Dismissed a politician for something potentially explosive (8)
I believe the answer is:
firedamp
'something potentially explosive' is the definition.
(firedamp is a type of methane)
'dismissed a politician' is the wordplay.
'dismissed' becomes 'fired' ('fire' can be a synonym of 'dismiss').
'politician' becomes 'MP' (Member of Parliament).
'fired'+'a'+'mp'='FIREDAMP'
'for' acts as a link.
(Other definitions for firedamp that I've seen before include "Methane found in coal mines" , "dangerously explosive" , "a particular horror of mine" , "Methane in coalmines" , "Gas lit by a member" .)