WELDING RESEARCH tions, namely, downward onto lower horizontal surfaces (1F, 1G, 2F, 2G, 3F, 3G), upward and downward (3F, 3G), and side to side on vertical surfaces (2F, 2G), and upward onto horizontal overhead surfaces (4F, 4G). During welding downward onto lower horizontal surfaces (1F, 1G, 2F, 2G, 3F, 3G) in the absence of local effective exhaust ventilation, the plume passes up the upper chest around the neck and up the back of the head or remains in front of the welder. During welding on vertical surfaces (2F, 2G), the plume moves up the vertical surface in front of the welder. During welding overhead (4F, 4G), the plume moves along the surface of the metal and can become trapped by vertical downward protrusions. Entrapment can cause immersion of the welder’s face into the plume. Table 4 presents results from sampling for chromium during operation of the ESAB A2 machine. The calculations in Table 4 are based on fractions of masses, rather than concentrations. This approach is necessary because of uncertainty in pump operating times. The duration of sampling reported here are approximate and represent values provided by pump timers. Since the pumps provide only whole numbers of minutes, rather than fractions, some error was possible. Normally an error of fraction of a minute in a sample obtained over hundreds of minutes may be minimal. A fraction of a minute could become important when the sample time is only a few minutes. Use of masses, rather than concentrations, of material minimizes errors in this type of situation. Calculations using IHDataAnalyst Lite Version 1.29 indicated the lognormal distribution applies to the data presented in Table 4 (Ref. 19). The lognormal distribution typically applies to data obtained in the field of industrial hygiene (Ref. 20). Table 4 indicates the geometric mean concentration 90-s WELDING JOURNAL / MARCH 2016, VOL. 95 of particulates in the plume was 676 mg/m3, with a geometric standard deviation of 1.19. The geometric mean of the ratio of total chromium and mass of material collected in the plume was 0.182 g of Cr/mg of fume and the geometric standard deviation was 1.08. Base metal and fume are not directly comparable because of the presence of oxides in the latter. The geometric means were 0.072 (gsd = 1.38) for the ratio of soluble Cr(VI) compounds to total Cr and 0.245 (gsd = 1.26) for the fraction of insoluble Cr(VI) compounds, respectively. The results obtained here suggest that soluble Cr(VI) would be 0.072 or 7.2% of total chromium; insoluble Cr(VI) would be 0.245 or 24.5%; and the balance 0.683 or 68.3% would be other forms of chromium. Table 5 provides results from sampling for chromium during manual production welding operations. Exposure to all forms of chromium during manual production welding ranged from 3 to 64 g/m3. These data have a geometric mean of 11.9 g/m3 and geometric standard deviation of 2.56. Calculations using IHDataAnalyst Lite Version 1.29 indicated the lognormal distribution applies to data presented in Table 5 (Ref. 19). Combining the results reported in Tables 4 and 5, and using the maximum measured concentration of total Cr during welding activity of 64 mg/m3, the maximum concentration of soluble Cr(VI) would be 0.072 64 g/m3 = 4.6 g/m3. This concentration is slightly less than the OSHA regulatory limit of 5 g/m3 and smaller than the TLV of 25 g/m3 for water-soluble Cr(VI) compounds that could occur in the welding plume. Similarly, the concentration of insoluble Cr(VI) would be 0.245 64 g/m3 = 16 g/m3. This concentration is considerably greater than the OSHA regulatory limit of 5 g/m3 for Cr(VI) compounds and greater than the TLV of 10 g/m3 for unspecified Cr(VI) compounds that could occur in the welding plume. When averaged over 8 hours in consideration to the duration of exposure over the period of the workshift, the average concentration would decrease. In the United States, all forms of Cr(VI), that is, both water soluble and water insoluble, are combined and indistinguishable from each other. At the level of exposure proposed here, even reduced in the calculation by the short duration of actual welding during the day, control measures such as specially designed exhaust systems or other means of ventilation are necessary. In addition, the maximum measured level chosen for use in the calculations is an extreme that may not occur in other situations. For jurisdictions regulated through use of the TLV and especially TLV + ALARA, the impact is the same, namely that control Table 3 — Welding Parameters during Sampling for Chromium Parameter Current Voltage A V GMAW horizontal fillet weld (5083 base material, ER5183 wire, 1.2 mm diameter) 190 to 240 24 to 25 vertical up fillet weld (5083 base material, ER5183 wire, 1.2 mm diameter) 160 to 190 24 to 25 overhead fillet weld (5083 base material, ER5183 wire, 1.2 mm diameter) 180 to 220 24 to 25 GTAW horizontal fillet weld (5083 base material, filler rod 2.5 mm, 5083 base material) 235 26 vertical up fillet weld (5083 base material, filler rod 2.5 mm, 5083 base material) 212 25 overhead fillet weld (5083 base material, filler rod 2.5 mm, 5083 base material) 240 25 Notes: •Current shall not vary more than ± 15% for both processes. •Voltage shall not vary more than ± 10% for both processes. •When using 6061 base material, current and voltage are higher. •CSACWB W47.2 Aluminum was followed during this work (Ref. 17).
Welding Journal | March 2016
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