Gas container
From Halopedia, the Halo wiki
The Forerunner's mining facilities use gas containers to move the volatile gases from location to location within the facility. They can explode if exposed to weapon fire or an explosion in the immediate vicinity. You can use these to kill Heretic forces on the level The Arbiter. The also appear on the Multiplayer level Colossus
The gas is possible used as a fuel to power the station and the containment shields of the Flood perimeter.
