Fire exit (2,3)
I believe the answer is:
go off
This clue is a double definition.
'fire' is the first definition.
(synonyms)
'exit' is the second definition.
(thesaurus)
(Other definitions for go off that I've seen before include "Rot; leave" , "Fire" , "Turn" , "Decay - become disenchanted with" , "Explode" .)