Bow-tie diagram

A bow-tie diagram is a graphic tool used to describe an accidental event in terms of its initial causes, ultimate negative consequences, and safety barriers designed to prevent or control the associated hazards. It can be considered as a simplified, linear representation of a fault tree (analyzing the cause of an event) combined with an event tree (analyzing the consequences), although it can maintain the quantitative, probabilistic aspects of the fault and event tree when it is used in the context of quantified risk assessments. The diagram visualizes an unintended event, usually one with the potential to escalate to undesired consequences, with all its credible initiating causes on the left of the event and its ultimate outcomes (such as injury, loss of property, damage to the environment, etc.) on the right. A number of barriers, either hard/engineered or administrative/procedural, are placed on the path from the initiators to the final outcomes. The shape of the diagram resembles a bow tie, after which it is named.

Bow-tie analysis is used to display and communicate information about risks in situations where an event has a range of possible causes and consequences. A bow tie is used when assessing controls to check that each pathway from cause to event and event to consequence has effective controls, and that factors that could cause controls to fail (including management systems failures) are recognized. It can be used proactively to consider potential events and also retrospectively to model events that have already occurred, such as in an accident analysis. The diagram follows the same basic principles as those on which fault tree analysis and event tree analysis are based, but, in being far less complex than these, is attractive as a means of rapidly establishing an overall scope of risk concerns for an organisation, only some few of which may justify those more rigorous and logical methods.

Bow-tie diagrams are used to analyze and manage risk in several industries, such as oil and gas production, the process industries, aviation, and finance.