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About Tripod Beta Method

The Tripod Beta methodology is based on the Swiss Cheese Model and the Human Behaviour Model. Both models are science-based and have their origins in the scientific research of Prof. dr. W.A. Wagenaar & Prof. dr. J.T. Reason for the universities of Leiden & Manchester (1986 - 1990).

Tripod Beta was created to help incident investigators analyse process disturbances (incidents) so that it would allow them to understand the influences on humans from the operational environment (where the risks are) in which the incident occurred. From this understanding, the organisational shortcomings that created this environment can be identified and understood, allowing for improvement actions to business processes.


Tripod Beta Method - Principles


Tripod Beta Incident Analysis is based on the theory that incidents, if not caused by uncontrollable external factors (e.g. meteorites, war), result from underlying causes that are deeply woven into the organization. These underlying causes are responsible for causing incidents of different kinds, at various locations, with other people involved and with varying types of damage or injury. Sooner or later, these underlying causes will cause disruptions of the intended process because they are a hidden part of the organization. However, only a small part of these disruptions will surface as actual incidents, with or without damage or injury.

Tripod Beta Incident Analysis uses incidents to find the underlying causes at system level, which are under management control. The incident investigation report contains the identified underlying causes that played a role in the incident. As a result, management will be able to improve their process control in order to eliminate or minimize these ‘seeds’ in the organization before they lead to other business disruptions.

Tripod Beta Method - trios

A Tripod Beta Incident Analysis results in a Tripod Beta diagram that shows how specific ‘agents of change’ form a threat for certain ‘objects’. Agents of change can cause harm to the objects as a result of an unwanted event, called incidents. A Tripod Beta diagram is a visual representation of the complete process, leading from the reported incident all the way back to the initiation of the intended activity that eventually led to the incident. The element of the diagram at the right-hand side usually describes the incident that people witnessed: a fire, a collision, etc. The unwanted events that took place prior to the final incident are displayed before that (to the left-hand side).


Thus, a Tripod Beta diagram consists of linked 'agent of change-event-object' trios. The diagram is built up from left to right, indicating a timeline. The trio on the left has happened first and going through the diagram towards the right, all elements are described that have led to the final reported incident on the right. The individual agent of change-event-object trios are called AEO trios, the complete series of trios are called the Tripod Beta diagram.

Tripod Beta Method - barriers

Every organizational system is designed to have control measures in place to prevent unwanted process disturbances. And in case these control measures fail, protective measures will prevent or mitigate damage or injury when unwanted events occur. These control and defensive measures are barriers that protect a system against incidents and the consequences.

Tripod Beta Method - causes

A Tripod Beta Incident Analysis creates a logical structure, clearly showing the relations between barriers, immediate causes, preconditions and underlying causes. Regarding the investigated incident, the Tripod Beta Incident Analysis explains which barrier has failed, which precondition has led to a certain substandard act (called ‘immediate cause’ in Tripod Beta) and which underlying cause has caused this precondition. Finally, the underlying causes are categorized in 11 Basic Risk Factors (BRF). Through identification of the Basic Risk Factors that have played a role in this and other incidents, the organization will have a good indication of how to allocate resources to the most vulnerable management areas.

A system containing failed barriers also includes certain preconditions that have led to the ineffectiveness of the barriers. These preconditions can develop when there is a lack of control in the organization where the incident took place. Therefore, these preconditions are the key to the underlying causes that have been present in the system for a more extended period. These underlying causes are responsible for creating different hazardous preconditions that can lead to various substandard acts  (immediate causes resulting in failed barriers) and eventually to different incidents.

Tripod Beta Method - causes (2)
About Tripod Beta

What does a Tripod Beta analysis
intend to tell you?

Tripod Beta Method - full diagram

A full Tripod Beta analysis shows you:

  • The sequence of undesired events (process disturbances) in the intended process;

  • The measures (barriers) that could have controlled the process and mitigated the consequences;

  • The human behaviour involved at operational level;

  • The context, circumstances, perceptions and beliefs that promoted this behaviour;

  • The shortcomings at system-level that influenced the creation of these contexts. In other words ... 'where did the system fail';

  • The actions needed to fix (or at least to improve) the system.

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