Contribution of Facial Feature Dimensions and Velocity Parameters on Particle Inhalability

Abstract

To examine whether the actual dimensions of human facial features are important to the development of a low-velocity inhalable particulate mass sampling criterion, this study evaluated the effect of facial feature dimensions (nose and lips) on estimates of aspiration efficiency of inhalable particles using computational fluid dynamics modeling over a range of indoor air and breathing velocities. Fluid flow and particle transport around four humanoid forms with different facial feature dimensions were simulated. All forms were facing the wind (0.2, 0.4 m s −1 ), and breathing was simulated with constant inhalation (1.81, 4.3, 12.11 m s −1 ). The fluid flow field was solved using standard k-epsilon turbulence equations, and laminar particle trajectories were used to determine critical areas defining inhaled particles. The critical areas were then used to compute the aspiration efficiency of the mouth-breathing humanoid. One-tailed t-tests indicated that models with larger nose and lip features resulted in significantly lower aspiration efficiencies than geometries with smaller features, but the shape of the orifice into the mouth (rounded rectangle versus elliptical) had no effect on aspiration efficiency. While statistically significant, the magnitudes of differences were small: on average, the large nose reduced aspiration efficiency by 6.5% and the large lips reduced aspiration efficiency by 3.2%. In comparison, a change in breathing velocity from at-rest to heavy increased aspiration efficiency by an average of 21% over all particle sizes, indicating a much greater impact of aspiration efficiency on breathing rate in the facing-the-wind orientation. Linear regression models confirmed that particle diameter and breathing velocity were significant predictors to the aspiration fraction, while the facial feature dimensions were not significant contributors to a unifying model. While these effects may be less pronounced as the orientation changes from facing-the-wind, their impact confirms the importance of breathing velocity and, to a lesser extent, facial feature dimensions on exposure estimates in low freestream velocities typical of occupational environments.

Influence of secondary aspiration on human aspiration efficiency

“…Anderson and Anthony (2013) found truncating the humanoid model affects the location of the critical area, but not the size or shape. Critical areas decreased with increasing particle size, similar to results from previous studies (Anthony, 2010, Anthony and Anderson, 2013 and King Se et al, 2010). As the humanoid model rotated away from the facing-the-wind orientation, critical areas decreased, as anticipated (Kennedy & Hinds, 2002).…”

“…Anthony (2010) reported differences in facial features affecting aspiration by 10% and differences in breathing velocity affecting aspiration on average 21%. Anderson and Anthony (2013) reported simplifications in torso geometry affecting aspiration by 9%.…”

“…1, a realistic human head, with a small nose, small lip facial geometry, was evaluated in this work, described fully in Anthony (2010). The mouth was modeled as a rectangular opening with rounded edges (area=1.385e −4 m 2 ) and the nostrils were modeled as ovals located 2.4 mm above the bottom plane of the nose (area=1.00614e −4 m 2 ).…”

An Empirical Model of Human Aspiration in Low-Velocity Air Using CFD Investigations

“…Detailed descriptions of the CFD simulations have been provided, (16–19) but highlights are given here. The new simulations used to obtain validation data were performed using the same geometry (small nose), equations, and solutions as the simulations used to develop the empirical model.…”

“…Two models of facial features were examined: small nose with small lips (proportioned to match laser Doppler velocity measurements in Anthony, Flynn, and Eisner (20) ) and large nose with large lips, both described in detail in Anthony. (16) This humanoid form was positioned in a wind tunnel, at a fixed orientation per simulation (0° = facing the wind, 15, 30, 60, 90, 135, 180° relative to the oncoming wind). Figure 1 illustrates the humanoid geometry in the simulated wind tunnel.…”