The Fundamentals of Face Masks and Respirators


Due to the recent COVID-19 pandemic, which was caused by the new coronavirus SARS-CoV2, there is a global scarcity of personal protective equipment (PPE) for health care workers, particularly face masks. There has been much uncertainty over the distinctions between various kinds of face masks and the appropriate use of these masks in various sorts of health care settings. We will explore the different forms of respiratory pathogen transmission in this lesson, with a focus on COVID-19. Additionally, we define the fundamental construction of various different kinds of face masks, as well as provide advice for their usage and maintenance. Conservation is critical in light of the continuing epidemic and related PPE shortages. 


Three components are required for disease transmission: a source, a susceptible host, and a mechanism of transmission.

The mechanism of transmission differs according on the pathogen.

Direct vs. Indirect Transmission

Direct transmission happens when germs are conveyed physically from an infected person to a vulnerable person. When there is no direct human-to-human touch, indirect contact transmission occurs. The microbe is transmitted through an intermediary item.

Droplet vs. Aerosol vs. ‘Airborne’ Respiratory Transmission

Droplets carrying pathogenic germs may be produced as a result of coughing, sneezing, or conversing. The majority of droplets are too massive to stay suspended in the air for an extended amount of time and will settle fast. Particles of droplet This method transmits light with a diameter of 5-10 lm.An aerosol is a finer droplet (,5-10 lm) that may stay suspended in air when the air current’s velocity exceeds the particle’s terminal velocity. Alternatively, the droplets may evaporate before to hitting the floor, resulting in even smaller droplet nuclei that are free to float across greater distances. In these instances, infections are believed to be ‘airborne.’ Airborne transmission is defined as dried infectious material less than 5 lm in diameter that may move great distances on air currents.

The distance a droplet can travel and cause disease transmission is determined by the following factors: the velocity and mechanism of propulsion; the density and infectious load of respiratory secretions; environmental factors such as concurrent airflow, temperature, and humidity; and the pathogen’s ability to maintain infectivity over that distance.

Aerosols in the respiratory system are produced spontaneously or as a result of aerosol-generating treatments (see below). They are capable of transmitting the disease straight from the carrier’s respiratory system to the recipient’s mucosal surfaces. Epidemiological studies of disease outbreaks, such as the SARS-CoV epidemic, as well as experimental investigations on aerosol dynamics, provided support for such transmission.

Aerosol-generating procedures (AGPs) are medical treatments that produce aerosols in addition to those produced naturally by the patient when breathing, coughing, sneezing, and speaking. They are capable of producing both big and minute droplets and, if used in sufficient concentrations, may result in opportunistic airborne transmission of bacteria that are not typically disseminated by the airborne pathway (eg, SARS-CoV2, influenza). Table 1.3 contains examples of AGPs. It is critical to remember that aerosols are often formed from a combination of tiny to big droplets. Thus, rather than two dichotomous entities, the contrast between droplet and airborne transmission should be seen as a spectrum. In summary, the SARSCoV2 virus may be transmitted by direct and indirect contact, droplet and aerosol transmission, with mounting evidence indicating that airborne transmission is conceivable. 


A face mask is a mask that covers the nose and mouth of the user and may or may not fulfill fluid barrier or filtration efficiency standards. In comparison, a surgical mask is a loose-fitting, disposable mask that covers the user’s mouth and nose and forms a physical barrier between the wearer and fluids and particulate matter. Contrary to popular assumption, it is intended to prevent the dispersion of droplets from the wearer to the surrounding area during expiration. However, a recent comprehensive analysis indicates that wearing surgical face masks may help prevent infected persons from transferring respiratory diseases to uninfected ones. 5

Whether broad use of surgical face masks should be established remains debatable, and further research is necessary.

Composition of Surgical Face Masks

Surgical masks are constructed from many layers of cloth, referred to as an SMS configuration or a three-ply design. SMS is an acronym for spunbond-meltblown-spunbond and refers to the production process for the three layers.

Outer layer: spunbond polypropylene nonwoven with a hydrophobic repellent coating

Middle layer: meltblown polypropylene nonwoven filter layer

Inner layer: spunbond polypropylene nonwoven layer treated with a hydrophilic surfactant

These materials have the following characteristics:

Polypropylene spunbond: Extrusion of polymers via a spinneret results in the formation of a web of small strands of polypropylene filament. The fabric sheet is then crushed and heat-treated in a process called calender bonding (Figure 2).

Meltblown polypropylene: Polypropylene polymers are extruded into increasingly finer filament strands using high-velocity hot air streams. The fabric thickens as the filaments overlap to produce the filtering layer (Figure 3).

Spunbond fabric is strong and durable, with high resistance to moisture and temperature changes. On the other hand, meltblown fabric has relatively low tensile strength but superior filtrating, wicking, and barrier qualities due to the smaller fiber size and increased cumulative surface area. The process of stacking these two materials together is simple and affordable, and results in a mask with high bacteria filtering effectiveness and excellent air permeability. Droplet transmission is minimized with the use of repellant and surfactant treatment.

Apart from polypropylene, other materials such as polystyrene, polyethylene, polyesters, and cellulose-based matter may be utilized to manufacture nonwoven fabric.

Face Mask Evaluation and Classification

After these nonwoven materials are manufactured, cut, and fashioned into the form factor of a surgical face mask, they are evaluated against the following criteria. 7\s:

Bacterial filtration efficiency: Aerosols containing Staphylococcus aureus germs are sprayed at regulated volumes and rates onto the masks. Minimum filtering efficiency of 95% is necessary.

Aerosols of polystyrene microspheres ranging in size from 0.1 to 5 lm are sprayed over the masks to guarantee that they can filter particles of varying sizes. The percentage shows the effectiveness of the mask’s particle filtering.

Breathing resistance is determined by blowing air at the mask and measuring the difference in air pressure between the mask’s two sides. The unit of measurement is millimeters of H2O per cubic centimeter.

Splash resistance: The mask is pushed with synthetic blood to guarantee that the liquid cannot enter and infect the user.

A pressure comparable to that of human blood is employed as the test pressure.

Flammability: To avoid a fire threat, all masks should be flame resistant.

Allergenicity: Face masks should be assessed for skin sensitivity according to an international standard (ISO 10993-5,10

Microbial cleanliness: Face masks are manufactured in a clean, controlled environment to maintain the lowest possible total viable microbial count (cfu/g) on the surface.

The masks are categorised into several tiers based on the results of the aforementioned examinations. The categories in Tables 2 and 3 are based on American and European standards, respectively.


A filtering facepiece respirator (FFR) is a kind of respiratory protection gear that covers the wearer’s nose and mouth to assist minimize exposure to harmful biological airborne particles. In comparison to a surgical mask, it is meant to provide a tight face fit and effective particle filtering.

Respirator Makeup

Disposable respirators, such as the widely used N95 or FFP2, are typically constructed with four layers. 9

Outer layer: nonwoven hydrophobic spunbond polypropylene treated with a repellent agent.

Prefiltration layer: needlepunched nonwoven material that has been thermally processed. It creates a thicker, stronger layer that may subsequently be shaped as required. Certain manufacturers use cellulose-based materials for this layer, which has varying consequences for decontamination (see below).

Filtration layer: polarised nonwoven polypropylene layer that influences the respirator’s filtration performance.

Inner layer: nonwoven hydrophilic layer of spunbond polypropylene treated with a surfactant.

While the production process is comparable to that of surgical masks, respirators have a greater filtering effectiveness and a more secure fit around the face (Table 4). They are intended to safeguard the user from airborne particles and smaller respiratory droplets. They are particularly advised in situations when a large concentration of infectious aerosols and droplets is expected.

Classification of Respirators

Respirators are classed as follows:

Characteristics of the barrier and filtering efficiency;

The filter’s oil resistance rating;

They are made to be worn in a certain way.

Characteristics of the Barrier and Filtration Efficiency

Respirators are classified and certified by a variety of tests. While various standardizing agencies use similar testing standards, their cutoff values may vary significantly. The American NIOSH42CFR84 (Table 5) and the European EN 149-2001 are the most often utilized FFR standards (Table 6). 9 The N95 and FFP2 are the two most well recognized FFRs certified to these two specifications. Although the Chinese-made KN95 (GB2626-2006) is gaining popularity due to increased demand, more testing may be necessary to demonstrate its dependability.

Respirator Evaluation

Prior to testing, respirators are conditioned for 24 hours at 388 degrees Celsius and 85 percent relative humidity. They are then evaluated using the following criteria11 (Table 7):

Efficiency of filtration: To determine particle penetration, a charge-neutralised sodium chloride aerosol with a median size of 0.3 lm is utilized. The effectiveness of filtration is expressed as a percentage of particles filtered.

Internal leakage is determined, since it should be kept to a minimum to avoid exposure to airborne illnesses. A leakage rate of less than 8% inward is acceptable. This is, however, solely necessary under European and Chinese regulations.

Flow rate: The respirator is evaluated for rapid airflow in and out, ensuring that the user can comfortably use it even with heavy/rapid breathing. A minimum flow rate of about 85 L/min is necessary. Breathing resistance is measured and should be maintained as low as feasible for a given air flow rate to minimize the labor of breathing.

Throughout the test, the respirators’ filtration capability must remain greater than their certification class level at all times. Additionally to these requirements, respirators should be flame resistant, hypoallergenic, and fluid resistant.

The phrases surgical N95 respirators and medical respirators refer to NIOSH-approved N95 respirators that have also been validated for use as surgical masks in medical facilities by the US Food and Drug Administration (FDA). In contrast to other ‘industrial’ N95 respirators, they are suggested solely for health care workers who need protection from both airborne and fluid threats. When high-velocity splashes, sprays, or splatters of blood or bodily fluids are predicted, regular N95 respirators with face shields should be used. Face shields protect the surface of the respirators from contamination and soiling but do not contribute to the filtration. Exhalation valves are included on some versions of respirators. These are intended to lower the resistance to expiratory airflow and add to the comfort of extended mask usage. They do not, however, protect others from infection if the person wearing the mask is sick. 

How Respirators Are Designed for Health Care Workers to Wear

According to NIOSH, respirators are classified into three types based on how the filters are intended to be worn by health care workers (Table 8).

FFRs: These are reasonably priced and lightweight. They are disposable, do not impair movement, and need no maintenance or cleaning after a single usage if disposed of properly. They do not protect the eyes, and their seal is inadequate for persons with facial hair.

Facepiece respirators made of elastomeric material with or without eye coverage: These filters are more effective in filtering airborne pathogens and may be used for an extended period of time, depending on the manufacturer’s requirements. They are, however, cumbersome and may obstruct movement and communication. The Centers for Disease Control and Prevention (CDC) have expressed worry about the use of valved respirators in surgical settings, stating that droplets spreading via their expiratory valves remain a problem. To mitigate this danger, some recommend putting a normal surgical mask over these respirators. 13

PAPRs (personal air purifying respirators): These devices cover the whole head, including the hair, eyes, face, and mouth (and, in certain versions, the neck). They give a more secure fit for those who have facial hair, missing teeth, or facial scars.

In comparison to N95 respirators, PAPRs have a greater filtration efficiency, reduced respiratory resistance, and a higher degree of comfort during continuous use, despite the extra weight of the headpiece, battery, and pump. They are, however, more costly, need charging, and require regular maintenance to guarantee that all connections stay secure.

Despite early fears, current research has shown that, unlike EFRs, PAPR use in the operating room does not enhance particle transmission to the surgical field.


The tables 9 and 10 summarize the guidelines of the European Centre for Disease Prevention and Control (ECDC) and the World Health Organization (WHO) regarding personal protective equipment (PPE) that health care personnel should wear while caring for COVID-19 patients.

The CDC’s PPE guidelines for health care professionals caring for COVID-10 patients are summarized in Table 11. Unlike the ECDC and WHO guidelines, the CDC recommendations include supply availability.

Respirators: Extended Use and Limited Reuse

Numerous nations have implemented ways to save respirators in response to drastically increasing demand for N95 or similar (FFR). 15 The CDC recommendations provide many strategies for conserving resources while protecting health care workers during times of scarcity. The most fundamental technique is extensive usage and restricted repurposing.

Extended usage is the practice of constantly wearing the same FFR for repeated close contact with several patients without removing the respirator between patient visits. It may be used when numerous patients are infected by the same respiratory infection and are housed in specialized wards. Health care employees may be obliged to wear the same FFR for many hours until they are permitted to remove it, such as at meals or at the conclusion of a shift.

The term ‘limited reuse’ refers to the practice of utilizing the same FFR for several patient contacts but deleting it (‘doffing’) in between. Between interactions, the FFR is saved and re-done (‘donned’) before to the next contact with the same or a new patient. The amount of times a single FFR should be reused should be limited; this is sometimes referred to as ‘limited reuse.’

While longer use and restricted reuse are being implemented in many countries as a result of the COVID-19 epidemic, NIOSH stipulates that such practices should still consider FFR hygiene, damage, and breathing resistance.

FFR should be changed if they become visibly damaged or filthy, or when breathing becomes difficult owing to increasing resistance. The CDC recommends the following actions to minimize contact transmission if the reuse of N95 or a comparable FFR is approved.

FFR Decontamination and Reuse

The US Food and Drug Administration does not suggest reusing or sharing disposable N95 respirators. 17 However, during a crisis, like as the COVID-19 pandemic, FFR cleaning and reuse may need to be considered to guarantee continuing availability. As a consequence, the CDC and the N95 DECON group recommend three decontamination methods: vaporized hydrogen peroxide, UV germicidal irradiation, and moist heat. 18,19 Whichever approach is utilized, each FFR should be properly labeled with the user’s name and saved separately. Additionally, a decontamination record should be kept to enable the FFR to be recognized and returned to its owner.

Hydrogen Peroxide Vaporous

Decontamination using hydrogen peroxide (H2O2) vapor and plasma is a well-established industrial decontamination process utilized in hospitals, health care, and the pharmaceutical sectors. 21 Hydrogen peroxide vapor (wet HPV or dry VHPe) and hydrogen peroxide gas plasma (HPGP) inactivate pathogens with a high level of resistance, including nosocomial bacterial spores and viruses. In a recent research, it was discovered that it inhibited the replication of SARS-CoV-2 on all N95 mask types evaluated. 22

Concerns about its usage include the possibility that hazardous quantities of hydrogen peroxide may linger on the mask for many days after cleaning.

23 Additionally, repeated decontamination procedures might distort the masks, reducing their filtering efficacy. Bioquell Battelle Decontamination System is an HPV decontamination system for N95 masks. It was granted emergency use authorisation by the FDA on 28 March 2020 and is capable of performing up to 20 cycles without compromising the filter quality or straps for the FFR 3M model 1860. 25 It is critical to remember that HPV, VHPe, and HPGP are incompatible with cellulose, which is not present in 3M model 1860 N95 masks but may be present in other FFR masks, such as 3M model 1870 and 1870 masks. The presence of cellulose is critical for using VHP techniques, since hydrogen peroxide destroys cellulose-based goods (eg, cotton, present in some head straps or some FFR layers). Additionally, cellulose absorbs hydrogen peroxide, which reduces the quantity of hydrogen peroxide vapor in the devices, impairing sterilizing efficacy.

Germicidal Ultraviolet Irradiation

UV germicidal irradiation (UVGI) kills or inactivates bacteria by damaging their DNA and critical biological activities. In comparison to ultraviolet A and ultraviolet B, UVC has the shortest wavelength (100–280 nm) and the most energy. UVGI is a promising technique, however its effectiveness is contingent upon the following variables. 2627 Dose (Energy Level and Duration of Exposure) UVGI at 1 J/cm2 was shown to be effective for inactivating a variety of viruses, including MERS-CoV and SARS-CoV, on the external surface of the face mask from 99.9 percent to.99.999 percent in around 60 seconds. 26 While a larger dosage of UVC may promote penetration, it may damage the materials and impair their suitability for reuse.

Effects of Shadows

Shadows indicate that ultraviolet (UV) light is being blocked, reducing the cleaning efficacy in the unexposed region. This shadow effect is most noticeable on masks with horizontal ridges or folds across the facepieces’ front. 26 Multiple UV lamps are necessary to provide enough exposure from a variety of directions. Additionally, cosmetics and sunscreen left on N95 by the user may diminish the effectiveness of decontamination.

Composition of the Mask and Strap

The FFR facepiece and straps are designed differently (e.g., material, thickness, shape, and elasticity), which may affect the decontamination efficacy. Due to the fact that UV light operates predominantly on surfaces, absorption of the viral inoculum under its surface may possibly protect the virus from exposure, hence reducing the UVGI decontamination efficacy. Hydrophilic materials absorb both mucin and virus, reducing the efficacy of UVGI.

Heat that is moist

Warm moist heat (60-758C with 80% relative humidity) applied for at least 30 minutes performs as a biocidal cleaning procedure using this approach. This method has been shown to be superior than dry heat sterilizing. Moist heat is more efficient in killing bacteria by protein denaturation and is less likely to degrade the effectiveness of the filter. 27

Although moist heat has been proven to efficiently disinfect FFRs infected with H1N1, no data on comparable inactivation of coronaviruses, other bacteria, or mould spores have been reported. Although the CDC has issued guidance on the use of moist heat to decontaminate N95 or comparable FFRs, the FDA has not validated this procedure and caution should be used when using it.

The following table summarizes key aspects of the many decontamination techniques that have been suggested.


Face masks used in health care settings are generally classified into two categories: surgical face masks and FFRs. Surgical face masks are loose-fitting and are often used to prevent the transmission of infections transferred by droplets, such as SARS-CoV-2.

They are constructed from nonwoven materials and subjected to stringent testing. Respirators, on the other hand, are form-fitting and have a better filtration efficacy. They are meant to protect the user from both droplets and airborne particles. They are classified as N95, EFRs, or PAPRs. Due to the scarcity of supply and the rapid growth in demand, decontamination and reusing FFRs may be necessary. Decontamination procedures now advised include ultraviolet germicidal irradiation, vaporized hydrogen peroxide, and wet heat decontamination. It is advised that you get familiar with the many kinds of possibly AGPs and that you choose the most suitable degree of face mask depending on your exposure risk.

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