Emergency priority system (6)
I believe the answer is:
triage
'emergency priority system' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for triage that I've seen before include "Determination of patient priority for treatment" , "Hospital procedure" , "Sorting and allocating aid on the basis of need" , "Assignment of urgency to illnesses" , "Selection and allocation for medical aid" .)