In the fire department, it's revolutionary! (3)
I believe the answer is:
red
'revolutionary' is the definition.
(informal term for communist)
'in the fire department it's' is the wordplay.
'in' says the answer is hidden in the clue.
'RED' can be found hidden inside 'fire department ts'.
(Other definitions for red that I've seen before include "Warning light colour" , "See it and become angry" , "Ruby" , "Colour for danger" , "Blushing" .)