table Use the Add button to add five Cases to the table, and then set the following names and Line lengths:

The Completed Cases

The distance from the point of rupture to the vessel is 5000 feet, and the other Cases represent intermediate positions of the pressure front.

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Click on OK to close the dialog. When you return to the Study Tree, you will see that an icon has been added for each Case below the Case List. If you click on any of these icons to edit the Case, the Case List dialog will open, allowing you to edit all of the Cases.

The Cases in the Study Tree

Setting Option for Immediate Discharge Results At this stage, all you are interested in is the discharge rate—you do not need the full results in the Discharge Report. In this case, you can use an option that is available in the program to write out selected results during the run of the calculations, so that you can see the results without having to open the Report and search for the discharge results for each Case. To use this option, select Preferences... from the Options menu. Move to the Results tab section, and set the options shown in the illustration.

Selecting Results for Logging

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The Averaged Mass Flow (i.e. discharge rate) will be written to the Output tab section of the Log Window during the calculations for each Case.

Running the Calculations Select the Pipeline Rupture Model or the Line Lengths Case List, and then pressCtrl+M to run the full calculations. You are only interested in the discharge results at this stage, but PHAST Professional will only run all of the Cases in a Case List when you are running the full calculations. If you press Ctrl+D to run the discharge calculations on their own, the program will only run the calculations for the Base Case.

Viewing the Results in the Log Window Move to the Output tab section of the Log Window, and scroll up to find the results for the Base Case, which will be the start of the results for the Case List. The results will appear as shown in the illustration.

The Discharge Rates in the Log Window

You can print the results if you place the cursor in the results text and then use the Print option in the File menu or the right-click menu. You can also save the results to a text file using the Save As... option in the right-click menu. The results are summaCase rized in the table.

(lb/hr)

(kg/s)

512,188

64.5

100 ft

353,602

44.6

500 ft

189,769

23.9

1000 ft

136,009

17.1

3000 ft

77,164

9.7

5000 ft

58,041

7.3

Vessel Leak (0 ft)

The Discharge Results

98

Discharge Rate


By the time the pressure front has reached the vessel, the discharge rate has dropped to nearly 10% of the initial value. This lower rate is assumed to be maintained throughout the steady state discharge, i.e. until all of the inventory in the vessel has been discharged.

Stage 2: Estimating the Time to Reach the Steady State To estimate the time taken to reach the steady state, you will estimate the amount of material that has been discharged from the pipeline by the time the pressure front reaches the vessel, and then calculate the time required to discharge this material, assuming some representative discharge rate.

Initial Density of Material in Pipeline One way of calculating the mass discharged is to calculate the difference between the initial density of the material in the pipeline, and the density of the material under steady state conditions. To obtain the saturated vapor density at 90°F, move to the Materials tab section of the Study Tree, select the AMMONIA icon from the Global Materials folder, and then select Point Property... from the Materials cascade in the Run menu. The Point Property dialog will open, and you should set the values as follows and then click on Calculate to obtain the value:

Calculating the Vapor Density

The volume for a pipeline of 8 inch diameter and 5000 ft length is 1745 ft3 (50 m3).The initial mass of material in the pipeline is therefore 1,051 lb (477 kg). This is in addition to the inventory of 40,000 lb in the vessel, which you will consider later.

99


Density of Material under Steady State The density of the material in the pipeline under steady state conditions is not a simple quantity, since the pressure and the state of the material vary along the length of the pipeline, and the density is not given directly in the discharge results. However, the discharge results do give the Orifice Velocity, and since you know the mass flowrate through the orifice and the area of the orifice, you can calculate the density of the material in the orifice as: Density = Mass Flowrate / (Orifice Velocity * Area of Orifice) To obtain the orifice velocity for each pipe length, select the Pipeline Rupture Model or the Pipe Length Case List and press Ctrl+R to view the Report If you expand the Report Tree for the Discharge Report, you will see that the Cases are arranged in the Report in alphabetical order, as shown. This order is contrary to the natural” order by pipe length, and may make it difficult to find the results in the Report, and increase the risk that you will make a mistake in reading the results. To overcome this problem, close the Report, and rename the Cases, adding a prefix of the form Cn:” to each, to make the alphabetical order the same as the natural order (e.g. C1: 100 ft, C2: 500 ft, etc.) When you open the report again, the Cases will appear in the natural order, starting with Base Case, and you should find it easier to read the Report.

Alphabetical Ordering of Cases

Using a pipe diameter of 8 inches, the density along the length of the pipe is calculated as follows: Distance

Discharge Rate

Orifice Velocity

(lb/hr)

(kg/s)

(ft/s)

(m/s)

(lb/ft3)

(kg/m3)

0 ft

512,188

64.5

1,640

500

0.249

3.981

100 ft

353,602

44.6

1,640

500

0.092

1.475

500 ft

189,769

23.9

1,640

500

0.051

0.813

1000 ft

136,009

17.1

1,618

493

0.249

3.981

3000 ft

77,164

9.7

1,210

369

0.092

1.475

5000 ft

58,041

7.3

983

300

0.051

0.813

Calculated Density along the Pipeline

100

Density


If you plot the density against the distance along the pipeline, the graph appears as shown:

Density versus Distance

At the beginning of the release, the density drops rapidly, but after the pressure front has travelled about 1000 ft, the density remains almost constant for the rest of the release. For this tutorial, this behavior will be approximated as two density regimes”, with the density declining in a linear manner in each regime, as shown:

A Linear Approximation for the Density

The conditions at the midpoint of each linear section will be taken as representative of that section. For the first section, the representative conditions occur when the pressure front is at 300ft, and for the second section, the conditions occur when the pressure front is at 2800 ft.

101


Mass Lost from Pipeline during Depressurisation The mass lost from thepipeline during a given density regime is given by: (Initial Density - Representative Density) * Distance Travelled by Pressure Front during Regime * Area of Pipe With an initial density of 0.603 lb/ft 3, and a pipe diamter of 8 inches, the calculations for the two regimes are as follows:

Regime 1

Regime 2

Representative Density (lb/ft3)

0.155

0.052

Difference from Initial Density (lb/ft3)

0.448

0.551

Distance Travelled by Pressure Front (ft)

600

4400

Mass Discharged (lb)

93.7

845.5

Mass Discharged (kg)

42.5

383.5

Mass Discharged

The total mass discharged is 939 lb, which means that the mass remaining in the pipeline during the steady state is 112 lb (50 kg).

Representative Discharge Rate for Density Regimes In order to calculate the time taken to discharge the material in each regime, you next need to obtain the representative discharge conditions for each regime. You can do this by modeling the pipelength that gives the same density as the representative density for the regime. For Regime 1, the density is equal to the representative density of 0.155 lb/ft3 when the pipelength is about 150 ft. For Regime 2, the relevant pipelength is 2800 ft. You could add Cases to the existing Pipe Lengths Case List in order to model these pipelengths, but this would not reflect the stages in the analysis very clearly. To make the design clearer, you will add a second Case List to the Pipeline Rupture Model, and define the lengths of 150 ft and 2800 ft in this Case List.

102


Make a copy the Pipe Lengths Case List, and give the copy the name Pipe Lengths for Density Regimes. Edit the list of Cases, setting the values as shown:

The Case List for the Density Regimes

Next, select the second Case List, and press Ctrl+M to run the calculations. The results are summarized below:

Regime 1

Regime 2

Regime 3 (Steady State)

309,037

80,125

58,041

85.8

22.3

16.1

8.6

0.0

0.0

1184.0

1230.0

983.0

-28.1

-24.2

-2.7

Discharge Rate (lb/hr) Discharge Rate (lb/s) Liquid Fraction (%) Discharge Velocity (ft/s) Temperature (F)

Representative Discharge Conditions

Time Taken to Discharge Material During Depressurisation With the representative discharge conditions, the durations of the two intermediate regimes are as follows:

Regime 1

Regime 2

Discharge Rate (lb/s)

85.8

22.3

Mass Discharged (lb)

93.7

845.5

Duration of Regime (s)

1.1

38.0

Duration of Density Regimes

103


Stage 3: Modeling the Release with the User-Defined Model You now have the information that you need in order to model the release in PHAST Professional.

Creating the User-Defined Source You can avoid some of the effort of data input if you create the User-Defined Source Model from the existing Pipeline Rupture Model. Select the Pipeline Rupture Model, then press Ctrl+D to run the discharge calculations, and then select Create Source from the Edit menu. The program is only able to create a User-Defined Source from a Vessel or Pipe Source immediately after the discharge calculations have been run; at any other time, the option is disabled in the Edit menu. The program will add a User Defined Source Model with the name Calculated Discharge. Change the name to 3 Regime Release, as shown.

Setting the Input Data for the Source Double-click on the new Model to work on the input data. Most of the tab sections in the input dialog for the User-Defined Source are the same as for the Vessel or Pipe Source, and for these tab sections the program simply copies the values when it creates the source. However, there are some tab sections that are not the same, and these are the tab sections that deal with discharge calculations or results. In the Material tab section, the fields for process conditions are all disabled, and the Scenario and Vessel tab sections are replaced by the Discharge tab section—which you will use to define the three regimes. First, set the inventory in the Material tab section to 41,000 lb, to add the pipeline inventory to the inventory in the vessel. For this release, the pipeline inventory is small compared with the vessel inventory, but this may not be the case for other releases that you model. Next, move to the Discharge tab section. The program has defined the User Defined Source as a leak, with the discharge results for the Base Case for the Pipeline Rupture Model (which had a pipe length of 0.1 ft), as shown in the illustration on the next page.

104


The Initial Discharge Input Values

This Base Case is not relevant to any of the regimes, and you must edit the values to set them to the values for Regime 1, and then add columns to the table for Regime 2 and the Steady State. First, set the values in the first column to those shown below:

Discharge Data for Regime 1

105


You can leave the droplet diameter with the value from the Base Case. Next, click on Add Segment to add another column to the table after the column for Regime 1. The program always adds columns to the end of the table. This new column will have the Release Phase set as Liquid, with all of the other fields blank. Set the phase to Vapor , and then set the values for Regime 2 as follows:

Discharge Data for Regime 2

To change the phase, click in the cell, then use the scroll bars that appear to select Vapor from the list, and then click on the cell again before clicking on any other cell in the table. If you do not click on the cell for a second time (i.e. after selecting the phase), then the program will not process your selection, and will return the phase to its initial value the first time you click on another cell. Next, click on Add Segment again to add a column for the Steady State regime, and set the values as follows:

The Completed Discharge Data

You do not need to change any values in any of the other tab sections, and can click on OK to close the input dialog.

106


Run the Calculations and View the Results Select the 3 Regime Release Model and press Ctrl+M to run the dispersion and effects calculations, and then view the results. The program models the sequence of segments in the same way as for a liquid release that includes rainout and evaporation, as described in detail in Chapter 4. It calculates the dispersion distances for each segment assuming that the segment has sufficient duration to become fully developed, and that is a very conservative assumption for this release, since the segment with the largest discharge rate has a very short duration. The illustration below shows the state of the cloud at 30 seconds, when the cloud for Segment 1 has reached about 1000 ft downwind, and the discharge has not yet reached steady state conditions.

The State of the Cloud at 30 Seconds

The segment for Regime 1 has a long dispersion distance and reaches the town, but with a duration of 1 second, this part of the cloud appears on the Map simply as a thin, wide line. There is a very large difference in the discharge rate and duration between this segment and the other two segments, and with this large difference, the cloud for Segment 1 appears to become detached from the cloud for the other segments.

107


This effect becomes more pronounced with time, since the cloud for Segment 1 takes over an hour and 30,000 ft to reach its full dispersion distance, while Regime 2 takes 200 seconds and 2,500 ft, and the steady state regime takes 180 seconds and 1,700ft. The illustration below shows the state of the cloud after 300 seconds, when steady state conditions have been reached in the pipeline, and the cloud from Regime 2 has finished dispersing. The gap between Segment 1 and the later segment has widened.

The State of the Cloud at 300 Seconds

In reality, the change in the discharge rate, although rapid, is smooth, and the cloud would be continuous. If you introduced additional intermediate regimes between Regime 1 and Regime 2 in order to reduce the discharge rate more gradually, then the gaps between the segments would not be as large, and might disappear entirely; however, the modeling of a fully-developed cloud for the short-duration regimes is still extremely conservative.

108


Chapter 7 Tutorial 4: Near-Field Flammable Effects This tutorial uses one of the direct input fire Models in PHAST Professional to investigate flammable effects on the site.

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 improved 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 PHAST , and to show you features that you may find useful in your own work. If you omit parts of the tutorial because of differences in the results, you may miss a feature or a discussion that would save you time or make you much more confident in modeling releases and interpreting results.

Aim of Tutorial: Evaluate Need for Radiation Protection The site has two Control Points for manual control of fire-fighting equipment, located to the north of the Control Room, as shown in the illustration on the next page. The aim of this tutorial is to evaluate the need for radiation protection on the paths between the Control Room and the two Control Points. What are the radiation levels at the Control Points in the event of a process fire? Are there any realistic fire scenarios that could give high radiation levels at both set of Control Points simultaneously?

109


HCN Process

Ammonia Process

3,500 ft 2,400 ft

Propylene Process

Ethylene Process

750 ft Manual controls for fire-fighting equipment

A

1,500 ft

B

600 ft

Control Room

Everychem's Anysite facility

Manual controls for fire-fighting equipment

Offices

Stage 1: Fires from Propylene Process You will start by considering worst case jet fires from the propylene process. The main inventory in this process is at saturation conditions of 90°F and 201 psig (32°C and 13.9 barg), and the diameters of the largest connections on the inventory are 8 inches for the gas side and 4 inches for the liquid side.

Create a Study for the Tutorial Insert a Study and give it the name Onsite Flammable.

Add a Jet Fire Model Add a Jet Fire Model to the Study, using either the Toolbar or the option in the Insert menu. Give the Model the name Propylene Vapor .

110


Set the Input Data Double-click on the icon to open the input dialog, and set the following values in the Material tab section: Material

PROPYLENE

Elevation

10 ft

The main gas connections are some distance above the ground, and the elevation reflects this. Next, move to the Discharge tab section, and enter the process conditions and hole size, as shown:

The Process Conditions for the Discharge Calculations

Click on Calculate now to run the discharge calculations with this input data. The program runs the calculations immediately, and reports the results in a message box, as shown in the illustration on the next page. 111


The Discharge Results

Click on Yes to copy these results to the relevant fields in the Flame Shape tab section. When the program copies the discharge results, it automatically takes you to the Flame Shape tab section. Complete the remaining fields in this tab section, so that the tab section appears as follows:

The Completed Flame Shape Data

112


Next, move to the Radiation Data tab section, and set the following values for the Radiation at a Point calculations:

Data for Radiation at a Point

This assumes that the fire is pointed directly towards Control Point A. The height is measured in relation to the elevation of the flame; five feet below the flame will be about the height of a person s head. Click on OK to save the values.

Setting the Results Option for the Output Window In this tutorial, you are principally interested in the incident radiation at a point, and you can save a lot of time if you select this item to be written to the Output Window during the calculations—as you did for the discharge rate in Tutorial 4. To make this setting, take the following steps: Use the Options menu to open the Preferences dialog Move to the Results tab section Click on Clear selections for all classes to remove any previous selections In the Results class of data, select Jet Fire Radiation Point In the list of Variables for this type of results, select Incident Radiation Click on OK to save the selection.

Run the Calculations and View the Results Select the Model and press Ctrl+M to run the calculations. When you move to the Output Window, you will see the radiation given as 1.6 Btu/ ft2.s (18.2 kW/m2). This radiation level can cause severe burns, and no one would be able to approach Control Point A under these conditions.

113


Next, open the Report and look at the Jet Fire Report. It is a long report, and contains information about the flame dimensions, and the results of the Radiation versus Distance and Radiation Ellipse calculations as well as the Radiation at a Point calculations. The amount of information in the report means that finding a given item of information can be relatively slow, and makes the option to write results to the Output Window particularly useful. However, the Report can give you information about the flame that can help you to visualize it, and this can make it easier for you to interpret the radiation results and to avoid errors. The flame size and power are given near the beginning of the Report, and are shown below:

The Flame Shape Results

The flame is 642 ft long, with a radius of 90 ft, and an emissive power of 5.6 Btu/ ft2s (63 kW/m2).

Add a Case List to Investigate Crosswind Locations Crosswind. You Insert a Case List below the Propylene Vapor Model, and give it the name Crosswind. will define Cases for a range of crosswind locations, and find out how quickly the radiation drops as you move along the line between Control Point A and Control Point B. Open the Case List dialog, select Radiation at a Point: Crosswind Distance from Distance from the list of variables, and define the five Cases as shown. The Crosswind Case List

114


When you run the Case List and view the results in the Output Window, you will see that the radiation level has dropped to 0.31 Btu/ft2.s (3.5 kW/m2) at a crosswind distance of 300 ft. This radiation level can cause pain, but not burns, and will not prevent people reaching Control Point B while Control Point A is inaccessible.

Create a Propylene Liquid Model Liquid. Copy the Propylene Vapor Model Model and name the copy Propylene Liquid. Open the input dialog, move to the Discharge tab section. The pressure and temperature for the vapor side are applicable to the liquid side, and you only need to make the following changes: Phase

Liquid

Hole Diameter

4 inch

now, and then copy the discharge results to the Flame Shape tab Click on Calculate now, section. Next, move back to the Material tab section, and make the following change: Elevation

1 ft

The release is from the bottom of the equipment, and this places the fire about 4 ft below the human face. To reflect this change, move to the Radiation Data tab section and make the following change: Height above origin

4 ft

When you run the Model and the Case List (which was also copied), the radiation results will be as follows:

Location

Incident Radiation Btu/ft2.s

kW/m2

Control Point A

6.0

68.1

300 ft crosswind

0.84

9.5

600 ft crosswind

0.25

2.8

Radiation Results

The higher discharge rates from the liquid side give a larger flame and and higher radiation levels, levels, but they still drop to harmless levels by 600 ft crosswind.

115


The flame could be directed between the two Control Points, giving higher levels at B and lower levels at A. However, with these results it is clear that there is no intermediate location that could make both points inaccessible at the same time.

Stage 2: Fires from Ethylene Process Copy the Propylene Vapor Model Model and name the copy Ethylene Vapor . ETHYLENE in the Material tab Open the input dialog and change the material to ETHYLENE in section. 500 psig Next, move to the Discharge tab section, and set the Storage Pressure to 500 psig 34.5 barg), and run the discharge calculations. (34.5 barg), Finally, move to the Radiation Data tab section and change the Downwind 1,500 ft, which is the distance from the ethylene process to Control Distance to 1,500 Point B. When you run the calculations, you will find that the radiation level at Point B is 0.22 Btu/ft2.s (2.5 kW/m2), which should not prevent anyone using the controls. The Ethylene is stored under supercritical supercriti cal conditions, so there is not liquid release to be modeled, and these results represent the worst case for a jet fire from the ethylene process. Therefore, there is no ethylene jet fire that can make both control points inaccessible.

Conclusion At least one Control Point will will always be accessible in the event of a jet fire, and there is no need for radiation protection protection or any other type of re-design.

116

Index

Index A

C

animated cloud Graphs 49 Atmospheric Parameters in Weather data 33 averaging time. See also Core Averaging Time; Flammable Averaging Time; Toxic Averaging Time; User-Defined Averaging Time affects concentration results 40 detailed Report 72 in Model data 40 in Report 72 introduction 40 models varying wind direction 40 use in Dispersion Report 68 Averaging Times Report for dispersion results 72

comparing results for Models 51 for same Weather 58 for Weathers 83 concentration set units to ppm 36 concentration of interest in Model data 40 LFL fraction for flammables 44 Copy Material inserting without links 30 Core Averaging Time in Dispersion Parameters 69 use in Dispersion Report 69

D B Baker-Strehlow Explosion Model in PHAST Professional 87 Batch Run selecting Models 17 selecting Weathers 18 setting up 17 starting calculations 18 Batch Setup selecting Models 17 selecting Weathers 18 bitmap file for Map 34 Bleve Model in PHAST Professional 87 bold in tab titles shows compulsory fields 14 bund area effect on rainout 78 bunded liquid release 76

C Case List tool example in tutorial 95 in PHAST Professional catastrophic rupture use in tutorial 59

88

default units choosing a system 10 default Weathers for New Study 32 defaults system bold in tab titles 14 hierarchy for Materials 8 hierarchy for Parameters 7 in Model dialog 13 italics in tab titles 14 use of green border 33 deleting icons from Study Tree 33 dialog-level Help 11 direct input Models in PHAST Professional 87 Direct Run of discharge only 18 of Models in Folder 18 of Models in Study 18 of single Model 18 selecting Weathers 47 direction of release effect on rainout 77 in Model data 41 discharge calculations running alone 18 Dispersion Preferences fields in Report 67

117


D

F

Dispersion Report discussion in tutorial 68 Preferences for fields 67 dispersion results for pool vaporization 69 distance of interest in Model data 40 setting for Graph 49 droplet modeling effect of bund area 78 effect of rainout location 76 effect of release direction 77 effect of release elevation 40, 78 Parameter to control rainout location dynamic cloud Graphs 49

Full Screen mode for viewing Graphs 21 for viewing Reports 21 leaving the mode 21 fully-developed cloud in dispersion modeling 71

E elevation for release effect on droplet modeling 40 evaporation of pool results in tutorial 66 Example Study Folder a quick tour 5 Existing Material inserting with link for defaults explosion model choosing in Model data 45 Explosion Models in PHAST Professional 87 export to file for Report 20 Exporting a Study in PHAST Professional 90

30

G

78

Global Materials added on use in Model 47 introduction 9 use in tutorial 58 Global Parameters introduction 8 Global Study for shared Maps 56 for shared Weathers 56 Graph animated cloud results 49 comparing Models 22, 51 comparing Weathers 21 distance of interest 49 dynamic cloud results 49 Graph Window 22 overpressures on Map 53 selecting a Map 21 selecting Models 22 selecting Weathers 21 setting overpressure to plot 53 time used for cloud results 48 Window menu 22 green border on field shows default value 33

F

H

F1 key for online Help 12 field-level Help 12 Fire Models in PHAST Professional 87 Flammable Averaging Time in Flammable Parameters 44 Folder icon in Toolbar 6 introduction 6

Help button for dialog-level Help 11 Help system dialog-level Help 11 field-level Help 12 introduction 11 use of F1 key 12

118

Index

I

M

Importing a Study in PHAST Professional 90 input dialog for a Material 15 for a Model 12 for a Weather 14 instantaneous release use in tutorial 59 italics in tab titles shows use of defaults 14

Map tab section of Study Tree 10 Material calculating point property 99 Copy of existing 30 input dialog 15 inserting as New 30 linked to Existing 30 Materials icons in Toolbar 9 Materials hierarchy Global level 9 introduction 8 Local level 9 System level 9 Materials tab section in Study Tree 8 Model first use in tutorial 36 icon in Toolbar 6 input dialog 12 introduction 6 Models tab section of Study Tree 6 Multi-Energy Explosion Model in PHAST Professional 87

J Jet Fire Model example in tutorial 110 in PHAST Professional Jet Fire Report example in tutorial 114

87

L Leak scenario first use in tutorial 60 liquid release dispersion results 69 example with bund 76 example without bund 65 pool vaporization results 66 Local Materials introduction 9 using in tutorial 30 Local Parameters introduction 8 logging results in Output Window 97

M Map changing wind direction 82 defining in Map Window 16 defining in tutorial 34 icon in Toolbar 10 selecting bitmap 34 setting origin 35 setting scale 34 use of Graph menu 16 using Global Study to share 56

N New Material option for inserting 30 New Study default Weather conditions

32

O online Help. See Help system origin for Map 35 Output Window for logging results 97 overpressure of interest setting for Graph 53

119


P Parameters hierarchy Global level 8 introduction 7 Local level 8 System level 8 Parameters tab section in Study Tree 7 PHAST Professional additional features 85 Plot Setup dialog for Graphs 21 point property calculating for Material 99 Pool Fire Model in PHAST Professional 87 pool vaporization results in tutorial 66 Pool Vaporization Model in PHAST Professional 87 ppm setting as concentration unit 36 Preferences fields for Dispersion Report 67 for file to open at startup 29 for Reports to include 20 for results to log 97 printing a Report 20 Professional ( PHAST ) additional features 85 property at a point calculating for Material 99

R rainout location inside bund 76 outside bund 76 rainout modeling. See droplet modeling red border on icon shows missing data 36 Report export to file 20 for multiple Models 20 generating for a Model 19 introduction 19 printing 20

120

R Report Report Window 19 selecting in Preferences 20 Window menu 21 Report Tree for quick navigation 20 shows Report structure 20 results logging in Output Window 97 option to save 23 running calculations Batch Run 17 Batch Setup 17 Direct Run 18 discharge only 18 introduction 17 selecting Weathers 47

S saving results 23 scale for Map 34 security on software for running calculations 4 license code 4 security chip 4 segments for release in Dispersion Report 69 sensitivity analysis with Case List 88 SmallFraction unit type for concentration 36 stand-alone Models in PHAST Professional 87 Startup Preferences for file to open 29 Study creating 56 icon in Toolbar 6 introduction 6 Study Folder creating in tutorial 29 introduction 4 opening automatically 29 startup Preferences for opening 29 tour of an example 5

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