Evacuation authorisation (9)
I believe the answer is:
clearance
I believe this clue is a double definition.
'evacuation' is the first definition.
(I've seen this before)
'authorisation' is the second definition.
(clearance is a kind of authorisation)
(Other definitions for clearance that I've seen before include "evacuation" , "eviction of tenants" , "Permission to proceed" , "Intervening space" , "Removing ball from defensive area" .)