Vacuum

A vacuum is an area that is virtually empty of matter, usually found in space. Most life forms cannot survive in a vacuum for very long. The few exceptions include Time Lords, for limited periods (DW: Four to Doomsday), Daleks (DW: The Parting of the Ways), Cybermen (DW: The Moonbase), and Toby Zed while possessed by the Beast. (DW: The Impossible Planet)

People known to be killed by exposure to vacuum include Katarina and Kirksen (DW: The Daleks' Master Plan) and Lynda Moss. (DW: The Parting of the Ways)