Hi Roland
I think in the same way as Erik. It's everyone decisition.
Pipe smoking had been considered as harmful as cigarrete smoking. But there is no paper about pipe smoking and freediving, and as far as I know there is no paper either about cigarrete smoking and freediving.
I can't tell you with 100% of certainty because all that I know is from my knowledge about the effects and from a few papers about smoking and scuba diving.
The main effect on bronchial wall is the inflammation. It makes that you produce more mucus, and the mucus can plug in some bronchi with the risk of ascent barotrauma (very rare). The inflammation and the bronchoconstriction(narrowing of bronchi) also make that breathing get more difficult and the energy cost of it becomes bigger, increasing Oxygen consumption. The difficulty in exhalation also affects residual volume and can increase lung volumes, an this can increase the risk for DCS.
The amount of CO in the lung of a Smoker is very low to produce clinical effects, but it can displace O2 from hemoglobin and affect the arterial concentration of it.
As I told you before, all of this is mainly theoretical and can't be taken as the plain truth. In fact, there is a huge difference of immune response in smokers, that many people smoke all live long without any noticeable problem.
Hope this help
ps: Here is two papers that you can read for detailed explanation: (but the first is quit difficult to obtain)
Dembert ML, Beck GJ, Jekel JF, Mooney LW. Relations of smoking and diving experience to pulmonary function among U.S. Navy divers. Undersea Biomed Res. 1984 Sep;11(3):299-304. 2: Buch DA, El Moalem H, Dovenbarger JA, Uguccioni DM, Moon RE.
Cigarette smoking and decompression illness severity: a retrospective study in
recreational divers. Aviat Space Environ Med. 2003 Dec;74(12):1271-4.