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

Birgersson E, Tang EH, Lee WL, Sak KJ - PLoS ONE (2015)

Bottom Line: The achieved reduction is quantified with a computational-fluid-dynamics model that considers conservation of mass, momentum and the dilute species, CO2, inside the FFR with and without the AVS.The results suggest that the AVS can reduce the CO2 levels inside the dead space at the end of expiration to around 0.4% as compared to a standard FFR, for which the CO2 levels during expiration reach the same concentration as that of the expired alveolar air at around 5%.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore.

ABSTRACT
During expiration, the carbon dioxide (CO2) levels inside the dead space of a filtering facepiece respirator (FFR) increase significantly above the ambient concentration. To reduce the CO2 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, CO2, inside the FFR with and without the AVS. The results suggest that the AVS can reduce the CO2 levels inside the dead space at the end of expiration to around 0.4% as compared to a standard FFR, for which the CO2 levels during expiration reach the same concentration as that of the expired alveolar air at around 5%. In particular, during inspiration, the average CO2 volume fraction drops to near-to ambient levels of around 0.08% with the AVS. Overall, the time-averaged CO2 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.

No MeSH data available.


Related in: MedlinePlus

Streamlines of the airflow during inspiration at 0.3, 0.5 and 1 s and during expiration at 2.5, 3 and 4 s for a standard FFR.The volume fraction of CO2 is shown in color with a range of 0.04% (blue) to 5.3% (red).
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pone.0130306.g005: Streamlines of the airflow during inspiration at 0.3, 0.5 and 1 s and during expiration at 2.5, 3 and 4 s for a standard FFR.The volume fraction of CO2 is shown in color with a range of 0.04% (blue) to 5.3% (red).

Mentions: Turning our attention to the local flow pattern and CO2 levels inside the mask in Fig 5, we find that during inspiration that lasts for 2 seconds, air from the ambient is sucked in more or less uniformly from all around the mask. At 1 s, i.e. half-way through the inspiration, the alveolar air has been almost completely replaced with ambient air. The flow pattern then changes significantly for the subsequent expiration that lasts 3 seconds: the expired jet from the nostril impinges on the filter and is then vented out all around the filter, which results in a steadily increasing CO2 concentration. The dead space is filled with alveolar CO2 at around 4 seconds. Clearly, the reason for the high levels of CO2 in a standard mask is because the jet—which is supposed to vent the air away from us—is stopped and the expired air vented in a diffusive manner.


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

Birgersson E, Tang EH, Lee WL, Sak KJ - PLoS ONE (2015)

Streamlines of the airflow during inspiration at 0.3, 0.5 and 1 s and during expiration at 2.5, 3 and 4 s for a standard FFR.The volume fraction of CO2 is shown in color with a range of 0.04% (blue) to 5.3% (red).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4482734&req=5

pone.0130306.g005: Streamlines of the airflow during inspiration at 0.3, 0.5 and 1 s and during expiration at 2.5, 3 and 4 s for a standard FFR.The volume fraction of CO2 is shown in color with a range of 0.04% (blue) to 5.3% (red).
Mentions: Turning our attention to the local flow pattern and CO2 levels inside the mask in Fig 5, we find that during inspiration that lasts for 2 seconds, air from the ambient is sucked in more or less uniformly from all around the mask. At 1 s, i.e. half-way through the inspiration, the alveolar air has been almost completely replaced with ambient air. The flow pattern then changes significantly for the subsequent expiration that lasts 3 seconds: the expired jet from the nostril impinges on the filter and is then vented out all around the filter, which results in a steadily increasing CO2 concentration. The dead space is filled with alveolar CO2 at around 4 seconds. Clearly, the reason for the high levels of CO2 in a standard mask is because the jet—which is supposed to vent the air away from us—is stopped and the expired air vented in a diffusive manner.

Bottom Line: The achieved reduction is quantified with a computational-fluid-dynamics model that considers conservation of mass, momentum and the dilute species, CO2, inside the FFR with and without the AVS.The results suggest that the AVS can reduce the CO2 levels inside the dead space at the end of expiration to around 0.4% as compared to a standard FFR, for which the CO2 levels during expiration reach the same concentration as that of the expired alveolar air at around 5%.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore.

ABSTRACT
During expiration, the carbon dioxide (CO2) levels inside the dead space of a filtering facepiece respirator (FFR) increase significantly above the ambient concentration. To reduce the CO2 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, CO2, inside the FFR with and without the AVS. The results suggest that the AVS can reduce the CO2 levels inside the dead space at the end of expiration to around 0.4% as compared to a standard FFR, for which the CO2 levels during expiration reach the same concentration as that of the expired alveolar air at around 5%. In particular, during inspiration, the average CO2 volume fraction drops to near-to ambient levels of around 0.08% with the AVS. Overall, the time-averaged CO2 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.

No MeSH data available.


Related in: MedlinePlus