08/25/2010

Performance of High Flow Rate Samplers for Respirable Particle Collection

The American Conference of Governmental Industrial hygienists (ACGIH) lowered
the threshold limit value (TLV) for respirable crystalline silica (RCS)
exposure from 0.05 to 0.025 mg m-3 in 2006. For a working environment with an
airborne dust concentration near this lowered TLV, the sample collected with
current standard respirable aerosol samplers might not provide enough RCS for
quantitative analysis. Adopting high flow rate sampling devices for respirable
dust containing silica may provide a sufficient amount of RCS to be above the
limit of quantification even for samples collected for less than full shift.
The performances of three high flow rate respirable samplers (CIP10-R, GK2.69,
and FSP10) have been evaluated in this study. Eleven different sizes of
monodisperse aerosols of ammonium fluorescein were generated with a vibrating
orifice aerosol generator in a calm air chamber in order to determine the
sampling efficiency of each sampler. Aluminum oxide particles generated by a
fluidized bed aerosol generator were used to test the uniformity of a modified
calm air chamber, the effect of loading on the sampling efficiency, and the
performance of dust collection compared to lower flow rate cyclones in common
use in the USA (10-mm nylon and Higgins-Dewell cyclones). The coefficient of
variation for eight simultaneous samples in the modified calm air chamber
ranged from 1.9 to 6.1% for triplicate measures of three different aerosols.
The 50% cutoff size (50dae) of the high flow rate samplers operated at the flow
rates recommended by manufacturers were determined as 4.7, 4.1, and 4.8 µm for
CIP10-R, GK2.69, and FSP10, respectively. The mass concentration ratio of the
high flow rate samplers to the low flow rate cyclones decreased with decreasing
mass median aerodynamic diameter (MMAD) and high flow rate samplers collected
more dust than low flow rate samplers by a range of 2-11 times based on
gravimetric analysis. Dust loading inside the high flow rate samplers does not
appear to affect the particle separation in either FSP10 or GK2.69. The high
flow rate samplers overestimated compared to the International Standards
Organization/Comité Européen de Normalisation/ACGIH respirable convention [up
to 40% at large MMAD (27.5 µm)] and could provide overestimated exposure data
with the current flow rates. However, both cyclones appeared to be able to
provide relatively unbiased assessments of RCS when their flow rates were
adjusted.


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