Like the Grim Guzzler, this room is another area which is safe to begin with. It is populated by the seven ghostly dwarves, the patriarchs of the Dark Iron nation - and the dwarves who helped Sorcerer-Thane Thaurissan summon Ragnaros into the world. These dwarves must be killed to pass on to the later areas, but before the attack, any miners in the group should speak with Gloom'rel and do his quest to gain the ability to smelt . When the group is ready, speak to Doom'rel and challenge him.
Once the dwarves are defeated, the Chest of The Seven will spawn, and the doors will open, allowing access to the last areas of the instance.