Background

Why REVaRS?

In 1990, psychologist James T. Reason proposed the Swiss Cheese metaphor as an accident causation model. Reason hypothesized that hazards are prevented from causing losses by a series of controls (or barriers). He states that controls/ barriers are never 100% effective. Each barrier has unintended (inconstant) weaknesses, and when these so-called 'holes' line up, a hazard can be released and cause harm. According to Reason, the common causes of the weaknesses in barriers can often be found in the organisation (latent failures) e.g. cost & time cutting on maintenance management can eventually lead to the deterioration of the integrity of many hardware controls within a system. 

James Reason's Swiss Cheese Model

Bowtie diagrams are an application of James Reason's model. A ‘Bowtie’ is a graphical representation of the pathways from the causes of an event (Threats) or risk to its consequences. The diagram is shaped like a bow-tie, creating a clear differentiation between reactive risk management (Right of the Bowtie) and proactive risk management (Left of the Bowtie).

Bowtie Diagram

Bowtie diagrams are typically developed to enable management of major risks via:

• Visualisation of representative major scenarios

• Illustration of barriers that are associated with representative scenarios, at system levels.

This enables the identification of SECEs for the development of performance standards. A key objective of developing Bowties is to ensure that relevant barriers are in place to prevent the realisation of a major accident.

Typically, before commissioning an asset or project, barriers are in the best condition possible. However, during operation, the barrier condition tends to deteriorate. It is not always readily clear how these deteriorations potentially cause holes to develop and line up in various barriers, thereby releasing a major hazard that cause harm.

The Barrier approach to managing major risk offers a way to actively monitor the condition of barriers, through established relation to its comprising elements, i.e., hardware and critical activity elements, and provide an indication of potential hole alignment in various deteriorating barriers, to allow proactive management of major risk.