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 six types of item that you can insert at the Equipment level:

•a Pressure Vessel for modelling releases from pressurised containment

•an Atmospheric Storage Tank for modelling releases from unpressurised containment

•a Standalones item for performing detailed modelling of 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 Warehouse for modelling a fire in a warehouse. The effects of the fire are modelled as a toxic plume which contains a mixture of hydrogen chloride, nitrogen dioxide and sulfur dioxide.

•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.

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.

•Scenarios for a Warehouse: The Scenarios for a Warehouse are known as Fire Scenarios where each Scenario is defined by the fire surface area, the duration, the ventilation conditions, and the relative probability. Each Scenario is represented by its own node in the Study Tree underneath the Warehouse Model and the set of Scenarios is generated automatically after you complete or edit the input data for the Warehouse.

Note: the Section Breach Scenario is not available in Safeti Lite.

You can define any number and combination of Scenarios under any Equipment item.