Bulkhead

A bulkhead was a wall-like partition that could be found in certain buildings. The Vault in Utah, having been designed as a bunker in the event of nuclear warm was equipped with a series of bulkheads, which were closed to prevent the Dalek named "Metaltron" from escaping, unable to penetrate the bulkheads with its gunstick. However, while Adam Mitchell was able to escape beforehand, Rose Tyler was left behind with the Dalek. Making contact with the office of Henry van Statten, the Dalek threatened to kill Rose if the bulkhead was not opened, forcing the Ninth Doctor to comply. (TV: Dalek)

Behind the scenes

In the video game NOTVALID: The Last Dalek, based on the episode Dalek, the Dalek is able to destroy the Vault's bulkheads with the Alien Weapon taken from the Doctor. From its specifications, the bulkheads are found to have been constructed from alien alloys, are promoted as being able to withstand all known attacks, activated by a timer, cannot be re-opened once shut, and only to be used as a last resort.