Incident Investigation: Rethinking the Chain of Events Analogy

Article on EHS Today By Allan Goldberg on 17 November 2003. It disputes the often used notion that incidents occur due to a 'chain of events' suggesting the logic behind the chain may be its weakest link.

The safety profession often refers to a chain of events and then looks for the weak link as a means of identifying what went wrong that allowed the incident to occur. We then very often go further and identify a specific human error that was made, and the person who made it. That person, and/or what they did or didn't do, is thought of as a weak link in the sense of a "performance" chain. Rigid adherence to this way of thinking can lead to some significant errors in improving safety performance. We can and should avoid them.

There are three main problems that this traditional thinking about the chain of events analogy can lead to:

1. Incidents are not linear sequences and instead multivariable meaning there are many different possible paths to an incident.

2. The "weakest link" approach implies that there is only one "main" cause for a given incident whereas most incidents have multiple causes

3. Looking for the weak link creates a focus on the point of failure which is usually well removed from the best point of control. This leads t overemphasis on behavioral approaches and misses the true root causes.

Every link in a physical chain is in fact only connected to one other on each end. The real world chain of events, however, has many more "options" in terms of inputs and outputs. Breaking a single "link" will not necessarily preclude the end event from occurring.

Human actions are a combination of attitudes, beliefs, moods, training, awareness and many other factors. The point being, we may not respond to a given situation today the same way we did yesterday. The key idea here is that many sets of inputs and outputs are possibilities in incident causation. We must be very careful to avoid thinking about causation in a purely linear manner.

Root causes are likely to apply to a whole series of potential incidents, not just one event. These root causes are in fact the key to prevention of future incidents. And contrary to what all too many people may think, human error is not one of them! Human error itself is a symptom that there are other problems in the management of the work that is taking place. These error problems themselves have root causes. When a worker makes an error or fails to follow a procedure, there are reasons that set up the situation. These are the root causes that must be found.

Avoiding Pitfalls

1. Recognize the multivariable nature of incident causation.

2. Understand the Principle of Multiple Causes.

3. Realize the point of failure and the point of control are not necessarily the same. Seek to understand the problem as part of the overall system, and identify where the system itself can be best controlled.

Andy Brazier