AbstractFour wire coating materials (two of them based on PVC and the two others based on XLPE) were assessed for the irritancy of their smoke, under non‐flaming conditions, by using the respiratory depression method, expressed as theRD50. The DIN 53 436 combustion tube was used as the fire model, at a temperature of 550°C (smouldering mode), and the animal model was the mouse. Animals were exposed for 10 min, at concentrations too low to cause lethality. It was found that there was relatively little difference between the irritancy of all four smokes. This was an unexpected result, since it had been predicted that PVC smoke would be much more irritating than XLPE smoke. In fact, the smoke from the PVC compounds had anRD50roughly in the range of 100–1000 ppm, while the smoke from the XLPE compounds had anRD50roughly in the range of 10–100 ppm. This means that PVC smoke is somewhat less irritating than XLPE smoke. The components in the smoke of all materials were determined by a combination of continuous gas analysis, ion chromatography and gas chromatography/mass spectrometry, with the objective of understanding the factors causing the irritancy. Hydrogen chloride, one of the major decomposition products of PVC, is also the most important smoke constituent causing irritancy of the smoke. Its irritancy, however, was insufficient, by a considerable margin, to explain the full degree of irritancy found. TheRD50of HCl is, like that of PVC smoke, in the range of 100–1000 ppm. On the other hand, the only compound found in the smoke of XLPE compounds with anRD50in the same 10–100 ppm range as he overall smoke is methyl vinyl ketone. Unfortunately, the concentration of methyl vinyl ketone was much too low to account for the irritancy levels encountered. Literature data indicate that polyethylene smoke is rich in long‐lived free radicals and that PVC smoke does not contain them. Moreover, such free radicals are associated with various illnesses, particularly with respiratory symptoms. Thus, it is speculated that such free radicals could be the cause of the high irritancy of the smoke from the XLPE wire coati