Is there a minismium distnace from the vent stack to a chimney. I guess worst case is that methane would travel down the chimney and explode when you light a fire. OK I said worst case. Is a chimney considered an "opening"?

I am thinking that sewer gas has to be lighter than air to go up and out of the pipe. It would have to be heavier than air to go down a chimney. So, I should be OK? What will the inspector think?

906.2 Each vent shall terminate not less than ten (10) feet (3048 mm) from, or at least three (3) feet (914 mm) above, any openable window, door, opening, air intake, or vent shaft, nor less than three (3) feet (914 mm) in every direction from any lot line–alley and street excepted.