Some nice info I found
Why Smoking and CF Are a Fatal Combination
Mucus clearance in a normal lung is accomplished by cilia, tiny hairlike projections lining the inside of the lungs which constantly move dirt, bacteria, and other irritants up into the throat where they can be swallowed. These cilia beat 16 times per second, and even a decrease in this rate impairs mucociliary clearance (MCF).
CF causes the lungs to become clogged with thick secretions of mucus, containing bacteria and primarily dead white blood cells. These thicker secretions interfere with cilia pulsation, and decrease this rate, sometimes obliterating the function altogether, leading to impaired or nonexistent MCF. Cigarette smoke, even second hand, causes the same impairment. Cigarette smoke paralyzes the cilia it contacts in the sinuses and lungs for twenty-minutes. (This is why heavy smokers have a morning "CF cough" -- the cilia regain their function during cigarette-free sleep, and must work overtime to gather all of the mucus and secretions that have built up -- 2 liters per day even in a non-CF individual.)
So a PWCF who inhales second hand smoke, is obliterating the body's mechanism to remove secretions from the lungs, a mechanism already stressed to the limit by CF. This would be akin to having two progressive lung disease processes occurring in one lung -- NOT HEALTHY!