Common surgical face masks (as required by law to contribute to the containment of SARS-CoV2) were used for the staining study. The disposable medical face masks measured 175 mm x 95 mm, consisted of three layers and were of the type IIR.
The staining study included the examination of a mask after having been worn conformable to law
(mask obligation). The mask was provided to us after having been worn for 1, 2, and 5 hours, respectively (Setting 1). Unworn masks served as controls.
In another environmental setting, masks were exposed in a room of 25 m2 with a ceiling height of 2.5 m filled with 10 people (Setting 2). The masks hung at a height of 2 m above the floor. This second experiment on masks lasted 1, 2 and 10 hours whereby the people left the room after 5 hours. The room was neither air-conditioned nor intensely ventilated.
In a third setting the inner side of the mask was placed 1 m away in the direction of the speaking person (reading a book) for 1, 2 and 5 hours (Setting 3). The human subject was healthy (no coughing or sneezing) and was advised not to scream or laugh violently. The control mask was placed 5 m away from the face. The large experimental room (40 m2) had been aired every hour for 5 minutes.
In the fourth setting, a mask was worn in compliance with the law (mask obligation), but was reused several times before it was handed over to us for further examination. After each use for about 3 hours per day for 2 weeks, it was kept in a bag by the wearer (Setting 4).
After each completed treatment of the masks (Settings 1-4), the masks were immediately preserved in 70% ethanol. Thereafter they were stained for qualitative and partly quantitative analyses (staining intensity). A solution of 0.1 g bengal rose sodium salt (SIGMA No. R3877-5G) / 0.5 l distilled H20 was used to stain the masks.
Macroscopic photographs were taken of both surfaces of the mask (externally and internally).
Microscopic images were made of selected areas when masks had been worn: the area around the mouth and nose, the edge of the mask adjacent to the nose and the chin. The magnifications were 7x and 30x.