•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.

Note: the Spill Scenario is not available in Phast Lite.

•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: The only scenario available for a Long Pipeline item is a Breach Scenario , which defines the location along the pipe for which a release is to be modelled, and the size of the release.

•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, and the ventilation conditions. 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.

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

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

The Weather tab section

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

performs a separate run of the consequence calculations for each separate weather conditions, giving a set of results that are specific to that Weather.

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

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