Do Your Accidents Have Special or Common Cause?

W. Edwards Deming explained a basic concept of manufacturing quality by elaborating on the cause of defects.  He explained that some defects had special cause (i.e., some unusual event caused the defect to happen).  Other defects happened due to causes that are built into the manufacturing processes itself.  He called these common causes. There is a debate among safety professionals these days about whether accidents are caused more by system issues or simply by human error.  The simple fact is that it could be either and that neither is mutually exclusive.  Your organization could be having accidents caused by either or both.  Finding out the cause is critical during accident investigations and making the distinction between common and special causes can be very useful. This dichotomy is less useful for fixing blame than it is for fixing problems.  Special causes alert us to outside forces to guard against in the future.  We can often extend our caution beyond the specific issue to other similar risks or situations.  When a foreign object gets into a product, we can protect against that object but also explore what other objects could find their way into our processes and how they could do so.  When a special outside issue impacts safety, we can use similar reasoning to increase our awareness and precautions against such risks. Common causes can be more difficult to recognize because they hide within our systems and influence other actions and decisions that can directly lead to defects and/or accidents.  However, it is critical to identify them because they will continue to influence risks until we see and address them.  Even what looks like simple human error can be influenced by systems issues.  This is one reason for always asking “why?” to find what may lie beyond worker decisions and actions. Deming left us with a warning about finding out and classifying causes.  He said that blame causes fear and that fear causes the hiding and skewing of information critical to understanding causation.  We should seek first to understand and then take intelligent action based on that understanding. -Terry L. Mathis

Terry L. Mathis is the founder and CEO of ProAct Safety, an international safety and performance excellence firm. He is known for his dynamic presentations in the fields of behavioral and cultural safety, leadership, and operational performance, and is a regular speaker at ASSE, NSC, and numerous company and industry conferences. EHS Today listed Terry as a Safety Guru in ‘The 50 People Who Most Influenced EHS’ in 2010, 2011 and 2012-2013. He has been a frequent contributor to industry magazines for over 15 years and is the coauthor of STEPS to Safety Culture Excellence, 2013, WILEY.