What Are Stun Grenades?

And when do they come in handy?

The Red Sox victory celebration at the University of Massachusetts-Dartmouth got out of hand on Wednesday night, when drunken students smashed windows and overturned a Dumpster. (The incident was separate from the one near Fenway Park, in which an Emerson College student was killed.) Police made 20 arrests in Dartmouth and used stun grenades to disperse the 800-strong crowd. What’s a stun grenade?

The weapon’s alternative name says it all: flash-bang grenade. Unlike the lethal ovoids lobbed in combat, stun grenades don’t scatter metal fragments every which way. Rather, they create an intensely bright flash—as bright as 1 million candles burning at once—along with a boom that registers at upwards of 175 decibels. One of the most common models, the XM84, features a perforated metal shell around a casing filled with a powder of aluminum and potassium perchlorate. When the time-delayed fuse is lit by pulling the pin, the powder burns, creating a deafening bang and a blinding flash. The exterior shell remains intact.

Stun grenades were first used in 1977 by Britain’s Special Air Service, an elite commando unit. In a joint operation with West Germany’s GSG9 special-operations team, SAS commandos stormed a hijacked Lufthansa Airlines flight, which had been flown to Mogadishu, Somalia. (The Palestinian hijackers were demanding that West Germany release 11 members of the Red Army Faction.) The novel, nonlethal grenades were used to disorient the terrorists prior to the successful assault.

Since then, stun grenades have become a staple of army and police arsenals, often used to “soften up” rooms or buildings before armed personnel come storming in. The sensory toll is great enough that some people report hearing and vision problems for days afterwards. Cops or soldiers who toss stun grenades are advised to wear earplugs and visors and to take cover once the device has been sent airborne.

Though the grenades are specifically designed to be nonlethal, they are not without hazards. They can still ignite secondary explosions if set off in proximity to a gasoline tank or other flammable materials. And the intensity of the blast can cause coronaries in the elderly and those with heart problems: Such was the case in May of 2003, when a mistaken New York Police Department raid caused a 57-year-old woman to have a fatal heart attack.

It’s a bit curious that the Dartmouth police used standard flash-bang grenades for crowd control, as that’s not common practice. There are other grenade varietals, such as the ABC-M7A3 CS, that are specifically designed for that purpose; they typically emit vast plumes of irritating smoke in order to discourage throngs from marching forward. There are also some hybrid models, like the XM99, which is designed for riot control and combines the flash-bang effect with small rubber projectiles.

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