Masks

• Summary
• Masks Use Cases
• Mask Handling for different Use Cases
• Mask Effectiveness
• Mask Types
  • Filter Performance
  • Usage Classes
• Mask Reuse and Cleaning
  • Cleaning Methods
  • Reasons for Clean Masks
  • Mask Recommendation
• References
• Appendix: Personal Mask Preferences
  • Tips & Tricks
  • Personal Mask Preferences
  • Personal Mask History

Summary

• Effectiveness: Mask reduce the transmission by half or more.
• Types: For reliable self protection dense mask with a good fit are important and sufficient in most situations.
• Use cases: Mask in general used public settings reduce the transmissions enable a more individual handling in private/voluntary settings.
• Handling: To protect others it is important to change the mask frequently (each 2 hours). Masks can be reused later.

Masks Use Cases

• Wearing masks in confined spaces helps to reduce overall transmission during waves.
• Wearing masks in public spaces helps to keep transmission rates low in these settings, so in private settings the handling of Covid can be individual.
• Dense masks with a good fit offer reliable self protection.

Mask Handling for different Use Cases

• For self protection, a good fit and a good outside-to-inside filter are important.
• In indoor rooms with aerosol transmission:
  • frequent changing/cleaning the masks is necessary to prevent the spread of aerosols, especially for low and mid filtration masks
  • high filtration masks are needed to reliably filter aerosols
• After coughing or sneezing into mask changing is needed (one should not cough into a mask but cough into the hand/handkerchief and downwards, then the hand should be washed or disinfected; moreover with heavy cough and without a negative Covid test, ideally one is out of public spaces). After speaking a lot into a mask, changing is appropriate. Especially for low and mid filter models.
• To avoid person to person droplet transmission e.g. when speaking, wearing in close distance face-to-face situations is necessary.
• Some mask have a big air resistance combined with a loose fit, in that case the air bypasses the mask. These are like wearable plexiglas: There’s still protection against droplets, but the bypassed air contains aerosol.

Mask Effectiveness

• Reduction upon exhalation is likely lower than in experiments Reasons: Most lab experiments are done with fresh masks and not with masks used for several hours. Long worn (cloths) mask even could have a spray effect for the aerosol spread: accumulation of exhaled breadth condensate in the inner side/layers of the mask and then spray like release upon strong exhales such as shouting.
• The effectiveness is likely better for inhalation than for exhalation. The air is exhaled often at higher speeds than inhaled and the air exhaled is directed => higher air pressure difference upon exhalation on the filter (The filter performance in turn decreases with higher pressure differences).

• Milton et al. measured the influenza viruses spread from patients with and without wearing a surgical mask. They found:
  • Particles greater than 5 micro meter: Surgical masks nearly eliminated viral RNA detection in the coarse aerosol fraction: resulting in a 25 fold reduction in the number of viral copies
  • Particles smaller than 5 micro meter: statistically significant 2.8 fold reduction in viral copies detected in the fine aerosol fraction.
  • Overall: Surgical masks significantly reduced the overall number of RNA copies by 3.4 fold.

  Assuming a reduction of exhaled particles by a factor of 2 (50% reduction) and a reduction by a factor 2 (50% reduction) for inhaling: everybody wearing a mask yields a total reduction factor of 4 = (2 times fewer particles inhaled) * (2 times fewer particles in the air since fewer exhaled) for aerosol transmission. This can yield a significant reduction of transmission in public indoor rooms (e.g. Supermarkets or Public Transport).

Mask Types

Mask can be classified either by

• Filter Performance How good is the filter?
• Usage Classes What is the intended usage?

Filter Performance

The filtration performance specifies how much and which particles are filtered out of the air at some fixed airflows and pressures. There are various standards to classify mask by their filtration quality: E.g. in Europe the FFP norms, in the US N95/P95 (e.g. Wikipedia page on FFP standards). High filtration is the safe option in situations with aerosol transmission.

• Very High Filtration

  FFP3

• High Filtration

  FFP2

  FFP2 (Europe), N95(US), KN95(China). (Correctly tested & certified) high filtration mask also have a good fit, since if the air sidelines the mask, no aerosols are hold back regardless of the filter (droplets are still hold back).

  • N95 (United States NIOSH-42CFR84)
  • FFP2 (Europe EN 149-2001)
  • KN95 (China GB2626-2006)
  • P2 (Australia/New Zealand AS/NZA 1716:2012)
  • Korea 1st class (Korea KMOEL - 2017-64)
  • DS2 (Japan JMHLW-Notification 214, 2018)

• Intermediate-High Filtration

  FFP1

  Most models are for dust protection.

• Intermediate Filtration

  Surgical Masks

• Low-Intermediate Filtration

  Textile mask often have low filter performance. They prevent the droplet exchange when face-to-face talking and offer some self protection regarding aerosols. However, they do not prevent the spread of aerosols, which is important in indoor rooms if possibly infected. Indoors where aerosol transmission is likely low filtration masks shouldn’t be used to protect others.

Usage Classes

• Dust Protection Masks

  Protection masks against dust are constructed for outside-in protection and therefore good for self protection. Sometimes they have valves which let out the air unfiltered i.e. no inside to outside filtration protection. Thus masks with valves offer protection for the wearer only and not for others. Dust mask exists for all mid to very high filter classes including all FFP filter classes. The fit is usually good and the comfort ok.

• Medical masks

  There are two types of medical mask.

  • Surgical Masks

    Surgical masks are constructed for comfort and the focus is on inside to outside droplet protection (during surgery, the body is open and so there is no skin protection). Mainly larger particles such as bacteria are filtered. They cover the entire mouth area to prevent nutrition rests or face hairs falling down. Usually they are very flat and don’t look muzzle like which is bad since the air pressure isn’t evenly distributed across the filter especially when mouth breathing/talking (the pressure peaks before the mouth and much of the airflow then gets a sideway momentum).

  • Medical protections masks

    Medical protections masks are constructed to protect medical staff against pathogens from infected patients. These masks are usually in a high filtration category such as FFP2 and offer good protection for all pathogens including viruses.

• Textile Masks

  Textile masks or Community masks are available in a lot of sizes and styles. A model with fitting comfort and style is usually available. The filtration performance is often low. The droplet spread is prevented but how relevant the droplet spread is, is unclear.

Mask Reuse and Cleaning

Cleaning Methods

The coronaviruses virions are not very stable especially if exposed to disinfectants, sunlight, soap and temperatures above 45 degrees (-> Page Virion Viability). So making a mask ‘coronavirus clean’ is easy:

• wash: wash with soap/hot water/machine-wash.
• heat: heat to around 70 degrees for 20 minutes e.g. hot water, steam or in the oven - all measures which have been scientifically proven to destroy the Sars-CoV-2 viruses and leave the mask intact [citation coming] Chan et al. have shown that Sars-CoV-1 is inactivated above 50 degrees.
• sunlight: if washing or heating is not available (e.g. water saving in dry areas or camping), putting the mask to the bright sunlight is an alternative in areas with intense sunlight.
• disinfect: spray with pure alcohol (not alcohol with additives which some cleaning products have). Other disinfectants are not recommended since they may have health hazards if inhaled.
• waiting: Usually half of the virions decay during several hours at room temperature (i.e. the halflife time is several hours). Thus the next day (or even better a few days) most virions are not infectious anymore.

Reasons for Clean Masks

The mask effectiveness is usually evaluated with fresh masks and not with mask worn for several hours. The problem if the mask is continuously worn for several hours is, that virions can be slowly breathed through the filter, which occurs more at exhalation than inhalation (mask effectiveness). Therefore masks should regularly be changed or cleaned. Even rotating a bunch masks through each day and reusing them the next day helps. Wearing the same mask as short as doable especially if its about protecting others.

Mask Recommendation

””” // written in Spring 2020

Officially recommend masks for spread reduction in indoor rooms. Without an official recommendation, people can be put off or look afraid of masks, at least [were] in Europe, which is not desirable, since masks are protective.

Reasons against masks seem sometimes rather searched:

• touching more often the face.

  Infection is not possible by touching the skin alone, this is true for the skin in the face too. Touching into the mouth or the nose is something else, but for this, masks are protective.

• Reserve for healthcare workers is needed for the big wave.

  If masks help to prevent the big wave in its roots, then that’s the better option.

”””

A third argument was, that the evidence of the usefulness is not yet strong enough for an official recommendation.

13.12.21: Looking back when the situation is judged unclear to withhold an official recommendation - from a health authorities perspective - seems reasonable.

References

milton2013

Milton, D. K., Fabian, M. P., Cowling, B. J., Grantham, M. L., & McDevitt, J. J. (2013). Influenza virus aerosols in human exhaled breath: particle size, culturability, and effect of surgical masks. PLoS pathogens, 9(3), e1003205. https://doi.org/10.1371/journal.ppat.1003205

Appendix: Personal Mask Preferences

Tips & Tricks

• Carefully rounding the wire above the nose helps to reduce the airstream to the eyes. Works best before putting the mask on.
• Putting the masks a couple of hours to the fresh air before wearing reduces smells. Fabric smells can indicate volatile substances which may not be healthy to inhale (although I don’t think these substance are any more hazardous than other substances we are daily exposed e.g. micro-plastic from car wires).
• FFP1 masks of fold type and surgical masks to my experience become more comfortable with use since they loose their stiffness. As noted mask shouldn’t be continuously over many hours; better to switch masks and reuse the next day.

Personal Mask Preferences

(December 2020 through May 2021)

• June to December 2021: Colorful surgical masks from CPS MASK (Type2R, EN 14683, distributed by Pro Dimi Pharma GmbH & Co, made in Turkey by CPS Pressform SAN). These masks are somewhat narrow which makes bypassed air passing on the sides instead of reaching the eyes) but the fit is quite dense and so - to my judgement - overall no more air bypasses than for ‘normal’ surgical masks. As a fallback for sensible situations: FFP2 (CX9501 or similar).
• April to June 2021: Often FFP1 masks of fold type, currently the model CX9501 (made by Jiangsu Sanfo Outdoor Products Co, Suqian, Jiangsu, China and sold for about 1$ at Migros). This mask has some foam protection above the nose which prevents an airstream into the eyes and provides comfort. Also behind-the-head clips are supplemented. The masks have a fabric when opened, open the package at least a day ahead of usage helps to reduce fabric smelling. Sometimes I also use surgical masks for day to day use.
• December 20 to May 21: Especially longer time periods (more than about half an hour e.g. during train travel): I mainly use FFP 1 dust protection masks (3M 8710 E made in Wroclaw PL; about 1$ a piece). The filtration requirements for FFP1 masks is less than FFP2 masks but stricter than surgical masks. To my judgement the 3M 8710 E model does protect others from very fine aerosol as good as FFP2 models. Nevertheless I recommend FFP2 models if infected (tested or strong evidence) if transmission opportunities can’t be avoided. Advantages: As for most dust protection masks, the fit is dense due to bands behind the head. They wear about as (un)comfortable as ski googles: tight but ok. Breathing is easy and there’s no sidelined air into the eyes. Drawbacks: Taken on/off is cumbersome, for short time usage I prefer surgical masks. As most dust protections masks, the 8710 E don’t look fashionable.

Early Summer 2021: [Dense] masks are less important if cases go towards zero (e.g. in summer). But there are also good reasons to continue using masks in certain indoor public spaces (e.g. large shopping centers, crowded public transport, airplanes). Not necessarily in facultative places (e.g. offices or libraries) and probably not a general mandate since there are miles between going to the next door shop/office and taking some international flight. One reason is, masks also reduce the spread of the other respiratory diseases:

• When mainly SARS-2 is around causing cough, it is much easier to detect outbreaks and take adequate precaution steps upon infection.
• Respiratory pathogens are sometimes underestimated so reducing the circulating strains, is a nice [side] effect. 28.11.21:depends on the virus type some are disease and some not disease associated (->Human virobiota).

Considering infections with other viruses and since both a past infection and vaccination seem unlikely to provide a reliable future proof protection against transmissions, there is no reason to make masks exceptions when it’s about protecting others (However past infections reliably prevent severe Covid and vaccination also do a good job at preventing severe Covid).

Personal Mask History

1. Started with FFP2 dust protection masks from a hardware store. Even though they weren’t made from cloth they felt like. Officially these masks weren’t washable but hand-washing with soap worked. The masks had a dense fit. However, the fit came at the cost of a reduced comfort: very tight bands around the head and not really comfortable at the nose. // Looking back this masks were bad (back then I didn’t know much about masks):
   • a very similar/even the same model was shown to have incorrect declarations and to fail both tests and specifications.
   • a direct (subjective and not scientific) comparison to the FFP2 masks of 2021, the 2021 models have much better filters.
2. In summer 2020 I bought some cloth mask but I didn’t like the fit since there was no fixation above the nose. I went to the hardware store to get some other dust FFP2s, however these were sold out but instead they had cloth masks. These had a good fit and were comfortable and I used them during summer.
3. In autumn when (evidence for) aerosol transmission increased combined with reports that many cloth mask were not dense enough, I went on to surgical masks. There are differences between the models of surgical masks: some are easier to breath through while others more air sidelines by the nose/eyes, which can be distracting.
4. Over the winter I tried different ‘Covid edition’ FFP2s. The bands usually went around the ears and so the fit was not very tight. The loose fit combined with dense filters sometimes produces purpose defeating and uncomfortable sidelined air. But usually no more than surgical masks, so overall the protection from FFP2 masks is better, even at decreased comfort (//back in late 2020).
5. Around christmas time I went once again to a hardware store to buy some dust FFP2. Sold out FFP2 dust masks again, but dust FFP1 were available. They fit and are in use since then (Introduction statement).
6. In spring 2021 I started using FFP2 masks of fold type. They are widely available to ok prices (about 1$/piece) and the breathing ability is good by now.
7. In summer 2021 I moved to (colorful) surgical masks since transmission of severe Covid is very low.
8. Autumn 2021, I mostly stayed with colorful surgical masks from CPS MASK (Type2R, EN 14683). As a fallback for sensible situations, FFP2 of fold type (CX9501-P).
9. Winter 2021. Similar to autumn, but with the advent of Omicron increasingly FFP2s e.g. in crowded settings.