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.