What’s the difference between a respirator and a mask? I’m so glad you asked!

First, let’s get some potential confusion out of the way. A VENTILATOR is a MACHINE that mechanically keeps lungs going. This is very different from a RESPIRATOR, which (despite the robot-sounding name) is a mask-like thing – BUT it’s *different* from a typical “surgical mask” which is different from the “cloth face coverings” we’ve been advised to wear. 

Ventilators are needed by really really sick patients to keep them breathing. Respirators (esp. the N-95 ones you’ve probably been hearing about) are needed by health-care providers to keep them from getting infected from their patients. Cloth face coverings are the DIY versions of surgical masks, which are the “official masks” that are also needed in a health care setting.

Masks & face coverings are needed by patients and the general public to keep our spittle from flying and unknowingly spreading disease. More scientifically-speaking, that “spittle” contains “respiratory droplets” – tiny suspended liquid pools that, even if we don’t have symptoms, or if we have really mild symptoms, could contain tons of viral particles.

I will explain the key differences between these in a minute, but first it’s important to know thy enemy – in the case of SARS-Cov-2, the “novel coronavirus” that causes the disease Covid-19, these particles consist of a single strand of RNA containing the virus’ genetic blueprint, wrapped up with some protein and surrounded by a fatty (lipid) membrane. Jutting out from that membrane are crown-like “spike proteins” that allow these particles to bind to a certain type of receptor on our cells and get taken in. 

On the molecular scale, scientists are working to develop antibody drugs that can bind to the spike proteins, “hiding” the part they normally use to bind cell receptors, and thus preventing this docking. But on the much larger scale we can all do a part to prevent the docking by preventing the virus from even getting near new cells – by wearing “masks” or “cloth face face coverings”

I made mine out of a pillowcase my mom had sewn for me. I tried to do it following a video from the CDC: https://bit.ly/3bTzaTq but I didn’t have any rubber bands so had to improvise a bit and give it a hairband ponytail. 

They also provide some instructions for making more snazzy ones, like with actual sewing – but I couldn’t even find a rubber band in my room and now is not the time to go out to the fabric store (if it’s open) and buy a sewing machine, so they also offer no-sew options. https://bit.ly/39P0NM3 

They recommend wearing these when public, especially in situations like grocery shopping where that 6-ft social distancing is hard to maintain. But it’s not enough to just wear a mask. Remember – that mask is going onto your face, so you want to make sure you wash your hands before putting it on, after taking it off (which you should do from the ear straps), and whenever you touch it – and try to make it so it stays on without you constantly having to adjust it…here’s a good article: https://bit.ly/2Rjo3eS 

There are tons of different “mask”-making instructions out there because it’s really important that we save the SURGICAL MASKS for healthcare workers. And we DEFINITELY need to save the respirators for them. What’s the difference?

Per the CDC, a surgical mask (aka a laser, isolation, dental, or medical procedure mask) “is a loose-fitting, disposable device that prevents the release of potential contaminants from the user into their immediate environment” (keeps spittle in) and “protect[s] the wearer from direct splashes and sprays of infectious blood or body fluids” https://bit.ly/3e3mzzd

So, basically, a surgical mask isn’t air tight, so things can potentially sneak in around the edges, but it offers a barrier from someone like directly spitting on your face or something. And if a spitter (or cougher/sneezer) is wearing one, it prevents their expelled gunk from getting onto others. Surgical masks have been used by medical workers for about a decade. 

Respirators have also been around for about that long, but they were initially designed to protect minors from dust, firefighters from ash, soldiers from chemical warfare agents, etc. Unlike surgical masks, which can only trap larger particles, respirators have a filter that can capture a range of particle sizes (<1 to >100 µm) (1 µm is 1/1000 of a mm)(note that here particle just refers to “anything” in the air). The N95 ones look kind like a bowl, and they fit tightly to the face – so wearers have to have an initial fit test to find the right size and then another fit check every year. 

The trick of the respirator is to let air in (so allow all that oxygen, etc, to flow through) and let air out (you certainly don’t want to trap all that CO2 by your face!), BUT trap particles that are suspended in that air. It does this using special filters. These filters can capture particles and keep them stuck through intermolecular interactions, but only if the particles come into direct contact with the fibers making up the filters’ mesh.

And this leads to an interesting thing about respirators – they don’t just act as sieves, where it’s all about mesh size and bigger things get trapped better – instead, respirators work worst somewhere around the middle of the range, at the “most penetrating particle size” (MPPS). This is because different mechanisms are responsible for trapping the bigger particles and the smaller particles and neither is optimal for middle-sized particles

Big particles get trapped by inertial impaction and interception

  • inertial impaction: inertia is that whole “an object in motion stays in motion while an object at rest stays at rest” thing – big and/or heavy particles have a hard time “keeping up” as the airflow gets diverted around fibers, so they get stuck 
  • interception: a particle (going about its business as usual) runs directly into the fiber & sticks

The bigger a particle, the more likely it is to just run into a fiber. But what about the small guys? They rely on diffusion – small particles get bounced around by air molecules in the airstream they’re traveling in, knocking them “off course” and causing them to crash into the fibers.

Those 3 methods relied on “random running into” but there’s a fourth way a particle can meet the fiber – if it’s actually attracted to it – if the fiber is charged and the particle is oppositely charged, they can get “electrostatically attracted.”

The type of respirator we’ve been hearing a lot about is the N95 respirator. 95 is a performance rating that means that the masks “got an A on the challenge aerosol test” – they’re able to trap at least 95% of particles in a stringent test that mimics a “worst case” scenario. And the N? That tells you that it is Not oil-resistant. If you see an R instead of an N, that means’ it’s somewhat oil-Resistant. And a P? That means it’s basically oil-Proof.

But remember – those are for the health care workers – so if you have some you should be donating them!

As for the rest of us, our DIY face coverings can provide some protection *for others* BUT don’t let them lull you into thinking you can go back to business as usual if you wear one – keep up that social distancing! And, please, wash your hands before handling your mask, wash your masks, and don’t litter them!

more Covid-19 resources: https://bit.ly/covid19bbresources

more on topics mentioned (& others) #365DaysOfScience All (with topics listed) 👉 http://bit.ly/2OllAB0

2 Thoughts on “Respirators, masks, and more”

  • The graph of efficiency vs particle size shows a minimum efficiency of ~45% but the caption refers to N-95 filters.

    That seems to be contradictory information.

    Can you explain?

    • that graph is just an example of a filter from the CDC which I guess would be an N45? Sorry for the confusion

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