Enhance your bowtie diagram with LOPA
LOPA will take your bowtie diagrams to the next level by using concrete quantitative data to evaluate the effectiveness of barriers in preventing or mitigating the top event. It ensures that the risk of the top event and associated consequences is reduced to a tolerable level through sufficient and effective protection layers.
Contents
- Editing Main LOPA Settings Visibility
- Assigning Initiating Frequencies to Threats
- Quantifying Likelihood of Occurrence
- Colour Coding for Barrier Failure Rates
- Comparing Consequences to Target Frequencies
Editing Main LOPA settings visibility
Step 1: Open your bowtie diagram in Bowtie Master.
Step 2: In the Diagram Editor, click on the ‘LOPA’ icon. A small drop-down menu will appear, hit the bottom ‘SETTINGS’ option.
Step 3: In the LOPA Settings pop up, you can edit the view of LOPA within your bowie diagram, showing/hiding frequency figures. Within this tab you can also set both ‘Good’ and ‘Bad’ PFD’s (Probability of Failure on Demand).
Assigning Initiating Frequencies to Threats
Step 1: Select the threat you would like to assign initiating frequencies to, a tab will pop up at the bottom of your bowtie. Within this tab select ‘LOPA’.
Step 2: After selecting ‘LOPA’ a new tab will open, here you can add the ‘initial frequency’ and ‘justification’ to the threat selected. Click the ‘SAVE’ button, you should now be able to see the new value displayed within the element.
Adding PFD (Probability of Failure on Demand) to Each Barrier
Step 1: Select the barrier you would like to assign a PFD value to. A tab will pop up at the bottom of your bowtie. Within this tab select ‘LOPA’.
Step 2: After selecting ‘LOPA’ a new tab will open. Here you can add the (PFD) ‘Probability of Failure on Demand’ and ‘Justification’ to the barrier selected. Click ‘Save’ when filled out.
Note: You do not need to add a justification to have the PFD values shown within your elements, this is just for extra information if necessary.
Quantifying Likelihood of Occurrence
Step 1: Open the LOPA Tab. In the drop-down menu select ‘Settings’.
Step 2: Within the ‘LOPA Settings’ tab set both the ‘Good’ and ‘Bad’ PFD values and turn on ‘Show Frequency’ across all tick boxes.
Step 3: Add your frequency value and any applicable justifications to all threats, barriers and consequences. The frequency value needs to be added to all elements for the top event to be calculated. To add the frequency value and or justification, click on an element and select ‘LOPA’ within the new tab.
Once all values have been filled in the frequency of the top event occurring will be calculated and the green rectangle below the top event will display a value.
Color Coding for Barrier Failure Rates
Step 1: Click on the ‘LOPA’ icon in the Diagram Editor.
Step 2: In the LOPA drop down menu, select ‘Toggle PFD Analysis’.
Step 3: Once selected, your bowtie diagram will enter the ‘Toggle PFD Analysis’. All elements will be coloured according to a traffic light system, based off the value range set for ‘Good’ and ‘Bad’ PFDs within the ‘LOPA Settings’ Tab.
Step 4: To exit ‘Toggle PFD Analysis’ mode, select the ‘LOPA’ button in the top tool bar, from the drop down menu select ‘Toggle PFD Analysis’. The bowtie diagram will revert back to the original colours.
Comparing Consequences to Target Frequencies
Step 1: Click the ‘LOPA’ icon in the Diagram Editor.
Step 2: In the LOPA Dropdown menu, select ‘Sensitivity Analysis’.
Step 3: A new pop up should open titled ‘LOPA Sensitivity Analysis’. Select the ‘+ ADD BARRIER’ button on the left-hand side.
Step 4: You will be taken into a new tab titled ‘Select Barrier’. Select which elements you would like to include within the analysis with the tick boxes presented down the left side. Once you are happy with your selection press ‘SELECT’.
Step 5: You will now enter back into the ‘LOPA Sensitivity Analysis’ tab with a view of the ‘Original PFD’ values. You will be prompted to add the ‘Adjusted PFD’ values. Once added select the ‘ANALYSE’ button on the right-hand side.
Now your bowtie diagram will show both ‘Original PFD’ and ‘Sensitivity PFD’ values on the selected elements. To stop the ‘Sensitivity Analysis’ select the ‘LOPA’ button in the top tool bar, click ‘Sensitivity Analysis’, within this pop up click ‘STOP ANALYSIS’ button.
