Unggoy combat harness

The Unggoy Combat Harness is a type of body armor issued to the Covenant's Grunt warriors. It provides basic protection from hostile fire and the elements, and is also equipped with a breathing apparatus for the methane breathing aliens like Grunts

Breathing Apparatus
The gas is stored in cooled tanks inside the suit, and is provided to the user through a breathing mask that covers over half of the alien's head. The methane is supercooled for storage. The triangular backpack attached to a Grunt's back contains a small methane tank. Attached to every Grunt's wrist is a readout (measured in Covenant units) of the amount of methane left in the Grunt's pack. When the tank gets low, a resupply of methane must be found quickly, or the Grunt will suffocate. The suit also has the color of the grunts rank on display. In Halo 3, both the breathing mask and backpack component of the suit can be knocked off; this causes the Grunt to suffocate. It is interesting to note that in Halo 3 even if grunts lose their methane tank on their back, they can continue fighting without suffocating. This may mean that there is emergency methane stored inside their combat harness, However this is more likely just for game play reasons.

Defense
In addition to its life support role, it is equipped with armor. This armor can withstand limited amounts of fire, especially from energy weapons. The M6D is capable of easily cracking through the armor, and is considered by some to be the standard weapon for such actions. The armor-piercing rounds of the Assault Rifle are also potent weapons against the harness. As well as defending against projectiles and plasma, it prevents a limited amount of fall damage to its user, like its surpassing counterpart. Despite this, most variants are vastly inferior to the other types of armor adorned and used by the Covenant. Some variants are also equipped with helmets, Active Camouflage, and a methane-filled breathing apparatus. A grenade can easily rip through the armor and kill the Grunt. A grenade is also capable of ripping off the breathing mask in Halo 3.

Trivia

 * Even though a grenade can tear off the breathing mask in Halo 3 you can't see the mask come off but you can see methane rise in the air.