On May 29, 1929, a series of explosions in the sewers of Ottawa, Ontario, Canada, killed one person.
[1] The first blast occurred just after noon in the Golden Triangle area, west of the canal; over the next 25 minutes, a series of explosions travelled the length of the main line of the sewer system.
At these points, the access to oxygen fuelled towering flames that erupted through the manhole covers onto city streets.
[3] Most of the damage from the sewer explosions occurred where sewage lines were attached to less sturdy pipes inside houses; blasts destroyed the plumbing in many residential basements.
Methane naturally occurs in sewers, but it never accumulates in a concentration powerful enough to cause explosions of the magnitude seen in Ottawa.