Our last two safety moments have discussed some aspects of root cause analysis. The first, Incident Investigation: Words, Words, Words, showed how words mean different things to different people. Hence we will never agree upon a true “root cause”. The second, Root Cause Analysis, developed this theme and suggested that Incident Investigation teams should be composed of people from different disciplines such as Information Technology, Human Resources, Process Engineering and Maintenance. None will identify the true “root cause” (because there is no such thing) but they can all provide valuable insights.
Let’s continue this discussion by quoting the lady who challenged William James with her belief that the earth rested on the back of a turtle. When asked what the turtle itself rested on she reputedly said, “It's no use, Mr. James – it's turtles all the way down.” (Philosophers refer to this as the infinite regress problem.) We see the this line of thinking in in the Why Tree approach to root cause analysis.
- Why did the pump seal fail?
Because the wrong type of seal was installed.
- Why was the wrong type of seal installed?
Because there was a mix-up in the ordering process.
- Why was there a problem with the ordering process?
Because the new enterprise management software was not configured properly.
- Why was the software not configured properly?
Because our equipment specialists were not consulted by the IT department.
- Why were they not consulted?
Because it was assumed that the old ordering system was up to date.
- Why was an unpublished change made to the ordering system? Because . . . . . .
And so on and so on.
A rule of thumb for Why Trees is that you stop at level five — at that point you are starting to come up with some form of root cause. But actually this question/answer process can go on indefinitely, all the way to the formation of the earth. Indeed, if the causes of an incident are pursued for long enough the team will eventually be discussing philosophical, moral, and theological issues to do with human nature. This is obviously absurd; a sensible stopping point is required.
Once more, it must be stressed that the inability to find a true “root cause” is not a sign of failure. The analysis to do with the pump seal, for example, provides useful insights. But there are likely to be many other equally useful insights.
The material in this Safety Moment is taken from Chapter 11 of the book Process Risk and Reliability Management.