Do existing empirical models for welding fumes estimate exposure to ultrafine particles among canadian welding apprentices?

To the Editor: W elders are at risk of a wide range of respiratory health problems, including bronchitis, airway irritation, and lung function changes.1–5 Despite short duration of exposure, an inception cohort study of apprentice welders in Quebec documented a significant respiratory function decline, incidence of welding-related respiratory symptoms suggestive of occupational asthma and sensitization to metallic salts.6 It is important to understand how these effects relate to exposures experienced by apprentices in order to develop adequately protective exposure standards. Welders may be exposed to numerous chemical hazards associated with welding and cutting processes, including welding fumes, inert gases, gas mixtures, and solvents.7 Welding fumes consist of metallic oxides and gaseous vapors as well as ultrafine particles (UFP; size <100 nm).8 The type and quantity of fumes generated greatly depend on many factors, including (but not limited to) the welding process, and within the process, electrodes, fluxing agents, coatings on the base metal, base metals, and the power configuration of the welding machine.9 An exposure study in Quebec showed that apprentices in welding profession have a high level of exposure to UFP during the whole training period.10 Nevertheless, investigation of welding exposure at voca-