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Inhalation Toxicology
International Forum for Respiratory Research
Volume 17, 2005 - Issue 14
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Research Article

Particle Inhalability at Low Wind Speeds

Pages 831-837 | Received 01 Jun 2005, Accepted 27 Jun 2005, Published online: 06 Oct 2008
 

Abstract

Accurate quantification of the dose delivered by aerosol exposures is essential for estimating the risk of potential adverse health effects. The fraction of airborne particles that can enter the nose or mouth during inhalation is referred to as the inspirable particulate mass fraction. This inhalable fraction is equivalent to delivered dose for particles greater than approximately 25 μm (aerodynamic particle diameter, dae), which deposit completely and almost exclusively in the extrathoracic airways. Particle inhalability at high wind speeds (1–9 m/s) has been well characterized. However, there is a paucity of data describing the inhalability of particles at low wind speeds (0.3 m/s), which are typical of indoor environments. High-wind-speed criteria poorly describe inhalability at low wind speeds. Based on the aspiration efficiencies of blunt and sharp-edged inlets, a function was developed for oral inhalability, P(IO), of particles at low wind speeds. This function predicts a slow decline in P(IO) from 0.95 at dae= 8 μ m, to 0.5 at dae = 74 μ m, and 0.1 at dae= 175 μm. Data available from the literature for inhalability at relatively low wind speeds during oral breathing are well described by this logistic function (r2= 0.69).

Notes

*e values were not provided in the original proceedings paper (Hinds et al., Citation1998) but were obtained from the full paper (Kennedy & Hinds, Citation2002).

*An r2 is calculated as the model sum of squares (MSS) divided by the total corrected sum of squares (TSS). The MSS equals the TSS minus the residual sum of squares (RSS). In typical linear regressions, when a model is fitted to a data set, the resulting r2 must be nonnegative since the least square fitting procedure assures RSS ≤ TSS. When r2 is computed on excluded data, that is, data not used to fit the model, RSS can exceed the TSS. In this case, r2 (which is not the square of r) can be negative, indicating that the mean of the data is a better predictor than the model.

*Aitken et al. (Citation1999) collapsed 22- and 35-mm inner diameter tubes into ellipses having an inner minor axis of 6 mm, but did not report the major axis. The inlet's inner major axis was back-calculated here by assuming a constant inner circumference for the circular and elliptical openings.

*The Yu et al. (Citation2001) definition of “moderate” work (e = 60 lpm) is inconsistent with that used in this article and exceeds the ICRP, (Citation1994) definition of “heavy” exercise. In addition, the ICRP, (Citation1994) characterizes heavy work that can be sustained over an 8-h workday as 7/8 light exercise (e = 25 lpm) and 1/8 heavy exercise (e = 50 lpm). More details regarding work loads, ventilation rates, and typical activity levels are available elsewhere (ICRP, Citation1994; de Winter-Sorkina & Cassee, Citation2002).

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