LOPA (Layer of Protection Analysis) is a risk assessment method used to evaluate whether sufficient protection layers exist to reduce risk to an acceptable level. 

In BowTiePro, the LOPA module helps users:

LOPA assessments work alongside BowTie diagrams and help provide a more quantitative approach to risk analysis.

What LOPA Does

The LOPA module allows users to:

This helps organizations better understand whether existing safeguards are sufficient.

Key Components of LOPA in BowTiePro

LOPA assessments in BowTiePro are built using several key elements.

Threat Frequency

Threat frequency defines how often a threat or initiating event may occur within a given period.

Example:

Enabling Factors

Enabling factors increase the likelihood of a threat occurring under specific conditions.

Example:

Condition Modifiers

Condition modifiers are additional factors that influence consequence probability or severity. These are applied during LOPA calculations to refine the overall assessment.

Independent Protection Layers (IPLs)

IPLs are safeguards or controls designed to reduce risk independently.

Examples may include:

Each IPL may contain a Probability of Failure on Demand (PFD) value.

Acceptance Criteria

Acceptance criteria define whether calculated risk levels are considered acceptable.

BowTiePro supports configurable criteria such as:

These values help determine whether additional controls are required.

LOPA Results

After all values are configured, BowTiePro calculates:

Results are displayed within the LOPA assessment screens and related hazard views.

Relationship Between BowTie and LOPA

LOPA assessments are linked directly to hazards, threats, and consequences already defined within BowTie diagrams.

This allows users to:

The LOPA (Layer of Protection Analysis) module in BowTiePro allows users to create and manage quantitative risk assessments linked to hazards, threats, and consequences. 

Users can access the LOPA module directly from the main navigation menu.

Accessing the LOPA Module

To access the LOPA module:

  1. Log in to BowTiePro.
  2. From the top navigation menu, click LOPA.

The system will open the LOPA List screen.

Understanding the LOPA List Screen

The LOPA List screen displays all available LOPA assessments for the selected case.

Each row represents a LOPA assessment linked to:

The list helps users quickly review the status of existing LOPA analyses.

Available Filters

The top section of the page contains several filters used to narrow down displayed results.

Case

Select the case containing the required LOPA assessments.

Example:

Location

Filter LOPA items by location.

Users can:

Hazard

Filter assessments by hazard. This helps users quickly locate specific risk scenarios.

Display

The Display filter controls which LOPA items are shown.

Example:

Understanding LOPA Columns

The LOPA list includes several important columns.

Hazard

Displays the linked hazard.

Example:

Threat

Displays the initiating threat associated with the assessment.

Example:

Consequence

Displays the consequence being evaluated.

Examples:

Full LOPA

Indicates whether the assessment is configured as a full LOPA analysis.

Met?

Displays whether the calculated result meets the defined acceptance criteria.

Typical values:

Colour indicators may also be displayed for quick visibility.

Creating a New LOPA Assessment

To create a new assessment:

  1. Click the Create New button.
  2. Configure the required hazard, threat, and consequence information.
  3. Continue building the LOPA assessment.

Detailed configuration steps are covered in later articles.

Viewing Existing LOPA Assessments

Users can open existing LOPA assessments directly from the list.

This allows users to:

BowTiePro allows users to create LOPA (Layer of Protection Analysis) assessments directly from existing hazards, threats, and consequences defined within BowTie diagrams.

Each LOPA assessment is linked to: 

This helps users evaluate whether existing safeguards reduce risk to acceptable levels.

Opening the LOPA Module

To begin:

  1. Log in to BowTiePro.
  2. From the top navigation menu, click LOPA.

The LOPA List screen will open.

Creating a New Assessment

To create a new LOPA assessment:

  1. Click the Create New button.

The system will open the Available Items screen.

Understanding the Available Items Screen

The Available Items screen displays combinations of:

These items are pulled from existing BowTie hazard data.

Users can filter items using:

Selecting a Threat and Consequence

To create a LOPA assessment:

  1. Locate the required threat and consequence combination.
  2. Click the Create button next to the selected item.

BowTiePro will generate a LOPA assessment for that specific scenario.

Opening the LOPA Diagram

After creating the assessment, the system opens the LOPA Diagram view.

The diagram visually displays:

Understanding the LOPA Diagram

The LOPA diagram provides a visual representation of the assessment.

Typical components include:

Threat

The initiating event being analyzed.

Example:

Protection Layers

Independent Protection Layers (IPLs) used to reduce risk.

Examples:

Hazard

The central hazard associated with the scenario.

Example:

Consequence

The outcome being evaluated if safeguards fail.

Example:

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:

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:

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:

Using the Justification Field

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

This helps:

Recommended information to include:

Understanding Enabling Factors

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

Examples include:

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:

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.

Enabling factors in BowTiePro are conditions or circumstances that increase the likelihood of a threat occurring. These factors are linked to threats within a LOPA assessment and help provide more accurate and realistic risk evaluations.

Enabling factors are commonly used to represent:

Adding enabling factors helps organizations better understand the conditions that may contribute to incidents.

Opening the Threat Details Screen

To add enabling factors:

  1. Open the LOPA module from the top navigation menu.
  2. Open an existing LOPA assessment diagram.
  3. Click the small information (i) icon below the threat.
  4. Click Edit from the popup window.

You will be taken to the Threat Details screen.

Adding a New Enabling Factor

Inside the Enabling Factors section:

  1. Click the green Add button.
  2. The Linked Enabling Factor Details screen will open.
  3. Select an enabling factor from the dropdown list.
  4. Enter justification or supporting notes if required.
  5. Click Save.

The enabling factor will now be linked to the selected threat.

Why Enabling Factors Matter

Enabling factors improve the quality of LOPA analysis by identifying additional conditions that may influence threat occurrence.

Benefits include:

Best Practices for Enabling Factors

When adding enabling factors:

Condition modifiers in BowTiePro are factors that influence the likelihood or effectiveness of risk scenarios within a LOPA (Layer of Protection Analysis) assessment.

These modifiers help organizations account for additional operational or environmental conditions that may impact the overall risk calculation.

Condition modifiers are commonly used for:

Using condition modifiers helps create more realistic and accurate LOPA assessments.

Opening the LOPA Diagram

To configure condition modifiers:

  1. Open the LOPA module from the top navigation menu.
  2. Open an existing LOPA assessment.
  3. The LOPA diagram will display:
    • Threats
    • Controls
    • Hazard
    • Consequences

Opening the LOPA Control Details Screen

Condition modifiers are configured through the control/barrier settings.

To open the control details:

  1. Click the small information (i) icon below a control/barrier.
  2. A barrier information popup will appear.
  3. Click Edit.

You will be redirected to the LOPA Control Details screen.

Configuring Control Values and Modifiers

Inside the LOPA Control Details screen, you can configure how the control behaves within the LOPA calculation.

Available configuration options include:

These values influence the effectiveness of the control and contribute to the final LOPA calculation results.

After entering the required values:

  1. Review the configuration carefully.
  2. Enter supporting justification if needed.
  3. Click Save.

Understanding PFD in Condition Calculations

PFD (Probability of Failure on Demand) represents the likelihood that a control or safeguard may fail when required.

Lower PFD values indicate stronger and more reliable safeguards, while higher values indicate weaker protection layers.

Accurate PFD values are important for:

Best Practices for Condition Modifiers

When configuring condition modifiers and control values:

In BowTiePro LOPA assessments, controls are assigned PFD (Probability of Failure on Demand) values to calculate how effective a safeguard is at reducing risk.

PFD values represent the likelihood that a control may fail when required during a hazardous event.

Accurate PFD values are essential for:

Opening the LOPA Diagram

To configure control PFD values:

  1. Open the LOPA module from the top navigation menu.
  2. Open an existing LOPA assessment.
  3. The LOPA diagram will display:
    • Threats
    • Controls/barriers
    • Hazard
    • Consequences

Opening the LOPA Control Details Screen

PFD values are configured within the control settings.

To open the control details:

  1. Click the small information (i) icon below a control/barrier.
  2. A barrier information popup will appear.
  3. Click Edit.

You will be redirected to the LOPA Control Details screen.

Configuring the PFD Value

Inside the LOPA Control Details screen, locate the Define PFD field.

To configure the value:

  1. Ensure Use In Calculation is enabled.
  2. Select the required Calculation Type.
  3. Enter the desired PFD value in the Define PFD field.
  4. Add justification or supporting notes if required.
  5. Click Save.

The configured PFD value will now be used in the LOPA calculation process.

 

Understanding PFD Values

PFD values determine how reliable a control is during demand situations.

General interpretation:

For example:

Organizations should use validated engineering or operational data when assigning PFD values.

Best Practices for Configuring PFD Values

When configuring PFD values:

Why Accurate PFD Values Matter

Incorrect PFD values can lead to:

Properly maintained PFD values improve both safety and compliance.

In BowTiePro LOPA assessments, the overall consequence value represents the final calculated risk associated with a specific consequence after considering threats, controls, enabling factors, and condition modifiers.

This value helps users understand whether the remaining risk level is acceptable or if additional protection layers are required.

Viewing Consequence Values

To review consequence values:

  1. Open the LOPA module.
  2. Open an existing LOPA assessment.
  3. Navigate to the LOPA Details page.
  4. Scroll down to the Consequence section.

The consequence section displays the consequence linked to the selected threat and top event.

Understanding How Consequence Values Are Determined

The final consequence value is influenced by several elements within the LOPA assessment, including:

BowTiePro combines these values to determine the remaining risk level after safeguards are applied.

Reviewing Threat and Consequence Controls

Controls directly affect the calculated risk value.

Threat controls reduce the likelihood of the event occurring, while consequence controls reduce the severity or impact after the event occurs.

Each control can include:

Understanding the Final Result

The overall consequence value helps users determine whether:

The value is continuously updated based on the inputs configured throughout the assessment.

Viewing Consequences in the LOPA Diagram

Users can also visually review consequences directly within the LOPA diagram.

The diagram provides a simplified visual representation of:

This helps users better understand how each protection layer contributes to overall risk reduction.

Best Practices

When reviewing overall consequence values:

Accurate configuration ensures more reliable LOPA calculations and better risk management decisions.

After configuring threats, controls, enabling factors, and condition modifiers, BowTiePro calculates the final Layer of Protection Analysis (LOPA) results.

These results help users determine whether existing safeguards reduce risk to acceptable levels.

Viewing LOPA Results

To review LOPA results:

  1. Open the LOPA module.
  2. Select an existing LOPA assessment.
  3. Review the assessment list and detailed analysis screens.

The LOPA List page provides a quick overview of all assessments, including:

Understanding the “Met?” Status

The Met? column indicates whether the calculated risk level meets the configured acceptance criteria.

Possible outcomes include:

A “No” result typically indicates that:

Reviewing the LOPA Diagram

Users can visually review the assessment using the LOPA diagram.

The diagram displays:

This visual representation helps users understand how each safeguard contributes to risk reduction.

Reviewing Detailed LOPA Information

Detailed calculation-related information is available within the LOPA Details page.

The details page includes:

This information is used by BowTiePro to calculate the final assessment result.

Understanding Risk Reduction

LOPA calculations evaluate how effectively controls reduce the likelihood or impact of hazardous events.

Risk reduction is influenced by:

Higher-quality and independent safeguards generally improve overall results.

Using Results for Decision Making

LOPA results help organizations:

Best Practices

When reviewing LOPA results:

Acceptance criteria and Safety Integrity Levels (SIL) are important concepts within Layer of Protection Analysis (LOPA).

BowTiePro uses these concepts to help organizations determine whether existing safeguards reduce risk to acceptable levels.

What Are Acceptance Criteria?

Acceptance criteria define the maximum level of risk considered acceptable for a specific scenario.

Within a LOPA assessment, BowTiePro evaluates whether the calculated residual risk meets these predefined criteria.

If the calculated risk exceeds acceptable limits, additional safeguards or protection layers may be required.

Reviewing Acceptance Status

Users can review acceptance status directly from the LOPA assessment list.

The Met? column indicates whether the scenario satisfies the configured risk acceptance requirements.

Possible results include:

Understanding SIL Levels

SIL (Safety Integrity Level) is a measurement used to evaluate the effectiveness and reliability of safety functions and protection systems.

SIL assessments help determine how much risk reduction is required for hazardous scenarios.

Higher SIL requirements generally indicate that stronger or more reliable safeguards are needed.

How BowTiePro Supports SIL-Related Analysis

BowTiePro uses LOPA calculations to help users understand whether current safeguards provide sufficient protection.

The assessment considers:

These elements collectively contribute to overall risk reduction.

Reviewing Risk Reduction in the LOPA Diagram

The LOPA diagram provides a visual representation of how controls reduce risk between threats and consequences.

The diagram helps users identify:

Reviewing Detailed Assessment Information

Detailed LOPA calculation information is available within the LOPA Details page.

The details page includes:

This information supports risk evaluation and SIL-related decision making.

Understanding “Met” and “Not Met”

A scenario marked as Met generally indicates that:

A scenario marked as Not Met may indicate that:

Best Practices

When evaluating acceptance criteria and SIL-related assessments:

Properly configured LOPA assessments help organizations improve safety, strengthen risk management, and support informed operational decisions.

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