The lungs of a long-time smoker are fragile entities, IMHO. They are not healthy.
It would therefore be difficult to guage the effect of anything on them, which is why, anyone attempting to do any kind of detective work would have to start out with a person with healthy lungs.
There are no smokers who have truly healthy lungs, so what they can and cannot withstand is more directly related to that. I'm sure there are situations and substances that can damage lungs, but smoking analogs would be a very overt and obvious one. Therefore, I'd say *anything* would be better......or has the chance of being better.