What happens when you try and light a firecracker on top of a manhole cover?
Nature gives you a first-hand lesson on the flammability of sewer gas...
http://www.youtube.com/watch?v=XIBeiwfwkmY&feature=youtu.be
Nature gives you a first-hand lesson on the flammability of sewer gas...
http://www.youtube.com/watch?v=XIBeiwfwkmY&feature=youtu.be