Methane Environmental Suit

Grunts (aka Unggoy) use a Methane environmental suit to mimic their homeworld's methane filled atmosphere. The methane is supercooled for storage (allowing their thermal signatures to be picked up easily). The triangular backpack attached to a Grunt's back contains several methane tanks. 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. When this begins to run out of methane it shrinks on the back so the grunt dosn't have to work as hard.