Categories of life The categories of life was a system used to classify people on Earth when , after Miracle Day , people stopped dying . Badly injured people , Categories 1 and 2 , were taken to overflow camp s . Those in Category 1 were secretly taken to module s and burned alive . This seemed the only way human s could die after the Miracle occurred . In theory , the category system was necessary because the global situation was thought of as an epidemic in which victims ' bodies would be burned " en masse " . The bodies of Category 1 individuals , potentially infectious , would otherwise remain eternally alive but legally dead under the new laws . Even after the Modules became common knowledge , they were still used . Governments gave law enforcement special powers to search premises without a warrant if there was suspicion of an unlicenced Category 1 located there . In reality , the line between the categories was dubious . A Category 1 could become Category 2 , should they recover ; Rex Matheson should have been killed when he was impaled by a rebar , but healed over time . Likewise , a Category 2 could slide into Category 1 without proper treatment . Individuals such as Geraint Cooper ( who lapsed into a deep coma after suffering a stroke ) were lumped into Category 1 with the truly brain - dead . Esther Drummond jokingly referred to Jack Harkness as " Category Jack " when he became mortal , as opposed to the rest of the planet ' s immortality . Slang developed for the concept , with some people referring to Category 1s as " Cat 1s . ( TV : " The Middle Men " ) Also , as death no longer existed on Earth , some replaced the verb " to kill " with " to Category 2 " . ( TV : " The Blood Line " ) Category 1 . Those people designated Category 1 were brain dead or otherwise unable to function . In the overflow camps , Category 1 patients were designated with a red clothes peg and sent to the modules to be burned . ( TV : " The Categories of Life " ) Category 2 . Category 2s were those with non - fatal but permanent injuries . Though Category 2s might be severely injured , they were not brain dead and could function with a degree of independence . In the overflow camps , Category 2 patients were identified with a blue peg . ( TV : " The Categories of Life " ) Category 3 . Category 3 referred to anyone who was completely healthy — anyone not in Categories 1 or 2 . ( TV : " The Categories of Life " ) Category 0 . Category 0 was a proposed category that would consist of anyone , of any category , deemed fit for the modules for moral reasons , such as criminals who would have received the death penalty prior to the Miracle . ( TV : " End of the Road " ) Rex Matheson unwittingly predicted this category after learning of the categories . He believed that after starting with the Category 1s , it would move onto convincted felons and illegal immigrants , " hell , anyone we don ' t like . " ( TV : " The Middle Men " ) Oswald Danes later learned from Jilly Kitzinger that he had been classified as Category 0 , after which he went underground ; Jilly implied that the category had been specifically created with Oswald in mind . ( TV : " End of the Road " ) Exceptions . Two people did not fall into any of the categories . Jack Harkness was mortal , ( TV : " Rendition " , et al ) and Angelo Colasanto was in a null field , so was therefore not affected by the Miracle and mortal too . ( TV : " End of the Road " )