FSI Investigates Unintentional Discharges: When Are You At Greatest Risk?

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When are you most likely to experience the shock and potentially deadly consequences of an unintentional discharge:

a) While clearing an area in response to a call?

b) While performing routine firearms tasks, including cleaning your weapon?

c) While already engaged with a suspect in high-risk circumstances?

And where is this unwanted firing most likely to occur:

d) On the range?

e) In your department’s parking lot or locker room?

f) At home?

According to a new study by a research team from the Force Science Institute, the answers decisively are “b” and “e”.

The good news, in the researchers’ estimation, is that most unintentional discharges [UDs] could be eliminated by adhering to simple safety procedures.

Recommendations for reducing these dangerous mishaps are included in a report of the study’s findings recently accepted by the peer-reviewed journal Applied Ergonomics. At this writing, publication date for the paper, titled “Toward a Taxonomy of the Unintentional Discharge of Firearms in Law Enforcement,” is still pending.


The FSI team consisted of staff behavioral scientists Dr. John O’Neill and Dr. Dawn O’Neill and executive director Dr. Bill Lewinski.

“UDs are a deadly threat to both officers and bystanders such as colleagues and civilians, yet they have been understudied in scientific literature,” O’Neill writes, and the “paucity of research” has left a “critical gap between science and practice.” His group’s primary goal, he explains, was to identify the circumstances and officer behaviors that tend to be associated with UDs in hope that an analysis would result in “proactive strategies to prevent or minimize their occurrence.”

The cooperation of law enforcement agencies for the study was solicited through Force Science News, and the researchers collected detailed “descriptive information” on 137 UD occurrences from a cross-section of departments within the United States.

The team parsed this total into 16 “discernable contexts” in which UDs occurred, 15 different behaviors officers were engaged in at the time of discharge, four general types of firearm involved (pistols, revolvers, shotguns, and rifles), four types of trigger action, and resulting injuries “ranging from flesh wounds to fatality.”

A comprehensive breakdown is contained in the pending publication and provides a cautionary cataloging for officers and trainers alike by identifying the conditions under which UDs may be most likely. Here are some of the highlights:


The researchers were able to confirm that over 70% of UDs occurred on duty.

By their assessment, over half “occurred in contexts with low threat potential”; that is, locations/situations “that did not involve response to a call” and where there was little “potential for encountering a threat during the incident.”

Roughly another one-fourth took place during a call and were rated as having an “elevated threat potential,” while about one-sixth occurred under a “high threat potential” where the involved officer was already engaged with a suspect or likely to become so. (For the rest, the source material was insufficient to assign a threat potential.)

Within these categories, the researchers documented these findings:

Low threat potential: In this group, UDs most often occurred on a firing range (22%), in departmental parking lots (20%), in a locker room (17%), or at an officer’s residence (10%).

Elevated threat potential: Most of these happened while the involved officer was clearing an area (over 65%) or at the end of a call (19%).

High threat potential: Here, UDs most frequently took place while the officer was conducting a felony traffic stop (29%), searching for an armed suspect (29%), providing cover (14%), or using physical restraint (nearly 10%).


When UDs occurred, the involved officers were engaged in some “routine firearm manipulation” 60% of the time. To a much lesser extent, they were performing a physical activity that produced an unexpected muscle reaction responsible for their firearm discharging (24%) or conducting “unfamiliar tasks” (11%).

Within these categories, specifics include:

Routine manipulation: UDs most often occurred when officers were clearing a weapon, accounting for about one-third of the incidents in this category. Other relevant manipulations included storing/moving the weapon (about 23%), holstering/unholstering (17%), conducting function checks (16%), and performing maintenance (10%).

Muscle reaction: This, O’Neill explains, involves “using any part of the body to climb, jump, kick, punch, pull, push, run, squeeze, or otherwise engage in an activity unrelated to the firearm’s trigger” but that provokes an involuntary reactive contraction of muscles in the finger that happens to be positioned on the trigger.

Specifically, this “muscle co-activation” resulted from an officer using another finger (to activate a frame-mounted flashlight or laser, for example) (36%), losing and trying to recover a grip on the firearm (21%), using a leg to jump or kick (18%), or losing balance (15%).

(Findings by other researchers regarding this phenomenon are covered in some detail in O’Neill’s paper.)

Unfamiliar tasks: UDs in this category occurred when officers were switching a gun from one hand to another (40%), handling unfamiliar firearms (33%), or dealing with unfamiliar holsters or belts (27%).


Most documentation submitted to the researchers did not specify whether injuries occurred as a result of the UD. However, about 15% did acknowledge injury, all involving officers, and there was one fatality.


The system for categorizing UDs that the research team developed allows for the pinpointing of problem locations and behaviors, which can then be addressed with enhanced training and procedural discipline, Lewinski told Force Science News.

Overall, the researchers estimate, a high percentage of UDs could be prevented. Among their suggestions for minimizing their occurrence:

  • Observe the fundamentals of safe firearms handling: Always consider every gun to be loaded and index your trigger finger along the slide or frame, outside the trigger guard, until you intend to shoot. Include practice with your non-dominant hand and with new or unfamiliar equipment.
  • Before dry-firing or disassembling a firearm, verify there is no ammunition in the chamber. “If not already in practice, trainers are encouraged to consider crucial clearing steps in firearms disassembly that officers must perform in order to pass training, such as ejecting the magazine, racking the slide, and visually inspecting the chamber,” O’Neill writes.
  • Reinforce safe habits “to fluency with speed and accuracy” through dynamic training scenarios. As O’Neill explains, “Officers may be able to perform a skill on the range in a static position and under low-stress conditions, but the same skill may not [automatically] generalize in other contexts involving dynamic movements and higher physiological arousal.” Reality-based training should include “scenarios designed to elicit muscle co-activation.”
  • In the absence of training to fluency, anticipate a possible uptick in UDs as officers transition to the new standard-issue weapons.
  • Mandating the reporting of all UDs, but with retraining substituted for punishment like days off or termination, may result in a more comprehensive picture of such incidents, which, in turn, will better “inform policies and procedures” for safe firearms operation.
  • The research team encourages trainers to “compare and contrast” the study’s findings with “UDs that have occurred within their own agency,” to tailor extra emphasis on “idiosyncratic” risks. “It is crucial that [agencies] continue to analyze the contexts, officer behavior, and firearm designs that contribute to UDs in order to inform qualification training, remediation/re-qualification training, policies, and procedures,” O’Neill writes.

Last month, the authors presented key findings of the study at the 7th International Conference on Applied Human Factors and Ergonomics in Orlando, FL. Next month, they’re scheduled for an oral presentation at the annual meeting of the Society for Police and Criminal Psychology in Austin, TX.

Meanwhile, O’Neill’s team would like to expand its database on UDs on a continuing basis, with an eye to further researching this vital subject. If your department is willing to share UD information on a confidential basis, please email O’Neill at john.oneill@forcescience.org or call FSI headquarters at 507-387-1290 and leave your contact information.

Currently, the research team is developing a standardized form that agencies can use to collect important UD data for their internal use and for outside reporting purposes when appropriate. We’ll let you know when this form is available.

When published, the title of the team’s study will be “Toward a Taxonomy of the Unintentional Discharge of Firearms in Law Enforcement.”

6 Responses
  1. Sgt. Jeffrey Weiss (Ret)

    I am a NRA Certified Chief RSO and Cert. NRA Instructor (30+ years) and SO at action matches for a Rifle and Pistol Club in VA with almost 500 members. I wonder if you would be interested in polling this population as an adjunct to this study. Now, at age 76, after 35 years being an instructor and SO, I have had two AD’s in the last two years in my home (no injuries) and am vitally interested in the subject of this study and any suggestions or procedures that might come from it. While my experience with LEO’s does not suggest that they are the most careful gun handlers any study of this kind must have a fair degree of carry over to armed civilians. We have an extremely well defined and monitored procedure at our matches for loading, handling, and clearing weapons and in 4 years have not had a single AD while over seeing our events.

  2. David Throop

    The study just shows UD’s and Accidental Discharges are in reality Negligent Discharges. All due respect to the FBI, the term UD is just like the term Active Shooter. UD’s are Negligent Discharges – the possessor of the firearm pressed the trigger. Active Shooters are Active Murderers – the shooter intends to kill.. Our society tries to use sweet language so we are lead to believe actions of people make them a victim. No, the victim is the unintentional result of where the bullet strikes. If we believe the trigger press is unintentional then all these problems are due to slam fires. Yes, I have had my share of ND’s, thankfully the firearm was pointed in the right direction. Cooper had it right all guns are always loaded.

  3. Storm

    The use of the euphemistic term UD (Unintentional Discharge) is an apologetic. The more accurate term is ND (Negligent Discharge). As a police officer Amd weapons instructor for over fifty years, I have had my share. All, of them were failures on my part to strictly abide by the fundamental rules of weapons safety we all know. No injuries or property damage occurred, but the incidents were the result of negligence on my part..

  4. As an instructor of firearm’s training, mostly pistol, I find new shooters having involuntary muscle movement to be most frequent,. TY for the report, I see dealing with LEO’s is the subject, yet I had to put my 2 cent’s in.

  5. Wade

    Please consider the potential advantage of a double action pistol that would serve as another fail-safe mechanism to help prevent UD’s. See Massad Ayoob’s article on the conversion of department issued striker fired guns to the Beretta 92. After adoption and training, UD’s were reduced substantially.


  6. The U.S. Army and the UK Army/MØÐ classifies these inciidents as Negligent Discharges. While these types of incidents may not be intended, they were considered as and classified as Negligent Discharges during my 30+ years of military and military-related civilian service.

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