The FDA and ASTM international play a role in the manufacture of medical face masks. The FDA recognizes ASTM F2100 as the standard specification for the performance of materials used in a surgical face mask, where specific criteria must be met in five categories. The masks can be labelled as surgical, laser, isolation, dental or medical procedural masks.
The first criteria for mask performance is bacterial filtration efficiency (BFE). This measures the mask’s ability to prevent bacteria from traveling through the material. It is represented by a percentage of aerosol particulates filtered at a size of 3 microns with the efficiency of the mask being able to filter the passing bacteria.
Particulate Filtration Efficiency (PFE) measures the effectiveness of a mask’s material to filter sub-micron particulates passing through. It is expressed by a percentage that indicates the amount of particles that do not pass through the fabric at a given aerosol flow rate.
Fluid Resistance measures the mask’s ability to resist penetration by synthetic blood under pressure, measured in mmHg. The higher the fluid resistance, the better protection against fluids traveling through and potentially becoming in contact with the wearer.
Differential Pressure (Delta P) measures breathability. It is the effort it takes to force air through the mask material. The lower the delta P, the more breathable and comfortable. It is important to note that a very breathable mask (such as fabric), may also have a low filtration efficiency.
Below is a comfort scale in Delta P testing:
Flame Spread is expressed by a ranking that is derived by laboratory standard test methodology of a material’s susceptibility to burn rapidly and spread flames. The rate at which the material burns determines the level of flammability. A sample material must have a minimum 3.5 second burn rate when a flame is held to the center surface of test material for 1 second. The FDA recommends only Class 1 and Class 2 flammability materials to be used in surgical masks.
Below is a chart depicting the test classifications in the different barrier levels:
|Test||Level 1||Level 2||Level 3|
|Bacterial Filtration Efficiency (BFE)||≥ 95%
|≥ 98%||≥ 98%|
|Particulate Filtration Efficiency (PFE)||≥ 95%||≥ 98%||≥ 98%|
|Fluid Resistance (mmHg)||80||120||160|
|Differential Pressure (Delta P)||<4.0||<5.0||<5.0|
|Flammability||Class 1||Class 1||Class 1|
It is important to be aware of the different criteria in what differentiates one face mask to another. It allows the user to make an educated choice of which level and barrier protection is needed to allow for optimal protection when providing direct care in healthcare settings.
NIOSH Testing Standards
The National Institute for Occupational Health and Safety (NIOSH) is responsible for conducting research and makes recommendations in prevention worker illness and injury. NIOSH inspects, tests and approves respirators once they have been evaluated in the laboratory. All requirements must be met according to Title 42, Code of Federal Regulations, Part 84 and a manufacturer’s quality plan is must be deemed satisfactory.
There are three classes of filters that are certified by NIOSH: N-, R- and P-series along with three levels of filter efficiency—95%, 99% and 99.97%. The filter tests will all utilize an aerosol size of 0.3 µm. N-series will be tested against a mild degrading aerosol of sodium chloride (NaCl). The R- and P- series are tested against a highly degrading aerosol of dioctylphthalate (DOP) with a particle size of 0.3 µm. Airflow rate of 85L/min is used to represent a moderately-high work rate and an initial breathing resistance should not exceed 35mm water column (measurement of small pressure differences) height pressure. An initial exhalation resistance should not exceed 25mm of water column height pressure and conditioning must be at 85% relative humidity at 38°C for 24hrs prior to testing. Aerosol loading is also conducted at 200mg—which represents a very high workplace exposure.
When it comes to usage, N-series filters are not resistant to oils, R-series filters are somewhat resistant to oils and P-series filters are strongly resistant to oils. A filter’s performance is crucial to providing a high level of performance to the overall facepiece. A good fit to the face alone will not be sufficient as a good filter.
|Filter Designation||Minimum Efficiency||Test Agent||Maximum Test Challenge Loading|
|N100||99.97%||NaCl||200 mg filter loading|
|N99||99%||NaCl||200 mg filter loading|
|N95||95%||NaCl||200 mg filter loading|
|R100||99.97%||DOP||200 mg filter loading|
|R99||99%||DOP||200 mg filter loading|
|R95||95%||DOP||200 mg filter loading|
|P100||99.97%||DOP||Maximum filter degradation|
|P99||99%||DOP||Maximum filter degradation|
|P95||95%||DOP||Maximum filter degradation|