Unintended Firearms Discharges in Law Enforcement – Principle and Contributory Causes; Part 5 of 7

Inspector (Ret) Chris Butler

Welcome back to our study into the causes of unintended discharges in law enforcement. If you have been reading along as we have explored this issue, you will recall that in Part  we took a look at the research into the human factors regarding how a sudden loss of balance can be catastrophic for an officer if his or her finger is inside the trigger guard. Also, we explored how a sudden loss of balance causes a rapid and unavoidable contraction of the muscles of the hand. If you have missed the previous articles on this subject, its important to take the time to review them as I am building upon concepts as we move along in this series.

This week, we are going to continue to wade through the science and research that pertain directly to the human factors that lead to unintended discharges.

I want to remind you that what the research on human error tells us, is that the higher an officers stress arousal, the urgency of the need to respond and the speed with which the incident is occurring, all exacerbate the risk of an unintended discharge occurring.

At the end of this series, we will briefly examine the importance of high-fidelity context-based training which the research tells us, greatly improves performance and reduces the chances of these tragic human errors occurring. But that’s for later. This week we are going to take another deep dive into the science and research behind biomechanics and decision errors – I know your up for the challenge!

Remember last week, I warned you that we were going to explore how ‘hand confusion’ contribute to unintended discharges.

Unintended Firearm Discharge – Involuntary Muscle Contraction Caused by Hand Confusion

Another possible cause of involuntary muscle contraction which might result in the trigger being inadvertently depressed, is an issue known as ‘hand confusion’. Research into how the brain makes sense of which limb is which (right or left) and where they are located in space and time, originated with Van Riper (1935)[1]. A substantial body of subsequent research continues to build upon this early work and support the theory that the coordination of the limbs (proprioception) involves the use of both the visual cortex and ‘body schema’ called somatropic coordinates. The overall ability of the brain to use various perceptions to determine correct limb location is called a ‘temporal order judgment task’, and it does so constantly and automatically, below the level of conscious awareness.

When a person crosses their hands (placing the right hand where the left hand is normally located and visa versa) the brain often has great difficulty incorrectly assessing which limb is which. Shore, Spry and Spence (2002) determined that when the hands were crossed, reaction time required for the brain to determine the correct limb and activate motor action went from an average of 34 ms in the normal anatomical position to 124 ms in the crossed hand condition. Moreover, it was determined that the error rate increased greatly under conditions of perceived time compression or urgency to respond. In other words, the higher the perceived stress arousal level, the greater the error rate of the brain contracting the muscles on the wrong hand.[2]

More recent research on this brain / limb confusion phenomenon (Hong, Xu, Kang and Tong – 2012) has refined the theory on the source of the hand-reversal brain confusion to be a combination of both the visual cortex (which is heavily involved in aiding the brain to determine which limb is which and where it is in space and time), and the brain map or body schema mentioned above. The researchers found a great degree of impairment on reaction time in the crossed-hands position.[3]

In taking the research into limb confusion and muscle contraction error into the law enforcement realm, it needs to be considered that one of the primary low-light shooting techniques taught to officers is a cross-handed method often called the ‘Harries Technique”[4]

Figure 1 demonstrates the standard Harries flashlight technique. If an officer intends to activate the light switch on the flashlight, it is possible, based upon the scientific research, that hand-confusion could result in the brain activating a contraction of the wrong limb. I.e. pulling the trigger instead of activating the light switch.

While I am not personally aware of unintentional discharges occurring in an operational law enforcement environment as a result of hand-confusion from this crossed-hand shooting method, I have observed unintended discharges in a training environment where officers are conducting high-stress, realistic scenario-based training utilizing this technique.

Figure 1. The Harries Flashlight shooting technique.

My dad used to tell me ‘son, I need to be clear enough so that you not only understand me, but so that you don’t mis-understand me!’ Now its important you do not misunderstand me here. I am not making an argument for the abandonment of the Harries flashlight technique. Truth be told, I have utilized this exact same technique for most of my career. So, I am neither advocating for nor warning against any specific flashlight shooting technique.

However, the vital point that I want you to take away from this week’s study is this – police officers sometimes experience human error in high-stress situations. If we consider that over 75% of officer involved shootings occur in low light or no-light environments, my question is – does the frequency of your training with your firearm represent the types of conditions, that we know from the research, officers will have an officer0involved shooting? Whether you use the Harries flashlight technique, or any other flashlight technique, you need to train frequently, and you need to train hard, hard, hard – under realistic combat conditions. We know from the research this will help you perform well, it will help you to win and it will reduce the chance of an unintended discharge occurring!

That’s all we have time for this week.

Come back next time for Part 6 and we will look at a very nasty and largely uncontrollable human error that causes unintended discharges (and other tragedies) – the ‘slip and capture error’.

Until then, stay alert, take care of yourself and thanks for your service!



[1] Van Riper, C. “An Experimental Study of the Japanese Illusion”, American Journal of Psychology; 1935, 47:252-263.

[2] Shore D, Spry E, Spence C; “Confusing the Brain by Crossing the Hands”, Cognitive Brain Research; June 2002, 14(1): 153-63.

[3] Hong SW, Xu L, Kang MS, Tong F.; “The Hand Reversal Illusion Revisited”, Frontiers in Integrative Neuroscience, Volume 6, Article 83; September 2012

[4] The “Harries” flashlight technique was developed by Michael Harries, USMC, in the 1970’s and gradually became a ‘staple’ in law enforcement low-light shooting techniques.