How do Tasers work?

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Nov. 21 2006 7:00 PM

How Do Tasers Work?

Heavy on the volts, light on the amps.

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Independent investigators will look into last Tuesday's incident on the UCLA campus, in which a student was subjected to five Taser shocks by the university police. (Here's a video.) Meanwhile, Taser International Inc. has filed lawsuits in Ohio and Indiana against coroners who have cited "electrical pulse incapacitation" as a cause of death. How do these things work, anyway?

They deliver a lot of volts, but very few amps. Stun guns shoot an electrical pulse that's designed to go through clothing and skin and give someone a nasty shock. A very high voltage ensures that the pulse will reach its target, and the very low amperage keeps it from doing any lasting damage. It's helpful to analogize these measures with water pressure: A high voltage is akin to water that's flowing at high pressure, while a low amperage is like water that's not flowing very quickly. The injury inflicted by an electric shock depends on the interaction between the "pressure" and "flow rate" of the electricity. (The area and duration of contact also make a difference.)

Daniel Engber Daniel Engber

Daniel Engber is a columnist for Slate

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Stun guns work by pressing a pair of electrodes against the victim in order to create an electric circuit. (Most use 9-volt batteries, or a handful of AAs.) Tasers differ from standard stun guns in that the electrodes are tethered to long, insulated wires and can be fired from the weapon with a burst of carbon dioxide. A standard stun gun or cattle prod can only be used at close range; Tasers can shoot someone from 20 feet away.

Once the electrodes hit their target, the Taser sends a pulse with about 50,000 volts and a few milliamps. On its standard setting, the pulse cycles for five seconds before shutting off. (The pulse continues for as long as you hold the trigger.) The five-second shock sends intense signals through the victim's nervous system, which causes considerable pain and triggers a contraction in all his muscles. Temporary paralysis can set in, and most victims fall to the ground. Tasers can also be used like regular stun guns in what's called "drive stun" mode. This causes more localized pain and less widespread muscle contraction.

The manufacturer warns that Taser shocks may cause breathing problems, skin irritation, small puncture wounds, or minor burns, and that the violent muscle contractions can result in "athletic-type injuries." Police officers are also instructed to "avoid weapon confusion"; i.e., don't mistake your handgun for a stun gun.

Amnesty International contends that Taser shocks may be implicated in the deaths of more than 150 people since 2001, and coroners have cited stun-gun shocks as a factor in more than 20 deaths over that period. Researchers who Tasered anesthetized pigs have found little permanent damage, and there's  scant evidence that the shocks would be fatal for healthy adults. Victims who are intoxicated or have pre-existing heart conditions may be at greater risk. Repeated shocks from a Taser may also be more dangerous.

Bonus Explainer: How do lightning strikes compare to Taser blasts? Lightning kills its victims 10 percent to 20 percent of the time. The bolts send a much nastier shock—a few milliseconds at 300,000 volts and tens of thousands of amps—but only a small portion of their energy actually penetrates the skin. (The rest runs over the surface of the body, in what's called lightning "flashover.") Taser pulses, which have only the tiniest fraction of this amperage, deliver a more efficient shock to the victim via the electrodes. Even so, Taser shocks do little or no lasting damage. Lightning strikes often cause heart attacks, severe burns, and long-term neurological problems.

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