That's an idea - but who would do the study? The municipality that would benefit from proving a higher risk? A group of smokers who want to be firefighters who would benefit from proving a lower risk?
I have an even fairer way.....government entities that will not hire smokers should forfeit tax proceeds from the purchase of tobacco products in the form of a rebate of taxes on those products.
Still not fair to the smokers who pay the normal taxes that all members of the public pay. That approach gives back only the taxes specifically related to smoking, not all taxes paid by smokers (or the percentage of same that could be considered proportional to the opportunity to be employed by the F.D.).
Ever think about that aspect?