After all the intense physics I covered, I thought I should mix things up a bit. So, this post is still kinda physics but it’s more relevant to what’s going on around us.
Let’s explore the mind muddling mask physics (it’s not that hard, I just wanted to use the alliteration).
N95 masks or respirators were practically unheard of before March 2020. I don’t imagine you ever came across the term in 2019 (the good ol’ days) unless you have experienced insane pollution or wildfire smoke or been in a construction environment with loads of dust.
When you hear of N95 masks, you might think of it as I did, a very very very fine strainer with gaps so small that even dust or minute airborne particles can’t get through. In fact, this isn’t how an N95 mask works. The particles they filter are generally much smaller than the gaps in the fibres of the mask (some of the very large particles do get filtered this way but that isn’t their major mechanism).
N95 masks are excellent at filtering the largest and smallest of the small particles. It’s the medium sized small particles that are trickier for it to block. It isn’t in the slightest like a strainer, an N95 is much cleverer, kinda like an Albert Einstein compared to a regular person.
The principle goal of an N95 mask is to make a particle touch a fibre in the mask. Regardless of the size of an airborne particle, once it touches a fibre, it stays stuck to it. This is mainly due to the size of the particles. At the microscopic scales (in microns/micrometres), everything is sticky because the weak attraction force between molecules known as the van der Waals force is more than enough to get the particles stuck to the fibres quite like a sticky spider web which catches insects as they touch a strand. N95 masks use several clever physical and mechanical tricks to maximise their filtering efficiency.
First, since many spider webs are obviously more efficient than one, so more layers of these sticky particles increases the chances of a particle getting stuck. The particle’s size is a major factor in deciding how likely a particle is to hit or miss a fibre.
Large small particles(>1micron)- These particles basically travel in a straight line due to inertia. So, they are guaranteed to eventually hit one of the fibres and stick.
Small small particles(<0.1microns) – These particles are so light that collisions with air molecules bounce them around in a zig zag pattern known as Brownian motion. This zig zagging pattern too makes it very likely that particles will hit a fibre and get stuck.
Medium small particles (≈ 0.3 microns) – These particles are rather tricky. Instead of travelling in a straight line or moving around in a zig zag pattern, these particles get carried along with the air as it flows around fibres, making it easy to sneak through several layers.
N95 masks have a final trick to catch these particles. They attract particles of all sizes using an electric field. In the presence of this field, even a neutral particle tends to develop an electrical imbalance, attracting them to the source. This is like when you rub a ruler on your hair and the ruler than attracts neutrally charged paper because it is charged with static electricity. The main difference here though is that an N95 mask doesn’t use static electricity, their fibres are permanent magnets but for electricity, electrets. Since you can permanently magnetise a piece of iron by putting it in a really strong magnetic field, you can permanently electretise plastic by keeping it in the presence of a strong enough electric field. This ability allows the fibres to attract particles and so N95 masks filter around 10 times more particles than a regular mask.
To summarise, an N95 mask:
- Takes advantage of the inherent stickiness of matter at the molecular scale
- Uses many layers of fibres
- Uses an electric field that attracts all sizes of particles
These 3 major functions give you a mask that filters almost all large and small particles and a significant chunk of medium sized particles. How much, 95%, thus the name N95. Just like these, you also have N99 and N100 masks which – you guessed it – filter 99% and 100% (99.7% if we’re being exact) of airborne particles. What about the N in the name though? That stands for not resistant to oil.
Lastly, who should use N95 masks in this pandemic?
Since the virus propagates through cough droplets which come in a variety of sizes, so the size of the virus is not that relevant.
Normal surgical masks do a pretty good job of keeping these fluids and droplets out. With a shortage of N95 masks in this pandemic, N95 masks should preferably be reserved for healthcare workers or others who frequently come in contact with Covid-19 patients. In fact, since N95 masks are in shortage, people need to reuse them but they are meant to be used only once. There is a lot of ongoing research and some methods being used but some experts suggest that N95 masks should only be used during certain treatments, though this is a debatable factor.
That’s as far as we are going to go about masks. Let me know in the comments if you enjoyed this post and would like to see similar posts in the future. I hope I didn’t bore you’ll.
Thanks for reading and byee!