This post is a comparative review of different types of protective masks which are used or suggested for use during the COVID-19 epidemic. These materials are continuation of the previous post COVID-19 and the Mask where some “theoretical” data the about SARS-CoV-2 virus and conditions of the virus distribution are discussed. N95 respirator is the most popular protective mask. It will be discussed in some detail.
Surgical mask, the mother of all protective masks, was tested more than 100 years. However, it was designed to protect the s space of manipulation from the care provider’s infectious contamination, as well as the ambient environment, namely the room.
Surgical mask, the older variant
Current variant of a surgical mask
Below is the optimal professional protective mask with or without a respirator for an anesthesiologist, respiratory therapist, or other person in charge for work with a patient on the ventilator for a short time of the actual procedure management.
The N95 respirator on the figure B looks superfluous, but perhaps, for operational purpose when the anesthesiologist spends the most time in procedures which do not assume the direct contact with the patient discharging infectious material.
Different types of N95 respirators/masks
Respirators are used predominately in construction, sometimes agriculture, and in healthcare for protection against airborne infections, including viruses and now in COVID-19 epidemic.
Respirators are tested in the direction of inspiration (from outside to inside). The tests take into account the efficiency of the filter and leakage to the face. N95 respirator (in Europe disposable particulate respirator FFP2) have a minimum of 94% filtration percentage and maximum 8% leakage to the inside. As a standard, insulating respirators are most used (the filtering consists of a facepiece and a filtering device, sometimes with an exhalation valve).
According to CDC “The ‘N95’ designation means that when subjected to careful testing, the respirator blocks at least 95 percent of very small (0.3 micron) test particles.” Each SARS-CoV-2 virion is approximately 50–200 nanometers in diameter. 50-200 nanometer is 0.05- 0.2 microns. It means that N95 cannot prevent SARS-CoV-2 virus transmission. However, the virus is not “naked”. It travels in mucus droplets and droplet nuclei, which are the dried-out residual of droplets presumably containing SARS-CoV-2 viruses. Mucus is of 95% water.
Again, an effective N95 respirator is designed to achieve a very close facial fit (8% leakage). Never mind that it is not achievable in hairy face.
Now, I want to address a significant, in my view, detail in using N95 respirator for individual’s protection from viruses in the air space which is in the person’s proximity. Otherwise, why bother to use a respirator.
The respirator catches droplets (>5 micro) and containing viruses droplet nuclei (≤5 micron) at the protected area in the same amount as at all other areas of the face, including adjacent to the respirator’s edges. While at the nose area the respirator is sealed by a metallic insert, the rest has certain narrow (8% leakage space between the face and the edges).
The droplet nuclei are water substances moving in the air, like fog, which is condensed water droplets. For understanding what is occurring in the narrow area (8% leakage) between the respirator’s edges the face, we need to apply some physics, particularly the Bernoulli principle.
When a fluid flows into a narrower channel, its speed increases (Bernoulli principle). With a higher pressure on the outside, the high-velocity fluid forces other fluids into the stream. This process is called entrainment. An aspirator uses a high-speed stream of water to create a region of lower pressure. A paint or perfume sprayers, a carburetor or a chimney are examples.
The kinetic energy of the droplets flow is generated by the gradient between air pressure outside the respirator and the negative pressure of the person’s inhalation. Dust or other firm particle would stop by friction. Their form is certain. The droplet nuclei is water. It can change its form. It sneaks inside the respirator without opportunity to go out because the exhale is passive. The number of sneaked droplet nuclei is minimal, but a person is breathing around 15-18 times per hour. The wet and warm mask provides the virus in droplets comfortable dwelling. The mask becomes a hotbed for viruses. The droplet nuclei viruses content can go without any difficulty in the” infection gates” as nose and mouth.
In a case of a mask similar to regular surgical mask, there is an air flow around the mask’s edges without forcible entrainment. Designed for preventing firm particles inhalation, the N95 respirator without 100% face fit, which is practically impossible, is, in my view, unacceptable for biological object like SARS-CoV-2 virus. I would appreciate any substantial objections to these considerations.
Additional problem of a regular N95 respirator is dome like relatively firm design. By a person’s exhale, the respirator accumulates on its wet and warm outside surface droplet nuclei with viruses, if they supposedly exist. They can dwell there comfortably until the respirator is taken off. However, the protective device should be taken off by slow careful rolling keeping the external surface inside the roll. This is difficult by the respirators form and fabric. Those are not unimportant details. The infectious material in semi-dried droplets appears in relatively large quantities directly in the areas most vulnerable for the entry during the taken off the respirator.
Other protective masks
As a practical solution, in my view, would be either complete sealing as Figures A and B or the Kimberly- Clark FLUIDSHIELD mask type with (better) or without shield.
Kimberly- Clark FLUIDSHIELD mask has five layers. Both the internal and external (orange stripes) layers are water permeable. The three layers between them have different degrees of water resistance. Although the company advertises them as LONCET breathable film, these layers, in my experience, make the mask uncomfortable for prolonged use because the area between the mask and the face is overheated and over-saturated with exhaled carbon dioxide that decreases the percentage of oxygen in the inhaled air.
Kimberly- Clark FLUIDSHIELD mask.
Protective Face Shield Visor, like offered by Htovila or Decdeal, is seemingly convenient. It definitely protects from dust and splashes and other situations of direct infectious material application. But it does not substitute the mask which it is necessary as protection from airborne infectious material, like coronaviruses. PET (polyester) material is relatively rigid and difficult to adjust to the protective gown for the neck protection. In my opinion, and experience of working with different masks, the Kimberly- Clark FLUIDSHIELD mask upside down (see above) wearing is preferable.
Decdeal Safety Face Shield
3M™ Full Facepiece Respirator 7800 Series looks solid, though intimidating, but it does not solve the main problem of the standard N95 respirator, namely face-fit adjustment that in the case of protection from viruses in crucial. Some suggestion to use this devise with reusable filter is controversial. In my view, it is unadvisable under condition of COVID-19 epidemic.
3M™ Full Facepiece Respirator 7800 Series
The development of protective mask will continue. Hopefully, the inventors would not think that the SARS-CoV-2 virus is going to reach specifically a cupper insert to be destroyed.
Meanwhile, if people feel comfortable by using a mask, let them do it, including bringing some creativity and fun, like the mask with owls on it. Positive spirit is part of healing from real dangers and unsubstantiated fears.
However, bandanas (bandannas) and similar creative protection “devices” are not innocent from infectious epidemiology point. We are not at the masquerade. This issues will be discussed in a special post later.
The main thing is that manufacturers understand design principles of a protective mask against the airborne infection. And the mask is correctly used. Both posts are written on the background of my experience in anatomic pathology as a pathologist, pathologists’ assistant, morgue attended, and grossing technologist.