Unintended Firearms Discharges in Law Enforcement – Principle and Contributory Causes

Part 6 of 7

Inspector (Ret) Chris Butler

Well welcome back to this week’s study on untended discharges. Last week, in Part 5, we explored the ‘hand confusion’ effect and how the brain can be tricked to confuse one hand with the other. The more exigent the circumstances and the higher the perceived consequences for the officer, the more likely an error of hand confusion can occur – and this can lead to the brain pulling the trigger when the officer intended something completely different to occur.

This week we are going to look at another contributing cause of unintended discharges occurring – the ‘slip and capture error’. We are going back into the science so grab a coffee and concentrate – this is important stuff and I want you to grasp these concepts!

Unintended Firearm Discharge – Muscle Contraction Caused by Slip and Capture Error

Another cause of muscle contraction creating an unintended discharge is a type of human performance error called a ‘Slip and Capture’.

All humans are prone to, and have often experienced, performance errors of one type or another. One of the leading researchers in the world on human error, James Reason, has identified that all human errors fall into two broad categories, ‘Slips and Lapses’ and ‘Mistakes’[1]. Mistakes are almost always categorized as rule or knowledge-based and they occur when we fail to apply a rule, or we misinterpret a situation. A simple example of a mistake would be an officer who misinterprets the movement pattern of an offender as behavior indicative of reaching for, or presenting, a weapon only to later discover the subject was in fact not armed or was reaching for a cell phone. These types of mistakes we call ‘mistake-of-fact’ shootings (which of course in no way implies the shooting may not have been justifiable based upon the context and the officers’ reasonable perceptions).

A slip error by contrast is a ‘skill-based’ performance error. Slip’s occur most frequently when an intended motor action is not performed (slips) but a behavior, usually one that we have performed so many times that we have an automatic or subconscious routine, takes its place (captured). An example of a slip error would be driving to the grocery store on a day off from work only to find that you have made an incorrect turn, or series of turns, to drive to your place of work before you ‘caught’ your error. Or, we have all experienced the phenomenon of renting a vehicle or driving an unfamiliar vehicle and find ourselves automatically reaching for the shift lever on the precise location where it is in our personal vehicle only to realize in the rental vehicle it is in an entirely different location. Or reaching to turn the headlights on in the rental vehicle and the brain activates the switch that comports with that intended outcome in your personal vehicle only to find you have just turned the windshield wipers on.

Reason stated that human ‘slips’ occur even when the intended action proceeds as planned but it is the wrong action to achieve the desired outcome. Another researcher on human error Norman (1983) stated the difference between mistakes and slips this way “If the intention is not appropriate, this is a mistake. If the action is not what was intended, this is a slip”[2]. We are most prone to ‘slip’ errors when our attention is diverted from the task we are performing and/or there is a sense of urgency to complete the task

These types of ‘slip’ errors happen to everyone and they occur frequently. When they do occur, usually the consequences are meaningless; nobody gets injured or killed. But what about human performance errors in critical occupations where such an error may result in serious harm?

Slip and capture errors have been studied as contributory causes to serious tragic events such as airplane accidents, naval accidents, nuclear reactor accidents, search and rescue accidents and offshore drilling accidents. In the medical profession slip and capture errors have been determined to result in medication and surgical errors resulting in serious injury or death. Prior to becoming a police officer, I served six years as a Search and Rescue Technician, specializing in high angle mountain rescue. On one occasion that I will never forget, our rescue team experienced a ‘slip and capture’ error during a rotary wing sling rescue on a vertical mountain face which was nearly catastrophic.

One research report examining medical errors identified that certain errors were caused by ‘action execution slips’ when an automatic activation of a well-learned motor skill over-rides the current intended activity’. An example of this type of slip and capture error in the medical field has been studied with respect to medicine administration errors with infusion pumps (IV) where nurses would press the wrong controls on new infusion pumps because their brains were running the automatic routines learned with use of previous models[3]. Contributing cognitive causes to these errors are associative activation of similar muscle motor programs, failure of memory retrieval of the correct action, cross talk (distraction drawing attention away from the task at hand).[4]

Examining slip and capture skill-based performance errors in law enforcement, I am familiar with several occasions of these errors occurring with police officers interacting with their equipment, often during high-stress, time compressed events. One tragic case of a slip and capture error occurred in the accidental shooting of Oscar Grant by a Bay Area Rapid Transit (BART) officer. In this incident the officer intended to draw his conducted energy weapon (Taser) to use against Grant who was vigorously resisting the control efforts of three police officers. The officer, who thought he was drawing his Taser, instead drew his handgun and fired a single, fatal, round into the back of Mr. Grant.[5] Originally charged with second-degree murder and voluntary manslaughter, the officer was found not guilty of those charges but found guilty by the jury of involuntary manslaughter. Police trainer Greg Meyer has documented at least seven similar incidents of slip and capture errors causing unintended discharges.[6]

As another example, some police agencies issue flashlights to their officers that are affixed directly to the handgun. These weapon-mounted lights have been used by special operations groups and emergency response teams in law enforcement and military for many years. These highly trained and conditioned officers do not often experience a performance error in operating the weapon and light properly during concurrent muscular activity however, it is not unheard of. In recent years two officers of a municipal police service tactical unit experienced unintended discharges on separate incidents. Both of these events were within the context of the officer attempting to activate the light switch on the weapon-mounted light but unintentionally pulling the trigger instead. Fortunately, in both of these events, no human injury occurred.

However, in recent years, some police agencies have been issuing front line, rank-and-file officers and some specialty units with weapon mounted lights; and herein lays the potential for more human error to occur. Rarely do agencies drive the officer’s training and conditioning to such a level that muscle motor activation is taken to the level of automaticity (the ability to be reliably performed without conscious attention to the task) with the likely consequence that the possibility of the risk of slip and capture errors causing discharges will increase. When required to ‘multi-task’ concurrent activities, such as manipulating a weapon while simultaneously manipulating controls on the weapon mounted light, there is a possibly of a slip and capture error occurring. For example, an officer may ‘intend’ to activate the switch on the weapon-mounted light but that motor action may ‘slip’ and be caught by a much more conditioned response, which may be depressing the trigger.

The risk of this type of error occurring is not merely hypothetical. I have witnessed unintended discharges on the range, during training exercises, as a result of officers attempting to operate a weapon mounted light but instead depressing the trigger and discharging the weapon. A simple open source search quickly reveals examples of police officers experiencing unintended discharges as a result of skill-based, slip and capture errors when they intended to operate their light but instead pulled the trigger on the firearm. In one incident (October 2010), an undercover Plano, TX police officer shot and killed a man during a drug takedown. The officer stated he was attempting to operate his flashlight by activating the pressure switch located under his trigger guard but accidentally pulled the trigger. In a subsequent lawsuit filed in Orange County Superior Court against SureFire LLC the suit claimed, “The location of this grip-switch under the trigger creates a substantial risk that the user will pull the trigger and fire the gun while intending only to activate the flashlight”.[7]

In another incident in the Bronx NY (January 2011) Detective Andrew McCormick was conducting a raid as part of a drug interdiction team. As he entered the residence he attempted to activate his weapon-mounted light switch (Surefire X300) and instead pulled the trigger of his Glock 9mm causing the weapon to discharge and striking 76-year-old Jose Colon in the abdomen. Three other similar cases of unintended discharges as a result of slip and capture errors with weapon-mounted lights are documented in a lengthy report by Christopher Osher of the Denver Post (2014)[8]

As I mentioned last week – its of utmost importance that you do not misunderstand me. I am not advocating for the abandonment of weapon-mounted lights. So, you folks at the flashlight gadget company can relax – no need to send me angry letters.

However, and this must be the ‘take away’ for you for this week – if agencies are going to issue weapon-mounted lights to officers, its completely negligent to let your officers shoot for a few hours on a static range under non-stress conditions with their new gadget and then let them hit the streets. This is a disaster waiting to happen and you are setting your officers up for a predictable and preventable tragedy. A deployment approach supported by the research on human error would be to ensure that significant high-fidelity, context-based scenario training occurred with these officers before signing-off on their deployment with weapon-mounted lights.

We have not even begun to look at, nor do we have the time in this article, to explore the ergonomics and design of flashlight / weapon systems and to how these should be configured to reduce the potential for a slip and capture error. However, I can’t end without at least saying this – we know from the research that similarity of motor action with the same limb contributes greatly to slip and capture errors. What does this mean? Don’t configure your weapon mounted light so that any portion of the same hand that is involved in pulling the trigger is also responsible for activating the light. This won’t guarantee an unintended discharge will never occur – but it will help!

Thanks for sticking with me on this 6-part series on unintended discharges. Come back next week for the concluding article where we will discuss some of the most current research that has been published specifically to unintended discharges which will be an very helpful resource for any investigator who gets a weapon discharge case which may have been unintentional.

Until next time – stay safe!


[1] J. Reason, “Human Error”; Cambridge University Press, 1992.

[2] DA Norman, “Categorization of Action Slips”; Psychological Review, 1981; 88:1-15

[3] J Zhang, V. Patel, T Johnson, E Shortliffe, “A Cognitive Taxonomy of Medical Errors”; Journal of Biomedical Informatics; 37 (2004), 193-204

[4] ibid

[5] Force Science Institute. “Slip and Capture Errors – and other psychological phenomena that drove the fateful BART shooting”; PoliceOne.com, July 22, 2010. http://policeone.com/police-trainers/articles/2144171-Force-Science-explains-slips-and-capture-errors/

[6] G. Meyer. “The BART shooting tragedy: Lessons to be Learned”, PoliceOne.com, July 12, 2010. http://policeone.com/legal/articles/2095072-The-BART-shooting-tragedy-Lessons-to-be-learned

[7] “Did gun-mounted flashlight cause fatal shooting?”, Andrew Gavin, Orange County Register, January 9, 2012. Accessed at http://www.ocregister.com/taxdollars/strong-478496-surefire-gun.html

[8] “Gun Mounted Flashlights Linked to Accidental Shootings”; C Osher and D Olinger, Denver Post, Published June 7, 2014, Updated April 26, 2016; http://denverpost.com/2014/06/07/gun-mounted-flashlights-linked-to-accidental-shootings/