That makes a lot of sense. Thanks for the logical thinking!
Time to update the exploding manhole cover list:
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Explosions/Fire Blow Manhole Covers into the Air (MI)
A series of underground explosions in Detroit blew two manhole covers high into the air Thursday morning.
http://www.wxyz.com/wxyz/nw_local_news/article/0,2132,WXYZ_15924_4029574,00.html
Manhole fires reported in Boston neighborhood (MA)
BOSTON --Boston firefighters are responding to at least four manhole fires in Boston's Charlestown section this afternoon
http://www.boston.com/news/local/massachusetts/articles/2005/08/25/manhole_fires_reported_in_boston_neighborhood/