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Patient Safety Tip of the Week

April 20, 2021

Taser “Slip and Capture Error” Again!



In the midst of a trial of a police officer in the death of an unarmed African-American man in Minneapolis, 10 miles away there was another incident in which a young African-American man was fatally shot by a police officer during a traffic stop. In the latter incident, the police officer apparently intended to use a taser on the man but instead fired her gun, killing the man. “How could that happen?” you ask. It’s not the first time this has happened. In fact, it has happened multiple times. Our April 21, 2015 Patient Safety Tip of the Week “Slip and Capture Errors” noted at least 8 prior instances where police intending to use tasers, instead pulled out their guns and shot someone. It is the classic example of what is known as a “slip and capture” error.


The police stopped the man for a suspected traffic violation but found there was an outstanding arrest warrant on him. When he got back into his vehicle against the commands of the police officers, one officer aimed a weapon at him and shouted “Taser! Taser! Taser!” (Bogel-Burroughs 2021, Broaddus 2021, Navratil 2021). She fired one round, and the man groaned in pain. “Holy shit, I just shot him,” the officer can be heard shouting. The man drove off in the car but crashed a couple blocks away and was pronounced dead at the scene.


A nearly identical incident occurred in 2018 in Kansas (Robertson 2019). A police officer thought she had her Taser in her hand as she watched an unarmed man beating a fellow officer. What she fired, however, was her gun — by mistake. “Oh s---, I shot him,” she shouted. During legal proceedings, she explained her brain immediately went ‘you need to tase this guy, you got to tase, you got to tase him” and she shouted “Taser! Taser! Taser!” She fired what was in her hand, and the assaulter shouted in pain — which would have been normal when hit with a Taser. But the officer said she was stunned that she didn’t see the wires of a Taser gun strike. At this point she realized she had pulled her gun and shot the assaulter by mistake, instead of pulling her Taser. She exclaimed aloud, “Oh s---, I shot him.”


We wrote our April 21, 2015 Patient Safety Tip of the Week “Slip and Capture Errors” after a volunteer police deputy fatally shot a man, thinking he was firing his taser, not his gun (Yan 2015). In 2009 a very similar shooting occurred on the Oakland BART system when the officer fired his gun rather than the intended taser (Force Science Institute 2010). At that time, retired Capt. Greg Meyer noted there were at least 6 similar incidents prior to that 2009 shooting (Meyer 2010). So, when we did our 2015 column, there were at least 8 similar incidents where a police officer inadvertently shot someone, mistakenly thinking they were using a taser and not their gun. After the recent Minnesota shooting, media reports put the number of similar incidents as high as 18 (Elinson 2021). One article actually lists 16 of the prior incidents (Ciavaglia 2021).


Sure sounds like a system problem to us! It’s reminiscent of concentrated potassium chloride issues in healthcare in the past. Multiple incidents occurred disseminated both in time and location, so it took years for us to see a pattern and look for root causes and, ultimately, solutions.


So, this is a patient safety column, not a crime column. Why are we discussing this at all? We discuss it because these are instances of a human factors concept, the “slip and capture error”, and we need to understand why they occur because similar errors can occur in healthcare. We gave many examples in our April 21, 2015 Patient Safety Tip of the Week “Slip and Capture Errors” and such are well worth reiterating.


Basically, a capture error occurs when two potential actions share the same or similar initial sequences, but one action is relatively unfamiliar and the other is a well-known and well-practiced action (the latter often carried out almost automatically or subconsciously). In effect, under certain circumstances the well-practiced action sequence will “capture” the action.


But the capture error is not a new concept. In fact, for years when we are teaching patient safety to medical students, residents, or other healthcare workers and tell them mistakes are inevitable we give them a classic example: “It’s Sunday morning. You intend to go to the grocery store. But you find yourself in your car on the route to your usual workplace/school, instead of the route to the grocery store.” (Usually about two thirds of the audience raises their hands when we ask if that has happened to any of them!) That happens to be a classic capture error. The more practiced activity “captured” the intended but less familiar activity.


Usually there are “enabling” factors that contribute to the occurrence of “capture” errors. These include stressful situations, emergencies, distractions or interruptions and others.


So, what are some healthcare examples of “capture” errors? A nurse or physician, confronted with a new version of a device (eg. ventilator, infusion pump, dialysis machine, etc.), programs in the sequence of keystrokes or dial manipulations he/she used on the old device even though he/she has been inserviced on the new device.


Another example might occur during CPOE. You almost always choose the first option from a drop-down list listing regimens for a certain anticonvulsant. Your software vendor updates the software and the drop-down list is now reordered. Still, you choose the first option and this time your patient gets the wrong drug or wrong dose.


A somewhat similar error may have occurred in the fatal NMBA incident we described in our Patient Safety Tips of the Week for December 11, 2018 “Another NMBA Accident” and February 12, 2019 “From Tragedy to Travesty of Justice”. In that case, a nurse was attempting to retrieve Versed from an automated dispensing cabinet (ADC). She recalled talking to an orientee about something unrelated while entering the first two letters “VE” into the ADC. The first medication on the list was chosen. The nurse did not recognize that the medication chosen was vecuronium, not Versed. The nurse looked at the back of the vial to see how to reconstitute the medication but did not recheck the name of the medication on the vial. Ultimately the fatal dose of the paralyzing agent vecuronium was administered to a patient.


In our April 21, 2015 Patient Safety Tip of the Week “Slip and Capture Errors” we also noted an example where we might incorrectly choose an order set for order set for DKA (diabetic ketoacidosis), which gets used very often, rather than the intended order set for nonketotic hyperosmotic state, which is used much less frequently.


There is probably also some relationship or at least overlap of “capture” errors with another human factors concept: inattentional blindness (ISMP 2009). In the latter, which is really a sort of confirmation bias, we tend to see what we expect to see rather than what we actually see. This is often a contributing factor in incidents where medications are drawn up from the wrong vials.


Another interesting thought: technology may cause some “capture” errors. Autotext or automatic completion of phrases by a word processor or smart phone may lead to such errors. We’ve noted several times that every time we type “EHR” (for electronic health record), our word processor converts it to “HER” and we might miss that on proof-reading. Or our smart phone automatically inserts one email address when we really intended a different one. These examples really meet the definition of a “capture” error in that two actions start with the same sequence of steps and one that is far more familiar than the other (at least far more familiar to the computer!) takes over for the intended action. You can bet that there will be analogies with healthcare technologies.


Capture errors have long been described by human factors pioneers like James Reason and Don Norman. How about some everyday examples of “capture” errors?


James Reason, widely known as the father of human factors research, provides numerous examples (Reason 1990):


Don Norman (see our November 6, 2007 Patient Safety Tip of the Week “Don Norman Does It Again!”) in his two great books on human factors and design of things (Norman 1988, Norman 2009) has some great examples:


Did you ever rent a car on a trip and turn on the windshield wipers instead of the lights because the control knobs were reversed from the car you usually drive?


In fact, the classic predictable error of using the previous year when you write a check in January of a new year is often referred to a “slip” but is probably also really a “capture” error.


In the taser/gun incidents, use of the taser is the relatively unfamiliar action and use of the gun is the more familiar and well-practiced action. Even if the officer has never fired his/her gun on duty, they all spend considerable time on the shooting range so have practiced use of the gun frequently. But we suspect most have practiced using the taser much less frequently and probably never practiced under stressful conditions.


As Don Norman would tell us, design of systems significantly impacts on how humans use those systems. Design of the taser and its holster likely contributed to each of the incidents. In many of the previous taser/gun mistakes the taser had apparently been drawn by the “strong” (dominant) hand, though the location of the taser holster was variable (Meyer 2010). One of the recommendations made by the Forensic Science Institute after the BART case was use “weak-side, weak-hand-draw” taser holsters to minimize the chance of unintentionally drawing one’s gun rather than the taser. It’s not known how the officer in the current Minnesota incident was wearing her weapons and holsters at the time of the shooting. Apparently, the policy was that the tasers were to be holstered on the nondominant side. But, even then, there is a problem. The video of the incident shows another officer wearing the taser holster on the nondominant side but the butt of the taser was positioned such that the officer could easily “cross-draw” the taser with his dominant hand (Hubler 2021). An article in USA Today (Loehrke 2021) has a good graphic showing not only holstering but also all the other equipment police officers typically carry on their belts.


And it’s clear it is not enough to just receive some education/training on use of the taser. Taser use must be practiced just as often (perhaps even more often) than practicing gun use and done under conditions closely simulating those in which a taser is likely to be needed.


But, let’s go back to the concentrated potassium issue in hospitals. You’ll recall that nurses withdrew fluid from what they thought were vials of heparin or insulin but were really vials of concentrated potassium. When injected, that would cause the heart to stop beating. One problem was the similarity of the vials of the various substances. The other problem was that there really was no need for vials of concentrated potassium salts to be on nursing units at all. Many years ago, nurses did have to add potassium to IV fluids but now IV fluids are typically prepared in hospital pharmacies, so nurses don’t have the need for vials of potassium any longer. The solution was to remove vials of potassium from floor stock on nursing units all together.


The taser dilemma needs a similar solution. Not removal of the tasers, of course. But rather redesign of the tasers. We’ve heard all the media pundits say “how could anyone mistake their gun for a taser? The gun and the taser have different weights and the officers are supposed to wear the taser on the side of their nondominant hand. The taser is a different color (usually a bright, often neon, color) to distinguish it from the gun. And officers are supposed to be trained on use of both guns and tasers. But, obviously, all those features have not prevented incidents where guns are mistaken for tasers.


Our take – the taser looks like a gun and has a trigger like a gun! So, it’s no surprise that, in the heat of an emergent situation, someone will pull that trigger. If nothing is done, it is inevitable there will be another inadvertent shooting after mistaking a gun for a taser. The solution should be to redesign tasers so they have a different shape and have an activation mechanism that is different than a gun-style trigger. Maybe add some sort of audible signal that appears when the taser is unholstered. Is that too much to ask? Just be careful the redesign does not have its own unintended consequences (like tasing oneself!).


We have no intention of getting into the discussion of whether tasers or any other forceful actions were appropriate in this incident and we’re focusing just on the taser issue. While there are clearly many other issues and factors contributing to the most recent taser/gun incident, the fact that so many such incidents have occurred tells us that there is a strong underlying system vulnerability that is a primary root cause of such incidents. Just as we had put our nurses in position to inadvertently administer lethal potassium doses years ago, the current design of tasers puts officers in position to inadvertently shoot someone. It’s time for thoughtful analysis and realistic solutions.







Bogel-Burroughs N, Bosman J. Minnesota Officer Who Shot Daunte Wright Meant to Fire Taser, Chief Says. New York Times 2021; April 12, 2021



Broaddus A, Yan H, Allen K, Silverman H, Minnesota officer shouted 'Taser!' but fired a gun instead, fatally shooting a man at a traffic stop, police say. CNN 2021; April 12, 2021



Navratil L, Montemayor S, Mannix A. Chief: Officer meant to use Taser, not firearm, on Daunte Wright. Minneapolis Star Tribune 2021; April 13, 2021



Robertson J. A Lawrence police officer meant to use a Taser. She shot a man by mistake.

The Kansas City Star 2019; September 06, 2018 Updated March 26, 2019



Yan H. How easy is it to confuse a gun for a Taser? CNN 2015; April 14, 2015



Force Science Institute. Force Science explains "slips-and-capture errors" and other psychological phenomena that drove the fateful BART shooting. July 22, 2010



Meyer G. The BART shooting tragedy: Lessons to be learned. July 12, 2010



Elinson Z. Kim Potter mistook her gun for a Taser, police say: How often does that happen? Fox News 2021; April 13, 2021



Ciavaglia J. How could a gun be mistaken for a Taser? There have been at least 16 incidents of 'weapon confusion' since 2001. USA Today 2021; April 13, 2021



ISMP (Institute for Safe Medication Practices). Inattentional blindness: What captures your attention?  ISMP Medication Safety Alert Acute Care Edition 2009; February 26, 2009



Reason J. Human Error. Cambridge: Cambridge University Press. 1990.  p. 68



Norman D. The Psychology of Everyday Things. New York: Doubleday. 1988. P. 107



Norman D. The Design of Future Things. New York: Basic Books. 2009. P. 107



Hubler S, White J. How Could an Officer Mistake a Gun for a Taser? New York Times 2021; April 13, 2021



Loehrke J, Padilla R, Petras G. Aftermath of fatal shooting: How can a handgun be mistaken for a Taser? USA Today 2021; April 14, 2021







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