A stun grenade, also known as a flash grenade or flashbang, 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 loud noise without causing permanent injury. It was first developed by the British Army's SAS in the 1960s.
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. The loud blast causes 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. The fires that occurred during the Iranian Embassy Siege in London were caused by stun grenades.
Unlike a fragmentation grenade, stun grenades are constructed with a casing made to remain intact during detonation, containing most of its explosive force and avoiding shrapnel 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 ammonium perchlorate or potassium perchlorate.
Lethality of stun grenades 
Although stun grenades are usually designed to be non-lethal, several deaths have been attributed to their use. These include:
- In 1989, police in Minneapolis, Minnesota, conducted a drug raid at the home of an elderly couple, Lloyd Smalley and Lillian Weiss, after receiving inaccurate information from an informant. The flashbang grenades police used in the raid set the home on fire. Police were "certain" no one was inside, and so, at first, made no attempt at rescue. Smalley and Weiss died of smoke inhalation.
- In May 2003, a woman named Alberta Spruill died from a heart attack after a police team detonated a stun grenade at her residence in Harlem, New York. Her family eventually won a $1.6 million civil suit against the city.
- In January 2011, a California man named Rogelio Serrato died of smoke inhalation after a flashbang grenade launched by a police SWAT team ignited a fire in his home. The man was believed to have been hiding in the attic when the fire broke out.
- In February 2011, North Carolina SWAT police officer was injured at his home when a stun grenade accidentally detonated while he was attempting to secure his equipment. He underwent emergency surgery, but later died of his injuries.
- Karren Mills, "City Image Tarnished By Allegations of Police Racism," Associated Press, March 21, 1989. Retrieved at http://news.google.com/newspapers?nid=861&dat=19890321&id=yCgcAAAAIBAJ&sjid=f1kEAAAAIBAJ&pg=5737,4567990
- David Chanen, "Police device used in search is considered safe, official says," Minneapolis Star Tribune, March 17, 2000, p. 7B. Retrieved at http://www.highbeam.com/doc/1G1-62420698.html
- The case is also cited in “Botched Police Raids not so rare” retrieved at http://webcache.googleusercontent.com/search?q=cache:frGznzVS2JAJ:www.mapinc.org/drugnews/v07/n1471/a03.html+&cd=1&hl=en&ct=clnk&gl=gr&client=firefox-a
- The case is also cited in “Botched raid costs Minneapolis $1 million”, Star Tribune December 9, 2011 http://www.startribune.com/local/135343023.html?page=all&prepage=1&c=y
See also 
- FM 3-23.30 "Grenades and Pyrotechnic Signals". globalsecurity.org, 1 September 2000. Ch. 1, Sec. 10. "Stun Hand Grenades". Retrieved on 26 May 2011.