What is known about the effectiveness of PPE and other control measures in combatting pathogenic hazards?  The complex answer is, unfortunately, not as much as we’d like.  But the simple, factual, answer is what you might expect: something is better than nothing. Studies have been conducted which have attempted to evaluate whether or not an N-95 respirator is or is not more effective than a common surgical mask; the results examined relative to this inquiry tended to be inconclusive.  What seems to have been concluded by the publications reviewed for this article, however, is that improper use of the masks/respirators, or not wearing the masks / respirators at all, does significantly increase a person’s chance of becoming infected with a respiratory viral infection.  This article examines the effectiveness of control measures specifically including personal protective equipment (or, PPE) for mitigating pathogenic hazards such as COVID-19, a respiratory viral infection which is drastically affecting global health care systems and economies.

Understanding the Hazard – COVID-19

One question many American’s may find themselves asking in the midst of this pandemic is whether or not the COVID-19 virus is in fact “airborne.”  Insufficient research exists to support a definitive answer as to whether or not the virus can be completely ruled out as being an airborne pathogen; for example, a recent study published in the New England Journal of Medicine has concluded that the virus can remain in the air for up to three hours (Ellerin et. al., 2020).  While this does not mean that the virus is just being carried around from community to community in the wind, or even from my front yard to my neighbors front yard for that matter,  it does mean that when the virus is “aerosolized,” that it can be contagious to persons exposed to that aerosol.1   

This is partially why the key focus for mitigating exposure to COVID-19 has been on “social distancing,” as anytime an infected person coughs or sneezes, they may create an infectious aerosol.  For the majority of American’s, practicing proper social distancing techniques should prove to be a profoundly useful tool in preventing transmission and exposure of the virus.  More critically, when a person does begin to exhibit symptoms they may spread the virus to others by creating these aerosols whenever they cough or sneeze.  COVID-19 is an illness that affects the respiratory system; even persons with mild symptoms are likely to be coughing and sneezing; after the aerosols generated by those coughs and sneezes fall out of the air, they may still be contagious on surfaces.  In fact, it is reported that COVID-19 may last as much as 2 – 3 days on some surfaces (Ellerin et al,. 2020). Accordingly, it is crucial that administrative control measures such as self-isolation/self-quarantine and proper sanitation be enacted in order to mitigate spreading the virus.  

For the brave men and women working in the healthcare sector, aerosols containing the virus may be generated by more than just coughing and sneezing.  Some procedures, commonly associated with critical-care, are known to generate aerosols; these procedures include, but are not necessarily limited to, bronchoscopy, respiratory/airway suctioning, and intubation (Bunyon et al. 2013). Further, some workers who may not be tasked with “critical-care” assignments, and thus arguably, less likely to be required to wear or have access to PPE, are likely to still have exposure to the “droplet” transmission associated with contaminated surfaces (Fernstrom and Goldblatt, 2013).  For these workers, selection of appropriate control measures, including appropriate PPE, is essential in controlling worker exposure as well as further spread of the virus.  Ensuring that the PPE and other control measures are used properly is equally critical.  

Control Measures – Surgical Masks vs N-95 Respirators

The two most commonly used types of nose and mouth protection utilized by workers in the health care sector are surgical masks and N-95 respirators.  There are significant differences between the two types of equipment.  A surgical mask is generally a piece of cloth or thick paper which covers the mouth and nose.  These masks are regulated by the FDA; however, the FDA standards were designed with the original use of the masks in mind; the protection from transmitting infections associated with surgeries, as opposed to preventing transmission of respiratory infections.  According to Bunyon et al., (2013), while standards exist regarding the use of surgical masks, no standardized definition on the dimensions or performance requirements of a surgical mask exists in the literature, leading to significant variation in the quality and design of masks available in the marketplace.  

An N-95 respirator also covers the mouth and nose; however N-95 masks do have a variety of standards they are required to adhere to. As N-95 respirators are in fact considered “respirators” (as opposed to surgical masks, which are solely considered a form of facial PPE), they are specifically designed to protect the user from inhaling harmful particles.  The National Institute for Occupational Safety and Health (or, NIOSH) regulates the testing and certification of respiratory protection equipment; it requires that an N-95 respirator filter out 95% of particles that are at least 0.3 µm in size.  There are more effective types of respirators as well; the N-99 will filter out 99% of these particles, and the N-100 will filter out 99.97% of particles 0.3 µm or greater.  

Exposed persons may be asking whether or not a particular type of respirator is or is not going to provide them the protection needed to eliminate or at least mitigate that exposure.  As hinted at in the introduction, a lack of information providing statistical significance, makes it hard to draw concrete conclusions.  Despite the limited realm of knowledge that exists, there are inferences that heightened types of PPE (such as, an N-95 over a surgical mask) will provide heightened levels of protection against infection, as well as basic guidance that can be drawn from various author’s conclusions.2 

Understanding the aerosol that’s present is also important in assessing the PPE and control selections. While a virus may vary anywhere from 0.02 µm to 0.30 µm in size, as stated above, their transmission is reliant upon them being aerosolized by various means.  In the instance of coughing or sneezing, it is estimated that most airborne particles will range from 0.5 µm to 5.0 µm.  Whether you are indoors or outdoors, air is always around you and is always moving.  We know that droplets in aerosols will settle from the air at a rate dictated by their mass.  Larger droplets are more likely to fall out of the air, but if air is flowing at a sufficient rate, smaller particles can be suspended in the air.  According to the World Health Organization (WHO), “airborne” particles associated with infections disease transmission are considered to be less than 5 µm in size (Fernstrom and Goldblatt, 2013).  Is it then logical to conclude that the use of N-95 respirators may be the “best choice” for a minimum level of respiratory protection where exposure to aerosolized pathogenic hazards may be a concern.  Is there a definitive answer as to whether or not an N-95 respirator performs better than a surgical mask in mitigating exposure to infection?  

In 2013, Bunyan et al. reviewed two studies that looked into whether an N-95 respirator was more effective than a surgical mask in preventing viral-infection.  One study concluded that there was no significant difference in infection rates between the group that used surgical masks and the group that used N-95 respirators; each group appeared to have an infection rate of about 23%.  However it is noteworthy that this study received a fair amount of criticism for a lack of standardization, including where the studies authors acknowledged that poor compliance with the use of the respirators was observed. The other study, MacIntyre et al., (2011) found that, after p-values were adjusted for clustering, “N95 respirators were significantly more protective than medical masks against CRI (clinical respiratory illness) ...” and that, “rates of infection in the medical mask group were double that in the N95 group.”

It seems that explicit statistically significant evidence which shows that an N-95 respirator provides a heightened level of protection against pathogenic hazards over a surgical mask has yet to emerge from the available literature, but that some literature exists which suggests it might.  While it may otherwise be logical to conclude that the careful design of the N-95 mask is guaranteed to provide a heightened level of protection against infection over the surgical mask, such a conclusion seems to yet be explicitly supported by the facts. In fact, specific to Covid-19, the authors of another small study also have inferred that no superiority of N-95 respirators over surgical masks appears to exist. As published in their letter to the editor of the Annals of Internal Medicine, Ng et al., (2020) stated, “Our observation is consistent with previous studies that have been unable to show that N95 masks were superior to surgical masks for preventing influenza infection in health care workers.”  While the statement references previous studies related to influenza, Ng et al’s observations were specific to health care workers working with patients infected with Covid-19.  

Despite that, the consensus that is presented by the studies reviewed for this article certainly suggests that no protection at all, will result in heightened levels of infection.  

Control Measures - Proper Use of PPE

Multiple publications reviewed for this article concluded that either improper use of PPE, or not using PPE at all resulted in a statistically significant increase in infection rates, or that using PPE properly was less likely to result in infection.  

In McIntyre et al., (2011), the test groups of healthcare workers required to wear masks and respirators was compared to a “convenience no-masks” group of health care workers working under otherwise similar conditions.  These were workers, including nurses, that were not explicitly required to wear masks/respirators as a result of their job assignments, or where mask/respirator use was otherwise not routine.  The study definitely concluded that the rates of respiratory infection were higher in the group of “convenience no-mask” workers.  

In its letter to the editor of Influenza and Other Respiratory Viruses, Seale et al., (2009), reported recent findings which found that proper adherence to use of any mask “significantly reduced the risk of ILI (influenza-like-illness).”  

And, data that is somewhat re-assuring, comes from Ng et al.’s study referenced above, where 41 health care workers were identified as having been exposed to aerosol generating procedures involving a patient infected with Covid-19 (including endotracheal intubation, extubating, noninvasive ventilation, and exposure to aerosols in an open circuit).  Of these 41 workers, 85% of the employees were wearing surgical masks, with the remaining 15% wearing N-95 respirators.  Other required infection control measures were properly followed as well, including proper hand hygiene.  After being required to self-isolate and under observation for two weeks, not one of the 41 workers ended up testing positive for Covid-19.

All studies reviewed seemed to have concluded that adherence to the employer issued protocols on proper PPE use, such as, proper fit and use of the respirator, the requirement to wear the respirator at all times when pathogenic hazards are present, proper storage and disposal, and ensuring that adequate training on the use of PPE which includes an accurate understanding of all tasks or workplaces which require such use, is critical in ensuring the effectiveness of infection control measures.  

Control Measures – Engineering and Administrative

Proper use of PPE is clearly not the only measure needing to be accounted for in controlling pathogenic hazards.  The variety of engineering and administrative control measures which may be available is likely significant.  A few specific areas of concern are worth considering in the days and weeks ahead however, for all organizations or entities to consider when determining how to best mitigate the spread of the virus.  

Studies have shown that droplets in aerosols as large as 100 µm in diameter can remain suspended in the air for extended periods of time (Fernstrom and Goldblatt, 2013).  This makes it necessary to consider that proper ventilation is also critical towards controlling exposure to the virus.  An analysis of studies suggests that where an infectious aerosol source exists in any given moment, effective air changes which include full capturing, and filtering of the air will reduce the airborne contamination to less than 1% of its original amount after 5 full air changes (Bunyan et al., 2013).  Arguably, not having a complete understanding of the ventilation system being provided, may only exacerbate the risk for potentially exposed individuals; or stated differently, simply putting a fan in someone’s face may not prevent them from being exposed to the virus, and may not prevent an infected person from exposing others.  This stresses the need for having a properly engineered ventilation system where the potential for aerosolized infection exists.  Those tasked with maintaining infection control protocols will need to consider proper ventilation as cities and states begin making plans on how to rapidly expand their hospital capacities including where vacant hotels or conference halls are being considered.  

From an administrative control’s perspective, ensuring that all potential sources of pathogenic hazards are properly being accounted for and that workers who are exposed to those sources are provided adequate protection is also critical.  The workers on the front lines are required to wear various levels of PPE; as previously discussed, it is necessary to ensure that health care workers which are known to carry out or even assist with aerosol-generating procedures be required to wear some form of protection, but are all workers who are potentially exposed to pathogenic hazards properly being protected?  Consider sanitation and environmental workers in a health care setting (or really, sanitation and environmental workers in any setting at this point in time); while efforts are being made to isolate/quarantine exposed patients, a critical issue that is developing in regards to COVID-19 is that the virus appears to spread so rapidly and widely before persons are even aware that they are symptomatic.  It is worth considering how this development may affect the workplace.  

One study found that 20,000 droplet or airborne particles may occur with a single bowel evacuation, and that those particles may be aerosolized with subsequent toilet flushes as long as 30 minutes after the initial flush (Fernstrom and Goldblatt, 2013). Ellerin et al., (2020) reports that Covid-19 has been confirmed to exist on metal and plastic surfaces for as long as three days, such as metal and plastic trash cans, that employees may toss their soiled masks or respirators into. These facts tend to stress that it is critical for all workers whom may have any exposure to any pathogenic hazards which may arise from blood or bodily fluids to be provided and required to use the most heightened level of protection possible, potentially including surgical masks or N-95 respirators.  Depending on the setting and anticipated level of exposure, this could potentially include a significant number of workers such as office-cleaning employees and waste-collection personnel. 


COVID-19 is a new hazard present in the American workplace; and the hazard is not exclusive to health care settings; however the degree of hazard is certainly heightened in health care settings due to the fact that these workers must work in close proximity with infected or potentially infected patients.  Surgical masks and respirators both appear to be effective in mitigating exposure to pathogenic hazards. While it is not explicitly confirmed, evidence exists to suggest that N-95 respirators will provide a heightened level of protection as compared to a surgical mask relative to “clinical respiratory infections.” Regardless of the type selected, proper use of the PPE, and proper enforcement of the rules regarding when the PPE must be worn is also critical towards mitigating the hazard.  

While not discussed at length above, the proper use of surgical masks and respirators likely requires an array of other types of PPE and engineering or administrative controls such as protective gloves and face shields, or providing appropriate facilities for disrobing and disposing of soiled clothing or equipment, in order to obtain effective protection. Finally, as the virus does not itself discriminate against what type of worker it chooses to infect, properly assessing the variety of exposures to potentially infectious aerosols, and the surfaces which may be affected by those aerosols, is also critical towards determining the control measures which may be necessary for effective infection protection for all members of an organization. 

1  Aerosolized disease transmission can occur by way of “droplet transmission” or “airborne transmission.”     
    “Droplet” transmission occurs when particles,
generally larger than 5 µm, are expelled (such as by
    coughing or sneezing) and then settle on surfaces within approximately 1 meter from where they are
    expelled.  Whereas, “airborne” transmission occurs when particles, generally smaller than 5 
µm are
    expelled, and suspended in the air for a period of time due to their smaller size (Fernstrom and Goldblatt, 2013).

2   As McIntyre et al., (2011) put it, “A benefit of respirators is suggested but would need to be confirmed by a
     larger trial, as this study may have been underpowered


Bunyan, D., Ritchie, L., Jenkins, D., Coia, J.E., (2013) Respiratory and facial protection: a critical review of recent literature.  Journal of Hospital Infection, 85, 165-169.  From

Ellerin, T., Farid, H., Krakower, D., LeWine, H.E., McCarthy, C., Memon, B., Sharp, J., Shmerling, R.H., Sperling, J.  2020-3-20, As coronavirus spreads, many questions and some answers.  Coronavirus Resource Center, Harvard Health Publishing, Harvard Medical School. From

Fernstrom, A., & Goldblatt, M. (2013). Aerobiology and its role in the transmission of infectious diseases.  Journal of pathogens, 2013, 493960.  From

MacIntyre C.R., Wang Q, Cauchemez, S., et al. A cluster randomized clinical trial comparing fit-tested and non-fit-tested N95 respirators to medical masks to prevent respiratory virus infection in health care workers. Influenza and other respiratory viruses, 5, 2011. 170-179. From

Ng, K., Poon, B.H., Puar, T.H.K., Quah, L.S., Loh, W.J., Wong, Y.J., Tan, T.Y., Raghuram, J.  (2020) COVID-19 and the Risk to Health Care Workers: A Case Report.  Annals of Internal Medicine.  Retrieved March 2020, from

Seale, H., Dwyer, D.E., Cowling, B.J., Wang, Q., Yang, P., McIntyre, C.R., (2009) A review of medical masks and respirators for use during an influenza epidemic.  Influenza and other respiratory viruses, 3 (5), 2009.  From

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