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William A. Levinson

Health Care

Using Face Masks and Respirators for Covid-19

Good, better, best. Something is better than nothing.

Published: Thursday, August 20, 2020 - 11:03

Face masks and respirators may well offer the only way to return to an even remotely normal living and working style in the second half of 2020, which means they will play a vital role in any kind of economic recovery. This article’s purpose is to discuss what we know about respiratory protection, and also what can be done to make masks more effective by reducing air leakage. The effectiveness of a mask made from a particular material can vary enormously as a function of how well it seals against the wearer’s face. If we can enhance the effectiveness of the masks currently in use, we can reduce the danger to everybody.

The article’s primary focus is individual self-protection outside the workplace, and in workplaces where respiratory protection is not required. None of this content, however, constitutes formal occupational health and safety (OH&S) or engineering advice, noting that, with the exception of what is available from the Occupational Safety and Health Administration (OSHA), the National Institute for Occupational Safety and Health (NIOSH), and ASTM International, definitive guidance is in short supply from authoritative sources.

Clearing up some misconceptions

Social media carries dangerous stories and rumors at the tinfoil-hat level that face masks are some kind of government-control plot to make people “comply”; that they deprive people of oxygen; and that they don’t work because the virus is much smaller than the 0.3-micron challenge particles that are used to test respirators. A meme that uses the analogy of a chain link fence to stop mosquitoes reinforces the latter position.

The latter misconception doesn’t recognize that the virus is carried by aerosol droplets that are in fact 0.3 microns and larger. A publication from 3M explains that, while larger particles are captured by inertial impaction and interception, smaller ones are captured by diffusion.1 Inertial impaction means the particle runs into a fiber, and interception means a flow streamline brings the particle into contact with the fiber. Brownian motion, on the other hand, often carries particles smaller than 0.1 microns into contact with a fiber. As the reference points out, 0.05 to 0.5 microns is generally the region of poorest performance, and a figure in the reference cites 0.3 microns as the worst case. The article is worth reading if you are interested in the details, and it includes a simple self-assessment quiz.

Information about face masks has meanwhile been so poor that the World Health Organization (WHO) published earlier this year that healthy people do not need to wear them unless they are caring for people who have Covid-19. The WHO’s most recent guidance says among other things, “At the present time, the widespread use of masks by healthy people in the community setting is not yet supported by high quality or direct scientific evidence and there are potential benefits and harms to consider....”2

The guidance goes on to say that, “However, taking into account the available studies evaluating pre- and asymptomatic transmission, a growing compendium of observational evidence on the use of masks by the general public in several countries, individual values and preferences, as well as the difficulty of physical distancing in many contexts, WHO has updated its guidance to advise that to prevent Covid-19 transmission effectively in areas of community transmission, governments should encourage the general public to wear masks in specific situations and settings as part of a comprehensive approach to suppress [Covid-19] transmission.”

While the subsequent warnings are worth heeding, I do not find any arguments against universal mask usage persuasive. One of the drawbacks consists of self-contamination from touching the front of a mask, so it is important to not do this, but if the mask was not present, it seems that the contamination would be in the user’s respiratory system instead. On the other hand, “masks may be uncomfortable to wear” is not and has never been a valid reason to not use personal protective equipment (PPE). Symptoms of Covid-19 such as fever, coughing, and being unable to breathe are far more uncomfortable than PPE, so I prefer the latter. There is currently no vaccine for Covid-19, and it can damage every vital organ in the human body.3 People need to take it seriously.

Another drawback cited by the WHO is “risk of droplet transmission and of splashes to the eyes, if mask wearing is not combined with eye protection,” which is an argument for wearing eye protection as well as a face mask, as opposed to an argument for foregoing the mask. Face shields and safety goggles are relatively cheap and also easy to clean.

As matters stand, enough people have made the same mistakes that were made in 1918—e.g., dropping their guard when the epidemic appeared to be under control—that we are now suffering about 1,000 deaths every day, and various state governments are talking about another round of shutdowns. This would cause enormous harm to an already damaged economy, which underscores the need to comply with social distancing, hygiene, and respiratory protection use.

Who do face masks protect?

The Ford Motor Co.’s “Don’t take it, don’t make it, and don’t pass it along” with regard to poor quality is highly applicable, and we don’t even need to worry about “don’t make it.” The human body cannot make a contagious disease; the only way to have it is to take it from somebody else. If you don’t take Covid-19 because you have a high-grade respirator, or the seasonal flu because you get the annual vaccine, you can’t pass it along. Anything we do to protect ourselves automatically protects others.

Not taking it in the first place is in fact the only 100-percent effective way to protect others, and face masks that impede exhalation of contagious aerosols come into play only if you get the disease. I bought a Honeywell North 7700 half-mask respirator (and I recommend this model for comfort and ease of use based on my experience so far) for the principal objective of protecting me. Its P100 filters are designed to stop 99.97 percent of challenge particles, which makes it about 166 times as effective as an N95 respirator that stops 95 percent of them.

It also has an exhaust valve which means it offers little if any protection for others if I happen to have the disease, but there is a very simple workaround for this. I found, and again this does not constitute any kind of OH&S advice because the procedure definitely doesn’t appear in the user manual, that putting a surgical mask over the exhaust valve does not cause any noticeable breathing issues (figure 1). This method is mentioned by the CDC in their “Personal Protective Equipment: Questions and Answers” page: “If only a respirator with an exhalation valve is available and source control is needed, cover the exhalation valve with a surgical mask, procedure mask, or a cloth face covering that does not interfere with the respirator fit.”

Figure 1: Use of a cloth or surgical ear-loop mask over exhalation valve to protect others

Respirators or face masks?

Respirators offer the best protection for the wearer, and they are mandatory in jobs that require respiratory protection as defined by OSHA. Face masks, whether improvised or surgical, will not suffice for these jobs. The company must not only supply appropriate respirators, it also must have a respiratory protection program that meets the requirements of 29 CFR 1910.134. The good news is that medium-risk jobs as defined by OSHA—and these are most jobs outside healthcare—are unlikely to require this level of protection.4

A respirator is more difficult to use than a face mask because the user must perform a user seal check every time it is put on, but one soon gets used to it. Mine requires positive and negative pressure seals to ensure that air is not leaking around the sides. Some of the better disposable N95 respirators have gaskets to ensure an airtight seal. Men need to remember that most beards, and even forgetting to shave in the morning, will interfere with the seal, although most mustaches will not.5 The seal between the respirator (or face mask) and the face is a major or even predominant determinant of performance.

Respirators must meet the requirements of 42 CFR Part 84 in terms of their ability to stop particles 0.3 microns and larger. Masks with a 95 designation means they stop 95 percent of the particles, 99 means they stop 99 percent, and 100 means they stop 99.97 percent. The prefix of N, R, and P (e.g., N95) refer to the respirator’s resistance to oily particles; N has no resistance, R has partial resistance, and P has strong resistance.6 This is not relevant, however, to protection against infectious aerosols. A good way to avoid counterfeit or substandard respirators is to ensure that the model you plan to buy is in NIOSH’s database.7

The Health and Safety Executive (the United Kingdom’s counterpart of OSHA) tested several forms of respiratory protection and obtained the following results in terms of protection against a simulated cough or sneeze.8 These results are important because they measure the ability of the PPE to protect the wearer compared to no protection at all.
• Screwfix mask respirator with P3R filters. You are 100 times less likely to get Covid-19 than you are with no protection. P3 is from the European EN 143 standard, and it is apparently comparable to P100 or R100 because it stops 99.95 percent of challenge particles.9
• 3M 9913 mask respirator. 78 times less likely. This is rated FFP1 (filtering face piece 1) or APF (assigned protection factor) 4. FFP1 means it will stop 80 percent of challenge particles.
• Standard surgical mask. Six times less likely.
• Improvised from a bra or sanitary towel. Two times less likely.

FFP3 is comparable to N99 (because it stops 99 percent of challenge particles); FFP2, which stops 94 percent of challenge particles, is comparable to N95. I don’t have detailed information on the test conditions, including the size of the challenge particles, because unlike 42 CFR Part 84, EN 143 is not available online. The exact numbers, however, aren’t important. The key takeaway is that a respirator (as defined by 42 CFR Part 84 or EN 142) is superior to surgical and other face masks.

Respirators must also be handled properly, and when possible, disinfected properly prior to reuse. They generally can’t be cleaned with water or alcohol because these solvents disrupt the electrostatic charge that helps intercept particles. Always follow the manufacturer’s instruction for handling and care. The virus can survive in air for up to 72 hours on plastic, 48 hours on stainless steel, and 24 hours on cardboard.10 My own solution to the issue of disposable respirators (as there was and still is a shortage) is therefore to leave them exposed to air for several days between uses.

Surgical masks

Like respirators that meet NIOSH requirements, surgical masks are known quantities. They must meet the requirements of ASTM F2100-19e1—“Standard specification for performance of materials used in medical face masks.” Bacterial filtration efficiency (BFE) is assessed per ASTM F2101, in which challenge organisms are pulled through the filter media at 28.3 liters or 1 cubic foot per minute into a cascade impactor (Anderson sieve sampler) that simulates the human respiratory system. The mean particle size of the bacterial aerosol is to be 3±0.3 microns, i.e., 3 microns plus or minus 10 percent. The bacterial filtration efficiency is then:

where C is the number of bacterial colonies formed for the control (no filtration media), and T is the number of bacterial colonies that form when the filter media are in place. If, for example, 1,000 colonies form when there is no protection, and 50 form for the media under test, the BFE is 95 percent. Note again, however, the issue of how well the mask seals to the face; the BFE is based on a test in which all the air must go through the filter, with none bypassing it.

Particulate filtration efficiency is assessed according to ASTM F2299—“Standard test method for determining the initial efficiency of materials used in medical face masks to penetration by particulates using latex spheres.” The test does not “assess the overall effectiveness of medical face masks in preventing the inward leakage of harmful particles” and adds that it does not assess the integrity of the mask’s seal to the wearer’s face, which could in fact be the underlying issue.

OSHA adds of improvised cloth masks and surgical masks alike, “Will not protect the wearer against airborne transmissible infectious agents due to loose fit and lack of seal, or inadequate filtration.”11 This underscores the need to improve the seal of the mask against the face to improve its effectiveness. Ear-loop type surgical masks allow considerable air flow around the sides, which underscores the need for improvements such as mask tighteners and sealers. Some surgical masks tie behind the head and also have aluminum nose pieces to improve the seal, and these are preferable.

Masks must meet the following requirements, with “submicron particulate efficiency (PFE) at 0.1 micron, percent,” per ASTM F2100-19e1. This implies that even a Level 1 mask is comparable to an N95 respirator, but only if the same airtight, or almost airtight, face seal can be achieved.
• Level 1, Low barrier protection: 95-percent BFE, 95-percent particulate filtration efficiency
• Level 2, Medium barrier protection: 98-percent BFE, 98-percent particulate filtration efficiency
• Level 3, High barrier protection: 98-percent BFE, 98-percent particulate filtration efficiency, and also superior resistance to penetration by synthetic blood. The latter is not an issue here, so Level 2 and Level 3 offer essentially the same protection from Covid-19.

Surgical mask tighteners and mask sealers

A major problem with these masks, as well as most of the improvised ones, is that they are not designed to deliver anything that even remotely resembles an airtight seal around the user’s nose and mouth, and ASTM F2299 cites this issue explicitly. Their primary purpose appears to be to absorb, or at least deflect, anything infectious that comes from the wearer’s respiratory system away from somebody (like a dental patient) who is directly in front of the wearer. Aerosols that linger in the air can still enter around the sides, which brings us to the subject of adjustable mask hooks, mask extenders, mask tighteners, and surgical mask sealers—all of which are meant to help a surgical mask perform a job for which it was not originally intended.

My first experience with an ear-loop surgical mask involved warm air going under my glasses, which means that there is leakage around the sides. A key clip can be used to pull the loops behind the head for a tighter fit (see figure 2). This reduces the leakage problem, although it doesn’t eliminate it. An online search for “adjustable mask hooks” and “mask extender” brings up similar products that not only take the ear-loop pressure off the ears but also deliver a tighter fit. Any action that forces incoming and outgoing air to go through the mask rather than around the edges improves the protection and suppresses the spread of the disease in both directions.

Figure 2: How to tighten an ear-loop surgical mask

Watch the video “How to Improve Your Surgical Mask Fit Quickly” in which the mask bulges during exhalation, which means little air is leaking around the sides.12 This is similar to what we want to see during the exhalation pressure test for a respirator. The face piece should bulge slightly, and air should not leak around the edges.

The next step up is something called a “surgical mask sealer” whose boundaries press against the face to eliminate most leakage, but those currently available seem to require a 3D printer to produce. A CPAP (continuous positive airway pressure) face mask ($30 to $80) looks like it would perform the same function. Adult oxygen masks also could conceivably be used, but a CPAP mask seems intended for a tighter fit because it needs to operate under positive pressure. With any luck, surgical mask sealers that are now available only to those with 3D printers will become commercially available.

Improvised masks

Various materials for homemade masks were tested with a procedure similar to ASTM F2101, and using 1.1 micron and 0.023 micron challenge organisms.13 The investigators discovered that, with the exception of surgical masks, vacuum cleaner bags, and something called a cotton mix, the filtration media offered only mediocre performance and also substantial variation. Although some vacuum cleaner bags are manufactured to be hypoallergenic and are in fact comparable to HEPA (high efficiency particle air) filters, there is conflicting guidance on their safety. Vacuum Cleaner Market contends, “Vacuum bags have not ever, and do not contain fiberglass,” which would be hazardous to inhale.14 ShopVac Store, on the other hand, warns against using its HEPA bags for respiratory protection.15 The eVacuum Store16 warns that the HEPA filters used in some vacuum cleaners do contain fiberglass and should never be cut open, although vacuum cleaner bags do not.16 The same website describes how to make a face mask from a vacuum cleaner bag.17 The end result, however, seems to allow for a lot of leakage around the sides—a drawback for any improvised face mask or ear-loop surgical mask—and the site adds, “Use at your own risk.”

The WHO’s “Advice on the use of masks in the context of Covid-19” (Table 3. Nonmedical mask filtration efficiency, pressure drop, and filter quality factor) cites filtration efficiencies ranging from 0.7 percent to 26 percent, although it adds that multiple layers increase the effectiveness substantially. A minimum of three layers is recommended. Composites of different materials, with an inner layer of hydrophilic (water-absorbing) material like cotton, and hydrophobic (water-repelling) materials like polyester, are recommended. Masks must also be handled properly, and when reusable, cleaned and disinfected properly. No mask should be used by more than one person, and it is important to not touch the front of the mask (where any intercepted viruses might be) when handling it.


Personal protective equipment (PPE) is always a last line of defense against airborne hazards. Social distancing is the best protection because, if the contagious aerosol can’t reach you, it can’t hurt you regardless of whether you have respiratory protection. OSHA recommends a minimum distance of 6 feet, while experiments performed in 1918 showed that contagion from ordinary respiration falls off short of this.18 No bacterial colonies were formed five or more feet from the experimenter, even under conditions of loud speech. The same experiments also showed, however, that a cough can project viable test organisms to no less than 10 feet. This underscores the fact that distance is our friend, and more is better.

When it is necessary to come within six to 10 feet of other people, however, my opinion is that PPE should be used. Respirators, when available, offer the best protection due to their superior filtration media and also their nearly-airtight fit if worn properly, and the latter can’t be overemphasized. When they are used in workplaces, a formal respiratory protection program is mandatory to ensure that this happens. People who use them for individual protection must follow the manufacturer’s instructions diligently and perform the user seal tests to ensure that air is not leaking around the sides.

When a respirator is not available, or can’t be worn due to potential exposure to water that will degrade the filter medium, an ASTM Level 2 or Level 3 surgical mask is the next best option, with even Level 1 being quite good and also a known quantity. Select, if possible, the kind that ties behind the head rather than the ear-loop type. Remember that we are calling on this mask to perform a task for which it was not designed explicitly, which means that mask tighteners or mask sealers should be used.

1. Johnson, Erik. “Filtration Mechanisms of Particulate Respirators.” 3M, March 2205.
2. World Health Organization. “Advice on the use of masks in the context of COVID-19,” June 5, 2020.
3. Wadman, Meredith; Couzin-Frankel, Jennifer; Kaiser, Jocelyn; and Matacic, Catherine. “How does coronavirus kill? Clinicians trace a ferocious rampage through the body, from brain to toes.” American Association for the Advancement of Science, April 17, 2020.
4. OSHA. “Guidance on Preparing Workplaces for Covid-19.” U.S. Dept. of Labor, March 2020. Medium-risk jobs are “...those that require frequent and/or close contact with (i.e., within 6 ft of) people who may be infected with SARS-CoV-2, but who are not known or suspected Covid-19 patients.” Additionally, “In rare situations that would require workers in this risk category to use respirators, see the PPE section beginning on page 14 of this booklet, which provides more details about respirators.”
5. Jaclyn Krah Cichowicz, Jaclyn Krah; Ron Shaffer, Ron; and Markee Shamblin, Markee. “To Beard or not to Beard? That’s a good Question!” CDC, Nov. 2, 2017.
6. Safeticorp. “Respiratory Protection Training Guide.”
7.  CDC. NIOSH-Approved Particulate Filtering Facepiece Respirators.
8. Howard, Harry; and Robinson, Martin. “Coronavirus face masks sell out as prices soar 800%: But do they really work, and which one should you buy?” Daily Mail, Feb. 27, 2020.
9. BLS. “300 Series Filters Data Sheet: 302 P3 R.” Cites a minimum filtration efficiency of 99.95 percent. June 2012.
10. Volkin, Samuel. “How long can the virus that causes Covid-19 live on surfaces?” HUB, Johns Hopkins University, March 20, 2020.
11. OSHA. “Covid-19 Frequently Asked Questions.” U.S. Dept. of Labor.
12. NurseMinder. “How to Improve Your Surgical Mask Fit Quickly.” YouTube, May 27, 2020.
13. Anna Davies, Anna; Thompson, Katy-Anne; Giri, Karthika; Kafatos,  George; Walker, Jimmy; and Bennet, Allan. “Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?” Disaster Medicine and Public Health Preparedness, May 2013.
14. Trapp, Lauren. “Do Vacuum Bags Contain Fiberglass?” Vacuum Cleaner Market, April 7, 2020.
15. Shop Vac Store. Type TT-9021733 HEPA Collection Bags.
16. eVacuum Store. “Do Vacuum HEPA Filters Contain Fiberglass?”
17. eVacuum Store. “How to Make a Face Mask From a Vacuum Cleaner Bag.”
18. Doust, Brewster C.; and Bates Lyon, Arthur Bates. “Face Masks in Infections of the Respiratory Tract.” Journal of the American Medical Association, Oct. 12, 1918.


About The Author

William A. Levinson’s picture

William A. Levinson

William A. Levinson, P.E., FASQ, CQE, CMQOE is the principal of Levinson Productivity Systems P.C. and the author of the book The Expanded and Annotated My Life and Work: Henry Ford’s Universal Code for World-Class Success (Productivity Press, 2013).