Where Bow-Ties Fit in Risk Management

A bow-tie is a picture of how one hazard could get out of control, what could happen next, and which defences stand in the way. It is one tool among many in risk management. Knowing where it fits stops people using it for the wrong job.

The risk management toolkit

Most organisations that manage serious hazards use several methods together:

• HAZID (hazard identification) — a broad workshop that lists the hazards of a site or project.
• HAZOP (hazard and operability study) — a detailed, line-by-line review of a process design using guide words such as "more pressure" or "no flow".
• Risk matrix and risk register — rank hazards by likelihood and consequence and record them.
• LOPA (layer of protection analysis) — a semi-quantitative check that enough independent protection exists for a specific scenario.
• Bow-tie — a qualitative picture of the barriers for one hazard and one top event, used to manage and communicate those barriers.

Bow-ties do not replace these methods. They draw on them. A HAZID tells you which hazards need a bow-tie. A HAZOP supplies the threats and many of the barriers. LOPA may confirm whether the barriers on a pathway are enough. The bow-tie then turns all this into something a crew, a manager and an auditor can read on one page.

How the course is organised

In this course you first learn where bow-ties come from and how to read them. Then you build each part of the diagram: top event, threats, consequences, barriers and escalation factors. Next you learn to run a bow-tie workshop and check its quality. Then you use bow-ties to manage barrier health and investigate incidents, and apply everything to realistic cases.

Two examples

A gas plant uses HAZOP for its process design, and bow-ties for its ten major accident hazards so that operators know which barriers they own. A construction company uses a risk register for most hazards and bow-ties only for lifting, excavation and work at height, where one failure could kill.