Someone in a previous post brought up the relation between 2nd hand smoke and outdoors smoking. My understanding is, years back, research indicated the harmful effects of excessive smoking, but a surgeon general observed that some smoking could be a healthful relaxant, since Vitamin N is a relaxant, not a stimulant.
This led to the reasonable Q, "Okay, what is a safe limit on tobacco use?" As I recall, an estimate for pipers was eight or ten bowls a day. (!!!) This freaked out the Nicotine Nazis who quickly turned the topic to 2nd hand smoke and, of course, the effect on children. The mantra became, ""There is no safe use of tobacco."
Intuitively, this seems to be a nonsensical claim. So, far as I know, there never has been satisfactory research on health effects of smoking on pipers. For that matter, the reports on second hand smoke should be taken with half a shaker of salt.
Also, as I've said before, I believe much of the relaxing effect of pipe smoking is the rhythmic, controlled breathing pattern used by experienced pipers.