PMC:7784787 / 5907-9263 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/7784787","sourcedb":"PMC","sourceid":"7784787","source_url":"https://www.ncbi.nlm.nih.gov/pmc/7784787","text":"Materials \u0026 methods\nThe experimental setup is shown in Figure 1. The aerosol consisted of 10% NaCl in water from a nebulizer (Omron NE-C28P, mass median aerodynamic diameter of 3 μm) fed through one of the lung ports of a dummy head (Laerdal airway management trainer) lying face upward on an optical bench. Prior to measurement, the airway was primed with aerosol by turning on the nebulizer briefly while squeezing the attached lung ten-times, then waiting for 30 s for the exhaled aerosol to disperse. A fume extractor was running continuously above the head (ULT Jumbo Filter Trolley 2.0 running at 0.3 m/s in a position 15 cm above the tip of the nose). After initiating the camera acquisition, the lung was squeezed by hand to deliver a breath. These were measured to deliver 300 ml quite reproducibly (wright respirometer). For the breath duration of 1 s, the average flow of 0.3 l/s is similar to the peak flow for a normal breath 0.5 m/s [26]. The aerosol was visualized with a conical laser sheet generated with a 488 nm DPSS laser (Coherent Sapphire 75 mW) and axicon lens (Thorlabs AX1220-A). The conical cyan sheet surrounds the face at a distance of approximately 2.5 cm from the nose and at a closer distance at the cheek to allow space for the masks. A beam block was used at the axicon’s aperture to prevent direct illumination of parts of the dummy.\nFigure 1. Photographs of the setup, showing the laser cone on an unmasked dummy.\nThe extractor is turned off to enhance laser appearance (A) view from the left (B) view from top parallel to laser (C) view from the right bottom. The camera was a 2048*2048 pixel sCMOS array (Andor Sona 4BV11) with Nikkor 50 mm F1.8 AI MF lens. It recorded a sequence of 30 frames at 7 Hz (acquisition time of 10 ms). Raw 16-bit images were processed in SAOimage DS9 by applying the ‘bb’ colormap on a value range of 100–20,000 counts using log scaling.\nThe masks and dummy used are shown in Figure 2. The three-layer mask in Figure 2B has two outer layers each 0.4-mm thick made of 80% polyester 20% elastane with the internal filter layer being 1.0 mm 100% polypropylene. The filter covers the area of the mouth and nose but around chin, cheeks and nose bridge the fabric is just a single layer. Compliance with the testing methods of the CWA 17553 was claimed by the supplier but packaging was not marked accordingly.\nFigure 2. Photographs of the test materials.\n(A) the unmasked dummy, (B) three-layer mask with middle filter layer removed, (C) single-layer textile mask. Bottom row: (D) CE marked FFP1 personal protective equipment mask, (E) CE marked Type 2 medical mask, (F) bandana. The single layer mask in Figure 2C is of unknown 1.0-mm thick material, of a design which was cheaply and widely available. Compliance with CWA 17553 was not claimed. The CE-marked FFP1 respirator mask in Figure 2D has no exhalation valve and it is marked as complying with EN 149. The CE-marked type 2 medical mask in Figure 2E had a metal nose clip which was cinched down firmly on the dummy. The packaging was marked as complying with EN 14683. The bandana or neck gaiter in Figure 2(f) was 0.33 mm thick 100% polyester and was folded into three layers in these experiments. Dating from 2019 this was never intended for infection control, although the same material has been seen to be used as a face 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