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
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.
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.
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.
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
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
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
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
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.
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.
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.
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.
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.
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.
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.
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.
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 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 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.
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.
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.
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
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 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.
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.
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.
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.
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
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
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.
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.
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.
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.
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 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
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.
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:
Tab Section Input Field Value
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
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.
