FFP mask, surgical mask or fabric mask made at home… We all have these words in mind that have been part of the common language since the beginning of the epidemic in December 2019. These 3 types of masks do not have the same level of protection against the SARS-COV-2 virus. We will try to see more clearly on the effectiveness of each of them. Much of the article is based on the WHO guide published on the use of masks in the context of Covid-19.
What are the threats?
When we talk about protection, we must separate two types of risks that can lead to Covid-19 disease: inhalation, one, water droplets and, two, suspended particles expelled by a person with the virus. When you cough, you sneeze, you talk or you breathe, your mouth and nose expel, so-called, aerosols: a magma of water droplets between 1 micrometer and 100 micrometers that carry bacteria (0.5 to 5 micrometers) and viruses. In the case of SARS-COV-2, the droplets are 0.1 micrometers in size. Where the heaviest water droplets quickly fall to the ground, fine particles remain suspended in the air, more than 1 hour for particles of 5 micrometers in size.
In this situation, the use of a mask to control the inhalation of these pathogens is highly recommended. It is impossible, however, to wear a mask without respiratory assistance with holes smaller than suspended particles. The reason is simple: it would be very difficult to breathe through the mask. To overcome this problem, the masks are composed of one or more intertwined (and unwoven) layers to trap particles passing through the mask.
In its guide (p 10), the World Health Organization emphasizes the importance of quality filtering of tissue that is a barrier against the virus. The level of filtration depends on the sealing of the fabric. It is preferable, the WHO recalls, to make a mask with 3 layers of fabric using materials such as cotton on the unexposed face, polypropylene in the middle layer and polyester (or polypropylene) for the exposed face. Effective filtering such as the one recommended by WHO has two drawbacks: breathing becomes difficult (as we have seen before) and the mask is not perfectly fitted to the face, allowing air to enter the interval between them, thus reducing the effectiveness of the mask against the virus.
The fabric mask: wrong idea?
This is the easiest type of mask to design. A large number of households were able to manufacture them during the confinement on the basis of a pattern proposed by the standards bodies. The textile used, on the other hand, appears to be less protective because it has different characteristics than medical masks and does not meet the quality standards imposed by the health sector.
In fact, few scientific studies have been launched on the filtration efficiency of these masks, which have not been subjected to the various tests developed by current sanitary standards. In France, IFTH, the French institute of textiles and clothing, developed a database for industrialists in May 2020, listing 1,200 materials and their responses to projections and air permeability. About 1/3 are non-compliant with professional use in contact with the public or collective use.
The surgical mask: the essential
The surgical mask is recognizable by its flat or pleated shape and its two-tone, often white on the outside and blue on the inside. Its protective performance has been tested through standardised standards such as ASTM F2100 in the United States or EN 14683 in Europe which gives them a good balance between high air filtration (blocking droplets up to 3 micrometers) protection against projections and good breathability (p2). It therefore provides protection to the entourage against projections emitted by the mask wearer and vice versa. The mask wearer, on the other hand, is not protected from inhaling droplets less than 3 micrometers in the air.
Its main objective is to avoid the transmission of large particles into the air and not to filter the air for finer droplets. Standardized tests on the non-transmission of 0.06 micrometer particles through surgical masks showed very heterogeneous success rates, ranging from 4 to 90. This discrepancy can be explained by the passage or not of air in the gaps between the mask and the face. It clearly does not fulfil its role in the case of prolonged contact with patients.
The FFP mask: for extreme situations
FFP (Filtering Facepiece) in Europe or FFR (Filtering Facepiece respirator) in the United States, we talk, in a few details, about the same type of mask. They are equipped with protective respirators with a degree of filtering, protecting the wearer from inhaling both water droplets and suspended particles. FFP2 and FFP3 can filter 94 and 99 of an aerosol containing solid particles of 0.075 micrometers, respectively. A leak tolerance is tolerated, below 8 and 2 respectively.
The high impermeability of these masks is more restrictive: faster temperature rise, difficulty breathing and risk of headaches in stressful situations when wearing the mask extends over a long period of time. To overcome these stresses, some FFP masks are equipped with a breathing valve. FFP masks are adequate to evolve with risk mimimum in difficult medical contexts. On the other hand, they must be used with great rigour and care to maintain maximum effectiveness against the transmission of the virus. Finally, FFP masks do not protect against gases and fumes.
In its recent study on the modes of transmission of sarS-COV-2 virus dated 29 March 2020, WHO argues that the majority of contamination is caused by the projection of water droplets with a range of 1 metre, not by fine particles suspended in the air. Although FFP masks offer better protection to the transmission of the virus, surgical masks are sufficient in most cases, outside medical structure.
The rules to follow
There are a few rules to follow when using these masks. Of course, wearing a mask does not exempt compliance with barrier gestures.
|Change as soon as it gets wet.
Failing that, every four hours.
For washable fabrics, do not exceed the number of cycles indicated by the manufacturer.
Washing at 60 degrees without drying on a 30-minute cycle.
Change as soon as it gets wet.
Failing that, every four hours.
Must be worn less than 8 hours on the same day.