Can You Really Prevent Unintentional Discharges?

Print Friendly, PDF & Email

You’re trained that the surest way to prevent an unintentional discharge is to keep your finger outside the trigger guard until you’ve made the decision to shoot.

But under stress, will you–can you–reliably do that?

Maybe not, according to a study of police performance under realistic conditions. Indeed, a significant percentage of officers not only unintentionally place their finger directly on the trigger in a stress situation, even though they’ve been drilled not to do so, but they’re completely unaware that they’ve made that risky movement. They’re so unconscious of it, they deny it afterward.

Researcher Christopher Heim concludes:

“It seems as if the finger does not in all cases obey the brain.”

Dr. Bill Lewinski, executive director of the Force Science Research Center (FSRC) at Minnesota State University-Mankato, describes Heim’s study as “pioneering” and says it raises important new questions about the dynamics of unintended discharges and the training required to prevent them.

With the help of a colleague and police instructors, Heim, a PhD candidate at the Institute of Sports Science at the University of Frankfurt (Germany), ran two critical experiments at the request of the Association of German Police Trainers. The Association was concerned about “an increasing number of people [being] injured, sometimes fatally, as a result of police weapons being discharged unintentionally,” Heim says.

That concern is shared in the U.S. Just last week the Washington (DC) Times reported a startling review by the federal government of 267 shootings by agents from the FBI, ATF, DEA and the U.S. Marshals Service during fiscal 2000 through fiscal 2003. More than 5% of the total (14) were determined to be “unintentional discharges during enforcement operations,” and nearly one-third (88) were “unintentional discharges during nonenforcement activities, such as training and weapons cleaning.” See “Justice Mulls Shooting Standard,” by Jerry Seper, Washington Times, Oct. 8, 2004.

Theoretically, researcher Heim points out, “unintentional discharge should be impossible” because police in Germany, America and most other modern countries are trained and under strict orders to keep the index finger on the trigger guard or on the frame until “a decision to fire has been made. If regulations were strictly followed, there would logically be no incidents” of shooting without intent.

Obviously that ideal is yet to be achieved. Heim’s work brings new insights to the problem.

In his first study, 33 male and 13 female officers of different ranks and years of service, were sent into a room to arrest a “suspect” and to “act in a way they thought appropriate” while doing so. The officers were armed with a SIG-Sauer P226 that was rigged with force sensors on the trigger and grip. All the officers were instructed that if they drew the gun during the exercise, they were to keep their finger off the trigger unless they had made the decision to shoot, per their training and department regs.

As the role-play evolved, 34 of the 46 officers drew the gun and one officer actually fired, intentionally. Of the 33 others who drew, all insisted that they had followed instructions to keep their finger outside the trigger guard, because they’d not made a decision to shoot.

The sensors told a different tale.

Seven of the 33–more than 20 per cent–had in fact touched the trigger hard enough to activate the sensor. Even the officer who eventually fired his weapon “not only touched the trigger twice before actually firing and once again afterwards, but also had his finger on it long before actually firing,” Heim notes. Yet he too maintained he’d kept his finger well clear of the trigger until the very split-second before he fired.

In a second series of experiments Heim explored how various body movements might affect an officer who has his or her finger on the trigger but does not have an immediate intention to shoot. Specifically, would certain movements cause an officer to involuntarily increase pressure on the trigger enough to unintentionally discharge a round?

Heim ran 25 participants (13 female and 12 male, average age 25, all armed with the sensor-equipped SIG) through repetitions of 13 vigorous movements common to police work while their index finger was on the trigger.

In about 6 per cent of cases, enough trigger pressure was registered to have fired the pistol had it been uncocked (that is, mechanically set for an initial double-action trigger pull). In about 20 per cent of cases, the pressure was sufficient to have fired the gun had it been cocked (as with secondary rounds). The gun used had a 12-pound double-action trigger pull and a 5-pound pull, single-action.

The motions that caused the greatest contraction of the trigger finger–and thus the greatest force exerted on the trigger–were all jumping motions, whether with both legs or a single leg on either side of the body. The next greatest contracting force was caused by an abrupt loss of balance. Next were single-leg kicks (especially using the gun-side leg).

The lowest amount of pressure on the trigger was caused using the non-gun hand to push or pull a solid bar and to push a pulley apparatus.

No emotional stress was involved in this experiment. “If stress were added, we might expect that the percentages of those officers pulling the trigger would go up,” says the FSRC’s Lewinski.

Heim’s research confirms the “contralateral contraction” theory originally credited to Dr. Roger Enoka, who runs the Center for Neuroscience at the University of Colorado at Boulder. This theory holds that the hand gripping a gun is affected by “sympathetic” reflexive reactions to the movement of other limbs, causing uncontrollable contraction of the gunhand fingers. “A large number of different groups of muscles in different parts of the body work together,” Heim explains, and such “involuntary muscle actions” can play a role in unintentional discharges by affecting the grip and trigger finger.

Besides a sudden loss of balance and the use of other limbs (during a rapid tactical building entry or a struggle with a suspect, as examples), Heim believes that a “startle reaction” can also stimulate a dangerous involuntary muscle reaction, although this has never been tested in a laboratory setting.

Lewinski suggests several of other possible causes of involuntary trigger squeeze as well:

  • In studies of his own involving subjects drawing a handgun and extending it out to a shooting position, Lewinski has found that roughly 1 in 5 individuals unintentionally fires the weapon as it is brought up to eye level and pushed forward. “There appears to be something about the way the gun is moved and manipulated that puts contractile pressure on the wrist and trigger finger,” prompting an involuntary shooting by some subjects, Lewinski explains.

Lewinski’s study, which employed a gun with a 12-pound trigger pull, is the first to suggest that even the mere biomechanical manipulation of a firearm may cause a discharge if the shooter’s finger is on the trigger.

His tests involved “naive” subjects without firearms training, but the results would likely hold with officers too, he speculates.

  • The Mayo Clinic has identified and studied a phenomenon found among some golfers called “yips.” This is an “uncontrollable, forceful spasmodic jerk” that is associated with an abnormally high heart rate and involves unusually intense muscle activity in the forearm and wrist, resulting in a putter being gripped with increased force.

“Some people seem more susceptible to this than others,” Lewinski says, “but we don’t know precisely why. There seem to be problems in the neuromuscular system, but for the most part it’s an undiagnosable and largely unexplained condition.”

He points out, however, that police activities involving drawn guns obviously tend to increase heart rate, one of the associated factors. In Heim’s first experiment, for example, the heart rates of participants were significantly elevated (by 50 per cent on average) just by the role-playing exercise.

  • Another phenomenon that may be involved is “hand confusion,” which is different from contra-lateral sympathetic contraction. “Hand confusion involves the inability of the brain to control what each hand is doing in a situation,” Lewinski explains. “It is evident most often under stress and in multi-tasking situations.”

For example, if you infrequently search a building with a flashlight in one hand and a gun in the other, your brain may become confused and send contraction signals to the wrong hand in a moment of stress, resulting in an unintentional discharge if your finger is on the trigger. Or, disastrously for you, you may push on your flashlight instead of your trigger when your life is suddenly threatened.

In analyzing Heim’s first study, which suggests that even if you want to keep your finger safely outside the trigger guard it may still end up inside, Lewinski offers some possible explanations of what may be to blame for this occurring:

  • One possibility is that distraction is involved. “Your intention may be to keep your finger in a safe place and initially you may consciously remind yourself of that,” he explains. “But then you get distracted from that focus by a more urgent emergency” and your finger unconsciously slips to the trigger.

As comparable illustration, “If you’re very conscious of not banging your knee when you get into your patrol car, it’s easy to avoid. But if something distracts you as you’re getting in and you switch your attention to that, you may very well bang your knee even though you intended not to.”

  • Your body may instinctively seek what’s most natural. Keeping your finger extended along the trigger guard or the frame “is not a ‘normal’ grip position,” Lewinski suggests, “and because it’s abnormal there may be an unconscious tendency to assume another less desirable but more natural position.”
  • Putting your finger on the trigger may reflect a psychological need for reassurance. One of the Force Science Research Center’s national advisory board members, firearms expert Tom Aveni, calls this tendency “trigger affirmation.” Aveni has pointed out that it’s his experience as a trainer that officers more often unconsciously put their finger inside the trigger guard when they are under potential threat conditions in dark surroundings. Lewinski says they may subconsciously be seeking “psychological reassurance that they are able to quickly defend themselves against a feared, anticipated threat.” Their fearful fantasies heighten their stress level and, ironically, make a potentially dangerous unintended discharge more likely.

Building on Heim’s intriguing findings, unintentional discharges are a problem the FSRC plans to study intently. Lewinski foresees a 3-part research approach:

  1. refining the testing technology to assure that the nature of the problem is fully and accurately defined;
  2. more deeply investigating the psychology and neurology involved in inappropriate finger placement and unintended trigger squeeze, as well as the little-researched hand-confusion phenomenon and
  3. exploring important training issues, including whether different or longer training can affect the incidence of unintentional discharges.

“We really don’t know the amount or nature of training that might be best,” Lewinski says. “But Heim’s studies suggest that current training is not providing wholly satisfactory solutions to the problem.”

Until better approaches can be documented, Lewinski proposes that more attention be given in recruit and in-service training to emphasizing and practicing under stress the importance of keeping the finger away from the trigger until there’s a definite decision to shoot. While present training may need improvement, he points out that most officers in Heim’s experiments did obey instructions and training in regards to trigger engagement. “Perhaps more emphasis and practice in training could improve that percentage,” Lewinski says. “Certainly we would not expect more training to worsen the situation.”

In addition, he proposes that officers devote more practice to mastering rapid reholstering. At least in some situations this will allow you to safely secure your gun when circumstances change and you no longer need it in hand. With your sidearm holstered, you’re then free to use both hands to control a nonlethal encounter without concern about an unintended firing. However, Lewinski emphasizes, this is another area where more research is needed to identify the best training methods.

As sobering reminders of the importance of all this, Lewinski cites numerous cases on record in which officers have shot each other, as well as civilians, in stressful situations because of unintentional discharges. He points to the case of a Texas officer he’s currently helping to defend as an expert witness.

During a struggle with a belligerent and uncooperative 14-year-old suspect, that officer’s gun discharged and killed the kid. The officer insists the shooting was not intentional.

He is now scheduled for trial for murder.

1 Response

Leave a Reply


  • Privacy Policy

Privacy Policy

Effective date: January 06, 2019

Force Science Institute, Ltd. (“us”, “we”, or “our”) operates the https://www.forcescience.org/ website (hereinafter referred to as the “Service”).

This page informs you of our policies regarding the collection, use, and disclosure of personal data when you use our Service and the choices you have associated with that data. Our Privacy Policy for Force Science Institute, Ltd. is based on the Privacy Policy Template from Privacy Policies.

We use your data to provide and improve the Service. By using the Service, you agree to the collection and use of information in accordance with this policy. Unless otherwise defined in this Privacy Policy, the terms used in this Privacy Policy have the same meanings as in our Terms and Conditions, accessible from https://www.forcescience.org/

Information Collection And Use

We collect several different types of information for various purposes to provide and improve our Service to you.

Types of Data Collected

Personal Data

While using our Service, we may ask you to provide us with certain personally identifiable information that can be used to contact or identify you (“Personal Data”). Personally identifiable information may include, but is not limited to:

  • Email address
  • First name and last name
  • Phone number
  • Address, State, Province, ZIP/Postal code, City
  • Cookies and Usage Data

Usage Data

We may also collect information on how the Service is accessed and used (“Usage Data”). This Usage Data may include information such as your computer’s Internet Protocol address (e.g. IP address), browser type, browser version, the pages of our Service that you visit, the time and date of your visit, the time spent on those pages, unique device identifiers and other diagnostic data.

Tracking & Cookies Data

We use cookies and similar tracking technologies to track the activity on our Service and hold certain information.

Cookies are files with small amount of data which may include an anonymous unique identifier. Cookies are sent to your browser from a website and stored on your device. Tracking technologies also used are beacons, tags, and scripts to collect and track information and to improve and analyze our Service.

You can instruct your browser to refuse all cookies or to indicate when a cookie is being sent. However, if you do not accept cookies, you may not be able to use some portions of our Service. You can learn more how to manage cookies in the Browser Cookies Guide.

Examples of Cookies we use:

  • Session Cookies. We use Session Cookies to operate our Service.
  • Preference Cookies. We use Preference Cookies to remember your preferences and various settings.
  • Security Cookies. We use Security Cookies for security purposes.

Use of Data

Force Science Institute, Ltd. uses the collected data for various purposes:

  • To provide and maintain the Service
  • To notify you about changes to our Service
  • To allow you to participate in interactive features of our Service when you choose to do so
  • To provide customer care and support
  • To provide analysis or valuable information so that we can improve the Service
  • To monitor the usage of the Service
  • To detect, prevent and address technical issues

Transfer Of Data

Your information, including Personal Data, may be transferred to — and maintained on — computers located outside of your state, province, country or other governmental jurisdiction where the data protection laws may differ than those from your jurisdiction.

If you are located outside United States and choose to provide information to us, please note that we transfer the data, including Personal Data, to United States and process it there.

Your consent to this Privacy Policy followed by your submission of such information represents your agreement to that transfer.

Force Science Institute, Ltd. will take all steps reasonably necessary to ensure that your data is treated securely and in accordance with this Privacy Policy and no transfer of your Personal Data will take place to an organization or a country unless there are adequate controls in place including the security of your data and other personal information.

Disclosure Of Data

Legal Requirements

Force Science Institute, Ltd. may disclose your Personal Data in the good faith belief that such action is necessary to:

  • To comply with a legal obligation
  • To protect and defend the rights or property of Force Science Institute, Ltd.
  • To prevent or investigate possible wrongdoing in connection with the Service
  • To protect the personal safety of users of the Service or the public
  • To protect against legal liability

Security Of Data

The security of your data is important to us, but remember that no method of transmission over the Internet, or method of electronic storage is 100% secure. While we strive to use commercially acceptable means to protect your Personal Data, we cannot guarantee its absolute security.

Service Providers

We may employ third party companies and individuals to facilitate our Service (“Service Providers”), to provide the Service on our behalf, to perform Service-related services or to assist us in analyzing how our Service is used.

These third parties have access to your Personal Data only to perform these tasks on our behalf and are obligated not to disclose or use it for any other purpose.


We may use third-party Service Providers to monitor and analyze the use of our Service.

  • Google AnalyticsGoogle Analytics is a web analytics service offered by Google that tracks and reports website traffic. Google uses the data collected to track and monitor the use of our Service. This data is shared with other Google services. Google may use the collected data to contextualize and personalize the ads of its own advertising network.You can opt-out of having made your activity on the Service available to Google Analytics by installing the Google Analytics opt-out browser add-on. The add-on prevents the Google Analytics JavaScript (ga.js, analytics.js, and dc.js) from sharing information with Google Analytics about visits activity.For more information on the privacy practices of Google, please visit the Google Privacy & Terms web page: https://policies.google.com/privacy?hl=en

Links To Other Sites

Our Service may contain links to other sites that are not operated by us. If you click on a third party link, you will be directed to that third party’s site. We strongly advise you to review the Privacy Policy of every site you visit.

We have no control over and assume no responsibility for the content, privacy policies or practices of any third party sites or services.

Children’s Privacy

Our Service does not address anyone under the age of 18 (“Children”).

We do not knowingly collect personally identifiable information from anyone under the age of 18. If you are a parent or guardian and you are aware that your Children has provided us with Personal Data, please contact us. If we become aware that we have collected Personal Data from children without verification of parental consent, we take steps to remove that information from our servers.

Changes To This Privacy Policy

We may update our Privacy Policy from time to time. We will notify you of any changes by posting the new Privacy Policy on this page.

We will let you know via email and/or a prominent notice on our Service, prior to the change becoming effective and update the “effective date” at the top of this Privacy Policy.

You are advised to review this Privacy Policy periodically for any changes. Changes to this Privacy Policy are effective when they are posted on this page.

Contact Us

If you have any questions about this Privacy Policy, please contact us:

  • By email: support@forcescience.org
  • By visiting this page on our website: https://www.forcescience.org/contact
  • By phone number: 866-683-1944
  • By mail: Force Science Institute, Ltd.