Steam
From Tardis Wiki, the free Doctor Who reference
According to the Second Doctor, trains were drawn by steam. (TV: The Evil of the Daleks)
Steaming was a method of execution used by the Company. It involved the victim being put into a condensation chamber with a heat exchanger, regulated by a water pump, that turned the water into high-pressure steam that scalded the victim. (TV: The Sun Makers)
Jack Harkness turned the Hub's conference room by pumping steam into it. (AUDIO: The Empty Hand)
