Study of the micro-climate and bacterial distribution in the deadspace of N95 filtering face respirators

Quan Yang,Yong Feng,Ruiyang Huang,Guoqing Zhang,Shiyue Ma,Hui Li,James Yang,Shengnan Shen

doi:10.1038/s41598-018-35693-w

Abstract

It is common for people to use N95 filtering facepiece respirators (FFRs) in daily life, especially in locations where particulate matter (PM2.5) concentration is rising. Wearing N95 FFRs is helpful to reduce inhalation of PM2.5. Although N95 FFRs block at least 95% of particles from the atmosphere, the deadspace of N95 FFRs could be a warm, wet environment that may be a perfect breeding ground for bacterial growth. This work studies the micro-climate features including the temperature distribution and water vapor condensation in the deadspace of an N95 FFR using the computational fluid dynamics (CFD) method. Then, the temperature and relative humidity inside the same type of N95 FFR are experimentally measured. There is a good agreement between the simulation and experimental results. Moreover, an experiment is conducted to study the distribution of bacteria sampled from the inner surface of an N95 FFR after donning.

Highlights

At a specific pressure, water vapor condensation may occur when the ambient temperature is lower than the condensing temperature
The values of liquid water volume fraction range from 0.6 × 10−5 to 2.4 × 10−5, and we can conclude that there will be more liquid water condensing on the N95 filtering facepiece respirators (FFRs) inner surface because it is subjected to direct exhaled airflow
The micro-climate features of water vapor condensation and temperature distribution in the deadspace of the N95 FFR during exhalation and inhalation were studied by use of computing fluid dynamic (CFD) simulation and experimental investigation

Summary

Thermal Conductivity

(IV) were discretized into tetrahedral elements, which amount to 142,831, 127,766 and 121,654, respectively. Monitoring point A located at the center of the core region of FFR deadspace has a rapid increase of temperature to approximately 304.3 K, but it is still 3.3 K lower than the initial inlet temperature of 307.6 K. This means there is a heat dissipation from both the surrounding and core regions of the FFR deadspace to the outside of the FFR during a human breath. The values of liquid water volume fraction range from 0.6 × 10−5 to 2.4 × 10−5, and we can conclude that there will be more liquid water condensing on the N95 FFR inner surface because it is subjected to direct exhaled airflow

Experiment and Comparison

Conclusion

Author Contributions

Findings

Additional Information