Story of a gas explosion (4)
I believe the answer is:
saga
'story' is the definition.
(saga is a kind of story)
'a gas explosion' is the wordplay.
'explosion' is an anagram indicator.
'a'+'gas'='agas'
'agas' with letters rearranged gives 'SAGA'.
'of' acts as a link.
(Other definitions for saga that I've seen before include "Norse narrative" , "Account of great heroism" , "Medieval Icelandic legend" , "Long heroic, family, story" , "Epic story" .)