Dust Kelvin, say, used in potentially explosive situation (6,3)
I believe the answer is:
powder keg
'potentially explosive situation' is the definition.
(I've seen this in another clue)
'dust kelvin say' is the wordplay.
'dust' becomes 'powder' (I've seen this before).
'kelvin' becomes 'K' (abbreviation for the unit of temperature).
'say' becomes 'eg' (both can mean 'for example').
'powder'+'k'+'eg'='POWDER KEG'
'used in' is the link.
(Other definitions for powder keg that I've seen before include "Volatile situation" , "Potential source of explosive violence?" , "potential disaster" , "one to go up?" , "Potentially explosive situation?" .)