The Times, January 2, 2017
‘May’ and ‘might’ are often confused but in this context the difference is reasonably simple. ‘May’ is for an event which has had a definite outcome, but it is not yet known. For example, ‘the Greens may have won the General Election, but we won’t know until the votes are counted’. ‘Might’ is for an outcome which is known, but which could have been different. For example, ‘England might have won the Ashes if they had scored more runs.’ Here the outcome is known (a lot of cars were destroyed) but with sprinklers some would probably have been undamaged. Therefore this should read:
Sprinklers might have stopped a fire wrecking . . .
If in doubt, ‘could’ is usually a suitable alternative.