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Root Cause Analysis

August 18 2014

A plant manager walks past the assembly line and notices a puddle of water on the floor. Knowing that the water is a safety hazard, he asks the supervisor to have someone get a mop and clean up the puddle. The plant manager is proud of himself for “fixing” a potential safety problem.

The supervisor, however, is suspicious. He is not sure why the puddle is there. It wasn’t there yesterday. He wonders what caused the puddle to be there today. Therefore, he looks for a root cause by asking ‘why?’ He discovers that the water puddle is caused by a leak in an overhead pipe. He asks ‘why’ again, and discovers that the pipe is leaking because the water pressure is set too high. He asks ‘why?’ again and discovers that the water pressure valve is faulty. He asks ‘why?’ again, and does not get a further answer. The faulty valve is the root cause of the problem. So, the valve is replaced, which solves the symptom of water on the factory floor.

Root cause analysis is a way to identify the ultimate cause of a problem. In the example above, there were many opportunities for solving the wrong problem.

  • The plant manager could have ordered more mops to be available on the factory floor.
  • The supervisor could have ordered that the overhead pipe be replaced.

However, these solutions would ultimately be wasteful and would not have solved the problem since they only addressed symptoms – not the problem itself.

Root cause analysis is usually accomplished by asking a series of ‘why’ questions. Just as the example above illustrates, you ask yourself ‘why’ a problem exists. Then you come up with one or more causes. For each of these causes, ask ‘why’ again. If you can answer that question again, then the first answer is probably a symptom brought on by the more fundamental cause. Continue to ask ‘why’ for each answer until you can no longer generate a logical response. This last answer is likely to be a root cause and is what generates the observed symptoms. You may discover more than one root cause through this analysis.

When you have identified the root cause(s), put an action plan in place to solve the problem. The symptoms should go away as well.

Not every problem has a root cause and root cause analysis is not the right problem-solving technique for all problems. But if you think that there is one underlying cause to your problem, root cause analysis may be the technique for you.