Dustiness of Fine and Nanoscale Powders

Abstract

Dustiness may be defined as the propensity of a powder to form airborne dust by a prescribed mechanical stimulus; dustiness testing is typically intended to replicate mechanisms of dust generation encountered in workplaces. A novel dustiness testing device, developed for pharmaceutical application, was evaluated in the dustiness investigation of 27 fine and nanoscale powders. The device efficiently dispersed small (mg) quantities of a wide variety of fine and nanoscale powders, into a small sampling chamber. Measurements consisted of gravimetrically determined total and respirable dustiness. The following materials were studied: single and multiwalled carbon nanotubes, carbon nanofibers, and carbon blacks; fumed oxides of titanium, aluminum, silicon, and cerium; metallic nanoparticles (nickel, cobalt, manganese, and silver) silicon carbide, Arizona road dust; nanoclays; and lithium titanate. Both the total and respirable dustiness spanned two orders of magnitude (0.3–37.9% and 0.1–31.8% of the predispersed test powders, respectively). For many powders, a significant respirable dustiness was observed. For most powders studied, the respirable dustiness accounted for approximately one-third of the total dustiness. It is believed that this relationship holds for many fine and nanoscale test powders (i.e. those primarily selected for this study), but may not hold for coarse powders. Neither total nor respirable dustiness was found to be correlated with BET surface area, therefore dustiness is not determined by primary particle size. For a subset of test powders, aerodynamic particle size distributions by number were measured (with an electrical low-pressure impactor and an aerodynamic particle sizer). Particle size modes ranged from approximately 300nm to several micrometers, but no modes below 100nm, were observed. It is therefore unlikely that these materials would exhibit a substantial sub-100nm particle contribution in a workplace.

Carbon Nanotube and Nanofiber Exposure Assessments: An Analysis of 14 Site Visits

“…A recent study on the dustiness of various nanomaterials (Evans et al , 2013) collected data on the respirable-to-total dustiness ratio using a Venturi-based device. Materials tested included a MWCNT, a CNF, and two types of SWCNT, which produced respirable-to-total mass ratios of 0.17, 0.28, 0.41, and 0.84, respectively.…”

“…In our study, where both the respirable and inhalable samples were collected side-by-side we found ratios of 0.05 and 0.12 at MWCNT sites while SWCNT sites had ratios of 0.22 and 2.49; the latter is likely explained by the small sample size and short durations of exposure at SM-electronics sites. Although only a small number of CNT and CNF materials were tested (Evans et al , 2013), and only a relatively small number of side-by-side respirable and inhalable samples were collected in this study, further research may be warranted to derive a mean ratio between size fractions that could be used to estimate EC concentrations in un-sampled fractions.…”

A system to assess the stability of airborne nanoparticle agglomerates under aerodynamic shear

“…Recently, a modified rotating drum method based on a downscaled version of EN 15051 was developed, which uses much less powder (6 g) per test (Schneider & Jensen, 2008). Other aerosolization systems which employs relatively lower amount of raw material include the Venturi dustiness testing device (Evans, Turkevich, Roettgers, Deye, & Baron, 2013) and the low-mass dustiness tester that simulates the powder falling process (O'Shaughnessy, Kang, & Ellickson, 2011). The powder quantities used in these two methods are 10 mg and 15 mg.…”

Refinement of the Nanoparticle Emission Assessment Technique into the Nanomaterial Exposure Assessment Technique (NEAT 2.0)

“…(33) This may include dustiness and toxicity testing to provide insight as to how the dry material will behave if aerosolized and inhaled. (33) Material characterization is not a routine part of NEAT 2.0, but could provide additional data to support the need for engineering controls in an occupational setting.…”