A stun grenade, also known as a flash grenade, flashbang or sound bomb, is a non-lethal explosive device used to temporarily disorient an enemy's senses. It is designed to produce a blinding flash of light and an intensely loud "bang" of greater than 170 decibels without causing permanent injury. It was first used by the British Army's SAS in the late 1970s.
The flash produced momentarily activates all photoreceptor cells in the eye, making vision impossible for approximately five seconds, until the eye restores itself to its normal, unstimulated state. An afterimage will also be visible for a considerable time, impairing the victim's ability to aim with precision. The loud blast is meant to cause temporary loss of hearing, and also disturbs the fluid in the ear, causing loss of balance.
The concussive blast of the detonation can still injure, and the heat created can ignite flammable materials such as fuel.