Tripod Beta Analysis in Incident Investigation Training

Tripod Beta Method

The tripod method is a way of conducting incident analysis. It is mostly used for high risk, complex incidents, since it is a very extensive and detailed method. Training is highly recommended when using the tripod method.

A Tripod Beta tree is built in three steps. The first step is to ask the question: ‘what happened?’. All the events that happened in the incident are listed as a chain of events. The next step is to identify the barriers that failed to stop this chain of events. The question that is asked in this step is: ‘How did it happen?’. When all the events and the failed barriers in between are identified, the reason for failure of these barriers is analyzed. The last question for this step is: ‘Why did it happen?’. For each of the failed barriers a causation path is identified.


1. What happened?

First it needs to be identified what happened during the incident; what events occurred. This is the core of the tripod diagram and is represented with three shapes, the head ‘trio’. These three elements are:




The trio can be explained as an AND gate, both the Hazard and the Object need to be present for the Event to occur. The Hazard acts on the Object to change its state or condition that is described as the Event. In a tripod tree there can be multiple trios. Hazards and Objects can form new Events.

2. How did it happen? 


The second step in the tripod analysis is to analyze how the incident could have happened by identifying the failed barriers. The barriers can be placed between the Hazard and the Event and between the Object and the Event. To identify these two types of barriers two questions are asked:

What Barriers should have prevented the exposure to the Hazard?

What Barriers should have protected the Object from the Hazard?

A Barrier is something that should prevented the meeting of an Object and a Hazard. It protects people, assets, environment from the negative consequences of a Hazard. Barriers can have their effect on the Hazard (e.g. insulation) or the Object (e.g. PPE). In a Tripod analysis a Barrier can be qualified as failed, missing or effective.

3. Why did it happen?

The last step is to identify why the incident happened; what caused the Barriers to fail. To analyze this we follow a certain pathway, called the ‘Causation Path’. The causation path consists of three items:

Immediate Cause


Underlying Cause