One of my Christmas presents was a mask. A thoughtful present, although a mask as a Christmas present says a lot about the sort of year 2020 was. Anyway, the mask’s packaging makes a number of scientific-looking claims, and as I have been working on understanding how masks work (preprints here and here), I thought I would go through them. Maybe the manufacturer of your mask makes similar claims.
The claims on the packaging are:
- It claims “>90%” for “Filtration PM3.0”. I think this means it filters out at least 90% of particles 3 micrometres across. Konda and coworkers have measured the filtration of particles of this size for a number of masks. 90% looks about equal* to a that of a surgical mask, and to some of the better cloth masks, so this looks both reasonable and pretty good. But this is for the air passing through the fabric of the mask. This mask, and other masks that we the general public wear (unlike the ones worn as part of PPE by health-care workers) don’t fit that well – there are gaps around the edges where air escapes. These gaps are likely to result in at least 10% and maybe more like 20 or 30% of the air going around the fabric of the mask, not through it. So the efficiency of filtration of particles 3 micrometres across is determined at least as much by how well your mask fits, as by the fabric of the mask. For a mask with say 20% of the air going around it, the filtering efficiency is going to be a bit less than 20% for 3 micrometre particles. Professional PPE masks — USA names N95, and EU/UK** name FFP2 — are not only made of material that filters better, when properly fitted as part of PPE, they fit much better around the edges, so much less air escapes there, which matters.
- In a comparison table, they also clam that the professional PPE masks filter out “>95%” of particles 3 micrometres across, i.e., 5% higher efficiency than their mask. Konda and coworkers find that these professional masks filter > 99% of particles of this size, and although 99% is indeed > 95%, I think the packaging here significantly understates the difference between their mask and a professional one.
- I would guess that the manufacturers have carefully chosen the particle size of 3 micromeres. Filtering out particles of that size is pretty easy — for reasons to do with some nice physics I have talked out in earlier posts. The standards for N95/FFP2 PPE masks are based on filtration efficiency not for 3 micrometre particles but 0.3 micrometre particles, which are much harder to filter. The virus SARS-CoV-2 is about 0.1 micrometres across, so particles much smaller than 3 micrometres can be infectious. Although we don’t know what fraction of infections are causes by these small particles, it may be quite a high fraction.
- The packaging claims “Water repellent technology: Repels droplets containing viruses”. For a product whose purpose is to filter out and trap droplets containing viruses, this is an eccentric claim. Fortunately, I don’t think the fibres inside the mask do actually repel the (mainly water) droplets containing virus. I think the droplets will stick to these fibres on contact and be filtered out.
- “Proven to reduce COVID-19 activity by 99.5% on contact. Tested according to ISO 18184:2019”. I don’t understand this claim. The ISO standard 18184:2019 does not appear to be available unless you pay and I am too cheap to pay. But apparently: “ISO 18184:2019 specifies testing methods for the determination of the antiviral activity of the textile products against specified viruses. Due to the individual sensitivities, the results of one test virus cannot be transposed to other viruses.” The SARS-CoV-2 virus is delicate, but I have not seen any claims in the published literature of surfaces that destroy the virus on contact. There is debate on how long lived the virus is once it has been breathed out, but it seems likely that the virus decays over maybe an hour or a few hours, on any surface, but is not inactivated on contact. Viruses are inert except when they are actually inside a cell they are infecting, so you can’t coat a surface with something to poison them, as you can with bacteria. So if you tell me that 10 hours after sticking to the fabric, viral activity is down by 99.5%, then OK I would believe that***, but I do not understand how contacting a surface would instantly reduce activity by 99.5%.
- “High Particle Retention: Tested according to EN 14683:2019”. Again this standard may not be available unless you pay but I think it is basically a standard for surgical masks, so maybe 90% filtration of 3 micrometre particles is enough to reach this standard, but am guessing a bit here.
- “Contains Dimethyloctadecyl Ammonium Chloride”. Despite having obtained a PhD in a chemistry department, this is not my speciality, but I don’t think this molecule exists, or can exist. However, Dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride does exist and has I think antimicrobial uses, i.e., can be used to resist bacterial infection. As far as I know does not work against viruses.
To summarise, I am not sure that all the claims make sense, but some of them I can’t really check. It is disappointing (but not the fault of the mask manufacturer) that the standards are not freely available. Given how many people in the world are wearing masks, and given that their use is, at least in some circles, controversial, some publicly available standards for masks/face coverings might be a good idea.
If you are wearing a mask, and I think you should be, then maybe you found this useful. Comments below are open if you have scientific-looking claims for your mask, that you don’t fully understand.
* There is quite a lot of scatter in the data of Konda and coworkers, some of their measurements found higher efficiencies for surgical masks.
** Although we are now apparently a proudly independent sovereign nation, the UK is I think still rule taking from the EU here.
*** But it would also be true the virus circulating in air for hours would also be greatly reduced in activity.