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The bottleneck might be the air in the room
(blog.mikebowler.ca)
This is a most excellent place for technology news and articles.
Actually, ppm in 1000 - 2000 makes for better sleep. But for worse thinking of course.
People who sleep in their cars, engine running and parked in a garage, sleep like babies!
It's carbon monoxide that's getting produced by combustion in an anoxic environment.