Tutorial Safeti and Safeti Lite

SAFETI and SAFETI LITE Tutorial Manual

SAFER, SMARTER, GREENER

Prepared by DNV GL – Software http://www.dnvgl.com/software

© DNV GL AS. All rights reserved This publication or parts thereof may not be reproduced or transmitted in any form or by any means, including copying or recording, without the prior written consent of DNV GL AS

CONTENTS Chapter 1:

An Introduction to Safeti ........................................ 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 ............................... 28

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

Chapter 3:

Performing the consequence analysis .................. 34

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 4:

Performing the risk calculations ........................... 51

In the final chapter you define population and ignition data and run the risk calculations to obtain individual and societal risk results.

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1

AN INTRODUCTION TO SAFETI

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 Safeti, 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. This tutorial does not cover the Multi-component and 3D Explosions functions of Safeti. There is a separate tutorial document for Safeti with the 3D Explosion extension. If you have a license for the 3D Explosion extension, you should complete this tutorial first, before starting the 3D Explosion tutorial. 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 go on to create an analysis file of your own, starting with a new, blank file, and setting up some background data in the form of a map and weather data. In the third chapter you will define a range of hazardous events and perform a consequence analysis for them, and in the final chapter you will define population and ignition data and complete the risk calculations. The tutorial should take 2-3 hours to complete. You do not have to complete it in a single sitting, and can take a break between chapters if you prefer. Note: all of the images of the program are taken from the Safeti product, without the 3D Explosion or Multi-component extensions. Some images will include features that are not present in Safeti Lite, and will not include the additional features associated with the extensions.

Starting the program running When you install the program, the installation process places a Phast & Safeti 7.2 folder inside a DNV GL - Software folder under Programs in your Start menu, and you can use this to start the program.

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.

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If you do not have a valid licence present, the program window will not open, and instead a dialog will appear as shown. To obtain a license, click on Request a licence. A Request license dialog will appear, and you must select the products and features for which you require a license. The dialog allows you to email the request directly to DNV GL software support, or to save the request to disc so that you can choose when to send it. Once DNV GL 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 Safeti 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 Safeti examples file When you start the program, 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 examples 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 on 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 Safeti 7 examples.psux file or the Safeti Lite 7 examples.psux file, as appropriate for your type of license, 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. Note: the Examples folder will contain files for the four main Phast and Safeti products, and for the 3D Explosions and Multi-component extensions to the products. If you do not have a license for a particular extension, then those examples files will not be relevant to you.

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The Risk Supertabs The Risk Supertabs appear in a separate pane inside the main window; this pane is normally located along the left side of the window. There are four tabs in this pane, arranged in an order from left to right that reflects the main stages in the process of performing a risk analysis. The first Risk Supertab is the Input Supertab, which contains a separate panel called the Study Tree. The Study Tree covers all of the aspects of the input data for the consequence and risk calculations, with the different aspects of the data organised in separate tab sections. For example, the Models tab covers the definition of hazardous Scenarios, and the Weather tab covers the definition of representative weather conditions for modelling. The different tabs of the Study Tree are described in the next section. The next two Risk Supertabs are the Run Row Grid Supertab and the Combinations Supertab, which cover different aspects of the definition of the Run Rows that specify different combinations of aspects of the input data. In Safeti, a Run Row is a combination of input data from across the other tab sections, and you can use different Run Rows to calculate the risk for alternative scenarios (e.g. for day conditions and for night conditions), and then to combine or to compare the risks. The concept of a Run Row should become clearer after you have seen the setup of the input data in the Study Tree, and when you see the method for defining a Run Row in a later section of the tutorial. The last Risk Supertab is the Results Supertab, which gives you a quick way of viewing risk results. The other feature of the Risk Supertabs is the Run Row Selector, which is a special pane that is normally “collapsed” along the left side of the Input Supertab, where it appears as a line of vertical text with a circular Hide/Show button at the top. If you click on the button or on the text, the Run Row Selector pane will become expanded, and will push the Study Tree pane to the right, as shown in the illustration. The Run Row Selector pane lists all of the Run Rows that are defined in the workspace, and you can see that four Run Rows are defined in the Safeti examples file: there are separate rows defined for day conditions and for night conditions for the propane and for the chlorine releases. You use the Run Row Selector to choose one of the Run Rows as the active Run Row, and also to select the Run Rows to be calculated and to perform the calculations. The selection for the active run row affects various aspects of how the input data are displayed and checked. The Row selected as the active Run Row is shown by an orange asterisk *, and when the Run Row Selector is collapsed, the name of the active Run Row is displayed in the line of vertical text; in the Safeti examples file, the active Run Row is set to Propane Storage Day.

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The tabs in the Study Tree pane At the start of an analysis, you will be working mainly in the Study Tree pane inside the Input Supertab. 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 tab section 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 most of 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 doubleclick 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 Study has a small set of input data, and the values that you define at the Study level will be used as defaults for equipment items under the Study. The Safeti examples file has two Studies: one for propane Scenarios and one for chlorine Scenarios.

Level 3: the Equipment item At the Equipment level, you define the process material and operating conditions. There are five types of item that you can insert at the Equipment level: •

a Pressure Vessel

•

an Atmospheric Storage Tank

•

for modelling releases from pressurised containment

a Standalones item

for modelling releases from unpressurised containment

for performing detailed modelling of specific hazards such as fire,

explosion and pool vaporisation, separate from the modelling of a particular release from containment. •

A Long pipeline

for modelling the time-dependent release from a long pipeline, including the

effects of the closure of valves on the pipeline •

A Route Model

for defining a transportation route and calculating the risk from representative

hazardous events modelled at intervals along the route. You define the hazardous events for modelling using the Pressure Vessel, Atmospheric Storage Tank and Standalones Equipment items, with Scenarios defined under these items.

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Note: the Route Model is not available in Safeti Lite. 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 examples file is a very simple analysis with only two Equipment items, both of which are Pressure Vessels. There is one propane Pressure Vessel and one chlorine Pressure Vessel.

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 depends 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, as it 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. Fire, explosion and toxic calculations where applicable, as well as representative effect zones for the dispersing cloud.

•

Scenarios for an Atmospheric Storage Tank: The Scenarios available for a Pressure Vessel are also available for an Atmospheric Storage Tank. There are two additional scenarios, a Spill Scenario

and a Vent from vapour space Scenario

. A Spill Scenario models a liquid spill

in which the entire released mass is assumed to spill onto the ground. A Vent from vapour space Scenario models the release of material from the vapour space of a unpressurized or refrigerated vessel. •

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

•

Scenarios for a Long Pipeline item: There are two types of Breach Scenario

that you can

define under a Long pipeline item. The Location Specific Breach models a release of a specified size at a specified location along the pipeline. The Section Breach Scenario also models a release of a specified size, but you do not specify the location because the program automatically models it at multiple locations along the pipeline. Note: the Section Breach Scenario is not available in Safeti Lite. You can define any number and combination of Scenarios under any Equipment item. The consequence calculations are performed at the Scenario level, which is the lowest level in the data structure. In the examples file, each Pressure Vessel has four Scenarios underneath it: a Catastrophic rupture, and three Leak Scenarios of different sizes.

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The Weather tab section In the examples file, the Weather tab section of the Study Tree pane contains two Weather folders: one containing three Weathers that are representative of day conditions, and one containing two Weathers that are representative of night conditions. In the definition of the Run Rows, the Day Weather folder is selected for the Day Row, and the Night Weather folder is selected for the Night Row. 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. For the examples file, the name of each weather gives the wind speed and the atmospheric stability category that are defined for it. In the calculations for a given Scenario, the program performs a separate run of the consequence and risk calculations for each separate weather condition, giving a set of results that are specific to that Weather. You use the Weather folder to define the windrose probabilities for the set of weather conditions. These are used in the risk calculation. You can define any number of Weather folders in an analysis.

The Parameters tab section 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 extensive, and it has been organized into several groups. The icons for the groups in the examples file have a green arrow at the top left of the icon. The program uses this arrow to show that all of the Parameters under that icon are using the default values that are supplied with the program. If you change the value of any of the Parameters then the green border around the icon will disappear. This allows you to see at a glance which aspects of an analysis are using all-default values, and which are using changed values. Each new workspace will be created with a Parameters 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 Run Rows. In the examples file there is a single Parameter set and all Run Rows are using this set of Parameter 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 Equipment items in the workspace, or for materials that you have added yourself while working in the Material tab section. You can define three types of material:

Pure Components All of the icons in the Materials tab for the examples 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 that are 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. However, we recommend limiting the number of components to a maximum of 6.

Warehouse Materials Warehouse Materials are provided for use in a Warehouse Fire Model, but this model is not currently available in Safeti 7.

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

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

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

Building types

and Buildings

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. They are also used for building wake modelling, chimney releases ad roof/lee releases.

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For these calculations, you do not define the location, dimensions or ventilation for the buildings directly on the storage Scenario. Instead, you set up Building Types and Buildings under the Buildings folder in the Map tab section of the Study Tree, and you use the Building Types 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. 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 examples 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, as shown below.

The Equipment items are represented by dots, and you can see that there are many dots distributed over the Chemical Plant area. The Buildings are represented by dark green/brown backwards diagonal pattern on the GIS and GIS Legend. 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.

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The Raster Image layers are always at the bottom so they appear in the background behind all of the other input data. In the illustration the Southpoint_OS image layer is above the Southpoint_Aerial image layer. If you swap these two image layers by dragging the Southpoint_OS to the bottom, the aerial photograph image will be displayed instead of the map image. You can also right click items in the legend and choose Display On or Display Off to show and hide items respectively. In the Ribbon Bar, the Settings tab, the Tools tab 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 whose name you want to view on the map (e.g. Propane). 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 General tab of the GIS Input Tools group in the Ribbon Bar, and click the Label option to turn it on. The name of the Equipment item will then be displayed underneath the dot, as shown.

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The Risk tab section You use the Risk tab to define data that are specific to the risk calculations.

Categories The program is supplied with a default list of Categories for Populations, with a different display style defined for each Category. Each Population is assigned to a Category, and the Category determines the style that will be used when displaying the Population in a GIS View. The Category is also used in the risk results, where some forms of results provide an analysis according to the populations assigned to each Category.

Ignitions The ignition sources are used in modelling the location and probability of delayed ignition, and the input data for each ignition includes the probability that it will ignite a flammable cloud. You can define ignition sources on the GIS View as points, straight lines, polylines, rectangular areas and polygon areas. The distribution and strength of ignition sources typically varies according to the time of day, and the examples file reflects this, with separate folders of ignitions for day and night. The Day and Night Run Rows have different sets of ignitions selected.

Populations The risk modelling calculates fatalities for each population, and also considers populations as a potential cause of delayed ignition. Each input data for each population includes the proportion of people indoors and out of doors. You can define populations on the GIV View as points and as areas. As with ignitions, the distribution of population varies according to the time of day, and the examples file has separate folders of population for day and night, and different selections of populations for the Day and Night Run Rows.

Vulnerabilities The Vulnerability data specify the criteria for causing fatalities or other types of damage from different types of hazardous effect. The program is supplied with two sets of data for personnel vulnerabilities, one for people out of doors, and one for people indoors.

Risk transects A risk transect is a line drawn on the map. You use it to view a Risk Transect Graph that shows the levels of risk along the line. You can define any number of risk transects. Risk transects are not available in Safeti Lite.

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Risk ranking points A Risk Ranking Point is a location drawn on the map, as a location of interest for detailed riskcontribution results. You can define any number of risk transects. Risk ranking points are not available in Safeti Lite.

Plant Boundaries You can draw the boundary of the plant as a polygon on the GIS View. The risk calculations uses the boundary to distinguish between onsite and offsite sources of ignition. Plant boundaries are not available in Safeti Lite.

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

The input dialog for the Propane Pressure Vessel Equipment item In the Models tab section of the Study Tree, expand the Propane Storage Study, and then double-click on the icon for the Pressure Vessel Equipment item named Propane. The Pressure Vessel Equipment input dialog will open as shown below. The dialog contains a large number of input fields organised over nearly fifteen tab sections, but you will not normally enter data in every section. For an Equipment item, the most important inputs are in the Material tab section, which covers the process material and operating conditions. Almost all of the fields in the other tab sections are also present in the Scenario dialogs, and you would set a value in the Equipment dialog if you want the value to be used as the default value for all of the Scenarios under that Equipment item.

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Describing every item of input data is beyond the scope of this tutorial. However, you can get a description from the online Help that is included with the program. Every input dialog contains a Help button at the bottom right. When you click on this button, the Help will appear in a separate window, as shown.

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 Propane Pressure Vessel 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 in the Study Tree 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 of the Pressure Vessel Equipment items, take the following steps: 1. Select the workspace node at the top of the tree. 2. In the Grid View, bring up the list 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 toolbar.

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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.

If you select one of the Studies from the tree, the Grid View will display only the Pressure Vessel in that Study, and if you change the selection in the filter list to Leak, the Grid View will display all of the Leak Scenarios under the selected node. 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 on using the Grid View, and you should refer to the online Help for a full description.

Running the consequence calculations and viewing the results The program divides the calculations into two stages: consequence calculations, followed by risk calculations. The consequence calculations determine the effect distances for the various hazardous effects associated with the hazardous event, and the risk calculations determines the risk that these effects will have a fatal impact on people in the surrounding area. If you wish, you can run both calculations in a single operation, but this is not good practice. Instead, you should first run the consequence calculations on their own, and then look at the consequence results in detail and decide whether they are realistic or whether you should adjust some of the input data to give a better representation of the hazardous event (e.g. changing the bund data, or the release height or direction). This assessment will require some experience, both of typical consequence results and of the relevant input data in the program, but you will only gain this experience through practice in reading the consequence results and in experimenting with input data (with guidance from the online Help). If you do not have a thorough understanding of the consequence results for your analysis, you will not be able to interpret the risk results properly or make sound decisions on the basis of the results.

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Running the calculations You will run the consequence calculations for all Run Rows. There are three stages in this process: 1. In the Home tab of the Ribbon Bar, change the selection for Mode from the default setting Risk to Consequence, as shown.

2. Expand the Run Row Selector pane at the left of the Input Supertab to see a list of all of the Run Rows, and click on the All Run Rows icon at the top of the list to select it. 3. Click on Run in the Home tab of the Ribbon Bar (or press [Ctrl]+M). The program will process the calculations for each Run Row in turn. In the calculations for each Run Row, it will process each Scenario that is selected for that Run Row in turn, performing the calculations for each Weather that is selected for that Run Row. The calculations should take less than a minute to complete, depending on the speed of your machine. When the calculations are complete, you will see that a green tick

is

displayed at the top right of the icon for some Scenarios. This shows that the calculations for the Scenario ran successfully and the Scenario has a complete set of results. If an error occurred in the calculations, then a red error icon

will be displayed next to the icon instead; ifyou

place the cursor over the error icon, a tooltip will appear, giving a description of the error. In the illustration, the green tick appears next to the Propane Scenarios, but not next to the Chlorine Scenarios. This is because the Run Row that is selected as the active Run Row is Propane Storage Day, as shown in the vertical text in the collapsed Run Row Selector pane. This Run Row has the Propane Scenarios and the three Day Weathers selected, so when this Run Row is set as the active Run Row, the Study Tree shows the calculation-status only of the Propane Scenarios, and only for the Day Weathers. If you changed the active Run Row to Chlorine Storage Night, the Study Tree would show the calculation-status of the Chlorine Scenarios instead, for the two Night Weathers. You do not have to run the calculations for all Run Rows, or even for all of the Scenarios that are selected for a single Run Row. If a particular Scenario is selected for the active Run Row, you can run the calculations for the Scenario on its own by taking the following steps: 1. Select the node for that Scenario in the Models tab of the Study Tree. 2. Click on Run in the Home tab of the Ribbon Bar (or press [Ctrl]+M). The program will run the consequence calculations for that Scenario, for all of the Weathers that are selected for the active Run Row.

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If the Scenario that you select in the Models tab is not part of the selection of Scenarios for the active Run Row, then when you click on Run a dialog will appear as shown. This dialog lists the Run Rows for which the Scenario is selected. If you want to proceed with running the calculations for the Scenarios, you must click on one of the Run Rows and then click on Finish. The program will change the active Run Rw to the selected Row and then run the calculations. This dialog will also appear if you try to open the input dialog or view the Graphs for a Scenario that is not part of the selection for the active Run Row.

Viewing the graphs for the Propane 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 two Propane 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 F 1.5m/s Weather under the Day Weathers folder. 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, listing all of the Scenarios that have been calculated for the selected Weather, for the active Run Row. The dialog is prompting you to choose the combination of Scenarios whose results you want to view. Check the box for the Propane Pressure Vessel, which will select all of the Scenarios for this Equipment item, and then click on the right arrow to move the items to the Selected items list at the right of the dialog. The Finish button will become enabled, and when you click on it there will be a pause of a few seconds, and then the Graphs View will open in the Document View area as shown on the next page.

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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 the Propane Vessel includes results for jet fires and fireballs, 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 one Scenario. For example, the Jet fire graphs contain results for the leaks only, and the Fireball graphs contain results for the Catastrophic rupture only.

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Viewing results on the GIS, against the background of map images The Graphs View does not display any of the results on the GIS. To view the results in this form, you must open a GIS Results View. The process of opening a GIS Results View for the Propane Scenarios is almost identical to the process of opening a Graphs View: 1. In the Weather tab of the Study Tree, select the F 1.5m/s Weather under the Day Weathers folder. 2. Click on GIS in the Home tab of the Ribbon Bar. 3. In the Results Scenario dialog, check the box for the Propane Pressure Vessel, which will select all of the Scenarios for this Equipment item. 4. Click on the right arrow to move the items to the Selected items list. 5. Click on Finish 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.

The view will be displaying Cloud Footprint concentration results, which are present for all except the Small leak Scenario. 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. The contents of the list for the Propane Scenarios is shown in the illustration above. You use this list to select the type of effect to display.

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Viewing the Reports for the Catastrophic rupture Scenario The program also presents results in the form of reports. If you wish you can view a report that covers multiple Scenarios – e.g. a report for both Propane Scenarios – but if you want to compare the reportresults for different Scenarios it is easier to view separate reports for each Scenario and compare between two reports. To view the reports for the propane Catastrophic rupture Scenario, select the Scenario and then click on Reports in the Home tab of the Ribbon Bar (or click [Ctrl]+R). The Results Selection dialog will open, with the Catastrophic rupture Scenario already selected as shown, and with both the Finish and the Next buttons enabled. The Next button will take you to screens that allow you to deselect Weathers and types of Report. If you click on Finish in the first screen of the dialog, the Reports View will cover all Weathers and all types of available Reports. When you click on Finish, there will be a pause of a few seconds, the Reports View will open in the Document View area as shown.

Note: 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 of the program running out of memory and crashing.

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As with the Graphs View, the Reports are organised in different groups. For a Scenario under a Pressure Vessel, there are three groups: Summary, Input, and Pressure and Atmospheric Vessel. The Summary and Input groups each contain a single Report and are present for all types of Scenario, but the Pressure and Atmospheric Vessel group contains many Reports, and is only present for Scenarios under Pressure Vessels and Atmospheric Storage Tanks. A given Report will present the results for all of the weather conditions that have been processed for the Scenario and selected for reporting. The different Reports for this Scenario are described briefly below:

Summary group: Consequence 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 example, if you click on Dispersion Results in the navigation pane at the left of the Reports View, you will move to the section of the Report that compares the effect distances to different concentrations, as shown below. For this Scenario, the D 5m/s Weather is the one that gives the greatest distances.

Summary group: Hazard Zones Report The Hazard Zones Report gives the details of the effect zones for hazardous flammable effects and the description of the flammable cloud, as they will be used as input to the risk calculations.

Input group: Input Report The Input Report lists the input data for the Scenario.

Pressure and Atmospheric Vessel group: 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 - it is a compact presentation of results that are given in more detail in other Reports

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Pressure and Atmospheric Vessel group: 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.

Pressure and Atmospheric Vessel group: Commentary Report As shown in the illustration, 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.

Pressure and Atmospheric group Vessel: 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 chlorine Scenarios, 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.

Pressure and Atmospheric Vessel group: 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.

Pressure and Atmospheric Vessel group: Early Explosion Report For the Catastrophic rupture Scenario, the tab for the Early Explosion report is named Early Explosion ME, and this is because for this Scenario the explosion method selected for the consequence modelling is the Multi-Energy: Uniform confined method. There are four explosion methods available for consequence modelling in Safeti, and you select between them in the Explosion parameters tab section for the Scenario. The Multi-Energy: Uniform confined method method is the default method. Note: the explosion effect distances that are presented in the consequence Reports and Graphs are not the values that are used in the risk calculations. The explosion modelling performed during the risk calculations is different: the method used depends on the setting for the Explosion method option in the Settings tab of the Ribbon Bar. The results for this modelling are part of the Risk Results, and are not included in any of the consequence results.

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The Early Explosion 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.

Pressure and Atmospheric Vessel group: 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. 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 a Pool Vaporisation Report describing the spreading and evaporation of the pool and describing the series of “dispersion segments” used to represent the vapour produced from the pool, and also a Pool Fire Report giving radiation results similar to those in the Fireball Report. For most of your work with the consequence results 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. Not all of the available reports are discussed within this tutorial. For full information on any Report or any other feature of the program, you should refer to the online Help. You can open the Help at any time using Show Help in the Help tab of the Ribbon Bar.

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Running the risk calculations and viewing the results When you have examined the consequence calculations, made any appropriate adjustment to the definitions of Scenarios or other input data and rerun the calculations, you can proceed to the risk calculations.

Running the calculations To run the risk calculations for all of the Run Rows, take the following steps: 1. In the Home tab of the Ribbon Bar, set the Mode to Risk. 2. Expand the Run Row Selector pane, and select All Run Rows at the top of the list of Run Rows. 3. Click on Run in the Home tab of the Rubbon Bar. The risk calculations will run very quickly. You can only run the risk calculations from the Run Row Selector pane, i.e. when a Run Row or a set of Run Rows is selected. You cannot run risk calculations for an individual Scenario selected in the Models tab of the Study Tree. When you select a Scenario and use the Run option, the program will run only the consequence calculations for that Scenario and will not proceed to the risk calculations, even when the Mode is set to Risk.

The list of available risk results When the risk calculations for a particular Run Row have been completed successfully, a green tick

will appear

next to the icon for that Run Row in the Run Row Selector. In addition, the Risk option will become enabled in the rightclick menu for the Run Row, and you can expand this option to view a list of the type of risk results that are available. The Risk option is also available for the All Run Rows node at the top of the list. The risk results are organised in three categories: 1. Societal Risk Results These results present the risk in terms of the number of fatalities caused by the different alternative outcomes of the hazardous events, and the frequency of the outcomes. The FN Curves show the results in the form of a graph of the frequency F of outcomes that cause N or more fatalities. The other types of societal risk results are reports in the form of tables or grids that list the individual outcomes, and give different types of analysis of the results, with different levels of grouping and breakdown. 2. Risk Ranking Point Results These results list all of the individual outcomes that contribute to the risk of exceeding vulnerability criteria at a given Risk Ranking Point. The different types of risk ranking point results give different types of analysis of the results, with different levels of grouping. The risk ranking point results are not available in Safeti Lite.

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3. Risk Contour Results These results present the geographical distribution of the risk of exceeding vulnerability criteria, in the forms of contours for a given level of risk displayed in a GIS View. The different types of risk contour results allow you to compare different aspects of the risk levels. For a full description of each form of risk results, you should refer to the online Help. Enter “Risk Results” in the Index tab of the Help window to view a summary list of all of the available types of risk results, with links to the details of each type.

Viewing the risk results To view a particular form of risk results, either select it from the right-click menu for a node in the Run Row Selector pane as describe aboved, or select it from the Risk gallery in the Home tab of the Ribbon Bar, as shown. The Risk gallery is always available, no matter which tab of the Study Tree or Supertabs you are working in. You do not have to have the Run Row Selector pane open in order to view risk results using the Risk gallery. Whenever you select the option to view a form of risk results, a Results Selection Wizard dialog will appear. This dialog is similar to the dialog that appears when you view a form of consequence results, though the details of the options in the dialog can be very different, depending on the type of risk results that you want to view. The other main difference from the selection dialog for viewing consequence results is that the selection dialog for risk results gives you the choice to save the definition of the combination of options that you have selected. You can then use that saved combination at any time and viewing the risk results more quickly. This tutorial describes the process of viewing two forms of risk contours and one of the grid-based forms of societal risk results, and of saving and using a Results Selection.

Multi-Level risk contours for day and night combined Select the Multi-Level option for risk contours from the Risk gallery. This type of plot allows you to select multiple risk contours levels for plotting, and will display a separate contour for each level. When the selection dialog opens, it will have some selections already made as shown in the illustration. These selections are discussed below. The risk levels to be modelled in the risk contour calculations are defined in the Risk Preferences dialog, which you open by clicking on the Preferences option in the Settings tab of the Ribbon Bar. When the dialog opens, all of these defined levels will be selected and in the Selected items list at the right of the dialog. If you do not want to plot a particular level, you can click on it and then click on the left arrow to move it to the Available items list.

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The dropdown field below the Available items field lists all of the Run Rows and also all of the Combinations, as shown. The results for a given Combination are the combination of the results for the different Run Rows, using the weighting factor for each Run Row that are defined for that Combination in the Combinations Supertab. The Safeti examples file has three Combinations, defined as shown. The All: Day and Night Combination includes the propane and the chlorine results, with a factor of 0.4 for the Day rows and a factor of 0.6 for the Night rows, meaning that daytime conditions are assumed to apply for 40% of the year. The other two Combinations use the same weighting factors for Day and Night, but cover only propane or only chlorine. When the selection dialog opens, the Propane Storage Day Row will be selected because it is the first in the list, but you should change the selection to Combinations\All: Day and Night. The dropdown field below the Selected items field lists all of the sets of vulnerability criteria that are defined under the Vulnerabilities folder in the Risk tab section of the Study Tree. The risk calculations for each Run Row produce separate risk contour results for each set of vulnerabilities, and you must choose which of these sets of results you want to view. When the selection dialog open, the Outdoor vulnerability set will be selected because it is the first in the list, and you can leave it with this selection. The other field in the dialog is the Save selection checkbox at the bottom left. This field is always checked when the dialog first open. If you leave the field checked, the program will add an entry for the current combination of options to the Results Supertab. For this contour plot, you should leave the box checked. The Next button will take you to the last screen in the Wizard dialog, which allows you to give a name and description for the saved selection. For this contour plot, you can click on Finish in the first screen of the Wizard dialog. After you click on Finish a GIS Risk Results View will open as shown. You can see that the highest risk level over the offsite populated areas to the south of the plant is slightly higher than 1x10-6/AvgeYear as the contours for 1x10-6 stop just reach the residential area and the town. The highest risk onsite is around the propane vessel, near the centre of the plant, but there is a visible contribution from the chlorine vessel, further to the west.

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If you move to the Results Supertab, you will see that it contains one entry, called ResultsSelection. This is the default name that will be used for any new Results Selection if you do not supply a name in the final screen of the Wizard dialog. You can rename a saved Results Selection at any time, and also delete or duplicate one. Rename this Results Selection All Combination. You will use it later for viewing societal risk results for the same Combination.

Multi-Row contours for a risk level of 1x10-6/AvgeYear The Multi-Row contour plot allows you to plot separate contours for different Run Rows, for a selected risk level. For this plot you will set the risk level as 1x10-6/AvgeYear, since this is the highest contour that crosses the populated areas in the combined plot. Most of the selections for this plot will be different than those for the previous plot, so you would not save time by using the saved Selection. Instead, select the Multi-Row option for risk contours from the Risk gallery to create a new Selection. When the Wizard dialog first opens, the list of Available items will include all Run Rows and all Combinations as shown. Check the box by the Run rows node and click on the right arrow to move all of the Run Rows to the Selected items list. For a Multi-Row plot, the dropdown field under the Available items field lists all of the risk levels available. 1x10-5/AvgeYear is the default setting in this situation, so you must change the setting to 1x10-6/AvgeYear. You can also leave the selection of vulnerability criteria with the default setting of Outdoor, and leave Save selection checked. When you click on Finish, the Multi-Row plot will open in a second GIS Risk Results View, as shown. It will initially appear that there are no results for Propane Storage Night, but if you right-click on Propane Storage Day in the legend and select Display Off, you will see that the results are present, and are identical to the day results. There are differences between day and night for chlorine, because of the differences in the weather conditions, but the propane risk is dominated by effects that are not weather-dependent.

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Category PLL societal risk results for day and night combined The Category PLL results give the societal risk in terms of the Potential Loss of Life. The PLL for a particular outcome is the number of fatalities multiplied by the frequency. The Category PLL results show the contribution to the total PLL from different Scenarios and types of hazardous effect, and also the contribution from fatalities in different Population Categories. You will use the saved All Combination Selection in the Results Supertab to view the Category PLL results. If you right-click on the Selection, you will see a list of the available types of risk results, as in the Risk gallery. When you select Category PLL from the list, the Wizard dialog for the Category PLL results will appear as shown below.

The form of the dialog for the Category PLL results is different from the form of the dialog for the MultiLevel Risk Contours, but the relevant aspects of the selection have been applied, and the All: Day and Night Combination has been selected. You can leave this selection unchanged. If you leave the Save selection box checked when viewing results from a saved Selection, the program will not create a separate saved Selection, but will update the definition of the saved Selection with the selections that you make in the current dialog. If you want to keep the original definition of the saved Selection, you must uncheck the box. For this tutorial, you can leave the box checked. The Wizard dialog for Category PLL also has several additional screens that allow you to select only specific Scenarios or specific types of hazardous effect, but for this tutorial you can click on Finish in the first screen to include all Scenarios and types of effect. The Category PLL View will open in a separate tab next to the contour plots, as shown. When it first opens it will be fully collapsed, and will be showing the total value for the PLL, calculated as a weighted average across all Run Rows.

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This type of results view is organised in several levels, and you can drill down level by level to analyse the contributions to the risk. In the illustration below, the report has been expanded to the fourth level, which shows the individual Scenarios (or “Models”).

In the Category PLL view, the second level is Areas; if you do not have a license for the 3D Explosion modelling, this will only ever show one row, with the name “Population grid” as shown. For this level and all levels below, there are columns that show the PLL for populations in different Categories in addition to the total PLL, and you can see that almost all of the PLL is in the Industrial Category. The third level is Buildings, which shows the contribution from outdoor and indoor populations. You can see that the Indoor PLL is about five times the Outdoor PLL. The fourth level is Models, which lists the individual Scenarios. Here you can see that the propane releases dominate the risk. You can expand under a Scenario down to the fifth level, which is the type of hazardous effects (known as the “outcome codes”), as shown below for the large Propane Leak. You can see that the risk is dominated by the flash fire and explosion from delayed ignition of the gas cloud, with only a small contribution from the jet fire from immediate ignition.

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

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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 described above, but for a vessel containing a flammable material

•

The equivalent three releases from a tank wagon containing a toxic material, for a range of release-locations along the route of a railway track inside the boundaries of the site.

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 to those that will be shown in this manual. The analysis is divided over three chapters. This chapter describes the process of creating a new Study Folder and of setting up the Map data and the Weather data, Chapter 3 describes the process of defining the Models and running the consequence calculations, and Chapter 4 describes the process of defining population and ignition data and running the risk calculations.

Creating a new workspace To create a new workspace if you have the examples file open, you can select either Close or New Workspace from the File tab of the Ribbon bar. The program will close the examples 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 DNVGL folder under Documents (the default location for saving workspace files), use the New Folder option to create a folder called Tutorial, and then save the new file to this folder with the name Safeti Analysis and the default file format of *.psux.

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The contents of a new workspace New workspace files are not empty but will have some default data set up: •

At least one default Run Row. In Safeti there is one Run Row with the name Run Row, whereas in Safeti Lite there are two, with the names Day and Night.

•

A Weather folder containing three Weathers where the Weathers are the same as those in the Day Weathers folder of the examples file.

•

A set of default Parameters.

If the data that are set up for a new workspace are not suitable for your work, you can set up a workspace that has the items and values that you want, and then use the Workspace Template > Save option in the File tab of the Ribbon Bar to make this workspace the new “workspace template”, which means that it will be used whenever you start the program or create a new workspace.

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 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 (also known as the “workspace” icon), and inset a Set using either the Insert option in the right-click menu or the Insert gallery in the Home tab of the Ribbon Bar. The Set is a folder for raster images, and you have to insert raster images inside such a folder.

Insert a Raster Image inside the Set Select the Set, then select Raster Image from under the Insert option in the right-click menu. A dialog will appear as shown, and you must first browse to locate the image file. The tutorial.tif file is located in the Examples folder for the installation of the program (which is typically under C:\Users\Public\Documents\DNVGL\Safeti_Phast_7_2_00\ Examples\Maps\). When you first browse to this folder you may not see any files if the list of File types is not set to *.tif by default.

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When you have selected a valid raster image file, the Placement Mode fields will become enabled as shown below. These are options for specifying the map co-ordinates covered by the image. Some files contain georeference data or header data that will automatically 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 be displayed if it is not displayed already, and it 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 click in two locations 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.

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Click once with the mouse ner the top-left of the GIS View to begin defining the location, then move the mouse diagonally down the GIS area. You will see a red box expanding from the point at which you clicked to the current cursor position. Click a second time to define the location of the bottom right hand corner of your raster image. The raster image has now been inserted, and you will see the map image in the GIS Input View. You can also place the image by clicking at the first point, then holding down the mouse button as you drag the cursor diagonally, and then releasing the button at the second point If you accidentally place the second point very close to the first point, you might find that you cannot see the map in the GIS Input view, even though a raster image icon called tutorial has been inserted in the Study Tree. This happens because you have defined coordinates for the raster image that make it too small to display with the default scale of the GIS Input View. If this happens, delete the raster image in the Study Tree and try placing the image again, making sure to move the mouse a visible distance before clicking a second time (or releasing the button).

Setting the co-ordinates and size of the image After you have placed the image in the GIS Input View, a tutorial icon is inserted 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 below. 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 Input View because it has moved to a location outside the area currently displayed in the view. To make it visible, click anywhere in the GIS View window to make sure that it has focus and that the GIS Input Tools group is included in the Ribbon Bar, and then click on Fit All in the General tab of this group. The GIS View will change to display the area covered by the image.

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

Setting up Weather data for day and night For this analysis, you will be performing separate calculations for day and night, as in the examples file, and you will define and use separate Weather folders for the two times of day.

Creating a second Weather folder In the Weather tab section of the Study Tree, select the existing Weather folder, and then use copy and paste to create a second folder as a copy of the first. The program will give the copy the name Weather folder (1), and you should use the Rename option in the Home tab of the Ribbon Bar to change the name to Night, and then change the name of the first folder to Day.

Defining representative day-time weathers The set of three default weathers includes a highly-stable F 1.5m/s Weather, which is not applicable to the day since conditions are less stable during the day. You will edit this Weather, and change it to an unstable B 3 m/s Weather. Rename the Category 1.5/F Weather to Category 3/B, and then double-click on the icon to open the input dialog and set the values as shown in the Weather tab section. The other tab sections take default values from the Parameters, and you can leave them with these default values for this tutorial. Click on OK to close the dialog.

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Defining representative night-time weathers The set of three default weathers includes a D 5 m/s Weather, which is not applicable to the night. Delete this weather, leaving the Night Weather folder with two Weathers with a low windspeed of 1.5 m/s.

Setting up the Run Rows To use the two sets of Weather data, you must set up separate Run Rows for day and night, and select the appropriate Weather folder for each Run Row. You use the Run row grid Supertab to create and define Run Rows. When you first move to the Supertab you will see that the value in the Models column is redbordered and incomplete, as shown. This is because the workspace does not yet have any Scenarios (or “Models”) defined, so the selection of Models for running is empty. As soon as you define a Scenario, the red border will disappear automatically.

Creating a second Run Row This step is not applicable to Safeti Lite, since all Safeti Lite workspaces have two Run Rows. Click on the Add button

in the toolbar above the grid to add a second Run Row to the list. It will be

created with the name Run Row (1), and with the same selections for input data as the first Run Row. Click on the name of the first Run Row, and then type “Day” to change the name. Use the same method to change the name of the second Run Row to “Night”.

Setting the selection of Weather folders Both Run Rows will initially have the selection for Weather Folder set to Day Weather. Click in the Weather Folder cell for the Night row. The cell will turn into a dropdown field, and if you expand the field you will see all of the Weather folders listed, as shown. Select Night Weather from the list, and then press [Enter] to commit the change.

Saving the changes to the workspace Click on the Save icon

in the far left of the title bar to save the changes you have made.

When you are ready you can proceed to the next chapter, which describes the process of setting up the Equipment items and Scenarios and performing the consequence analysis.

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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 Settings 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 In the Models tab of the Study Tree, select the Study, then insert a Pressure vessel using either the right-click menu or the Insert gallery in the Home tab of the Ribbon Bar. The GIS Input View will become selected, the cursor will turn to crosshairs, and you should click at a point near the centre of the site as shown to place the Pressure Vessel. After you have clicked, an icon will be added to the Study Tree, and a dot will appear in the GIS View to show the location of the Pressure Vessel. In the Study Tree, rename the node to Chlorine, Saturated 10 degC.

Setting the input data for the vessel The Pressure Vessel node will have a red error icon at the top left, indicating 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 in the dialog to open the online Help if you want further information at any point.

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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? box 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 below. When you move the cursor away from the Temperature field the program will calculate the saturation pressure for this temperature and display it in the Pressure field.

To define the process conditions for a material that is not held under saturation conditions (e.g. a gas or a padded liquid), you must set the Specified condition to Pressure/temperature and give values for both. After you have set the storage conditions, the Phase to be released will be set to Liquid, which is the default value.

The Geometry tab section Set the East co-ordinate to 198492 m, and the North co-ordinate to 435063 m.

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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 very 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.

East Co-ordinate

198492 m

North Co-ordinate

435063 m

Geometry

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 insert a Catastrophic rupture Scenario using either the rightclick menu or the Insert gallery in the Home tab of the Ribbon Bar. 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 (i.e.their location) 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.

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Setting the input data The node will be shown as incomplete when you insert it. Most of the fields take default values from the Pressure Vessel, but the frequency for the rupture event must be set directly at the Scenario level. For this tutorial, you will edit the Scenario, complete the input data, 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.

Event frequency in Risk tab section Move to the Risk tab and enter a value of 1E-5 /AvgeYear in the Event frequency field. You can use scientific notion when entering values. The other fields in the tab section are all disabled for this Scenario because they are not applicable to a material that has only toxic properties and no flammable properties. Finally, click on OK to close the dialog.

Run the calculations for the Scenario and view the results Select the Scenario in the Study Tree and select Run from the Home tab of the Ribbon Bar. This will run the consequence calculations for the Scenario, for each of the three Weathers in the Day Weathers folder. The calculations run the Weathers for day because the Day Run Row is currently selected as the active Run Row.

Viewing the set of Graphs When the calculations are complete, view the graphs for all of the Weathers. To do this, select the Scenario, then click on the Graphs option in the Home tab of the Ribbon Bar, and select all three Weathers in the Results Selection dialog. You will see that there is no Pool Vaporisation tab in the Graphs View, which means that the liquid in the release did not rain out; if you want more information about the behaviour of the liquid droplets in the cloud, you should view either the Commentary Report or the Dispersion Report. 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.

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The Lethality graph shows that the greatest downwind effect distance is for the 1.5 m/s D weather outdoors, with a distance of about 2.4 km to a lethality level of 10%. The indoor effects for this weather reach about 2.0 km to 10% lethality. The shortest downwind effect distances are for 3 m/s B indoors, which reaches about 1.2 km for a lethality level of 10%.

Viewing outdoor toxic lethality results against the map Select the Catastrophic Rupture Scenario in the Study Tree, and then click on the GIS button in the Home tab of the Ribbon Bar. A Results Selection dialog will appear, as when you view Graphs. Make sure that all of the Weathers are in the Selected items list, and click on Finish to proceed. After a pause a GIS Results View will open, appearing as a separate tab in the Document View area. GIS Results Views display effect 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 effects that are available for the Scenarios and Weathers included in the current GIS View, and you use this list to view a different type of effect. For this tutorial, select Toxic Outdoor Lethality Footprint, as shown.

If a Graphs View or GIS Results View is displaying results for a single Scenario and Weather, it will display results for more than one effect level when it first opens (e.g. it will have separate contours for 0.1%, 1% and 10% lethality). However, if it is displaying results for multiple Scenarios or Weathers, it will display results for a single effect level when it first opens. The effect levels of interest are defined in the Toxic Parameters tab of an Equipment item and a Scenario. 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 by default. To view the lethality contours for a different level, click on the Edit Settings button in the Consequence tab of the Ribbon Bar to open the Edit Settings dialog. 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.

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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, as shown. 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 will be different for each Weather.

Note: the Edit Settings dialog also allows you to change the number of effect levels to display. By default this is initially set for one to multiple Scenarios or Weathers, but you can change this 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 oneinch 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 in Safeti 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 timevarying 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 Time-varying Scenario, select the Pressure Vessel and insert a Time varying short pipe release using either the right-click menu or the Insert gallery in the Home tab of the Ribbon Bar. Name the Scenario Line rupture, liquid.

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Setting the input data for the Scenario The new Scenario will be shown as incomplete. This type of Scenario has mandatory input data for the consequence calculations, in addition to the mandatory event frequency field. 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 internal 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 internal diameter is 1 inch, and the easiest way to set this is to type “1 in” in the input field and press [Tab]. The program recognises “in” as a defined unit for length, and will convert it to the default display units of mm when you press [Tab] or click in a different field. The Scenario tab includes the Outdoor release direction field, which you should leave with the default value of Horizontal, which is the correct setting for this type of unobstructed rupture of horizontal pipework. The list of directions includes a second horizontal option: Horizontal Impingement. You should select this option if the release is in a congested area and the release is likely to impinge on a wall or other equipment; the program will reduce the momentum of the release, which will reduce the amount of air mixed into the jet during the initial stages.

Risk tab section Set the Event frequency to 1E-5 /AvgeYear, i.e. the same value as for the rupture. For pipework failures, the frequency represents a specific length of pipework, e.g. the length between the sphere and an isolation value.

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. Leave the tab section with these values. You will perform an initial run of the discharge calculations, then examine the results and decide on the most appropriate way to represent the behaviour for the rest of the consequence analysis, which may involve changing these settings. This completes the input data for this stage, and you can click on OK to close the input dialog.

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Supplying the tank shape data for the Pressure Vessel The settings described above will complete the mandatory input data for the Scenario, but when you close the dialog, you will find that the Pressure vessel node is now shown as incomplete in the Study Tree. If you hover the mouse over the error icon

for the Pressure vessel node, a tooltip will appear

saying that the data are incomplete. If you have any Time varying Scenarios present under a particular Equipment item, you will need to define the shape of the item, and additional fields will become mandatory in the Equipment item dialog. Open the input dialog for the Pressure Vessel again and move to the Time varying releases tab. Set the Tank shape 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 then display the results in the Inventory data section at the bottom of the tab section.

This is the only change you need to make to the Pressure vessel data, so you can click on OK to close the dialog.

Running the discharge calculations Before you run the calculations, use the Mode option in the Home tab of the Ribbon Bar to change the run mode from Risk to Discharge. With this setting, the program will run the discharge calculations only, and will not then proceed to the dispersion and effects calculations. Select the time-varying Scenario and then click on Run to perform the calculations. For some Scenarios the time-varying discharge calculations can be time-consuming, but for this Scenario they should run in a matter of seconds. When the results are complete, view the reports and move to the TV Discharge Report in the Pressure and Atmospheric Vessel group. 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.

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If the time-varying discharge calculations for a Scenario are time-consuming, you can make the analysis easier to work with if you bypass the time-varying discharge modelling for the hazardous event. There are two possibilities in this situation:

Using 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 option from the bottom of the right-click menu as shown. There is a separate Create source option for each Weather for which you performed the discharge calculations. For this Scenario, the results will be the same for all Weathers, and when you select the Weather the program will create a User-defined source Scenario with the name User defined source for Category 1.5/F . The dialog for the User-defined source Scenario does not include the Short pipe or Time varying release tab sections, and instead of containing fields for the pipe diameter and length, the Scenario tab section contains a Release segments table in which you specify the discharge rate and conditions directly, since the User-defined source Scenario does not perform any discharge modelling itself. The Scenario will be created with discharge data taken from the averaged results from the Time varying Scenario, but you can edit these values if you choose.

Inserting 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.

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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 internal diameter

25.4 mm

Pipe length

9m

Elevation

0.1 m

Tank head

4.6 m

Material

Phase to be released

Liquid

Short pipe

Frequency of bends in pipe

0.11 per m

You will see that there is no Risk tab in the dialog. This is because the Mode is set to Discharge instead of Risk. When the Mode is set to either Discharge or Consequence, the input dialogs only include the fields that are used in the consequence calculations, and the fields that are specific to the risk calculations do not appear. To complete the full data for the Scenario, change the Mode to Risk, and then open the dialog again, move to the Risk tab, and set the Event frequency to 1E-5 /AvgeYear.

Run the consequence calculations for the Short pipe and view the results Select the short pipe Scenario and select Run. 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, and the formation and behaviour of the pool will have an effect on the dispersion and on the toxic effects. In the Toxic Lethality graph, the greatest effect distances are for the 1.5 m/s D weather outdoors, with a distance of about 500 m to a lethality level of 10%, which is approximately a fifth of the distance reached by the catastrophic rupture. The least stable condition, 3 m/s, B, reaches only about 220 m for 10% lethality outdoors. If you open a GIS Results View for all three Weathers and view the Toxic Outdoor Lethality Footprint, you will see that the effects for 0.1% lethality do not reach the village or the town.

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Defining the third scenario: toxic vapour from pipework The vapour release is the rupture of a two-inch pipe attached to the top of the sphere. The line runs 3.4 m horizontally, then vertically downwards, and the rupture is assumed to occur 1 m from the ground. Create the Scenario as a copy of the Line rupture, liquid Scenario, rename the copy to Line rupture, vapour, and change the input data as follows: Tab Section

Input Field

Value

Scenario

Pipe internal diameter

50.8 mm

Pipe length

13 m

Elevation

1m

Outdoor release direction

Down – impinging on the ground

Risk

Event frequency

1E-5 /AvgeYear

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 geographical co-ordinates for the vessel.

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 the mass for the inventory, and then displays the changed values in the dialog.

Changing the coordinates In the Geometry tab, set the new location as shown in the illustration. After changing each value you should press [Enter] to “commit” the changed value. This completes the work on the input data, and you can OK the dialog.

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

Running the consequence calculations and viewing the results Select the Propane Equipment node and run the calculations for all three Scenarios. You can view the results for all three Scenarios at the same time, as long as you view the results for the same single Weather for all Scenarios. To do this, move to the Weathers tab of the Study Tree, select the Category 1.5/D Weather, and then click on the Graphs option in the Home tab of the Ribbon Bar. In the Results selection dialog that appears, check the box next to the propane Equipment item to select all of the propane Scenarios for plotting, click on the right arrow to move the items to the Selected items list, and then click Finish to view the Graphs. The Graph View will contains tab sections for Concentration graphs, as with the toxic Models, but it will contain Jet fire, Fireball, Pool Fire, Explosions and Flash Fire tab sections instead of the Toxic tab section. The main features of the graphs are described below.

Jet Fire Graphs The Jet Fire tab section contains three graphs, which are presenting results for the two pipework failures. The first graph shows radiation level versus distance, the second shows Intensity Radii to the lowest of the three default radiation levels set in the input data (4 kW/m2), and the third graph shows Lethality Radii to a lethality level of 100%. The maximum downwind effect distance shown in these graphs is around 34 m, which is the distance for 4 kW/m2 for the liquid line rupture release. If a given Fire Radii graph is showing results for more than one Scenario or more than one Weather, then it will initially only be displaying results for a single level, which will be the lowest level set for that type of result (e.g. the lowest intensity level, or the lowest lethality level). This is different from a graph for a single Scenario and Weather, which will initially always display results for all available levels. To see results for additional Fire Radii levels, click on Series… in the Configuration tab of the Ribbon Bar to open the Edit Series Properties dialog as shown. This dialog lists each of the available level-results for each Scenario, and you can check the boxes for additional levels to include them in the graph.

Pool Fire Graphs There are two sets of Pool Fire Graphs: a set for the early pool fire, which is modelled for a continuous release only and occurs at the beginning of the release, at the time when the spill rate into the pool equals the fire burn rate, and a set for the late pool fire, which occurs at a time when the pool has reached its maximum radius. Each set contains three graphs, as with the jet fire graphs. The pool fire graphs are showing results only for the liquid line rupture release, as this is the only Scenario that gives rainout, and this means that the two Radii graphs will initially be showing the results for more than one level. The maximum downwind effect distance is about 28 m, to a radiation level of 4 kW/m2 for late pool fire, and the distance to a.lethality level of 1% is about 21 m.

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Fireball Graphs The Fireball tab section also contains three graphs. These are showing results only for the rupture, and this means that the two Radii graphs will initially be showing the results for more than one level. The maximum downwind effect distance is about 600 m, to a radiation level of 4 kW/m2, and the distance to a .lethality level of 1% is about 290 m.

Explosion Graphs The two Early Explosion graphs contain results only for the Rupture, since immediate explosions are assumed not to occur for continuous releases. However, the Late Explosion graphs contain results for all three Scenarios. The Late Explosion Worst Case graph shows the effect radii for the explosion-time which gives the greatest downwind distance for the lowest overpressure set in the parameters (0.02 bar). The greatest downwind effect distance is about 1,500 m, for the Rupture. As stated earlier, the explosion effect distances that are presented in the consequence results are not the values that are used in the risk calculations. The explosion modelling performed during the risk calculations is different: the method used depends on the setting for the Explosion method option in the Settings tab of the Ribbon Bar. The results for this modelling are part of the Risk Results, and are not included in any of the consequence results.

Flash Fire Graph The Flash Fire Graph shows the zone for the cloud at the time that it covers the maximum area. For the rupture, this gives a maximum downwind effect distance of 400 m to 10,000 ppm, whereas for the two pipework releases this gives a distance of about 80 m to the same concentration. 10,000 ppm is 50% of the LFL, which is the fraction set by default in the Flammable Parameters as the boundary of the flash fire effect zone.

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Defining toxic releases from a rail tank wagon This section is not relevant to Safeti Lite. It involves the use of the Route Model, which is not available in Safeti Lite. The chlorine is delivered to the facility by tank wagon from a marshalling yard 10 km to the north. The deliveries take place once a week, involving two tank wagons, and are always during the day and never at night. The wagons are 10.6 m in length, 2.6 m in diameter with a volume of 54 m3, are raised 0.5 m above the ground, and are delivered with a fill-level of 80%. The chlorine is under the same conditions as in the sphere: under saturation conditions at atmospheric temperature (taken as 10oC). There are many hazardous events that could be modelled for the tank wagons, including leaks during the unloading process. This tutorial will consider only releases that occur while the tank wagons are in transit inside the site. The railway track inside the site runs from the northern corner along the east side of the site to the unloading point 100 m to the north of the chlorine sphere. The releases that will be modelled are a rupture, a one-inch leak from the liquid side of the tank wagon, and a one-inch leak from the vapour side.

Inserting a Route Model The hazardous events may occur at any point along this track, and the program contains a special Model called the Route Model

for performing risk calculations for such events.

Select the Study node and insert a Route using either the right-click menu or the Insert gallery in the Home tab of the Ribbon Bar. Rename the Route node Chlorine tank wagon. Each Route Model is created with two folders underneath it, as shown. You use the Scenario group folder to define Equipment items and Scenarios to represent the range of hazardous events that could occur over a given section of the route, and you use the Route segments folder to define the layout of the route in relation to the map and to specify how the sets of representative events should be modelled in the Risk calculations along different parts of the route.

Defining the rupture and leak Scenarios You will define one Pressure Vessel Equipment item under the Scenario group folder, with a Catastrophic rupture Scenario and two Leak Scenarios underneath it.

Copying the existing Chlorine Equipment item A lot of the input data for the existing chlorine Pressure Vessel is applicable to the tank wagon, and you will create the Equipment item for the tank wagon by coping the existing item and pasting it into the Scenario group folder. The leaks from the tank wagon are from the body of the tank wagon and not from pipework. You will use Leak Scenarios to model these releases, so the Line rupture Scenarios are not relevant to the tank wagon and you should delete all of them.

Editing the Equipment item You need to make changes to the Equipment item data for the differences in dimensions between the chlorine sphere and the tank wagon. Open the dialog and change the Volume inventory in the Material tab to 43.2 m3. Notice that the Equipment item dialog does not contain a Geometry tab. For a Route Model, the geographical data are taken from the Route segments data, not from the Equipment item.

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Editing the Catastrophic rupture Scenario Open the dialog for the rupture Scenario and set the following values: Tab Section

Input Field

Value

Scenario

Elevation

1.8 m

Risk

Event probability

0.1

When a Scenario is placed under a Route Model, the Risk tab has an Event probability field instead of the Event frequency field. The Event probability is the relative probability that a release from the tank wagon at a given location on the route is a rupture rather than any other type of hazardous event. For this tutorial it is assumed that 10% of events are ruptures. A frequency for the hazardous event is still required for the risk modelling, but you define this elsewhere in the input data for the Route Model, as you will see later.

Defining the liquid leak Insert a Leak Scenario under the Equipment item, name it Leak, liquid, and set the following values: Tab Section

Input Field

Value

Scenario

Orifice diameter

25.4 mm

Elevation

0.5 m

Tank head

1.95 m

Outdoor release direction

Down – impinging on the ground

Event probability

0.6

Risk

A Leak Scenario will give a larger discharge rate than a Short pipe Scenario since there are no frictional losses during the flow to the leak-location. The leak is assumed to be at the bottom of the tank, which is the most conservative assumption for the tank head and the duration.

Defining the vapour leak Insert a second Leak Scenario, name it Leak, vapour, and set the following values: Tab Section

Input Field

Value

Scenario

Orifice diameter

25.4 mm

Elevation

2.45 m

Outdoor release direction

Angled from horizontal

Outdoor release angle

30 degrees

Risk

Event probability

0.3

Material

Phase to be released

Vapour

The leak is assumed to be just above the liquid level.

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Defining the rail route inside the site The railway track inside the site runs from the northern corner along the east side of the site to the unloading point 100 m to the north of the chlorine sphere.

Drawing the route on the GIS You will define the route by drawing it as a single polyline on the GIS Input View, as follows: 1. Move to the GIS Input View, and use Zoom and Pan options in the General tab of the Ribbon Bar to arrange the view so that the site fills most of the display area. 2. Select the Route segments folder, then insert a segment. 3. Click at the northern corner of the site to place the first point on the route, then click to place each intermediate point, and finally double-click about 100 m to the north of the chlorine sphere as shown to stop drawing the segment. A node named Route segment will be added to the tree. 4. Change the name of the segment node to Track inside site.

Completing the input data for the route segment The input data for a route segment has several mandatory input fields, as shown. You can define any number of Scenario groups under a given Route Model, and you must use the Scenario group dropdown list to select the group that you want to model at each failure location for this route segment. There is only one group for this Route Model, but you must still select it from the list in order to complete the input data. The program will model the same set of hazardous events at regular intervals along the segment, where the interval is set by the value for Spacing of events. You should set the spacing to be less than the minimum effect distance for the group of hazardous events, since this will ensure that the effect zones from adjacent failure-locations overlap, giving the smooth distribution of risk along the route that would be observed in reality. For this tutorial, you should set an initial value of 50 m. After you have run the consequence calculations and assessed the range of effect distances you can adjust this if appropriate. If you find that the spacing that you have chosen is too large, and is producing visible distortions in the risk contour results (e.g. “bumps” in the contours every 50 m), then it may be necessary to reduce the spacing and rerun the calculations.

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In setting the Failure frequency along the segment, you can either specify the total failure frequency for the segment, or give the frequency for a given length, e.g. per km. For this tutorial, set the Failure frequency to 10-5 /AvgeYear, the Failure frequency supplied option to Per supplied length and the Supplied length to 1000 m, as shown.

Running the consequence calculations and viewing the results Select the Scenario group folder and run the calculations. The smallest effect distances are likely to be for the vapour leak as it will have the smallest release rate. If you view the outdoor toxic lethality graphs for this Scenario, you will see that the minimum effect distance to 10% lethality is about 50 m. The value of 50 m that you set for the Spacing of events is therefore of the same order as the smallest significant fatal effect distances, and you can leave the route segment with this value.

Saving the workspace You have now completed the input data for the consequence analysis, and you should save the workspace.

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4

PERFORMING THE RISK CALCULATIONS

For the consequence analysis you were able to work entirely in the Models tab section of the Study Tree, but to perform the risk calculations you will need to make some settings in other parts of the program: •

The Settings tab of the Ribbon Bar You use the Settings tab of the Ribbon Bar to select the method that will be used for modelling explosions in the risk calculations. This setting affects the options available in some other parts o the program.

•

The Weather tab section of the Study Tree You work in the Weather tab section to define wind rose probability data for each set of weather data. The default new Study Folder is supplied with some dummy wind rose data which you will use for this tutorial, but you should always check the data before starting the calculations.

•

The Risk tab section of the Study Tree For this tutorial, you will set up some simple population data for day and night, define an ignition source, and define some risk ranking points in order to obtain details of the contributions to individual risk.

•

The Run row grid Supertab The Day and Night Run Row will have different selections for the Model Playlists and for the Population Playlists. The Model Playlists are different because the chlorine tank wagons only run during the day.

The sections below describe the work for part of the program in turn.

Setting the Explosion method to 2D Damage Zone The Settings tab of the Ribbon Bar includes an Explosion method option as shown. Thie option gives a choice of methods for modelling explosions in the risk calculations. This option will be set to 3D Cloud ME/Purple Book Explosions when you create a new workspace, but for this tutorial you should set it to 2D Damage Zone. This is a simple method, which was the only method available in early versions of the program. The Contents tab of the online Help includes the topic “The different explosion methods available”. This gives a summary of the differences between the methods.

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Viewing the wind rose data for the Weather folders In the Weather tab of the Study Tree, open the dialog for the Day Weathers folder as shown. There is a table at the bottom of the dialog with a column for each wind direction and a row for each Weather, and with a probability for each combination. The dialog shows the windrose diagram for the current values for the probabilities, as shown.

In the new workspace, the wind rose data are dummy data, with the same probability set for each weather. The 3/B Weather has a full set of data because you set it up by editing the existing 1.5/F Weather, but if you had inserted B 3m/s as a new, blank weather, the probabilities would initially have been set to zero. You do not need to make any changes for this tutorial so can click on Cancel to close the dialog.

Setting up the population data For this tutorial, the information for residential population is assumed to be taken from census data, and the census-numbers are assumed to describe the situation at night-time, when all of the people are at home. You will set up the night population first, as the “base” population, and then later copy and modify it for day.

Defining the night population data Move to the Risk tab section of the Study Tree, insert a folder under the Populations node, and name the folder Night population. For this tutorial, you will only define population around The Village, to the east and south of the site. You will define the population nearest to the facility in some detail, identifying individual houses or groups of houses, but represent the main village, further from the site, with a single shape.

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Drawing the shapes Draw all of the shapes first, as shown in the table below. The exact location and shape are not important for this tutorial. Name

Description

Type of shape

Four nearest

The group of four houses nearest to the site

Rectangle

West house

The house immediately to the east of the four houses

Rectangle

East house

The house further to the east of the four houses

Rectangle

The street of about eight houses immediately to the

Rectangle

Short street

south of West house and East house Long street

The street of about 20 houses to the north-west of

Rectangle

the main town The village

The areas of the village that have a fairly uniform

Polygon

density of buildings Select the Night population folder, then select the appropriate type of population shape from the rightclick menu or the Insert gallery. The techniques for drawing the different types of shapes are as follows: •

To insert a rectangle, click once to place the first corner, click again to place the second corner, and click a third time to place the third corner and finish drawing the shape.

•

To insert a polygon, move around the shape in a consistent direction (i.e. either clockwise or anticlockwise), clicking to insert each corner. Double-click when you have completed the shape, to finish the drawing operation.

To display the name next to a shape, as shown in the illustration below, click on the shape in the GIS View, and then turn on the Label option in the General tab of the Ribbon Bar.

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When the icons for the shapes are added to the Study Tree, you will see that they are all shown as complete. For point shapes, the population will initially be set to zero, whereas for rectangles and polygons it will be greater than zero and proportional to the area of the shape. The program has a default value for population density that is set in the Population preferences dialog - that you open using the Population option in the Settings tab of the Ribbon Bar – and the program uses this density to calculate an initial population value for shapes that have an area.

Using the Grid View to set the population values The Grid View gives the easiest way to set the values for the population. To view the population data in the Grid View, take the following steps: 1. Select the Night population folder in the Study Tree. 2. Move to the Grid View. 3. Click on the Lock icon at the top left of the Grid View to unlock it. When you create a new workspace the Grid View is initially locked and disabled, and you must unlock it if you want to use the Grid View. 4. Select Population from the dropdown list in the Grid View. The Grid View will display all of the populations in the form of a table as shown, allowing you see and review all of the input values. Change the values for Category, Population and Fraction of population indoors to those shown in the table below. You can use copy and paste with the grid, to copy values between cells, and to copy value from Excel into the grid. Name

Category

Population

Fraction of population indoors

Four nearest

Public

10

0.95

West house

Public

4

0.95

East house

Public

4

0.95

Short street

Public

24

0.95

Long street

Public

60

0.95

The village

Public

400

0.8

When you change the Population value for the area shapes, you will see the value for Density change as the program recalculates it based on the new value for Population.

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Defining the day population data For the night population, it was assumed that people were at home for the majority of the time-period. For the day population, you will assume that half of the people are at home, that 40 are at the local school, and that the remainder are at work outside the area. Create a copy of the Night population folder, and name it Day population.

Adding the shape for the school The school is a large building on the south-west outskirts of the village as shown. Select the Day population folder, insert a Population rectangle, and draw the population shape on the GIS Input View. In the Study Tree, rename the population node to The school.

Setting the population values Select the Day population folder, view the Grid, and select Population from the dropdown list to view the seven day populations in the Grid. Set the values as shown in the table below: Name

Category

Population

Fraction of population indoors

Four nearest

Public

5

0.8

West house

Public

2

0.8

East house

Public

2

0.8

Short street

Public

12

0.8

Long street

Public

30

0.8

The village

Public

200

0.75

The school

Vulnerable public

40

0.7

Setting up the ignition source data The pattern of ignition sources might be different for day and night, but for this tutorial you will define a single ignition source, to be used for both day and night. The ignition source is a flare located just inside the north-west corner of the site and to the north of the propane sphere, as shown. Select the Ignitions folder in the Risk tab of the Study Tree, insert an Ignition point and place it on the GIS View, then rename the node to Flare. Then open the dialog and set the input data as shown below.

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Setting up the risk ranking point data This section is not applicable to Safeti Lite because risk ranking points are not available in Safeti Lite. For this tutorial you will define two risk ranking points, as shown by the blue dots in the illustration: 1. At the group of four houses nearest to the boundary of the site. 2. At the village school. Select the Risk ranking points folder in the Risk tab of the Study Tree, insert the two points, placing them in the GIS Input View, and name the nodes Nearest houses and School. Risk ranking points do not have any input data apart from their geographical location. If you find that the population shapes are preventing you from seeing the map image properly when you are placing the risk ranking points, you can hide the population shapes by right-clicking on the Population item in the Map Legend, and then selecting Display Off from the right-click menu. The population shapes have been hidden in the illustration above.

Defining the Models and Populations Playlists for the two Run Rows You have now completed all of the input data in the Study Tree, and the final step is to select the appropriate sets of input data for day and for night. This involves working in the Run row grid Supertab to define Playlists, which are selections of items of input data.

Defining a Models Playlist for the Day Run Row A Models Playlist is a selection of Scenarios. When you click in the Models cell for the Day Run Row, you will see that the cell changes to display a dropdown list and a Playlist Properties icon

.

You use the dropdown list to choose between the Models playlists that have been defined in the workspace. There is currently a single Models Playlist called All. Each type of input data that uses a Playlist always has a Playlist called All defined, and this Playlist is selected by default for the first Run Run row in each new workspace, and for each new Run Row that you add to the grid. The All Playlist always has all relevant items selected (e.g. all Scenarios, or all Populations), and you cannot edit the definition of this Playlist. For this tutorial, you will not use the All Models Playlist for the Day Run Row. The Models tab section of the Study Tree still includes the time-varying line rupture Scenario for the chlorine sphere, which you will keep in the workspace as background information, but this Scenario should not be included in the risk calculations because that would involve double-counting the risk for the line rupture. You will create a new Models Playlist called Day, with all Scenarios selected except the time-varying Scenario.

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To create a new Playlist, click on the Playlist Properties icon

. The Run

row grid will change to displaying the Playlist Editor, as shown. The All Playlist is selected, and this means that all of the Scenarios are in the Selected items list. It also means that the fields in the editor are disabled, as it is not possible to edit an All Playlist. The Day Playlist will be very similar to the All Playlist, with just one Scenario deselected, and this means that the easiest way to create the Day Playlist is as a copy of the All Playlist. To make the copy, click on the Copy icon

above the Selected items list.

The fields in the editor will become enabled as shown, and the name of the new Playlist will be set by default to Copy of All. First, change the name to Day. Next, check the box next to the timevarying Scenario under Chlorine, Saturated 10 degC, and click on the left arrow to remove it from the Selected items list. Finally, click on OK to close the editor and return to the Run Row table. You will see that the selection of Models Playlist for the Day Run Row is now set to Day.

Defining a Models Playlist for the Night Run Row The process is almost identical to the process for defining the Day Playlist: 1. Click on the Models cell for the Night Run Row. 2. Click on the Playlist Properties icon to open the Playlist Editor. 3. Click on the Copy icon to create the new Playlist as a copy of the All Playlist. 4. Set Night as the name of the new Playlist. 5. Deselect the time-varying chlorine Scenario and the chlorine tank wagon Route Model. 6. Click on OK to close the editor and return to the Run Row table.

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Defining the Populations Playlists The workspace also has an All Playlist for Populations, which is currently selected for both Run Rows. Follow the same procedure as described above for the Models Playlists to create separate Day and Night Playlists for populations, with only the appropriate folder of populations selected for each Playlist. You have now completed all of the input settings for the risk calculations, and you should save the workspace before proceeding to run the calculations.

Running the risk calculations and viewing the results To run the calculations, move to the Input Supertab, expand the Run Row Selector, select the All Run Rows node at the top of the list, and click on Run. The calculation should run quickly, i.e. in one or two minutes.

Comparing the Multi-Level Risk Contour Plots for Day and Night The quickest way of viewing the Multi-Level risk contour plot for a particular Run Row is to right-click on the Run Row in the Run Row Selector and select Multi-Level from the list of Risk Results. The Results Selection Wizard dialog will have that Run Row already selected, with all available risk levels and the Outdoor vulnerability also already selected. These settings for risk levels and vulnerability are suitable for the tutorial, so with this method you can immediately click on Finish in the Wizard dialog to view the plot. Use this method to view the Multi-Level contour plot for Day, and then the Multi-Level contour plot for Night. If you “drag” the tab header for the Night plot downwards, you can move it to a separate pane below the Day plot, and compare the two plots sideby-side as shown. For a full description of how to rearrange results views in this way, enter “Views” in the Search tab of the Help Window to see the topic on “Options for working with Views”. You can see that the risk contours are large for night than for day, even though the Day Run Row has additional Scenarios selected. The weather conditions defined for night are more stable than for day, and include the very stable 1.5 m/s F condition that is not modelled for day. Dispersion distances are longer in stable conditions, and this has a noticeable effect on the size of the risk contours. You can see that the risk contours are centred on the chlorine sphere, although there is a small contour centred on the propane sphere.

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Viewing the individual risk ranking results for the school This section is not relevant to Safeti Lite because the risk ranking results are not available in Safeti Lite. The school is only inhabited during the day, so you will view the results for the Day Run Row only. To view the results, take the following steps: 1. Right-click on the Day row in the Run Row Selector and select the Individual Risk Ranking Grid results. 2. Move through all of the screens in the Results Selection Wizard dialog, taking the default selection in all screens except two: In the Risk ranking point selection screen, deselect the Nearest houses point. In the Vulnerabilities selection screen, deselect the Indoor vulnerability. 3. Click on Finish in the final screen to view the results. 4. Expand the grid down to the fourth level, which shows the contributions from individual Scenarios as shown. These results show that 99.95% of the individual risk at the school comes from the rupture of the chlorine sphere. Most of the rest of the risk comes from ruptures of the chlorine tank wagon, with different levels of contribution from different locations along the route (identified by the Location Index). There is some contribution from leaks from the tank wagon, but it is less than 10% of the risk from the rupture of the wagon at the same location.

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Viewing the societal risk results for day, night, and the whole year The FN Curve presents an overview of the societal risk results in a way that makes it easy to compare the level of risk for day and for night separately, and to see the weighted average of the risk levels for the entire year, i.e. for day and night combined.

Setting values for the Combination Factors Before you view these risk results, you must make sure that appropriate values are set for the weighting factors for combining the results for the two run rows. For this tutorial, the following factors will be used: •

Day: 0.4

•

Night: 0.6

When you move to the Combinations Supertab, you will see that there is a single Combination defined, with the name Combination 1. In Safeti the factors will initially be set 1 for Day and 0 for Night, and you must change them to the values given above. When you create a new Safeti workspace, it will have one Combination defined, with a factor of 1 for the initial single Run Row, and when you use the Add button

in the Run row grid to add a new Run Row, that Run Row is created with a

factor of 0. In Safeti Lite, the new workspace is created with the factors of 0.4 and 0.6 already set for the two Run Rows, so you will not need to change the factors for this tutorial. The name Combination 1 is not informative, and you will change the name for this tutorial to 40% Day. To rename the Combination, double-click on the name in the column header. The text will become selected for editing, and you can type the new name. When you have completed these settings, the Combinations Supertab should appear as shown.

Viewing the FN Curve Select FN Curve Smoothed from the Risk gallery in the Home tab of the Ribbon Bar. In the Wizard dialog, select both Run Rows and the Combination, as shown, and then click on Finish.

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The FN Curve shows higher levels of societal risk for night than for day, which is the effect of the greater dispersion distances with the more table weather conditions.

Saving the workspace You have now completed the tutorial. Save the workspace to save the settings you made in the Combinations Supertab, and to save the results.

What next? This tutorial has not covered every feature of the program, but you should now have enough of an understanding of the approach and methods used in the program to be able to explore the remaining features yourself, with the assistance of the Help. In the Contents tab of the Help window, there is a folder called Commonly-used features that gives quick access to details of all of the main features, and you can also use the Index and Search tabs to find help on a particular topic. If you need further details on any aspect of the program, or if you need guidance on how to model a particular situation for your facility, you should contact software support using the details given in the Help tab of the Ribbon Bar.

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