A stun grenade, commonly called a flashbang, is a non-lethal explosive device designed to temporarily blind and deafen anyone nearby without causing fatal injuries. It produces a blinding flash of around 7 million candela and a bang exceeding 170 decibels, both intense enough to overwhelm the senses for several seconds. Law enforcement and military units use them primarily to disorient people during hostage rescues, building entries, and other high-risk operations.
How a Stun Grenade Works
The basic mechanism is surprisingly similar to a standard military grenade, minus the shrapnel. A user pulls a pin and releases a spring-loaded lever (called a spoon), which strikes an internal primer. That primer ignites a delay column, giving the user roughly one second to throw the device before it goes off.
Once the delay burns through, the fuse fires into a small charge of black powder propellant, about 3 grams. This ruptures internal seals and disperses a fine aluminum powder out of the casing. The aluminum ignites on contact with the hot combustion gases and surrounding air, producing the characteristic massive flash of light. In some designs, magnesium replaces the aluminum. The core chemical mixture, aluminum and potassium perchlorate (known as flash powder), combusts faster than the speed of sound, which technically qualifies it as a detonating explosive. That rapid combustion, combined with the pressurized dispersal of material, creates the intense acoustic blast.
The casing is typically designed to stay intact rather than fragment, which is the key difference between a stun grenade and a lethal fragmentation grenade. The goal is sensory overload, not physical destruction.
What It Does to the Body
The M84, the standard U.S. military stun grenade, produces 170 to 180 decibels and 6 to 8 million candela within a 5-foot radius. To put that in perspective, a jet engine at close range is about 150 decibels, and the sun on a bright day measures roughly 100,000 candela per square meter. A stun grenade’s output is orders of magnitude beyond what human senses can handle.
The flash causes immediate but temporary blindness. During daylight, when your pupils are already constricted, flash blindness typically lasts only a few seconds and rarely more than two minutes. At night, when pupils are fully dilated and let in far more light, the effect lasts longer. The bang causes temporary deafness and tinnitus (ringing in the ears) and can disrupt the inner ear’s balance system, making it difficult to stand or move in a coordinated way. Combined, these effects leave a person disoriented and unable to resist for a brief window, usually five to ten seconds, which is exactly the point.
Who Uses Them and When
Stun grenades are primarily tools for law enforcement tactical teams (SWAT) and military special operations units. Police departments deploy them during barricaded suspect situations, hostage rescues, and critical incidents where a dangerous suspect poses a life-threatening risk. The device creates a momentary window for an entry team to move into a room and gain control before occupants can react.
Deployment follows strict protocols. Officers are trained to visually clear an area for bystanders before throwing a device. Stun grenades are not supposed to be thrown at or next to people. Teams also check for fire hazards, since the intense heat can ignite carpeting, curtains, or other flammable materials. Fire department and medical personnel are typically staged nearby when flashbangs may be used. Officers carrying the devices use safety clips and pins to prevent accidental detonation, and expired devices are restricted to training use only.
Risks and Injuries
Despite being classified as “less than lethal,” stun grenades can cause serious harm. The injuries fall into several categories. Pressure shock waves from the blast can damage delicate internal membranes, particularly the eardrum. At close range, the sound intensity alone can cause permanent hearing damage. The explosion can also fragment nearby objects, sending debris into people as secondary projectiles. The displacement of air can push someone into a wall or piece of furniture, causing blunt trauma. And the heat output causes severe burns, especially when the device detonates at close range, in an enclosed space, or in a dense crowd.
Physicians for Human Rights has documented cases involving all of these injury patterns. Crush injuries can also result indirectly when a crowd panics and stampedes after a detonation. Psychological trauma is another recognized consequence, particularly for people who were not the intended target of the device.
Multi-Burst and Other Variants
The classic stun grenade produces a single flash and bang. More advanced versions, sometimes called “multi-bangs” or colloquially “9-bangs,” detonate in a rapid series of flashes and blasts rather than one. The purpose is to extend the disorientation window. Instead of a single burst that lasts a fraction of a second, a multi-bang device produces repeated stimuli over several seconds, making it harder for a person to recover and react between detonations. Some designs also incorporate irritant chemicals like tear gas alongside the flash and bang for a combined effect.
Legal Status in the United States
Stun grenades are heavily regulated. Under federal law, devices that use explosive charges fall under the jurisdiction of the Bureau of Alcohol, Tobacco, Firearms and Explosives. Explosive anti-personnel devices are generally classified as destructive devices under both the Gun Control Act and the National Firearms Act. That classification means they require federal registration, serial number identification, and compliance with the same legal framework that governs other restricted weapons. Civilians cannot simply purchase stun grenades off the shelf. Possession without proper federal licensing and registration is a serious criminal offense. In practice, access is limited to military, law enforcement, and federally licensed entities.