Fire prisoner getting standard share (13)
I believe the answer is:
conflagration
'fire' is the definition.
(I know that conflagration is a type of fire)
'prisoner getting standard share' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'getting' is a charade indicator (letters next to each other).
'standard' becomes 'flag' (standard is a type of flag).
'share' becomes 'ration' (a ration is a share of a limited resource).
'con'+'flag'+'ration'='CONFLAGRATION'
(Other definitions for conflagration that I've seen before include "Big blaze" , "Burning" , "Large destructive fire" , "Inferno" , "Great fire" .)