Coronavirus, Equipment & Gear, Exclusives, Operations

Understanding the Difference Between a Surgical Mask and N95 Respirator

Photo provided by the author.

From the onset of the COVID-19 pandemic, it quickly became clear the United States lacked enough personal protective equipment (PPE), including masks, to properly protect healthcare providers (HCPs) from exposure to COVID-19. As early as February, the Department of Health and Human Services (HHS) reported that the U.S. had only 42 million of the estimated 3.5 billion masks required through the course of a pandemic.1 Of those, only 12 million were N95 respirators. By mid-April, 90% had been distributed.2

Related

Due to the international shortages of PPE, in February, the World Health Organization (WHO) began recommending that healthcare workers use medical masks when interacting with COVID-19 patients in an effort to conserve N95 respirators for aerosol generating procedures.3 The Centers for Disease Control and Prevention (CDC) continues to recommend N95 respirators for providers who are caring for unmasked COVID-19 patients or for the EMS provider in the patient compartment during transport of a known or suspected COVID-19 patient.4,5 However, due to scarce resources, they are permitting the use of fluid resistant simple face masks (medical masks) for non-aerosol generating procedures and while caring for masked COVID-19 patients.4,5

Is this really safe?

Let’s start with the basics of both types of masks. Both simple masks and N95 respirators use the same melt-blown fabric as their filters. However, the main differences between them are their attachment method, seal, fluid resistance and regulatory agency.6

Simple masks actually include different types of medical masks including traditional surgical masks that are secured with ties as well as procedure masks that are secured with earloops. All masks that provide fluid resistance, which includes all surgical masks and most procedure masks, require Food and Drug Administration (FDA) approval.4 Additionally, the FDA issued an Emergency Use Authorization on April 18th, allowing for the production of medical face masks without fluid resistance to be used as source control.7, 8 These may be manufactured from materials other than meltblown fabric such as cloth.5, 7 When available, the CDC recommends EMS providers wear medical facemasks instead cloth masks because they will provide the wearer protection in addition to acting as source control.5 Cloth masks cannot be used as PPE.5, 7

FDA approved simple masks are produced according to American Society of Testing and Materials (ASTM) standards and are rated on five metrics.9 An ASTM Level 1 face mask is able to filter out ≥ 95% of bacteria and ≥ 95% of 0.1 µm particles as well as provide fluid resistance to simulated blood at 80 mmHg. ASTM Level 2 and 3 masks provide higher levels of protection and all three levels meet specific breathability and flame resistance requirements. The masks often contain multiple filter layers as well as components such as a nose piece to help form a seal to the face. However, this seal is not airtight which can result in airborne particles leaking in around the mask as the wearer inhales. For this reason, these masks are not considered to be respiratory protection and can only be used while treating patients on droplet, not airborne, precautions.10

Standard N95 respirators are rated by National Institute for Occupational Safety and Health (NIOSH) and designed to provide ≥ 95% filtration efficiency of 0.3 µm non-oily particles.11 Healthcare workers historically have used a subset of N95 respirators, the surgical N95 respirator, which is also approved by the FDA as a surgical mask and provides fluid resistance.10 All N95 respirators are equipped with elastic straps which hold the mask tightly to the users face and require fit testing to ensure a proper seal.

While N95 respirators are actually tested with a larger particle size than simple masks, NIOSH considers 0.3 µm to be the “most penetrating aerosol size” and uses them to simulate the “worst-case” a mask would likely encounter.11 This particle size is chosen because filters do not function like nets, but instead use different methods to capture different particle sizes. Fine particles are captured by diffusion, meaning airflow and their random motion eventually causes them to become trapped by a mask fiber whereas larger particles are predominantly subject to interception and impaction with the filter fibers.12 Particles the size of 0.3 µm fall between these methods and are difficult to trap, which is why they are the testing standard for N95 respirators.

With the supply of surgical respirators in short supply, industrial N95 respirators are now being sold to hospitals.13 However, these N95s lack the fluid resistance of a surgical N95 respirator. Although a face shield can often solve this problem, the industrial N95s often contain an exhalation valve embedded in the mask in an effort to make the mask more comfortable to wear. However, when the user exhales, their unfiltered breath can contaminate their patients, which is why these are not recommended for source control and prohibited during sterile procedures.5,14

So where does this leave healthcare workers?

The CDC guidelines for respiratory protection are based on the belief that COVID-19 is primarily spread by respiratory droplets as the CDC states that it is uncertain if droplet nuclei (aerosols) are viable vectors for transmission.15 While existing research shows that influenza may be locally spread through airborne particles, the infection rate of healthcare workers is comparable between those who wear an N95 respirator and those wearing surgical masks. This may be generalizable to COVID-19 infection if there is, in fact, airborne transmission.16, 17, 18, 19, 20, 21 However, limitations of these studies included lack of control for poor compliance or self-contamination during donning/doffing.22

While the CDC guidelines permitting use of simple masks in place of N95s respirators takes this evidence into account, they are ultimately a crisis strategy designed to minimize risk when “routinely practiced standards of care” regarding HCP safety “are no longer possible.”4

If CDC and WHO are correct and COVID-19 is only spread by droplets, or the studies on influenza infection and mask use are applicable, then a simple fluid resistant face mask should provide sufficient protection. However, COVID-19 is a new disease and we will only develop the comprehensive evidence to support the current recommendations by studying the results of their implementation. One thing is certain: studies show that a simple face mask will provide better protection than a homemade cloth mask, and they are certainly better than nothing.23

References

  1. Lovelace, B, Jr. HHS clarifies US has about 1% of face masks needed for ‘full-blown’ coronavirus pandemic. CNBC [Internet]. 2020 Mar 4 [cited 2020 Jun 13];Health and Science:[about 2 pages]. Available from: https://www.cnbc.com/2020/03/04/hhs-clarifies-us-has-about-1percent-of-face-masks-needed-for-full-blown-pandemic.html.
  2. Eilperin,  J; Stein, J; Butler, D; Hamburger, T. U.S. sent millions of face masks to China early this year, ignoring pandemic warning signs. Washington Post [Internet]. 2020 Apr 18 [cited 2020 Jun 13];Health:[about 11 pages]. Available from: https://www.washingtonpost.com/health/us-sent-millions-of-face-masks-to-china-early-this-year-ignoring-pandemic-warning-signs/2020/04/18/aaccf54a-7ff5-11ea-8013-1b6da0e4a2b7_story.html.
  3. Rational use of personal protective equipment for coronavirus disease 2019 (COVID-19) [Internet]. Geneva: World Health Organization; 2020 Feb 27 [cited 2020 Jun 13]. Available from: https://apps.who.int/iris/bitstream/handle/10665/331215/WHO-2019-nCov-IPCPPE_use-2020.1-eng.pdf.
  4. Strategies for Optimizing the Supply of N95 Respirators [Internet]. Atlanta: Centers for Disease Control and Prevention (US); [reviewed 2020 Apr 22; cited 2020 Jun 13]. Available from: https://www.cdc.gov/coronavirus/2019-ncov/hcp/respirators-strategy/index.html?CDC_AA_refVal=https%253A%252F%252Fwww.cdc.gov%252Fcoronavirus%252F2019-ncov%252Fhcp%252Frespirators-strategy%252Fconventional-capacity-strategies.html.
  5. Interim Recommendations for Emergency Medical Services (EMS) Systems and 911 Public Safety Answering Points/Emergency Communication Centers (PSAP/ECCs) in the United States During the Coronavirus Disease (COVID-19) Pandemic [Internet]. Atlanta: Centers for Disease Control and Prevention (US); [updated 2020 July 15; cited 2020 Aug 14]. Available from: https://www.cdc.gov/coronavirus/2019-ncov/hcp/guidance-for-ems.html.
  6. Feng, E;  Cheng, A. COVID-19 Has Caused A Shortage Of Face Masks. But They’re Surprisingly Hard To Make. National Public Radio [Internet]. 2020 Mar 16 [cited 2020 Jun 13];Goats and Soda:[about 4 pages]. Available from: https://www.npr.org/sections/goatsandsoda/2020/03/16/814929294/covid-19-has-caused-a-shortage-of-face-masks-but-theyre-surprisingly-hard-to-mak.
  7. Face Masks and Surgical Masks for COVID-19: Manufacturing, Purchasing, Importing, and Donating Masks During the Public Health Emergency [Internet]. White Dove: Food and Drug Administration (US); [reviewed 2020 May 5; cited 2020 Jun 16]. Available from: https://www.fda.gov/medical-devices/personal-protective-equipment-infection-control/face-masks-and-surgical-masks-covid-19-manufacturing-purchasing-importing-and-donating-masks-during.
  8. Enforcement Policy for Face Masks and Respirators During the Coronavirus Disease (COVID-19) Public Health Emergency (Revised) Guidance for Industry and Food and Drug Administration Staff [Internet]. White Dove: Food and Drug Administration (US); 2020 May [cited 2020 Jun 16]. Available from: https://www.fda.gov/media/136449/download.
  9. The right mask for the right team! MaskEnomics: The Crosstex guide to face mask selection and use [Internet]. Hauppaugue: Crosstex International; 2014 Mar 26 [cited 2020 Jun 13]. Available from: https://cdn.vivarep.com/contrib/va/documents/al_lib_44.2015112134294585.pdf.
  10. Infographic – Understanding the Difference, Surgical Mask, N95 Respirator [Internet]. Atlanta: Centers for Disease Control and Prevention (US); [cited 2020 Jun 13]. Available from: https://www.cdc.gov/niosh/npptl/pdfs/UnderstandDifferenceInfographic-508.pdf.
  11. NIOSH Guide to the Selection and Use of Particulate Respirators [Internet]. Atlanta: Centers for Disease Control and Prevention (US); [reviewed 2014 Jun 6; cited 2020 Jun 13]. Available from: https://www.cdc.gov/niosh/docs/96-101/default.html.
  12. Perry, J;  Agui,  J; Vijayakumar, R. Submicron and Nanoparticulate Matter Removal by HEPA-Rated Media Filters and Packed Beds of Granular Materials [Internet]. Washington D.C.: National Aeronautics and Space Administration (US); 2016 May [cited 2020 June 13]. Available from: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20170005166.pdf.
  13. Whalen, J. Change in U.S. law will make millions more masks available to doctors and nurses, White House says. Washington Post [Internet]. 2020 March 20 [cited 2020 Jun 13];Business:[about 6 pages]. Available from: https://www.washingtonpost.com/business/2020/03/19/change-us-law-will-make-millions-more-masks-available-doctors-nurses-white-house-says/.
  14. Personal Protective Equipment: Questions and Answers [Internet]. Atlanta: Centers for Disease Control and Prevention (US); [reviewed 2020 Mar 14; cited 2020 Jun 13]. Available from: https://www.cdc.gov/coronavirus/2019-ncov/hcp/respirator-use-faq.html.
  15. Interim Infection Prevention and Control Recommendations for Patients with Suspected or Confirmed Coronavirus Disease 2019 (COVID-19) in Healthcare Settings [Internet]. Atlanta: Centers for Disease Control and Prevention (US); [reviewed 2020 May 18; cited 2020 Jun 13]. Available from: https://www.cdc.gov/coronavirus/2019-ncov/hcp/infection-control-recommendations.html.
  16. Bischoff WE, Swett K, Leng I, Peters TR. Exposure to influenza virus aerosols during routine patient care. J Infect Dis. 2013;207(7):1037‐1046. doi:10.1093/infdis/jis773.
  17. Yan J, Grantham M, Pantelic J, et al. Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community. Proc Natl Acad Sci U S A. 2018;115(5):1081‐1086. doi:10.1073/pnas.1716561115.
  18. Prevention Strategies for Seasonal Influenza in Healthcare Settings [Internet]. Atlanta: Centers for Disease Control and Prevention (US); [reviewed 2018 Oct 30; cited 2020 Jun 13]. Available from: https://www.cdc.gov/flu/professionals/infectioncontrol/healthcaresettings.htm.
  19. Radonovich LJ Jr, Simberkoff MS, Bessesen MT, et al. N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel: A Randomized Clinical Trial. JAMA. 2019;322(9):824‐833. doi:10.1001/jama.2019.11645.
  20. Loeb M, Dafoe N, Mahony J, et al. Surgical Mask vs N95 Respirator for Preventing Influenza Among Health Care Workers: A Randomized Trial. JAMA. 2009;302(17):1865–1871. doi:10.1001/jama.2009.1466.
  21. Gralton J, McLaws ML. Protecting healthcare workers from pandemic influenza: N95 or surgical masks?. Crit Care Med. 2010;38(2):657‐667. doi:10.1097/ccm.0b013e3181b9e8b3.
  22. Smith JD, MacDougall CC, Johnstone J, Copes RA, Schwartz B, Garber GE. Effectiveness of N95 respirators versus surgical masks in protecting health care workers from acute respiratory infection: a systematic review and meta-analysis. CMAJ. 2016;188(8):567‐574. doi:10.1503/cmaj.150835.
  23. Davies A, Thompson KA, Giri K, Kafatos G, Walker J, Bennett A. Testing the efficacy of homemade masks: would they protect in an influenza pandemic?. Disaster Med Public Health Prep. 2013;7(4):413‐418. doi:10.1017/dmp.2013.43.