Untold trade secrets of bow tie analysis and use

Taking its name from the shape that resembles ties worn by many around the world, bow tie analysis was introduced as a hazard and risk analysis method some 40 years ago. It has attracted much attention in the last two decades.

Tying the bow

Ahmad Hosni is a Safety, Reliability & Environment lead engineer, Hazop (Hazard and Operability) and SIL (Safety Integrity Level) assessment leader, Certified Functional Safety Expert, Certified Fire Protection Specialist , Certified Maintenance & Reliability Professional and TÜV Rheinland FS Eng in Norway. He has just published his second book Untold Trade Secrets of Bowtie Analysis & Use.

“Using bow tie to give a witty and comprehensive presentation of hazards contributed significantly to help recognize bow tie analysis to depict the pathway from the causes of an event to its consequences,” he added. “It can be considered as a simplified representation of a fault tree or success tree (analyzing the cause of an event) and an event tree (analyzing the consequences).”

Bow tie diagrams can be created starting from fault and event trees, but are more often drawn directly by a team in a workshop scenario.

“Bow tie analysis applications range from engineering and design to construction, operation, maintenance, incident investigation and even de-commissioning activities. The method applies to numerous industries and applications ranging from oil, gas, power, nuclear, chemicals, petrochemicals, fertilizers, pharmaceuticals as well as transportation, aviation and biomedical,” Hosni specified.

Hosni explained that some software applications have been developed and some books about bow tie analysis published. He stressed that several standards and engineering practices about safety, risk analysis, assessment and management have been published but not many mentioned the bow tie technique in depth.

Hosni specifically mentioned IEC 31010:2019, Risk management – Risk assessment techniques. This standard defines bow tie analysis as "a diagrammatic way of describing the pathways from sources of risk to outcomes, and of reviewing controls". The standard points out that "bow tie analysis can be used to represent causes and consequences graphically, and show how they are controlled".

Still a lot more to say, and it's in the book

However, Hosni told e-tech, there is a lot more to say, adding that details are to be found in his book, in which he adds reviews of the available relevant literature and illustrates the terminology used.

The book describes in depth how to carry out a bow tie analysis and what its benefits are. Furthermore, it explains case studies and gives practical examples of real major incidents that bow tie analysis could have prevented along with bow tie diagrams for their plants. Examples of such incidents include the Valero Mckee Refinery fire and explosion, and the Tesoro Refinery Fatal Explosion and Fire.

The book shows their timeline and how bow tie analysis could have avoided them. It explains the relation between bow tie analysis and other safety and risk assessment methods, shedding light on the As Low as Reasonably Practicable (ALARP) principle, which generally requires that the level of risk be reduced to ALARP, as well as on the relation with incident investigation.

It also includes lessons drawn from interviews with several practitioners and experts, and is complemented with real and practical experience in design, engineering, modification and support to operation and maintenance of many plants worldwide, etc.

It provides several templates of bow tie diagrams that can be used for many plants and applications.

The book is also very useful for training courses and can be used for many applications including medical and transportation ones. In addition, it gives useful information on how to do efficient bow tie analysis and how to run bow tie analysis workshops.

Graphic representation of bow tie analysis