Be said to survive explosion (5)
I believe the answer is:
blast
'explosion' is the definition.
(blast is a kind of explosion)
'be said to survive' is the wordplay.
'said' indicates a 'sounds like' (homophone) clue.
'to survive' becomes 'last' ('last' can be a synonym of 'survive').
'be' is a homophone of 'b'.
'b'+'last'='BLAST'
(Other definitions for blast that I've seen before include "Sudden strong gust of wind" , "Noise of explosion" , "Severe reprimand; strong gust" , "Explosion - mild oath" , "Report" .)