Perhaps emergency exit leads to steel duct (8)
I believe the answer is:
stairway
'perhaps emergency exit' is the definition.
(I know that emergency exit is a type of stairway)
'steel duct' is the wordplay.
'steel' becomes 'st' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'duct' becomes 'airway' (airway is a kind of duct).
'st'+'airway'='STAIRWAY'
'leads to' acts as a link.
Can you help me to learn more?
(Other definitions for stairway that I've seen before include "- to Heaven, Led Zeppelin song" , "A flight of fixed indoor steps" .)