How does filtration work with surgical masks?

During the last several months, a lot of people who had never had to think about face masks or any type of personal protective equipment have been hearing a lot about them. Sometimes the terms can be confusing, and with all this new information is easy to get lost. Many of us in the United States have been wearing the famous surgical masks for the majority of the year, but a lot of people don't know how they work. In this article, we'll discuss surgical masks, their effectiveness for virus protection, and how they filter out particles from the air.

Surgical face masks are a type of disposable face mask used widely in the healthcare profession. As the name suggests, they’re used during surgeries, but they can also be called medical masks as they’re used during other procedures. They’re often referred to as ‘regular’ face masks, but not any type of face mask can substitute them in healthcare settings, as these are tightly-regulated face masks made specifically for the healthcare field.

They act as a physical barrier against fluids in the form of droplets, sprays, splashes or splatter, that may be infected or contaminated. These fluids can sometimes carry airborne particles considered pathogenic, and when they reach the mucous membranes in the nose or mouth, they can start replicating and colonizing the airways. Surgical masks can prevent them from reaching these mucous membranes, and preventing the potential diseases they can cause.

As a filter, these face masks can only trap large particles, and they can’t filter out smaller airborne particles like dust and smoke, and viruses like the flu, from the air. As we mentioned, a surgical mask acts primarily as a physical barrier to prevent the fluids from being in contact with the wearer’s mouth or nose. They’re usually also used with face shields for protection of the eyes as well.

This protection works in both ways, as the fluids released by the wearer when they talk, cough, or sneeze, are also prevented from reaching the environment. This is why surgical masks are often used in the healthcare field to maintain a sterile field during surgeries to prevent the contamination of the wound, as well as other medical procedures where keeping the field sterile is also important. They're also often used when treating immunocompromised patients in which usually harmless pathogens released by healthy people can cause serious infections.

Unlike N95 masks, surgical face masks aren’t recommended by the Centers for Disease Control and Prevention (CDC) to be used for virus protection during the COVID-19 pandemic. Besides their lower filtration and antiviral properties, we just mentioned, they’re also loose-fitting, which leaves spaces between the face and the mask where air can leak. This way, the air can either come out of the wearer’s mouth and nose or reach them without being filtered first. This is why N95 masks are considered the best option for virus protection during the COVID-19 pandemic, along with KN95 masks.

Since they’re disposable face masks, as the name suggests, they’re designed to be used only once and then discarded. As soon as the face mask is wet or damaged, it must be removed and replaced immediately. They’re also not meant to be shared with other colleagues. Before and after handling the face mask, washing the hands properly is always recommended, as well as handling it by the ear-loops o straps and never touching the inner or outer part of the face mask. This ensures no contamination is happening in either way.

As we mentioned, surgical masks aren’t made to filter out small particles, and they allow air leakage which decreases their filtration rate. However, they share the same filtration method with N95 masks, it’s just that the latter are much more efficient. Like the respirators, surgical masks use non-woven material, also known as melt-blown material, which is a raw material made out of the plastic called polypropylene.

Polypropylene has many uses in a wide variety of fields, but they have a particular main role in most medical supplies and PPE, including masks and respirators. The non-woven fabric is obtained by putting the polypropylene through mechanical, chemical, or thermic processes, resulting in a fabric with a lot of holes in it. This material, the non-woven fabric, is used as the filtering part of the respirators and the masks, and the little holes are small enough to trap certain particles.

Airborne particles have a diameter of 0.3 microns, which means that to filter them out, the holes in the melt-blown material need to be smaller than that. Face masks and respirators, besides being effective to filter out these particles, they also need to meet breathability requirements, and holes with such a small diameter would not allow that. This is why many manufacturers use a combination of other filtration methods that would allow them to have holes in the filter material with a larger diameter.

One of the most used methods is electrostatic filtration, a method in which electrostatic charges are added to the naturally neutral non-woven fabric. The principle of this method is that the charges will attract particles, both small and large, with the opposite charge, trapping them and preventing them from entering the airway. This way, the holes in the filter media can be larger, ensuring proper breathability.

In the USA, authorities have been urging the general public to wear non-medical-grade face masks for virus protection. These can be found for sale easily online, with options in a smaller size for kids, and to buy in bulk and wholesale. Medical-grade masks like the 3M N95 masks in the models 3M 8210 and 3M 8511 need to be reserved for the healthcare workers on the frontlines of the pandemic.

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