Update On Force Science Research About Unintentional Discharges

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A Force Science research team has completed an update of its ongoing analysis of unintentional firearms discharges by LEOs in the US and Canada.

We reported on the initial phase of the team’s work in a previous Force Science News, when the researchers had studied 137 UD occurrences.

Now 171 additional instances have been analyzed, offering a broadening picture of the causes, circumstances, and consequences of “an unplanned activation of the trigger that is outside a handgun’s or long gun’s prescribed use;” i.e., an unintentional discharge.

A full report of the latest findings is headed for publication in a peer-reviewed, scientific journal, but here are highlights of the new study, according to Dr. John O’Neill, a behavioral scientist with the Force Science Institute, who led the research.


More than half of the UDs happened on-duty, overwhelmingly while officers were performing “highly routine activities,” such as cleaning, clearing, checking, moving, or storing their guns. “A large number of UDs occurred because officers falsely assumed the firearm was not loaded,” O’Neill observes.

More than one-quarter, however, occurred in high-stress, potentially high-threat situations, O’Neill reports. Most often, the discharges happened on traffic stops, followed in frequency while searching for armed suspects, pursuing subjects on foot, or physically restraining arrestees.


About half the time, UDs cause property damage. But one in five produce injury, to the shooting officer, a suspect, or another officer. Most often, injurious discharges occurred while officers were performing commonplace “routine tasks” with their weapon.

A small minority of UDs are fatal, usually to a suspect or sometimes to a fellow officer. “No officers [in the study] died as a result of a UD with their own firearm,” O’Neill says. Most reported deaths apparently occurred from “involuntary muscle contraction” while officers were “restraining or chasing a suspect.”


For the first time, O’Neill claims, the study provides evidence to suggest that UDs can be caused by a “startle response”; that is, an officer is surprised by a sudden sight, sound, or physical contact, causing him to pull the trigger if his finger is inside his trigger guard.

Other researchers have speculated that a startle reaction could be a factor in some UDs, O’Neill says, but “our data provides the first known empirical support” for this theory, having documented six cases where a startle-response discharge occurred.

Included is a case in which two UDs occurred at the same scene, one of them involving a startle response. An officer carrying a shotgun jumped over a small ditch after completing a call, lost his balance, fell, and unintentionally discharged his weapon because of a “muscle co-activation response.” His partner, nearby with a .22-cal. rifle, “was startled by the unexpected shotgun blast, causing him to unintentionally discharge his rifle.”


FSI’s research team offers several training tips:

  1. To help counter the startle response, “officers may benefit from exposure to high-stress training scenarios that incorporate unexpected and intense auditory, visual, and [physical] stimuli,” O’Neill writes.
  2. When handling firearms for routine tasks, such as dry-firing or disassembly, “a critical step is making certain that ammunition is not in the chamber.”
  3. Maintaining finger indexing away from the trigger until intentional shooting is imminent is also critical. Unfortunately, “routine range practice may facilitate a strong-but-wrong response by conditioning officers to automatically position the finger on the trigger immediately after the firearm is drawn,” O’Neill notes.

“Trainers may consider instructing officers to always index before shooting on the range and to practice indexing during various conditions (e.g., static, dynamic, high and low stress).”

Besides O’Neill, the FSI research team included: Mark Hartman, a doctoral student in the Dept. of Kinesiology at Iowa State U.; Dr. Dawn O’Neill, a staff behavioral scientist with the Force Science research division; and Dr. Bill Lewinski, FSI’s executive director.

Dr. John O’Neill can be reached at: john.oneill@forcescience.org.

NOTE: O’Neill and his team are continuing to collect examples of unintentional discharges, and at this point are particularly interested in UDs that have occurred while a sidearm is holstered. Please contact him with any relevant information you are willing to share on a confidential basis.

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