Stun grenade

A stun grenade, also known as a flash grenade, flashbang, thunderflash or sound bomb, is a less-lethal explosive device used to temporarily disorient an enemy's senses. It is designed to produce a blinding flash of light of around 7 megacandela (Mcd) and an intensely loud "bang" of greater than 170 decibels (dB). It was first used by the British Army's Special Air Service in the late 1970s.
The flash temporarily activates all photoreceptor cells in the eye, blinding it for approximately five seconds. Afterward, victims perceive an afterimage which impairs their vision. The sheer volume of the detonation also causes temporary deafness in the victim and also disturbs the fluid in the ear, causing a loss of balance.
The concussive blast still has the ability to cause injuries, and the heat created may ignite flammable materials. The fires that occurred during the Iranian Embassy siege in London were caused by stun grenades coming into contact with flammable objects.
Construction.
British technical experts created the first "flash bang" or "stun" grenade for the Special Air Service's Counter terrorist wing.
Unlike a fragmentation grenade, stun grenades are constructed with a casing made to remain intact during deflagration and avoiding fragmentation injuries, while having large circular cutouts to allow the light and sound of the explosion through. The filler consists of a pyrotechnic metal-oxidant mix of magnesium or aluminium and an oxidizer such as potassium perchlorate or potassium nitrate.
Hazards.
While stun grenades are designed to limit injury to their targets, permanent hearing loss has been reported. If a stun grenade detonates too close to a person it has a chance of being lethal. The intact casing can also cause injury if it hits someone.
If the explosion occurs too close to any flammable material there is a chance of fire. There have been many such incidents where stun grenades failed to serve their intended purpose by causing death or permanent injury. These incidents include the following: