Knowing about N95 Respirators & Surgical Masks
Both N95 respirators & surgical masks are a type of PPE (personal protective equipment) that is used to safeguard the wearer from liquid or airborne particles that contaminate the wearer’s face.
Performance of Filter
The masks are gauged based on the performance of their filters and the latest surgical respirators are made of fine fibers. The diameter, thickness and porosity of the fiber decide the collection capacity of the filters.
The filtration mechanisms in the respirators can be described as
• Inertial Impaction
• Interception
• Diffusion
• Electrostatic attraction
In all the mechanisms mentioned above once the particle comes in touch with the filter fiber it is eliminated from the airstream and the molecular attractive forces hold it.
Testing of surgical masks & respirator filters
Respirator filters are tested thoroughly and they need to meet the strict certification NIOSH tests - 42 CFR Part 84. The parameters followed for testing are
• For N series- sodium chloride
• For R & P series - dioctyl phthalate oil and test aerosol having a 0.3 µm mass median aerodynamic diameter particle ( MPPS range for many filters)
• Airflow rate - 85 L/min
The filtration capacity should meet such certification tests
The strict parameters used to check the performance of filters are
• Fiber diameters
• Porosity
Filter thicknesses of all particulate filters (utilized in NIOSH-certified respirators, like N95). They are made to offer a high level of collection of particles at their MPPS.
How respirator filters and surgical masks perform?
• Respirator filters having the collection efficiency of 95% of aerosol are rated as 95
• Respirators that capture 99% are rated as 99
• Those collecting a minimum of 99.97% get a rating – 100. So respirator filters are rated based on their protection efficiency against oil aerosols. They are rated as
• N – if not oil resistant
• R – little resistant to oil
• P- Highly resistant to oil
Hence they are categorized in 9 different kinds of particulate respirator filters
• N95, N-99, & N-100
• R-95, R-99, & R-100
• P-95, P-99, & P-100
The FDA tested & cleared surgical masks are called as Surgical N95 Respirators. This is the only surgical mask that meets strict NIOSH standards. All the surgical masks of this class are regulated by NIOSH as N95 respirators
Collection efficiency
Talking about the collection capacity of surgical mask filters, it can vary anywhere from 10% or less to almost 90% collection efficiency.
N95 Masks
Masks that come with N95 rating come with the filtration efficiency of 95% particulate element 2.5 present in air
N99 Masks
N99 air masks have filtration efficiency of 99% of the particulate element 2.5 present in the air. Just like N95 masks they are not efficient to deal with oil-based pollutants.
P95 masks
The main difference between P and N rated masks is their ability to eliminate oil-based pollutants. That is P rated masks are capable of not only filtering out 95% of particulate element present in air but also clear out the oil based pollutants.
Reference: https://blogs.cdc.gov/niosh-science-blog/2009/10/14/n95/
