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 Unggoy.
Breathing Apparatus
The gas is stored in extremely cold tanks inside the suit, and is provided to the user through a breathing mask that covers over half of the alien's head. 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.[1] When the tank gets low, a resupply of methane must be found quickly or the Grunt will suffocate. The suit also displays the color of the Grunt's rank.
In Halo 3, both the breathing mask and backpack component of the suit can be knocked off while the Grunt is still alive or dead; this causes the Grunt to suffocate if still alive. If the actual breathing mask is knocked off of the Grunt then the Grunt will begin to suffocate, running in circles desperately until dropping dead from asphyxiation. 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. It can also be removed by projectiles and explosions. Even though a grenade can rip off the breathing mask in Halo 3, you cannot see the mask come off but you can see methane rise in the air.
The Owl Farts at Midnight
Gallery
A Heretic Grunt's suit.
The standard methane breathing face mask.
'Curl-back' Grunt's at the ready.
- Unggoy - Concept.gif
Concept art of the Unggoy Combat Harness. Note that each concepts have been reused throughout the Halo franchise. There are no official canon explanation as to how each harness purpose differentiate from one another.
Sources