Dissertation/Thesis Abstract

Assessing exposures to particulate matter and manganese in welding fumes
by Liu, Sa, Ph.D., University of California, Berkeley, 2010, 90; 3449005
Abstract (Summary)

A respiratory health survey conducted in an automobile assembly plant in 2000–2001 found that welders had elevated rates of self-reported respiratory symptoms compared to painters and assembly workers. Subsequently, the ventilation system was improved at the body weld department. In a follow-up study, particle spatial distributions were analyzed, following a mapping protocol developed specifically for this work place, to evaluate the effectiveness of the changes. Significant temporal and spatial variations were observed. Temporal variation during a shift was monitored with over-shift stationary sampling at fixed locations. Spatial variation was evaluated with 1-minute time-weighted average particle concentrations measured throughout the process areas (212 locations). The arithmetic spatial mean across 212 locations for the respirable particles varied from 305µg/m3 to 501µg/m 3 on six sampled days, with a standard deviation of 71µg/m 3, indicating that the difference between before and after countermeasures must be at least 191µg/m3 in order to be considered statistically significant at the given sample sizes. The available data were not sufficient to evaluate the reduction of the particle concentrations after the countermeasures. The map of particle mass concentration revealed several high concentration areas, requiring further investigation and potentially higher level of controls. Resistance welding needed to be effectively controlled as it could be the major particle emitting source in the facility. The map of submicrometer (0.014µm to 1.0µm) particle count concentration presented different patterns from that of respirable particle mass concentration, indicating that the submicrometer particles tended to be more evenly distributed over the process areas. Workers not in close proximity to intensive welding operations might be exposed to fine particles at levels higher than had traditionally been thought.

A pilot study was conducted in three Chinese manufacturing facilities to characterize welders’ exposure to particulate matter (PM) and airborne manganese (Mn) from common welding processes, with emphasis on Mn distribution in submicrometer particles. Particle air concentration was measured as 8-hour time-weighted averages (TWAs) for total and respirable particles. Mn air concentration (8hr TWA) was measured as Mn in total and respirable particles. Mn size distribution was assessed using multi-stage impactors with cut-points of 0.25µm, 0.5µm, 1.0µm and 2.5µm. The welding processes investigated were shielded metal arc welding, gas metal arc welding, submerged arc welding and plasma arc welding. Overall arithmetic means (AMs) across processes and factories were 2.58 mg/m3 (range: 0.338 mg/m3 – 27.8 mg/m3, GM: 1.28 mg/m3, GSD: 3.27) and 1.46 mg/m3 (range: 0.011 mg/m3 – 14.7 mg/m3, GM: 0.698 mg/m3, GSD: 3.37) for total and respirable particles (8hr TWAs), respectively. Overall AMs for Mn air concentrations were 0.122 mg/m3 (range: 0.001 mg/m3 – 1.30 mg/m3, GM: 0.058 mg/m3, GSD: 3.40) and 0.073 mg/m3 (range: 0.001 mg/m3 – 0.650 mg/m3, GM: 0.036 mg/m3, GSD: 3.33) for Mn in total and respirable particles, respectively. Particle and Mn concentrations varied over 4-fold by process. Shielded metal arc welding produced higher air concentrations for both agents compared to gas metal arc welding and submerged arc welding. Plasma arc welding resulted in the lowest concentrations. Manganese was found to be more concentrated in respirable particles than in total particles. Four percent of the particle mass of total particles was composed of Mn, while it was 5% for respirable particles. Data from the multi-stage impactor further revealed that majority of Mn mass, 97% for plasma arc welding and over 85% for shielded metal arc welding and gas metal arc welding, was distributed in particles smaller than 0.5µm. Percentage of particle mass made of by Mn increased three to twenty times as particle size decreased from 2.5µm – 10µm to <0.25µm. These findings are of great significance in that Mn primarily targets the central nervous system and Mn in small particles in the nano-size range has higher potential to reach the brain than Mn in larger particles. Therefore, welders’ risk of developing neurological effects due to exposures to Mn may be higher than it had been traditionally thought. It was also observed that Mn size distribution varied by processes. Plasma arc welding and gas metal arc welding could be more hazardous than submerged arc welding when particle and Mn air concentrations are comparable. Shielded metal arc welding should be evaluated and controlled with high priority. (Abstract shortened by UMI.)

Indexing (document details)
Advisor: Hammond, S. Katharine
Commitee: Balmes, John R., Hubbard, Alan
School: University of California, Berkeley
Department: Environmental Health Sciences
School Location: United States -- California
Source: DAI-B 72/06, Dissertation Abstracts International
Subjects: Occupational health, Environmental Health
Keywords: Exposure assessment, Manganese, Particle mapping, Particulate matter, Welding fumes
Publication Number: 3449005
ISBN: 978-1-124-55382-5
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