What does the National Institute for Occupational Safety and Health say about N95 mask filtration?

NIOSH has recommended specific and approved factors that make the N95 mask apt for the pandemic.

The Occupational Safety and Health ACT of 1970 established the National Institute for Occupational Safety and Health (NIOSH) as a research agency that focused on studying worker safety and health and empowering employers and workers to create safe and healthy workplaces. NIOSH is a part of the U.S. Centers for Disease Control and Prevention in the U.S. Department of Health and Human Services. The institute assures that every man and woman in the nation is safe and healthful working conditions and to preserve human resources. NIOSH has more than 1,300 employees from  various fields including epidemiology, nursing, industrial hygiene, chemistry, economics, medicine, safety, psychology, and many branches of engineering. NIOSH uses the best science to the highest data quality-level and the most transparent and independent reviews. Thus NIOSH is a body that recommends proper mask usage and approves the masks that are safe for use during the coronavirus pandemic.

What is an N95 respirator?

An N95 respirator filters out both large and small particles when the wearer inhales. It is called N95 it blocks 95% of microscopic particles. An N95 respirator is a respiratory protective device that gives a very close facial fit. It effectively filters the airborne particles. The N95 respirator also comes in various designs but is a double strap, flat folded filtering facepiece respirator. It has multiple layers of non-woven fabric. The filtration layer provides a barrier to particles of various sizes through mechanical entrapment in a tortuous pathway by the surface attraction of electrostatic force. The outermost layer is coated to capture and inactivate viruses. The layer of non-woven fabric is ultrasonically sealed together at the outer perimeter. The pair of elastic strips are stapled or welded to the edge of the respirator and prevent the mask from falling off the wearer’s face. The N95 mask is also a single-use mask, like the surgical masks. However, various studies are doing rounds to sanitize it or make it fit for reuse. The respirator is coated with virucoat on the outer layer. 

NIOS approval for the N95 masks- 

It has been clearly stated that N95 masks work efficiently in filtering the airborne particles, but then there are specific types of N95 masks that work efficiently. Not all types of N95 masks are efficient in filtering the airborne particles. NIOSH  has stated the specific requirements as per 42 CFR Part 84 for certifying N95 masks. These are the worst-case parameters that are to be cleared for getting certification. The specifications are as follows:


The N95 mask should be made of flat woven fibrous material. The fiber diameter, porosity, and filter thickness are of prime concern as they play a crucial role in collecting particles. In the N95 masks, it should collect inertial impaction, interception, and diffusion. The inertial and interception are mechanisms that collect large particles, while diffusion is the mechanism that collects smaller particles. There should be an electrostatic attraction that works to enhance the particle collection without increasing breathing issues.

How does NIOSH  test the filters of the N95 masks?

The tests are done keeping in mind the worst-case, and thus, the procedure is strict:

  1. Sodium chloride for the N series test aerosol with a mass median aerodynamic diameter particle of about 0.3 mm, which is set in the MPPS-range for most filters.
  2. Airflow rate of 85L/MIN is set for moderately high work rate.
  3. Conditioned at 85% relative humidity and 38 degrees for 24 hours before the test.
  4. A charged neutralized aerosol.
  5. Initial breathing resistance should not exceed 35 mm water column height pressure, and initial exhalation resistance exceeding 25 mm water column height pressure.
  6. Aerosol loading was conducted to a minimum of 200 mg, which represents a very high workplace exposure.  
  7. The filters efficiency should fall below the certification class level at any time during the NIOSH certification tests.

The reason for conducting stringent tests related to porosity, filter, material, and performance parameters used in the NIOSH certified respirators is to get high levels of particle collection efficiencies at the MPPS. The test conditions for surgical masks are relatively easier, and the products need to prove that they are as good as masks and then can be marketed. Manufacturers can choose from filter tests using a biological organism aerosol at an airflow of 28L/min. FDA specifies that the latex sphere aerosol should not be neutrally charged. NIOSH tests the masks at the time of application and then periodically after to ensure that the masks continuously meet the standards.    

While selecting the N95 masks over the other options, keep in mind that it is a precautionary measure and not an antiviral drug. FDA elaborates that the N95 mask has the same filtering and barrier properties as the predicate device. 

The N95 masks are the most effective category of masks. FDA and NIOSH have recommended and approved the use of these as a means of protection from the disease. All the N95 masks are not NIOSH approved, but all the NIOSH approved N95 masks are FDA approved. The ones that are not approved by NIOSH but have FDA approval can be used in settings outside the medical fields. Most importantly, the mask needs to fit properly on the face to perform well; even a certified mask will not perform the task of filtering.

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