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How are surgical masks made and tested?

Surgical masks were originally designed and made in order to keep operating rooms sterile. It was mandated in order to reduce the risk of surgical site infections on patients who undergo operations. Surgical masks prevent microorganisms from escaping the mouth and nose of a wearer which can pose a risk of contamination of a patient during surgery. However, during the pandemic such as the spanish flu and Coronavirus, surgical masks were utilized not only by healthcare workers but also by normal people in order to reduce the risk of transmission. 

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Today, surgical masks are a necessity. You need to wear them not only to follow health protocols set by the government but to also protect yourself from the risk of being possibly infected with Coronavirus that is present in respiratory droplets floating in the air. Hence, surgical masks are indeed growing in popularity. Most, if not all, are wearing this protective equipment these days. However, even with such fame, many are still questioning the efficacy of surgical masks because they do not understand how these protective devices are made and tested. With that, in order to give light to that topic, here’s how surgical masks are made and tested.  

How are Surgical Masks Made?

Surgical face masks are produced using tissue formation techniques. With that, surgical masks can be classified into three types which include woven masks, unwoven masks, and knitted masks. Although these three techniques are utilized for the production of fabrics, today, most surgical face masks are produced through non-woven masks techniques with the goal of disposing them after one use. In addition to that, it is significantly cheaper to produce surgical face masks using the non-woven technique rather than utilizing the woven or knitted type. 

Non-woven fabric is used for the production of surgical masks because they have better bacteria filtration and air permeability. Non-woven fabric is also more comfortable and less slippery compared to woven and knitted fabric. The material most commonly used to make non-woven fabric is polypropylene, either 20 or 25 grams per square meter (gsm) in density. Furthermore, surgical face masks can also be produced using polystyrene, polycarbonate, polyethylene, or polyester.

Non-woven fabrics are usually made by combining small fibers together in the form of a sheet or web and then binding them either: (1) mechanically by interlocking them with serrated needles such that the inter-fiber friction results in a stronger fabric just like in felt; (2) with an adhesive; (3) thermally through the application of a binder in the form of paste, polymer melt, or powder and melting this binder onto the web through a very high temperature. It must be noted that most factories produce these surgical masks using Spunbond Meltblown Spunbound (SMS) technology

As stated above, the GSM density layers of non-woven fabric for surgical masks vary. It can either be a 20 GSM density layer or a 25 GSM density layer. On one hand, the 20 GSM density layers are produced through the membrane process which includes a melted plastic extrude on a conveyor. The material is cultured in a net, where threads are bonded with each other while being cooled down.  On the other hand, the 25 GSM layers are made through a melting technology. This is a similar process where plastic is cultured through a mold with hundreds of small openings and blown in hot air into small fibers, and again these fibers are cooled by their extruding on a conveyor. These fibers are characterized by a diameter of less than one micron. 

Once non-woven fabrics are made, surgical masks are assembled as a multi-layered structure, typically by covering a layer of textile with non-woven bonded fabric on both sides. Non-woven  layers are usually three to four layers. Furthermore, these disposable masks are usually designed with two filter layers effective at filtering out particles. It must be noted that the filtration capacity of a surgical mask depends on the fiber - the way the fiber was made, the fiber’s structure, and the fiber’s cross-sectional shape. Masks are made on a machine line that assembles the nonwovens from bobbins, ultrasonically welds the layers together, and stamps the masks with nose strips, ear loops, and other pieces. Once the masks are done, they are sterilized and then sent out of the factory.

How are Surgical Masks Tested? 

Once surgical masks are made, they should be tested in order to check for their quality and effectiveness. 

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ASTM is the american society for testing and materials. ASTM International sets the preferred international standard in healthcare for best practices inclusive of testing and requirements for performance of materials.  There are currently five assessments that will be carried out by ASTM for surgical masks. These include: 

  1. Bacteria filtration efficiency in vitro (BFE)
    This test aims to address the capacity of the surgical masks to filter out bacteria. This method works by firing a staphylococcus aureus bacteria aerosol at a rate of 28.3 liters per minute. They will measure the data based on how many bacteria that the mask will contain vs the expected value it should have.

  2. Particle Filtration Efficiency (PFE)
    This test is also known as latex particle challenge. The PFE involves spraying the aerosol with polystyrene microspheres in order to make sure that the mask will absorb the size of the particle it is meant to process.

  3. Breathing resistance
    Other than the filtration capacity, it is important that masks are comfortable for users to wear. With that, a breathing resistance test is performed in order to ensure that the mask maintains its form and provides adequate ventilation as the wearer breathes. Respiratory resistance is measured by aiming the air flow at it and then calculating the change in air pressure on both sides of the mask.

  4. Splash resistance 
    This test is conducted to ensure that solvents such as blood, infectious droplets, and others cannot penetrate the mask. This test is done through splashing artificial blood using actual blood pressure-like pressure to the surgical masks.

  5. Flammability 
    The flammability of surgical masks are checked because certain components in the operating room can potentially cause fire. This test is done through placing the surgical masks on fire in order to determine how slowly the substance is ignited and how long it takes to burn. It must be noted that ASTM levels 1, 2, and 3 are all necessary to be flame resistant to Class 1.

Passing such tests, the ASTM will then give a certification for that surgical mask and where it is classified in, depending on the level of protection. These certifications include: 

  • Limited protection face masks - These masks are manufactured for brief operations or tests not requiring gas, water, or aerosol.

  • Level 1 surgical masks - These surgical masks are considered as low barrier protection. 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.

  • Level 2 surgical masks - This is considered as the moderate barrier protection surgical mask. 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.

  • Level 3 surgical masks –This is considered as the maximum barrier protection surgical mask. 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. 

Bottomline

Now that the process of manufacturing and testing surgical masks were presented, we hope that you put more faith in the effectiveness of these facial coverings in reducing the risk of transmission of infectious pathogens such as the Coronavirus. These surgical masks undergo a tedious process just to make sure that the adequate protection level is reached. Hence, people can trust that these surgical masks are made and tested excellently. 

References: 

  1. Ming Hui Chua, Weiren Cheng, Shermin Simin Goh, Junhua Kong, Bing Li, Jason Y. C. Lim, Lu Mao, Suxi Wang, Kun Xue, Le Yang, Enyi Ye, Kangyi Zhang, Wun Chet Davy Cheong, Beng Hoon Tan, Zibiao Li, Ban Hock Tan, Xian Jun Loh, "Face Masks in the New COVID-19 Normal: Materials, Testing, and Perspectives", Research, vol. 2020.
  2. Science Alert. 2020. How to Test Your Face Mask to Make Sure It Actually Works. Retrieved from: https://www.sciencealert.com/how-to-test-your-face-mask-to-make-sure-it-actually-works. Retrieved on 7 May 2021. 
  3. Thomas Publishing Company. 2020. How Surgical Masks are Made. Retrieved from: https://www.thomasnet.com/articles/other/how-surgical-masks-are-made/. Retrieved on 7 May 2021. 
  4. UL. 2020. Surgical, Nonsurgical and Nonmedical Face Mask Testing. Retrieved from: https://www.ul.com/services/surgical-nonsurgical-and-non-medical-face-mask-testing. Retrieved on 7 May 2021. 

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