If your roommate smokes, and you can smell the smoke later, is that harmful smoke you are inhaling or is that just the odor of smoke?
Answer by Michael J. McFadden:
In terms of "how harmful" it is, you will find people out there who will tell you that *any* exposure is *very* harmful — but they will have a very hard time supporting that statement if you ask them for studies and figures. The main basis justifying smoking bans in the U.S. (which is one of the places where the ban movement most strongly started) was the EPA Report of 1992 that claimed a 19% increase in lung cancer among workers "exposed to smoke."
That sounds pretty serious, right?
BUT… when you look at the number more closely (which most people never do of course, since it's not part of the glitzy news story or antismoking literature they're seeing) things begin to look different. Lung cancer in nonsmokers is a pretty rare disease: only about 0.4% of non-exposed nonsmokers will ever get it: about one out of every 250 people. A 19% increase would mean one extra case of lung cancer for every thousand people who had forty years of constant daily work exposure: One lung cancer for every 40,000 worker-years of exposure. When you look at it that way it doesn't sound nearly as frightening as just talking about a 19% increase, right?
Of course that's a very different kind of exposure than the one you're asking about. How different? Well, you're talking about "smelling the smoke later" which would indicate that you're not even around when they are smoking, and you don't mention seeing the smoke hanging in the air or clouds of it being constant around you for eight hours a day (as in one of those old poorly ventilated workplaces of the 1940s through 1970s). So, it would probably be fair to guess that, at most, you're getting about one-tenth or maybe even only one-one-hundredth of that old working-lifetime dose. That would mean that, on the average, you'd have to live with that roommate for between 400,000 and 4,000,000 (four million) roommate-years to get lung cancer.
The real risk might even be much smaller: the EPA Report was not able to validate its figures at the standard statistically acceptable level of 95% so they argued their case based on a 90% confidence interval instead. When the tobacco companies disputed the report a federal judge who had previously ruled *against* the tobacco companies in a similarly important case involving the FDA took several years to examine the evidence. That judge (William Osteen) threw their findings out as being insufficiently supported on several different grounds. If the EPA had actually tried to make a binding regulation based on their findings it would have been ruled invalid, but since they simply issued a "report" rather than try to make a ruling, the judge's decision had no real effect and was dismissed on appeal for lack of jurisdiction.
I don't know the figures on what the chances are of being knifed to death by a roommate in a given year, but my guess is they're they're a good deal higher than the chances of you getting cancer from them smoking when you're not around.