08/02/2010

Characterization of Exposures to Airborne Nanoscale Particles During Friction Stir Welding of Aluminum

Friction stir welding (FSW) is considered one of the most significant
developments in joining technology over the last half century. Its industrial
applications are growing steadily and so are the number of workers using this
technology. To date, there are no reports on airborne exposures during FSW. The
objective of this study was to investigate possible emissions of nanoscale
(<100 nm) and fine (<1 µm) aerosols during FSW of two aluminum alloys in a
laboratory setting and characterize their physicochemical composition. Several
instruments measured size distributions (5 nm to 20 µm) with 1-s resolution,
lung deposited surface areas, and PM2.5 concentrations at the source and at the
breathing zone (BZ). A wide range aerosol sampling system positioned at the BZ
collected integrated samples in 12 stages (2 nm to 20 µm) that were analyzed
for several metals using inductively coupled plasma mass spectrometry. Airborne
aerosol was directly collected onto several transmission electron microscope
grids and the morphology and chemical composition of collected particles were
characterized extensively. FSW generates high concentrations of ultrafine and
submicrometer particles. The size distribution was bimodal, with maxima at 30
and 550 nm. The mean total particle number concentration at the 30 nm peak was
relatively stable at 4.0 x 105 particles cmwhereas the arithmetic mean counts
at the 550 nm peak varied between 1500 and 7200 particles cmdepending on the
test conditions. The BZ concentrations were lower than the source
concentrations by 10 times at their respective peak maxima and showed higher
variability. The daylong average metal-specific concentrations were 2.0 (Zn),
1.4 (Al), and 0.24 (Fe) µg mthe estimated average peak concentrations were an
order of magnitude higher. Potential for significant exposures to fine and
ultrafine aerosols, particularly of Al, Fe, and Zn, during FSW may exist,
especially in larger scale industrial operations.


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AplusA-online.de - Source: Annals of Occupational Hygiene