User guide

Considerations

All about the filter

The models of reusable masks that I have used are 3M masks as they are a reliable brand and widely available in the Netherlands. But the underlying principles can be used for any brand of face masks. I cross-checked with 3M with their list of official resellers before buying a mask from an online shop. In practice you will find that the masks and filters are more readily available at paint, chemical and industry related online shops that medical supply stores.

First of all you want the mask to be compatible with a reusable filter otherwise you are going from a mask shortage to a filter shortage. In the asbestose industry they work for a month with a reusable personal filter. Also some people within the metal and chemical industry use a smell test (strong smell like terpentine or aceton) to ascertain that the filter still properly works.   I have reached out to 3M and they have not specified a certain amount of time you can reuse a filter as it depends on the concentration of exposed particles, type of room, level of ventilation and intensity of use. They have informed me that you can keep on reusing the filter until the breathing resistance increases due to filter loading (clogging of the filter from
captured particulates). However loading or clogging of filters is typically not an issue with airborne biological aerosols such as droplets containing viruses or bacteria. In the unlikely event of the filter clogging, you should replace it immediately. In a context of shortage there is still a possibility to reuse it even then as long as the filter has not sustained any structural damage. Set the filter aside for enough days for the virus to not be able to survive on the surface (adding one or two days for safe measure) before reusing it. 

They are several types of filter, the P2 has been found to be safe against COVID-19, but the P3 is better. Sometimes the filters are typed as P3R, where the R stands for reusable. In some countries instead of P3/FFP3 or P2/FFP2 they use the denomination P100 and P95 respectively. Take into consideration the connector between filter ans mask. The masks shown below all have a bayonet connector because they are compatible with a wide array of filters. For example the secure-click connectors can limit the amount of compatible filters you will be able to find if one type of filter is sold out in your country.

Lastly you will want a filter with a hard plastic casing. Filters that are exposed to the outside world without this protective encasement have a risk of being contaminated by sputum, blood or vomit and will then need to be discarded. Although they will provide the right amount of protection as long as they are P2 or P3, they are less durable and reusable as the filters with a hard outer casing and should therefore not be your plan A. I will link to the cleaning protocol from 3M for the masks and filters. The same principles can be applied for other brands if needed.

 

All about the seal

There are two major components for safety for mask use: filtration and leakage. It is therefore important to chose a model that is the right size. You can choose between small, medium and large with 3M, and you can find sizing aids online, the sizes have different number. For example the 6900 mask is the same as the 6800 mask but in large instead of medium. About 80% of the population will be good with a medium size. As with all masks: clean shaved gives a better seal. To check if the straps have been adequately adjusted to provide a good seal for you individually you can check de seal by inspiration while blocking the filter and expiration by blocking the expiration valve to give you any indication of leakage (see instruction video down below)

Glasses

If you wear glasses you will not be able to combine them with a full face mask without compromising the seal. The 6800 full face mask can be completed with a spectacle kit (6878/07141(AAD), but this is a costly solution as the kit retails at around 95 euro and you then still need to add your prescribed lenses in. Adding the price of the full face mask at around 160 euro, you will need to cash out about 350 euro. The simpler and more affordable solution is choosing a half face mask and combining it with goggles.

Full face vs half face

Full face masks have several advantages over half face masks. First off they protect the entire face, better than with half face with a face shield. One point of entry for the virus that you want to block is trough the tear ducts, witch a face shield does not. If you use a half face mask I would recommend using a googles that create a seal around the eyes, like the 3M GoggleGear 6000 series (around 23 euro). If you have very large glasses you can consider googles from Uvex. But even then part of your face will be exposed and at risk of secondarily contamination after touching your face. 

The seal tends to be better with the full face mask because it will be less affected when you talk. Also the sizing is less precise with the full face mask compared to the half face mask where variation in nose and eyes morphology can affect the seal more significantly. Simply put if you choose the wrong size for a full face mask it tends to be more forgiving than having the wrong size with the half face mask.

Furthermore the full face mask will be more comfortable to wear due to the pressure being distributed at the edge of the face rather than around the mouth and nose. Even so, I personally found the half face mask more comfortable than the disposable folding FFP2 from 3M due to a better pressure distribution by the silicone face seal, less breathing resistance due to a larger filter surface and less heat build-up due to the expiration valve. With prolonged use you will have some discomfort from pressure and can have some sweating where the silicone touches your face.

The only draw back of the full face mask is its price, especially if you wear glasses. But if possible, I would recommend using the full face mask.

Further Considerations

It is important to realize that reusable masks are made to protect only yourself from contamination, not your direct surrounding because the expiratory air is not filtered. In most COVID-19 wards that will not be an issue. The only exception being the OR where you do not want te be breathing down upon an open patient. It is possible to attach a standard surgical mask over the expiration valve in this setting (either by the cords of with tape). It may not be the best look, but it will do the trick. If you are able, you can get a more elegant solution by adding a 3D printed exhalation filter holder that can hold the surgical mask material either on the inside or the outside of the mask. To see several models that are available you can go to thingyverse and type: "3M (modelnumber) respirator filter". 

I believe it is handier to make the reusable mask personal, but if you have a disinfection protocol in place, you could also share it among health care workers in case of shortage. The filter is always personal and cannot be shared. 

Communication while wearing the mask is possible. I found that I could be easily understood, but that I had to raise the level of my voice a bit. If you are in a setting where you have te have extensive communication while being in full PPE and you dislike having to raise your voice for an extended periode of time, you might consider a wireless microphone that can be combined with the full face mask (as seen in the instruction video with an example of a full set).

Instructions

Cleaning and Disinfection

There are basically 2 steps for treating your mask after every use: cleaning off any contaminants with a soap solution and disinfecting it with a product that is effective against coronavirus. To clean the mask you can use a soap wipe (for exemple the 3M™ 105 Face Seal Cleaner) or immerse in warm cleaning solution of water and household soap, and scrubbing with
a soft brush until clean. Parts may also be cleaned in a domestic washer. CAVE: 3M mask should not be subjected to washers or water with a temperature above 50 degree Celsius. If you use a different brand always check the highest allowed temperature the mask may be exposed to. 

The CDC has a document for the disinfection in Health care setting and the EPA has a extensive list of disinfectants that are effective against coronavirus, including how long contact time should be. So you can chose what is most practical and available for you. The most used disinfectants are bleach or 70% alcohol. Solutions for immersion can be used for cleaning several times, but should be changed at least once a day.  

The hard case filter can be cleaned by wiping the outside surface with a damp cloth soaked in disinfecting solution until visibly wet for the appropriate contact time and then removing the disinfecting solution with a clean, water-soaked cloth and air drying. Do not allow the disinfecting solution to reach the internal filter media (so never hold it with the opening upwards while cleaning) and do not submerge the hard-case filters in the disinfecting solution or water.

EPA list CDC guideline 3M guideline
A Health Care  Workers guide to mainstream reusable FFP3 masks

Technical data

Here you can find the technical data for the different masks. Clicking the button will take you to the officiel 3M page and the technical data sheet can be found at the bottom.

There is also a list of compatible filters with bayonet fitting, hard plastic casing and sufficient level of protection against COVID-19. The 60921 till 60930 series is a combination of gas and particle filters. The casing is made of hard plastic, but there are some small openings witch could possibly be an entry port for contamination. As the openings are so small and angled away in practice the chance is very small unless a large amount of fluid gets on the filter. It also means that you have to disassemble the filter before cleaning and disinfecting the casing.