Defining three flammable releases
2. Set the value for Number of input radiation levels to 5, and then press [Tab] to commit this changed value, and update the number of rows in the Radiation
levels table.
3. Drag the triangle made of six dots at the bottom right of the table in order to resize the table within the dialog until you can see the Lethality levels column, and can see the rows for all five levels.
4. Set value of 0.01, 0.1, 0.2, 0.5 and 1, as shown. After entering each value, press [Enter] to commit the value.
Next, repeat these steps in the Jet fire tab section and then in the Pool fire tab section.
The values for radiation lethality levels that you set for the Propane Pressure Vessel will be used in the calculations for all of the Scenarios under the vessel. If you want to set values that will be used for all flammable Scenarios in the analysis, you should set them in the Parameters tab section of the Study Tree instead of in the data for individual Equipment items or Scenarios. In this situation you would need to perform the steps above in the dialogs for three different Parameter nodes: Fireball and BLEVE Blast parameters, the Jet fire parameters, and Pool fire parameters.
This completes the work on the input data, and you can OK the dialog.
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 use the Run option to 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/F Weather, and then click on the Graphs option in the Home tab of the Ribbon Bar.
A Select dialog will appear as shown, showing all of the nodes in the Models tab section, and you can check the box next to the Propane Equipment item to select all of the propane Scenarios for plotting.
When you click on OK, the Graphs View will open. The Graphs 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 1%, which is the lowest of the five lethality levels that you set. The maximum downwind effect distance shown in these graphs is around 32 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
To see results for additional Fire Radii levels, you can 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.
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. There is no ellipse for a lethality level of 100%, because the fireball does not produce the necessary radiation dose at the height of interest.
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), and the legend for the Late Explosion Time graph gives the time at which the worst-case explosion occurs. The greatest downwind effect distance is about 1,150 m, for the Rupture, and it occurs at 9.3 s.
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 70 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.
Alternative methods for modelling early explosions
When you were setting the input data for the flammable Scenarios you left the Flammable tab section with the default settings, which means that the early explosion for the rupture Scenario was modelled with the default method, which is the TNT method.
In this section you will create versions of the rupture Scenario that use the other methods for modelling early explosions, and compare the results.
Creating a Folder and Scenarios for the other methods
Insert a Folder under the Propane Equipment node, and name the Folder Early explosion method.
Select and copy the rupture Scenario for the propane vessel, and then select the Folder and use Paste three times to create three copies of the rupture Scenario inside the Folder.
Name the first copy TNT ground burst, the second copy Multi-energy, and the third copy Baker-Strehlow-Tang.
Setting the inputs for the TNT explosion method
For the TNT ground burst Scenario, move to the Explosion parameters tab section to check the input data for the modelling.
You can leave the Explosion Efficiency with the default value, but for this Scenario you should set the location to Ground burst, which means that you are assuming that the explosion is sufficiently close to
the ground that there will be reflection effects in the pressure waves.
Click on OK to close the dialog for the Scenario.
Setting the inputs for the Multi-Energy explosion method
Open the input dialog for the Multi-energy Scenario, move to the Flammable tab section, and choose Multi-Energy for the Explosion method field.
A Multi Energy tab section will appear in the dialog, and you use this tab section to define up to seven regions of confinement within the cloud and also specify the strength of an explosion in the unconfined regions of the cloud.
By default the number of confined is set to zero, which means that there are no mandatory fields in the tab section and that the Scenario will run even if you do not set any values in the tab section – but it also means that by default the Scenario will not produce any explosion results.
For this tutorial you will define three regions of confinement, each occupying 30% of the volume of the cloud, and with a range of confinement strengths between 6 and 8, as
The strength of an explosion in the unconfined region of the cloud will be 2, as shown.
After setting the Number of confined sources to 3, press [Tab] to update the number of rows in the blast sources table. Press [Enter] after entering each value in the table, to commit the value.
Click on OK to close the dialog for the Scenario.
Setting the inputs for the Baker-Strehlow-Tang explosion method
Open the input dialog for the Baker Strehlow-Tang Scenario, move to the Flammable tab section, and choose Baker Strehlow-Tang for the Explosion method field.
The Baker-Stehlow-Tang tab section will appear in the dialog.
For this tutorial you will not use the default option to supply a value for the speed of the flame (i.e. the Mach number), and instead you will have the program calculate the speed of the flame from other inputs, as shown.
For a propane release you should set the Fuel Reactivity to Medium, and for this release you should set the number of dimensions for the Flame expansion to 2, and the Obstacle density to Medium, as shown.
The release is relatively close to the ground and there is likely to be some reflection of the pressure-waves off the ground, so you should set the Correction for the ground effect to 1.6. Finally, the volume of the cloud assumed to be involved in the explosion is 500 m3.
Click on OK to close the dialog for the Scenario.
Running the calculations and viewing the results
Select the Early explosion method folder, run the calculations, and then view the graphs for the 1.5/F Weather, selecting all Scenarios in the folder.
The Early Explosion Distance graph will initially be showing the Baker-Strehlow-Tang Scenario as giving the highest peak overpressure, of about 1.02 barg, with the pressure declining rapidly with distance, with no effects beyond about 300 m. The TNT ground burst Scenario produces a peak pressure of 1 barg and the pressure declines less rapidly with distance, so the pressure at 300 m is 0.2 barg, and there are effects out to 1,400 m.
For the Multi-energy Scenario, the graph initially shows the results for the unconfined
With the three confined regions strength of 7). It seems reasonable – and simplest - to take the default method as representative for this analysis.