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During expiration, the carbon dioxide (CO 2 ) levels inside the dead space of a filtering facepiece respirator (FFR) increase significantly above the ambient concentration. To reduce the CO 2  concentration inside the dead space, we attach an active lightweight venting system (AVS) comprising a one-way valve, a blower and a battery in a housing to a FFR. The achieved reduction is quantified with a computational-fluid-dynamics model that considers conservation of mass, momentum and the dilute species, CO 2 , inside the FFR with and without the AVS. The results suggest that the AVS can reduce the CO 2  levels inside the dead space at the end of expiration to around 0.4% as compared to a standard FFR, for which the CO 2  levels during expiration reach the same concentration as that of the expired alveolar air at around 5%. In particular, during inspiration, the average CO 2  volume fraction drops to near-to ambient levels of around 0.08% with the AVS. Overall, the time-averaged CO 2  volume fractions inside the dead space for the standard FFR and the one with AVS are around 3% and 0.3% respectively. Further, the ability of the AVS to vent the dead-space air in the form of a jet into the ambient – similar to the jets arising from natural expiration without a FFR – ensures that the expired air is removed and diluted more efficiently than a standard FFR.

Reduction of Carbon Dioxide in Filtering Facepiece Respirators with an Active-Venting System: A Computational Study