How N95 Masks Filter 95% of Particles

May 04, 2020

What are N95 Masks?

Originally developed for industrial applications, N95 respirators are specialized masks that filter out at least 95% of particles above .3 microns. There are also N99 and N100 respirators (N100s stop at least 99.97% of particles from entering). Legitimate surgical respirators are approved by both the FDA and NIOSH (the National Institute for Occupational Safety and Health). N95s come in several different shapes, which can help healthcare workers with finding a model that better fits their faces, but they cannot provide a seal for beards. Some N95s feature exhalation valves, which help the wearer to breathe more easily.

It’s important to note that not all N95 respirators are designed for medical applications; some are manufactured for industrial use. Medical N95s are single-use products regulated as class II products under the FDA (Food and Drug Administration) and NIOSH (the National Institute for Occupational Safety and Health).

How do N95 Masks Work?

N95 respirators work by filtering out particles thanks to the structure of their nonwoven material. Particles get trapped as they are forced to make twists and turns through the dense network of the material’s fibers, which are as thin as a single micron. Masks also have electrostatically charged material to further attract particles. As particles build up, the mask becomes a more efficient filter. However, the buildup also makes the mask more difficult to breathe through, which is why the masks and filters are made to be disposable.

What is the difference between N95 Masks and Surgical Masks?

N: This is a Respirator Rating Letter Class. It stands for “Non-Oil” meaning that if no oil-based particulates are present, then you can use the mask in the work environment. Other masks ratings are R (resistant to oil for 8 hours) and P (oil proof).

95: Masks ending in a 95, have a 95 percent efficiency. Masks ending in a 99 have a 99 percent efficiency. Masks ending in 100 are 99.97 percent efficient and that is the same as a HEPA quality filter.

.3 microns: The masks filter out contaminants like dusts, mists and fumes. The minimum size of .3 microns of particulates and large droplets won’t pass through the barrier, according to the Centers for Disease Control and Prevention (CDC.)

Material: The filtration material on the mask is an electrostatic non-woven fabric.

Valve: Some disposable N95 masks come with an optional exhalation valve. “The presence of an exhalation valve reduces exhalation resistance, which makes it easier to breathe (exhale,)” according to the CDC. 

How are N95 Masks Made?

A medical N95 respirator consists of multiple layers of nonwoven fabric, often made from polypropylene. The two outward protective layers of fabric, covering the inside and outside of the mask, are created using spunbonding. Spunbonding uses nozzles blowing melted threads of a thermoplastic polymer (often polypropylene) to layer threads between 15-35 micrometers on a conveyor belt, which build up into cloth as the belt continues down the line. Fibers are then bonded using thermal, mechanical, or chemical techniques. The two outer layers of the respirator, between 20 and 50 g/m2 in density, act as protection against the outside environment as well as a barrier to anything in the wearer’s exhalations.

Between the spunbond layers there’s a pre-filtration layer, which can be as dense as 250 g/m2, and the filtration layer. The prefiltration layer is usually a needled nonwoven. Nonwoven material is needle punched to increase its cohesiveness, which is accomplished by sending barbed needles repeatedly through the fabric to hook fibers together. The prefiltration layer is then run through a hot calendaring process, in which plastic fibers are thermally bonded by running them through high pressure heated rolls. This makes the pre-filtration layer thicker and stiffer, so it can be molded to form the desired shape and stay in that shape as the mask is used.

The last layer is a high efficiency meltblown electret (or polarized) nonwoven material, which determines the filtration efficiency. Meltblowing is a process similar to spunbonding, in which multiple machine nozzles use air to spray threads of melted synthetic polymers onto a conveyor. However, these fibers are much smaller, as less than a micron wide. As the conveyor continues, the threads build up and bond by themselves as they cool, creating the fabric. However, sometimes meltblown fabric is also thermally bonded to add strength and abrasion resistance, although the material then begins to lose some of its fabric characteristics.

The full respirators are made through converting machinery, which combines the layers through ultrasonic welding and adds straps and metal strips to adjust the mask over the user’s nose. The respirators are then sterilized as a last step before being shipped.

What does this mean for you?

Due to social distancing requirements, many establishments including grocery stores and other retail outlets require customers to use masks prior to entering while turning away customers who do not have masks.  Many people think that surgical or cloth masks offer protection from airborne particles which is not true - cloth masks still allow the passage of particles in both directions including airborne droplets.  The best protection from airborne particles are N95 masks.  We offer a limited supply of N95 masks to Everflush customers.    

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