As Omicron rips thru the world, we know one simple thing that can really help. PROPERLY WORN MASKS.
Masks work.
But practically, with cloth masks, surgical masks, and"N95"s around, how does one choose? Can we reuse masks? How?
With @cspramesh's help a long🧵(1/n)
RT if helpful!
The most important thing is a proper fit. The best “N95” mask that doesn't cover the nose & mouth and seal tightly against the face without gaps is useless! Unfortunately, many people take the mask off their nose if no one's watching, even worse, think it's a chin ornament! (2/n)
Can't emphasize this enough. *Proper fit is more important than filtration efficiency!* No gaps over the nose! If you wear glasses and they fog - bad fit. Make sure the mask has a nose bridge that can be pressed in place. Need to take that phone call? don't remove the mask! (3/n)
As the pandemic has progressed, the advice on this from various agencies, intl and local, on what mask to use has however kept changing (understandable - initially there were shortages, our knowledge of how the virus spreads in air improved). What are our options? (4/n)
There are cloth masks (with at least 3 layers), the typical blue pleated surgical masks, and the most efficient N95 / KN95 masks. An N95 mask filters out >95% of tiny 0.3 micron-sized particles. It is usually tied behind the head, the KN95 mask, very similar, has ear loops. (5/n)
A high-quality “surgical mask” has the same filter layer as an N95 but is not designed to seal tightly against the face, with gaps at the sides. Stay away from (K)N95s with exhalation valves - they might make breathing easier, but offer zero protection to others around. (6/n)
Aside: N95 is a US NIOSH spec, KN95 a Chinese equiv., Korea has KF94, in Europe it is FFP2. India has IS 9473:2002 Class FFP2, but N95 is the more common term in use. Don't fall for marketing jargon like W95, LN95, XYZ99 etc. Many fakes floating around, cannot look & tell! (7/n)
Cloth masks can easily be washed, dried & reused. But the cloth fibres only mechanically filter the air (like a sieve) and are not very efficient (as N95s) in removing the tinest particles. But the viral particles can be airborne in very small droplets for a long time! (8/n)
One option to improve things is to "double mask". First wear a surgical mask, and then a cloth mask over it, to to help seal down the edges of the surgical mask. (order is important!) This provides much better protection than either a cloth or surgical mask used by itself. (9/n)
N95 masks have layer of very fine meltblown polymer fibres, that are electrostatically charged, and can attract tiny particles, and hence get to 95%+ filtration efficiencies while still being breathable. Compare the micrographs of a cloth mask and the layers in an N95! (10/n)
Why all this physics? Washing an N95 mask (or using hand sanitizer) removes the electrostatic charge that is critical to filtration, and lowers the efficiency. So how does one re-use them without compromising filtration efficiency? At home, without fancy heat/UV treatments (11/n)
No worries. N95s are now not that expensive & can be easily reused. As they say, "time heals everything"- well masks too! The SARS-COV2 virus does not survive on any surface > 96 hours. So, if there is a 5 day gap between using the same mask again, it can be safely reused.(12/n)
Practically: Get a set of 5 masks (label them!). Use Mask 1 on Day1 … Mask 5 on Day 5. The 1st mask can be safely reused on Day 6.. Not too tough. Keep the mask in an open airy place, e.g in a paper bag in between uses. A set of masks can cycled ~5-10 times this way. (13/n)
Given pollution, dust, etc. the mask pores slowly clog up, so one can't do this forever. But most probably the straps will break, or there'll be sweat/dirt/lipstick stains before the mask loses its ability to filter! Please discard a dirty mask before it gets too gross! (14/n)
Important: Masks tied tightly around the head provide much better fit than those fixed by elastic loops around the ears. And ears hurt after a while. If you use a KN95 style mask find some way (a paperclip or two can do the trick) to tie it around the head. Save your ears!(15/n)
Mask up India! For everyone's sake, it is time to wear our masks properly. Please!
And if I may add, disposable masks add to non biodegradable waste. Even in the best of times, for the sake of our planet, let's try and reuse masks if we can safely do it! (16/n)

• • •

Missing some Tweet in this thread? You can try to force a refresh

Keep Current with Arnab Bhattacharya

Arnab Bhattacharya Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!


Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @TifrArnab

8 Aug 21
Now that everyone finally knows about #javelin throwing thanks to @Neeraj_chopra1's phenomenal gold medal at the Olympics, it's time to look at some delightful #Physics trivia and history behind this beautiful sport! A lazy Sunday thread on the Javelin throw! #scicomm (1/n)
Observation 1: High school physics says "for max range, a projectile should be launched at a 45 degree angle". That's true only for launch & target at the same height! Here, launch ~2m above ground, target at ground + LOTS of aerodynamics -> optimal angle is ~36 degrees! (2/n)
Trivia: The Javelin throw is a rare event where the IAAF (now called @WorldAthletics) intervened to change rules to force throw distances to be REDUCED, as changes (based on physics!) such as hollow, designer cross section, surface texture... made javelins more aerodynamic (3/n)
Read 12 tweets
10 Jun 21
As promised a detailed thread on washing surgical masks:
I've HAND washed several surgical, and "cloth with polymer interlayer" masks to test their particle filtration efficiency at 0.3um. There are both high quality and cheaper masks, sourced from India and Bangladesh. (1/n)
New masks have hydrophobic outer layer (see water balling up?) Rub a bar of detergent and it gets wet. Scrub 2 min, rinse well. Hang to dry. First few washes, will recover hydrophobic nature, after lots of scrubbing it gets rough. (2/n)
Since most high-quality masks depend on a charged layer of meltblown polypropylene fibers for filtration (same as in N95s) one expects a sharp drop on washing once the charge is removed. So we measured particle filtration efficiency (PFE) at 0.3um after 1, 10, 20 washes. (3/n)
Read 8 tweets

Did Thread Reader help you today?

Support us! We are indie developers!

This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Too expensive? Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal

Or Donate anonymously using crypto!


0xfe58350B80634f60Fa6Dc149a72b4DFbc17D341E copy


3ATGMxNzCUFzxpMCHL5sWSt4DVtS8UqXpi copy

Thank you for your support!

Follow Us on Twitter!