The doom cloud is far more real than some of the devices used for the show. Mixing household ammonia with household bleach does create a toxic gas that can do lasting harm to people using these common household cleaners in combination, especially in enclosed spaces.
Russell Boyes' question to Murdoch about what he would do to save the woman he loves foreshadows the storyline of the final 2 episodes of this Seaaon.
This episode takes place in 1900.