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What does the evidence say on the fitted filtration efficiency (FFE) of various consumer-grade and improvised face masks, as well as several popular modifications of medical procedure masks during the Corona Virus Disease 2019 (COVID-19) pandemic?

Comment by InpharmD Researcher

Please see the table below for your response. The mean (SD) FFE of consumer grade masks tested on one adult male with no beard ranged from 79.0% (4.3%) to 26.5% (10.5%), with the 2-layer woven nylon mask having the highest FFE. Unmodified medical procedure masks with ear loops had a mean (SD) FFE of 38.5% (11.2%).
Background

The Centers for Disease Control and Prevention (CDC) recommend wearing masks in public settings. Masks should have two or more washable layers of breathable fabric, and should completely cover your nose and mouth. [1]

Masks are effective at preventing the spread of COVID-19. Researchers suggest that face masks reduce the spread of viral respiratory infection, and that N95 respirators and surgical masks both provide substantial protection (compared with no mask). Surgical masks provide greater protection than cloth masks. [2]

A meta-analyses investigating the use of face masks and eye protection to prevent transmission of viruses found that face mask use could result in a large reduction in risk of infection (n=2647; aOR 0·15, 95% CI 0·07 to 0·34, RD −14·3%, −15·9 to −10·7; low certainty), with stronger associations with N95 or similar respirators compared with disposable surgical masks or similar (eg, reusable 12–16-layer cotton masks; p-interaction=0·090; posterior probability >95%, low certainty). Researchers used data pooled from observational studies, with a total of 172 studies from 16 countries across six continents used for the meta-analyses. [3]

References:

1. CDC. Covid-19 and your health. Centers for Disease Control and Prevention.

2. Wiersinga WJ, Rhodes A, Cheng AC, Peacock SJ, Prescott HC. Pathophysiology, Transmission, Diagnosis, and Treatment of Coronavirus Disease 2019 (COVID-19): A Review. JAMA. 2020 Aug 25;324(8):782-793. doi: 10.1001/jama.2020.12839. PMID: 32648899.

3. Chu DK, Akl EA, Duda S, Solo K, Yaacoub S, Schünemann HJ; COVID-19 Systematic Urgent Review Group Effort (SURGE) study authors. Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. Lancet. 2020 Jun 27;395(10242):1973-1987. doi: 10.1016/S0140-6736(20)31142-9. Epub 2020 Jun 1. PMID: 32497510; PMCID: PMC7263814.

Literature Review

A search of the published medical literature revealed 1 study investigating the researchable question:

What does the evidence say on the fitted filtration efficiency (FFE) of various consumer-grade and improvised face masks, as well as several popular modifications of medical procedure masks during the Corona Virus Disease 2019 (COVID-19) pandemic?

Please see Table 1 for your response.


Study Name

Evaluation of Cloth Masks and Modified Procedure Masks as Personal Protective Equipment for the Public During the COVID-19 Pandemic

Design

In-lab, comparative study

Objective

To evaluate the fitted filtration efficiency (FFE) of various consumer-grade and improvised face masks, as well as several popular modifications of medical procedure masks that are intended to improve mask fit or comfort.

Methods

Seven consumer-grade masks and five medical procedure mask modifications were fitted on an adult male volunteer, and FFE measurements were collected during a series of repeated movements of the torso, head, and facial muscles as outlined by the US Occupational Safety and Health Administration Quantitative Fit Testing Protocol.

 

Consumer-grade masks and medical procedure mask modifications were tested as personal protective equipment against a test aerosol of 0.05-μm NaCl particles. These analyses were designed to quantify the protection that masks offer to the wearer when exposed to others who may be infected.

 

The following consumer-grade masks were tested:

 

(1) A 2-layer woven nylon mask (54% recycled nylon, 43% nylon, 3% spandex) with ear loops tested with an optional aluminum nose bridge and non-woven-filter insert in place

 

(2) A cotton bandana folded diagonally once “bandit” style  

 

(3) A multilayer rectangle according to the instructions presented

by the US Surgeon General

 

(4) A single-layer woven polyester/nylon mask (80% polyester, 17% nylon, 3% spandex) with ties  

 

(4) A nonwoven polypropylene mask with fixed ear loops

 

(5) A single-layer woven gaiter/neck cover balaclava bandana (92% polyester and 8%spandex)

 

(6) A 3-layer woven cotton mask with ear loops

 

The baseline FFE of unmodified medical procedure masks with elastic ear loops was measured and compared with the FFE of the same type of mask with various modifications designed to enhance its function.

 

The following modifications were tested:

(1)  enhancing the mask/face seal by tying the ear loops and tucking in the side pleats

 

(2) fastening ear loops behind the head with 3-dimensional–

printed ear guards

(3) fastening ear loops behind the head with a 23-mm claw-type hair clip

(4) enhancing the mask/face seal by placing a ring of three ganged rubber bands over the mask, with the center rubber band placed over the nose and chin of the participant and the left and right side bands looped over each ear

(5) enhancing the mask/face seal by sliding a 10-inch segment of nylon hosiery over the fitted mask

 

Duration

June to August, 2020

Outcome Measures

The primary study outcome was the measured FFE of the different masks.

Results

 

Face Mask FFE Against Submicron Particle Penetration:

 

Consumer-grade face masks

 

Condition

%FFE (SD)a

Two-Layer woven nylon mask with ear loops:

Without aluminum nose bridge

New

44.7 (6.4)

With aluminum nose bridge

New

56.3 (6.5)

With Aluminum nose bridge and one nonwoven insert

New

74.4 (4.8)

With Aluminum bridge, washed (no insert)

Washed one time

79.0 (4.3)

Cotton bandana:

Folded surgeon general style

New

49.9 (5.8)

Folded “bandit” style

New

49.0 (6.2)

 

Single-layer woven polyester gaiter/neck cover (balaclava bandana)

New

37.8 (5.2)

Single-layer woven polyester/nylon mask with ties

New

39.3 (7.2)

Nonwoven polypropylene mask with fixed ear loops

New

28.6 (13.9)

Three-layer woven cotton mask with ear loops

New

26.5 (10.5)

  

Medical face masks and modifications:

Conditions for all medical masks - new

Mask

FFE (SD)a

3M 9210 NIOSH-approved N95 respirator

98.4 (0.5)

Surgical mask with ties

71.5 (5.5)

Procedure mask with ear loops

38.5 (11.2)

 

Procedure mask with ear loops – modifications:

Loops tied and corners tucked in

60.3 (11.1)

Ear guard

61.7 (6.5)

23-mm Claw hair clip

54.8 (5.1)

Fix-the-mask (3 rubber band)

78.2 (3.3)

Nylon hosiery sleeve

80.2 (3.1)

 

Study Author Conclusions

Simple mask-fit modifications can improve filtration efficiency.

The demonstrated practical effectiveness of consumer-grade masks may be equivalent to or better than their non-respirator medical mask counterparts.

InpharmD Researcher Critique

It is important to note that all FFE tests were performed on a single individual, and that interperson heterogeneity could account for differences in FFE and mask fit. Additionally, the size of the NaCl particles used in this study (0.05μm) may not reflect the most penetrating particle size for all of the mask materials tested.

 

References:

Clapp PW, Sickbert-Bennett EE, Samet JM, Berntsen J, Zeman KL, Anderson DJ, Weber DJ, Bennett WD; US Centers for Disease Control and Prevention Epicenters Program. Evaluation of Cloth Masks and Modified Procedure Masks as Personal Protective Equipment for the Public During the COVID-19 Pandemic. JAMA Intern Med. 2020 Dec 10:e208168. doi: 10.1001/jamainternmed.2020.8168. Epub ahead of print. PMID: 33300948; PMCID: PMC7729588.