ABSTRACT
Facemasks are widely used as a protective measure by general public to prevent inhalation of airborne pathogens including seasonal, swine and other forms of influenza and severe acute respiratory syndrome (SARS), etc. However, scientific data on effectiveness of facemasks in reducing infections in the community are extremely limited and even inconsistent. In this work, two manikins labelled as ‘source’ and ‘susceptible’ were used to measure the protection provided by facemasks under various emission scenarios. The source was modified to generate polydisperse ultrafine particles, whereas the susceptible was modified to mimic a realistic breathing pattern. The facemask was challenged by both pseudo-steady and highly transient emissions generated by an expiratory process where parameters, such as separation distance between manikins, emission velocity and expiratory duration, were controlled and measured systematically. Performances of four different types of facemask fits, varying from ideal to normal wearing practice, were also investigated. Under the pseudo-steady concentration environment, facemask protection was found to be 45 per cent, while under expiratory emissions, protection varied from 33 to 100 per cent. It was also observed that the separation between the source and the manikin was the most influential parameter affecting facemask protection.
… The distance between the source and the susceptible was varied from 30 to 60 cm. [approximately 1 to 2 feet] This represents a common social behaviour. People have been reported to have four proxemics zones, where the intimate and personal distances were within 18 inch (45.7 cm) and 18 inch to 4 feet (45.7–121.92 cm), respectively [34]. The testing separations represent a normal distance between two people conversing, while one of them (the source) coughs or sneezes during the conversation.
…Four facemask wearing conditions were mimicked to represent different ways people might wear facemasks. The first was a fully sealed facemask, regarded as the ideal case, where all sides were sealed onto the manikin's face by double-sided tape, i.e. penetration was possible only through the facemask. The second was a three-side-sealed facemask, where three sides were sealed and the upward side was shaped in a normal way to mimic natural wearing. Since only one side of the facemask was not sealed, the penetration pathway for unintentional leakage could be studied. The third wearing condition was also a three-side-sealed facemask, but with a 4 mm artificial leakage on both sides of nose, such a small area was provided in order to study the penetration pathway for intentional leakages. The last one was the closest to the normal wearing pattern as no artificial seal or leakage was applied. In order to mimic the normal wearing as close to practice as possible, the facemask was worn by pinching the stiff metal edge to mould to the bridge of the nose and by fully covering the chin.
… The pseudo-steady condition was achieved in a well-mixed chamber, while transient scenarios were realized by the expiratory process. One of the key features of the measurements was that practical breathing was mimicked by using a thermal breathing manikin. The level of protection was parametrized by reduction of exposure. It was observed that under pseudo-steady conditions, the PD is 45 per cent for normal wearing scenarios. Under transient scenarios, the PD varied from 33 to 100 per cent with different parameters. It was observed that fully sealed facemasks provide the highest protection, while the least protective was the normal wearing. It was also observed that the reduction of exposure decreases with increasing emission velocity and emission duration, and with decreasing separation distance between source and susceptible manikins.
… In addition, the relative humidity (RH) should also be considered for follow-up studies, since wearing facemasks will undoubtedly increase the RH between the face and the facemask. Such further studies would be very important as the humid environment may provide a hotbed for viruses and bacteria.
