[Buckeye McFrog]

Except for the gas.

if IC were the cause Pittsburgh would have been blown off the face of the earth sometime prior to 1972

[ArrogantBustard]

A methane/air mixture will combust only in a very narrow range of ratios ... people who make fuel/air explosive devices have to design them very carefully to make sure that they will 'go'.

Perhaps Pittsburgh has been saved by an accident of chemistry.