Did not know that. Very interesting.
I have known for a long time that the hysteria over second-hand smoke is profoundly unscientific. SHS is unpleasant, and I’m the first to admit I don’t miss having to breathe it in the bar. But it is very doubtful it ever posed much of a risk for anyone other than those with extreme exposure levels. (Such as those working in the smoky bars and restaurants 40 or 50 hours a week.)
Tobacco smoke isn’t inherently any more risky to inhale than any other smoke. It’s just that people don’t inhale massive amounts of smoke voluntarily under other circumstances.