phast tutorial manual

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 1In 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 18The second chapter guides you through the process of setting up a Study Folder for performing consequence calculations for a range of common types of hazardous event. The tutorial supplies all of the input values that you will need to complete the analysis.

Chapter 1: Introduction

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 two 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, defining a range of hazardous events and performing 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 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.

The Main Window on Startup

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The first line in the Message Log should state that the “Licence is valid”. You must have a valid license for PHAST set up on your computer in order to be able to enter data and run the calculations. If the Message Log says that you do not have a valid license, you should contact product support using the details given under Product Support in the Help menu.

The window will normally open with no Study Folder loaded – where a “Study Folder” is a file that contains the definition of a consequence analysis – and you must open or create a Study Folder file before you can perform any modelling work with the program. If you wish, you can change the Installation Preferences under the Options menu so that the program starts by automatically opening a Study Folder (e.g. the Study Folder you worked on most recently).

Opening the PHAST Example Study Folder The program is supplied with an example Study Folder called “PHAST Example Study”, which is used in this chapter to give a quick introduction to the terminology and approach used in the program.

To open the Study Folder, choose Open Example… from the File menu. A File Open dialog will appear as shown, displaying the contents of the Examples folder installed with the program files. There are several file-formats available for Study Folder files, but the default format is the *.psu format, and the PHAST Example Study file is in this format. Select the file, and click on Open.

The appearance of the main window changes when a Study Folder is open: there are many more toolbars, and there is a pane with five tab sections at the left side of the window, as shown. The pane is known as the “Study Tree” pane, and you work in its various tab sections to set up the input data for the analysis.

The Main Window with a Study Folder Open

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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 The term “Model” is used in two different ways in PHAST, though these different meanings are unlikely to cause you confusion.

“Model”: a set of available calculations

The program has several different sets of calculations available, and each of these sets is known as a sModel and has its own icon. For example, there is a Model known as the “Vessel/Pipe Source Model” thhas a blue icon that represents a process vessel; this Model considers the release of material from its storage or process conditions in a vessel or pipe, through all the stages in its dispersion to a harmlconcentration, and it also performs fire, explosion toxic calculations to obtain representative for the dispersing cloud. There is another Model known as the “Fireball Model” that has a red anyellow icon that represents a fireball flame; this Model considers only the radiation effect zones from afireball, and does not perform any of the release andby the Vessel/Pipe Source Model. There are eleven different types of Model in total.

You define a given hazardous event that you want to analyse by s

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electing the most he

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suitable Model from the list of the eleven Models. When you select the Model from tlist, the program will insert an icon for that Model into the Models tab section. The icon represents an “instance” of that Model and will have its own set of values for the input data, and you can define any number of instances of a given Model in your Study Folder, each with its own set of input data to represent a particular hazardous even

As shown in the illustration, the PHAST Example Study Study Folder contains ten instances of one Model (the Vessel/Pipe Source Model), and one instance of eaceight other kinds of Model.

“Model”: one instance of a part

In practice, people rarely use the term “instance” to refer toModel, and instead refer to the instance directly as a “Model”, so it would be more typical to say that the PHAST Example Study Study Folder contains eight Vessel/Pipe Source Models, one Pool Fire Model and one Fireball Model.

The Model icons are organised in a tree structure. The top leveStudy Folder, with the name PHAST Example Study, the next level is the Study (named example), the third level contains several Folders, and the fourth level contains the Models themselves. You can create any number of Studies or Folders, depending ohow you want to organise your analysis.

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Inserting a Model

You cannot place a Model icon under the Study Folder itself, but only under a Study or Folder. To add a Model at a particular point in the structure, select the Study or Folder, and then select the appropriate Model from the Insert menu as shown. You can also insert a Model by selecting the Model from the Insert cascade at the top of the right-click menu, or by selecting the icon for the Model from the toolbar.

The Weather Tab Section The Weather tab section contains a folder named Global Weathers with three definitions of weather conditions. 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.

The Weather tab section also contains a Study icon called Example Cases. In the Model tab section, all of the Models have been placed inside the Example Cases Study, but you create and use any number of Studies in an analysis.

You can insert Weathers underneath a Study in the Weather tab section. Such Weathers are known as “Local Weathers”, whereas those in the Global Weathers folder are known as “Global Weathers”. When the program is processing the consequence calculations for a given Model, it will perform the calculations for every Global Weather and for any Local Weathers under the Study that contains the Model, i.e. the Local Weathers are specific to the Models in that particular Study.

The Parameters Tab Section In PHAST, Parameters are background inputs that are applied to all calculations and are not specific to a particular Model.

As with the Weathers, there is a set of Global Parameters, and you can also define Local Parameters that are specific to a given Study. If you define a local set of Explosion Parameters, for example, the values in this set will be used instead of the values for the global Explosion Parameters during the calculations for the Models in that Study.

Green border to icon: shows use of default values

All of the icons in the Global Parameters folder have green borders. The program uses this border 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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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 Models ithe Study Folder, or for materials that you have added yourself while working in the Material tab section.

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PHAST currently only allows you to define Global Materials, and the same set of Materials data will be used in the calculations for all Model. You cannot currently define Local Materials to be used only for the Models in a given Study.

There are three types of icon present in the Material tab section of the PHAST Example Study Study Folder:

Green Icon: a Pure Material

The eight green icons are all pure Materials. Each icon has a green border, which shows that all of the input fields for the material 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 border will disappear.

All of the icons in the PHAST Example Study Study Folder are for pure materials that are supplied in the System Parameters, but the program also allows you to add your own materials.

Yellow-and-Red Icon: a Mixture

The yellow-and-red icon is a Mixture, and in the PHAST Example Study Folder it represents the plume of hydrogen chloride, nitrogen dioxide and sulphur dioxide produced by a fire in a pesticide warehouse – which is the situation modelled by the Warehouse Fire Model.

This particular Mixture is generated automatically when you run the Warehouse Fire Model, but you can also define your own Mixtures, using any combination of the materials in PHAST, and select these Mixtures for use in the dispersion, fire and explosion calculations.

Pink Icon: a Pesticide

The six pink icons are all Pesticides, and are used to describe the contents of the warehouse for the Warehouse Fire Model. Pesticides are only relevant to the Warehouse Fire Model and cannot be selected for any other type of modelling.

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The Map Tab Section The Map tab section allows you to set up map image and geographic data so that you can view the regions and features affected by consequence results.

The map image is defined by the powerstation raster image, and you view the image by selecting Map from the View menu. The Map Window will open in the area to the right of the Study Tree pane, and you can use the options in the Map menu, the right-click menu and the Map toolbar to zoom in and out, to move around in the Map Window, and to control the display of the features of the window such as the scale bar and the legend.

The Map tab section and the Map Window

The Models are represented by dots on the Map. These dots can sometimes be difficult to see and to relate to the individual Models, but there are several options that can make this easier:

Changing the Size and Colour of the Dots

Select Map from the Preferences cascade of the Options menu to open the Map Preferences dialog, and then move to the Model tab section.

By default the colour is turquoise and the Point Size is 7 pixels, but if you change the colour to blue and the size to 10 pixels as shown, then the dots will be easier to see on the powerstation Map.

Displaying the Model Names on the Map

If you move to the Models tab section, select any Model, and then select Labels from the View menu, the names of all of the Models will be displayed on the Map. To hide the names, deselect the Labels option.

If there is more than one Model at a given location – as with the Chlorine Models and the Butadiene Models – then the names will be superimposed and may be difficult to read, although this will make it clear that there are multiple Models at the location.

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Pinpointing an Individual Model

If you select a Model in the Study Tree and then select Pinpoint from the View menu (or press the F4 key), the dot for that Model will become centred in the Map window and will also be highlighted (i.e. displayed in a light turquoise colour). This allows you to locate a specific Model, which is useful if you cannot identify the name for that Model on the Map.

You can close the Map Window by selecting Close All from the Window menu.

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 Rupture Model Move to the Models tab section and double-click on the icon for the Model named Chlorine Rupture. The Vessel/Pipe input dialog will open as shown below.

The dialog contains a large number of input fields organised over sixteen tab sections, but many of these fields are relevant only to advanced modelling options (e.g. for a sensitivity analysis), and you will typically only need to supply a small set of input data when defining a Model for use in an analysis, as you will see in the next chapter.

Input Dialog for the Chlorine Rupture Model

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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.

Most dialogs also have a “What’s This Help” button in the form of a question mark at the right of the title bar. If you click on this button, the cursor will change to a question mark, showing that you are in “What’s This Help” mode, and if you then click on a field in the dialog, a popup window will appear over the field, describing the field and giving advice on setting values, as shown.

There are some tab sections that appear in the input dialog for more than one Model. For example, the Material tab section is used for both the Vessel/Pipe Source Model, the User-Defined Source Model and the Bleve Blast Model. The Help is written in order to give full guidance for either Model, so there may be references in the Help to features that are not currently relevant to you.

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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Running the Calculations and Viewing the Results In the Models tab section, select the Example Cases Study, and select the Models option from the Run menu.

The program will process the calculations for each of the eighteen Models in turn, performing the calculations for each of the three Global Weathers, and showing the progress through the calculations. When the calculations for a given Model have been completed for all three Weathers, the name of that Model will change from black to blue, which is the colour-coding that the program uses to show that a Model 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 Models and all Weathers. If you select a single Model or folder, then you can run the calculations just for that Model or for the Models in that folder, or you can select Batch/Weather Setup from the Run menu to select Models across different folders or to select only specific Weathers. The selection of Weathers in the Setup dialog will be used for all calculations, but the selection of Models will be used only when you select Batch Run from the Run menu.

Viewing the Graphs for the Chlorine and Butadiene Releases Select the Vessels or Pipe Sources folder and then select Graph from the View menu, from the right-click menu or the toolbars. A dialog will appear as shown, prompting you to chose the weather conditions whose results you want to view.

If you had selected a single Model rather than a folder with multiple Models, then the dialog would have checkboxes next to the Weathers instead of radio buttons, and you would be able to compare the results for several Weathers for that Model. If you choose a single Weather in this situation, then the graphs will have additional features that are not available when you are viewing the results for multiple Models or Weathers.

For this example, select the F 1.5m/s Weather. This is the weather with the most stable conditions, and is likely to give the longest dispersion distances. When you click on OK there will be a pause of a few seconds, and then the Graph Window will open as shown in the space to the right of the Study Tree pane.

The Graph Window

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The Graph Window will usually contain many tab sections, each with a different type of graph. The tab sections included for a particular combination of Model will depend on the type of the Models (e.g. Vessel/Pipe Source Model or Fireball Model), 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 Chlorine and Butadiene Models have graphs for cloud concentration, for pool vaporisation, for toxic effects, for jet fire, fireball and flash fire effects, and for explosion effects.

The Concentration Graphs

The first graph is of centreline concentration. This will be showing the results at the time at which the cloud footprint covers the greatest area, which occurs at a different time for each weather.

The graph will initially be showing results only for the four Chlorine Models. In the dispersion calculations, the program uses an averaging time that takes into account changes in wind direction over the course of the release, to give an average concentration at a given location, and it uses different averaging times for toxic and for flammable materials, reflecting the different time-scales that are relevant to each type of release. The concentration graphs always display results calculated with a specific averaging time, which is displayed in the legend for the graph. The default averaging time for this set of results is the Toxic averaging time, and the Butadiene Models were not modelled with that time so have no results to display.

To view the concentration results for the Butadiene Models, you must change the selection of averaging time to display. To do this, select Properties… from the right-click menu or the Graph menu to open the Plot Properties dialog, and then move to the Averaging Times tab section as shown.

If you change to the Flammable Averaging Time, the graph will display the results for the four Butadiene Models only.

The User Defined option will also be enabled, which shows that some of the Models have a user-defined averaging time defined in the Location tab section. In fact, all of them have such a time defined, and if you select User Defined as the averaging time for the graphs, the graph will display results for all eight Models.

Results Displayed on the Map

After the six tab sections that show the results in terms of concentration, the next tab section is the Map graph, which allows you to view different types of effect zones superimposed on the map.

When you first move to the Map tab section, the Map graph will be displaying Cloud Footprint results for a concentration of 10,000 ppm for the Toxic averaging time, and the only results displayed will be for the Chlorine Rupture and Chlorine Liquid Leak Models. The other Chlorine Models don’t produce this concentration level at the default height of ground level – as you can see from the Sideview graph – but if you open the Plot Properties dialog, move to the Distance tab and set the Height to 10 m, results for the Chlorine Vapour Leak Model will also appear in the plot.

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The Footprint concentration results are the default form of results for the Map graph, but the Event field in the Display tab sof the Plot Properties dialog allows you to change to a different form, as shown. The list of types of effect will depend on the types of Models that are covered by the Graph, and will be similar to the range of tab sections in the Graph window.

ection

upture

If you select Toxic effects, then the Radiation/Toxic field will become enabled and you can choose between dose, probit and lethality results.

If you view the Lethality footprint on the Map, you will see that the Chlorine Liquid Leak gives the greatest downwind effect distance for lethality. The Rupture Model produces higher peak concentrations at any given downwind location, but the short duration of the rmeans that the total dose received is lower than for the leak.

The Map graph initially shows the effect zone with a northerly wind, but you can choose Wind Direction from the Graph menu or the right-click menu to change the wind direction.

The Pool Vaporisation graph does not show any hazardous effect distances, but the Toxic graph and the various Fire and Explosion graphs all include footprint-results of the form shown on the map, and most of them also include graphs that show the effect-level along the cloud centre-line as a function of distance downwind (e.g. radiation level for a jet fire, or lethality for a toxic release).

If you look through the Fire and Explosion graphs, you will see that the greatest downwind effect distance is reached by the Late Explosion Worst Case for the Butadiene Rupture Model, which reaches a distance of about 880 m downwind. A late explosion is one that occurs after the cloud has started dispersing away from the release point, and by default the explosion is assumed to be centred at the cloud front, which means that the explosion radius will reach beyond the flammable region of the cloud. The program calculates the results for such an explosion at regular intervals, and the Worst Case graph displays the results for the ignition-time that gives the greatest downwind effect distance.

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

To view the reports for the Butadiene Rupture Model, select the Model and then select Report from the View menu or from the right-click menu or the toolbars. After a pause of a few seconds, the Report Window will open to the right of the Study Tree pane as shown. The Report Window will probably hide the Graph Window, but you can use the options in the Window menu to move between the windows. You can have any number of Graph Windows and Report Windows open at the same time.

The Report Window

As with the Graph Window, the Report Window 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 Model.

For the Butadiene Rupture Model, the first tab section is the Input tab section, which lists the input data. The Audit tab section gives version details for the program, for parameters and materials, but 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 the Butadiene Rupture, D 5m/s is the weather that gives the greatest distances, although the difference between the three weathers is small.

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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 differest 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 Butadiene Rupture these alternative times are the Flammable Averaging Time (whose value is set in the Flammable Parameters) and the User-Defined Averaging Time (whose value is set in the Location tab section for the Model). In this analysis both of these times are also set to 18.75 s so for all the Butadiene Models the Averaging Times report gives the same concentrations as the other reports. However, if you viewed the report for one of the Chlorine Models, 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 Model – 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 Butadiene Rupture, the tab for the Early Explosion report is named Early Expl.(TNT), and this is because the explosion method selected for this Model is the TNT method. There are three methods available, and you select between them in the Flammable tab section for the Model. 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 occuring 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 graph, as described in the section above.

The range of reports presented for a particular Model will depend on the type of Model and on the behaviour of a release, and there are additional reports that do not appear for the Butadiene Rupture Model. 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, since they present the results in the most direct form and allow easy comparison between different Models and Weathers.

After you have finished examining the results, you can use Close All from the Window menu to close the windows.

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Viewing the Results for the Chimney Release and Long Pipeline Models The other two Vessel/Pipe Source Models in the PHAST Example Study Study Folder illustrate some of the special modelling features that are available.

The Chimney Release Model

This models a release of methane from a chimney stack on top of a building, and takes into account the effects of t

If you view the graphs for the Mod

he building wake on the dispersion.

el for all

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of a 250 m propane pipeline that has a pumped flowrate of 10

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the graphs for the F 1.5m/s weather. For this analysis the

ab. This contains a

the most important variable.

three Weathers and thenmove to the Sideviewgraph, you will see an outline of the building with the chimney on toand with the three plumes emerging from the chimney.

The building wake produces a zopressure, and this pthe plumes downwards.The model deals with this by adjusting the height at a specific downwind distawhich is 100 m in this case. In some situations the plume may be pulled down low enough that all or part of the plume is entrained in the building wake, but that hasoccurred for any of the weathers for this Model.

The Sideview graph showabout 58 m, but if you look at the Explosion graphs and the Flash Fire graph, you will see Worst Case Late Explosion distances of over 900 m, and Flash Fire distances of about 600 m to 50% of the LFL. When performing the modelling of late explosions aflash fires, the program can calculate the flammable footprint of the cloud either at the cloud centreline or at a specific height. The centreline method is selected by default in the Flammable Parameters since this will give the most conservative results, but you should check the Sideview graph and make a judgement about whether or not the effect zone would actually reach the areas of interest for your analysis. A flash fire iplume 60 m in the air would not affect people on the ground, but an explosion in such a plume might well produce significant overpressures at ground level.

The Long Pipeline Model

This models the rupturekg/s, where the rupture occurs 100 m downstream from the pump. The program performs discharge modelling for the complex, time-dependent flow regime insideruptured pipeline and then performs dispersion modelling for a representative averaged discharge rate.

Select the Model, and viewdischarge calculations are the same for all weather conditions, so you only need to view one weather if you are only interested in the discharge results.

The first tab section in the Graph window will be the Long Pipeline tlarge number of sub-tabs, each of which shows the behaviour of a particular discharge variable against time. Move to the Flowrate sub-tab, since this shows the behaviour of

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The Flowrate graph appears to show theflowrate d

ropping instantly

wn. lt to

Automatic Scaling and set the Maximum Time to

about 45 s to drop to

of

m lines show the pumped inflow into the section, which is ro for Section B, and the two Orifice lines show the flow

e

owever, at 9 s the flash-front reaches the end of section A, and from this

the

roceed to model the depressurisation of the section until it has emptied

from about 230 kg/s to about 10 kg/s, as shoHowever, it is difficutell whether or not the drop is instant because the default scale on the time axis goes up to nearly a million seconds. To see theinitial behaviour in more detail, you must set the scale yourself.

Select Scale and Labels from thdialog, then uncheck the option for 60 s.

e right-click menu or the Graph menu to open the Scale

With the changed scale, you can see that the rate takes a steady rate of 10 kg/s, which is the pump rate.

There are five lines plotted on the graph, and their meaning may not be immediately obvious. The two A lines describe the 100 m pipe-section upstreamthe rupture, the two B linesdescribe the 150 m section downstream of the rupture, atwo sections. The two

nd the Total line is the sum of the rate released from the Upstrea

10 kg/s for Section A and zefrom that section at the point of rupture. If you want to hide any of these lines (e.g. thUpstream lines), open the Plot Property dialog and deselect the lines in the Long Pipe tab section.

For the first nine seconds, the orifice flowrates from both sides are almost identical, as the flash-front travels along each section at a similar speed, giving a similar flow-regime. Hpoint onwards the pressure profile in that section is maintained at the profile producedby a pumped flowrate of 10 kg/s; the program stops the discharge calculations for Section A at this point which means that there are no results available to display ongraph after 9 s, but the 10 kg/s flow from Section A is added in to the Total, as you can see.

If you move to the Distance sub-tab, you can see that the flash-front reaches the end of Section B after 14 s. However, the calculations do not stop for Section B at this point, and pcompletely at 45 s.

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If you view the Discharge report for the Model, you will see that the average rto represent the beh

ate used aviour is 10.5 kg/s, taken over a time-scale of one hour. This may

underestimate the hazard produced by the release, and there are options available for representing a time-varying release with more than one “release segment” so that you can investigate the significance of the type of short-term behaviour seen in this release. These options are described in more detail in the next chapter.

Viewing the Results for the Other Models The other eight Models in the Study Folder are not Source Models. Each models one specific type of behaviour and will produce a fixed set of graphs and reports.

The Warehouse Fire Model

This models a fire in a pesticide warehouse and you can define multiple scenarios for each warehouse, where each fire scenario is defined by the surface area of pesticide involved and by the duration of the fire. There are special calculations that determine the release rate and composition for the toxic plume produced by the fire, and the dispersion and effects of this plume are then modelled in the same way as for the toxic cloud for the four Chlorine Models.

The Three Flammable Models

The Pool Fire, Fireball and Jet Fire Models perform the same type of radiation modelling as that associated with a Source Model, 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 Four Explosion Models

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

The BLEVE Blast Model 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 Source Model.

The form of the results for all of these Models is similar to the corresponding dispersion, toxic, fire and explosion results for a Source Model, 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.

17

Chapter 2:Setting up your own Analysis

Chapter 2 Setting up your own Analysis

m of the Analysis The ForThis chapter will guide you through the process of setting up a Study Folder for

The Models Defined in the Analysis

iquid side of a vessel containing a toxic material the gas side of a vessel containing a toxic material

t. wagon.

efine different events, or change the input values in s

.

Creatin

performing consequence calculations. The tutorial supplies all of the input values that you will need to complete the analysis.

The main aim of the analysis is to show you how you can define Models 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 l• A pipework leak from• 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 impingemen• A liquid leak from the body of the propane tank

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

g a new Study Folder To create a new Study Folder, select New from the File menu or the Toolbar. The program will close the PHAST Example Study Study Folder and a new Study Folder will

Savinh a

As… from the File menu. The File Save dialog will appear and you should locate the DNVuser folder (the default location for saving Study Folder files), use the Create 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 *.psu.

open, with a name shown as “Untitled”.

g the Study Folder You cannot save the Study Folder with the name “Untitled” and should save it witreal name immediately.

Select Save

18


The Contents of a new Study New Study data set up:

A Global We

those in the PHAST Example Study Study Folder.

Setting up the Map Dat

Folder Folder files are not empty but will have some default

ather Folder containing three Weathers

The weathers are the same as

A Set of Default Parameters

As with the PHAST Example Study Study Folder, there is a set of Global Parameters, all of which are using the default values.

a 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 *.tiIf you ha

f file. ve an image file for the area around your facility, you might prefer to use that

instead.

Insertin hIma er ima sprodef d

The ropro s deals only with raster

et in the Map tab section

eady contain a Raster Image Set icon, select the Tutorial

de the Set

will appear as

n you first browse to this folder you will not see any files, since the list of File types is not set to *.tif by default.

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.

g t e Raster Image ge files that contain a description of each pixel in the image are known as rastge , and most common image files are in this form, e.g. *.tif, *.bmp, *.gif files. The gram can also display map data taken from a GIS Database, where an image is ine by describing the lines that form the image.

p cess of inserting a raster image into a Study Folder is very different from the ces of inserting a connection to a GIS Database. This tutorial

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 S

If the Map tab section does not alricon at the top of the tab section, and use the Insert menu to insert a Set.

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

Insert a Raster Image insi

Select the Set, then select Raster Image from the Insert menu. A dialogshown, and you must 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 Program Files\DNVS\PHAST_6_5). Whe

19


Selecting a Co-ordinate System for the Map

em g a co-ordinate system for the e Placement Mode is set to

nalysis. teractive Placement Mode and will not be connecting to a

in this tutorial - you can click on Cancel in the

The Wizard dialog contains a button, and this gives you a quick way of viewing an efinition of co-ordinate systems in PHAST.

will then open to the right of the

the image covered by the image; if the menu bar does not include a Map option, e

es for Edit Dialogs

in the national co-ordinate system for the by the map are six-digit numbers. By ificant figures of any number that you are

have entered

ificant figures, select Preferences > General menu and move to the Miscellaneous tab. The first field in the tab

ake

f lues

When you click on OK in the Place dialog, a dialog called the “Co-ordinate systwizard” will open; this is the first step in selectinanalysis. It is only essential to select a system if thGeoreferenced or to By Header, or if you want to use a GIS database in the aWhen you are using the InGIS database – which is the situation Wizard dialog and leave the co-ordinate system undefined.

Helpoverview of the user and d

Placing the Image in the Map Window

When you click on Cancel in the Wizard dialog, there will be brief pause and the Map Window Study Tree pane.

The cursor will be in the form of crosshairs, and you must drag and drop to place the image in the window. 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

Double-click on the tutorial 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 systemfor the country.

When you click on OK the image will probably disappear from the Map Window because it has moved to a location beyond the scope of the window. Select Fit > All from the Map menu, and the Map Window will change to display click on the Map Window to mak sure it is selected, and the Map menu will appear in the menu bar.

Setting a Large Number of Significant Figur

The co-ordinate values for the image will becountry, and the values for the area covereddefault, input dialogs display only four signediting, and with this setting you will find it difficult to be sure that you the co-ordinates.

To change the setting for the number of signfrom the Optionssection is the Number of significant figures for edit windows, and you should msure that this is set to six or more.

Click on OK to close the General Preferences dialog and return to the Map tab section. Iyou open the dialog for the raster image again, you will be able to see that the vathat you entered were stored in full.

20


The Location of the Site on the Map

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

nd rallel

The Location of the Facility on the Map

Definin Rupture g the First Model: for a ToxicIn the Tutorial.psu Study Folder, move to the Models tab sectiodefine represents the rupture of a vessel containing a toxic material, which is one of several Models dealing with a toxic material.

The vessel is a sphere with a radius of 3.37 m and volume of 1fill-level of 85%,

n.

20 m3 and a maximum containing chlorine at saturation conditions and ambient temperature.

ated 4 m above the ground.

Inser

the name “Toxic”. You will place all of the Models that represent toxic

Turn

ked on the Map to set the location for the Model.

The first Model you will

The sphere is located near the centre of the site and is elevThere is no bund surrounding the sphere.

t a Folder to Group Toxic Releases Select the Study icon, then select Folder from the Insert menu or the toolbar to insert a folder. Use Rename from the Edit menu or the right-click menu (or press the F2 key), andgive the folder releases in this folder.

on the Option to Insert Models on the Map In the Options menu, select the option to Insert Models on Map. By default this option is turned off, and when you insert a Model the icon will appear immediately in the StudyTree. If you turn the option on, then the Model icon will not appear in the Study Tree until you have clic

In this tutorial you will insert the Models on the Map in approximately the correct location, and then correct the location as necessary in the input dialog.

21


Insert a Vessel/Pipe Source Model

already open and the cursor will turn to crosshairs., and you should click at a point near the centre of the site as shown to place the Model.

After you have clicked, an icon will be added to the Study Tree, and a dot will appear on the Map to show the location of the Model. Rename the icon to Cl2 Rupture.

The icon will have a red border around it, showing that it does not have a full set of input data. You will not be able to run the consequence calculations for the Model until you have supplied values for all of the mandatory input fields, as will be described below.

You use the Vessel/Pipe Source Model when you want to perform dispersion and effects calculations for a release from containment and you want to use the program’s 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.

d the “User Defined Source s, but instead allows you to

Setti

datory field: you must supply a value for n the calculations for a Model that has any

n at any point.

esent the vessel

Select the Toxic folder, then select Vessel or Pipe Source from the Insert menu or the right-click menu. The Map window will open if it is not

The program contains a second Source Model which is calleModel”. This Model does not perform discharge calculationspecify 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.

ng the Input Data Double-click on the icon for the Model to open the input dialog.

All of the fields in the first tab section are blank, and those that are enabled have red borders . A field with a red border is a mansuch a field, and you will not be able to rumandatory 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 youwant further informatio

The Material Tab Section

To set the Discharge Material, click on the button with three dots to the right of theDischarge Material field, and select CHLORINE from the list that appears. The list contains all of the materials that are defined in the System Materials.

The vessel is a sphere with a volume of 120 m3. This Model will reprwith the maximum degree of filling, which is 85%. Select Volume as the method ofspecifying the Inventory, and enter a value of 102 m3.

22


23

The chlorine is held under saturation

Saturated Liquid from the first ropdown list, and set the Temperature

cursor away from the Temperature field the will calculate the saturation pressure for this temperature and display it in the

at is not held under saturation st select both Temperature and Pressure

values for both.

the type of hazardous

one Scenario

insulated

e dispersion calculations will start with the released from the ventilation system.

The Vessel Tab Section

All of the fields in this tab section are disabled when the scenario is set to Rupture. For all of the other scenarios, some of the fields in the tab section will be enabled, with the combination depending on the scenario as you will see later.

conditions at atmospheric temperature. The temperature will vary depending on the season and time of day, but for this Model a value of 10oC will be used as representative. To set these Process Conditions, choose dropdown list and Temperature from the second dto 10 degC, as shown. When you move the programPressure field.

To define the process conditions for a material thconditions (e.g. a gas or a padded liquid), you mufrom the lists and give

The Scenario Tab Section

You use this tab section to specify event you want to model. The range of types available will depend on the process conditions you have specified.

There is only Type available for modelling the rupture of a pressurised vessel; this is Catastrophic Rupture, which is selected by default. The other scenarios are either longer-duration releases, or applicable only to tanks.

The vessel is out of doors, so you can leave the Outdoor / In-Building fields with the default selection of Outdoor. If you select In-Building Release, the program will model the build-up of concentration inside the building and thstate of the plume as it is

The other fields in the tab section are not relevant to a rupture scenario. You can takethe default settings for all of the fields in this tab section.

The Pipe Tab Section

All of the fields in this tab section are disabled when the scenario is set to Rupture. They are relevant only to the Line Rupture, Disc Rupture, Relief Valve and Long Pipeline scenarios, as you will see later.


24

at this to 7.37 m, which is the elevation of the

et the East co-ordinate to 198492 m, and the

field below the concentration will acquire a red border, showing that it

e Toxic a00 s.

s you to select additional averaging times for which you ou make any selections in the final section of the tab, the

veraging Times report, as you saw in the previous

essel and you want to take this into account in the and evaporation, you can check the Bund exists box and

nd. For this sphere there is no bund, so you can leave the ues.

on are disabled then the scenario is a catastrophic fields are enabled for the longer-duration scenarios as

e enabled for in-building releases.

are disabled when the material is toxic only. For a u to choose between the three models for a vapour

choose between two models for jet fires.

tion

ulations are set to Unselected performed), but for this

out ing

tration is lower outdoors than indoors. By ill be taken from the Toxic parameters tab section for the Model, Speed Dependent for the , then the values

The Location Tab Section

First, set the release coordinates. The Elevthe System Parameters, but you should secentre of the sphere above the ground. SNorth co-ordinate to 435063 m.

The program requires a criterion for stopping the dispersion calculations: either a maximum distance, or a minimum concentration. For this tutorial, set the Concentration of interest to 100 ppm. When you set this concentration, the Uses averaging time

tion has a default value of 1 m, taken from

is mandatory; 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.

For this release, select th veraging time, which is set in the Toxic Parameters and has a default value of 6

The Location tab section allowwant concentration values. If yresults will be appear in the Achapter.

The Bund Data Tab Section

If there is a bund around the vmodelling of pool-spreading enter a description of the butab section with the default val

The Indoor/Outdoor Tab Section

All of the fields in this tab sectirupture outdoors. Some of theyou will see later, while others ar

Flammable Tab Section

The fields in this tab section flammable release, they allow yocloud explosion, and to

The Toxic Parameters Tab Sec

The fields in this tab section are used in modelling the buildup of toxic concentration inside a building, and the exposure of a person inside the building.

By default, these calc(i.e. they will not be tutorial you should change them to Selected. The calculations require information abthe ventilation-rate for the building and about how long people remain in the buildafter the cloud has passed and the concendefault these values wbut if you choose Wind Ventilation Specificationwill be taken from the data for the Weather, which means that the values may be different for each weather.


For this tutorial, leave the Ventilation Specification with the default value of Case

r cloud explosion.

the

ab Section Input Field Value

Specified, and take the default values for the Building exchange rate and the Tail time.

The TNT, Multi Energy and Baker Strehlow Tab Sections

The fields in these tab section are disabled when the material is toxic only. They are used in the modelling of a vapou

The Discharge Parameters Tab Section

The fields in this tab section are always enabled, and take their default values fromSystem Parameters. They are used in the discharge modelling for the Line Rupture, Disc Rupture and Relief Valve scenarios, so are not relevant to this Model.

The Jet Fire, Pool Fire and Fireball Tab Sections

For a flammable release, these tab sections allow you to choose between options for modelling each type of flame.

A Summary of the Input Data

The input process involves examining a large number of input fields, but the number of values that you have to enter in order to complete the data for this Model is small, as shown in the table below:

TDischarge Material Chlorine Material Inventory 102 m3

Process Conditions Saturated Liquid at 10oC. Elevation 7.37 m East Co-ordi

Location nate 198492 m

North Co-ordinate 435063 m Concentration of 100 ppm interest Uses averaging time Toxic

Toxic Indoor Toxic Selected parameters Calculations

The default scenario for a Vessel/Pipe Source Model is a catastrophic rupture odoors, so there is no need to change any settings in the Scenario tab section for this particular Model.

ut of

tings, the input should see that the icon no longer has

nput data.

If you have made all of these set data for the Model are now complete, and you can click on OK to close the dialog. You a red border, showing that it has a full set of i

25


Run

e weathers.

ns want more information about the

e cloud, you should view either the Commentary

y

ethality graph shows that the greatest

l of 10%. The indoor effects for this weather reach about t downwind effect distances are for D 5 m/s

t 1.3 km for a lethality level of 10%.

Definin

the Calculations and View the Results Select the Model and select Run Model from either the Run menu or the toolbar. When the calculations are complete, view the graphs for all of th

You will see that there is no Pool Vaporisation tab in the Graph Window, which meathat the liquid in the release did not rain out; if you behaviour of the liquid droplets in thReport or the Dispersion Report.

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 displaseparate results for indoor and outdoor effects, and that there are separate Footprint graphs for outdoor and indoor effects. The Ldownwind effect distance is for the F 1.5 m/s weather outdoors, with a distance of about 2.5 km to a lethality leve2.25 km to 10% lethality. The shortesindoors, which reaches abou

g the Second Release: Toxic Liquid 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 h be 4.6 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 v

Copy the First Model Much of the input data f re is also applicable to the pipework failure, so you can use copy and t menu or the right-click menu to create a copy of the Rupture Mode folder copy the name Cl2 Liquid Pipework.

Setting the Input Data Open th og an ut data as follows:

he same as for the rupture.

be Released to Liquid.

The line rupture scenario models the full-bore rupture of pipework attached to a vessel, and the discharge calculations take into account the effect of friction in the flow from the vessel to the point of rupture. To model a release from the body of the vessel, with no frictional losses in the discharge, you would choose the Leak scenario.

When the vessel contains saturated liquid, you will be offered a choice of release-phase for the line rupture scenario: a vapour release from the top of the vessel, or a liquid release from the bottom of the vessel. The list of phases includes “two-phase”, but this is only enabled for the disc rupture and relief valve scenarios, for modelling over-filling of the vessel.

ead will . The line runs 4 m

alve.

or the vessel ruptuEdi paste from the

l, also in the Toxic . Give the

e input dial d set the inp

Material Tab Section

Leave this tab section with the same values as for the rupture, since the material and process conditions are t

Scenario Tab Section

Set the Scenario Type to Line Rupture, and the Phase to

26


Pipe Tab Section

The Pipe Length is the length of pipework between the vessel and the point of rupture, and you should set it to 9 m as shown.

To set the Internal Diameter to one inch, click on “mm”

ve

d

be enabled

with the initial uration

red to

normally

st supply

resent

he ing selected, then examine the results and decide on the most

appropriate way to represent the behaviour for the rest of the consequence analysis.

to the right of the field, and then select “in” from the list of units that appears as shown. You can then enter the diameter directly in inches, rather than having to perform the conversion yourself into the default unit of mm.

Leave the pipe roughness with the default value taken from the System Parameters. The number of valves is used in the modelling of frictional losses, and you can leathem as zero.

The other fields in the tab section are relevant only to the long pipeline scenario, anare all disabled for the line rupture scenario.

Vessel Tab Section

For the line rupture scenario and most of the other scenarios that involve a continuous release, the Time Varying Release option will in the Vessel tab section.

If you do not check this option, then the release will be modelledrelease rate, and the dwill be the time requidrain the inventory at this initial rate. This willgive conservative results in the consequence calculations.

If you select the time-varying option, then you muinformation about the dimensions of the vessel. The discharge calculations will model the effect of the release on conditions in the vessel and the way that these conditions and the release rate change over time, and will repthese time-varying results 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 your selection for the Rates versus time.

For this release, you will perform an initial run of the discharge calculations with ttime-varying modell

27


Set the Liquid Head to 4.6 m, select tischarge to zero, and the Diameter to 6.74 m. Leave

Average rate with an averaging o make a final selection after you have viewed the

ab Section

d form a vaporising pool.

pture. In reality, the release- of the sphere but this

ces for chlorine and can be d

hanged, with no bund specified.

rupture you must specify the Direction ose Horizontal

pipework.

cludes a second horizontal option: Horizontal Impingement. You if the release is in a congested area and the release is likely to

ipment; the program will reduce the momentum of the amount of air mixed into the jet during the initial stages.

Frequency of Bends to

ata for this stage, and you can click on OK to close the input

Runn lations t Run Discharge from the Run menu, the right-click menu discharge calculations alone, without peforming the ns. The calculations may take several minutes,

view the reports and move to the TV Discharge Report. in two hours of release, so the time-varying behaviour There are two options for bypassing the time-varying uation:

sults to Create a User-Defined Source Model

te Source from the Edit menu or the right-

he Time Varying Release option, set the Tank Type to Spherical, the Height of Dthe Rates versus time set to the default selection of time of 3600 s; you can return tdischarge results.

Location T

Set the Elevation to 0.1 m. With this setting, the liquid drevaporate inside the cloud, and will probably rain out an

Leave the other fields with the same values as for the rulocation would be offset by a few metres from the centredifference is insignificant compared with the effect distanignore

oplets will probably not

Bund Data Tab Section

Leave this unc

Indoor/Outdoor Tab Section

For a continuous release scenario such as lineof the release. Cho from the list, which is the correct setting for this type of unobstructed rupture of horizontal

The list of directions inshould select this option impinge on a wall or other equrelease, which will reduce the

Discharge Parameters

There is one bend in the 9 m of pipework, so you can set the 0.11 per m.

This completes the input ddialog.

ing the Discharge CalcuSelect the Model and then selecor the toolbar. This will run the dispersion and effects calculatiodepending on the speed of your machine.

When the results are complete,The rate drops by less than 3%can be ignored for this release.discharge modelling in this sit

1: Use the Averaged Discharge Re

When you performed the discharge calculations, the program calculated the average rate over the first 3600 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 select the Model, then select Creaclick menu.

28


The program will show a list of the weather conditions for which you performed the discharge calculations and for which it has results, and when you select one of these weathers the program will create a User-Defined Source Model with the name Calculated Discharge, as shown.

urce Model has many of the same tab

r-d

sults

Model and Deselect Time-Varying Release

the time-varying discharge modelling if you entire release, and this is the

r this tutorial. The discharge calculations for this Model will

The User-Defined Sosections as the Vessel/Pipe Model, but instead of the Scenario and Vessel tab sections it has a Discharge tab section in which you specify the discharge rate and conditions directly, since the UseDefined Source Model does not perform any discharge modelling itself. The CalculateDischarge Model will be created with Discharge data taken from the averaged refrom the Liquid Pipework Model, but you can edit these values if you choose.

2: Edit the

This is the simplest method for bypassing decide that you want to use the initial rate to represent themethod that will be used forun much more quickly with the time-varying option turned off.

After this adjustment, the final set of input data for this Model can be summarised as follows, not including the values that are the same as those for the rupture model:

Tab Section Input Field Value Scenario Type Line Rupture Scenario Phase Released Liquid Pipe Length 9 m Pipe Internal Diameter 1 inch Time-Varying Release? Not selected Vessel Tank Head 4.6 m

Location Elevation 0.1 m Discharge Parameters Frequency of Bends 0.11 per m

The default direction for a line rupture scenario is change any settings in the Indoor/Ou

Horizontal, so there is no need to tdoor tab section for this particular Model.

Run hen the

ill have little effect on the dispersion or toxic

r

the Consequence Calculations and View the Results Select the Model and select Run Model from either the Run menu or the toolbar. Wcalculations are complete, view the graphs for all of the weathers.

You will see that there is a Pool Vaporisation tab in the Graph Window, 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 only about 1%, so the formation and behaviour of the pool weffects.

In the Toxic Lethality graph, the greatest effect distances are for the F 1.5 m/s weatheoutdoors, with a distance of 900 m to a lethality level of 10%, which is approximately athird of the distance reached by the catastrophic rupture. The least stable night-time condition, D 5 m/s, reaches only 350 m for 10% lethality outdoors.

29


Definin g the Third Model: Toxic Vapour from Pipework The vapour release is the rupture of a two-inch pipe attachThe line runs 3.4 m horizontally, then vertically downwarassumed to occur 1 m from the ground.

ed to the top of the sphere. ds, and the rupture is

name the copy to Cl2 Vapor Create the Model as a copy of the Liquid Pipework Model, rePipework, and change the input data as follows:

Tab Section Input Field Value Scenario Phase Released Vapour

Pipe Length 13 m Pipe Internal Diameter 2 inch

Location Elevation 1 m Indoor/Outdoor Direction Down – Impinging on

the Ground Discharge Parameters Frequency of Bends 0.08 per m

When the phase is set to Vapour in the Scenario tab section, the Building Wake Effect

The release similar to that from the one-inch liquid li pipework r ry similar e

Defining Thre lammable Rel

fields will become enabled. The sphere is in an open area so building-wake effects are not relevant to this release, and you can leave these options unchecked.

rate from the two-inch vapour ne, and the two

line iseleases give ve ffect distances.

e F eases There is a propane sphere at the far The prop here has the same dimens the chlorine sphere a pip s also operating under saturation conditio pheric temper

Setting the ta for the ModeYou can d the res by e three toxic

-

harge

ng t and then typing “P”, which will take you to the first material with this initial

north of the site. ane spions as nd the same design of ework, and i

ns at atmos ature.

Input Da ls define the rupture an two pipework failu copying th

Models and simply changing the selection of discharge material and the eastern coordinates.

Copying the Models

Select the Toxic folder, copy and paste it, and name the copy Flammable. In the name for each Model, change Cl2 to C3.

Changing the Material Selection

Open the input dialog, click on the button with three dots to the right of the DiscMaterial field, and change the selection from CHLORINE to PROPANE. The list of materials is arranged alphabetically, and you can move quickly to PROPANE by clickiin the lisletter.

When you return to the Materials tab section you will see that the program has recalculated the saturation pressure at 10oC and also the mass for the inventory.

You must make this change for each of the three Models.

30


Changing the Location and Concentration of Interest

When you move to the Location tab section, you will see that the Toxic averaging time is

uded you to make a different selection for the

want to concentratiovalue as low as 1 since thewill not zard once it hasbelow t er flammable limit o20,000 ppm. You could set this concentration yourself, but for a flamma an also leConcentration of interest blank, as shown, auto is culations once the

and

You must make this change for each of the three Models.

ose, cted by default

o you would normally only select them if you

– but you will do this in the Parameters instead of in the Model data, since

ant to set values that will be used by all

log for

he values set in the System

for

Finally, open the input dialog for the Fireball and BLEVE Blast Parameters, and set the same values.

no longer set for Uses averaging time and that this field is now shown as unset and mandatory. The material is flammable only so the Toxic averaging time is not inclin the list, and the program is promptingcalculations of the stopping-concentration.

For a flammable release you would not calculate the

00 ppm,n to a cloud

diluted pose a hahe low f 2% or

ble release you c ave the

and the program will matically stop the d persion calconcentration has reached a given fraction of the LFL as calculated with the Flammable averaging time. By default the fraction is 50%, but you can change this in the Flammable Parameters if you prefer.

For this tutorial, delete the value for the Concentration of interest, and set the EastNorth coordinates as shown above.

Setting the Input Data for the Fire Modelling If you move to the Jet Fire, Pool Fire or Fireball tab sections, you will see that three levels of radiation intensity are specified, but that the calculations for radiation dprobit and lethality are all unselected. These calculations are not selebecause they can be time-consuming, sknow that you need them for a particular analysis or a particular Model.

For this tutorial you will set the lethality calculations to Selected and specify five levelsof lethality this is the most efficient method if you wModels.

Move to the Parameters tab in the Study Tree, open the input diathe Jet Fire Parameters, and set theRadiation Lethality data as shown. After you have clicked on OK to close the dialog you will see that the Jet Fire Parameters icon no longer has a green border, which shows that not it is not using tParameters for all of the fields.

Next, open the input dialog for the Pool Fire Parameters, and set the same valuesRadiation Lethality.

31


If you move to the Models tab of the Study Tree and look at the Jet Fire, Pool Fire or

Runnall

e er

ts

gle ons

xic

ection. The propane releases do not l Fire tab sections.

d effect distance shown in these graphs is just less than 25 m, which is the

re

results for more than one Model or more than single level, which will be the lowest level set for ensity level, or the lowest lethality level). If you

then you must view the graphs for a single

lso contains three graphs. These are showing results eans that the two Radii graphs are able to show the

pse for a lethality level of 100%, because the fireball does not

rameters).

Fireball tab sections for any of the flammable Models, you will see that the lethality calculations are now selected, with the five levels set.

ing the Consequence Calculations and viewing the Results Select the Flammable folder and use the Run Models option to run the calculations for three Models.

You can also view the results for all threModels at once. Select the Flammable foldand then select View Graphs. A Plot Setup dialog will appear, prompting you for the Weather for which you want to view resulWhen you are viewing results for multipleModels you can only choose a sinWeather, so the Weathers have radio buttbeside them, whereas they have check boxes beside them when you are viewing results for a single Model. Select the 1.5/F Weather, which should give the greatest effect distances for dispersion.

.

The Graph Window contains tab sections for Concentration graphs, as with the toModels, but it contains Jet Fire, Fireball and Flash Fire tab sections instead of the Toxic tab sproduce any liquid rainout, so there are no Poo

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 twopipework failures. The first graph shows radiation level versus distance, the second shows Intensity Radii to the lowest of the three radiation levels set in the Parameters (4kW/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 in the parameters. The maximumdownwindistance for 4 kW/m2 for the liquid

If a given Fire Radii graph is showing one Weather, then it will only plot athat type of result (e.g. the lowest intwant to see results for all of the levels,Model and Weather.

Fireball Graphs

The Bleve (or Fireball) tab section aonly for the rupture, and this m

lease.

results for more than one level. The maximum downwind effect distance is about 560 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 elliproduce the necessary radiation dose at the height of interest (set to ground level in the Flammable Pa

32


Explosion Graphs

The two Early Explosion graphs contain results only for the Rupture, since immediateexplosions are assumed not to occur for continuous rel

eases. However, the Late

e greatest downwind distance for the lowest overpressure set in the gend for the Late Explosion Time graph

ccurs at 11.2 s.

loud at the time that it covers the maximum downwind effect distance of

ework releases this gives a distance of pm is 50% of the LFL, which is the

ters as the boundary of the flash fire

Alter rly Explosions e input data for the flammable Models you left the

s, which means that the early explosion t method, which is the TNT method.

Rupture Model that use the other methods e results.

Rupture.

e Model inside this folder and then create two copies of the Model. TNT, name the first copy Multi-Energy, and the second copy

location to

s for the Multi-Energy Explosion Method

Explosion graphs contain results for all three Models.

The Late Explosion Worst Case graph shows the effect radii for the explosion-time which gives thExplosion Parameters (0.02 bar), and the legives the time at which the worst-case expldistances is 1,100 m, for the

osion occurs. The greatest downwind effect Rupture, and it o

Flash Fire Graph

The Flash Fire Graph shows the zone for the cmaximum area. For the rupture, this gives a350 m to 10,000 ppm, whereas for the two pipabout 70 m to the same concentration. 10,000 pfraction set by default in the Flammable Parameeffect zone.

native Methods for Modelling EaWhen you were setting thFlammable tab section with the default settingfor Rupture was modelled with the defaul

In this section you will create versions of thefor modelling early explosions, and compare th

Creating the Model Icons

Insert a folder inside the Flammable folder, and name it

Drag the RupturRename the original Model Baker-Strehlow.

Setting the Inputs for the TNT Explosion Method

For the TNT Model, move to the TNT tab section to check the input data for the modelling.

You can leave the Explosion Efficiency with the default value, but for this Model you should set the 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 TNT Model.

Setting the Input

Open the input dialog for the Multi-Energy Model, move to the Flammable tab section, and choose TNO Multi-Energy as the Explosion Method.

Next, move to the Multi Energy tab section, where you can 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.

33


By default there are no confined regions selected, which means that there are no

e propane sphere is

section,

option to have the eed of the flame (rather

Flame Expansion

ves off the ground, so you should set of th

hen view the graphs for the 1.5/F

el produces a peak pressure of 1

gion of the cloud, for which the peak overpressure is

only about 0.02 barg.

mandatory fields in the tab section and that the Model will run even if you do not set any values in the tab section – but it also means that by default the Model 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 threlatively open.

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

Click on OK to close the dialog for the Multi-Energy Model.

Setting the Inputs for the Baker-Strehlow Explosion Method

Open the input dialog for the Baker Strehlow Model, move to the Flammable taband choose Baker Strehlow as the Explosion Method.

Next, move to the Baker-Stehlow tab section. This tab section contains many mandatory fields, and you must complete this tab section before you can run the Model.

For this tutorial, use the program calculate the spthan supplying it yourself). For a propane release you should set the Material Reactivity to Medium, and for this release you should set the number of dimensions for the 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-wathe Ground Reflection Factor to 1.6. Finally, the volume involved in the explosion is 500 m

e cloud assumed to be 3.

Click on OK to close the dialog for the Baker-Strehlow Model.

Running the Calculations and Viewing the Results

Select the Rupture folder, run the calculations, and tWeather.

In the Early Explosion Distance graph, the Baker-Strehlow Model has the highest peak overpressure, of about 1.02 barg, but the pressure declines rapidly with distance and there are no effects beyond about 300 m. The TNT Modbarg and the pressure declines less rapidly with distance, so the pressure at 300 m is 0.2barg, and there are effects out to 1,400 m. For the Multi-Energy Model, the graph showsresults only for the unconfined re

34


However, in the Early Explosion Radii graph the results shown for the Multi-EnergyModel are those for the worst case, and in this comparison the Multi-Energy Model givesthe greatest effect distances of the three Models, with a distance of about 2 km to 0.barg.

02

rgy Early Explosion Distance results for each of

that the over-pressure levels close to the nt on the value that you set for the strength of

e default TNT method gives results that are h a medium strength of confinement (i.e. with a

sonable – and simplest - to take the default method as

Flammable Releases from a Rail Tank Wagon

If you view the graphs for the Multi-EneWeather, you will be able to see separatethe regions in the cloud. These results showrelease are very strongly dependeconfinement.

This analysis shows that, for this release, thclose to the multi-energy results witstrength of 7). It seems rea

Model on its own and select only the 1.5/F

representative for this analysis.

The propane is delivered to the facility by tank wagon from a marshalling yard 10 km lving two tank wagons, and

der the same conditions as in the C).

g leaks during the unloading process. This tutorial will consider only the co

pture of a wagon under flame le the wagons are at the unloading

Defingon, and then copy the TNT Model from the

point for defining the release. Name

to the north. The deliveries take place once a week, invoare 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 unsphere: under saturation conditions at atmospheric temperature (taken as 10o

There are many hazardous events that could be modelled for the tank wagons, includinrupture of a wagon under normal operatingwagon, and a fireball produced by catastrophic ruimpingement. All events are assumed to occur whipoint 100 m south of the propane sphere.

ing the Rupture of the Wagon First, create a folder and name it

nditions, a leak from the liquid side of a

Tank WaRupture folder, which you will use as the starting the Model Wagon Rupture.

Open the input dialog and set the data as follows:

Tab Section Input Field Value Material Inventory 43.2 m3

Elevation 1.8 m Location North co-ordinate 435581 m

Definpture Model and name the copy Wagon Liquid Leak, and then open the input

ing the Leak from the Liquid Side of a Wagon Copy the Rudialog and set the data as follows:

Tab Section Input Field Value Scenario Type Leak Scenario Hole Diameter 1 inch

Vessel Tank Head 1.95 m Location Elevation 0.5 m Indoor/Outdoor Direction Down – Impinging on the Ground

35


For a release from the body of a vessel rather than from attached pipework, you shset the Scenario Type to Leak. This will give a larger discharge rate since there are no frictional losses during the flow to the leak-location. For the leak scenario, you specify the lea

ould

k-size in the Scenario tab section.

Definllows you to model immediate-ignition effects from fireballs and

select the option to insert a Fireball Model. Name the Model Wagon Fireball, then open the input dialog and set the data as follows:

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.

ing the Fireball Failure under Flame Impingement The program apoolfires on their own, separated from any modelling of dispersion and delayed-ignition effects, and you do this by using the Fireball Model or Poolfire Model rather than the Source Models.

Select the Tank Wagon folder, then

Tab Section Input Field Value Material PROPANE East Location 197327 m North Location 435581 m

Material

Burst Pressure 8.57 barg Released Mass 22.2e3 kg Fireball Shape Mass Vapour Fraction 0.25 Radiation vs Distance Selected Maximum Distance 500 m Angle from Wind 0 degrees Height above Origin 0 m Radiation Ellipse Selected

Radiation Data

Incident Radiation 4 kW/m2

The Burst Pressure is 60% greater than the normal operating pressure and is used in

n and emissive power, or entering your own values. For this

The dialog also contains a Contour Data tab section ows you to define a plane and up adiation lev ich you want

Running the Calculations and the ResultsRun the calculations for the and th e graphs for the 1.5/F

.

2 compared with 440 m. This shows the effect of the higher vesse Model t ame impingement, whereas the l con a rupture under normal operating conditions which then has a probability of ig immediately and giving fireball effects.

calculating the surface emissive power of the fireball.

The Fireball Shape tab section gives you the choice between using a correlation to obtain the radius, duratioModel, you are using the correlation.

that allto three r els for wh contour results.

Viewing Tank Wagon folder en view th

Weather, and then examine the Bleve or fireball results

The Fireball Model gives slightly larger effect distances than the Rupture Model, with a distance of about 460 m to 4 kW/m

l pressure used in the Fireball Rupture Mod

o model failure under flsiders eniting

36


Savin

e the

ption from the File menu, the Save As r input data. If you select

l be

What Next?

g the Study Folder with the Results You have now completed the tutorial, and you should save the Study Folder in order to save the changes you have made.

By default, the program will only save the input data, which means that the next timyou open the Study Folder, you will have to rerun the calculations in order to view full results. However, if you select the Save As… odialog will contain an option to Save results as well as youthis option, the program will save the full set of consequence results and you wilable to view the results immediately the next time you open the Study Folder – although you should be aware that the file may be large, e.g. 25 MB or more.

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 .

If you need further detai ct of the program, or if you need guidance on how to model a particular situation for your facility, you should contact product support using the details duct Support menu.

the assistance of the online Help

ls on any aspe

given under Pro in the Help

37

phast tutorial manual

Documents

phast example study

example analysis

study folder file

introduction chapter

consequence analysis

contents chapter

new analysis

dnv software folder