There are times when law enforcement officers or military personnel need to subdue a person or group of people without using lethal force. They rely upon a variety of tools and tactics to achieve this goal. Some of those tools include items like riot shields, batons and tear gas. One less-than-lethal tool is the Thomas A. Swift Electric Rifle, or Taser.
A Taser is an electronic control device (ECD). The typical Taser device is a handheld gadget that fires a pair of pins tethered to the handset by electrical wires. The handset sends pulses of high voltage electricity to the pins. Anyone shot by a Taser will experience neuromuscular incapacitation (NMI). That means the subject will lose the ability to control his or her muscles -- the electric pulses cause muscles to tense. This usually results in the person falling down and gives law enforcement or military personnel time to restrain him or her.
But the typical Taser has a couple of limitations. Because the pins connect to the firing mechanism through wires, the typical Taser has a range limited to the length of the wires -- about 35 feet (10.6 meters). And while a Taser works well for taking down a single subject, it's not easy to reload a fired Taser device -- something that may be necessary in crowd control situations.
With that in mind, Taser introduced a new concept in ECD technology -- the Taser eXtended Range Electronic Projectile (XREP). The XREP looks like a high-tech shotgun shell. That's not by accident -- Taser designed the XREP so that military or law enforcement officers could fire one from a standard 12-gauge shotgun. But instead of firing pellets or a slug, these shells fire a small, self-contained Taser device capable of delivering the same NMI effect as a handheld Taser gun.
Creating a device small enough to fit into a shotgun shell casing but powerful enough to incapacitate a subject was no easy task. The development team at Taser had to find a way to balance power with size. Not only did they need the device to travel farther than a standard Taser, but also to have the right amount of mass. If it had too little mass, it wouldn't travel far enough. But if it had too much mass, it could become a deadly projectile rather than a non-lethal solution.
Let's take a closer look at the XREP shell.
The Taser XREP Projectile
The XREP fits inside a special shotgun shell casing. Unlike standard shells, the cases for XREP devices are transparent. Taser chose transparent shells to make it easier for officers to identify the correct shell before loading it into a shotgun.
Just like a normal shotgun shell, the XREP shell uses gunpowder as a propellant. The shotgun ejects the XREP casing just as it would any normal shotgun round. But instead of firing a slug or round of shot, the shotgun fires an electronic projectile weighing 3.4 grams (about .12 ounces) [source: Taser].
This projectile has two main sections. The nose of the projectile has four sharpened electrodes. These electrodes pierce the clothing and skin of the subject and serve as the main point of contact for the electric charge. Before impact, the nose and second stage of the projectile move as a single unit. A pair of Kevlar-coated wires tether the nose to the second half of the projectile.
The second half of the projectile contains the electronics that allow the XREP to transmit voltage to a target. This includes a battery, a transformer and a microprocessor that acts as both a trigger and a monitoring device. The battery stores the electricity the XREP uses upon deployment. The transformer's job is to convert the electricity from the battery into a higher voltage.
A transformer converts alternating current from one voltage to another through a series of coils wrapped around a core -- two wires coiled around an iron nail could be a simple transformer. As electricity travels through the first coil of wires around the core, it creates a magnetic field. The magnetic field induces an electric field, which causes electrons to travel through the second coil of wires. There are step-up transformers that increase the voltage from an incoming source of electricity or step-down transformers that decrease the voltage.
The reason the XREP needs a step-up transformer is to create enough voltage to induce NMI in the target. Too few volts and the subject won't be incapacitated. Too many, and the target could be killed. To keep the Taser XREP from becoming a lethal weapon, Taser limits the amount of current flowing through the system to a few milliamps.
The base has six electrodes that unfold from the body of the projectile upon impact with a target. To help stabilize flight, the base of the projectile also has three spring-loaded fins that deploy upon ejection from the shotgun.
Let's look at what happens when you fire the XREP.
Firing the Taser XREP
A group of prison guards face the worst case scenario -- a full-blown prison riot. The inmates pose a danger to one another and to the personnel working at the prison. The guards hope to use non-lethal force to end the riot early and spare human lives. Using shotguns loaded with XREP shells, they take aim at rioting prisoners and fire. What happens next?
Upon firing an XREP shell, the small charge in the shell activates, propelling the projectile down the barrel of the shotgun. A ripcord connecting the projectile to the shell goes taut and then breaks. This activates the projectile's battery, and 20 seconds of high-voltage charge begins to flow through the device.
As the projectile clears the end of the shotgun's barrel, three spring-loaded fins deploy at its base. The fins cause the projectile to spin in flight, stabilizing its path. The projectile will spin even if the officer uses a smooth-bore shotgun.
Once the projectile makes contact with the target, several things happen in sequence. First, the four electrodes pierce the clothing and skin of the subject. Next, the impact causes a series of fracture pins to break. The fracture pins hold the nose to the base of the projectile. Once the pins break, the base of the projectile swings free of the nose. But it's still connected to the nose through two Kevlar-coated wires.
As the base of the projectile falls free, six Cholla electrodes unfold. The electrodes take their name from the Cholla cactus, which has barbed spines. If the Cholla electrodes pierce the subject's clothing and make contact with the skin, the microprocessor in the XREP channels electricity through both the nose and Cholla electrodes. This spreads the NMI effect over a larger area of the subject's body.
Taser's Web site says that most people tend to react the same way after suffering a blunt impact: They instinctively reach for the impact site. That's not such a great idea with the XREP. If the subject's hand makes contact with the XREP's reflex engagement electrodes, the microprocessor in the XREP diverts electricity and creates a circuit. Electricity flows from the electrodes into the subject's body and out through the hand that is touching the XREP. This spreads the effect of the XREP through more of the subject's body.
If the only contact with the subject is through the nose of the XREP, the microprocessor directs all pulses through those electrodes. That means a smaller area on the subject's body will be subject to the NMI effect.
The 20 seconds of voltage emission allows the officer time to close the distance to the subject and restrain him or her. But the shotgun shell form factor also means the officer can load a second round into the gun and fire at another subject if necessary.
What happens physiologically when you're hit by a device like the XREP?
Why do Tasers work? What is it that makes them capable of incapacitating a human, no matter how large or strong that person might be? It all has to do with muscle physiology.
Our bodies work using a combination of electrical and chemical signals to communicate commands from the nervous system to and from our other systems. When we want to flex a muscle, our brain sends electrical signals to special nerve cells. These nerve cells are transducers -- they convert energy from one format into another. In this case, the nerve cell converts the electrical energy from the brain into a chemical compound called a neurotransmitter.
The neurotransmitter tells your muscle cells to contract. On a chemical level, the neurotransmitter causes muscle cells to release calcium within the cell. The calcium binds with the protein troponin, which regulates contraction. Muscle cells work together in huge numbers, making it possible for you to flex a bicep or lift a finger. When the cells stop receiving the command to contract, the calcium returns to a series of intercellular vesicles called the sarcoplasmic reticulum [source: National Skeletal Muscle Research Center].
When you apply a high-voltage, low-amperage electric charge to muscle tissue, it's as if you're overloading its communication system. Taser's electric pulses cause affected muscles to contract up to 19 times per second. Under normal conditions, your body moves by relaxing one set of muscles while contracting another. But if an electronic pulse hits your body, both sets of muscles may try to contract at the same time. Generally speaking, the stronger muscles win out. But because the pulses override the commands from your brain, you have no conscious ability to control their movements.
As a result, the affected area of your body will tense up as the surrounding muscles contract. You may lose your balance and fall. Depending upon where you've been hit, you may not be able to break your fall or catch yourself. That's why people who have been hit by a Taser sometimes suffer superficial cuts, bumps and bruises.
Because Taser uses low-amperage currents, there's little danger of suffering electric burns or more serious side effects. But there's still the potential for complications. While Taser claims the amperage levels are well within safe levels, others aren't convinced. Several individuals have brought lawsuits against Taser charging that the company's product contributed to a person's death.
Until June 2008, Taser either won every case or settled out of court. Taser lost its first case in California -- a jury found the company liable for the death of Robert C. Heston. Police officers hit Heston multiple times with Taser devices while attempting to subdue him in 2005. The jury concluded that the Taser strikes caused Heston's death. The Taser company plans to appeal the decision [source: Johnson].
While the court decision is a setback for Taser, many people depend upon the company's products to provide a solution for situations that don't call for lethal force. It's likely we'll see more controversy as law enforcement and military personnel adopt the XREP in their weapons repertoire. One thing's for certain -- the results will be shocking.
To learn more about stun guns, take a look at the links on the next page.
How the Taser Shotgun Shell Works: Author's Note
Attending CES (formerly known as the Consumer Electronics Show) in Las Vegas is something I both look forward to and dread each year. The dread stems from the fact that the show is enormous -- it occupies the Las Vegas Convention Center, a 3.2-million square foot (297,290 square-meter) facility, with exhibition space spilling over into neighboring mega hotels. But each year I somehow discover something I find particularly interesting. The Taser Shotgun Shell definitely falls into that category. It's fascinating technology and absolutely terrifying all in one go. The idea of shooting someone with an electrified slug seems like the stuff out of a science fiction film but it's reality. The stopping power of a Taser is impressive and legitimately scary. The invention left such a huge impression on me -- figuratively speaking -- that I've sought out the Taser booth every year since.
Related HowStuffWorks Articles
- All About Circuits. "Physiological effects of electricity." (Jan. 16, 2009) http://www.allaboutcircuits.com/vol_1/chpt_3/2.html
- Ask Science Theatre. "Why is electricity so dangerous?" Lansing State Journal. Jan. 8, 1992. (Jan. 16, 2009) http://www.pa.msu.edu/sci_theatre/ask_st/010892.html
- Carman, Brent G. "Sub-lethal, Wireless Projectile and Accessories." U.S. Patent 6,880,466 B2. Filed June 20, 2003 and issued Apr. 19, 2005.
- Carman, Brent G. "Sub-lethal, Wireless Projectile and Accessories." U.S. Patent 7,096,792 B1. Filed Dec. 24, 2004 and issued Aug. 29, 2006.
- CBC News. "Tasers." Sept. 4, 2008. (Jan. 15, 2009) http://www.cbc.ca/news/background/tasers/
- Crane, David. "TASER XREP Less-Lethal Shotgun Round." Defense Review. Sept. 1, 2008. (Jan 16, 2009) http://www.defensereview.com/taser-xrep-extended-range-electronic-projectile-less-lethal-shotgun-round/
- Encyclopedia Britannica. "Opuntia." 2009. Encyclopedia Britannica Online. 16 Jan. 2009 http://www.britannica.com/EBchecked/topic/430610/Opuntia.
- Johnson, Andrew. "Taser's stock hurt by 1st lawsuit loss." Arizona Central. June 10, 2008. (Jan. 15, 2009) http://www.azcentral.com/business/articles/2008/06/10/20080610biz-taser0610.html
- Martin, Charlotte. "High voltage: How safe are the cops' new Tasers?" Yale Daily News. Nov. 29, 2006. (Jan. 16, 2009) http://www.yaledailynews.com/articles/view/19125
- McNulty, Jr., James F. "Multi-stage Projectile Weapon for Immobilization and Capture." U.S. Patent 6,877,434 B1. Filed Sept. 13, 2003 and issued Apr. 12, 2005.
- National Skeletal Muscle Research Center. "Muscle Physiology." University of California, San Diego. (Jan. 16, 2009) http://muscle.ucsd.edu/index.shtml
- Shalev, Ilan et al. "Non-lethal Wireless Stun Projectile System for Immobilizing a Target by Neuromuscular Disruption." U.S. Patent Application Publication 2007/0101893 A1. Filed June 12, 2006 and published May 10, 2007.
- Smith, Patrick W. and Nerheim, Magne H. "Systems and Methods for Target Impact." U.S. Patent 7,327,549 B2. Filed Jul. 12, 2006 and issued Feb. 5, 2008.
- Taser. "Neuromuscular Incapacitation (NMI)." March 12, 2007. (Jan. 16, 2009) http://www.taser.com/research/technology/Pages/NeuromuscularIncapacitation.aspx
- Taser. "TASER XREP." (Jan. 14, 2009) http://www.taser.com/products/law/Pages/XREP.aspx
How the Taser Shotgun Shell Works: Cheat Sheet
Stuff you need to know:
• The Taser Shotgun Shell's official name is the eXtended Range Electronic Projectile (XREP) and it works through neuromuscular incapacitation (NMI).
• Our muscles rely on electrochemical signals sent from our nervous system. Millions of the signals pass through our bodies every second. A Taser overloads this communication system by introducing low-amperage, high voltage electricity.
• A hit from a Taser can cause your muscles to contract up to 19 times per second.
• The purpose of the Taser is to incapacitate the target without causing severe injury, but there have been reports that some people have died as a result of being hit by a Taser. Taser disputes these claims and says that its products are safe to use under normal circumstances.