Hazard Vault 305 was a facility built on the planet Balmorra by the time of the Cold War. It was part of the Balmorran government's initiative to protect their thriving industrial world that led to the creation of a series of tightly sealed underground vaults. These were to be used for the storage of toxic waste that was produced by the world's many factories. Hazard Vault 305 itself was built in a pre-existing cave and intended to collect the waste from the Balmorran Arms Factory.
Unknown to anyone, the cave was in fact used by the Sith Lord Tulak Hord to hide one of his artifacts. During the Sith Empire's invasion of Balmorra, missile barrages damaged the hazard vault and led to its contents leaking. However, this also provided a means of entry into Hazard Vault 305 for anyone that was able to survive the deadly waste and Mutated Colicoids infesting it.