WELDING RESEARCH Table 2 — Eight Hour Exposure Limits for Chromium and Compounds Form Possible Source Exposure Limit Source of Contaminant mg/m3 Cr(0) grinding dust, spatter 500 TLV (Ref. 10) Cr(III) welding fume 500 TLV (Ref. 10) Cr(VI), water soluble welding fume, other source 25 TLV (Ref. 10) Cr(VI), insoluble welding fume 10 TLV (Ref. 10) calcium chromate, as Cr other source 1 TLV (Ref. 10) lead chromate, as Cr other source 12 TLV (Ref. 10) strontium chromate, as Cr other source 0.5 TLV (Ref. 10) zinc chromate, as Cr welding fume, other source 10 TLV (Ref. 10) Cr(VI), all compounds 5 OSHA (Ref. 12) MARCH 2016 / WELDING JOURNAL 89-s An ESAB A2 automated welding machine (ESAB, Mississauga, ON, Canada) outfitted with a local exhaust collecting hood and associated curtains (Figs. 1, 2) was used during these experiments to obtain samples to analyze for Cr(VI) compounds. Four runs, each involving three samples, were performed using the A2 welding machine under normal operation (22.5 V, 180 A). Table 3 summarizes equipment settings during welding. Air samples during operation of the ESAB A2 welding machine were collected using portable, constant-flow pumps (SKC, Inc., Eighty-Four, Pa.) and microporous polyvinylchloride (PVC) filters held in plastic cassettes. The pumps were calibrated prior to and after sampling. The cassettes were positioned closed-faced in groups of three (Fig. 3) under the top of the hood, which is about 46 cm above the arc. Immediately after sample collection, the interior and exterior of the cassettes were flushed with argon. The interior of the packaging used for shipment to the lab (a cardboard box and loose-fill material to prevent damage) also was flushed with argon. These actions were taken to exclude air and to prevent contact with oxygen to the extent possible prior to disassembly and analysis in the analytical laboratory in response to a concern that change in the chemical form of chromium can occur after collection when oxygen is present. Air samples during manual arc welding were obtained as described. The cassettes were positioned on the lapel below the shoulder. In the case of automated welding using the ESAB A2 machine, the operator wore the sampling device. The position of the cassettes on the lapel below the shoulder was the only one in the breathing zone that was common to all individuals, regardless of the type of respirator in use. The cassettes were packaged for shipping as described previously. Manual arc welding during collection of individual samples occurred in general orientations as described by the welder. Mass of material on filters was determined by weighing the loaded filter and comparing against an identical unloaded filter. One sample from each run was digested in 20% nitric acid for measurement of total chromium by inductively coupled plasma (ICP) spectrophotometry according to National Institute for Occupational Safety and Health (NIOSH) Method 7300 (Ref. 18). The remaining two samples from each run were combined and sequentially extracted to determine soluble and insoluble Cr(VI) compounds according to NIOSH Method 7600 (Ref. 18). Calculations were performed using IHDataAnalyst Lite Version 1.29 (Ref. 19), a software package used in the practice of industrial hygiene. WorkSafeBC, the regulator in British Columbia, requires employers to assess the conditions of work. This assessment required cooperation and active participation from welders and other workers at the shipyard. Everyone who participated was a volunteer and gave informed consent. Prior to the start, each prospective participant received a brief explanation about what the monitoring system did and what information it created and stored. Anyone uncomfortable with participation was excused, no questions asked, and without repercussion. No names were recorded to ensure there was no means to identify participants. This work involved about 20 production welders, 5 tackers, and 5 fitters, in addition to the laborer who managed portable ventilation equipment, and two supervisors. Individual participation varied considerably from one session to multiple sessions depending on comfort in wearing the sampling equipment (described previously), interest in the project, and the type of work that was occurring. The strategy underlying the monitoring activity was to obtain samples from all relevant types of activity during production welding. Sampling was spread among the group of workers over the duration of the sample period, which occurred over the span of several weeks. Sampling was dictated in part by availability of work in specific structures and different geometric configurations. The realities intrinsic to this situation introduced considerable randomness because the schedule of work was not known in advance of seeking volunteers for a particular day. Results During welding, the welder positioned his/her face in close proximity to the flow of argon shield gas. This action ocurred regardless of whether the welding process was manual or automated using a portable welding machine. The self-propelled ESAB A2 portable welding machine was used on the shop floor to weld together large plates of aluminium. In both cases, the welder positioned his/her face in close proximity to the arc so as to be able to observe the progress and quality of the weld and tracking of the machine along the joint to be joined together. Close proximity to the arc inevitably exposes the welder to the particulate substances in the plume. Welding occurred in multiple posi-
Welding Journal | March 2016
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