What is a Bow-Tie Model?
The Bow-Tie Model is a visual risk assessment and risk communication tool used to analyze how specific hazards can lead to critical events and how preventive and mitigative barriers control those risks. It clearly illustrates the relationship between hazards, threats, top events, consequences, and safety barriers.
Bow-Tie Analysis is widely applied across Oil & Gas, Chemical Processing, Power, Aviation, Mining, and Healthcare industries to strengthen process safety, improve risk awareness, and prevent major incidents.
How Does Bow-Tie Analysis Work?
Bow-Tie Analysis is primarily used for high-consequence and major accident hazards (MAH). It represents risk as a sequence of events, starting from a hazard, leading to a top event, and potentially resulting in severe consequences.
The method visualizes:
- What can go wrong
- Why it can go wrong
- How it is prevented
- How consequences are mitigated
This makes Bow-Tie an effective decision-making and barrier management tool.
Bow-Tie Analysis Approach / Methodology
The Bow-Tie diagram focuses on clarity and understanding rather than excessive analytical complexity. Its primary objective is to ensure that hazards and controls are easily understood by all stakeholders.
Fundamental Steps in Bow-Tie Analysis
- Identify the Hazard
Determine the source or condition with the potential to cause harm. - Define the Top Event
Identify the point at which control over the hazard is lost. - Identify Threats
Determine credible scenarios or causes that could trigger the top event. - Evaluate Consequences
Identify potential outcomes following the top event, such as fire, explosion, injury, or environmental damage. - Identify Preventive Barriers
Safeguards that prevent threats from leading to the top event. - Identify Mitigation (Recovery) Barriers
Controls that reduce or limit the severity of consequences after the top event. - Identify Escalation Factors
Conditions that could degrade or reduce the effectiveness of barriers. - Identify Escalation Factor Controls
Measures that prevent or manage escalation factors.
The completed Bow-Tie diagram provides a comprehensive overview of threats, barriers, consequences, and barrier vulnerabilities.
Now with the escalation factors in place, our complete diagram is as follows:
Bow-tie diagram showing threats, barriers, top event, consequences, and escalation factors.
Barrier Performance Assessment
Each identified barrier is further evaluated by:
- Barrier type (engineering, procedural, human, or organizational)
- Supporting management system elements (procedures, standards, training)
- Assigned ownership and responsibility
- Barrier effectiveness and reliability
This allows organizations to understand how risks are controlled and where improvements are required.
Bow-Tie Study Team Composition
A Bow-Tie Analysis is conducted by a multidisciplinary team, typically comprising:
- Design Consultant / Project Manager
- Production / Operations Manager
- Chemical or Process Engineer
- Maintenance Manager
- Electrical Engineer
- Instrumentation Engineer
- Quality Control Engineer
- HSE Representative
A competent and experienced Lead Facilitator is nominated to guide the study and ensure methodological consistency.
How to Use Bow-Tie Risk Assessment
Step-by-Step Process
Step 1:
Define the hazard and top event clearly using simple and understandable language.
Step 2:
Identify and plot all credible threats on the left side of the diagram.
Step 3:
Identify all possible consequences on the right side of the diagram.
Step 4:
Validate the logical flow from threat → top event → consequence.
Step 5:
Identify preventive controls for each threat and assess their effectiveness.
Step 6:
Identify mitigation measures to reduce the severity of consequences.
Step 7:
Define safety-critical actions, responsibilities, and management system support.
Step 8:
Identify safety-critical equipment and prioritize based on functionality, availability, and survivability.
Bow-Tie Risk Analysis Example
A hazard is any source with the potential to cause harm. For example, a glass plate placed on a high shelf is a hazard. If the shelf is struck and the plate falls (top event), it may injure a person or cause property damage (consequences). Preventive and mitigative barriers are identified to control this risk.
Advantages of Bow-Tie Analysis
- Provides a structured and systematic hazard analysis
- Supports ALARP (As Low As Reasonably Practicable) decision-making
- Improves visibility of safety barriers and their effectiveness
- Enhances risk communication and workforce awareness
- Helps prioritize safety investments
What is a Bow-Tie Barrier Model?
Barriers are placed on both sides of the top event:
- Preventive barriers stop threats from causing the top event
- Mitigative barriers reduce the impact of consequences
Barriers may be technical, procedural, or human-based. Evaluating barrier effectiveness helps identify strengths, weaknesses, and improvement actions while linking barriers to the Safety Management System.
Technical Challenge in Bow-Tie Risk Management
Identifying risks alone is insufficient. Risks must be managed, monitored, reviewed, and communicated. Bow-Tie Analysis helps organizations answer critical questions such as:
- Where are the highest risk exposures?
- Are safety barriers adequate and effective?
- Are barriers performing as intended?
Software Requirement
BowTieXP is a widely used and industry-recognized software tool for Bow-Tie risk assessment and barrier management.
Bow-Tie Analysis Deliverables
- Bow-Tie Terms of Reference (ToR)
- Bow-Tie Worksheets
- Bow-Tie Diagrams
- Bow-Tie Analysis Report
Applicable Standards & Guidelines
Bow-Tie Analysis aligns with multiple international standards, including:
ISO Standards
- ISO 31000:2018 – Risk Management
- ISO 45001:2018 – Occupational Health & Safety
- ISO/IEC 31010:2019 – Risk Assessment Techniques
CCPS (AIChE)
- Guidelines for Hazard Evaluation Procedures
- Guidelines for Risk-Based Process Safety
Oil & Gas Industry
- IOGP Report 456 – Bow-Tie Risk Management
- OGP Report 415 – Managing Major Incident Risks
Other Guidance
- ICAO Safety Management Manual
- UK HSE HSG 65
- Dutch Standard NTA 8620
Conclusion
Bow-Tie Analysis is a powerful and visual method for managing operational and process safety risks. By clearly linking hazards, threats, barriers, and consequences, organizations can effectively protect people, assets, and the environment while improving overall safety performance.
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Frequently Asked Questions
Bow Tie Analysis is a visual risk assessment method that shows how hazards can lead to a top event, along with the barriers that prevent or reduce its consequences.
It improves process safety, identifies weak barriers, enhances communication, and supports ALARP decisions.
Bow-Tie XP is the industry’s leading Bow Tie Analysis software.
It improves hazard visibility, enhances risk communication, strengthens barrier management, supports ALARP decisions, and helps prioritize critical controls.
The core steps include:<br>Identify the hazard and top event<br>Identify threats and consequences<br>Define preventive and recovery barriers<br>Evaluate barrier effectiveness and escalation factors
