Dustiness testing - A tool for risk assessment of bulk nanopowders

Speaker:

Keld Alstrup Jensen Senior Researcher, Ntl. Research Centre for the Working Environment

Co-Author(s):

Ismo K Kopponen, National Research Centre for the Working Environment, Denmark Thomas Schneider, National Research Centre for the Working Environment, Denmark

Handling of powders generates dust causing potential exposure of workers. Handling scenarios can vary greatly making it difficult to determine and compare dustiness properties of different materials of different primary particle sizes. Bench-scale dustiness tests subject the test material to a standard challenge and very reproducible results can be obtained. We have used a specially developed rotating drum dustiness tester that requires only 6 g of test material per run. Particle size distribution is measured real time using a TSI Fast Mobility Particle Sizer and a TSI aerodynamic particle sizer, APS. A range of nanosized powders have been tested. Among the results to be presented are: • Generated dust usually consisted of agglomerates of primary nanoparticles • Two or more particle size modes were generated. The smallest size mode was typically in the range 100-300 nm, the larger modes were above one micron • The smallest 100-300 nm modes were roughly similar in diameter range suggesting a fundamental agglomerate formation process • One product of nanosized TiO2 was about 300 times as dusty as a product of pigment grade TiO2 • Loose nano-clay had lower dustiness than loose Bentonite. For the compacted versions it was the opposite. • Compacted Bentonite was less dusty than loose Bentonite. For nano-clay it was the opposite. • Some materials released most of the dust during a brief initial burst. At the other extreme, the dust generation rate increased during the entire test period. Such results could not have been predicted theoretically illustrating the usefulness of a dustiness test. The results suggest that for scenarios involving handling of bulk nano-sized powders • Sampling only nanosized particles would greatly underestimate exposure to nanoparticles if the agglomerates would de-agglomerate in the lung fluids • Since airborne particles were mostly in the conventional size range, existing dust control technologies validated for conventional materials are likely to be effective In addition dustiness tests can provide quantitative data for use in exposure control banding schemes and can serve as a tool for responsible product development.