Assign Consequence Values

To obtain the risk for each dispersion case as well as the total risk for all of the simulations run, a consequence value needs to be entered.

 

For the purposes of this tutorial, the consequence entered will be based on the cube root of the mass of the flammable gas cloud for each case. This value can be obtained from the monitor region defined earlier in the tutorial.

 

It is important to add a consequence in addition to the frequency as some leaks could produce very small gas clouds (small consequence) but have a high frequency and thus might not be as applicable to the analysis as a much larger gas cloud (large consequence) with slightly less frequency. This is why consequence is needed for risk-based analyses as risk is calculated by multiplying the frequency by the consequence. These risk results can then be used for gas detector optimizations or other analyses.

 

Before continuing, check that Monitor Region 01 has been updated with the dispersion data by right-clicking its name in the Project Items Tab and selecting 'Regenerate.' If the option does not exist, then the monitor region is up to date.

  1. Open the Gas Cloud Analysis Window, shown below, and ensure that the dispersion cases each have a calculated cloud volume and mass.

     

    Picture 37

    Tutorial 11 - Figure 21 - Gas Cloud Analysis window showing results for the 120 dispersion cases

     

  2. With the monitor region updated, open the Risk Manager by clicking the Picture 38 icon on the toolbar or selecting the option from the Project Menu.

  3. Click the Simulation Summary Tab, currently the Consequence for each case is set to 1 as it has not been defined yet, this is by default. At the bottom left of the window, various Methods can be selected for assigning consequence values. For this example choose By Mass (LFL-100%) and set the Scaling to Cube Root Normalized and ensure the monitor region defined earlier in the project is selected as the Monitor Region.

  4. Click the All checkbox (blue arrow in Figure 22) or press Ctrl+A to select all cases in the Simulation Summary and click the Confirm button (red arrow in Figure 22). This will then update the consequence and risk columns for all the cases in the project. 

 

Tutorial 11 - Figure 22 - Selecting the 'Consequence by Flammable Mass' option to apply to each simulation case

 

With the consequence and risk values for each case updated, the values for the total risk of the simulated cases (on the right side of the Risk Manager) will have updated as well, indicated in Figure 23. Each of the columns in the table below can be sorted to view the cases with highest and lowest frequency or risk.

 

Tutorial 11 - Figure 23 - Updated Risk Manager showing the applied consequence values as well as the calculated risk for the simulations run

 

The frequency, consequence and risk values for each case can be added or edited before or after simulations have calculated. Updating for this information only takes a few seconds. The above actions will not affect the dispersion results but will affect the resulting risk contours.

 

Other options for consequence weighting exists such as:

  1. Un-normalized - useful when comparing risk data sets for large projects containing multiple .ifx files, as it provides a way of comparing risk directly.

  2. Scaled - allows the user to enter a value for the chosen variable (e.g. flammable mass) that will result in a consequence of 1, other cases will be scaled accordingly. The units of te reference will sync with the method chosen, i.e. kg for mass and m3 for volume

  3. Step function - used so that clouds below a certain volume can be removed from consideration.

  4. User-scaling - useful for company-wide or project-wide comparisons of risk data sets, that may exist in different .ifx project files.

 

Close the Risk Manager and continue to the next section to add a contour of a risk data type to the project.