Bowtie Overview

Bowtie analysis is a barrier-based risk management tool that uses a visual diagram to identify, analyze, and manage high-risk accident scenarios. It provides an overview of accident scenarios and the barriers put in place to either prevent those scenarios from happening or mitigate the consequence. 

Specific to one hazard only, the bowtie method helps manage both the accident risks and the barriers by identifying which barriers are more critical. 

Bowtie diagrams are created for major accident hazards as not all hazards are equal in terms of their potential accident impact. That is why, before you begin making your bowtie diagrams, major accident hazards must be identified. This identification is done by performing PHA (Process Hazard Analysis) studies such as HAZID (Hazard Identification), HAZOP (Hazard and Operability), LOPA (Layers of Protection Analysis), etc., and preparing the major accident hazards list based on the findings of those earlier studies. By prioritizing and focusing on the risks that matter most to your organization, you can distribute resources effectively and address critical areas of concern. 

In IMS SIS Bowties can be created from a HAZOP.

The name “Bowtie” derives from the shape of the diagram, which resembles that traditional type of necktie. It is divided into three parts: the left side, the right side, and the center. The left side of the bowtie represents the causes of the top event, while the right side represents the consequences. The center of the bowtie represents the top event itself. The left and right sides of the Bowtie are larger than the center because many causes can lead to a Top Event, while a Top Event can have many Consequences.The Bowtie diagram together with the HAZOP elements.

The Bowtie diagram depicts the HAZOP elements as follows:

• Left side:
  • Threats: The potential Causes (Initiating Evets) of the Top Event. In IMS we show the Consequence description on the card and when you open the details you will see the relevant Causes (Initiating Events). 
  • Control Barriers: The measures put in place to prevent the threats from causing the Top Event.
• Center:
  • Hazard: The potential source of danger or harm. This is defined in the HAZOP Consequence.
  • Top Event: Event that leads to the loss of control of the hazard. This is defined in the HAZOP Consequence.
• Right side:
  • Conditional Modifiers: Conditions that reduce the probability of occurrence of the final Consequences.
  • Recovery Measures: The measures put in place to mitigate the Consequences if the Top Event and Hazard occurs.
  • Consequences: The potential outcomes of the Top Event and Hazard. The eventual impact on people, assets, community, and environment. This is predefined in Hazard and Effect register.

If the HAZOP Consequence is linked to a LOPA, then the LOPA details will also show in the Bowtie. Below you can see how the LOPA elements align.

Alignment of the LOPA elements in terms of the Bowtie and HAZOP.