The authorities don't want you to know it but if conditions are right simply removing a manhole cover from its base can cause a spark that causes the methane and other naturally forming biogases inside to explode. A firecracker dropped inside could do the same thing. As a matter of fact: It's happened before.
And as I noted in my post What Underground Electrical Wiring? Updated, not only have I seen it demonstrated, the fires can travel from manhole to manhole and is explained in this Mythbusters video.
Are you scared yet, Mayor Vaughan? Wait until Summer comes.
