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Research: Why 21 feet is not a ‘safe’ distance

Key officer safety takeaways from a multiphase study that put the 21-foot rule to the test

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The 21-foot rule has been a topic of conversation in law enforcement since the 1980s when Salt Lake City Police Department Lieutenant Dennis Tueller developed a training drill for his fellow officers.

In this drill, an officer played the role of a suspect with an edged weapon who would charge another officer who was standing about 21 feet away with a holstered weapon.

Over the years Lt. Tueller found that an average person could cover 21 feet in about 1.5 seconds, which was also about the amount of time it took an officer to draw and fire their sidearm. As this information was disseminated in the law enforcement community, the idea of this “tie” in running and draw speeds led to 21 feet being misconstrued as a safe enough distance for an officer to be able to draw and fire their weapon before a charging suspect with an edged weapon could reach them.

Interestingly, Lt. Tueller considered this distance to be a “danger zone” rather than a “safe distance.“ Anecdotally, many law enforcement officers agree that 21 feet is not a safe distance.

Multiphase study of the 21-ft rule

While several studies have tested the 21-foot rule and found it to be inadequate, none have taken a truly scientific approach.

The ALERRT Center at Texas State University and Missouri State University conducted a multiphase study to scientifically determine whether 21 feet was a safe distance.

In phase one, we examined the average run speed of someone covering 21 feet. Phase two tested officers’ draw and fire speed against a silhouette target under no stress. Phase three, like phase two, looked at officers’ draw and fire speed with the addition of a charging suspect to simulate a more stressful environment. The final phase was added on after seeing the results from the first three phases, which fully covered the 21-foot rule. This fourth phase examined various movement tactics in an attempt to increase the survivability of such encounters.

Phase one

Laser timing gates were constructed to test how quickly someone could cover 21 feet. The first laser was placed at the starting line and would trigger a timer to begin as soon as the individual began to move forward. The second laser was set up 21 feet away and would stop the timer as soon as the individual crossed that 21-foot mark. We found that, like in Lt. Tueller’s test, the average person could run 21 feet in 1.5 seconds. The slowest runner completed the 21-foot run in 1.83 seconds while the fastest runner did it in 1.24 seconds.

Phase two

In phase two, officers were set up 21 feet away from a silhouette target with a holstered training pistol that fired simunition rounds. The officers were instructed to draw and fire their weapons at the silhouette when a light bulb was turned on. This was designed to test what the draw and fire speeds would be with a simple stimulus under no stress.

Officers were told to stand in an interview stance, which involved having their hands in front of them and not resting on their weapons. This was done to have the experiment approach a more real-world situation in which the officer is not primed to draw and fire their weapon.

On average officers were able to draw and fire their weapons in 1.8 seconds. The times ranged from 1.03 seconds to 3.4 seconds. Accuracy was also collected. Breaking it down by hits and misses, 14% of officers missed the silhouette altogether.

Phase three

Phase three tested the same information as phase two but with the addition of stress and a moving target.

In this phase, a suspect with his hands in his pockets was standing 21 feet away from the officer. The officers were told they were responding to a disturbance and should act accordingly. They were given a single simunition round and told to stay within the marked box on the floor.

The officers were told they would run through multiple scenarios and that they may not have to use the training pistol at all. This was a deception in the study so as to reduce the amount of priming for the participants. Each officer only participated in a single scenario and was charged by the suspect every time.

Officers were once again told to start in an interview stance. After talking to the officer for a while the suspect would draw a shock knife out of their pocket and charge the officer. The shock knife is a knife-shaped training device that arches electricity around where the blade would be. It seems to induce a good amount of stress in officers.

The suspect was instructed to never actually make contact, but the participating officers were not aware of that fact. The average time it took an officer to draw and fire their weapon was 1.42 seconds. This average time comes from the officers who were able to draw and fire their weapons in time. There were several officers (12%) who were unable to extract their firearms before a cease-fire was called. The range of times for those officers who successfully fired their weapon was 0.93 seconds to 2.4 seconds. Of the officers who fired their weapon, 24% missed the suspect altogether. This is a decrease in accuracy of 10% from phase two.

These three phases completed the examination of the 21-foot rule. The officers’ average draw and fire speeds of 1.42 seconds while under stress are slightly faster than the average run speed of 1.5 seconds. Converting that difference of time into distance means that the suspect is a mere 13.4 inches from the officer when they fire their first shot on average. That is 13.4 inches from chest to chest, not with an outstretched weapon. This short distance also demonstrates how truly impacted officer accuracy is when under stress.

Recall that 24% missed the charging suspect when they were an average distance of just over a foot away. Additionally, that is for a single shot, which unless it hits the central nervous system will likely not stop the attacker.

Figure 1 shows a boxplot of the three phases. The colored boxes represent the middle 50% of the participants (i.e., 25%-75%). It can easily be seen that overlap exists in all three phases. More significantly, there is overlap between phases one and three. These data show that a suspect would have to be 32 feet away from an officer for 95% of officers to be able to successfully draw and fire their weapon once. Based on these findings, the 21 feet does not appear to be a safe distance for officers facing a suspect with an edged weapon.

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Figure 1. Phases 1, 2 and 3 boxplots measured in seconds.

Phase four

These findings led us to ask what could be done to increase the potential survivability of such encounters being that staying 32 feet away from everyone they interact with is not a practical standard for officers.

Phase four introduced different movement tactics in an attempt to disrupt the assailant’s OODA loop. This study used four tactics including a control where the officer did not move, a scenario where the officer moved at a 45-degree angle toward the suspect, one where the officer backpedaled and one where the officer sidestepped the suspect.

In this phase, the officer was held constant, and the suspect was changed for every scenario so that the assailant role would be unaware of the movement tactic being used.

The suspects were given a chalk knife that allowed us to see if the officer was touched with the knife or not. A chalk knife is a knife-shaped piece of plastic with a felt edge round where the blade would be. Chalk was rubbed on the felt and would leave a mark wherever it touched the officer.

The suspect was placed 21 feet away from the officer and told to charge the officer whenever they felt like it. We found that the officer was touched with the chalk knife 25.6% of the time when moving at a 45-degree angle toward the suspect, 7.7% of the time when backpedaling, 5.3% of the time when sidestepping and 33% when the officer did not move.

While there is no singular movement tactic that would work for every situation, this phase showed that officers can significantly decrease the risk of being reached with an edged weapon by employing some type of movement. Much law enforcement firearm training is conducted from a stationary position, which could create training scars. Training with some type of movement could create muscle memory and better heuristics.

Key takeaways

While most officers would agree that the 21-foot rule is a bad standard in policing, it is important scientific information is used to support its abolition.

This study showed that on average 21 feet is not a safe enough distance for an officer to be able to successfully draw and fire their weapon at a charging suspect with an edged weapon. Based on this research, there are several key takeaways to shape future discussions around the idea of a safe distance:

  1. Reject the notion of a standardized safe distance. Police interactions with citizens are fluid and it does not seem practical to set a standard distance for such encounters. Having an officer attempt to keep 32 feet from an individual is not practical in most interactions.
  2. Introduce movement tactics with firearms training. Having an officer employ some sort of movement seemed to dramatically decrease the chances of being touched with an edged weapon. The environment will have the largest impact on how officers can move in any given situation. While there is no standard movement that should be employed, it is important to create muscle memory for “getting off the X.”
  3. Work to increase accuracy when movement tactics are used. Merely moving to increase the survivability of such encounters is only half of the equation. Officers must then be able to accurately fire their weapons. The increased percentage of officers missing the suspect when they are mere feet away shows the importance of such accuracy. When under real-world stress, this accuracy is likely to decrease even further.
  4. Recognize the implications of real-world encounters. As this study was conducted in a laboratory setting, it should be noted that these encounters were all best-case scenarios meaning that real-world scenarios are much more unpredictable and stressful. That makes these results more important because officers in the real world are more likely to be in danger within 21-feet of a suspect with an edged weapon.
  5. Use caution when interpreting these results. This study was not conducted to justify an officer firing their weapon at someone within 21 feet because they have an edged weapon. Distance is only one factor of many that play a role in determining whether to use force. While it is easy to say that 21 feet is not a safe distance, this study does not necessarily imply that officers should draw and fire their weapons sooner. Officers must consider a variety of situational factors when deciding to use force.

For a more comprehensive explanation of this study, see Sandel et al.’s (2020) study entitled A scientific examination of the 21-foot rule.


Sandel WL, Martaindale MH, Blair JP. (2020). A scientific examination of the 21-foot rule. Police Practice and Research, 2020, 22(3):1314-1329.

NEXT: New knife-attack decision: Court ponders how far is close enough to be an “immediate” threat

William L. Sandel, Ph.D., is an assistant professor of Criminology and Criminal Justice at Missouri State University and the Director of the Graduate Certificate in Crime Prevention. Prior to joining the faculty of MSU, Dr. Sandel worked as the research specialist at the Advanced Law Enforcement Rapid Response Training (ALERRT) Center. The ALERRT Center has been named the national standard by the FBI for active shooter training and response.

Dr. Sandel has led multiple research projects resulting in publications. He has experience in experimental design research, survey research, vision tracking software and virtual reality software. Dr. Sandel has conducted national studies in policing that have resulted in working relationships with police officers at all levels of government. Additionally, he has guided several graduate students through the research process resulting in manuscripts and national presentations.

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