Today, we have been confined for almost a month now. On the internet, I have seen some more or less crazy initiatives concerning the creation of masks. Indeed, faced with the shortage of FFP2 filtering masks, and also surgical masks, many people are making their own masks: We decipher the effectiveness of these masks on Greeny Bird Dress*.
*Disclaimer: What follows here is the result of the reflections and research of several doctors, teachers and researchers or professionals specialised in the field of non-woven fabrics and filtering materials, this article is only intended to help you understand the conclusions reached. In this article, I propose to check the effectiveness of fabric masks (the homemade ones, the HomeMade masks) versus FFP2 masks (the microparticle masks) and surgical masks (the surgical masks, which are the masks for hospitals in general).
First, let’s review some textile basics
What are masks made of? Filter masks are mainly made up of a filter which is a composite and belongs to the non-woven textile family:
These nonwovens are very different from woven fabrics and knitted fabrics (pullovers, sweaters, T-shirts) for several reasons:
- They do not have a textile construction, these nonwovens are created in an “anarchic” way, and form a “mass of material”.
- These nonwovens have different finenesses, as mentioned by the researcher Julien PAYEN in his thesis “Study and development of nonwoven fibrous structures dedicated to the filtration of fine particles in the air.
Here is an extract from his thesis:
- “Fine filters are used to filter out dirt particles (dust), germs, bacteria-laden dust, agglomerated oil and soot fumes, tobacco smoke, metal oxide smoke… They are therefore used as filters for air treatment in rooms with low requirements (workshops, garages, warehouses) or as pre-filters and filters for air handling units or as final filters in air conditioning systems for shops, offices and production rooms and as pre-filters for absolute filters.- High efficiency filters (HEPA) are used for the filtration of germs, bacteria, viruses, tobacco smoke, tobacco smoke, etc,They are used in final filters for rooms with high demands such as laboratories, foodstuffs, pharmacies, optical and physical industries.
- Ultra high efficiency filters (ULPA) are used for the filtration of oil vapour and soot formation and radioactive particles. They are used as final filters for clean rooms, operating theatres or as final filters for air removal in nuclear facilities.
- Mask filters are used to filter out dust, smoke, mist, viruses, bacteria… FFP2 masks are recommended in cases of pandemic influenza such as H5N1 or recently H1N1…”
Then, let’s look at the different types of masks: FFP, surgical, barrier
- FFP mask: intended for nursing staff, made of fabric + non-woven, used up to 8 consecutive hours, PPE type product
- Surgical mask: lower level of FFP, for medical use, intended for patients, made of fabric + non-woven, used for up to 4 consecutive hours, these are DM
- Face masks: can be DM or PPE, made of plastic– Barrier mask (or alternative, HomeMade mask): design close to “medical use protection” but very inferior performances, for the population or to save medical masks, made of fabric, they are products of common use, neither PPE, nor DM
Here PPE stands for Personal Protective Equipment and MD for Medical Device.
- MDs are regulated by Directive 93/42/EEC.
- PPE is regulated by Regulation (EU) No. 2016/425.
As you will have understood, these same masks are different with distinct uses. In addition, their test standards are different, and the protection offered between these two masks is totally different. Concerning the HomeMade mask, it has a much lower performance than the PPE or DM masks, but can be made to save medical masks, made of fabric…
Now look at this diagram and look at a hair:
You can see that a hair is 30 to 50 microns thick (this is the µ symbol). Bacteria are thinner, with a thickness of between 0.5 and 30 microns. The Corona virus has a thickness of less than 0.1 micron!
Here we understand the interest and the function of each type of filter: each filter can filter specific thicknesses according to its own fineness and electrostatic charges (but it is quite technical for this point).
To summarise: the efficiency of filtration of airborne particles in a textile depends strongly on the size of the particles (these are the thicknesses, measured in microns: µ). Everything becomes complicated between 0.1 and 2 µm of thickness to be filtered, where the Corana Virus is located…
Researchers have tested the protection factors you can get with a cloth mask versus other masks specifically designed to filter out Corona Virus-sized particles:
In light blue, we see that there is some non-zero protection factor with homemade fabric masks, but much lower than specialised masks.
Any type of general mask use is likely to reduce viral exposure and infection risk at the population level, despite imperfect fit and adherence, with personal respirators providing the greatest protection. Masks worn by patients may not offer as high a degree of protection against aerosol transmission.Research article: Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population by Marianne van der Sande , Peter Teunis, Rob Sabel
Namely, the textile structures developed for medical masks and respiratory protection masks (FFP) applications are based on very advanced technologies such as meltblown and an optimised efficiency/air permeability compromise. Everything becomes more complicated in a zone between 0.1 and 2 µm. A textile with 94% efficiency at 3 µm can let 60% of 1 µm particles through… The second type of filter capable of filtering the virus is the Spunbond type filter. Interview by Philippe Vroman
What to do with the 0.5 to 12µm droplets that are expelled from our mouths and which may contain the virus?
The droplets we expel are wet. The tests performed on certified surgical masks are tests from the outside of the mask to the inside:
Conclusions: “Protection at the start of the test was similar for the wipe and the surgical mask, but for the FFP2, protection was double. Children had considerably less protection”.VAN DER SANDE ET AL 2007
Some people make masks out of bra shells. Is this a good idea?
It is a very bad idea because the components of a bra (the foam in the shell, the dyes, the chemicals…) are not supposed to be in contact with the face and mouth and can have harmful effects. This is quite important: Apart from the fact that they are not non-wovens, but polyurethane foam, itself surrounded by polyester or polyamide, the chemicals in these bra shells should not come into prolonged contact with the mouth.
What is the difference between an FFP mask and a surgical mask?
- An FFP mask has a much more restrictive standard, the mask must be “watertight”, i.e. there must be no leakage on the face when breathing in, and all breathing in must be through the filtrate. Interview by Nicolas Deneuville
- A surgical mask must filter droplet type particles, and unlike the FFP mask (filtration in both directions), the filtration is done from the inside to the outside (important especially if the mask has to respond to blood splashes), and it doesn’t filter particles in the air because it is not watertight to filtration, but rather droplet type particles (postillon) Interview by Nicolas Deneuville
Alternative masks, called barrier masks, HomeMade or homemade masks, made of fabric are mainly there to compensate for the shortage of masks but it is important to note that the risks of contamination linked to COVID-19 remain identical with an individual who does not wear one because the virus will necessarily pass through the fabric mask. On the other hand, they offer the possibility of limiting the sputum to 0.5 microns and also of dispersing the virus less if you have Corona Virus, as the sputum will be less volatile.
I hope that I have been able to answer the questions of my clients, friends and family with this post. You can ask your questions in the dedicated comment space, I will answer them personally. I would like to thank Philippe Vroman, teacher-researcher at ENSAIT, who shares his knowledge and expertise in nonwovens. I would also like to thank Dr Julien Payen for his clear thesis on the subject, which helped me better understand the issues related to nonwovens.
Other initiatives :
Studies and sources :
Julien Payen. Study and development of nonwoven fibrous structures dedicated to the filtration of fine particles in the air. Mechanics [physics.med-ph]. University of Valenciennes and Hainaut-Cambresis, 2009. French. fftel-00474263e: https://tel.archives-ouvertes.fr/tel-00474263/document
Sui Huang. Institute for Systems Biology : https://medium.com/@Cancerwarrior/covid-19-why-we-should-all-wear-masks-there-is-new-scientific-rationale-280e08ceee71
Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population
Publications LinkedIn de Philippe Vroman, Associate Professor chez ENSAIT: “Innovative and Bio-inspired Nonwoven Materials Research and Development – Private and Collaborative Research Project Management – MSc and PhD Projects Supervision – Nonwoven process and product innovation design lecturer – Learner-centered Pedagogical Innovation”
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