Shares of Taser International Inc. (TASR) rose sharply Thursday for the second straight day, helped by Defense Department (search) support for Taser's assertion that a Pentagon study found the company's stun guns are generally safe.

In midday trading, the stock rose $4.64, or 27 percent, to $21.65 on the Nasdaq Stock Market (search). In recent days, the stock had fallen more than 50 percent from a 52-week high of $33.45 set Dec. 30.

The Securities and Exchange Commission (search) is investigating the Scottsdale, Ariz., company's safety claims about its stun guns.

In October, Taser announced that a Pentagon study had determined its stun guns "will generally be effective ... without a significant risk of unintended severe effects."

"This puts to bed the SEC inquiry, because it should help to answer the questions of safety," Source Capital Group analyst Joe Blankenship said Thursday.

The Pentagon's Joint Non-Lethal Weapons Directorate commissioned the Air Force Research Laboratory to study the health effects of Taser's products. Wednesday, Capt. Dan McSweeney, spokesman for the directorate, upheld the findings and Taser's representation of them, noting that the Pentagon had reviewed the company's press release before it was issued.

"We have stated that Tasers are generally safe and effective," McSweeney said. "If we didn't that think that was the case, we wouldn't have recommended that the services purchase and field Tasers."

Taser was also in the news Thursday as a study characterized the weapon's danger to the heart as "extremely low."

The Pacing and Clinical Electrophysiology Journal reported that the stun gun has a very little likelihood of triggering ventricular fibrillation — a fatal form of heart arrhythmia.

Source analyst Blankenship said neither of Taser's top two competitors, Stinger Systems and Law Enforcement Associates Corp., has effective products to compete with Taser's stun guns.