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All About Surgical Masks: Level 1 vs Level 2 vs Level 3

Today, safety should be your priority. With the ongoing health crisis, it is a must that you are equipped with the knowledge so that you can protect yourself and your family. There are many ways to prevent being sick these days - one of them is wearing surgical masks. These facial protection are scientifically proven to prevent transmission and control sources of infection.

Image lifted from: https://www.pexels.com/photo/set-of-medical-protective-face-masks-4197564/

So What Are Surgical Masks? 

The term surgical mask is utilized in order to refer to Food and Drug Administration (FDA)-cleared surgical, laser, isolation, dental, medical procedure or face masks with or without a face shield.  These single use, fluid-resistant, disposable and loose fitting protection devices create a physical barrier between the mouth and nose of the wearer and the immediate environment but may not achieve a close seal to the wearer's face. Before the pandemic, surgical masks are usually utilized by healthcare personnel in order to provide protection against respiratory droplets that may contain infectious matter. Today, with the health crisis that the world is facing, most, if not all, are using surgical masks to protect themselves from droplets that may come into contact to the nose and mouth. In addition to that, infection control guidance strongly recommends wearing surgical masks on everyone in order to limit the dissemination of infectious respiratory secretions from one person to others.

There are definitely a lot of different surgical masks you can choose from in the market. All of them vary greatly by quality and levels of protection. With that, there are certainly variations on how surgical masks can protect you against respiratory droplets in the air that may contain infectious viruses, bacteria, and other microorganisms.  So if you want to know more about what surgical masks are and the differences between level 1, level 2, and level 3 masks, keep on reading this article.

How Are Surgical Masks Produced?

Before we go onto the different levels of surgical face masks. It is important to simply understand how they are produced, so that we can know how surgical masks are able to protect us from infectious materials. 

Image lifted from: https://www.pexels.com/photo/man-people-woman-technology-4492074/

Surgical masks are made out of non-woven fabric.  This type of fabric has greater ability to  filter bacteria, viruses, and other microorganisms. Furthermore, compared to woven materials, it has better air permeability which makes it more suitable for surgical masks. Polypropylene, usually 20 to 25 grams per square meter (gsm) in diameter, is the material of choice that is widely utilized to produce surgical masks.  is polypropylene. However, other materials such as polystyrene, polycarbonate, polyethylene or polyester can also be used to produce surgical masks.

On one hand, the 20 gsm mask material is produced through the spunbond operation. This procedure includes the extrusion of the molten plastic onto the conveyor. The content is extruded in a chain in which the strands bind with each other as they cool. On the other hand, the 25 gsm of cloth is produced through meltblown processing. This procedure is a common method in which plastic is extruded through a die with hundreds of small nozzles and blown by hot air to make tiny fibers, cooling and binding again to a conveyor.  

A multiple layers are combined in order to produce surgical masks. These layers are usually achieved through covering the cloth sheet with a non-woven bonded fabric on both sides. Nonwovens are composed of three to four layers. They are easier to produce and safer because  they are lightweight in nature. Such disposable masks are also made of two filter layers. With that, they are effective in removing matter such as bacteria and viruses above 1 micron. However, it must be noted that the degree of filtration of the mask depends on many factors such as the type of fiber used, the process how it is made, the structure of the fiber network, and the cross-sectional shape of the fiber. 

Surgical masks are made on a machine line that assembles nonwovens from bobbins, ultrasonic welds layers together, and stamps masks with nose strings, ear clips, and other bits. Once the surgical mask is done, both the masks and breathers are then sterilized before being shipped out of the facility.

What is ASTM (American Society for Testing and Materials)?

The American Society of Testing and Materials (ASTM) International is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services. With that, it is the organization responsible for the global implementation of face mask standards. Since its establishment, there have been over 12,500 ASTM standards in use around the world in order to establish safety and quality reports and standards across a wide variety of industries and services. Healthcare organizations worldwide adopt ASTM recommendations in order to implement the best health practices. 

  • Performance Metrics and Related Tests:
  • ASTM standards are referenced by the Food and Drug Administration (FDA), as the endorsed standard in the United States. With that, the Standard Specification for Performance of Materials Used in Medical Face Masks or ASTM F2100-11 has indicated a comprehensive set of tests for procedure and surgical face masks. These tests are vital in order to make sure that the performance properties are validated to support claims and classify mask types. ASTM F2100 specifies the performance requirements for Surgical Face Masks with five basic criteria:

    1. BFE (Bacterial Filtration Efficiency
      The bacterial filtration efficiency measures how effective medical face masks are in filtering out bacteria when challenged with a bacteria-containing aerosol. ASTM utilizes a droplet size of 3.0 microns containing Staphylococcus aureus which has an average size of 0.6 to 0.8 microns. A minimum 95% filtration rate is required in order to be called a medical or surgical face mask. A bacterial filtration rate of equal to or greater than 98% is required for the moderate and high protection masks. In order to determine the BFE rating, the Modified Greene & Vesley method is utilized by some manufacturers. However, it must be noted that the Modified Greene & Vesley method is not recommended by ASTM for product comparison or evaluating consistency.
    2. PFE (Particulate Filtration Efficiency)
      The ASTM has set Particulate Filtration Efficiency in order to measure how well a face mask filters sub-micron particles with the expectation that viruses will be filtered in a similar manner. It must be noted that the higher the percentage, the better the mask filtration. ASTM F2100 specifies that a particle size of 0.1 micron be utilized, however testing is available using a particle size from 0.1 to 5.0 microns. A misleading PFE rating may occur when manufacturers use a larger particle size. Hence, it is important to note that when comparing test results, it is important to note the size of the test particles utilized for the test. 
    3. Fluid Resistance: 
      The ability of the surgical mask to minimize the amount of fluid that could transfer from the outer layers through to the inner layer as the result of a splash or spray is reflected by its fluid resistance. In order to qualify for low, medium, or high fluid resistance, ASTM specifies testing with synthetic blood at pressures of 80, 120, or 160 mm Hg, respectively. These pressures correlate to blood pressure such that 80 mm Hg is equivalent to venous pressure (Level 1); 120 mm Hg is equivalent to arterial pressure (Level 2); and 160 mm Hg (Level 3) is linked to possible high pressures that may happen during trauma, or surgeries that uses high pressure irrigation including those that are done in orthopedics.
    4. Delta P (Pressure Differential)
      The objective measure of how breathable a face mask is done through testing the pressure differential. Furthermore, the Delta P measures the air flow resistance of the surgical mask. The Delta P is measured in units of mm H2O/cm2. It must be noted that the lower this value, the more breathable the mask feels. According to the ASTM standard, a moderate and a high barrier mask should have a Delta P of less than 6.0, whereas low barrier masks should have a Delta P of less than 5.0.
    5. Flame Spread
      The ASTM standards require testing for flame resistance as hospitals contain sources of oxygen, heat, and fuel. The ASTM standard testing dictates that all hospital masks must withstand exposure to a burning flame, within a specified distance, for three seconds. 

    In addition to the above tests, all surgical face masks must be ISO Certified. With that, surgical masks are tested to an international standard (ISO 10993-5, 10) for skin sensitivity and cytotoxic tests. These tests are conducted in order to make sure that no materials are harmful to the wearer. Tests are conducted on materials utilized in construction of the mask which come in contact with the user's skin.

    Levels of Surgical Masks

    Image lifted from: https://www.pexels.com/photo/face-mask-on-blue-background-3786126/

    Now that the standards of the ASTM certification were introduced, there basically are four levels in which surgical masks are identified. These levels are based on the level of defense they provide to the individual wearing them. These include: 

    1. Limited Protection face masks - These masks are manufactured for brief operations or tests not requiring gas, water, or aerosol.
    1. Level 1 surgical masks - These surgical masks are considered as low barrier protection. These surgical masks also come with ear ties and are the general standard. This is considered as the low barrier protection surgical mask. The level 1 surgical mask is intended for general use. The general purpose of these surgical masks is for medical procedures where the wearer is not at risk of blood or body fluid splash or to protect staff and/or the patient from droplet exposure to microorganisms. These surgical masks features a Bacterial filtration efficiency equal to or greater than 95%, Sub-micron particulates filtration efficient at 0.1 micron  equal to or greater than 95%, Differential pressure of less than 4 mm H2O/cm2, Resistance to penetration by synthetic blood (minimum pressure in mm Hg for pass) of 80 mm Hg, and a Class I flame spread.
    1. Level 2 surgical masks - This is considered as the moderate barrier protection surgical mask. The level 2 surgical mask is intended for use in areas with low to moderate levels of aerosols, spray and/or fluids. The general purpose of these surgical masks is for use in emergency departments, dentistry, changing dressings on small wounds or healing wounds where minimal blood droplet exposure may possibly occur. These surgical masks features a Bacterial filtration efficiency equal to or greater than 98%, Sub-micron particulates filtration efficient at 0.1 micron  equal to or greater than 98%, Differential pressure of less than 5 mm H2O/cm2, Resistance to penetration by synthetic blood (minimum pressure in mm Hg for pass) of 120 mm Hg, and a Class I flame spread.
    1. Level 3 surgical masks - are for heavy and maximum possible exposure to aerosol, fluid and spray, with 160 mmHG fluid resistance. This is considered as the maximum barrier protection surgical mask. The level 3 surgical mask is intended for use in areas with high risk of fluid, spray or aerosol exposure. The general purpose of these surgical masks is for all surgical procedures, major trauma first aid or in any area where the health care worker is at risk of blood or body fluid splash. These surgical masks features a Bacterial filtration efficiency equal to or greater than 98%, Sub-micron particulates filtration efficient at 0.1 micron  equal to or greater than 98%, Differential pressure of less than 5 mm H2O/cm2, Resistance to penetration by synthetic blood (minimum pressure in mm Hg for pass) of 160 mm Hg, and a Class I flame spread. 

    References:

    1. Chua, M. H., Cheng, W., Goh, S. S., Kong, J., Li, B., Lim, J. Y. C., Mao, L., Wang, S., Xue, K., Yang, L., Ye, E., Zhang, K., Cheong, W. C. D., Tan, B. H., Li, Z., Tan, B. H., & Loh, X. J. (2020). Face Masks in the New COVID-19 Normal: Materials, Testing, and Perspectives. Research, 2020, 1–40. 
    2. Interim infection prevention and control guidelines for the management of COVID-19 in healthcare settings – Version 1.14. 2020. Retrieved from: https://www.health.qld.gov.au/__data/assets/pdf_file/0042/969297/properties-of-PPE-for-use-in-healthcare.pdf. Retrieved on 2 April 2021.  
    3. Matuschek, C., Moll, F., Fangerau, H., Fischer, J. C., Zänker, K., van Griensven, M., Schneider, M., Kindgen-Milles, D., Knoefel, W. T., Lichtenberg, A., Tamaskovics, B., Djiepmo-Njanang, F. J., Budach, W., Corradini, S., Häussinger, D., Feldt, T., Jensen, B., Pelka, R., Orth, K., . . . Haussmann, J. (2020). Face masks: benefits and risks during the COVID-19 crisis. European Journal of Medical Research, 25(1), 1. https://doi.org/10.1186/s40001-020-00430-5

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