Possible cause of explosion in Nagasaki (3)

I believe the answer is:

gas

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'possible cause of explosion' is the definition.
I can't tell whether this defines the answer.

'in nagasaki' is the wordplay.
'in' indicates a hidden word.
'GAS' is hidden within 'nagasaki'.

Can you help me to learn more?

(Other definitions for gas that I've seen before include "Carbon dioxide, say" , "may fill American car" , "Hydrogen, for example" , "Eg, oxygen" , "idle chit-chat" .)

I've seen this clue in the Evening Standard.

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