BowTiePro uses Threat Frequency values in LOPA assessments to estimate how often a threat is expected to occur before safeguards and protection layers are applied.

Threat frequency is one of the core components used in LOPA calculations and directly affects the overall risk evaluation of a scenario.

The frequency value works together with:

• Enabling factors
• Condition modifiers
• Independent protection layers (IPLs)
• Probability of Failure on Demand (PFD)

to calculate the final residual risk.

Using accurate threat frequency values helps organizations perform more realistic and reliable risk assessments.

Accessing Threat Frequency Settings

To configure or review a threat frequency value:

1. Open the LOPA module from the top navigation menu.
2. Open an existing LOPA assessment or create a new one.
3. In the LOPA diagram, locate the Threat node on the left side.
4. Click the small information (i) icon below the threat.
5. Click Edit in the popup window.

This opens the Threat Details screen where the threat frequency can be configured.

Understanding Frequency in the LOPA Diagram

The LOPA diagram displays the threat frequency directly beneath the threat node.

Example:

• Frequency: 0

This value represents the estimated number of times the threat may occur annually before safeguards reduce the risk.

The displayed value automatically updates whenever changes are saved in the Threat Details screen.

Editing Threat Frequency

After clicking Edit, the Threat Details screen opens.

The following fields are available:

Field	Description
Threat	Name of the identified threat
Frequency (per year)	Estimated annual occurrence rate of the threat
Justification	Optional explanation for the selected value
Enabling Factors	Additional conditions that increase threat likelihood

Configuring Frequency Values

Enter the estimated occurrence rate in the Frequency (per year) field.

Examples:

Frequency Value	Meaning
1	Expected once every year
0.1	Expected once every 10 years
0.01	Expected once every 100 years

The selected value should ideally be based on:

• Historical incident data
• Industry standards
• Engineering analysis
• Expert judgement
• Operational experience

Using the Justification Field

The Justification field allows users to document why a particular frequency value was selected.

This helps:

• Maintain audit records
• Support compliance reviews
• Improve consistency across assessments
• Provide evidence during risk evaluations

Recommended information to include:

• Data source
• Assumptions
• Reference documents
• Historical observations

Understanding Enabling Factors

Enabling factors are additional conditions that may increase the likelihood of the threat occurring.

Examples include:

• Human error
• Poor maintenance
• Environmental conditions
• Equipment degradation

These factors can be added directly within the Threat Details screen and are included in the overall LOPA calculations.

Saving Threat Frequency Changes

After entering or modifying the threat frequency:

1. Click Save
2. Return to the LOPA diagram
3. Verify the updated frequency is displayed beneath the threat node

The updated value will now be included in the overall LOPA risk calculations.

Best Practices

To improve LOPA accuracy:

• Use evidence-based estimates whenever possible
• Avoid arbitrary values
• Document assumptions in the Justification field
• Review frequency values periodically
• Align calculations with organizational risk standards
• Validate calculations during risk review sessions

Conclusion

Threat frequency is a foundational component of LOPA analysis in BowTiePro. Properly configuring frequency values helps organizations produce more accurate risk calculations and better evaluate whether existing safeguards sufficiently reduce operational risk.

Using realistic values, documented assumptions, and properly configured enabling factors improves the overall reliability of the LOPA assessment process.