Common Cause vs. Special Cause

August 09 2015
By: Terry L. Mathis

When defects in product quality occur, we try to determine the cause for the defect. Causes fall into two categories: Special causes (events that are not standard, such as bad raw material or abnormal human failures), and Common Causes (events that can occur due to regular production and procedures, such as a jam or web-break).

Accidents, like defects, also have one of these two causes. Accidents that involve unusual events often have special causes. Preventing the recurrence of special causes can prevent future accidents in this category. However, some accidents are caused by regularly-occurring events that have a low probability of causing an accident. Some of these recurring events can be stopped, and some cannot.

After an organization has made a good effort toward safety, they have often identified and eliminated the majority of their special causes. The remaining accidents are either largely or wholly the result of common causes. These are difficult to deal with because they are so built into the normal work they are not always recognized. Lesson: Don't look for a special cause or scapegoat too long before looking for that low-probability built-in risk that may be the true cause of your accident.






Terry L. Mathis

Terry Mathis, Founder and CEO of ProAct Safety, has served as a consultant and advisor for top organizations the world over. A respected strategist and thought leader, Terry has authored five books, numerous articles, videos and blogs, and is known for his dynamic and engaging presentations. EHS Today has named him one of the '50 People Who Most Influenced EHS' four consecutive times. Business leaders and safety professionals seek Terry's practical insight and unique ability to introduce new perspectives that lead to real change.