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Manufacturing

NORA Manufacturing Sector Strategic Goals

R019290 - 021H: CFD Investigation of Particle Inhalability in Low Windspeeds (9290)

Start Date: 6/1/2008
End Date: 5/31/2013

Principal Investigator (PI)
Name: Lata Kumar
Organization: NIOSH
Sub-Unit: OEP
Funded By: NIOSH

Primary Goal Addressed
5.0

Secondary Goal Addressed

None



Attributed to Manufacturing

100%


Project Description

Short Summary

Once health effects studies are applied to these exposure estimates, risk estimates will be based on overestimated exposures. This will result in risk assessments that actually underestimate the risk of exposure to workers. This research will identify whether the sampling criterion to assess exposures to large particles in workplaces requires adjustment to improve exposure and risk estimates.



Description

Computational fluid dynamics (CFD) modeling techniques can be used to examine contaminant transport and to estimate personal exposure. This work proposes to use CFD to investigate particle aspiration in low velocity environments, typical of the occupational environment. The long-term objective of this work is to provide guidance to the development of an international performance criterion for inhalable particle samplers when used indoors with little air movement. The existing criterion was developed from experiments in larger windspeeds, which may overestimate the amount of particles that are inhaled by a worker in an indoor setting. CFD methods allow the simulation of uniform particle concentration fields, allowing us to avoid the experimental difficulties associated with uniform suspension of large particles. Initial research has developed, validated, and verified a computer representation of a single humanoid form to investigate particle aspiration using the standard k-epsilon turbulence model in the facing-the-wind orientation. This research will: (1) examine the sensitivity of aspiration efficiency estimates to facial feature dimensions, turbulence equations, and bounce parameters to quantify uncertainty in aspiration efficiency estimates; (2) investigate particle aspiration at orientations other than facing-the-wind to understand the influences of orientation and velocity parameters on particle aspiration for a humaniod form; (3) to propose a low velocity aspiration efficiency curve for use in the development of an inhalable particle sampler criterion. This work supports the Exposure Assessment Methods NORA priority research area. There is current concern that occupational exposure samples collected using the existing high-velocity IPM criterion collects particles at efficiencies greater than what can be inhaled by workers. If so, mass-based exposure estimates will overestimate the true exposures of individuals. Once health effects studies are applied to these exposure estimates, risk estimates will be based on overestimated exposures. This will result in risk assessments that actually underestimate the risk of exposure to workers. This research will identify whether the sampling criterion to assess exposures to large particles in workplaces requires adjustment to improve exposure and risk estimates.



Objectives

The specific aims of this project are to:



Aim 1: Examine the sensitivity of the CFD simulations to predicted particle aspiration efficiency. Namely, examine the effects of physical features (torso dimensions, nose size, lip size, orifice shape) and turbulence kinetic energy models. Variability attributed to physical feature variability will be included in the recommended low velocity inhalability criterion in Aim 3. Turbulence models will be examined to address uncertainties in turbulence predictions identified in previous work.



Aim 2: Develop a predictive model for orientation-specific and -averaged aspiration efficiency for a range of low velocity and breathing conditions. Two conditions of freestream velocity and three breathing rates will be assessed (6 velocity conditions). Comparisons to reported aspiration efficiencies in the literature will serve as validation data for this model. A 7th condition of freestream and suction velocity will be analyzed to validate the resulting predictive model.



Aim 3: Determine whether aspiration efficiency of a breathing human in low velocity environments is significantly different from the existing inhalable curve appropriate to outdoor velocity conditions. From this, an inhalable particle sampling criterion will be proposed for indoor environments.



 
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