Event Investigation Guidelines

• Step Five:  Determine Cause(s)

By now (depending upon the nature of the event and your investigation), you've preserved, gathered, sorted, and analyzed a ton of information. By using the various tools we've provided, you have also identified at least one cause (and likely more).

What's left now is to specifically differentiate between the root and contributing causes. From time to time, you will find that there is more than one root cause. For most events, however, you will be able to determine a single root cause and one or more contributing causes.

A root cause is the most basic cause of a failure or occurrence that, if corrected or eliminated, will preclude repetition of the event. In other words, with the root cause corrected/fixed/eliminated, the event could not possibly happen again.

A contributing cause is a cause in addition to the root cause that might have increased the severity of the event or added additional problems / consequences. The test to determine whether a cause is a contributing cause (vice a root cause) is that while the cause might have provided an opportunity to prevent the event from occurring, it does not provide a credible barrier (in other words, the event could have occurred whether or not the cause was present).

Here's an example to help make this a bit more clear:

Let's pick a very simple event- someone (Fred) slips and falls on a patch of ice as he is leaving the building. During the investigation, the potential causes identified are (1) ice accumulated in the walkway outside the door, and (2) as he stepped out of the building, Fred turned to talk to Sheila, who had called out to him from the parking lot.

Clearly, had Fred not turned to talk to Sheila, he might have been paying more attention and not have slipped on the ice. Is this then a root cause? Clearly not. It is a contributing cause. Why? Because even if Sheila had not been present, Fred still could have slipped on the ice. In other words, while this might have provided an opportunity to prevent the event (Fred not turning to talk with Sheila), its absence does not provide a credible barrier [to slipping on ice].

Note:    In some cases, it is not possible to determine a root cause. In such cases, the root cause is termed, "indeterminate". When you arrive at a conclusion of "indeterminate", you will want to include the following in your documentation:

• Explain the basis for not determining the root cause
• Describe what unavailable information is required to determine the root cause
• Identify what possible additional actions might be needed to determine the root cause
• Identify the potential cause(s)
• Provide documentation to support the stated potential cause(s)