Homemade protective mask project

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Due to the COVIDpocalypse, there's suddenly a worldwide (and nationwide, and statewide) need for surgical masks and N95 masks. Current supply is not enough for the wave of demand that is rushing through US hospitals as of 2020-03.

Meanwhile, the rest of us need them, too. We should learn from the countries that experienced SARS earlier this century, and are generally faring better than most other countries experiencing the SARS-CoV-2 pandemic now. We should also learn from studies that have been done on various aspects of this problem, rather than just taking something off the shelf and hoping it works.

Even the CDC has ultimately admitted that in a “crisis capacity” situation, homemade masks are an option. Their definition of “homemade masks” is things like bandannas and scarves; we can do better than that.

Commercial PPE

Personal protective equipment (PPE) for hospitals is regulated, and the stuff health care workers (HCWs) are supposed to use is regulated and standardized/specified.

With regard to protective masks, there are three basic kinds:

  • Surgical mask: Loose-fitting, tied round the back of the head.
  • N95 respirator: Tight-fitting, roughly dome-shaped singular piece of filter paper/fabric specified to filter (block) 95% of particles 0.3 microns in size. These masks have a metal nose-piece that the wearer should form to their nose, and two elastic bands that are meant to go over the crown of the head and the base of the neck, in order to form a seal around the edge of the mask. Accordingly, there are also standards for keeping facial hair shaved where the edge of the mask makes contact, so the diameter of one's facial hairs does not become the width of a gap.
  • Cartridge respirator: Often labeled as “P100” (a designation similar to N95 but different in ways that aren't relevant here). Here, the respirator is a hard plastic reusable enclosure, and the filters are cartridges that one changes out from time to time (e.g., when visibly dirty or when breathing is difficult). These are used more in construction than health care.
  • Face-shields: Made of a headband and a full-face clear plastic window that flips down. Probably the most reusable option, though often used in complement with a surgical or N95 mask.

Surgical masks and N95 masks are normally treated as consumables: wear for some limited time, then dispose of as a biohazard. But given shortages, we're quickly going to see HCWs reusing the supplies they've got, all while getting priority on all supply being produced—so don't expect to be able to buy these at retail for awhile.

Requirements

Safety

“First, do no harm” is the golden rule whenever doing anything medical, including making (essentially) medical equipment.

The biggest hazard with masks is hypoxia. If the material does not permit gas exchange, it will trap dead air (CO2) and not admit fresh air, and the wearer will gradually become more confused as they breathe in their own exhaust and blood oxygen saturation (SpO2) drops.

Effectiveness

The material must permit gas exchange, but not be too permissive; it must also function as a filter. Nor should it be so occlusive that exhalation pushes the mask out and creates an opening for unfiltered air to enter.

These two properties are called filtration efficiency (percentage of contaminants blocked) and pressure drop (difference in fluid/air pressure between the outside and the respirating wearer's side).

It must be said that perfect is the enemy of the good, here. We're necessarily not working to the standards of commercial PPE; that would require specialized material (non-waven polypropylene fabric) and equipment (heat-sealing rather than sewing) that we don't have. It's OK for a homemade mask to be not as good as real PPE; it just has to be better than nothing, and not a false sense of security or actively harmful.

The fact that we're mainly concerned with droplets means N95 is not a goal. We need to catch and block droplets; virus particles should be blocked in the process. We're also not trying to pass an N95 fit test; the design will mimic that of a surgical mask, not a respirator.

(There is also the option of wearing a reusable mask over a commercial N95 mask, to prolong the life of the latter.)

Ability to obtain materials

Even on a good day, non-woven polypropylene is not something you find at your average fabric store. The sort of materials we're most likely to have on hand include:

Body materials

  • quilting cotton
  • denim
  • canvas (e.g., duck canvas)

Nosepiece

  • floral wire
  • pipe cleaner (might be hard to get in bulk)
  • paper clip, straightened

Earpieces

  • string or twine
  • ribbon
  • lengths of scrap fabric, turned into a tiny sleeve of appropriate length
  • elastics

Other materials and equipment

  • cotton or polyester thread
  • sewing machines
  • wire cutters for floral wire (note: beware of sharp points; you may need to fold them over with needle-nose pliers)

We're hampered by the shelter-in-place orders: most fabric stores are probably not open. Delivery may be an option, and Cliff's Variety in the Castro (which is also a hardware store, and thereby “essential” under at least the City's order) is still open. So we're limited to whatever supplies we've got on hand.

This requirement also means using materials rather than off-the-shelf finished parts such as commercial filter cartridges. You can buy cotton fabric from lots of places (even if we can't), but the WidgetDyne 9003A (not to be confused with the 9003B, which is incompatible) could become scarce quickly.

Not subtracting supply from commercial masks

Supposing we did buy a roll of non-woven polypropylene, that would be a roll that wouldn't go to making certified masks. Masks we make for the benefit of ourselves and others shouldn't come at the expense of someone else's.

This also applies to things that are spare parts for medical equipment, such as air filters for CPAP machines. The CPAP machines already need those.

Ease of production

Novices and intermediate sewists who aren't familiar with sophisticated patterns may have trouble cutting out and sewing curved pieces. Simpler construction—e.g., from rectangular pieces—will streamline construction (as well as improve material efficiency).

Demand points

When we make masks, we need to think of what demand—i.e., whose need—we'll be addressing. (Making masks without addressing someone's need is a waste of time, labor, and materials.)

  • Average/not-yet-infected wearers seeking everyday protection when they have to break isolation
  • Patients receiving oxygen (freeing up real surgical masks for elsewhere in the hospital, or possibly vice versa depending on how the facility chooses to approach this)
  • HCWs extending the lifetime of their N95s by any means necessary/available

What we know about making masks

This is a list of studies of homemade masks, improvised masks, and mask reuse on which to build a basis of knowledge for those of us who aren't HCWs to work from.

  • Simple Respiratory Mask “can provide a good fit and a measurable level of protection from a challenge aerosol”.
    • Made by cutting out and assembling pieces of “A Hanes Heavyweight 100% preshrunk cotton T-shirt … [that] was boiled for 10 minutes and air-dried to maximize shrinkage and sterilize the material in a manner available in developing countries.”
    • Structure is similar to an N95 mask, with two arms that fasten around the head. Unlike the elastics of an N95, these are fastened in opposite places; the lower (jaw) arm is fastened atop the head, while the upper (cheek) arm is fastened round the back of the head.
    • “When made by naive users, this mask may be less effective because of variations in material, assembly, facial structure, cultural practices, and handling. No easy, definitive, and affordable test can demonstrate effectiveness before each use. Wearers may find the mask uncomfortable.”
  • Simple respiratory protection--evaluation of the filtration performance of cloth masks and common fabric materials against 20-1000 nm size particles. Tested “five major categories of fabric materials including sweatshirts, T-shirts, towels, scarves, and cloth masks”. “Results obtained in the study show that common fabric materials may provide marginal protection against nanoparticles including those in the size ranges of virus-containing particles in exhaled breath.”
  • A cluster randomised trial of cloth masks compared with medical masks in healthcare workers: Confirmed that reusable cloth masks are not nearly as good as disposable masks properly disposed of: “Moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection.” “… the finding of a much higher rate of infection in the cloth mask arm could be interpreted as harm caused by cloth masks, efficacy of medical masks, or most likely a combination of both.”

[This list is incomplete. You can help by expanding it.™]

Possible filter media

  • Scraps from N95 mask or surgical mask: Violates the rule of not subtracting supply from commercial masks. If we have N95s, we should simply donate those to mutual aid efforts to collect N95s for HCWs.
  • Coffee filter: May not have enough filtration efficiency; coffee filters are pretty porous.
  • HEPA filter: Tends to be more of a cartridge form factor, but may be fine with a sufficiently thin filter (or unbothered wearer). Often some variety of these is used in hard-enclosure designs.
  • Scraps from a vacuum cleaner bag: Interesting prospect. Vacuum bags likewise are made to pass air but block particles (normally dust).
  • Paper towel: The HK Mask site says this is pretty occlusive (note the pressure drop for “kitchen paper”).
  • Facial tissue: The HK Mask site says one layer is pretty good at pressure, but bad at filtering 0.3µm particles. OTOH, a facial tissue may work way better at catching droplets…
  • Plain old fabric: Most designs take this option, leaving it to one or more layers of fabric to do the work of filtration.
    • Denim or canvas: Tighter weaves mean more occlusion and filtration. These would need to be tested to ensure they're suitable and better than nothing.

Materials that definitely won't work

Production safety precautions

Making masks, especially for others (e.g., to donate to a donation drive), is something that needs to be done with attention to cleanliness of the finished product and any packaging it's carried in between the fabrication point and the delivery.

You're making these masks to keep people safe; you do not want your masks to become a vector.

Strategy #1

  • If you bought any fabric recently (after community transmission of the virus started), consider basting a rolled hem at the ends and then washing it.
  • For thread and other materials, you'll have to figure out a way to disinfect it. Leaving materials around for a few days is one way; virus does not remain viable indefinitely.
  • For floral wire or other stiff metal, you might be able to wash it with dish soap or all-purpose cleaner. (Probably not an option for pipe cleaners.)

Strategy #2

  • Throw finished masks directly into the washing machine (or, if you're nervous about your nosepiece material escaping and wrecking the machine, hand-wash them in a bucket).

Common elements

  • Clean any containers you'll be keeping this stuff in with all-purpose cleaner or disinfectant spray.
  • Clean work surfaces, your sewing machine, etc. with APC/disinfectant.
  • Wear a mask (either the first one off the line, or a commercial mask) during cleaning and any production runs.
    • If you wear the first mask off the line, you'll have to re-sanitize your machine and materials after you finish it, since all of that was just in close contact with someone who wasn't wearing a mask.
  • WASH YOUR FUCKING HANDS before handling anything clean. Don't waste your cleaning/disinfectant efforts.
    • Also, wash your hands after handling your own mask, including putting it on or taking it off.
  • The same goes after production is done. Keep the box clean, clean anything it's going to touch (maybe put the box into a washable bag or basket or bucket before putting that into your car trunk), don't set it on the bus seat, etc.

Known patterns

There is a much longer list of known patterns maintained by the OpenCovid19 project, so this list will focus primarily on mask patterns published by HCWs and health care facilities.

Delivery options

Making masks, by itself, does not alleviate a shortage. They need to be delivered to relevant demand points to relieve that demand and free up supply that is contended for by other demands.

Organizing delivery efforts is beyond the scope of this document, but here are some ideas you can get started on (or seek out people who are already doing these things):

  • First off, make a mask for yourself, everyone in your household, and extended family members.
  • Friends and neighbors may be your next recipients. Remember to practice social distancing; consider arranging a pick-up spot or something along the lines of a Little Free Library but for homemade masks.
  • HCWs and other front-line workers may be seeking masks. Seek out existing donation drives first before you reach out to a facility to bother them with what might be the thousandth “do you need my homemade masks?” inquiry that day. KQED and Mission Local have donation drive lists for the Bay Area.
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