Written by Jacob Liu | Edited by Mehr Bawa
Photo by CDC
With our current state of public health affairs, face coverings have become a divisive political point, but the foundational science behind the certification of face coverings from surgical masks to respirators still stands. Of particular recent media interest in the United States has been the usage of N95 respirators and KN95 masks, familiar to those who work in workplace environments with hazardous particulates such as the industrial sectors of mining, construction, and painting [1]. However, the meaning behind the abbreviations and numbers may still be unfamiliar, as guidelines are being updated consistently.
The N95 filtering facepiece respirator is a common face covering that meets the U.S. National Institute for Occupational Safety and Health (NIOSH) N95 classification of air filtration. The “95” stands for its filtering efficiency (FE) of at least 95% of airborne particles while the “N” letter indicates a certification that the respirator is “not resistant to oil,” specifically against dioctyl phthalate oil particles [2]. The KN95 certification is colloquially known as the Chinese equivalent of the N95 certification. Similarly, the European Union’s FFP2 respirators are required to meet at least 95% FE. While they utilize similar technology, they are not necessarily being reliably certified by NIOSH as they follow different guidelines.
The inventor of the N95 mask filter, Peter Tsai, recently published his proposed methods of cleaning the N95 respirator and reusing it through adjusting its material construction. In new N95 masks, the middle filtering layers could be made of polypropylene fibers with an embedded electrostatic charge, increasing the mask’s FE by as much as 10 to 20 times [3]. The typical face covering may be composed of a variety of materials in all matters of blends, including nylon, cotton, polyester, and polypropylene, each offering its own unique benefit. Nylon is resistant to rubbing, and cotton filters are environmentally friendly. Polyester offers mild resistance against acids and excellent durability at temperatures up to 150°C. Polypropylene is among the lightest among the synthetic fabrics and likewise has good resistance to acids and alkalis [4]. As such, face coverings’ materials and structure can vary widely, but the N95 respirator requires a fine mesh of synthetic non-woven polypropylene fabric produced by a process called melt blowing [5].
Melt blowing involves pushing molten polymer into a jet of hot air through a die to produce small fibers, which are deposited to make the fabric material of randomly fibrous webs with a tight filtrating ability [6]. It is this particular construction and certification enables the N95 respirator to have a higher filter efficiency (FE) than typical cotton or nylon cloth masks. In fact, they are even more so than the typical medical masks that many are familiar with. However, the careful manufacturing process of these respirators and their packaging means that the production process can be difficult [5].
Currently, researchers are looking to improve N95 respirator technology by improving the FE and its lifespan to be more accessible and convenient during times of crisis. N95 respirator technology is also being made more efficient to provide them to less industrialized areas at cheaper prices. In addition to N95 respirators, other respirators still provide some degree of protection, which is better than none. It ultimately comes down to achieving sufficient protection to serve our purposes amidst situations involving dangerous particulate matter to decrease our chances of particular harm as we take care to protect ourselves and others.
References:
5. Feng, Emily. “COVID-19 Has Caused A Shortage Of Face Masks. But They’re Surprisingly Hard To Make.” National Public Radio, National Public Radio, Inc, 16 Mar. 2020, www.npr.org/sections/goatsandsoda/2020/03/16/814929294/covid-19-has-caused-a-shortage-of-f ace-masks-but-theyre-surprisingly-hard-to-mak6. Soltani, I., Macosko, C.W. (2018). Influence of rheology and surface properties on morphology of nanofibers derived from islands-in-the-sea meltblown nonwovens. Polymer, 145:21-30.