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Dustiness of fine and nanoscale powders.

Evans DE, Turkevich LA, Roettgers CT, Deye GJ, Baron PA - Ann Occup Hyg (2012)

Bottom Line: For many powders, a significant respirable dustiness was observed.Neither total nor respirable dustiness was found to be correlated with BET surface area, therefore dustiness is not determined by primary particle size.It is therefore unlikely that these materials would exhibit a substantial sub-100 nm particle contribution in a workplace.

View Article: PubMed Central - PubMed

Affiliation: National Institute for Occupational Safety and Health, Chemical Exposure and Monitoring Branch, Division of Applied Research and Technology, 4676 Columbia Parkway, MS-R7, Cincinnati, OH 45226, USA. dje3@cdc.gov

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 300 nm to several micrometers, but no modes below 100 nm, were observed. It is therefore unlikely that these materials would exhibit a substantial sub-100 nm particle contribution in a workplace.

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Sequential photographs of the dispersion of 5 mg of Aeroxide P25 TiO2 powder in the dustiness chamber.
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Figure 2: Sequential photographs of the dispersion of 5 mg of Aeroxide P25 TiO2 powder in the dustiness chamber.

Mentions: A qualitatively different method was introduced (Boundy et al., 2006) in order to test pharmaceutical powders. The aim was to utilize small quantities (~5mg) of powder under confined conditions (cost considerations and reproducibility, and also so as not to expose the test operator to potentially toxic or pharmacologically active material). A powder is placed in a holding tube (d = 0.44cm) exterior to but piercing the dispersion chamber. Air is introduced into the dispersion chamber (5.7 l) via the holding tube at a volumetric flow rate Q = 60 l min−1, resulting in nozzle air flow v ~70 m s−1. Aerosolization presumably occurs via aerodynamic lift and pneumatic drag mechanisms acting on the powder; particulate velocities are one to two orders of magnitude larger than the gentler falling powder and rotating drum methods discussed above. In addition, the aerosolization proceeds under turbulent conditions (Reynolds number, Re = Qd/vA ~8000, where Q is the volumetric flow rate, d and A the tube diameter and cross-sectional area, respectively, and v the kinematic viscosity), whereas in the gentle tests, the airflows can be considered at larger scale and in the laminar regime. For a small number of the more cohesive powders, impaction residue has been detected on the far wall of the chamber (see Fig. 2h for example), but it is not believed that this mechanism significantly contributes to the aerosolized dust.


Dustiness of fine and nanoscale powders.

Evans DE, Turkevich LA, Roettgers CT, Deye GJ, Baron PA - Ann Occup Hyg (2012)

Sequential photographs of the dispersion of 5 mg of Aeroxide P25 TiO2 powder in the dustiness chamber.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750099&req=5

Figure 2: Sequential photographs of the dispersion of 5 mg of Aeroxide P25 TiO2 powder in the dustiness chamber.
Mentions: A qualitatively different method was introduced (Boundy et al., 2006) in order to test pharmaceutical powders. The aim was to utilize small quantities (~5mg) of powder under confined conditions (cost considerations and reproducibility, and also so as not to expose the test operator to potentially toxic or pharmacologically active material). A powder is placed in a holding tube (d = 0.44cm) exterior to but piercing the dispersion chamber. Air is introduced into the dispersion chamber (5.7 l) via the holding tube at a volumetric flow rate Q = 60 l min−1, resulting in nozzle air flow v ~70 m s−1. Aerosolization presumably occurs via aerodynamic lift and pneumatic drag mechanisms acting on the powder; particulate velocities are one to two orders of magnitude larger than the gentler falling powder and rotating drum methods discussed above. In addition, the aerosolization proceeds under turbulent conditions (Reynolds number, Re = Qd/vA ~8000, where Q is the volumetric flow rate, d and A the tube diameter and cross-sectional area, respectively, and v the kinematic viscosity), whereas in the gentle tests, the airflows can be considered at larger scale and in the laminar regime. For a small number of the more cohesive powders, impaction residue has been detected on the far wall of the chamber (see Fig. 2h for example), but it is not believed that this mechanism significantly contributes to the aerosolized dust.

Bottom Line: For many powders, a significant respirable dustiness was observed.Neither total nor respirable dustiness was found to be correlated with BET surface area, therefore dustiness is not determined by primary particle size.It is therefore unlikely that these materials would exhibit a substantial sub-100 nm particle contribution in a workplace.

View Article: PubMed Central - PubMed

Affiliation: National Institute for Occupational Safety and Health, Chemical Exposure and Monitoring Branch, Division of Applied Research and Technology, 4676 Columbia Parkway, MS-R7, Cincinnati, OH 45226, USA. dje3@cdc.gov

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 300 nm to several micrometers, but no modes below 100 nm, were observed. It is therefore unlikely that these materials would exhibit a substantial sub-100 nm particle contribution in a workplace.

Show MeSH