Totally not important but
(Gas must not smell like rotten eggs in the AU)
didn't they open the door to that room? I understood that the gas was collecting in a adjacent room so they could have not smelled it, especially if the doors were closed? No? The lighter ignited in the moment they opened the door, so they wouldn't have had the time to stop the action even if they noticed the smell in that time.

Anyway I love your reviews :) A great beginning for sorting everything out after an episode :)