Abstract
The National Institute for Occupational Safety and Health (NIOSH) has conducted an occupational exposure assessment study of manganese (Mn) in flux core arc welding fume at three facilities. The objective of this study was to evaluate exposures to different Mn fractions using a sequential extraction procedure. Sixty-seven worker-days were monitored for either total or respirable Mn. The samples were analyzed using an experimental method to separate four Mn fractions based on chemical solubility: soluble Mn in a mild ammonium acetate solution; Mn0,2+ in 25% acetic acid; Mn3+,4+ in hydroxylamine hydrochloride in 25% acetic acid; and insoluble Mn fractions in hydrochloric/nitric acid. The full-shift total particle size Mn time-weighted average (TWA) breathing zone concentrations ranged from 0.51 to 43; 2.9 to 850; 1.7 to 620; and 0.56 to 331 µg·m-3, for the different Mn fractions, respectively. The summation of all the total particulate Mn fractions yielded results that ranged from 16 to 1,530 µg m-3. The ranges of respirable size Mn TWA concentrations were 0.27 to 75 for soluble Mn; 1.6 to 690 for Mn0,2+; 1.3 to 740 for Mn3+,4+; 0.52 to 570 for insoluble Mn; and 3.8 to 1,800 µg·m-3 for Mn (sum of fractions). Total particulate TWA GM concentrations of the Mn(sum) were 56 (GSD = 4.0), 380 (GSD = 2.7), and 176 (GSD = 3.3) µg·m-3 for the shipyard, structural steel and custom parts facilities. Although most of the workers’ exposures measured were below the NIOSH Recommended Exposure Limit for Mn (1,000 µg·m-3), 44 welders’ exposures exceeded the ACGIH Threshold Limit Values® for total Mn (100 µg·m-3) and 46 exceeded the new respirable Mn TLV (20 µg·m-3). This study shows that a welding fume exposure control and management program is warranted for Mn, which includes improved exhaust ventilation and may necessitate the use of respiratory protection, especially for welding in enclosed or confined spaces.
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