A FIRST STUDY ON THE SUBJECT
A first scientific study on the effectiveness of face protection visors demonstrates their effectiveness (link to the complete study here and at the end of the article). Conducted by scientists from the IIBR (Israeli Institute for Biological Research, one of the leading centers on Covid-19 and other topics, see here), this first serious study published on the MEDRXIV website (awaiting peer review) highlights the complete protection of the face provided by face shields compared to masks.
Even better, and this may surprise some, this study suggests that face shields are 10 times better at protecting against fine particles (0.3 microns and above) than commonly used disposable masks.
"Also, despite the considerable scatter among different repetitions, the clear advantage of face shields in comparison to medical masks is evident. While the medical mask reduces the number of inhaled particles by roughly a factor of two, the face shield provides better protection and blocks more than 90% of the otherwise inhaled particles." (page 12 of the study)
In addition, the study shows that the visors provide better protection from sprays, which commonly range in size from 0.8 to 1.8 microns, likely to carry much farther than the very fine 0.3 to 0.8 micron droplets, which evaporate very quickly and are short-range, and therefore not very dangerous unless they are exchanged very closely.
The study also shows that the limitations of almost all face shields: the lack of serious protection from projections coming from above and from the sides, typically at the forehead, for example for a user sitting facing a standing interlocutor.
TO FULLY UNDERSTAND THE SUBJECT
It is worthwhile to recall some essential data on the elements addressed.
First of all, concerning particles, aerosols and droplets:
an aerosol measures between 0.3 and 5µm
a droplet more than 10µm ;
an individual who speaks / breathes emits essentially particles from 1 to 3 µm;
Covid-19 particles measure between 0.06 and 0.14 µm when they are not carried by an aerosol or a droplet. If they are carried, then the size of the aerosol or droplet is important.
Concerning the different types of masks :
the surgical mask (EN 14683 standard, European directive 93/42/EEC, for reference and sources) only protects against droplets (>10µm) since it is only standardized to protect against aerosol particles >3µm, with 95% filtration at this size only, and much, much, much less for particles of - 2µm ;
the FFP1 mask (EN 149 standard, European directive 89/686/CEE) protects from droplets AND particles, in the proportion of 80% of aerosols >0,6µm, with 22% max of leakage towards the inside;
the FFP2 mask (also EN 149 standard) protects against 94% of the same aerosols >0.6m, with a maximum of 8% inward leakage.
All this assumes that the mask (whatever it is) is perfectly worn, with a correct seal at the edges, a satisfactory conformation to the face etc. This is far from being the case, as we can all see in the street every day.
A PVC screen of only 200µm, which does not even meet the EN 166 standard, stops more than 90% of the droplets and aerosols that come to crash into it, and diverts the rest downwards, to clothes and the ground (Edit: see video section "To go further") . Droplets which will crash there almost entirely, aerosols which will partly crash there and partly slide by the air around (hence the interest to switch to the mechanics of the flows to see how such or such visor works), particles whose behavior around the visors had on the other hand never been studied, until this Israeli study.
NOT ALL VISORS ARE EQUAL
The study clearly reminds us that not all visors are equal, and that the vast majority of them offer a level of protection from the top and the sides that is clearly insufficient, with the particles entering the unprotected areas, especially the top, being diffused all over the back of the visor. A very frequent case, and not only between a seated and a standing person.
These limitations do not concern PROFASTER ALPHA, the only visor model approved at the end of the official French Covid-19 call for projects, ahead of nearly a thousand other proposals (and whose STL files for printing are freely downloadable online, see below), which, thanks to its additional protection and its particular geometry, blocks more than 95% of the projections arriving by the top and the quasi totality of the side projections, thus offering a level of protection without equal compared to the other visors, in particular those tested within the framework of the approached study. All this while offering a much lower printing time and material cost for the makers than most of the widespread models, as PROFASTER ALPHA can be printed in 10' on a 0.4mm nozzle with only 5.5 grams of material (PLA).
WHAT THIS STUDY COULD CHANGE QUICKLY
The reading of this background study reveals that wearing a visor would be much more advantageous for the general population, which is not directly exposed to a high viral load, contrary to healthcare workers where the surgical mask + visor combo, or the FFP2 solution, is preferable considering the risks (Edit: see below "To go further" for sourced data on the performances of different types of masks and their adequacy to such or such problem).
This is particularly interesting in view of three major points noted by all in recent months:
the discomfort of surgical or fabric masks in hot weather, particularly for staff forced to wear them for long periods of time at their workstations because of their professional obligations (shopkeepers, cashiers, call center operators, establishments receiving the public, etc.);
the opacity of the masks, limiting the capacity of communication between individuals, both vocally (attenuated sounds, alteration of frequencies sensitive to the telephone or in noisy spaces) and visually (lip-reading for deaf or hard of hearing people, see here);
the ecological impact of disposable masks, particularly worrying at a time when the entire world population is concerned and no large-scale solution for the management of this waste has been found, whereas visors can be used in the long term and are fully recyclable (see here).
While the opinions against visors / face shields were only arbitrary and not based on studies conducted with the rigor that science imposes, this first study shows all the relevance of visors, and especially of PROFASTER ALPHA which exceeds all the criteria set by the scientists who wrote it, and benefits from an official approval of the French Covid-19 call for projects.
Moreover, the study shows that wearing a visor is also relevant for contaminated people, limiting better the aerosol propagation of contaminated particles than a surgical mask. Especially since the latter is massively misused, by a population not trained in its use, who reposition it by holding it from the outside, then slips it into the pocket, puts it on the arm, lowers it to the chin or mounts it on the forehead ... reducing the usefulness of the mask and turning it into a formidable vector of self-contamination.
The potential of a shield worn by an infected individual to prevent transmittance was tested (...). In this configuration, no indication of droplets could be found in the close vicinity of the breathing simulator, positioned 60 cm apart, not by the water sensitive papers, nor by the APS instrument. This implies that a shield worn by an infected individual can effectively block the infected spray emitted in an expiratory event (page 17 of the study).
We can therefore only understand the relevance of the visor + mask combo for infected individuals recommended by many scientists, in order to reduce almost totally the risks of transmission of the virus without having to resort to partial or total containment.
This is done to assess the protection provided to the surrounding when an infected individual is wearing a shield. For this configuration, no particles could be identified in the vicinity of the manikin head, by neither the APS nor the water sensitive papers. The important conclusion is that wearing a face shield can protect the surrounding from exposure to an infected person (page 19 of the study)
The study concludes by calling on public authorities to observe that face shields are, because of their many advantages, an alternative to surgical masks to be seriously considered for the general population:
Overall, our results imply that blocking efficacy of face shields is similar, and for some parts of the face, even higher, than the efficacy of medical masks. This is even more true for fine particles, which are blocked much more efficiently by a shield compared to a medical mask. Considering other advantages of shields over medical masks, public health policy makers may consider, for the general population, the usage of face shields as an alternative to medical masks.
Of course, in the case of health care workers/rescue workers/paramedics/volunteer aid workers who may be exposed to high viral loads, the best protection remains at least the FFP2 mask, intermediately the FFP2 mask + protective visor combo, and if necessary, the addition of a cap and covering clothing. However, this is not the subject of the Israeli study discussed here.
EDIT of August 19, 2020: TO GO FURTHER
An interesting video on the protection of masks and visors to flows and aerosols, with demonstrations and interviews of international specialists. Video put on line by Jean-Michel Wendling (Doctor of Medicine, specialist in occupational health and industrial hygiene, former intern of the Hospitals of Strasbourg in pneumology, allergology and respiratory functional exploration) who carried out the experiment visible at the beginning.
A study commentary and its 62 reference studies on the relevance or not of surgical and/or textile masks for the general population, ending with the legitimate question: "If masks had been the solution in Asia (Editor's note: where they have been massively worn since well before Covid-19), shouldn't they have stopped the pandemic before it spread elsewhere? ": https://www.cidrap.umn.edu/news-perspective/2020/04/commentary-masks-all-covid-19-not-based-sound-data
If masks had been the solution in Asia, shouldn't they have stopped the pandemic before it spread elsewhere?
A 2008 (!) study on the performance of surgical masks, ending with the interesting conclusion that "none of these surgical masks exhibited sufficient filtering performance and facial conformation characteristics to be considered as respiratory protective equipment": https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7115281/
None of these surgical masks exhibited adequate filter performance and facial fit characteristics to be considered respiratory protection devices.
The very recent observations of Professor Xavier Girerd (APHP, Cardiologist, Professor of Universities) on the general obligation of surgical masks for the general population in public places:
There is no convincing scientific evidence of the benefit of the surgical mask. By an irony of history, an article published on August 11, 2020 in JAMA Internal Medicine shows that only the FFP2 mask is protective (98% filtration of particles). By comparison, the surgical mask with straps provides 71% protection and the mask with elastic 38%.
Find the complete study here (overview and PDF viewable and downloadable):
And find the files to print your PROFASTER ALPHA visor here :
As well as our other voluntary contributions to the fight against the coronavirus here, including :
the first chart made on the resistance of 3D parts to common sterilants
and CROVHYD, our hygiene hook printed by the French Army.