Efficacy of face masks, neck gaiters and face shields for reducing the expulsion of simulated cough-generated aerosols

Figures & data

Figure 1. Cough aerosol simulator system for source control measurements. The system consists of an aerosol generation system, a bellows and linear motor to produce the simulated cough, a pliable skin head form on which the face mask, neck gaiter or face shield is placed, a 105 liter collection chamber into which the aerosol is coughed, and an Andersen impactor to separate the aerosol particles by size and collect them. More information about the cough aerosol simulator is provided in the SI.

Figure 2. Mass of aerosol collected in each size fraction. The graph shows the amount of simulated respiratory aerosol that was collected from the collection chamber in each aerosol particle size fraction after a single simulated cough. The bars show the mean and standard deviation. A larger color version of this figure is shown in the SI.

Figure 3. Collection efficiency of face masks, neck gaiter and face shield. The collection efficiency is the percentage of aerosol particles that were blocked by the face mask, neck gaiter or face shield compared with experiments without a device. The plot shows the means and standard deviations of the collection efficiency in each size fraction. A larger version of this figure is shown in color in the SI.

Table 1. Total mass of aerosol expelled into collection chamber and device collection efficiencies.

Device tested	Number of experiments	Fit factor	Aerosol mass (µg)	Collection efficiency
No device	12	n/a	512 (64)	n/a
Procedure mask	6	2.9 (0.5)	212 (23)	58.5% (6.9%)
Cloth mask	6	1.3 (0.1)	251 (23)	50.9% (7.7%)
Neck gaiter (single layer)	6	1.7 (0.5)	270 (18)	47.2% (7.5%)
Neck gaiter (double layer)	6	1.9 (0.4)	206 (26)	59.8% (7.2%)
Face shield	6	n/a	502 (46)	1.8% (15.3%)
N95 respirator	6	198 (3.5)	7.2 (1.2)	98.6% (0.3%)

Note: The fit factor, aerosol mass, and collection efficiency are given as mean (standard deviation).

Table 2. Comparison of aerosol mass expelled into the collection chamber while wearing face masks, neck gaiters and face shields.

PPE types compared		95% confidence intervals for mean differences (µg)			P-value
		Lower limit	Mean difference	Upper limit
N95 respirator	No device	−567	−504	−442	<0.0001
Procedure mask	No device	−361	−299	−237	<0.0001
Cloth mask	No device	−322	−260	−198	<0.0001
Gaiter (single layer)	No device	−304	−241	−179	<0.0001
Gaiter (double layer)	No device	−368	−306	−243	<0.0001
Face shield	No device	−71	−9	53	0.9993
N95 respirator	Face shield	−567	−495	−423	<0.0001
Procedure mask	Face shield	−362	−290	−218	<0.0001
Cloth mask	Face shield	−323	−251	−179	<0.0001
Gaiter (single layer)	Face shield	−304	−232	−160	<0.0001
Gaiter (double layer)	Face shield	−369	−297	−225	<0.0001
N95 respirator	Gaiter (double layer)	−271	−199	−127	<0.0001
Procedure mask	Gaiter (double layer)	−65	7	79	0.9999
Cloth mask	Gaiter (double layer)	−26	46	118	0.4505
Gaiter (single layer)	Gaiter (double layer)	−7	64	136	0.1051
N95 respirator	Gaiter (single layer)	−335	−263	−191	<0.0001
Procedure mask	Gaiter (single layer)	−130	−58	14	0.1900
Cloth mask	Gaiter (single layer)	−91	−19	53	0.9825
N95 respirator	Cloth mask	−316	−244	−172	<0.0001
Procedure mask	Cloth mask	−111	−39	33	0.6336
N95 respirator	Procedure mask	−277	−205	−133	<0.0001