Cascade Impactor Measurements Guidance for collection of inhalable ni dust

An evaluation of currently commercially available gravimetric dust samplers was
performed to select suitable candidate samplers for measuring personal respirable
and inhalable Nickel (Ni) dust exposure. This involved a literature review on the
performance of the different samplers. The selection was based on the following
requirements:
· the samplers should follow the recognised ACGIH/CEN/ISO criteria for collection
of inhalable and respirable airborne particles;
· evidence of agreement of the sampler performance with these criteria should be
available in the peer-reviewed literature;
· the sampling medium should not impede the chemical analysis of Ni and Ni
compounds; and
· the samplers should be readily commercially available worldwide.
The IOM Inhalable Dust sampling head is widely recognised as a sampler that closely
follows the inhalability criteria, although it is acknowledged that the sampling efficiency
deviates with low (< 0.5 m s-1) and high wind (> 4 m s1) velocities and with increasing
particle size (Kenny et al. 1997a, Sleet and Vincent, 2011). The sampler is easy to
assemble, not expensive, and it is used worldwide.
The respirable fraction of airborne dust is most commonly sampled using cyclones. The
two main cyclones, the Higgins Dewell (HD) and Dorr Oliver (DO) cyclone have been
reported to have similar performance. The former is most widely used in the EU,
whereas the DO cyclone is more common in the US. The advantage of the HD cyclone
is that cassettes are re-usable, resulting in lower costs.
Multi-fraction samplers offer the advantage of sampling both respirable and inhalable
fractions simultaneously. However, the performance of these samplers has been
studied less than single fraction samplers such as the IOM sampling head and the
cyclones. The Conical Inhalable Sampler (CIS) and IOM dual samplers are multifraction samplers that use polyurethane foam (PUF) as the separating medium. Foams
have higher gravimetric instability than filters, may contain relatively high and variable
levels of Ni, and the use of a filter plus foam to derive the inhalable fraction results in
higher LODs. The 3-stage impactor Respicon offers an easy alternative for collection of
the three health-relevant fractions: inhalable, thoracic and respirable. However, the
sampler is relatively expensive (€1,091) compared to the other samplers and its
performance in terms of particle separation is sensitive to variations in the flow-rate.
In summary, the IOM and cyclone heads are well recognised for following the
ACGIH/ISO/CEN curves for inhalable and respirable dust, respectively. Both samplers
have been widely studied and their sampling efficiencies are well characterized. The
IOM and CIS dual samplers and the Respicon offer the advantage of sampling
simultaneously both particle size fractions, allowing direct estimation of the respirable
amount of Ni contained in the inhalable fraction. However, fewer studies have
assessed the performance of these multi-fraction samplers and therefore their biases
are less well characterised. Therefore, it is recommended to use the IOM Inhalable
sampling head for inhalable dust and a Higgins-Dewell or Dorr Oliver cyclone for
respirable dust.