/aerospace engineering mode on
Your average homemade masks inflate to 100 ml. The better fitting the mask, the less the tidal volume. Your tidal volume, the volume of air that is inhaled or exhaled in an average single breath at a resting state is 7 ml/kg.
For a 150 lb (68 kg) person, that comes to 476 ml. Call it 500 ml for easy comparison.
In other words, you’re rebreathing 20% of the air, but breathing 80% fresh air.
However, that’s when you’re sedentary, which is what you’re not when you’re walking around a grocery store. In fact, within a few seconds, you move to roughly double tidal volume. This reduces your rebreathing to just 10% of the air, which is minimal.
Furthermore, your own lungs naturally respond to changes in CO2 concentrations by increasing both respiration rates and volumes, which further flushes out any residual exhalent in your mask.
Finally, the net fractional change in carbon dioxide for each breath averages 0.0786. That is, for every 1 of CO2 inhaled, you’re exhaling 1.0786 units, less than an 8% difference.
Since the global average atmospheric carbon dioxide in 2018 was 407.4 parts per million (ppm for short), with a range of uncertainty of plus or minus 0.1 ppm, you inhaled 407.4 ppm yet exhaled 407.4 x 1.0786 = 439.4216 ppm.
Since your mask retained 10% of this… Ok, I’ll be generous. Since your mask retained 20% of this, your mean CO2 intake increases to 413.8 ppm.
“Oh, my stars!” Right?
Not at all: “Submarines routinely operate with higher levels of ambient carbon dioxide (CO2) (i.e., 2000 – 5000 ppm) than what is typically considered normal (i.e., 400 – 600 ppm)”
“They’re brain dead!” Right?
Not at all: “Results: There were no significant differences for any of the nine SMS measures of decision making between the CO2 exposure conditions” (Chabal, S. Clarke, J. M., Fothergill, D. M., Rodenheffer, C. D. (2018). Acute exposure to low-to-moderate carbon dioxide levels and submariner decision making. PMID: 29789085 DOI: 10.3357/AMHP.5010.2018)
Thus, the ENTIRE “rebreathing” argument is complete and utter HOGWASH.
As for unfiltered exhalent: Medical professionals today are wearing N95 surgeons masks over their N95 masks to filter the exhalent. I know, as I’ve actually been to the doctor’s office, lately, on May 5, to be exact.
As for the particulates:
N95 masks actually filter 96% of all particles 0.3 micron in size or larger.
P100 masks filter 99.97% of all particles 0.3 micron in size or larger.
The filtration rate ratio between these two is calculated by:
Thus, a P100 mask isf 133 times more effective at filtering 0.3 micron or larger particulates.
Now, to the virus itself:
“The SARS-CoV-2 is a large sized virus (approximately 120 nm in diameter) (25-27). The relatively large size and lipid envelope makes it highly susceptible to steps with virus inactivation and removal capacity used during the manufacturing processes, such as solvent-detergent (S/D) (28), low pH incubation, caprylate-, pasteurization- (29) or dry-heat treatments (30), nanofiltration or fractionation processes and others (31). The effectiveness of these processes has been demonstrated on other lipid-enveloped model viruses which are quite similar to SARS-CoV-2, e.g. human coronavirus 229E and OC43, SARS-CoV, and porcine coronavirus TGEV (32-33).”https://www.pptaglobal.org/media-and-information/ppta-statements/1055-2019-novel-coronavirus-2019-ncov-and-plasma-protein-therapies
Put simply, it’s super sticky!
In contaminated environments, they’re also enveloped by large quantities of mucous, so much so that it dwarfs the virus itself.
For example, if the virus is the size of a soccer ball, the smallest mucous droplets would be the size of the soccer field whereas the largest droplets are the size of the entire county.
You’re not filtering 0.12 micron virus. You’re filtering the 10 micron and larger droplets containing the virus.
Finally, since you’re a nurse, you’re undoubtedly familiar with just how sticky mucous droplets are, too. ?
/aerospace engineering mode off
But, hey, I’m not a NURSE, so what the HELL do I know about the physics behind how masks work, right? After all, that’s aerospace engineering stuff, right?
27. Lim, Y.X.; Ng, Y.L.; Tam, J.P.; Liu, D.X. Human Coronaviruses: A Review of Virus–Host Interactions. Diseases 2016, 4, 26.
28. Rabenau HF, Biesert L, Schmidt T, et al. SARScoronavirus (SARS-CoV) and the safety of a solvent/ detergent (S/D) treated immunoglobulin preparation. Biologicals 2005;33:95-9.
29. Gröner A, Broumis C, Fang R et al. Effective inactivation of a wide range of viruses by pasteurization. Transfusion. 2017 May;57(5):1184-1191 [Accessed January 27, 2020]
30. Yunoki M, Urayama T, Yamamoto I, et al. Heat sensitivity of a SARS-associated coronavirus introduced into plasma products. Vox Sang 2004;87:302-3
31. Keil SD, Bowen R, Marschner S: Inactivation of Middle East respiratory syndrome coronavirus (MERS-CoV) in plasma products using a riboflavin-based and ultraviolet light-based photochemical treatment. Transfusion. 2016 Dec;56(12):2948-2952.
32. Lamarre A, Talbot PJ. Effect of pH and temperature on the infectivity of human coronavirus 229E. Canadian Journal of Microbiology. 1989;35(10):972-4. 51.
33. Bucknall RA, King LM, Kapikian AZ, Chanock RM. Studies with human coronaviruses II. Some properties of strains 229E and OC43. Proceedings of the Society for Experimental Biology and Medicine. 1972;139(3):722-7.27.