Similar situation in NY last year:
"WNY blast sparks terror fears
Friday, July 29, 2005
By RANEEKA J. CLAXTON and CRAIG GARRETSON
JOURNAL STAFF WRITERS
WEST NEW YORK - An explosion was accompanied by a power outage and followed by the wail of sirens and the buzz of TV news helicopters yesterday evening as town residents worried that a terrorist attack might be underway.
The cause wasn't a bomb, but a faulty underground power circuit that overheated and ignited sewer gas, causing an explosion that blew three manhole covers out of the street and injured at least five people, town officials said. "
http://www.nj.com/news/jjournal/westny/index.ssf?/base/news-0/1122628379201950.xml&coll=3
I used to live there. Rather dumpy place.