phast onshore 7

Phast

Tutorial Manual

DNV SOFTWARE Palace House, 3 Cathedral Street, London SE19DE, UK

http://www.dnv.com/software

© Copyright Det Norske Veritas. All Rights Reserved. No reproduction or broadcast of this material is permitted without the express written consent of DNV.

Contact [email protected] for more information

http://www.dnv.com/software

mailto:[email protected]

Contents

Chapter 1 An introduction to Phast 1

In the first chapter you open an example analysis provided with the program, explore its main features, and run the calculations and view the results – without having to enter or change any input data.

Chapter 2 Setting up your own analysis 19

The second chapter guides you through the process of setting up a new workspace and setting up the background map for consequence analysis.

Chapter 3 Performing the consequence analysis 23

In the third chapter you define a range of common types of hazardous event and perform the consequence analysis to obtain the size of the effect zones. The tutorial supplies all of the input values that you will need to complete the analysis.

Phast Tutorial Chapter 1: Introduction

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Chapter 1 An introduction to Phast

What to expect of this tutorial

The aim of this tutorial is to make you familiar with the ideas and techniques involved in performing a consequence analysis with Phast, and to give you practice in defining a range of common types of hazardous events. By the time you have finished the tutorial you should have a firm understanding of the issues involved, and be ready to start work on an analysis of your own.

The tutorial is divided into three chapters. In this first chapter you will open an example analysis provided with the program, explore its main features, and run the calculations and view the results – without having to enter or change any input data. In the second chapter you will create a new analysis. First you will set up the background data, and then in the third chapter you will define a range of hazardous events and perform a consequence analysis for them.

The tutorial should take 1-2 hours to complete. You do not have to complete it in a single sitting, and can take a break between chapters if you prefer.

Starting the program running

When you install the program, the installation process places a DNV Software folder under Programs in your Start menu, and also adds a Phast 7.0 shortcut to your Desktop. You can use either method to start the program running.

The main window

When you start the program running, the main window will open as shown if you have a valid licence for the program present on your machine.

The main window on startup


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If you do not have a valid licence present, the program window will not open, and instead a dialog will appear as shown.

To obtain a license, click on Request a licence. A Request license dialog will appear, and you must select the products and features for which you require a license. The dialog allows you to email the request directly to DNV software support, or to save the request to disc so that you can choose when to send it.

Once DNV software support have emailed you the appropriate license file, you should save it to disc. If you then click on Import a license file in the Phast licensing dialog, a File Open dialog will appear, and you must browse to select the license file. The program will then copy the file to the appropriate location, and the next time you start the program, it will find a valid license and will start successfully.

Opening the Phast example file

When you start the program running, you do not have to take any specific action to start a new analysis, as the program always starts with a new, blank analysis (or workspace) already open. You can explore the features of the program using the blank workspace as all of the features will be displayed, but this tutorial uses one of the example files installed with the program to give a quick introduction to the terminology and approach used in the program.

To open the file, choose Open Example… from the File tab of the Ribbon Bar. The Examples dialog will open, showing all of the folders and *.psux workspace files under the Examples folder that is installed with the program. Select the Phast 7 examples.psux file, and click on OK. There will be a brief pause, and then the data for the example workspace will be displayed in the program window, as described in the sections below.


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The Study Tree pane

The Study Tree pane allows you to organise and edit the input data for your consequence analysis. The pane contains a number of tab sections, each of which covers a different type of input data, and these tab sections are described below.

The Models tab section

You use the Models View to define the hazardous events or Scenarios that you want to model, and to run the calculations for these events and view the results. You can define a range of Scenarios, such as different types of accidental release from different equipment items. This is the main type of input data in the program, and the other types of data can be seen as “background” or “supporting” data.

The data are organised in a tree structure, with four levels of input data:

Level 1: the workspace

The workspace node appears at the top of the tree in every tab section of the Study Tree. If you double-click on the icon, a dialog will appear that allows you to set options that will be applied throughout the workspace. The settings will be saved with the workspace file, so you can set different options for different workspaces.

The workspace dialog covers settings that affect the behaviour of the program (e.g. the level of information given in messages), but does not cover any aspect of the definition of hazardous events. The details of hazardous events are defined at lower levels, with nodes that appear only in the Models tab section of the Study Tree.

Level 2: the Study

The Study level is the level immediately underneath the workspace node. Each new workspace is created with a Study already defined in the Models tab, ready for you to start inserting equipment items under the Study.

The input data for a Study covers two types of setting:

• Values to be used as defaults for equipment items under the Study.

• The selection of the set of Weather conditions and the set of Parameter values to be used in calculations for the Study.

Weather conditions and Parameter values are defined in separate tabs of the Study Tree that will be described further below. Each new workspace is created with one set of Weathers and one set of Parameters, which are selected by default for each Study. However, if you insert additional sets of Weathers or Parameters, you can edit any Study and change the selection of the Weathers or Parameters for that Study.

The combination of Weather Set and Parameters Set that is selected for a particular Study is known as the global context for that Study. One of the main reasons for defining more than one Study in a workspace is to be able to select different global contexts for different Studies.


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The example file has a single Study called Study.

Level 3: the Equipment item

At the Equipment level, you define the process material and operating conditions. There are three types of item that you can insert at the Equipment level:

• a Pressure Vessel for modelling releases from pressurised containment

• an Atmospheric Storage Tank for modelling releases from unpressurised containment

• a Standalones item for performing detailed modelling of fire, explosion and pool vaporisation, separate from the modelling of a particular release from containment.

In addition to defining the process material and operating conditions, you can also use the input data for the Equipment item to set default values to be used for the Scenarios underneath the Equipment item.

The example file has a large number of Equipment items. Most are Pressure Vessels, but there are also some Atmospheric Storage Tanks and some Standalones.

The Equipment items have been organised into folders under the Study in order to make the design of the workspace clearer and easier to work with. For example, there is a Tank farm folder, and a Toxic cases folder. You can have an number of levels of folders under a Study and also under an Equipment item, but the folders are not described here as a level in the data-structure as they do not contain any input data for defining the hazardous events.

Level 4: the Scenario

A Scenario is a hazardous event associated with the Equipment item to which it belongs. The types of scenario that you can define under a given equipment item depend on the type of the equipment item:

• Scenarios for a Pressure Vessel The Scenarios available for a Pressure Vessel are shown in the illustration of the Insert menu for the item, which appears in the right-click menu. These Scenarios model the release of material through all the stages in its dispersion to a harmless concentration. The modelling includes discharge calculations to obtain the release rate and state, and fire, explosion and toxic calculations to obtain representative effect zones for the dispersing cloud.

• Scenarios for an Atmospheric Storage Tank The Scenarios available for a Pressure Vessel are also available for an

Atmospheric Storage Tank, and there is also a Spill scenario which models a liquid spill in which the entire released mass is assumed to spill onto the ground.

• Scenarios for a Standalones item The Scenarios available for a Standalones item include four types of explosion, three types of fire, and pool vaporisation.

The consequence calculations are performed at the Scenario level, which is the lowest level in the data structure.


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In the example file, the Tank farm folder contains a typical set of Equipment items and Scenarios, with four Pressure Vessel Equipment items representing LPG and LNG storage and pipework, one Atmospheric Storage Tank Equipment item representing diesel storage, and a Standalones Equipment item representing a flare stack, for performing detailed radiation modelling. For each sphere and tank there are several Scenarios, including a catastrophic rupture, and leaks of various sizes from the liquid side of the vessel. You can define any number and combination of Scenarios under any Equipment item.

The Weather tab section

The Weather tab section of the Study Tree pane contains a folder named Weather folder with three definitions of weather conditions. Each Weather icon represents a particular set of weather conditions for use in the modelling of a release and its effects—i.e. a particular combination of wind speed, atmospheric stability, atmospheric temperature, etc. In the calculations for a given Scenario, the program performs a separate run of the consequence calculations for each separate weather conditions, giving a set of results that are specific to that Weather.

For the example file, the name of each weather gives the wind speed and the atmospheric stability category that are set for it.

Each new workspace will normally be created with a number of default Weathers pre-defined in this Weather folder. You can edit these Weathers, delete them or add Weathers of your own to the folder.

If you want to run different sets of Weathers for different sets of Equipment items, then you can insert additional Weather folders in the Weather tab of the Study Tree and define the sets of Weathers in these folders. If you organise the different sets of Equipment items under different Studies in the Models tab section, you can then use the input settings in the Study dialog to choose the appropriate set of Weathers to use in the calculations for each Study.

The Parameters tab section

In Phast, Parameters are background inputs that are applied to all calculations and are not specific to a particular Equipment item or Scenario. Some of the parameters in the program are used to provide default values for the aspects of Equipment item and Scenario input that are usually shared between groups of Equipment or Scenarios. Other parameters deal with advanced modelling assumptions and do not appear in the Equipment or Scenario input data.

The full set of Parameters is very large, and it has been organized into several groups. The icons for the

groups in the example file have a green arrow at the top left of the icon. The program uses this arrow to show that all of the Parameters under that icon are using the default values that are supplied with the program. If you change the value of any of the Parameters then the green border around the icon will disappear. This allows you to see at a glance which aspects of an analysis are using all-default values, and which are using changed values.


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Each new workspace will be created with a Parameter set folder, with a full set of Parameter groups defined in the folder. As with the Weather data, you can edit the values in this set, and you can also define more than one set, and select different sets for use with different Studies.

The Materials tab section

The program is supplied with a set of System Materials that contains full property data for more than sixty materials. However, the Materials tab section does not show icons for all of these materials, but only for materials that have been selected in the input data for the various Equipment items in the workspace, or for materials that you have added yourself while working in the Material tab section.

You can define two types of material:

Pure Components

Most of the icons in the Materials tab for the example file are pure Components. As with a Parameters group, a Component will have a green

arrow at the top left of the icon if all of the input fields for the Component have the values set for that material in the System Materials. You can change the values if you wish - e.g. to enter different probit values for a toxic material – and if you make changes the green arrow will disappear.

Mixtures

You can define any number of Mixtures, selecting up to eighteen pure Components in any mixture. An LPG Mixture is defined in the example file.

The Map tab section

You use the Map tab to describe various aspects of the surroundings such as buildings, the local terrain and bunds around equipment, and to define the images and other graphical data that you want to use as the background for displaying consequence results.

Bund types

Bund type data are used in the program in the modelling of pool spreading and vaporisation. You use the Bund types folder to define each type of bund or evaporation-surface that you want to use in the analysis, and then select the appropriate Bund type in the input data for the Equipment item or Scenario.

Terrain types

Terrain type data are used in the modelling of pool vaporisation and dispersion. You use the Terrain types folder to define each value of surface roughness and terrain type that you want to model, and then select the appropriate Terrain type in the input data for the Equipment item or Scenario.


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Building types

Building type data are used for modelling concentration build-up for a release inside a building, and for modelling toxic effects inside buildings in the path of the cloud. You use the Building types folder to define each type of building that you want to model for concentration-buildup and each type of building that you want to model for indoor toxic effects, and then select the appropriate Building type in the input data for the Equipment item or Scenario.

Each new workspace is created with a default Bund type, Terrain type and Building type defined, and you can edit these or define any number of additional types.

Raster Image Set

The example file has two raster images defined - a map (OS) image and an aerial photograph of an area called Southpoint – and you can see these images in the GIS Input View in the Document View area to the right of the Study Tree pane.

The map images in the GIS Input View

The Equipment items are represented by dots, and you can see that there are many dots distributed over the Chemical Plant area. The location data for a hazardous event is defined on the Equipment item, rather than on the Study or the Scenario.

The Display Order tab of the Legend for the GIS Input View controls the order in which the different “layers” of information are displayed in the view. The Equipment layer is at the top, which means that the dots that represent the Equipment items will always be visible, and in the illustration the Southpoint_OS image layer is above the Southpoint_Aerial image layer, which means that the map image is hiding the aerial image.


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The Tools tab of the Ribbon Bar and the GIS Input Tools tabs contain various options for working with the GIS Input View. For example, you can use these options to display the name of an Equipment item in the GIS View, as follows:

1. In the Models tab of the Study Tree pane, select the node for the Equipment item.

2. In the Tools tab of the Ribbon Bar, click on the Pinpoint option in the GIS section. The dot for that Equipment item will become highlighted in the GIS Input View, and the View will become centred on that dot.

3. Move to the Input tab of the GIS Input Tools group in the Ribbon Bar, and check the Label option.

The name of the Equipment item will then be displayed underneath the dot, as shown.

The name of an Equipment item displayed in the GIS Input View


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Viewing input data

The section above introduced the main types of input data and their organisation, and this section describes how to work on the details of the input data.

Opening the input dialog for the Chlorine tank Equipment item

In the Models tab section, expand the Toxic cases folder, and double-click on the icon for the Pressure Vessel Equipment item named Chlorine tank. The Pressure Vessel Equipment input dialog will open as shown below.

The dialog contains a large number of input fields organised over nearly ten tab sections, but you will not normally enter data in every section. For an Equipment item, the most important inputs are in the Material tab section, which covers the process material and operating conditions. Almost all of the fields in the other tab sections are also present in the Scenario dialogs, and you would set a value in the Equipment dialog if you want the value to be used as the default value for all of the Scenarios under that Equipment item.


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Getting Help on the input data

This tutorial does not attempt to describe every item on input data, but the program is supplied with comprehensive online Help.

Every input dialog contains a Help button at the bottom right. When you click on this button, the online Help will appear in a separate window, as shown.

The Help Window

The Help Window will be displaying a description of the current tab section, but you can use the links inside the topic and the Contents, Index and Search tabs to reach any topic in the Help system and gain a full understanding of the way that the input data will be used in the calculations and the appropriate values that you should set for the hazardous events that you want to model.

After you have finished exploring the input dialog, click on Cancel to close the input dialog without saving any changes you might have made. If you wish, you can move to the other tab sections and explore the input dialogs for other types of data.


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The Grid View allows you to work on input data for multiple items

The input dialogs allow you to work on the input data for a single item at a time, and the Help button and the organisation of the tab sections mean that the dialogs are the best way to work on data when you are still becoming familiar with the details of the input data.

However, once you have become familiar with the data, you may find the Grid View useful, as a method of working with input data that allows you to view and edit the data for more than one item at a time. The Grid View appears in a separate tab section in the Document View area, i.e. in the same area as the GIS Input View.

To view the data for both Pressure Vessel Equipment items under the Toxic cases folder, take the following steps:

1. Select the Toxic cases folder in the tree.

2. In the Grid View, bring up the list to the left of the Filter Options button in the toolbar, and select Pressure vessel from the list as shown. This list is known as the “filter list”, and it allows you to choose the type of item whose data you want to view in the area below the tooltab.

Once you have made the selection from the list, the data for the two Pressure Vessels under the folder will be displayed in the Grid View as shown, with the data fields displayed as a wide list of columns, as in a spreadsheet.

The data for two Pressure Vessels shown in the Grid View

If you select the Study from the tree, the Grid View will display all of the Pressure Vessels in the workspace, and if you change the selection in the filter list to Leak, the Grid View will display all of the Leak Scenarios under the Study or folder.

This can be very useful for obtaining an overview of the input data, and for comparing values between different items. The Grid View can also be a convenient way of setting up input data, as you can copy and paste values between cells in the Grid View, and also between a spreadsheet and the Grid View.

This tutorial does not give further details of using the Grid View, and you should refer to the Help for a full description.


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Running the calculations and viewing the results

In the Models tab section, select the Tank farm folder, and then click on Run in the Home tab of the Ribbon Bar (or press [Ctrl]+M).

The program will process the calculations for each of the 21 Scenarios in turn, performing the calculations for each of the three Weathers, and showing the progress through the calculations. When the calculations for a given Scenario have been

completed for all three Weathers, a green tick will appear to the top right of the icon for that Scenario, which is how the program shows that a Scenario has run successfully and has a complete set of results. The calculations will take several minutes to complete, depending on the speed of your machine.

You do not have to run the calculations for all Scenarios and all Weathers. If you select a single Scenario or Equipment item, then you can run the calculations just for that Scenario or for the Scenarios under that Equipment item. You can also right-click on a Weather or on an node in the Models tab and select Exclude from calculations, and that Weather or set of Scenarios will be shown as greyed-out in the tree and will not be included when calculations are run; to stop excluding a greyed-out node, right-click on it and select Include in calculations.

Viewing the graphs for the LPG sphere Scenarios

In the program, a given Graphs View can show results for multiple Weathers for a single Scenario, or for multiple Scenarios for a single Weather. To compare graphical results for the different LPG sphere 101 Scenarios, you must first move to the Weathers tab of the Study Tree and select the Weather whose results you want to see. For this example, select the Category 1.5/F Weather. This is the weather with the most stable conditions, and is likely to give the longest dispersion distances.

Once you selected the Weather node, click on Graphs in the Home tab of the Ribbon Bar (or press [Ctrl]+G). A dialog will appear as shown, prompting you to choose the combination of Scenarios whose results you want to view. The folders for which you have not yet run the calculations are included in the dialog, but with a disabled checkbox.

Check the box for the LPG sphere 101 Pressure Vessel, which will select all of the Scenarios for this Equipment item.

When you click on OK there will be a pause of a few seconds, and then the Graphs View will open in the Document View area as shown on the next page.


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The Graphs View

A given Scenario or set of Scenarios may have many Graphs available, and to make them easier to work with, they are organised within groups, where each group covers a different category of results. Each group has its own tab header at the bottom of the

Graphs View, with an icon that identifies the type of results, e.g. for Dispersion , or

for Fireball effects , or for Toxic effects . Within the tab for a given group, there are tab headers for the individual graphs within that group.

The graphs included for a particular combination of Scenarios will depend on the type of Scenario (e.g. a Leak Scenario or a standalone Fireball Scenario), on the type of the materials (toxic or flammable), and on the details of the dispersion and effect behaviour (e.g. whether or not liquid rainout occurs). The Graphs View for LPG sphere 101 includes results for pool vaporisation, for all types of fire and for explosion, but there are no graphs for toxic effects as the material is not toxic.

The graph that is displayed when the Graphs View first opens is the Centreline Concentration graph in the Dispersion group. This graphs shows the results at the time at which the cloud footprint covers the greatest area. This occurs at a different time for each Scenario, as shown by the Time entries in the Legend. The Footprint, Side View and Cross Section graphs in the Dispersion group also show results at this time, but the Concentration vs Time graph shows the concentration as a function of time at a given distance, and the Maximum Concentration graph shows the maximum distance reached for a given concentration of interest.

The graphs in the Dispersion group contain results for all four Scenarios, but if you move to the other groups, you will see that most graphs contain results only for a selection of Scenarios. For example, the Jet Fire graphs contain results for the three leaks only, the Fireball graphs contain results for the Rupture only, and the Pool Fire and Pool Vaporisation graphs contain results for the 150 mm leak only, as this is the only Scenario for which liquid rainout occurs.


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Viewing results on the GIS, against the background of map images

The Graphs View does not display any of the results on the GIS, and to view the results in this form, you must open a GIS Results View.

The process of opening a GIS Results View for the LPG sphere 101 Scenarios is almost identical to the process of opening a Graphs View:

1. Select the Category 1.5/F Weather in the Weather tab.

2. Click on GIS in the Home tab of the Ribbon Bar.

3. In the Select Scenarios dialog, check the box for the LPG sphere 101 Pressure Vessel, which will select all of the Scenarios for this Equipment item.

4. Click on OK to close the dialog.

There will be a pause of a few seconds, and then the GIS Results View will open in the Document View area as shown below.

The results shown in a GIS Results View

When the View first opens, it will be displaying Cloud Footprint concentration results, which are present for all four Scenarios. This is the default form of results for storage Scenarios, but the Event field in the Consequence tab of the Ribbon Bar gives an alphabetical list of the types of effect for which results are available for the set of Scenarios and Weathers covered by the GIS Results View, and you use this list to select the type of effect to display.

Changing the type of results to display on the GIS Results View


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Viewing the Reports for the Catastrophic rupture Scenario

The program also presents results in the form of reports. If you wish you can view a report that covers multiple Scenarios – e.g. a report for all Tank farm Scenarios – but if you want to compare the report-results for different Scenarios it is easier to view separate reports for each Scenarios and compare between two reports.

To view the reports for the Catastrophic rupture Scenario for LPG sphere 101, select the Scenario and then click on Reports in the Home tab of the Ribbon Bar (or click [Ctrl]+R). After a pause of a few seconds, the Reports View will open in the Document View area as shown. You can have many Graphs Views, GIS Results View and Reports Views open at the same time, but it is best to close a View once you have finished working with it, as this will reduce the risk that the program will have problems with low memory.

The Reports View

Similar to the Graphs View, the Reports View will normally contain several types of results presented in different tab sections. A given tab section will present the results for all of the weather conditions that have been processed for the Scenario.

For the Catastrophic rupture Scenario for LPG sphere 101, the first tab section is the Input tab section, which lists the input data. All of the other tab sections give details of the consequence results that you saw summarised in the Graph window:

The Summary Report

This report summarises the maximum downwind distance to different types of effects, and gives a direct comparison between the different weather conditions. For this Scenario, the 5/D Weather is the one that gives the greatest distances.


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The Discharge Report

This gives details of the discharge modelling, and the condition of the release immediately after expansion to atmospheric pressure – which is the condition used for the start of the dispersion calculations.

This report and all the other results-reports give the results for each weather in turn. The Summary report is the only report which presents a direct comparison between the different weathers.

The Dispersion Report

This report contains a table which describes the location and state of the cloud at a series of time-steps during the dispersion. You might refer to this report if you wanted to understand a particular aspect of the dispersion behaviour in greater depth.

The Commentary Report

This report highlights the main events in the course of the dispersion, and allows you to see easily if and when different types of behaviour occurred, e.g. touch-down on the ground, or the rainout of liquid droplets.

The Averaging Times Report

The centreline concentrations given in the Dispersion and Commentary reports are all calculated using a “core” averaging time that is set in the Dispersion Parameters and that has a default value of 18.75 s. The Averaging Times report gives the centreline concentrations at a series of steps during the dispersion, calculated using alternative averaging times.

For the rupture Scenario the only alternative time is the Flammable Averaging Time (whose value is set in the Flammable Parameters). In this analysis this time is also set to 18.75 s so for this Scenario the Averaging Times report gives the same concentrations as the other reports. However, if you viewed the report for one of the Scenarios in the Toxic cases folder, you would see results for the Toxic Averaging Time (whose value is set in the Toxic Parameters), and which has the default value of 600 s.

The Fireball Report

The Fireball report gives radiation results for a fireball resulting from immediate ignition of the released material. The report first gives a description of the fireball flame (emissive power, liftoff height, etc.), then it gives the dimensions of the elliptical effect zones for up to five different radiation levels – where the levels are set in the Fireball tab section for the Scenario – and finally gives the radiation levels at a series of points downwind from the centreline of the release.

The Jet Fire and Pool Fire reports have a similar form, giving the same three types of results.


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The Early Explosion Report

For rupture Scenario, the tab for the Early Explosion report is named Early Expl.(TNT), and this is because the explosion method selected for this Scenario is the TNT method. There are three methods available, and you select between them in the Flammable tab section for the Scenario. The TNT method is the simplest, requiring the smallest amount of input data, and it is the default method.

The report is similar in form to the Fireball report, giving the dimensions of the circular effect zones for up to five explosion overpressures – where the overpressures are set in the Explosion Parameters – and also giving the overpressure levels at a series of points downwind from the centreline of the release.

The Late Explosion Report

This report gives the overpressure effect distances for late explosions occurring at a range of times during the dispersion. For each ignition time, the report gives the location of the cloud-centre, the location of the centre of the explosion, the downwind distance to up to five overpressure levels, and the flammable mass in the cloud at the time of the explosion. By default the centre of the explosion is taken as the cloud front to 50% of the LFL, but you can change this setting in the Explosion Parameters.

Results for Two Time-Steps in the Late Explosion Report

The ignition-time that gives the greatest downwind effect distance is the one presented in the Worst Case Late Explosion graphs.

The range of reports presented for a particular Scenario will depend on the type of Scenario and on the behaviour of a release, and there are additional reports that do not appear for this Scenario. For example, if the material is toxic then there will be a Toxic report with a table of dose, probit and lethality results as a function of downwind distance, and if the liquid in the release rains out to form a pool, then there will be reports describing the spreading and evaporation of the pool and describing the series of “dispersion segments” used to represent the vapour produced from the pool.

For most of your work with the program you will probably refer mainly to the Graphs Views and GIS Results Views, since they present the results in the most direct form and allow easy comparison between different Scenario and Weathers.

After you have finished examining the results, you can use the Close button at the right of the title tab for each View to close that View.


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Viewing the results for other types of Scenario

There are other Scenarios in the file that are not storage Scenarios. The standalone Scenarios each model one specific type of behaviour and will produce a fixed set of graphs and reports.

The Standalone flammable Scenarios

The Pool fire, Fireball and Jet fire Scenarios under the Standalone flammable folder perform the same type of radiation modelling as that associated with a storage Scenario, but they give you more control over the definition of the flame and they also allow you to specify in more detail the locations for which you want to calculation the radiation levels.

The Standalone explosion Scenarios

The TNT explosion, Multi-Energy explosion, and Baker-Strehlow-Tang explosion Scenarios perform the same type of vapour-cloud explosion modelling as that associated with a storage Scenario, but they give you more control over the definition of the flammable cloud and of the results-locations.

The BLEVE Blast Scenario calculates the overpressure levels produced by the rupture of a vessel under flame impingement, which is a type of explosion modelling that is not performed for a storage Scenario.

The form of the results for all of these Scenario is similar to the corresponding dispersion, toxic, fire and explosion results for a storage Scenario, and you should find interpreting the graphs and reports very straightforward.

You have now seen the main features of Phast. When you are ready you should proceed to Chapter 2, which takes you through the stages in setting up your own analysis.

Phast Tutorial Chapter 2:Setting up your own analysis

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Chapter 2 Setting up your own analysis

The form of the analysis

This chapter will guide you through the process of setting up a workspace for performing consequence calculations. The tutorial supplies all of the input values that you will need to complete the analysis.

The Equipment and Scenarios defined in the analysis

The main aim of the analysis is to show you how you can define Equipment and Scenarios to represent the most common types of hazardous event, and how to take into account the main variables. The types of hazardous event that are considered in the analysis are as follows:

• A rupture of a vessel containing a toxic material

• A pipework leak from the liquid side of a vessel containing a toxic material

• A pipework leak from the gas side of a vessel containing a toxic material

• The equivalent three releases for a vessel containing a flammable material

• The rupture of a propane tank wagon under normal operating conditions.

• A fireball or BLEVE of the propane tank wagon as a result of fire impingement.

• A liquid leak from the body of the propane tank wagon.

If you wish, you can omit events, define different events, or change the input values in order to define conditions that are more typical of your facility. However, if you do this you will obtain results that are different from those that will be shown in this manual.

Creating a new workspace

To create a new workspace if you have the example file open, you can select either Close or New Workspace > Phast from the File tab of the Ribbon bar. The program will close the example file and open a new workspace with a name shown as “New Workspace”.

Saving the workspace

You cannot save the workspace with the name “New Workspace” and should save it with a real name immediately.

Select Save As… from the File tab of the Ribbon bar. The File Save dialog will appear and you should locate the DNVuser folder (the default location for saving workspace files), use the New Folder option to create a folder with your name, and then save the new file to this folder with the name Tutorial and the default file format of *.psux.


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The contents of a new workspace

New workspace files are not empty but will have some default data set up:

• A Weather folder containing three Weathers

The Weathers are the same as those in the example file.

• A set of default Parameters

As with the example file there is a set of Parameters, all of which are using the default values.

Setting up the map image

The tutorial uses a map of an area near two rivers, in a country which has a national grid system. The image for this map is supplied with the program the form of a *.tif file. If you have an image file for the area around your facility, you might prefer to use that instead.

Inserting the raster image

Image files that contain a description of each pixel in the image are known as raster images, and most common image files are in this form, e.g. *.tif, *.bmp, *.gif files. The program can also display map data taken from a GIS database, where an image is defined by describing the lines that form the image.

The process of inserting a raster image into a workspace is very different from the process of inserting a connection to a GIS database. This tutorial deals only with raster images, and you should refer to the online Help for details of working with GIS databases.

The process of inserting the raster images involves several stages.

Ensure that there is a Raster Image Set in the Map tab section

If the Map tab section of the Study Tree does not already contain a Raster Image Set icon, select the Tutorial icon at the top of the tab section, and use the Insert option in the right-click menu to insert a Set.

The Set is a folder for raster images, and you have to insert raster images inside such a folder.

Insert a Raster Image inside the Set

Select the Set, then select Raster Image from under the Insert option in the right-click menu. A dialog will appear as shown, and you must first browse to locate the image file. The tutorial.tif file is located in the Examples folder for the installation of the program (which is typically under C:\DNVUser\PHAST_7_0_0\Examples\Maps\

tutorial.tif). When you first browse to this folder you may not see any files if the list of File types is not set to *.tif by default.


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When you have selected a valid raster image file, the Placement Mode fields will become enabled; these are options for specifying the map co-ordinates covered by the image. Some files contain georeference data or header data that you can use to set the co-ordinate data for the image, but the tutorial.tif file does not and the only option available is the Interactive option, which is available for any raster image file.

Placing the image in the GIS Input View

When you click on OK in the Insert dialog, the GIS Input View will become selected if it is not selected already, and will display the instruction “Drag a box to define the raster image size and location” inside the View, as shown in the illustration.

The cursor will be in the form of crosshairs, and you must drag and drop to place the image in the View. This sets the initial values for the map co-ordinates for the images, which you will set to the correct values in the next step.

Setting the co-ordinates and size of the image

A tutorial icon will now be present under the Raster Image Set. Double-click on this icon to open the input dialog for the image, move to the Geometry tab section, and set the values shown. The origin for a map image is the top-left corner, and the values are in the national co-ordinate system for the country.

When you click on OK the image will probably disappear from the GIS View because it has moved to a location beyond the scope of the view. To make it visible, click in the GIS View to make sure that it has focus and that the GIS Input Tools group is included in the Ribbon Bar, and then click on Fit All in the General tab of this group. The GIS View will change to display the area covered by the image.


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The location of the site on the map

For the tutorial, the facility occupies the long, narrow section of land to the north and west of The Village, between the east bank of the river and the road that runs parallel to the river, shown shaded yellow in the illustration.

The location of the facility on the map

Phast Tutorial Chapter 3:Performing the consequence analysis

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Chapter 3 Performing the consequence analysis

Defining the Pressure Vessel that contains a toxic material

Move to the Models tab section. You will start by defining the Pressure Vessel Equipment item that contains a toxic material.

The vessel is a sphere with a radius of 3.37 m and volume of 120 m3 and a maximum fill-level of 85%, containing chlorine at saturation conditions and ambient temperature. The sphere is located near the centre of the site and is elevated 4 m above the ground. There is no bund surrounding the sphere.

Turn on the option to insert Equipment on the GIS

In the Tools tab of the Ribbon Bar, check the option to Insert Equipment on GIS. By default this option is turned off, and when you insert an Equipment item the icon will appear immediately in the Study Tree. If you turn the option on, then the Equipment icon will not appear in the Study Tree until you have clicked on the GIS Input View to set the location for the Equipment item.

In this tutorial you will insert the Equipment items on the GIS View in approximately the correct location, and then correct the location as necessary in the input dialog.

Insert a Pressure Vessel Equipment item

Select the Study, then select Insert > Pressure vessel from the right-click menu. The GIS Input View will become selected, the cursor will turn to crosshairs, and you should click at a point near the centre of the site as shown to place the Pressure Vessel.

After you have clicked, an icon will be added to the Study Tree, and a dot will appear in the GIS View to show the location of the Pressure Vessel.

In the Study Tree, rename the node to Chlorine, Saturated 10 degC.


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Setting the input data for the vessel

The Pressure Vessel node will have a red error icon at the top left, showing that it does not have a full set of input data. You will not be able to run the consequence calculations for any Scenarios under the Pressure Vessel until you have supplied values for all of the mandatory input fields, as described below.

Double-click on the icon for the Pressure Vessel to open the input dialog.

Most of the fields in the first tab section will be blank, and those that are enabled will have red borders and error icons. A field with a red border is a mandatory field: you must supply a value for such a field if it is enabled, and you will not be able to run the calculations for Equipment items or Scenarios that have any mandatory fields unset.

This section describes each tab section in turn, including those that are not relevant to this particular hazardous event. Click on the Help button to open the online Help if you want further information at any point.

The Material tab section

To set the Material, select CHLORINE from the dropdown list of all of the materials that are defined in the System Materials.

The vessel is a sphere with a volume of 120 m3. This Equipment item will represent the vessel with the maximum degree of filling, which is 85%. Check the Specify volume inventory? to select this method of specifying the inventory instead of giving the mass and enter a value of 102 m3 in the Volume inventory field.

The chlorine is held under saturation conditions at atmospheric temperature. The temperature will vary depending on the season and time of day, but for this Equipment item a value of 10oC will be used as representative. To set these process conditions, set the Specified condition to Temperature/bubble point and set the Temperature to 10 degC, as shown. When you move the cursor away from the Temperature field the program will calculate the saturation pressure for this temperature and display it in the Pressure field.

To define the process conditions for a material that is not held under saturation conditions (e.g. a gas or a padded liquid), you must set the Specified condition to Pressure/temperature and give values for both.

After you have set the storage conditions, the Phase to be released will be set to Liquid, which is the default value.

The Dispersion tab section

The program requires a criterion for stopping the dispersion calculations: either a maximum distance, or a minimum concentration. You will set values in the Pressure Vessel dialog, to be used as the defaults for all Scenarios under the vessel.

For this tutorial, set the Concentration of interest to 100 ppm. When you set this concentration, the Averaging time for concentration of interest field will become enabled and mandatory, as you must specify the averaging time to be used in the calculations for stopping the dispersion. For a toxic release, the list allows you to choose the Toxic averaging time or the times associated with the ERPG, IDLH or STEL measures of toxicity, or to specify a User-defined time.


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For this release, select the Toxic averaging time, which is set in the Toxic Parameters and has a default value of 600 s.

The Dispersion tab section allows you to select additional averaging times for which you want concentration values. If you make any selections in the final section of the tab, the results will appear in the Averaging Times report, as you saw in the previous chapter.

The Toxic parameters tab section

The fields in this tab section are used in modelling the toxic effects for people indoors, in buildings in the path of the dispersing cloud.

By default, these calculations are not performed, but for this tutorial you should turn them on by checking the option to Specify the downwind building. The calculations require information about the ventilation-rate for the representative building and about how long people remain in the building after the cloud has passed and the concentration is lower outdoors than indoors, and this information is defined using the Building Type nodes in the Map tab section of the Study Tree. The new workspace is created with one Building Type called “Default building” already defined, with the ventilation value and evacuation values set to the defaults.

This default Building Type is selected by default, and for this tutorial you should leave the Specified downwind building field with this default setting.

The Geometry tab section

Set the East co-ordinate to 198492 m, and the North co-ordinate to 435063 m.

A Summary of the Input Data

The dialog includes a large number of input fields, but the number of values that you have to enter in order to complete the data for this Pressure Vessel is small, as shown in the table below:

Tab Section Input Field Value

Material Discharge Material Chlorine

Specify volume inventory? [checked]

Volume inventory 102 m3

Specified condition Temperature/bubble point

Temperature 10oC.

Dispersion Concentration of interest 100 ppm

Averaging time for concentration of interest

Toxic

Toxic parameters Specify downwind building [checked]

Geometry East Co-ordinate 198492 m

North Co-ordinate 435063 m

Make sure you have set all of these values correctly, and then click on OK to close the dialog.


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Defining a Catastrophic rupture Scenario

Now that you have defined the Pressure Vessel, you can define any number of different Scenarios underneath it. The Catastrophic rupture Scenario is defined here first, as it has the simplest set of input data.

Inserting the Scenario

Select the Pressure Vessel node, and then select Insert > Catastrophic rupture from the right-click menu.

The Scenario node will be added to the Study Tree immediately, i.e. you do not have to place Scenarios on the GIS Input View, as Scenarios take their Geometry data from the Equipment item to which they belong.

You can leave the node with the default name of Catastrophic rupture. You will only be defining one Catastrophic Rupture Scenario for this Pressure Vessel so do not need to distinguish it from other Scenarios of the same type.

Setting the input data

The node will not be shown as incomplete when you insert it, as the Catastrophic rupture Scenario does not have any mandatory input fields. All of the fields take default values from the Pressure Vessel.

For this tutorial, you will edit the Scenario and set a non-default value for one field.

Elevation in Scenario tab section

The default value for the release Elevation is 1 m, but for the rupture you should set this to 7.37 m, which is the elevation of the centre of the sphere above the ground. You could have set the value of 7.37 m in the input data for the Pressure Vessel, but the other Scenarios will have different values for the Elevation, and to reduce the risk of confusion, the Pressure Vessel has been left with the default value of 1 m, and the Elevation is being set individually for each Scenario.

Dispersion and Toxic parameters tab sections

If you look at these tab sections, you will see that the values that you set in the Pressure Vessel dialog are present, and shown as defaulted. The settings for the concentration of interest and the indoor toxic modelling are the same for all Scenarios for this Equipment item – as they are likely to be for most Equipment items – so it is appropriate to set the values at the Equipment item level.

Finally, click on OK to close the dialog.

Run the calculations for the Scenario and view the results

Select the Scenario and select Run from the Home tab of the Ribbon Bar.

Viewing the set of Graphs

When the calculations are complete, view the graphs for all of the Weathers. To do this, select the Scenario, then click on the Graphs option in the Home tab of the Ribbon Bar, and select all three Weathers in the Select Weathers dialog.

You will see that there is no Pool Vaporisation tab in the Graphs View, which means that the liquid in the release did not rain out; if you want more information about the behaviour of the liquid droplets in the cloud, you should view either the Commentary Report or the Dispersion Report.


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The concentration graphs only ever show the outdoor concentration, but if you move to the Toxic tab section you will see that the Probit, Lethality and Dose graphs display separate results for indoor and outdoor effects, and that there are separate Footprint graphs for outdoor and indoor effects. The Lethality graph shows that the greatest downwind effect distance is for the F 1.5 m/s weather outdoors, with a distance of about 2.5 km to a lethality level of 10%. The indoor effects for this weather reach about 2.25 km to 10% lethality. The shortest downwind effect distances are for D 5 m/s indoors, which reaches about 1.4 km for a lethality level of 10%.

Viewing outdoor toxic lethality results against the map

Select the Scenario in the Study Tree, and then click on the GIS button in the Home tab of the Ribbon Bar. A Select Weathers dialog will appear listing the Weathers for which calculations have been performed, the same as when you view Graphs. Make sure that all of the Weathers are selected, and click on OK to proceed.

After a pause a GIS Results View will open, appearing as a separate tab in the Document View area, which is the area that contains the Graphs View and the GIS Input View. GIS Results Views display footprint and contour results on the GIS, i.e. against the background of the map.

By default, GIS Results Views display the Cloud Footprint results, but the Event field in the Consequence tab of the Ribbon Bar lists all of the types of footprint and contour results that are available for the Scenarios and Weathers covered by the GIS View, and you use this list to view a different type of effect. For this tutorial, select Toxic Outdoor Lethality Footprint, as shown.

If a Graphs View or GIS Results View is displaying results for a single Scenario and Weather, it will display results for more than one effect level when it first opens (e.g. it will have separate contours for 0.1%, 1% and 10% lethality). However, if it is displaying results for multiple Scenarios or Weathers, it will display results for a single effect level when it first opens.


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By default the effect level displayed for multiple Scenarios or Weathers will be the lowest effect level of interest defined for the Scenarios, which is 0.1% lethality for toxic effects, as shown in the illustration above.

You can change the effect level displayed in the GIS Results View by clicking on the Edit Settings button in the Consequence tab of the Ribbon Bar. The Edit Settings dialog will open, as shown.

To change the toxic lethality level to 10%, move to the Toxic Parameters tab, and enter a value of 0.1 in the Lethality Levels table, pressing [Enter] after you have typed the value in order to commit the change.

When you click on OK to close the dialog, there will be a pause and the GIS Results View will then display the results for a 10% lethality level, which will show that the effect contours for all Weathers are able to reach both the village and the town, although the range of wind directions for which they will be reached is smaller for the 5 m/s D Weather than for the 1.5 m/s Weathers.

The Edit Settings dialog also allows you to change the number of effect levels to display. By default this is initially set for one for multiple Scenarios or Weathers, but you can change that in the dialog.


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Defining the second Scenario: a liquid release from pipework

The second release is from the same chlorine sphere, but the hazardous event is the rupture of a one-inch liquid line attached to the bottom of the sphere, where the initial liquid head will be 4.6 m. The line runs 4 m vertically downwards to 10 cm from the ground, then 5 m horizontally to an isolation valve; the rupture is assumed to occur just before the isolation valve.

Insert a Time varying short pipe Scenario

There are two types of Scenario available for modelling pipework rupture:

• The Short pipe Scenario, which models the release using the initial release rate for the start of the release, with a duration that is the time required to drain the inventory at this initial rate. This will normally give conservative results in the consequence calculations.

• The Time varying short pipe Scenario, which models the effect of the release on conditions in the vessel and the way that these conditions and the release rate change over time. These time-varying results can be represented either with a single rate (e.g. an average rate, or a rate at a particular time) or with a series of rates, depending on the options that are set for the Scenario.

For this tutorial, you will use the Time varying short pipe Scenario, perform an initial run of the discharge calculations, then examine the results and decide on the most appropriate way to represent the behaviour for the rest of the consequence analysis.

To add the Scenario, select the Pressure Vessel and select Insert > Time varying short pipe release from the right-click menu.

Name the Scenario Line rupture, liquid.

Setting the input data for the Scenario

The new Scenario will be shown as incomplete, as this type of Scenario does have mandatory data.

Open the input dialog and set the input data as follows:

Scenario tab section

Make sure the Scenario type is set to Line rupture (rather than Disc rupture or Relief valve).

Set the Pipe diameter to 25.4 mm, the Pipe length to 9 m, the Release height from vessel bottom to 0 m, and the Elevation to 0.1 m. With this value for Elevation, the liquid droplets will probably not evaporate inside the cloud, and will probably rain out and form a vaporising pool.

Note: the Pipe diameter is 1 inch, and the easiest way to set this is to type “1 in” in the input field and press [Tab]. The program recognises “in” as a defined unit for length, and will convert it to the default display units of mm when you press [Tab] or click in a different field.

The Scenario tab includes the Outdoor release direction field, which you should leave with the default value of Horizontal, which is the correct setting for this type of unobstructed rupture of horizontal pipework.

The list of directions includes a second horizontal option: Horizontal Impingement. You should select this option if the release is in a congested area and the release is likely to impinge on a wall or other equipment; the program will reduce the momentum of the release, which will reduce the amount of air mixed into the jet during the initial stages.


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Material tab section

When the vessel to which the Scenario belongs contains saturated liquid, the Phase to be released field in the Material tab section will offer a choice of release-phase for the line rupture: a vapour release from the top of the vessel, or a liquid release from the bottom of the vessel.

By default this will be set to Liquid, which is the value set for the Phase field in the Material tab section for the Pressure Vessel, and for this Scenario you should leave the field with the default value.

Short pipe tab section

The Short pipe tab section contains details for the modelling of frictional losses.

Leave the pipe roughness with the default value taken from the Parameters, and leave the numbers of valves as zero.

There is one bend in the 9 m of pipework, so you should set the Frequency of bends in pipe to 0.11 per m.

Time varying releases tab section

For a newly-inserted Time varying Scenario, the Method for

calculating the average rate is set to Average between 2 times, with the times set to 0 s and 20 s, as shown.

Leave the tab section with these values. You will perform an initial run of the discharge calculations, then examine the results and decide on the most appropriate way to represent the behaviour for the rest of the consequence analysis, which may involve changing these settings.

This completes the input data for this stage, and you can click on OK to close the input dialog.


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Supplying the tank shape data for the Pressure Vessel

The settings described above will complete the mandatory input data for the Scenario, but when you close the dialog, you will find that the Scenario is still shown as

incomplete in the Study Tree. If you hover the mouse over the error icon for the Scenario node, a tooltip will appear saying that the “Tank shape” is missing. The Tank shape field is actually part of the input data for the Pressure Vessel, and it becomes mandatory if you have any Time varying Scenarios present under the vessel.

Open the input dialog for the Pressure Vessel again. You will find that two tab sections are now shown as incomplete:

Scenario tab section

The Release height from vessel bottom is shown as incomplete. You set this to 0 m for the Scenario, but the Pressure Vessel needs a value in order to perform checks on the data, and you should enter a value of 0 m here, as well.

Time varying releases tab section

Set the Tank type to Spherical and the Tank diameter to 6.74 m, as shown, and then press [Tab]. The program will use the process and inventory data from the Material tab to calculate the vapour and liquid contents of the vessel, and displays the results in the Inventory data section at the bottom of the tab section.

When you click on OK to close the input dialog, a message will appear warning you that the changes in the input data will make the results for the Catastrophic rupture Scenario out of date. After you have clicked on OK to proceed with the changes and return to the Study Tree, you will find that both the Pressure Vessel and the Time varying Scenario are now shown as complete.


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Running the discharge calculations

Select the Time varying Scenario and then click on Run Discharge Only in the Home tab of the Ribbon Bar. This will run the discharge calculations alone, without performing the dispersion and effects calculations. The calculations may take several minutes, depending on the speed of your machine.

When the results are complete, view the reports and move to the TV Discharge Report. The report shows that the rate drops by less than 3% in two hours of release, which means that the time-varying behaviour can be ignored for this release.

The time-varying discharge calculations are time-consuming, and the analysis will be easier to work with if you bypass the time-varying discharge modelling for this hazardous events. There are two possibilities in this situation:

1: Use the averaged discharge results to create a User-defined source Scenario

Most of the Scenarios for a Pressure Vessel perform in-built discharge calculations to determine the state of the material after expansion to atmospheric pressure, which is the state required for the start of the dispersion calculations. However, the User-defined source Scenario is also available: this Scenario does not perform discharge calculations, but instead allows you to specify directly the state of the material after expansion to atmospheric pressure. You use it if you want greater control over the inputs to the dispersion and effect calculations, as will be described later in this chapter.

When you performed the discharge calculations, the program calculated the average rate over the first 20 s, and this is the representative rate given in the Discharge Report. If you decide that you want to use this average rate rather than the initial rate, you should right-click on the Scenario, and then select the first Create source options from the bottom of the right-click menu as shown.

There is a separate Create source option for each Weather for which you performed the discharge calculations. For this Scenario, the results will be the same for all Weathers, and when you select the Weather the program will create a User-defined source Scenario with the name User defined source for Category 1.5/F .

The dialog for the User-defined source Scenario does not include the Short pipe or Time varying release tab sections, and instead of containing fields for the pipe diameter and length, the Scenario tab section contains a Release segments table in which you specify the discharge rate and conditions directly, since the User-defined source Scenario does not perform any discharge modelling itself. The Scenario will be created with discharge data taken from the averaged results from the Time varying Scenario, but you can edit these values if you choose.


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2: Insert a Short pipe Scenario and set up the equivalent input data

The Short pipe Scenario models the same type of hazardous event as the Time-varying short pipe release Scenario, but it calculates the initial discharge rate, without performing any time-varying discharge modelling. Inserting this Scenario involves repeating some of the data-input, but this is the approach taken in this tutorial as it will make the analysis clearer and easier to maintain: if you need to change some aspect of the input data you can edit the Scenario and rerun the calculations, whereas if you used a User-defined release Scenario you would have to edit and rerun the Time-varying Scenario first, then create a new User-defined release Scenario, and delete the previous User-defined release Scenario.

Before you insert the Short pipe Scenario, rename the Time varying Scenario to add “- time-varying not needed” at the end of the name, and then right-click on the Scenario and select Exclude from calculations from the menu. The Scenario will become greyed out in the tree and will not be included if you run the calculations for the Pressure Vessel or Study, which will make the calculations quicker.

Next, insert a Short pipe Scenario, name it Line rupture, liquid, and then edit it and set the values as follows:

Tab section Input field Value

Scenario Scenario type Line rupture

Pipe diameter 25.4 mm

Pipe length 9 m

Elevation 0.1 m

Material Phase to be released Liquid

Short pipe Frequency of bends in pipe 0.11 per m

Run the consequence calculations and view the results

Select the Scenario and select Run from the Home tab of the Ribbon Bar or the right-click menu. When the calculations are complete, view the graphs for all of the Weathers.

You will see that there is a Pool Vaporisation tab in the Graphs View, which means that the liquid in the release did rain out. If you view the reports and look at the Commentary Report, you will see that rainout fraction is about 0.7 for all three Weathers, so the formation and behaviour of the pool will have an effect on the dispersion or toxic effects.

In the Toxic Lethality graph, the greatest effect distances are for the F 1.5 m/s weather outdoors, with a distance of 900 m to a lethality level of 10%, which is approximately a third of the distance reached by the catastrophic rupture. The least stable condition, D 5 m/s, reaches only 300 m for 10% lethality outdoors.

If you open a GIS Results View for all three Weathers and view the Toxic Outdoor Lethality Footprint for 10% lethality, you will see that the effects do not reach the village or the town.


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Defining the third Scenario: toxic vapour from pipework

The vapour release is the rupture of a two-inch pipe attached to the top of the sphere. The line runs 3.4 m horizontally, then vertically downwards, and the rupture is assumed to occur 1 m from the ground.

Create the Scenario as a copy of the Line rupture, liquid Scenario, rename the copy to Line rupture, vapour, and change the input data as follows:


Scenario Pipe diameter 50.8 mm

Pipe length 13 m

Elevation 1 m

Outdoor release direction Down – impinging on the ground

Material Phase to be released Vapour

Short pipe Frequency of Bends 0.08 per m

The release rate from the two-inch vapour line is similar to that from the one-inch liquid line, and the two pipework releases give very similar effect distances.

Defining three flammable releases

There is a propane sphere at the far north of the site. The propane sphere has the same dimensions as the chlorine sphere and the same design of pipework, and is also operating under saturation conditions at atmospheric temperature.

Setting the input data for the propane Equipment item

You can define the propane sphere Equipment item and all of the Scenarios by copying the chlorine Equipment item and its Scenarios and simply changing the selection of discharge material and the eastern co-ordinates.

Copying the Equipment item

Select the Chlorine Pressure Vessel, copy and paste it, and name the copy Propane, Saturated 10 degC.

Changing the Material selection

Open the input dialog for the propane Pressure Vessel, and change the selection for the Material field from CHLORINE to PROPANE. After you make the selection there will be a brief pause while the program calculates the saturation pressure at 10oC and also the mass for the inventory, and then displays the changed values in the dialog.

Changing the Concentration of interest in the Dispersion tab section

When you move to the Dispersion tab section, you will see that the Toxic averaging time is no longer set for Averaging time for concentration of interest and that this field is now shown as unset and mandatory. The material is flammable only so the Toxic averaging time is not included in the list, and the program is prompting you to make a different selection for the calculations of the stopping-concentration.

For a flammable release you would not want to calculate the concentration to a value as low as 100 ppm, since the cloud will not pose a hazard once it has diluted below the lower flammable limit of 2% or 20,000 ppm. You could set a concentration yourself, but for a flammable release you can also leave the Concentration of interest blank, and the program will automatically stop the dispersion calculations once the concentration has reached a given fraction of the LFL calculated with the Flammable averaging time.


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By default the fraction of the LFL used is 50%, but you can change this in the Flammable Parameters if you prefer.

Delete the value in the Concentration of interest field and then press [Tab] to commit the changed value and update the dialog. When you do this, the Averaging time field will become disabled, as you do not have to supply an averaging time if there is no concentration specified.

Changing the coordinates

In the Geometry tab, set the new location as:

East co-ordinate = 197327 m

North co-ordinate = 435681 m

After changing each value you should press [Enter] to “commit” the changed value.

Setting the input data for the fire modelling

If you move to the Fireball, Jet fire or Pool fire tab sections, you will see that three levels of radiation intensity are specified, but that the calculations for radiation dose, probit and lethality are all unselected. These calculations are not selected by default because they can be time-consuming, so you would normally only select them if you know that you need them for a particular analysis or a particular Equipment item or Scenario.

For this tutorial you will set the lethality calculations to selected and specify five levels of lethality.

In the Fireball tab, take the following steps to specify the lethality levels:

1. Check the Calculate lethality box.

2. Set the value for Number of input radiation levels to 5, and then press [Tab] to commit this changed value, and update the number of rows in the Radiation levels table.

3. Drag the triangle made of six dots at the bottom right of the table in order to resize the table within the dialog until you can see the Lethality levels column, and can see the rows for all five levels.

4. Set value of 0.01, 0.1, 0.2, 0.5 and 1, as shown. After entering each value, press [Enter] to commit the value.

Next, repeat these steps in the Jet fire tab section and then in the Pool fire tab section.


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The values for radiation lethality levels that you set for the Propane Pressure Vessel will be used in the calculations for all of the Scenarios under the vessel. If you want to set values that will be used for all flammable Scenarios in the analysis, you should set them in the Parameters tab section of the Study Tree instead of in the data for individual Equipment items or Scenarios. In this situation you would need to perform the steps above in the dialogs for three different Parameter nodes: Fireball and BLEVE Blast parameters, the Jet fire parameters, and Pool fire parameters.

This completes the work on the input data, and you can OK the dialog.

You do not need to make any changes to the input data for the Scenarios, as the values that are set in the Scenario dialogs are appropriate for the propane vessel. However, you can delete the Time varying Scenario, as you will not be performing the investigation of the time-varying behaviour for the propane vessel.

Running the consequence calculations and viewing the results

Select the Propane Equipment node and use the Run option to run the calculations for all three Scenarios.

You can view the results for all three Scenarios at the same time, as long as you view the results for the same single Weather for all Scenarios. To do this, move to the Weathers tab of the Study Tree, select the Category 1.5/F Weather, and then click on the Graphs option in the Home tab of the Ribbon Bar.

A Select dialog will appear as shown, showing all of the nodes in the Models tab section, and you can check the box next to the Propane Equipment item to select all of the propane Scenarios for plotting.

When you click on OK, the Graphs View will open. The Graphs View will contains tab sections for Concentration graphs, as with the toxic Models, but it will contain Jet Fire, Fireball, Pool Fire, Explosions and Flash Fire tab sections instead of the Toxic tab section.

The main features of the graphs are described below.

Jet Fire Graphs

The Jet Fire tab section contains three graphs, which are presenting results for the two pipework failures. The first graph shows radiation level versus distance, the second shows Intensity Radii to the lowest of the three default radiation levels set in the input data (4 kW/m2), and the third graph shows Lethality Radii to a lethality level of 1%, which is the lowest of the five lethality levels that you set. The maximum downwind effect distance shown in these graphs is around 32 m, which is the distance for 4 kW/m2 for the liquid line rupture release.

If a given Fire Radii graph is showing results for more than one Scenario or more than one Weather, then it will initially only be displaying results for a single level, which will be the lowest level set for that type of result (e.g. the lowest intensity level, or the lowest lethality level). This is different from a graph for a single Scenario and Weather, which will initially always display results for all available levels.


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To see results for additional Fire Radii levels, you can click on Series… in the Configuration tab of the Ribbon Bar to open the Edit Series Properties dialog as shown. This dialog lists each of the available level-results for each Scenario, and you can check the boxes for additional levels to include them in the graph.

Pool Fire Graphs

There are two sets of Pool Fire Graphs: a set for the early pool fire, which is modelled for a continuous release only and occurs at the beginning of the release, at the time when the spill rate into the pool equals the fire burn rate, and a set for the late pool fire, which occurs at a time when the pool has reached its maximum radius. Each set contains three graphs, as with the jet fire graphs.

The pool fire graphs are showing results only for the liquid line rupture release, as this is the only Scenario that gives rainout, and this means that the two Radii graphs will initially be showing the results for more than one level. The maximum downwind effect distance is about 28 m, to a radiation level of 4 kW/m2 for late pool fire, and the distance to a.lethality level of 1% is about 21 m.

Fireball Graphs

The Fireball tab section also contains three graphs. These are showing results only for the rupture, and this means that the two Radii graphs will initially be showing the results for more than one level. The maximum downwind effect distance is about 600 m, to a radiation level of 4 kW/m2, and the distance to a.lethality level of 1% is about 290 m. There is no ellipse for a lethality level of 100%, because the fireball does not produce the necessary radiation dose at the height of interest.

Explosion Graphs

The two Early Explosion graphs contain results only for the Rupture, since immediate explosions are assumed not to occur for continuous releases. However, the Late Explosion graphs contain results for all three Scenarios.

The Late Explosion Worst Case graph shows the effect radii for the explosion-time which gives the greatest downwind distance for the lowest overpressure set in the parameters (0.02 bar), and the legend for the Late Explosion Time graph gives the time at which the worst-case explosion occurs. The greatest downwind effect distance is about 1,150 m, for the Rupture, and it occurs at 9.3 s.

Flash Fire Graph

The Flash Fire Graph shows the zone for the cloud at the time that it covers the maximum area. For the rupture, this gives a maximum downwind effect distance of 400 m to 10,000 ppm, whereas for the two pipework releases this gives a distance of about 70 m to the same concentration. 10,000 ppm is 50% of the LFL, which is the fraction set by default in the Flammable Parameters as the boundary of the flash fire effect zone.


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Alternative methods for modelling early explosions

When you were setting the input data for the flammable Scenarios you left the Flammable tab section with the default settings, which means that the early explosion for the rupture Scenario was modelled with the default method, which is the TNT method.

In this section you will create versions of the rupture Scenario that use the other methods for modelling early explosions, and compare the results.

Creating a Folder and Scenarios for the other methods

Insert a Folder under the Propane Equipment node, and name the Folder Early explosion method.

Select and copy the rupture Scenario for the propane vessel, and then select the Folder and use Paste three times to create three copies of the rupture Scenario inside the Folder.

Name the first copy TNT ground burst, the second copy Multi-energy, and the third copy Baker-Strehlow-Tang.

Setting the inputs for the TNT explosion method

For the TNT ground burst Scenario, move to the Explosion parameters tab section to check the input data for the modelling.

You can leave the Explosion Efficiency with the default value, but for this Scenario you should set the location to Ground burst, which means that you are assuming that the explosion is sufficiently close to the ground that there will be reflection effects in the pressure waves.

Click on OK to close the dialog for the Scenario.

Setting the inputs for the Multi-Energy explosion method

Open the input dialog for the Multi-energy Scenario, move to the Flammable tab section, and choose Multi-Energy for the Explosion method field.

A Multi Energy tab section will appear in the dialog, and you use this tab section to define up to seven regions of confinement within the cloud and also specify the strength of an explosion in the unconfined regions of the cloud.

By default the number of confined is set to zero, which means that there are no mandatory fields in the tab section and that the Scenario will run even if you do not set any values in the tab section – but it also means that by default the Scenario will not produce any explosion results.

For this tutorial you will define three regions of confinement, each occupying 30% of the volume of the cloud, and with a range of confinement strengths between 6 and 8, as shown. Values of 8 and 9 are typically used for process units, but the region around the propane sphere is relatively open.


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The strength of an explosion in the unconfined region of the cloud will be 2, as shown.

After setting the Number of confined sources to 3, press [Tab] to update the number of rows in the blast sources table. Press [Enter] after entering each value in the table, to commit the value.


Setting the inputs for the Baker-Strehlow-Tang explosion method

Open the input dialog for the Baker Strehlow-Tang Scenario, move to the Flammable tab section, and choose Baker Strehlow-Tang for the Explosion method field.

The Baker-Stehlow-Tang tab section will appear in the dialog.

For this tutorial you will not use the default option to supply a value for the speed of the flame (i.e. the Mach number), and instead you will have the program calculate the speed of the flame from other inputs, as shown.

For a propane release you should set the Fuel Reactivity to Medium, and for this release you should set the number of dimensions for the Flame expansion to 2, and the Obstacle density to Medium, as shown.

The release is relatively close to the ground and there is likely to be some reflection of the pressure-waves off the ground, so you should set the Correction for the ground effect to 1.6. Finally, the volume of the cloud assumed to be involved in the explosion is 500 m3.



Select the Early explosion method folder, run the calculations, and then view the graphs for the 1.5/F Weather, selecting all Scenarios in the folder.

The Early Explosion Distance graph will initially be showing the Baker-Strehlow-Tang Scenario as giving the highest peak overpressure, of about 1.02 barg, with the pressure declining rapidly with distance, with no effects beyond about 300 m. The TNT ground burst Scenario produces a peak pressure of 1 barg and the pressure declines less rapidly with distance, so the pressure at 300 m is 0.2 barg, and there are effects out to 1,400 m. For the Multi-energy Scenario, the graph initially shows the results for the unconfined region of the cloud, but if you click on Series… in the Configuration tab of the Ribbon bar to open the Edit Series Properties dialog, you can use the options in the dialog to add the three multi-energy confined regions to the graph.


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With the three confined regions displayed, you will see that Confined Region 1 - with a confinement strength of 8 - gives the highest peak overpressure of all, with a value of 2 barg.

This analysis shows that, for this release, the default TNT method gives results that are close to the multi-energy results with a medium strength of confinement (i.e. with a strength of 7). It seems reasonable – and simplest - to take the default method as representative for this analysis.

Flammable releases from a rail tank wagon

The propane is delivered to the facility by tank wagon from a marshalling yard 10 km to the north. The deliveries take place once a week, involving two tank wagons, and are always during the day and never at night. The wagons are 10.6 m in length, 2.6 m in diameter with a volume of 54 m3, are raised 0.5 m above the ground, and are delivered with a fill-level of 80%. The propane is under the same conditions as in the sphere: under saturation conditions at atmospheric temperature (taken as 10oC).

There are many hazardous events that could be modelled for the tank wagons, including leaks during the unloading process. This tutorial will consider only the rupture of a wagon under normal operating conditions, a leak from the liquid side of a wagon, and a fireball produced by catastrophic rupture of a wagon under flame impingement. All events are assumed to occur while the wagons are at the unloading point 100 m south of the propane sphere.

Defining a folder and creating the Equipment data node for the wagon

Insert a Folder under the Study, and name the folder Tank wagons.

Create a copy of the Propane pressure vessel inside the Tank wagons folder. The name Propane, Saturated 10 degC is also suitable for the tank wagon, and you do not need to rename the node.

The rupture Scenario is the only Scenario that was copied with the Equipment node that is relevant to the tank wagon, and you should delete all of the other nodes.

Open the dialog for the tank wagon Equipment node, and change the values for the following fields:


Material Volume inventory 43.2 m3

Geometry North co-ordinate 435581 m

Setting the Elevation for the Rupture Scenarios

Edit the rupture Scenario and change the value for the Elevation to 1.8 m.


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Defining the Leak from the liquid side of the wagon

Insert a Leak Scenario under the Equipment node and name it 1 inch, liquid. For a release from the body of a vessel rather than from attached pipework, you should use a Leak Scenario. It will give a larger discharge rate than a Short pipe Scenario since there are no frictional losses during the flow to the leak-location.

The leak is assumed to be at the bottom of the tank, which is the most conservative assumption for the tank head and the duration.

Edit the Scenario, and set the data as follows:


Scenario Orifice diameter 1 inch

Tank head 1.95 m

Elevation 0.5 m

Outdoor release direction Down – impinging on the ground

Defining the Fireball Failure under Flame Impingement

The program allows you to model immediate-ignition effects from fireballs and poolfires on their own, separated from any modelling of dispersion and delayed-ignition effects, and you do this by using the Fireball Scenario or Pool Fire Scenario under a Standalones Equipment item rather than one of the discharge Scenarios under the Pressure Vessel or Atmospheric Storage Tank items.

Defining a Standalones Equipment item

Select the Tank wagons folder, then select the option to insert a Standalones Equipment item. The GIS Input View will become selected, and you should click on the map somewhere next to the dot for the tank wagon pressure vessel item; you will adjust the location as necessary in the next step.

Name the Standalones node Propane wagon, then open the input dialog and set the data as follows:


Material Material PROPANE

Geometry East Location 197327 m

North Location 435581 m

The input data for a Standalones Equipment item is much simpler than for the two storage Equipment items.


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Defining a Fireball Scenario

Under the Standalones node, insert a Fireball Scenario and name it Fireball under flame impingement.

Open the input dialog for the Fireball Scenario and set the data as follows:

Tab section Input field Value

Fireball Released mass 22.2e3 kg

Vapour mass fraction 0.25

Supply burst pressure? [checked]

Burst pressure - gauge 8.57 bar

Radiation calculations Radiation vs distance [checked]

Radiation ellipse [checked]

Radiation vs distance Maximum distance 500 m

Angle from release direction 0 degrees

Height above origin 0 m

Radiation ellipse Ellipse type required Incident Radiation

Specified radiation intensity 4 kW/m2

The Burst pressure is 60% greater than the normal operating pressure and is used in calculating the surface emissive power of the fireball.

The Fireball tab section gives you the choice between using a correlation to obtain the radius, duration and emissive power, or entering your own values. For this Scenario, you are using the correlation.


Run the calculations for the Tank wagons folder and then view the graphs for the 1.5/F Weather, and then examine the Bleve or fireball results.

The Fireball Scenario gives slightly larger effect distances than the Rupture Scenario, with a distance of about 460 m to 4 kW/m2 compared with 435 m. This shows the effect of the higher vessel pressure used in the Fireball Scenario to model failure under flame impingement, whereas the Rupture Scenario considers a rupture under normal operating conditions which then has a probability of igniting immediately and giving fireball effects.

Saving the workspace

You have now completed the tutorial, and you should save the workspace in order to save the changes you have made.

What next?

This tutorial has not covered every feature of the program, but you should now have enough of an understanding of the approach and methods used in the program to be able to explore the remaining features yourself, with the assistance of the online Help. The topics under Commonly-used features in the Contents tab of the Help window give quick access to details of all of the main features, and you can also use the Index and Search tabs to find help on a particular topic.

If you need further details on any aspect of the program, or if you need guidance on how to model a particular situation for your facility, you should contact software support using the details given in the Help tab of the Ribbon Bar.

phast onshore 7

Documents

consequence analysis

startup phast tutorial

example analysis

new analysis

program window

program present

main window

main features