ASTM F2101–19. Standard Test Method for Evaluating the Bacterial Filtration Efficiency (BFE) of Medical Face Mask Materials, Using a Biological Aerosol of Staphylococcus aureus.

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The risk of occupational exposure of health professionals to infections caused by various agents, especially viruses and bacteria, has become a threat to them, since in their activity they must manipulate biological fluids that may contain pathogens. The biological risk is ubiquitous and of wide variety, since it can be blood, air, oral or contact.

This risk is not only for healthcare professionals, involved in the treatment and care of injured or sick people, but also for patients. The diseases they can cause can be generated by a wide variety of biological agents that can pose significant risks to life and health. Therefore, it is important to reduce contact with air that may contain pathogens through the use of medical masks.

This test method evaluates the efficiency of bacterial filtration of the materials used in the manufacture of medical masks and not their design, fastening or facial adaptation, nor any property that affects the ease of breathing through them. To perform the test, the materials are exposed to a higher air current containing bacteria. In order to evaluate the effectiveness of the materials used to prevent the spread of the pathogen through them, the concentration in the lower air stream is determined, after crossing the material. The test method, in addition to being applied to medical mask materials, can also evaluate the efficiency of bacterial filtration of other porous medical products such as surgical gowns, surgical curtains and sterile barrier systems (excluding respirators).

The organism used as an aerosol in this test method is Staphylococcus aureus frequent in the normal flora of the body, in addition to being a human pathogen and an important cause of nosocomial infections.

To perform the test, the filtering product under evaluation is positioned between an aerosolization chamber and a six-stage cascade impactor. The culture suspension of Staphylococcus aureus which is dispersed using a nebulizer is introduced into the aerosolization chamber. Aerosol droplets impact with the medical mask and, in case of passing through it, are collected throughout the six stages of the process. Both positive and negative controls are used in the test. The positive controls determine the aerosol counts introduced by the aerosolization stream, while the negative controls show that no microorganisms are introduced by any other route. The number of microorganisms grown in the culture plates shows the microorganisms that have passed from the aerosolization chamber. In this way, the relationship between the counts present in the upper current generated by the nebulizer is evaluated, with respect to the counts obtained in the lower current after having passed the mask material, informing the percentage of efficiency of the bacterial filtration exerted for the material evaluated. The method described by ASTM F2104-14 does not define acceptable levels of bacterial filtration efficiency.

The tests can be performed with exposure to the spray directed either through the facial side (in contact with the person´s skin) or from the external side (external to the person), of the material under test, thus allowing to evaluate the efficacy of filtration that are related both to the aerosols generated by the patient, and to the aerosols generated in the environment. Unless otherwise specified, the test will be performed with the facial (inside) of the medical mask.

Degradation due to physical, chemical and thermal conditions could adversely affect the performance of the medical mask material. The integrity of the material can also be compromised during use due to the effects generated by its flexion, when wetted with contaminants such as alcohol and perspiration. The trial without considering these situations could lead to a false safety statement. Therefore, it is offered to evaluate the performance of the medical mask material for the effectiveness of bacterial filtration following appropriate pretreatment procedures that are representative of the expected conditions during use. The client must choose whether or not to pre-condition the material to be tested and how to proceed if necessary. In addition, it must indicate the area of the material you want to evaluate, if it is not the inner (facial) area of the mask.