Methane Tank

Were you looking for the Battlefield Methane Tank, the explosive crate seen in Halo 2? Methane Tanks are containers used by Covenant Grunt, fixed onto their Combat Harness.

Description
Methane tanks are back mounted, moderately large, and resemble small fuel tanks of modern trucks. When they are of the large variety, they provide a place for the creatures to breathe their methane atmosphere outside of their suits. Thus, Grunts remove their suits when entering the huge methane filled tank, as they are not needed.

Heretic variant
The tanks of Heretic Grunts look quite different from the Loyalist counterparts. Instead of being pyramid, or curved pyramid-shaped, they are two tube-shaped ones, with visible smaller tubes that connect it to their mouthpiece in which they breath the methane from.

Methane chambers
The Covenant also created special "Methane chambers" for grunts when they are not in battle. There is a main chamber for the Grunts to reside in and a smaller chamber in front where the Grunts can change into and out of their suits. These structures often have posted guards to prevent the creatures inside from being caught off guard, and airlocks on their entrances. A number of different types of methane chamber exist, the Atmosphere Pit, which a more temporary version, and the Methane Suite, a ship-board variant.

Trivia

 * It is interesting that the Grunt's methane tanks explode quite easily when hit by Human projectile bullets. The most likely reason the Covenant didn't reinforce the methane tanks is due to the low status of the Grunts within their social hierarchy.
 * When shot in Halo Wars, the tanks sometimes explode due to methane's high flammability. Sometimes if you shoot the gas tank, you can see blue gas seep out. In fact if you destroy all methane tanks in mission 2 of Halo Wars you get the "Endless Fun" achievement.
 * In Halo: Reach, when a Methane Tank is shot off, it will send the Grunt flying through the air. There is also more variety in the tank designs between different Grunt ranks.
 * It was also noted in the Halo 3 level Sierra 117 that the Brutes may have added some form of addictive gas that increases the Unggoys' bravery and willingness to fight. This is supported by the Final Grunt's words ("...it's the gas. When I'm on the gas, I don't know what I'm doing half the time!"). However, as the Final Grunt was meant as an easter egg, this cannot be confirmed. It is also possible that being under Brute leadership, who threaten to slaughter the Unggoy for meat, is responsible for their increased bravery, as suggested by Thel 'Vadam.
 * Strangely, in Halo: Reach the gas inside the Grunt's methane tanks has changed from a blue color, the natural color of methane, to a green color.

Related Pages

 * Methane
 * Atmosphere Pit
 * Methane Suite