Unintended Firearms Discharges in Law Enforcement – Principle and Contributory Causes – Part 2 of a 7 part series
Inspector (Ret.) Chris Butler
In Part 1 of our exploration of unintended discharges in law enforcement, we briefly explored the seriousness of this issue. Every year in north American law enforcement officers are experiencing unintended discharges in operational settings. Often these occur during high-stress, rapidly unfolding and complex incidents. The outcome or consequences range from minimal property damage to civilians or fellow officers being injured or killed.
Now in Part 2, we are going to begin to explore how the existing body of research into human factors helps us understand the causes and contributors to unintended discharges – if we understand the causes better, then presumably we can take steps to mitigate against these errors occurring.
In looking at the causes of unintended firearms discharges, aside from mechanical malfunctions already mentioned, one needs to understand that the gun discharges because the user has pulled the trigger. Despite the fact that an officer’s training dictates that the trigger finger be kept outside of the trigger guard and along the frame of the weapon at all times until the decision has been made to fire, officers will sometimes find that their trigger finger has either knowingly or unknowingly slipped inside the trigger guard – and when this happens it is a recipe for disaster.
The amount of force necessary to pull a trigger on the average operational police semi-automatic pistol typically ranges from between 6-12 pounds, depending upon the make and model of the firearm and the type of trigger spring in the weapon. Research by Dr. Roger Enoka (Dept. of Integrative Physiology, University of Colorado) has shown that the hand-grip strength of the average adult male is 125 lbs. The index finger contributes between 30-60% of the force to peak hand-grip strength, depending upon the position of the thumb and the width of the grip. Based upon an average index finger (trigger finger) contribution of 45%, the index finger is capable of exerting an average of 56lbs of force during maximal contraction.
With the average trigger pull weight of only 6-12 lbs to discharge a semi-automatic pistol, it is easy to see, if the trigger finger is inside the trigger guard, how index finger contraction force can immediately cause the trigger to be pulled and why keeping the finger outside of the trigger guard is critical to safe firearms handling.
Why does the trigger finger go inside the trigger guard? If police officers are indoctrinated to keep their trigger finger outside of the trigger guard unless they have made the conscious decision to fire, why are there so many cases of unintended discharges? In shedding light on this important problem, it is first necessary to understand that handguns are designed ergonomically so that when it is picked up and held, the index finger naturally falls directly where the trigger is positioned. It is not contrary to the anatomy of the human hand for the index finger to rest on the trigger, it is completely natural and guns are designed to accommodate this anatomical reality.
The point here is this – guns are intentionally designed for anatomical compatibility for the index finger to naturally rest on the trigger. For an officer to keep his or her finger outside of the trigger guard and straight along the frame of the weapon is not anatomically normal and requires a high degree of training and conditioning for this to reliably occur. What has been discovered is that in high-stress arousal situations, there is a higher possibility of the index finger finding its way inside the trigger guard and when this occurs, it is almost always outside the conscious awareness of the officer because they are focused on the threatening circumstances unfolding in front of them and not paying attention to where their index finger is presently located.
In years of conducting reality-based training and research on officer performance in high-stress environments, I have consistently witnessed officers place their index finger on the trigger of the weapon during the scenario even though they had no intention of firing their weapon. In other words, the officer violated the fundamental rule of firearms safety by placing their finger on the trigger. When interviewed post scenario, these officers almost always have no memory of having put their finger on the trigger and even sometimes will become aggressive in their assertion that they did not. Officers will usually maintain this denial until shown video of the scenario and are faced with the clear objective evidence that their finger was in the trigger guard and on the trigger. I suspect the majority of experienced firearms trainers and reality-based scenario instructors have extensive personal experience of witnessing these same effects in their students.
That’s all the time we have available for today, join me next time as we continue to explore the research that helps us understand the principle causes of unintended discharges. Thanks for stopping by and until next time ‘keep your powder dry!’
 Roger M. Enoka, Ph.D.; “Involuntary Muscle Contractions and the Unintentional Discharge of a Firearm” Law Enforcement Executive Forum; February 2003.