Fire blankets left hanging (5)
I believe the answer is:
slack
'hanging' is the definition.
(thesaurus)
'fire blankets left' is the wordplay.
'fire' becomes 'sack' (dismiss someone from their job).
'blankets' indicates putting letters inside (I've seen this in other clues).
'left' becomes 'l' (common abbreviation).
'sack' placed around 'l' is 'SLACK'.
(Other definitions for slack that I've seen before include "coal dust" , "Lax" , "Not taut" , "Loose" , "Limp - negligent" .)