In the global fight against COVID-19, N95 masks have been at the forefront of public awareness regarding their efficacy in reducing viral transmission. Just why are N95 masks so effective?
N95 masks were originally designed to protect the wearer against harmful particle inhalation in industrial and manufacturing settings. Small dust and contaminate particles are harmful upon inhalation and can cause lung disease in humans over long periods of exposure. N95 masks, due to their use of Meltblown Polypropylene (MBPP) filtration fabric, and their ability to create a seal on the wearer’s face prevent at least 95% of particles above .3 microns to pass through.
Due to the high efficacy of particle filtration, N95 masks have been used in surgical settings to reduce cross contamination and prevent the spread of disease. N95s designed and regulated by the FDA (Food and Drug Administration) and NIOSH (the National Institute for Occupational Safety and Health) for medical use are regulated as single-use class II products as a measure of curbing viral transmission.
Since these masks are available in a variety of shapes, wearers can choose the model that best fits their individual features to ensure a proper seal around the edge of the mask. Masks that fit properly enable easier breathing, and are designed to create a seal to restrict particle exit and entry. Persons with beards may have increased risk of viral transmission as it limits the ability of the mask to create a tight seal around all edges of the mask.
The N95 models that have exhalation valves designed to increase airflow and comfort for the wearer; however, it has recently been determined that these masks may in fact spread disease as the valves allow the exit of contaminated particles.
Due to the increase in usage of N95 masks, the CDC has created guidelines for medical professionals to avoid product shortages. As medical usage by regulation is restricted to single use, the CDC has created scenarios to extend the lifetime of each mask, while ensuring low risk of viral disease transmission.
Medical professionals may extend the life of their masks by removing them in-between patients up to five times for low-risk activities, such as general patient visits where the patient is also masked. Reusable cloth masks can be used on top of the N95 for additional protection. However, the reuse of masks would not be advised for surgeries or other encounters that would generate air droplets. In those situations, N95 masks should continue to be used according to regular single-use standards. Since N95 masks have a shelf life, the new CDC guidelines suggest that expired masks can be used for low-risk patient contact, but the wearer needs to ensure that the seal is intact for maximum protection.
Masks and respirators that have been approved by other international standards similar in nature may also be used in place of N95 masks. Outside of the above controls, hospitals may choose to have patients convalesce at home if they do not need urgent hospitalization, and organize staff scheduling to keep immuno-compromised workers away from coronavirus patients.
N95 respirators are made using polypropylene to create multiple layers of non-woven fabric for the exterior surfaces as well as the internal filtration layers.
First, the two outward facing protective layers are created using a process called spun bonding. Melted threads of a thermoplastic polymer such as polypropylene are blown via nozzles onto a conveyor belt to form layers of thread reaching 15-35 micrometers. This builds up into cloth, and is then bonded through either thermal, mechanical or chemical processes. These two layers which are between 20 and 50g/m2 in density provide protection as they prohibit the passage of particles.
Between the two outward facing layers are two additional layers for added protection. The first layer is known as the pre-filtration layer, followed by the filtration layer. The pre-filtration layer is made from a dense, needled nonwoven material, which is needle-punched by barbed needles in order to lessen gaps in the fabric by hooking fibers together. Finally, this layer is sent through a hot calendering process, which thermally bonds the plastic fibers to allow the mask to maintain shape through wear.
The final filtration layer is made through a process similar to spun bonding called meltblowing. Nozzles spray melted polymer threads on a conveyor belt which bond into fibres less than a micron wide. This fabric is known as a high efficiency melt-blown electret, nonwoven material. On occasion, a thermal bonding process follows this step, however the end result creates a material too stiff to be considered a ‘fabric’.
Finally, the fabrics are sent through converting machinery and the layers are combined through ultrasonic welding, and straps, ear loops and metal strips are added before the final sterilization occurs.
It is important to compare different masks with their intended uses versus their capabilities when deciding which mask is best. There are many options available, however all masks are not created equal in the prevention of virus transmission.
Single-use masks that are one layer in thickness can capture dust particles, but have not been proven to prevent small, virus-sized particles from passing through. Surgical masks, while also able to capture virus-sized particles, have varying standards by region, unlike the N95.
The strict regulatory standards that govern the product standards, the secure mask fit, and the use of the Meltblown Polypropylene filtration fabric (MBPP), all ensure the efficacy of the N95 mask. When purchasing a N95 mask, you can be assured that your purchase is of the highest quality and meets all standards as set out by the FDA and NIOSH.
Sources: thomasnet.com, smartairfilters.com
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