In-depth survey report: the effect of weld process and ventilation method on physical work load, weld fume exposure, and weld performance in a confined-space welding task at Jeffboat Shipyard, American Commercial Barge Lines (ACBL), Jeffersonville, Indiana.
Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB 229-11b, 2000 Nov; :1-134
The ergonomic factors affecting safety and performance of shipyard welders, especially those working in confined spaces, have not been adequately studied. Such workers typically weld in conditions that provide inadequate ventilation and require static muscular work and awkward, constrained postures. Thus, there is a need to establish the effectiveness of engineering interventions, such as static load reduction and alternative ventilation methods, on the basis of reducing musculoskeletal/physiological demand and weld fume exposure among confined-space welders while also enhancing worker performance. To accomplish these aims, this study measured the effect of weld process and ventilation method on the physical work load, weld fume exposure, and weld performance associated with a simulated confined-space welding task. Ten male shipyard welders performed eight flat welding tasks [four wire-fed welding tasks (Flux Core Arc Welding or FCAW) and four stick-welding' tasks (Shielded Metal Arc Welding or SMAW)] in a functional mock up. The mock up was constructed by NIOSH to match the actual dimensions (-2ft by 2ft by 16 ft) of a particular type of barge hull assembly that required inside welding during its manufacture at the participant shipyard. For each of the ten welders, two ventilation methods were evaluated in the mock up to determine the resulting weld performance, associated workload, and fume concentrations in the welder's breathing zone, while the eight welding tasks were performed. One ventilation method employed a standard air horn that was currently used at the shipyard. The other method used a prototype fresh air diffuser designed to improve ventilation. Heart rate, ratings of perceived exertion (RPE), electromyographic (EMG) activity from seven upper extremity and torso muscles, discomfort assessment surveys (DAS), total personal particulate concentrations (mg/m3), and area elemental concentrations (mg/m3) from air samples were recorded for each task. In addition, welding performances in terms of weld quality (_s determined visually by an expert welder) and weld efficiency (arc time/total weld time, as determined by videotape analysis) was also evaluated for each task. Overall, statistical results indicated that weld process (wire versus stick welding) had significant effects on subjective physical workload and __rd performance. Wire welding was associated with significantly higher RPEs (ANOVA, P = 0.0001; estimated difference = 1.06), general DAS outcome (ANOVA, P = 0.0076, estimated difference = 0.42; Friedman Chi Square, p = .3865), and weld efficiency (ANOVA, p=O.0335; estimated difference = 2.19), while stick welding was ' associated with significantly higher weld quality (ANOVA, p=O.OOO1; estimated difference = 0.80). These subjective results indicated that exertion was perceived to be "fairly light" during both types of welding, with the 'general state of comfort right now' described as "average". Overall, the low back, knees, and shoulder regions were reported to be the body areas most . affected by this welding job. In addition, weld process was also found to have a significant effect on objective physical workload! in terms of spectral analyses of the EMG data. Specifically, for most muscles tested during left side trials, the percentage of the total signal power in the 10-30 Hz frequency band was found to increase at a significantly (ANOVA, P < 0.05) greater rate for the existing stick electrode welding process than a wire welding process the shipyard has considered adopting. Weld process was also found to have a substantial effect on weld fume concentration, as stick welding was associated with greater (ANOVA, P = .0621) personal total particulate concentrations. Ventilation method was found to have a significant effect on weld fume exposure, such that the standard air horn was associated with lower total particulate concentrations (ANOVA, P = 0.0184). In addition. projected minimum TWAs for personal particulate concentrations and area elemental concentrations in many cases exceeded the established ACGIH TL Vs, NIOSH RELs and OSHA PELs for stick and wire processes, using both ventilation methods. Thus, it is suggested that additional air sampling be conducted on the actual confined-space welding task that this Study modeled, so that alternative ventilation methods can be devised. In conclusion. this study suggests that engineering interventions for confined-space welders involving weld process and ventilation method changes should be considered carefully, because of the potential significant impact on work load, weld fume exposure, and weld performance. Overall results indicate that a reduction of localized muscle fatigue and weld-fume generation in this specific operation may be realized by a change from the stick-electrode to the wire welding process detailed. However, results also suggest that this change may be associated with higher subjective work loads. Different model welding units, consumables, and operational set-ups may also produce different fatigue states and fume generation rates. Thus, it is. suggested that musculoskeletal injury rates and air quality measures be closely monitored before and after any specific process change. Since current ventilation methods appear to be inadequate, it is suggested that additional air sampling be conducted on the actual confined-space welding task that this study modeled. Based on the results of this sampling, which will estimate actual welder exposures, further ventilation control research and alternative PPE options (e.g., full-face air-purifying respirators, positive-pressure supplied-air respirators) may be needed.