By Todd D. Hillam, SM(NRCM) Aerobiology Section Leader and Sarah Smit, Study Director at Nelson Laboratories
Surgical face masks are subject to FDA and other regulatory requirements and approval prior to being marketed and sold in public. Some of the guidance and standards that will help manufacturers meet these requirements are,
- FDA guidance: Surgical Masks – Premarket Notifications [510(k)] Submissions
- ASTM F2100 in the U.S.
- EN 14683 in Europe
Bacterial Filtration Efficiency (BFE) is one of the basic tests that must be conducted to measure bacterial filtering capabilities of face masks. The test is conducted by introducing a measured amount (1700 to 2700 colony forming units) of aerosolized Staphylococcus aureus bacterial particles upstream of the mask and measuring the number of bacterial particles downstream of the mask to determine its filtering capabilities. The bacteria are approximately 1 micron in size and are attached to liquid particles that are approximately 3 microns.
Using a vacuum pump to pull the aerosolized bacteria through the mask, the bacterial particles are captured on the downstream side by a six-stage cascade impactor called an Andersen sampler which simulates the human respiratory system.
ASTM F2100-07 allows manufacturers to establish a barrier rating for their face mask materials. To meet the lowest level of classification the mask must meet a greater than or equal to 95 % filtration efficiency and greater than or equal to 98% filtration efficiency for a moderate or high level. In order to claim a barrier rating on face mask materials the following additional tests must be performed:
- Differential Pressure (Delta P)
- Sub-micron particulate filtration efficiency (PFE) at 0.1 micron
- Resistance to penetration by synthetic blood
- Flame Spread
Often manufacturers will test the raw materials to check the filtration abilities before actually manufacturing the mask. The test can also be conducted for other devices or products that provide filtering capabilities such as sterilization wrap materials and housed filters.
It is important for manufacturers to be aware of this test so when they submit their product for approval to regulatory agencies they know how to classify their product and know it will protect both the wearer and the patient.