Influence of wearing masks on exhaled air aerodynamics

Figures & data

Figure 1. Schlieren imaging system at Bauhaus-Universität Weimar.

Figure 2. Test subject equipped with respiratory inductance plethysmography (RIP) belts seating in front of the schlieren mirror during N95 mask (left picture) and Barrier® blue surgical mask (right picture) investigation.

Table 1. Tested RPD types, standards, manufacturers, and photographs.

RPD type	Manufacturer	Application
Type: Surgical mask,	Sanimed, Ibbenbüren, Germany
Standard: EN 14683
Product name: Surgical mask green
Type: Surgical mask	Mölnlycke Health Care GmbH, Düsseldorf, Germany
Standard: EN 14683
Product name: Barrier® standard blue
Type: Community mask	N/A
Standard: N/A
Product: Unmarked 1, 2-fold layer cloth
Type: Community mask	N/A
Standard: N/A
Product: Unmarked 2, 2-fold layer cloth
Type: Community mask	N/A
Standard: N/A
Product: Unmarked 3, Knitwear + inner layer
Type: Community mask	N/A
Standard: N/A
Product: Unmarked 4, Knitwear + inner layer
Type: FFP2	3M Deutschland GmbH, Neuss, Germany
Standard: EN 149
Product name: Aura® 9320+
Type: FFP3 + valve	Ampri GmbH, Winsen/Luhe, Germany
Standard: EN 149
Product name: Med-Comfort P-3900
Type: N95	Dasheng, Songjiang, Shanghai, China
Standard: US 42 CFR Part 84, NIOSH
Product name: DTC3X
Type: NV FFM	ResMed Healthcare
Standard: EN 140
Product name: AcuCare Full Face
Type: Replaceable filters
Standard: EN 143	Teleflex Medical Sdn. Bhd., Kamunting, Perak, Malaysia
Product name: Iso-Gard® CE 0124

Figure 3. Range of expired air and corresponding expiratory tidal volume when wearing a N95 mask.

Figure 4. Schlieren image of thermal plume above thermal manikin. The thermal manikin is used to simulate heat release from the human body.

Figure 5. Schlieren image of the lateral and anterior views of the coughing manoeuvre with an N95 face mask. The proportions of the amount of air expired into the different directions is calculated by the size of areas of expired air in the different directions defined by a two-dimensional cartesian system.

Table 2. Lateral view investigations.

RPD Type	Range [m]	Direction (quadrants)			Uplift- effect
		I	II	III
Surgical mask (green)	0.26	72%	20%	8%	100%
Barrier® blue surgical mask	0.27	62%	3%	35%	65%
Unmarked 1	0.45	93%	7%	–	30%
Unmarked 2	0.30	36%	64%	–	100%
Unmarked 3	0.37	78%	22%	–	65%
Unmarked 4	0.30	78%	22%	–	40%
FFP2	0.10	60%	14%	26%	100%
FFP3 + valve	0.40	73%	15%	12%	70%
N95	0.25	58%	28%	13%	87%
NV FFM + replaceable filters	n/a	n/a	n/a	n/a	n/a

Mean expired air range during 3–4 cough manoeuvres, major direction/s of the expiration air corridors, estimated proportions of expired tidal volume per air corridor, and video-visible uplift-effect by thermal plume convection.

Axes of a two-dimensional cartesian system were placed exactly at the RPD tip in the lateral view. Quadrants defined as: I forward upwards direction, II perpendicular upwards direction, III forward downwards direction, IV backwards downwards direction, Uplift-effect: Amount of exhaled air that is raised up vertically by the human bodies thermal plume convection, n/a: not applicable.

Table 3. Anterior view investigations.

RPD Type	Range [m]	Direction (quadrants)		Uplift- effect
		I, II	III, IV
Surgical mask (green)	>0.40	73%	27%	45%
Barrier® blue surgical mask	0.10	55%	45%	100%
Unmarked 1	>0.40	100%	–	40%
Unmarked 2	>0.45	100%	–	100%
Unmarked 3	>0.37	74%	26%	55%
Unmarked 4	>0.38	100%	–	65%
FFP2	0.24	20%	80%	100%
FFP3 + valve	0.26	63%	37%	63%
N95	0.24	64%	36%	64%
NV FFM + replaceable filters	>0.33	–	100%	None

Mean expired air range during 3–4 cough manoeuvres, major direction/s of the expiration air corridors symmetrically to the left and right side, estimated proportions of expired tidal volume per air corridor per side, and video-visible uplift-effect by thermal plume convection.

Axes of a two-dimensional cartesian system were placed exactly at the RPD in the anterior view. Quadrants defined as: I upper right direction, II upper left direction, III lower left direction, IV lower right direction, Uplift-effect: Amount of exhaled air that is raised up vertically by the human bodies thermal plume convection.

Table 4. Range of expired air in lateral and anterior views during cough manoeuvre.