Phoenix ? From Korean Air to U.S. police and corrections officers and even beat cops in Britain, orders are pouring in for stun guns made by Taser International Inc.

The Scottsdale, Ariz., company even recently launched a regional ad campaign urging private citizens to arm themselves with the weapons, which temporarily paralyze people with a 50,000-volt jolt.

Yet while Taser’s stock has soared with the booming business, concerns are growing about whether the shock-inducing guns truly are as nonlethal as advertised.

In a report being released today, Amnesty International says stun guns routinely are being abused, and that at least 74 people have died in the United States and Canada in the past four years after being shocked with Taser stun guns.

A Defense Department-sponsored report also calls for more testing, and some health professionals are expressing concern that the potential for cardiac arrest could be too high.

“We are using currently available technology to potentially document minute-by-minute torture,” said Ed Jackson, Amnesty spokesman. Among cases that alarmed Amnesty are those in which officers turned stun guns on the mentally disturbed, children and the elderly.

Amnesty’s report expresses worry that “the deployment of Tasers, rather than minimizing the use of force, may dangerously extend the boundaries of what are considered ‘acceptable’ levels of force.”

Similar to a device first developed in the 1970s, Tasers became available to consumers in the early 1990s and now are used by more than 6,000 law enforcement agencies worldwide as well as the U.S. military, which has used them in Iraq and Afghanistan and ordered nearly $2 million worth of stun guns and accessories this summer.

Taser officials bill the guns — which shoot two barbed darts up to 21 feet and whose current can penetrate up to 2 inches of clothing — as among the safest ways of subduing violent individuals in high-risk situations.

“We get e-mail from police every week … thanking us for developing a weapon so (that) they didn’t have to shoot somebody,” said Phil Smith, company chairman. “We’re saving lives every day and cops love them.”

Taser International Inc. employee Lucy Lazarova assembles a law enforcement version of the popular stun gun. She worked on the guns last week at the company's headquarters in Scottsdale, Ariz. The company's stock has soared, but there are growing concerns whether the stun guns are as nonlethal as advertised. Below, Steve Tuttle, director of communications for Taser International, holds the X26c stun gun.

Phoenix police officers credit Tasers with helping police shootings drop by more than half, and reducing the number of fatal shootings by 31 percent last year.

“We’ve seen them reduce injury to suspects … who in the past we would have had to strike multiple times with fists or batons,” said Sgt. Randy Force, a department spokesman.

While not opposed to stun guns in principle, Amnesty International wants law enforcement to stop using Tasers until scientific evidence can show they don’t kill.

In a majority of Taser-related fatalities, coroners have attributed the cause of death to heart problems, drug overdose or asphyxiation. But some medical experts believe Taser shocks may exacerbate a risk of heart failure in cases where people are agitated, under the influence of drugs or have underlying health problems.

“If I hit the heart or create electricity in the wrong time of the (beat) cycle, it could send the whole heart into an electrical tailspin,” said Dr. Kathy Glatter, an electrophysiologist and assistant professor of medicine at the University of California-Davis.

Amnesty International claims stun guns are being fired too often in cases where the use of force is unacceptable. In many of the deaths cited by Amnesty, the person was shocked multiple times or subjected to other forms of force, like pepper spray, batons or hogtying.

In one such case, 47-year-old James Borden died in a Georgia jail after being stunned at least half a dozen times with a Taser. An autopsy report listed his cause of death as consistent with cardiac dysrhythmia, secondary to abnormal thickening of the heart, drug intoxication and electrical shock.

Most of the deaths documented by Amnesty occurred this year, just as sales picked up amid positive reviews.

A Department of Defense-ordered study cited by Taser company officials in defending their technology does, however, also recommend more research on how Tasers affect sensitive or intoxicated people.

The study, done by an Air Force laboratory for the Joint Non-Lethal Weapons Directorate, found that when used as intended, Tasers are safe. But it also said that, although uncommon, some severe unintended effects might occur after a shock.

The military has not released the entire study, only an abstract.

A military spokesman said the study’s author, James Jauchem, couldn’t be reached for comment. But the center that employs Jauchem did say that the center did not endorse nor approve use of the systems it studied.

Taser International, meanwhile, says it has documented 600 cases of lives saved with Taser devices and that it has not settled or lost any lawsuits involving deaths or injuries related to the guns.

“Fact is … this thing has been around for 30 years, never ever has a Taser been listed as the primary cause of death,” said Smith, the company chairman.