Bow-Tie Analysis: A Practical Guide to Understanding and Managing Risk

What is a Bow Tie Model?

The Bow Tie Model is a visual risk assessment tool used to show how hazards can lead to unwanted events and how barriers prevent or mitigate consequences. It is widely used in Oil & Gas, Chemical Processing, Aviation, Power, and Healthcare to improve process safety and incident prevention.

How Bow Tie Analysis Works

Bow Tie Analysis is applied for risks with high severity outcomes. It illustrates how a threat can trigger a top event, and how consequences unfold if barriers fail.

Bow Tie Methodology

A standard Bow Tie diagram is built using eight steps:

1. Determine the Hazard — Identify the source of potential harm.
2. Identify the Top Event — Define the loss of control over the hazard.
3. Identify Threats — List events that could cause the top event.
4. Evaluate Consequences — Define what happens if the top event occurs.
5. Identify Preventive Barriers — Controls that stop threats from leading to the top event.
6. Identify Recovery Barriers — Controls that reduce or limit consequences.
7. Identify Escalation Factors — Conditions that weaken barrier effectiveness.
8. Identify Escalation Factor Barriers — Measures that protect barrier integrity.

A complete Bow Tie diagram displays threats, top event, consequences, barriers, and escalation factors.

Who Conducts the Study?

A multidisciplinary team typically includes:

• Process / Chemical Engineers
• Operations & Maintenance Personnel
• Instrumentation & Electrical Engineers
• Quality and HSE Representatives

A trained lead facilitator guides the session.

How to Use Bow Tie Risk Assessment

1. Define the event clearly.
2. Plot causes on the left.
3. Plot consequences on the right.
4. Check logical flow and relationships.
5. Assign preventive controls to each cause.
6. Assign mitigation controls to each consequence.
7. Define responsible roles and safety-critical actions.
8. Prioritize safety-critical equipment.

Simple Example

• Hazard: Glass plate stored on a high shelf
• Top Event: Plate falls
• Threat: Shelf gets knocked
• Consequences: Injury, property damage, breakage

Advantages of Bow Tie Assessment

• Systematic hazard analysis
• Helps evaluate adequacy of controls (ALARP)
• Identifies where resources reduce risk most
• Improves awareness and communication

Bow Tie Barrier Model

Barriers exist:

Left side: prevent threats from causing the top event
Right side: mitigate consequences after the top event

Barriers may be procedural, human, technological, or mechanical. Evaluating barrier strength highlights weaknesses and safety improvement needs.

Software

BowTieXP is the most commonly used Bow Tie risk analysis tool.

Deliverables

• Terms of Reference
• Bow Tie Worksheets
• Bow Tie Analysis Report

Applicable Standards

Bow Tie aligns with several recognized standards and guidance documents, including:

ISO Standards

• ISO 31000 — Risk Management
• ISO 45001 — OH&S Management
• ISO/IEC 31010 — Risk Assessment Techniques

CCPS Guidelines

• Hazard Evaluation Procedures
• Risk Based Process Safety

Oil & Gas / Industry Guidance

• IOGP Report 456 — Bow Tie Risk Management
• UK HSE HSG65
• Dutch Standard NTA 8620
• ICAO Safety Management (Aviation)

Conclusion

Bow Tie Analysis provides a clear and intuitive way to understand hazards, causes, consequences, and the effectiveness of safety barriers. It strengthens operational risk management, improves decision-making, and enhances safety performance.

Need a Bow-Tie Analysis for your facility?

iFluids Engineering delivers accurate, detailed, and compliant Bow-Tie Studies for Oil & Gas, Chemical, Power, and Industrial sectors.

Contact us for reliable Bow-Tie Analysis and risk management support.