The Perfect Shock?

Although the authors’ physiological analyses of the Taser seem sound [”How a Taser Works,” December 2007], I think the articles carry two flaws.

Technically, in terms of single-pulse energy integral (amperes squared per second), the 1 percent heart-fibrillation threshold is 1.5 x 10-3, the 5 percent threshold being 4 x 10-3. Therefore, the Taser single pulse, with approximately 0.6 x 10-3, seems safe by a 2.5 factor if one looks for fewer than 1 percent fatal issues. However, there are bursts of 19 pulses per second whose cumulative effects cannot be disregarded. Mark W. Kroll calculates that a 90-ampere current would be needed to electrocute someone using a Taser because its 100-microsecond pulse length is one-thirtieth that of the 3-millisecond pulses at 3 A it takes to dead-stop a heartbeat. This is not correct. Energy is related to the current squared; therefore the safety factor is not 30 but 5.5. This, too, has to be weighed by the statistical distribution of lethal current threshold.

Socially, although the benefits of disabling dangerous suspects without shooting or killing is undisputable, another issue appears: soon, criminals will get Tasers too. What a handy gizmo for a successful robbery, hold-up, or other crime, without risking capital punishment or long sentences, since no killing or injuring takes place.

Michel Mardiguian

IEEE Member

Saint-Rémy-lès-Chevreuse, France

The Taser article ”Crafting the Perfect Shock” by Mark W. Kroll includes a graph labeled ”Levels of Shock.” It shows Taser shock at 2 milliamperes and compares it with sine wave data at 60 hertz, which ”causes the heart to behave erratically” at about 100 mA. But the 60-Hz sine wave data are for hand-to-hand currents, which result in very low current density in the heart, whereas the Taser dart may land over the heart in the ”zone of maximum cardiac sensitivity,” which results in very high current density in the heart. A dart over the heart has been shown to cause ventricular fibrillation in pigs by Nanthakumar et al. in ”Cardiac Electrophysiological Consequences of Neuromuscular Incapacitating Device Discharges,” Journal of the American College of Cardiology , 48 (4): 798–804, 2006, and by Dennis et al. in ”Acute Effects of Taser X26 Discharges in a Swine Model,” The Journal of Trauma , 63: 581–590, 2007.

John Webster

IEEE Life Fellow

Madison, Wis.

What a shock that you have a person associated with the product make an assessment of the safety of the Taser [Mark W. Kroll]; he even uses the product numbers and names as if he were writing a promotional piece. You should at least have had a point (by Kroll) and a counterpoint by another, ”real” expert on the opposing side. The Tchou piece was a good addition, but that, too, was weak. There was no mention in the article of age as a factor, the assumption being that the healthy and young would be the only ones so subjected.

Azmat Malik

IEEE Member

San Carlos, Calif.