July 25, 2021 Update

Not all of this may be correct anymore with the Delta variant. Vaccinations are generally available in the United States and hopefully where you live. This is still your best bet. If you are eligible for vaccination and there is supply where you live, start with that.

Supply chains for respirator masks have mostly recovered at this point, so it’s a good idea to pick up a supply of N95 masks to have on hand.


We’re coming into winter 2020 and based upon wastewater data where I live in Eastern MA, infections haven’t been this high since the start of the pandemic: MWRA Wastewater COVID-19 Tracking.

Wearing a PAPR Wearing a PAPR

Your chance of hospitalization due to COVID-19 varies depending upon a number of factors, but even healthy adults have around a 1% chance of that happening, and we don’t currently know why. It’s currently speculated that similar infections could have built some degree of immunity, but we don’t know.

We know that universal masking does a good job at cutting the spread of COVID-19 by reducing the respiratory droplets that spread it, but there’s a significant amount of pandemic fatigue the longer that people need to keep up preventative habits, and getting 100% compliance with masking can be challenging.

We now have two vaccines that are known to work, but they will not be generally available until around April 2021 because high-risk groups and healthcare workers need to be vaccinated first.

At the moment, your best option is to stay home if you can. Barring that, you should wear a mask and wash your hands after going out. Note that hand sanitizer works in a pinch, but soap works really well, and you should prefer that when it’s an option. Ideally you avoid indoor spaces that are poorly ventilated for any length of time. Here is a good infographic that explains why.

Unfortunately, avoiding indoor spaces isn’t always practical. You might not be able to get grocery delivery or curbside pickup, or it may be impractical. If you need to do repairs to your home or a vehicle, you may not be able to avoid going inside a building, especially during the winter. For these things, you can wear personal protective equipment to reduce the risk.

Before I go into more details on PPE, remember that I’m just someone on the internet. Talk to an actual expert before doing any of the things recommended below. I’m writing this up partially for my own reference and partially because folks have asked about it. Hopefully you find this to be a good starting point.

Cloth Masks

A cloth face mask is the most basic option that you can get to filter the air that you both breathe and exhale. This isn’t really PPE, but it’s worth talking about here for comparison.

The CDC has recommendations on the type of masks that they recommend wearing. Unfortunately, there is no certification process in the US for a mask that complies with all of the recommendations. Meanwhile, France does have such a thing.

It’s difficult to find masks in the US that advertise complying with the French AFNOR Barrier Mask 1.0 (AFNOR SPEC S76-001) spec, but I’ve found that $10-$15 Lacoste masks are conform to it. These masks buy you lab-tested filtering capacity of 70% of solid or liquid particles up to 3μm.

Measured drop size distribution Measured drop size distribution

Given that a lot of the droplets are larger than 3μm when people cough and that many droplets are larger than 3μm when people talk, this mask provides reasonable protection for both the wearer and people around them.

These masks don’t save you from having to keep a distance of at least a meter apart, but they are about as good as you can get from a cloth mask.

For convenience, I tend to wear these during lower-risk activities, such as when I’m answering the door, going through a drive-through, or popping into a building for a minute or so to grab some food.

Disposable Respirators (Filtering Facepiece Respirators / FFRs)

The next level up is a disposable particulate respirator. These come in a variety of types, but the most common ones are N95 and KN95 masks. I think others cover this topic better, but the general gist is that the N95 is the US standard and the KN95 is the Chinese standard.

As an aside, if you’re asking why a mask that can filter 300 nm is effective against a virus that is 125 nm, remember that the virus does not survive long outside of a liquid, and the liquid particles used to transmit it are larger. The liquid particles will run up against an electrostatic charge on the outside of the filter and that’s what catches them. Here’s a video that talks about the physics if you’re interested.

If you have a mask made to spec, wear them tightly with no facial hair along the seals, and verify them with a fit test, then these are perfectly good for protecting you. The problem is that for KN95 masks in particular, it may be difficult to tell if they are coming from a reputable manufacturer. The CDC has a list of ones known to be effective, and it’s a good idea to consult this list if you intend to rely upon one. If you can find an N95 NIOSH certified mask, then that’s a pretty good bet, but those may be hard to come by these days.

Unfortunately the CDC does not really have the ability to test every single mask made by every single company, so you’ll need to do some due diligence before using them. One way to do this is via a qualitative fit test using sodium saccharin (a/k/a the pink sweetener packet, also called “Sweet ‘n Low”). This serves two purposes: validate that the mask is well fitting and that it is filtering as advertised.

Also note that there are also N100 masks, which filter more particles at the cost of making it harder to breathe through them. There are also masks that can handle oil (P) and are resistant to oil (R). These will also filter particulates just fine.

One last note: If you have a cool valve on your N95, you’ll want to cover your mask with another one (such as a surgical mask) or tape up the valve. You don’t want to get anyone sick in the case that you’re pre-symptomatic or asymptomatic.

Elastomeric Respirators

The next step up are your gas mask variety of respirators. You can get these in full-face and half-face varieties. These are nice because the filters tend to last longer and are easier to get tight fitting.

Before I go into this a bit further, you should know that many of the military surplus gear that you can buy for this purpose isn’t super safe. The materials may be degraded to where they are no longer airtight, and many of the old filters contain things like arsenic, asbestos and chromium. Much of it is inexpensive, but that’s for a reason.

The half-mask varieties (when fit properly) cover the same part of your face as the disposable masks, and it’s slightly easier to get filters for them right now. The main disadvantage to them is that you aren’t covering your eyes and the ACE2 receptor that SARS-CoV-2 uses is present in eye cells. It’s unlikely, but possible in theory to get it that way.

Looking at my local hardware store website, a half-face OV/P95 painting mask runs around $30, and a full-face OV/KN95 mask runs around $100.

One last point on this topic, most of these types of respirators have exhalation valves. You want to minimize the impact of exhalation on people around you, so if your elastomeric respirator does not clearly say that it is designed for covid-19, you should find the valve and filter/disable it.

Powered air-purifying Respirator (PAPR)

All of the other systems above rely upon a tight fitting mask or respirator. This makes them less comfortable, and means that you need to fit test them. For a full-face mask, you can’t wear glasses, and for both full-face and half-face masks, you can’t have facial hair. You also have to rely upon your lungs to pull air through the filter, which makes them less comfortable to breathe through.

A PAPR solves these problems. These work by using a blower to pull air through a set of high-efficiency (HE) particulate filters and create positive pressure inside some kind of headgear. The filtered air pushes itself out of the headgear so that you can breathe normally. You can get them in tight-fitting or loose-fitting variants, but I personally prefer the loose-fitting one. The loose-fitting one will bleed air out of the seams where it contacts your face.

You may be wondering how a PAPR fares compared to a surgical mask or cloth mask for protecting those around you. There is literature that indicates that a PAPR is as good or better than wearing a surgical mask in terms of spreading disease. There’s a group of doctors at a medical center in Brighton, MA who agree, but it’s not uncommon practice for healthcare professionals to still wear a surgical mask or N95 respirator underneath.

Brief History of 3M PAPRs and Comparison

A number of manufacturers make these units, but I’ve spent the most time researching 3M (formerly Racal Health & Safety) products, so I’m going to talk about those. 3M has a lot of different PAPR offerings, including 3M Scott and 3M Jupiter, but I mainly focused on the products in the 3M Powered and Supplied Air Purifying Respirator Systems Matrix.

If that seems like a confusing matrix of semi-overlapping products, it’s because it is. 3M likes gobbling up companies that make products in this space. Namely, Racal (Air Mate / Breathe Easy / Powerflow) and Hornell (Adflo). 3M designed built the GVP model a few years before it bought Racal and then Hornell. The Racal stuff lives on in the Breathe Easy, the Hornell stuff lives on in Adflo/Versaflo and of 3M kept the GVP system alive as well.

Which one to pick?

Are any of these systems better than another? Well, the Adflo/Versaflo stuff seems to be the least finicky to use. You push the start button, it can do a self-flow test and it can alarm on low battery or low flow. It’s a compact unit and comes with Li-ion batteries. The other systems are older, and therefore often available for less on eBay. All other things equal, the Versaflo is the easiest to use as a portable HEPA filter.

The GVP system and the Breathe Easy system both take cartridges. The GVP system takes a proprietary 3M cartridge and the Breathe Easy System takes what I believe is a standard NATO 40mm cartridge. They both operate off a Ni-Cd or Ni-MH battery, but there are adapter kits that allow them to use a Versaflo Li-ion battery.

I think GVP is really geared towards painting whereas the Breathe Easy (BE) is more geared towards towards first responders. The BE system is easier to find as surplus on eBay as a result of that. The main downside to the BE is that it has a marginally lower flow rate, and the battery situation. More on that below.

For the most part, all of these systems can be made to use the same headgear with the right breathing tube. The Breathe Easy does have some of its own, but those are mostly discontinued, so I’d get a Versaflo one (which requires a BE-324 tube).

In terms of filtration, all of these minimally operate as HEPA (P100) filters, though all but the TR-300 series have weird and wonderful filtration capabilities. You can buy filters to handle formaldehyde, ammonia/methylamine, different kinds of acid gasses, organic vapors, and other misc. gasses.

Most of these units even work on a plane, aside from the first-generation TR-300, which was fixed in the TR-300+, and possibly the Breathe Easy because I can’t find any specifications that says it does.

The Breathe Easy even has the FR-57 available, which is effective against certain chemical warfare gases, and is often available off surplus. They do point out that it is only rated for CS gas with a tightly fitting respirator, but a loose-fitting respirator is probably better than nothing.

Side note on the FR-57: This is the filter type that comes with the Breathe Easy CBRN kits stocked by first responders. Because first responders need to be sure that the activated carbon filter is still effective against somewhat dangerous substances, these things come vacuum sealed and have an expiration date. Once they are past the expiration date, many end up as surplus, but they are still perfectly good as a HEPA filter and often cost less. As a bonus, the activated carbon in the cartridge filters most nuisance odors, some of which can be particularly intense when you have air forced across your face (think your local fish market).

Versaflo Headgear

There are a ton of options for a variety of applications. For the purposes of just having a HEPA filter, which one you get isn’t super important.

For the most part, there are the M-series, which are plastic and have a visor, and the S-series, which are mostly soft and less expensive. There are some other Breathe Easy specific ones, but I’d just go with the Versaflo stuff because there is more of it available.

I generally prefer the M-200 series headgear because it’s durable and comfortable. It also looks like a spacesuit to the S-series beekeeper / semiconductor fab worker look. The M-100 series may still be available, but I wouldn’t pay more than it over the M-200 series.

Unless you need a hardhat, shroud, or are going for the Cobra Commander look, I’d probably avoid the M-300 or M-400 series because they are heavier.

The S-series stuff does tend to be less expensive, so you might buy some just to have on hand in case you damage the face shield headgear or want something that is disposable, such as for painting.

Breathe Easy Battery Fix

If you do pick up a Breathe Easy (BE), you’ll find that it’s hard to find the battery that is listed in the above matrix, and were you to buy a rebuilt one, that it weighs around 800g and requires a hard to find charger that 3M stopped making due to supply chain issues. The good news is that it only consumes around 500mA at 4.8V, which is essentially the same standard as any Li-ion USB battery pack.

If you have access to a 3D printer and want to non-destructively power the BE it’s not too hard to make a USB power adapter. If you want to make your own adapter or permanently change the plug, the left pin (facing you) is negative, the right pin is positive, and the third pin (on the bottom) is floating. There is an older video that makes a modification to the cable, if you’d like to see how that is done.

Other Safety Concerns

Assigned Protection Factors

One thing to note about all of these things is that they have different assigned protection factors depending upon the type. Nothing is 100% effective, there’s just relative protection factors. For example, the N95/N99/N100/FFP2/KN95 half-masks have an APF of around 10. A negative pressure full-face respirator and P100 has an APF of around 50. A PAPR typically has one of 25, in the absence of the manufacturer stating otherwise.

For the 3M PAPRs mentioned above, you can find a technical bulletin from July 2020 that has more specific numbers for different product combinations. Most of the combinations have an APF of 1,000, though they don’t specifically call out anything but the M-400 helmets, despite them being similar to the M-200/M-300 series. The main difference may be the shroud, but it’s unclear why this is the case.

The way to use an APF is to calculate the hazard factor for the dangerous area and then see if it’s above the safe level when the factor is used. This is tricky business. For COVID-19 in particular, the CDC points out that a higher APF is better, but doesn’t say what APF that you’d want. 3M notes that “safe exposure levels have not been established for biological particles.” but that “none can entirely eliminate the risk of exposure, infection, and illness”.

Recalled 3M Hoods

Many of the kits on eBay come with a BE-10BR Hood due to being first responder surplus. If you buy one of these kits, you should know that these don’t have the assigned protection factor (APF) of 1000 if they are over 10 years old or have a known bad valve in them. That’s not to say that they definitely won’t work, but it’s not a bad idea to replace them with something else.

3D Printed Parts

You might have noticed that I’m not talking about a lot of DIY 3D printed stuff. Certain things you can 3D print in a pinch, such as a face shield holder. This is nice when you can’t get another option, and can be sanitized in a pinch.

When you get to respirators, it starts getting a lot dicier. 3D printed parts are typically not airtight without some amount of finishing or very careful extrusion. I wouldn’t trust one to be airtight that wasn’t coated in an epoxy, but I would feel most comfortable replacing a temporary part with something that was tested.

Counterfeit Filters

Be aware that there are counterfeit filters available for sale online. Keep this in mind when you’re purchasing them online.

Intrinsically Safe

If for some reason you want to use this gear in a mine or some other place that has flammable gas, you’ll want to look for gear that labels itself as “intrinsically safe”. This is one of the more unlikely scenarios for me, so I haven’t really considered it, but you’ll want to research that for the Breathe Easy, GVP or TR-800 if this matters to you.


You should do whatever the manufacturer recommends for cleaning your unit, but I will point out that alcohol can weaken rubber seals. There is general guidance from 3M that you can use for cleaning. A good starting point is a BZK towelette for disinfection (~$10/100) and mild detergent for cleaning, but obviously defer to the instructions for your exact gear.

PAPR Donning Tips

You should read all the instructions that come with your PAPR unit, but there are some general things to keep in mind:

  • While a PAPR is loose fitting, it still needs to have positive pressure to work properly
  • It should ideally sit along a part of your face without facial hair, so you might need a clean neckline if you wear a beard
  • If you feel air gushing out, such as when you lift up the seal with your hand, then that’s probably not sealed properly
  • You should check it for cracks or leaks before putting it on
  • You should do a flow test and make sure that it’s at least putting out 6 cfm before use. If it’s not, may need to uncap a filter cartridge, replace the cartridge, or replace your battery or replace your blower unit.
  • If you’re using a battery bank that tells you how much power is remaining, it’s a good idea to check that it will last the amount of time that you need to use the PAPR

Hopefully you found this helpful, or at least entertaining. Feel free to leave any comments below, and stay safe out there.