 FACT: SPOILER: When Denethor catches fire, he is in the Hallows of  Minas Tirith, on the sixth of seven levels of the city (according to  the books). However, he dies not by immolation but by plummeting off  the prow of the city, meaning that he ran, fully engulfed in flames,  "...about a mile..." (as Peter Jackson later revealed in the audio  commentary). Now THATS determination!