Gas container

A container can be seen behind two Heretic Grunts.

The Forerunner's mining facilities use Gas Containers to move the volatile gas mazes from location to location within the facility. They can detonate if exposed to weapons fire or an explosion in their immediate vicinity. You can use these to kill Heretic forces on the level The Arbiter and The Oracle. They also spawn in Halo 2 on the Multiplayer level Colossus. The gas inside these containers is possibly methane; it appears to be similar in color to that of which the Unggoy have on their backs. Also these containers are better to use when there are groups of enemies to damage their energy shields for an easier kill.

The substance could also be a possible fuel used to power the station and the containment shields of the Flood perimeter.