A laboratory model demonstrating the protective effects of surgical masks, face shields, and a combination of both in...

The protection against aerosol transmission provided by masks vs face shields or in combination when speaking indoors is not well understood.

To simulate a human source, an aerosol generating system was made using a bacterial suspension in a nebulizer attached to an oxygen cylinder. A fan connected to the nebulizer created aerosols. Transmitted aerosols were detected using blood agar plates at 0.1524 and 1.8288 meters from source, simulating exposed person. The study was performed under controlled conditions at room temperature in a biohazard hood with high-efficiency particulate air (HEPA) filter and UV light.

When face shields were used alone, significant numbers of bacterial colonies grew on blood agar plates. When a mask used alone for both the subjects (source and exposed), the blood agar yielded minimal colony forming units at both distances. When face shields were used in combination with masks, no significant improvement was observed as compared to masks alone.

Our results were similar to what have been observed in related studies.

Surgical masks alone provided good protection, surpassing the protection provided by face shields alone. Both used together provided the best protection, although the combined protection was similar to surgical masks use alone.