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ASTM F2101

Evaluating the Bacterial Filtration Efficiency (BFE) of Medical Face Mask Materials

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ASTM F2101: Assessing bacterial filtration efficiency of medical face masks

ASTM F2101 provides a standardized method for evaluating the bacterial filtration efficiency (BFE) of medical face masks. This test measures how effectively medical face mask materials can filter out aerosolized bacteria by comparing the upstream bacterial concentration to the downstream residual concentration. 

The BFE test is a quantitative method, capable of determining filtration efficiencies up to 99.9%. While primarily used for medical face masks, ASTM F2101 can also assess the bacterial filtration efficiency of other porous medical products such as surgical gowns, drapes and sterile barrier systems. 

In the test, bacterial efficiency is calculated based on colony-forming units (CFUs), which are converted into percentages to provide a clear measure of the material’s effectiveness. This standardized approach ensures consistent evaluation of filtration performance across various medical products.

Test organism

The test organism used is Staphylococcus aureus, a bacterium that forms a part of the normal microflora in humans but can also be an opportunistic pathogen. Due to its clinical significance as a leading cause of nosocomial infections, Staphylococcus aureus is used as a representative test strain for bacterial filtration efficiency.

ASTM F2101 test methods and requirements

  • Bacterial aerosol challenge
  • The testing begins with the introduction of aerosolized bacteria into the aerosol chamber using a nebulized culture suspension containing Staphylococcus aureus with 5 x 10⁵ CFU/mL.
  • The aerosolized bacteria are then drawn through the medical face mask material using a vacuum connected to a six-stage viable particle cascade impactor.

 

  • Control runs and aerosol particle size
    • Before testing the mask material, a positive control run is performed without a test specimen to determine the number of viable aerosol particles generated. 
    • The mean particle size (MPS) of the aerosol is calculated based on the results of these control plates. 
    • The mean particle size is critical as it influences the filtration performance of the material and for the test, it is maintained at 3.0 µm ± 0.3 µm​.  

 

  • Testing process
    • During the test, the face mask material sample is clamped between the six-stage cascade impactor in the aerosol chamber. 
    • The aerosol challenge is introduced and drawn through the mask material. After the challenge, agar plates in the cascade impactor collect the bacteria that penetrate the mask. 
    • These agar plates are then incubated at 37 ± 2 °C for 48 ± 4 hours​.

 

  • Viable bacteria count
    • After incubation, the number of viable bacteria collected on each stage of the cascade impactor is counted. 
    • These counts are expressed as colony-forming units (CFUs) and converted into percentages to determine the bacterial filtration efficiency (BFE) of the material. 
    • The bacterial challenge solution is nebulized at a rate of approximately 1700 to 3000 viable particles per test​.

 

  • Challenge delivery and negative control
    • The challenge delivery rate is based on the results of positive control plates, where no test specimen is clamped into the test system. 
    • Additionally, a negative control is performed by collecting a 2-minute air sample from the aerosol chamber without introducing a bacterial challenge. 
    • Incubate agar plates at 37± 2 °C for 48 ± 4 h.
    • This ensures that no contamination or unintended aerosol introduction affects the results.

Passing criteria

Face masks are categorized into the following levels based on their barrier performance:

  • Level 1 Barrier: Lightweight and breathable, ideal for low-risk settings like doctor visits or public transport. 
  • Level 2 Barrier: Thicker materials for moderate-risk scenarios, such as dental procedures. 
  • Level 3 Barrier: Maximum protection for high-risk situations, like surgery. 

Depending on these levels the performance criteria of medical face masks vary as::

For Level 1 masks:  ≥ 95% BFE

For Level 2 and 3 masks: ≥ 98% BFE.

Precautionary measures to undertake while testing

  • Staphylococcus aureus used in the test is a human pathogen, and is a common cause of nosocomial infections; therefore, microbiological training is required for technicians conducting the testing.
  • Gloves and all other personal protective equipment shall be worn at all times during the execution of the test in order to prevent contamination and exposure.
  • Any aerosol produced in the course of testing shall be contained to prevent exposure of personnel and reduce the risk of laboratory contamination. Proper containment techniques and equipment shall be employed.

Importance Of ASTM F 2101

The BFE of medical face mask materials is an important test as it ensures that these masks are effective in preventing the transmission of bacteria and hence protect healthcare workers and patients from possible hospital-acquired infections. This test is critical for compliance with health and safety regulations and also plays a key role in maintaining a sterile environment within medical settings. BFE testing of medical face mask materials helps manufacturers enhance product reliability, build trust among consumers and contribute to public health protection.

Benefits of performing the test

  • Regulatory compliance: Many regulatory bodies and healthcare administrators require these test results to validate and approve the face mask products for market release.
  • Quality assurance: Testing assures manufacturers that their products meet consistent mask quality, thereby upholding consumer trust in the product.
  • Product differentiation: A high BFE rating for a face mask will enhance its marketability, positioning it as a reliable and effective product for healthcare and general use.
  • Protect the end user: Testing helps ensure that the face masks used by healthcare professionals are effective in protecting them from bacterial exposure thus contributing to public health and safety.

Other relevant standards

At MIS, we also perform various other tests such as ASTM F2100, EN 14683 and ISO 22609 for testing medical face mask materials. These tests are designed are evaluate the various aspects of medical face masks such as breathability, particle filtration efficiency, splash resistance and more.

Why choose Microbe Investigation (MIS)?

At Microbe Investigations Switzerland, we specialize in ASTM F2101 testing to assess the bacterial filtration efficiency (BFE) of medical face masks. Our expert team ensures your masks meet stringent regulatory standards, providing reliable protection for healthcare settings and beyond.

To learn more about our ASTM F2101 testing services or to schedule a consultation, please contact our specialists today.

FAQs

ASTM F2101 describes the procedure for measuring the bacterial filtration efficiency (BFE) of materials used in medical face masks.

Medical face mask materials are tested using this standard.

The test takes 5-6 weeks to complete.

The test is performed against Staphylococcus aureus.

A higher Bacterial Filtration Efficiency (BFE) percentage indicates that the mask material is more effective at filtering out bacteria. For example, a BFE of 99% means that 99% of the aerosolized bacteria did not pass through the mask material, providing better protection against bacterial transmission.

Environmental conditions such as temperature and humidity can affect the results of the test. The standard specifies that test specimens should be conditioned at 21 ± 5 °C and 85 ± 5% relative humidity for at least 4 hours before testing. 

The test only measures bacterial filtration efficiency and does not assess other important factors like breathability, mask fit, or protection against all aerosolized biological particles.

Thicker masks typically have better bacterial filtration efficiency because they provide a more substantial barrier to particles. However, increased thickness can reduce breathability, which is not assessed in this test.

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