The International Society for Respiratory Protection

pdf Vol. 36. No. 2. 2019 pp. 66 - 76 Xu (open access)

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Numerical Simulations of Exhaled Particles from Wearers of Powered Air Purifying Respirators

Susan S. Xu, Zhipeng Lei, Ziqing Zhuang and Michael Bergman

In surgical settings, infectious particulate wound contamination is a recognized cause of post-operative infections. Powered air purifying respirators (PAPRs) are worn by healthcare workers for personal protection against contaminated aerosols. Healthcare infection preventionists have expressed concern about the possibility that infectious particles expelled from PAPR exhalation channels could lead to healthcare-associated disease, especially in operative settings where sterile procedural technique is essential.

This study used computational fluid dynamics (CFD) modeling to simulate and visualize the distribution of particles exhaled by PAPR wearers. Using CFD simulations, the PAPR inside to outside ratio of particle concentrations was estimated. Also, the effects of particle sizes, supplied-air flow rates, and breathing work rates on outward leakage were evaluated.

This simulation study reconstructed a geometrical model of a static median headform wearing a loose-fitting PAPR by capturing a 3D image. We defined a mathematical model for the headform and PAPR system and ran simulations with four particle sizes, three breathing workloads and two supplied-air flow rates (a total 24 configurations; 4x3x2=24) applied on the digital model of the headform and PAPR system. This model accounts for exhaled particles, but not ambient particles. Computed distributions of particles inside and outside the PAPR are displayed.

The outward concentration leakage was low at surgical setting, e.g., it was about 9% for a particle size of 0.1 and 1 μm at light breathing and a 205 L/min supplied-air flow rate. The supplied-air flow rates, particle sizes, and breathing workloads had effects on the outward concentration leakage, as the outward concentration leakage increased as particle size decreased, breathing workload increased, and the supplied-air flow rate decreased. The CFD simulations can help to optimize the supplied-air flow rates. When the loose-fitting PAPR is used, exhaled particles with small size (below 1μm), or heavy breathing workloads, may generate a great risk to the sterile field and should be avoided.

Keywords: Exhaled particles, outward leakage, powered air purifying respirators, Computational Fluid Dynamics, simulation, surgical setting, sterile surgical field