A normal mask works like a window-shield for insects, where the holes are of a smaller size than that of an insect. This method is good enough for a simple protective mask but not when dealing with serious issues like heavy pollution or wild-fire smoke or in our current scenario, the Covid-19 pandemic. In cases like the ones mentioned, we need the protection of an N-95 mask or higher.
N-95 mask is a mask that captures by ‘electrostatic attraction’ and doesn’t allow 95% of particles of 0.3-micron size to pass through. Here, the letter stands for the response to the oil.
N – Not to be used when oil is present.
R – Resistant to oil for 8 hours
P – Oil Proof
The material used for manufacturing the mask is an electrostatic non-woven polypropylene fibre.
(Sometimes the masks may come equipped with an exhalation valve making it easier to breathe(Exhale)).
During the need of protection from airborne diseases, we are looking at particles smaller than 1 micron, and that means having a mask like the mesh filter will not be helpful as the particles are too small for mesh system to work. This is where the smartness of N-95 comes into play.
The particles that need to be filtered out by a mask are segregated into three size categories, viz
Greater than 1 micron
Smaller than 0.1 microns and
Between 1 micron and 0.1 microns.
Capturing of the Particles
Particles of the microscopic sizes are very sticky in nature due to the weak attractive force between molecules being strong enough to make them stick to whatever surface they touch, including the fibres of the N-95.
In a mesh system, if a particle is smaller than the filtering size, it will pass through no matter how many layers of filter you may apply. But in a sticky mesh like the one in N-95 Masks, the layers help because if it misses the fibre in the first layer, there is a high chance that it will stick to the next layer. The only difference in the three sizes of the particles is the movement that they have, and that decides whether the particle will collide with the fibre or not.
Capture by Inertial Impaction
A particle, greater than 1 micron, moves in almost a straight line due to their inertia, which makes them an easy target for the mesh to which they can stick to.
Capture By Diffusion
A particle, smaller than 0.1 microns, moves in a random motion known as Brownian Motion, this occurs as the collision with other air molecules bounce these particles in a zigzag motion. This motion is the reason that makes it most likely that these particles will hit one of the fibres of the mask and stick to them.
A particle in between, approximately 0.3-micron size, are the hardest to trap. This mainly happens because these particles do not have enough inertia to travel in a straight line nor are they small enough to move in Brownian motion. Rather these particles get carried by air and thus move through the mask along with the air without bumping into the fibres.
Capture By Electrostatic Attraction
Due to static electricity, even a neutral particle near it can develop an electric polarity and get attracted to the object with a static electric charge. An N-95 mask’s fibres are electrets, just like permanent magnets but for electric poles rather than magnetic poles. This is what differentiates an N-95 mask from an ordinary mask.
This makes an N-95 mask able to attract 10 times more particles than an ordinary mask.
The entire process of using the sticky behaviour of the microscopic particles and combining it with the use of electrets as fibres makes the mask a smart mask that is very effective at performing the task, almost all particles of the size smaller than 0.1-microns and larger than 1-micron get filtered by the mask. But the trickiest one, of the size approximately 0.3-microns is what gives the mask its name, if it filters 95% of the particle of that size, its called N-95 but if it filters 99% the particles of that size then it is called N-99.
But you have to understand that correctly using the mask is just as important as using the mask, having a gap between the mask and your face will completely devalue the use of the mask.
For information on Covid-19, visit WHO site for up-to-date information.
As always, Thanks For Reading.