Gas grenade

Sleep gas grenades, sometimes known simply as gas grenades, knockout gas grenades, or neutralizing gas grenades, are a type of grenade that, as the names suggest, utilize a knockout gas to incapacitate soldiers or other people when activated.

Usage
During the Peace Walker Incident in 1974, Big Boss and his mercenary group, the Militaires Sans Frontieres, procured design specs for sleep gas grenades after a mission to neutralize an enemy unit within the U.S. Missile Base in Nicaragua's small maintenance dock.

Zanzibar Land used the ABC M25A2 sleep gas grenade whenever a riot breaks out, with it expelling CN-1 gas when detonated. Solid Snake procured some ABC M25A2 sleep gas grenades, and used them to determine the wind's direction before using a hang-glider to cross the ravine between Zanzibar Tower and the Detention Camp after Gray Fox destroyed the Bridge of Sorrow.

Gameplay
"A non-lethal grenade that releases sleeping gas when it detonates. Anyone who inhales the gas will fall asleep within a certain amount of time. Throwing multiple grenades will increase the potency of the gas and make targets fall asleep faster. Of course, the gas also affects the user, so make sure to throw the grenade a safe distance away."

- Sleep Gas Grenade description from Metal Gear Solid: Peace Walker