Sewer main explosion - GIF

[mwmkravchenko]

Maybe a build up of flammable gas (methane) and it ignited...

(I feel sorry for the old lady covered in sh!t)

Remember that sewers are open to the atmosphere for exactly this reason. The secondary reason is that the water flow in a sewer not being under pressure pushes and displaces air in the pipe as it flows. That air must go somewhere. It is vented into the atmosphere. It prevents air locks.

Mark