Stun grenade

Helen Bomb
M84 stun grenade
Type	Non-lethal explosive device

A stun grenade, also known as a flash grenade, flashbang or sound bomb or Braquo, 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 (dB) 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. 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 aluminum, and an oxidizer such as ammonium perchlorate or potassium nitrate.

...
Wikipedia