Bow-tie diagram

Bow-tie diagram
Name	Bow-tie diagram
Type	Risk assessment diagram
Caption	Schematic representation of a bow-tie risk analysis
Invented	1970s–1980s
Inventor	Various safety engineers
Field	Industrial safety, risk management

Bow-tie diagram The bow-tie diagram is a visual risk assessment tool that links potential causes and consequences of a central hazardous event, combining elements of event tree and fault tree analysis to support barrier-based safety management. It is used across British Petroleum, Shell plc, ExxonMobil, Chevron Corporation, TotalEnergies operations and by regulatory bodies such as the International Maritime Organization, Occupational Safety and Health Administration, and European Commission safety programs. Practitioners include engineers from Det Norske Veritas, Lloyd's Register, Bureau Veritas, and academic groups at Imperial College London, Massachusetts Institute of Technology, and Delft University of Technology.

Overview

A bow-tie diagram centers on a hazardous event and maps pathways of threats on the left and consequences on the right, with preventive and mitigative barriers placed between threats and the event and between the event and consequences. The diagram synthesizes methods developed in United Kingdom process safety practice, Norway offshore safety, and United States industrial risk assessment, and is integrated into standards such as ISO 31000 and IEC 61511-aligned workflows used by Shell plc and BP. It supports decision-making by safety managers at BP, Shell plc, ExxonMobil, Chevron Corporation, TotalEnergies, and agencies including the Health and Safety Executive.

History and development

Origins trace to fault tree analysis and event tree analysis work by engineers influenced by studies following incidents like the Piper Alpha disaster and regulatory responses in the United Kingdom and Norway. The technique evolved in the 1970s–1980s through practitioners affiliated with consultancies such as Det Norske Veritas and Lloyd's Register and operators including BP and Shell plc. Adoption accelerated after major industrial accidents investigated by panels including members from National Transportation Safety Board and reports influenced by the European Commission and International Association of Oil & Gas Producers. Academic formalization occurred at institutions such as Technical University of Denmark and Imperial College London, while industry guides emerged from International Association of Oil & Gas Producers and standards bodies like ISO.

Structure and components

Core elements include a central hazardous event, left-side threats, right-side consequences, and intervening barriers and controls. The central event is analogous to nodes in Event tree and Fault tree analyses used by NASA and IEEE researchers; threats parallel initiating events studied by National Aeronautics and Space Administration and U.S. Nuclear Regulatory Commission safety frameworks. Barriers are categorized as preventive or mitigative and mapped alongside organizational elements such as procedures from Occupational Safety and Health Administration guidance, technical systems certified by Lloyd's Register and human factors considerations researched at Massachusetts Institute of Technology and University of Cambridge.

Applications and use cases

Bow-tie diagrams are applied in offshore oil and gas operations by Shell plc and BP, in aviation safety management by Federal Aviation Administration and European Union Aviation Safety Agency, in chemical process safety by DuPont and BASF, and in healthcare risk reduction initiatives promoted by World Health Organization and national agencies like NHS England. Regulators such as Environmental Protection Agency and Health and Safety Executive reference barrier-based analyses for licensing and incident investigation. Industries from mining operators like Rio Tinto to utilities including Duke Energy and EDF adopt the model for emergency planning and resilience assessments.

Methodology and implementation

Implementation commonly follows stages: hazard identification (often using techniques from Hazard and Operability Study practice), selection of a central event, mapping of threats and consequences, identification and verification of barriers, and assignment of performance standards and monitoring protocols per ISO 31000 and IEC 61511. Software tools developed by vendors and consultants such as DNV GL (formerly Det Norske Veritas), ABS Group, and specialist providers integrate bow-tie templates with incident databases used by BP, Shell plc, and research groups at Massachusetts Institute of Technology for quantitative overlay. Training programs are provided by institutions including Imperial College London and professional bodies like Institution of Mechanical Engineers.

Advantages and limitations

Advantages include intuitive visualization embraced by frontline teams at operators like Shell plc and ExxonMobil, suitability for communicating with regulators such as Health and Safety Executive and Occupational Safety and Health Administration, and facilitation of barrier performance management used by BP and TotalEnergies. Limitations noted by researchers at Imperial College London and Delft University of Technology include potential oversimplification compared with probabilistic risk assessment methods used by NASA and U.S. Nuclear Regulatory Commission, challenges in quantifying barrier reliability without data from sources like National Transportation Safety Board and industry incident databases, and risk of checkbox compliance criticized in audits by European Commission panels.

Related models and comparisons

The bow-tie diagram is related to Fault tree analysis, Event tree analysis, Layer of Protection Analysis, and Hazard and Operability Study, and is often compared with probabilistic risk assessment approaches used by NASA, U.S. Nuclear Regulatory Commission, and International Atomic Energy Agency. Comparative studies at Imperial College London and Massachusetts Institute of Technology assess trade-offs between qualitative visualization favored by industry players such as BP and Shell plc and quantitative modeling preferred by regulators like U.S. Nuclear Regulatory Commission and European Commission.

Category:Risk management