It was a methane/biogas explosions caused by debris that runs off the streets into the manholes and rots forming methane/biogas. I once saw 11 manhole covers in a row blown off in succession on the campus at A&T when a smart ass we worked with tossed a wad of burning paper into a manhole and closed the lid.
These manholes are connected by concrete conduits (pipes) in which wires are pulled through. Once one manhole explodes the fire can travel through the conduit to the next manhole where if by chance the correct amount of methane/biogas and oxygen are collected the damned thing blows up.
Most of the conduits under Greensboro are 9-12 pair meaning they have 9-12 individual pipes surrounded in concrete, passing from one manhole to the next. They are AT&T Long Lines used for long distance telephone communications.
It's possible but less likely to do the same thing with sewer lines but as the liquids often fill the lines the oxygen is displaced and the fire can't pass from one manhole to the next... usually.
The question is: who started it? What started it? Even if it was an electrical explosion, what blew up-- a transformer? Transformers and other high voltage electrical equipment isn't placed in manholes because manholes flood causing such things to short out. Only plastic coated wires are below ground with all the connections and equipment above ground.
I'm not saying this was a terrorist attack, probably just a prank. But as usual our local media is clueless and anyone who has ever worked in underground telephone or electric construction can quickly verify this to you.
Update: Video made available by the City of Greensboro shows smoke coming out from under a car moments before the explosion that knocked the windows out of the Biltmore Hotel. News 2 also reported that workers inspecting the manhole found nothing unusual.
Update 2: Mythbusters shows how it works:
Update 3: News 2 reports Duke Energy and Piedmont Gas say they are not responsible in video titled Ohio Family's Car Damaged During Greensboro Explosion.
Milton Kern blames Eric Robert.
From the book, The American City:
So who's right, me or the Greensboro Police who are still claiming an electrical problem despite the fact that Duke Energy found nothing out of the ordinary? Will we ever know?
