🌬️ 📤 💆🏿 Hold COVID-19. All about pandemic air filtration 🛅 🥞 ✝️

Based on materials from the telegram channel LAB66 and the chat attached to it.

This is a time for facts, not fear. This is a time for science, not rumors. This is a time of solidarity, not a witch hunt ...
WHO Director Tedros Adhanom Ghebreyesus on the COVID-19 epidemic

It has been a little time since the publication of my article on respiratory protection during an epidemic. During this time, partly due to the active discussion in the “channel” chat, a certain system was developed that I would like to share with the readers of the Habr. I was forced to write this article because an unhealthy hype climbed up due to the coronavirus, on the wave of which not at all the information that should have surfaced (as well as the respirator prices suddenly jumped up to x40 times, moreover, indiscriminately ) So you need to dot the i. Under the cat, we read about choosing the right respirator, about assembling custom filters and sterilizing infected protective equipment. Answers on questions.

I highly recommend bookmarking. I will be glad to any feasible distribution of the article. A brief summary FAQ is at the end of the article.

UFO Care Minute

The pandemic COVID-19, a potentially severe acute respiratory infection caused by the SARS-CoV-2 coronavirus (2019-nCoV), has officially been announced in the world. There is a lot of information on Habré on this topic - always remember that it can be both reliable / useful, and vice versa.

We urge you to be critical of any published information.

Official sources
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Wash your hands, take care of your loved ones, stay at home whenever possible and work remotely.

Read publications about: coronavirus | remote work

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You read these messages, and you understand what you need to write. Well, we begin the next longrid. In the first article, it was mentioned that “respirators like FFP3 / P3 / N99” according to various classifications have the best protection against aerosols. Moreover, all the sellers' stories that they say “this dustproof it will not protect against aerosol”, and “this anti-aerosol protection doesn’t protect”, in my opinion, aren’t worth a damn and give people away without the slightest idea in the field of colloid chemistry. Because, by definition, an aerosol is a dispersed system consisting of suspended in air (dispersion medium), small particles (dispersed phase). Moreover, the type of the dispersed phase (solid / liquid) is practically not separated anywhere. The fine dust in the air and the micro droplets formed by sneezing are all aerosols (often even close in dimension).Therefore, the effectiveness of the retention of the dispersed phase by respirators will be approximately the same. The stories about industrial aerosols and fumes deserve a separate book on colloid chemistry, but I will probably dwell on biological aerosols in more detail.

Biological aerosols

Biological aerosols are aerosols whose particles carry viable microorganisms or toxins. They occur in the premises during each sneezing, snorting of animals, as well as the implementation of various technological processes: feeding animals, caring for the premises, as a result of evaporation and drying of the liquid and the excrement of sick animals and humans with dust in the air. Depending on the particle size, 4 phases of the biological aerosol are distinguished: large-droplet (particle diameter> 100 μm), small-droplet (particle diameter <100 μm), nuclear droplet (particle diameter <1 μm), and so on. bacterial dust (particles of tens and hundreds of nanometers in size).

The particles of the large droplet phase are in suspension for several seconds and quickly settle. The range of their dispersion does not exceed 2-3 meters. From the point of view of the spread of pathogens, large drops pose the greatest danger only at the time of formation and in the immediate vicinity of the patient. Settling on various surfaces, they mix with dust and, drying out, form bacterial dust, which when the air moves in the premises rises and settles many times on the surface, which makes it a source of constant re-infection of the air.

Particles of the dust phase of an aerosol larger than 50 μm in their kinetic characteristics are similar to particles of a large droplet phase, but differ from the latter in that, when deposited on surfaces under the influence of convection air flows, they again become in suspension and are able to repeatedly reinfect the room air, creating it contains extremely high concentrations of microorganisms. Under certain conditions (cleaning, bedding, high motor activity of people), the number of dust aerosol particles in the air can reach 90–95% of the total number of particles of all phases of the bacterial aerosol. By the way, the number and size of particles of biological aerosol created by an infectious patient in the room air depends on the strength and frequency of physiological acts of sneezing, coughing, talking,as well as the intensity of sputum formation.

The small-droplet fraction of particles with a size of 30 or more microns slowly settles, forming bacterial dust together with the particles of the large-droplet phase. Small particles (up to 10 μm) dry out and turn into nucleoli 1 μm in size and smaller, forming a droplet-nuclear fraction. These particles are a complex structural formation containing infection pathogens enclosed in a protein shell that protects them from the harmful effects of environmental factors. The evaporation process is very fast - it takes hundredths of a second to turn small droplets into particles of the nuclear droplet phase. The sedimentation rate of the particles of the droplet phase smaller than 10 μm and the particles of the droplet-nuclear phase are vanishingly small, in fact, it is an almost stable aerosol. Therefore not surprisingthat for long-term maintenance of such particles in suspension, a small amount of air movement (1-10 cm / sec), which almost always takes place in any room, is sufficient. The particles of the small droplet fraction have a high ability to be transported with air currents over considerable distances. Particles less than 10 microns in size in their kinetic characteristics are similar to the particles of the droplet and droplet-nuclear phases and have an epidemiological characteristic similar to them. Due to their small size (1-10 microns), such particles are able to penetrate into the deepest parts of the respiratory tract and are one of the key driving factors in the spread of airborne infections.The particles of the small droplet fraction have a high ability to be transported with air currents over considerable distances. Particles less than 10 microns in size in their kinetic characteristics are similar to the particles of the droplet and droplet-nuclear phases and have an epidemiological characteristic similar to them. Due to their small size (1-10 microns), such particles are able to penetrate into the deepest parts of the respiratory tract and are one of the key driving factors in the spread of airborne infections.The particles of the small droplet fraction have a high ability to be transported with air currents over considerable distances. Particles less than 10 microns in size in their kinetic characteristics are similar to the particles of the droplet and droplet-nuclear phases and have an epidemiological characteristic similar to them. Due to their small size (1-10 microns), such particles are able to penetrate into the deepest parts of the respiratory tract and are one of the key driving factors in the spread of airborne infections.Due to their small size (1-10 microns), such particles are able to penetrate into the deepest parts of the respiratory tract and are one of the key driving factors in the spread of airborne infections.Due to their small size (1-10 microns), such particles are able to penetrate into the deepest parts of the respiratory tract and are one of the key driving factors in the spread of airborne infections.

The size of the particles of biological aerosol determines the depth of their penetration into the respiratory tract of a person and, accordingly, the localization and severity of the disease. Particles larger than 30 microns settle mainly on the mucous membrane of the nose, larynx and trachea, particles 3-10 microns in size penetrate into the deeper parts of the respiratory tract - bronchioles, and particles with a size of 0.3-1 microns in 51-82% of cases reach the alveoli.

Half of the aerosol particles with a diameter of less than 0.5 microns, as a rule, are exhaled back. The most dangerous are highly dispersed aerosols, particles of which have a size of up to 2 microns. It is these particles that penetrate into the deep sections of the lungs, causing their primary lesions in the form of pneumonia. Coarse aerosols with particles larger than 10-15 microns are mainly retained on the mucous membrane of the upper respiratory tract.

note - virus sizes

Summing up, we can say that the smaller the size of the aerosol particles, the longer they remain in the air and the deeper they penetrate the respiratory tract when inhaling. The duration of the aerosol in the air (its stability) depends on its temperature, humidity, speed, particle concentration, their electric charge and other factors that are actively studied in the course of colloid chemistry, so we will not dwell on this separately.

Filters for cleaning air from bacteria and viruses

A fairly large number of methods have been developed to control aerosols. But as applied to an ordinary resident of a megalopolis, this is most often the use of filtering material. When aerosols are filtered on strainers, dispersed particles are retained mainly due to the fact that their sizes are larger than the mesh sizes of the filter material (due to the sieve effect). It is logical that the cell size of such an impromptu sieve can be reduced not infinitely. Therefore, there is such a thing as fiber filters. If only particles larger than holes are retained in the sieve, then all particles (large and small) in the fibrous structure, but with different efficiencies. The principle of operation of fiber filters is based on the fact that the flow of air with particles passes between the fibers. Particles touching the surface of the fiberremoved from the stream and held firmly by the fiber due to intermolecular forces. When filtering a monodisperse aerosol, each elementary layer of fibers captures the same fraction of the particles entering it. Any polydisperse aerosol can be represented as a set of monodisperse fractions, each of which is captured by its own mechanism. In general, the mechanism for filtering aerosols on fibrous materials is the sum of various effects, among which, in addition to the sieve (of least importance), some others (under the spoiler) play a significant role:each of which is captured by its own mechanism. In general, the mechanism for filtering aerosols on fibrous materials is the sum of various effects, among which, in addition to the sieve (of least importance), some others (under the spoiler) play a significant role:each of which is captured by its own mechanism. In general, the mechanism for filtering aerosols on fibrous materials is the sum of various effects, among which, in addition to the sieve (of least importance), some others (under the spoiler) play a significant role:

The scheme of action of various effects of deposition of aerosol particles in the fibrous layer

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In general, in a fibrous material, which consists of several layers of randomly arranged fibers, the effects of particle deposition listed under the spoiler act with varying degrees of manifestation, and filter materials are characterized by the efficiency of aerosol trapping and resistance to the flow of passing air. As a rule, the smallest particles smaller than 0.3 microns are captured mainly due to the diffusion effect, and particles of large sizes are predominantly affected by the mechanisms of contact, inertia and sedimentation. The electrostatic precipitation effect is manifested to a large extent in the presence of highly charged particles and / or fibers.

Some things are easier to explain with illustrative examples, so let's move on to the specifics. To date, only fiber filters are suitable for filtering aerosol particles (aka HEPA or their domestic counterpart, Petryanov-Sokolov filters, aka FP)

about Soviet HEPA

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What can this Soviet respirator give us today? Firstly, in the absence of any imported RPD, Petal can be used to protect against viral aerosols, as well as using tissue from it to replace, for example, filter elements. Secondly, due to a lack of information on the materials from which foreign HEPA filters are made, old publications on Petryanov filters can be used as guidelines for disinfection / sterilization. Well, in addition, focusing on the material of the fibers, you can choose the working conditions, etc.

list of materials FP - clickable

For example, Petryanov's perchlorovinyl filters are resistant to strong acids and aqueous solutions of alkalis, but do not tolerate temperatures above 60 degrees Celsius. Petryanov’s polyacrylonitrile filters are resistant to organic solvents, and polyacrylate filters can withstand temperatures up to 270 degrees. Modern foreign “custom” aerosol filtration filters are also made of various materials and have different resistance to external influences. As an example, aerosols from 3M:

An important remark that appeared thanks to the work of photographer Dmitry Kruglov : despite the fact that polypropylene is indicated for pre-filters 5935, this is not entirely true. I focused on American counterparts. And it turns out that "for us they are made of polypropylene, and 5N11 and another model of the P2 level for the US market is made of polyester." Take this into account!

Additionally, as an illustration of the thesis stated above about “submicron particles are delayed due to the diffusion effect, large particles due to touch and inertia” I would like to cite one fact. The figure below shows the values of a(= filtering coefficient) for FPP-25 material. The experiments were carried out using monodisperse aerosols in the size range 0.04–2 μm and a density of about 1 g / cm3. Air flow rates were 0.3 - 30 cm / s. To exclude the effect of the electrostatic effect , FPP-25 material was discharged upon irradiation with a ⁶⁰ Co source .

Dependence of the filtering coefficient of the FPP-25 material on the size of aerosol particles at different filtration rates. The numbers on the curves are the air velocity, cm / s

. Three areas are clearly distinguishable in the figure. In the left region, aerosol capture occurs mainly due to the diffusion deposition of particles on the fibers. With decreasing particle size, and flow rate and increases. In the right region, the deposition of particles occurs mainly due to the inertial mechanism. Efficiency is greater the larger the particles and the higher the flow rate. In the intermediate region athe smallest. All curves in the figure go through a minimum. Here, diffusion and inertial mechanisms manifest themselves insignificantly. Particle capture is determined by the touch mechanism. The range of particle sizes corresponding to the minimum values of acharacterizes the most penetrating particles. The figure clearly shows that for each speed it is different. In this case, with increasing flow velocity, more and more small particles become more penetrating. If for a speed of 1 cm / s their diameter is about 0.4 μm, then for a speed of 30 cm / s it is about 0.15 μm. From the presented data it can be concluded: if at a certain flow rate the filter is designed to capture the most penetrating particles with a certain efficiency, then it will deliberately delay both smaller and larger particles with a certain efficiency. Velocities of 0.3 - 10 cm / s are characteristic of air currents in personal respiratory protection equipment (RPE) , and more than 10 cm / s are present in stationary treatment filters and various analytical aspirators.

So if we assume that the phase transition is ≈ HEPA, then we can say that the mechanism of electrostatic capture is important, but by no means basic. This is not surprising, since during prolonged storage, compression and pressing, in conditions of high humidity, under the influence of ionizing radiation, charges from the filter materials flow off. Quick discharge occurs during the long-term operation of a charged fibrous material due to the accumulation of electrically conductive dust (soot aerosols (!), Metal particles, salt aerosols, etc.). Although electrostatic charges on hydrophobic polymer fibers of materials are stored during storage (closed) for a long period of time, during filtration, electrostatic charges gradually drain from the fibers.The almost electrostatic charge of the fibers provides increased efficiency for capturing aerosol particles from atmospheric air for several tens and hundreds of hours. It is important that after discharge, the materials still retain high filtering properties, due to the structural characteristics of the materials. During prolonged filtration of aerosols with solid particles, the filtering layer gradually becomes clogged and newly arriving aerosol particles are deposited on already deposited particles, as a result of which the efficiency does not decrease, but the material resistance gradually increases. The rate of clogging depends on the concentration, dispersion and nature of the aerosol particles.that after discharge, the materials still retain high filtering properties, due to the structural characteristics of the materials. During prolonged filtration of aerosols with solid particles, the filtering layer gradually becomes clogged and newly arriving aerosol particles are deposited on already deposited particles, as a result of which the efficiency does not decrease, but the material resistance gradually increases. The rate of clogging depends on the concentration, dispersion and nature of the aerosol particles.that after discharge, the materials still retain high filtering properties, due to the structural characteristics of the materials. During prolonged filtration of aerosols with solid particles, the filtering layer gradually becomes clogged and newly arriving aerosol particles are deposited on already deposited particles, as a result of which the efficiency does not decrease, but the material resistance gradually increases. The rate of clogging depends on the concentration, dispersion and nature of the aerosol particles.and the resistance of the material is gradually increasing. The rate of clogging depends on the concentration, dispersion and nature of the aerosol particles.and the resistance of the material is gradually increasing. The rate of clogging depends on the concentration, dispersion and nature of the aerosol particles.

:in addition to the already mentioned HEPA-like materials, aerosols can be filtered using asbestos, which by its chemical nature already represents ultrafine fibers. Therefore, asbestos filters (the so-called CAC, cellulose-asbestos cardboards) were the first fiber filters. Pulp and asbestos paperboards are made from specially treated cellulose grades mixed with ultra-thin asbestos fibers. Wool, cotton and glass fibers with binders are added to certain types of cardboard. Such filter cartridges provide a sufficiently high efficiency of aerosol collection. However, they have low elasticity, low dust absorption and are not resistant to moisture, which limits their use in respiratory technology. Well, in addition, asbestos and its microfibers have a fixed carcinogenic effect,which caused widespread rejection of this material.

Choosing a respirator

Having talked about materials in general, now it’s worth stopping at products with their use. In the first article, it was mentioned that “all FFP3 respirators have the best aerosol protection.” We have the following options available:

FFP3 crafts from 3M

9332+/K113P*/8132*/9153R*/9153RS*
* = c

domestic FFP3 descendants of the petal

100-2/ -200/ 310/ 316/ 319/-2/

After some time, I came to the conclusion that, in addition to the FFP3 / P3 class (and HEPA body material), an ideal respirator must have an exhalation valve and (!) An obturator (soft case made of silicone or rubber, which ensures the tightness of the mask). Because all the incredible properties of the fibrous material can be negated by the suction of air through the gap between the mask and face. This was still known at the time of the first petals:

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So make conclusions, and complete with a regular disposable respirator, keep something like BF-6 glue on hand. And it is better to immediately look for a suitable respirator. A couple of notes in the channel ( amb , two ) were devoted to this subject.

And now, in the presence of these conditions, such a manufacturer of protective equipment as the German company UVEX (not uniform glasses ...) comes to the fore . Respirators of this company, in contrast to 3M consumer goods, look like BMW next to the Lada, but ... But, accordingly, they are not widespread and not cheap.

suitable FFP3 respirators from UVEX

: 3310, 5310, 5310+, 5320+
: 2310-2312, 7313, 7333, 7310-7312-7315-7320-7330

Well, 3M is rather weakly represented in this niche. One model is called 8833 and in fact is an excellent option in the class of anti-aerosol respirators.

These same RBI respirators include the 8835+ model . By the way, he is the cutest

As reminded me Merllinn, there are other models with an obturator, for example the SPIROTEK VS2300V respirator , which is much cheaper than 3M products. Perhaps this is the cheapest “ideal anti-crown respirator” in our area ...

In the subject of a disposable respirator a couple of thematic notes:

how to wear a respirator

the difference between a three-layer dressing from a respirator

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about Belarusian traders

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Summing up, it is possible to say that a respirator with a shutter is certainly more convenient than gas masks, but it is quite difficult to find this very shutter. And given the fact that there are everywhere such prokhendeys as in the spoiler “about Belarusian traders”, it may turn out to be much more profitable (albeit not so beautiful) to buy a half mask. There is a beautiful silicone shutter, reliable mounts and an abundance of replaceable cartridges.

Half mask selection

If initially I did not make much difference between the 3M masks of the 6xxx and 7xxx line, now I do it. And I recommend taking exactly 7 matches (although 6 matches are cheaper). This is due to the fact that masks 7xxx (the most common 7502 - medium size) allow you to disassemble the respirator into its components, and therefore simplify the washing and disinfection process.

choosing the right half mask size

In addition, a forced air supply system ( S-200 ) can be connected to this mask, in which case . If you have money, you can take a full-face mask, such as 6800 .

With such a mask, you do not need tight glasses, which are a must-have accessory (= "in the kit") for half masks and respirators.

Note fromspygatesdue to the fact that it’s not “3M single” - “full-face UNIX masks are no worse than 3M, if you do not go into small minor nuances, but at a price 3-4 times lower. The mask is very high quality, has a silicone seal and belts, with excellent visibility and a good selection of replaceable filter cartridges. The other day I compared them in a store, without a doubt bought myself a UNIX 5100. " Here is a video review from the author, and here is a detailed description of the mask itself and replaceable cartridges for it. In general, the option is interesting, but not available everywhere + unix and 3M mounts are not compatible with each other ...

Selection of sealed glasses

From the fact that coronavirus can easily penetrate the body through the cornea of the eye, it follows that for the eyes it is necessary to provide protection no worse than for respiratory organs. Everything is simpler here - any tight glasses with a snug fit to the skin are enough. Any goggles suitable for swimming , preferably with transparent lenses, or ordinary goggles of the closed type (= without ventilation) are suitable for working with dangerous vapors (acids, alkalis, solvents, etc.). There are many options - such (with polycarbonate glass), or such(with mineral glass). Mineral glasses, although they are easier to break, are easier to treat against fogging. You need to rub the glass with a piece of soap (on the side of the face) and polish with a soft cloth. For glasses with plastic "lenses" you need a special anti-fog agent (more on that separately).

Note about fogging glasses

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Although it is worth noting that there are also special non-fogging UVEX glasses .

Swimming goggles can also be a good alternative, especially with large glass options such as the Aqua Sphere Seal 2. They are comparable in price to UVEX.

Aqua Sphere Seal 2

3M has its own analogue of sealed (the key word "gas-tight goggles" is for those who live abroad and try to find something suitable there) of glasses - Fahrenheit .

Well, the most comfortable ones (after the “chemist glasses” of course :)) are Hazchem's closed Xcalibur glasses.

But when choosing glasses, it’s important not to rush. Points must be selected directly under the mask, because it may happen that these two PPE will conflict with each other. And to find ready-made kits like General Personal Protection Kit in our area is difficult, if not impossible at all.

Here I would like to mention such a thing as a means of protection for children. Unfortunately, all respirators and half masks are designed for the average adult. A possible option would be to use masks for snorkeling (swimming with a breathing tube). Manufacturers produce masks of different sizes:

examples of masks for snorkeling

True, you still have to make a home-made adapter in order to get something like a combination of a “children's mask + adult filter”:

like this

Well, there are children's gas masks. For example, a gas mask for children filtering PDF-2Sh or a gas mask for children filtering PDF- Breeze with a filter box having "P3" in the name.

Of course, it looks like some kind of 3M half mask is more terrible, but it is suitable for children from 1.5 years old.

Note about operating temperatures: this is important if you decide to autoclave / sterilize glasses at elevated temperatures. Review in advance the instructions that are valid for your model. Often there is a spread from 55 to 130C. Accordingly, 130C can be disinfected even with boiling water, but 55C can float.

Adapters

Since the conversation has come about the need to create adapters, it should be noted that the solution to the problem of finding sealed glasses can be the use of a domestic gas mask + a modern cartridge from 3M for it (we'll talk about them separately). All you need is to find a suitable adapter "3M mount <=> domestic thread". After all, it’s easier for someone to find the 3rd, someone domestic. The lack of old gas masks in their filter boxes (it’s difficult to guess at least Petryaev’s filter cloth there). Newer models already have threaded cartridges marked P3. But it is necessary to determine in advance what type of thread on your "grandfather gas mask." In modern Russian full-face masks (or panoramic) like PPM-88thread type 404 is used, which coincides with the common foreign thread NATO40. If someone has a 3D printer at home, you can easily print the following adapters for gifts to friends:

From a 3M mount to a NATO40 threaded connection

three-dimensional view

Or, in our realities, the more popular adapter from NATO40 to 3M mount .

With this approach, any of our gas masks + 3M cartridges will be the cheapest and easiest option. You should get something like this:

in situ adapter

And you can even make an adapter for HEPA filter vacuum cleaner. But it depends on what was lying around in the pantry (the domestic gas mask is still a more frequent guest there)

Filter selection

Finally, we got to one of the most important points, because the quality of the air coming in under the mask depends on it. If with respirators everything is more or less clear, then for owners of half masks and full face masks it is important to choose the right “cartridge” cartridge.

Initially, I advised everyone to anti-aerosol in the form of “pancakes” - 2135 , but then I decided that in the event of an epidemic, these replaceable filters would quickly become a hotbed of viruses.

These filters can be installed both in the as is version and through the mount 502 on a standard gas filter.

Then I began to advise everyone P3 anti-aerosol filters type 6035 in the form of separate cartridges

These filters, unlike "pancakes" are much easier to find in our area (they are cheaper). Well, the likelihood of contamination with sprayed contaminated liquid is much less for “boxes” with HEPA material folded accordion than for a plate, the entire filtering surface is open to the whole world. In principle, the average holder of a half mask can stop at cartridges 6035/6038. By the way, a small life hack - 6035, by virtue of the design, blocks the air flow during compression and in this way allows you to check the tightness of the half mask to face.

Refinement from Ksantor or a custom cover for 6035 filters. You can download STLs at Thingverse . It will be useful to someone who does not really like the white color of the original cartridges, etc.

Description from the author

A set of covers for 6035. one is simple, the second is slightly reinforced and more authentic and the third (closest to the viewer) with a "skirt" that goes a little towards the filter and protects from rain (on request Merllinn) Weight - 11 g, 14 g, 16 g (in ascending order)

Continuing the conversation about cartridges, IMHO, for DIY enthusiasts, you need to take any, the simplest and cheapest standard cartridge (like 6054 ), and to it is a holder-holder for pre - filters of type 501

Note on the “disposability” of 501 mounts. Here in this video , at timing 5.53, the phrase “single use” skips. But how corrected meanprs, disposability refers to the adapter 502 (cartridge-mount "father"). So - we sleep peacefully! :)

To the aforementioned “constructor” an anti-aerosol pre - filter of type 5935 is bought (it is possible in the amount of several sets).

In addition to the P3 insert, you can take a penny P1 / P2 insert ( 5911 and 5925, respectively) and impregnate it with biocidal impregnations (see article ). Such a system will make it easy to remove pre-filters for subsequent processing and sterilization. The general scheme of elements compatible with 3M half masks is shown in the picture:

More recently, I found out that 3M has such an adapter as 603

This piece, of course, costs more than conventional carbon filters, but it is also lighter. And in combination with an adapter 501 may be suitable for assembling your own filter constructor.

Address to 3M company : I am sincerely ready to become your brand ambassador in the Republic of Belarus. Guys, well, good luck, excellent products, do you really have enough strength to put a couple of adequate specialists for user consultation? Without false modesty, I’ll say that now any of my regular interlocutors (especially co-admins) in the chat on the channel will answer the question without any problems with filters, prefilters, differences between masks and many other issues that make it difficult to give the answer is "company officials"

Respirator / filter life. Theory

Finally, we got to the most burning issues. About the service life. In general, the service life of filters made of fibrous material is determined, for aerosols of high weight concentration, the time during which the mass of the dispersed phase of the aerosol deposited on the filter becomes equal to the mass of the filter material, for aerosols of high activity - the time of destruction of the filter material under the action of active compounds, etc. . etc. Now many consultants (3M for example) forget about this and begin to become attached to the loss of electrostatic charge by the filter. I remind you that a charge can be lost under the influence of moisture, electrolyte solutions, and intense ionizing radiation. A complete charge loss can be observed due to the destruction of the polymer from which the fibers are made (including due to the loss of the properties of the electret) It is important that the destroyed material is unlikely to be able to perform filtration using other mechanisms.

In short, for any fibrous filters, the main factors determining the service life should be considered as dustiness of the air and linear filtration rate, i.e., the load on the sediment. The lower the dust level in the air and the filtration rate, the longer the service life. Dust increases the resistance of the material, leads to the fact that less and less air begins to pass through the filter. But the efficiency of aerosol trapping does not decrease, since the dust layer is an additional filter. The practice of operating filter materials shows that the maximum accumulation of dust should not exceed 50-100 g / m2. Moreover, the absolute increase in material resistance (at a speed of 1 cm / sec) will be no more than 5-10 mm of water. Art.An excellent option when using fiber filters can be the use of coarse prefilters with them, which reduce the weight concentration of aerosols by trapping the largest aerosol particles with a size of at least 1-3 microns. Thus, we capture coarse dust and leave for HEPA only trapping of submicron particles, extending its validity period (almost unlimited).

As for respiratory protection, the filtration rate is constant, the service life depends only on the number of particles. Therefore, most often, the service life of filters for various conditions of their application is determined practically during operation. For example, when cleaning atmospheric air with a specific load of about 150 nm3 / h * m2 and a concentration of 0.2–0.4 mg / m3, the service life of filters using FPP-15-1.5 material is 4000–5900 hours of continuous operation. It can be said that for cases of viral infection, the filter media will last for years (if there is no other dust in the air except for bacterial). Despite the fact that in Soviet times, electrostatic materials in respirators were labeled precisely by the loss of charge, for example, I saw this sign when applied to the Lepestok-200 respirator:

But when using similar filter cloths in production filters, the service life was calculated as if the materials had no charge. Electric charges provide greater filter efficiency only in the initial period of operation, and in the future, when significant amounts of sediment accumulate on the filter material, there is no certainty that the filter material will remain in a charged state. Studies of filter materials that have been working in filters for several years have shown that, as a rule, there are no electric charges on the material.

In general, the efficiency of an aerosol filter is determined by the standard resistance (thickness) of the filter layer and the rate of aerosol filtration. The thicker the layer of filter material, the higher its efficiency. However, an increase in the thickness of the filter layer leads to an increase in its resistance, but it does not always allow to retain particles of the desired diameter. The figure shows the dependence of the number of layers of filter material FPP-15-2.0 for 95% capture of aerosols at a density of 1.7 g / cm3 (average density of atmospheric dust) depending on the particle radius (the number of the curves is the filtration rate in cm / s )

From the above dependence it follows that particles with a radius of more than 0.4 μm at the considered speeds can be caught in one layer. The most stable particles in the free atmosphere (0.2 <r <0.4 μm) with an efficiency of 95% are captured in three layers. Particles with a radius of 0.1 μm at a speed of 1 cm / s are captured in one layer, but with an increase in the filtration rate, the number of layers must be increased. At 50 cm / s, 6 layers of material must be installed. However, a further increase in velocity leads to an increase in filter efficiency due to inertial deposition, and even at 250 cm / s only two filters are required. When considering even smaller particles (radius 0.05 μm), it should be borne in mind that the inertial effect is absent even at 250 cm / s. Therefore, if 95% capture of such particles at 1 cm / s requires one layer,then, with increasing speed, the number of required layers continuously increases, and at 250 cm / s they are already required 13. With high-speed filtration, the efficiency of inertial deposition can decrease due to the rebound of particles from the filter fibers. You can reduce the probability of a rebound by choosing a filter material with a large fiber diameter.

!A great influence on the efficiency of filtering with fibrous filters is also exerted by the liquid, which can get onto the filter / condense on it. In this case, the filter quickly fails due to a sharp increase in resistance when the pores of the filter material are blocked by a liquid film. Therefore, filters with fibrous materials cannot be used if there are significant concentrations of oil aerosols, plasticizers, tributyl phosphate, dibutyl phthalate in the air, as well as saturated vapors of organic solvents, such as dichloroethane, acetone, etc., since they cause swelling or dissolution of polymer fibers. If significant amounts of aerosols of oils get on the filter material, it swells the fibers and reduces the mechanical strength of the material while increasing its resistance. Allowable amount of oilcaught filtering material should be considered 3-4 mg / cm2.

When capturing aerosols with fiber filters, it is believed that solid particles trapped in the fiber do not move in the filter. A different picture is observed if the aerosol particles are liquid, i.e., the filter picks up fog. Although the capture of liquid particles by fibers occurs according to the general laws of trapping aerosol particles, the further behavior of the dispersed phase in this case is different. Particulate matter settles mainly in the frontal layer, forming a dust-permeable gas sediment, even participating in aerosol filtration. But droplets of fog spread over the surface of the fibers in the form of a liquid film, thickening as the aerosol arrives. Under the influence of the gas flow and gravity, the liquid can move in the fibrous layer to the intersections of the fibers and collect in droplets. First, these drops overlap the smallest pores of the filter, then larger ones.Outwardly, this is expressed in a gradual increase in filter resistance. The air velocity through the free largest pores increases. If the filter worked in diffusion mode, then an increase in speed will lead to an increase in the mist slip. With further flow of liquid into the filter layer, the moment will come when the liquid fills the entire free volume between the fibers and thus closes all the pores of the filter. This leads to a sharp increase in the resistance of the filter layer and the complete cessation of its gas permeability. In order for the gas to pass through the pores filled with liquid, it is necessary to overcome the hydrostatic resistance - the rupture of the liquid film that overlaps the pores.then an increase in speed will lead to an increase in fog through. With further flow of liquid into the filter layer, the moment will come when the liquid fills the entire free volume between the fibers and thus closes all the pores of the filter. This leads to a sharp increase in the resistance of the filter layer and the complete cessation of its gas permeability. For the gas to pass through the pores filled with liquid, it is necessary to overcome the hydrostatic resistance - the rupture of the liquid film that overlaps the pores.then an increase in speed will lead to an increase in fog through. With further flow of liquid into the filter layer, the moment will come when the liquid fills the entire free volume between the fibers and thus closes all the pores of the filter. This leads to a sharp increase in the resistance of the filter layer and the complete cessation of its gas permeability. In order for the gas to pass through the pores filled with liquid, it is necessary to overcome the hydrostatic resistance - the rupture of the liquid film that overlaps the pores.In order for the gas to pass through the pores filled with liquid, it is necessary to overcome the hydrostatic resistance - the rupture of the liquid film that overlaps the pores.In order for the gas to pass through the pores filled with liquid, it is necessary to overcome the hydrostatic resistance - the rupture of the liquid film that overlaps the pores.

Full filling of the filter with water (or another liquid) increases its resistance by almost a thousand times. Naturally, for example, a fiber filter designed for a maximum resistance of 50-100 mm of water. Art., when pouring it with liquid will be practically impermeable to the air flow. Although the operating experience of filters that capture aerosols with a liquid dispersed phase shows that the real service life of such a filter is much longer, and sometimes even unlimited. The fact is that the liquid entering the filter can move in the filter layer and gradually - under the influence of gravity and capillary forces - be removed from the filter layer. The speed of such a tap, of course, depends on the viscosity and nature of the fluid. For example, the oil trapped in the FP filter penetrates the fibers themselves, causing them to swell.Therefore, the speed of its tap is low. Sulfuric acid, trapped in the form of a mist by an FP filter (for example, an FPP-15 or FPP-70 filter from perchlorvinyl, which is resistant to its effect), is removed from the filter layer at a noticeable speed. You can choose such a filtration mode that the amount of liquid entering the filter will not exceed the discharge, and in this mode, the fiber filter can work for an unlimited time.

/.

As follows from the foregoing, when using disposable (conditionally) respirators in which the body is the main filter, all that remains for us is to hope that in the air that passes through this respirator there will not be too many large aerosols and dust (= small city, village, etc.). With an emphasis on bacteriological filtration (i.e. filtering only virions) - you can use respirators for months, taking care only properly disinfection / sterilization. The material will accumulate and concentrate on itself the viral particles, and with the life of the virus on the surface for about a month - this is a serious application. And the main problem that the user will encounter will not be a slip of virus particles, but contamination of the filter housing, masks, sealed glasses, clothes, etc. etc. Things will be much worseif dust / smoke / exhaust is present in the air (= conditions of a large metropolis), etc. Their negative effect is likely to quickly reduce the effectiveness of the respirator. And nothing can be done in this situation, respirators do not imply the installation of coarse prefilters. Only half masks and full-face masks and cartridges for them will remain.

The widespread filter cartridges for 3M half masks already did not differ in low cost (relative to domestic products, comparable in terms of performance characteristics), and in connection with the epidemic, this cost was made where x2, and where even x5. Of course, there may be a reason in unscrupulous dealers, but as they say, the sediment remained.

hybrid of snake and hedgehog

If now, armed with theory, take the most common anti-aerosol cartridge type 6035, then we can say that its resource is limitedonly by ease of breathing - becoming clogged, it becomes difficult to breathe through aerosol filters. By blowing, you can, for example, blow large particles of dust and, theoretically, the filter should start working, but 3M 6035 cartridges are not designed for excess pressure (more than a person can create when inhaling) and there is a risk that the filter simply breaks when blowing from the line of compressed air (the effect is very similar to the result from blowing and the “failure” is very easy to confuse with “success” - through the openings and breakouts of the filter it will become easier to breathe and it will seem that the blowdown has worked, but all the protection of the filters will disappear, because .all particles go not n filter, as it was before, and straight into the newly formed hole). When working with paint materials, you should be doubly careful with similar purges: paint materials,hitting the surface of the filter, they cure and form a film impermeable to air, in this case, blowing them, it is likely that excessive pressure is created, which simply “tears” the filter from the housing. Those. blowing off formally is not recommended, and it is necessary to change the filter after breathing difficulties. But if you just blow a little and carefully just a stream of air without pressure, then it will give a ride. Well, or remove the lid and tap.

Therefore, if it was finally decided to make the half mask the main RPMD, then you should prefer a prefabricated design (like the one I wrote above, 603 + 501 + 5911 + 5935) to an individual "all inclusive" cartridge like 6035.

Sterilization of filter materials

If everything is approximately clear with the term of work, then with questions of sterilization of filtering materials (respirators and cartridges) one continuous questions. The vast majority of manufacturers who have bothered to mention their equipment along with “work in a viral epidemic” recommend replacing replaceable filters after use as biological hazardous waste. Although thanks to workMerllinnthere were articles that showed high efficiency (while maintaining filtering ability - this is very important) of disinfection of disposable respirators. For example, using steam sterilization of hydrogen peroxide (HPV). In general, steam peroxide sterilization is one of the most promising substitutes for quartzization / ozonation. Although the latter are also not going to give up positions, see another foundMerllinn article describing the high efficiency of processing disposable masks using ultraviolet radiation (treatment against contamination with influenza virus). In general, it can be argued so far that sterilization in pairs / ultraviolet gives an excellent effect in the short term and is able to extend the life of a disposable respirator by an N-time. Why N - but because the filtering ability of fiber filters completely depends on their internal microstructure, and with repeated processing, materials can be destroyed (for example, the so-called ultraviolet degradation of polymers). How quickly this effect can manifest itself is difficult to say, it will depend on the power of the lamps used / the concentration of peroxide vapor and the polymers used in the respirator and, of course, on the processing frequency.

About UV sterilization:literally today in the channel such information slipped :

To decontaminate 99% of the influenza virus in a disposable mask, it is necessary to hold a bactericidal lamp (254 nm, 800 μW) at a distance of about 3 cm from the mask for 10 seconds

Ultraviolet coronavirus is even less resistant than the flu virus. But! But how many times the mask can withstand exposure to harsh UV before it crumbles in your hands - it's hard to say. Theoretically, manufacturers of polymer fibers add substances that reduce UV exposure to their composition. Most often this is done for products intended for outdoor use (the so-called outdoor). Those. it is not difficult to potentially rebuild the manufacturing process of masks for their UV sterilization. But is it profitable for the manufacturers of masks themselves ...

We go further. If we rely on the assumption voiced at the beginning of the article that AF ≈ HEPA and look at the “daughter” of the Lepestok-200 respirator, Alina-316 respirator, you can see that the manufacturer himself recommends that the respirator be decontaminated with an antiseptic. It is advisable to do this after “contact with bacillary patients or highly hazardous biological and viral infections (turbeculosis, SARS, bird flu)”:

domestic version of respiratory sterilization

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TAED . — , , , . , 60C. TAED + , ( !) 30-40C. — ( , )

(TAED) :

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As for the filter cartridges (like 3M 6035), the manufacturer himself indicates in the instructions that:

filters should be replaced when they become clogged with particulate matter. the user will be able to determine when this will occur by increasing the effort of inspiration. aerosol filters are designed to capture particles under industrial conditions at concentrations much higher than the concentrations of bacterial and viral particles in the air. therefore, it is expected that one set of filters will be able to endure a pandemic wave without replacement, after which they should be replaced for reasons of infection control

.
Those. confirms all the conclusions that I voiced earlier = “aerosol anti-aerosol can work tens and hundreds of times longer with respect to virus filtration than with solid particles”, but with the condition that the outer surface of the cartridges must be disinfected (the filter itself does not need to be touched).

So for filter cartridges the situation with disinfection is even simpler than with respirators - all that is needed is to remove them from the half mask and process them with preservation of safety measures. How to do this is a debatable question. You can, for example, withstand filters in dry heat conditions (coronavirus deactivates at 60 degrees with an exposure of 30 minutes). It is possible to purge in pairs of hydrogen peroxide or alcohol (ethyl alcohol (> 60 vol.%), Isopropyl alcohol (> 60 vol.%)). It is advisable to prevent moisture from entering the closed cartridges (see the theoretical part of this article). Although nothing bad will happen, but the efficiency will be restored only after the moisture is removed from the fiber using the capillary effect (you can speed up the process by blowing a stream of warm air from the hair dryer).The best option is to use constructors from 603 + 501 + P3 prefilters. Pre-filter plates can be removed and sterilized / dried as you wish. In addition to P3 (5935), you can use coarse P1 (5911) impregnated with an antiseptic (miramistin, cetylperridinium, pgmg).

Important! Do not forget that removing “infected” filters is also necessary under strictly aseptic conditions, i.e. at least in gloves. Gloves then need to be either sterilized or discarded. But do not forget that they need to be able to shoot correctly. Doctors and microbiologists teach this, and I will remind you in a separate note. As an instruction - watch the video carefully

or follow the picture

If there is no emphasis on reusability, then simply dispose of all disposable masks, gloves, capes, shoe covers after use. Collect in bags and pour sodium hypochlorite with a concentration of at least 1%. In the near future I will try to collect all frequently asked questions on disinfection, compositions, concentrations and attach here as a separate RTFM. While there is time - I strongly recommend that anyone interested in the topics voiced in the article move to LAB66 and read / take an active part in the discussion. Without false modesty, one of the most competent “anticoronavirus” communities in our territories gathered there.

SHORT RTFM (will be replenished)

Answers to frequently asked questions

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2019-nCoV. FAQ .

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: — FFP3 (P3)/N99 . — UVEX 2310-2312, 3310, 5310, 5310+, 5320+, 7313, 7333, 7310-7312-7315-7320-7330; 3M 8833, 8835+. — SPIROTEK VS2300V. — , ( FFP3) — 3M 9332+/K113P*/8132*/9153R*/9153RS* (* = c ; 100-2/ -200/ 310/ 316/ 319/-2/. FFP3 — FFP2 -> FFP1 -> .

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: . , ( «gas-tight goggles») . : 3H1 1 Panorama, UVEX: Uvex Ultravision, 3M: Fahrenheit, 2890S, 2890SA, 2895; Hazchem: Xcalibur. , , , Aqua Sphere Seal 2. «» () ( ).

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: , 3M ( ). 7500, 6000, /. 3 — (.. « 3») (=« »). :

7500/6000 + 6035/6038
7500/6000 + 2135/2138
7500/6000 + 603 + 501 + 59 ( = 11 1, 25 2, 35 3)
7500/6000 + + 501 + 59 ( = 11 1, 25 2, 35 3)
7500/6000 + + 502 + 2135/2138

, 6035 , . «» 3, , .. .. , — 6035 , .

:

Unix 2100 + UNIX 303 P3D Unix 2100 + 3D (UNIX 203 P3) +Unix 2100 + ( UNIX 501 A1) + UNIX P3

JetaSafety JETA6500 + 6521 JetaSafety JETA6500 + 6510+ 5101/5030 + 3. 3.

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: (/), . . — . (, 30% ) 3% . , :

833,3 (641 ) 96% + 41,7 3% (41,7 ) + 14,5 (18,27 ) (98%) + 110,5 (110,5 ) = 1
751,5 (590 ) 99% + 41,7 (41,7 ) 3% + 14,5 (18,27 ) (98%) + 192 (192 ) = 1

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Acknowledgment: The author expresses his sincere gratitude to the guys scattered throughout the Eurasian continent, who joined together in the search for optimal remedies and antiseptics and discussion in our small telegram community . @catraccoon, @ vinzekatze, @ravengo, @craneop, @ kaputmaher, @aswsh, @t_samoilova, @ fogree, @ evgeniiSi, @besyaya - thanks guys!

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Hold COVID-19. All about pandemic air filtration

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