as far as butane burning cleaner than propane, well that is mostly a bad assumption. there are thousands if not millions of homes across the country that have propane cook tops. just as clean as butane. in some areas of the country "propane" delivered to homes is a mix of propane/butane especially in the summer. both can be very clean burning. there are tons of propane fired "direct vent" room/space heaters that their exhaust fumes/gasses are just dumped into the room. no chimney or vent pipe to the outside.
many of those come with built in O2 (oxygen) depletion sensors that shut them down or sound alarms if the O2 % drops to much but i have yet seen one with a built in CO (carbon monoxide) sensor
lots of fork lifts, floor waxers, zambonies as such run on propane instead of gas or diesel as the fumes/exhuast is far less toxic