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Joshua C. Agar Profile picture
@JoshuaCAgar
Jan 8, 2022 • 21 tweets • 9 min read • Read on X
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Admittedly there's a research gap concerning face shields since they are mainly intended for hospital settings, hence scenarios limited to hospital settings. The general consensus is that face shields are intended for ballistic droplets, not for aerosols.

Below are the studies:
Lindsley et al. (2014). Efficacy of Face Shields Against Cough Aerosol Droplets from a Cough Simulator

Face shields are evaluated to stop the initial impact of the cough which brought heavy droplets, however, airborne droplets still make way around.

ncbi.nlm.nih.gov/pmc/articles/P…
Akagi et al. (2020). Effect of sneezing on the flow around a face shield. Phys. Fluids 32. doi:10.1063/5.0031150

A numerical simulation of a sneeze on a face shield, showing that transient effects actually directs aerosols inside even during impact.

aip.scitation.org/doi/10.1063/5.…
Pan et al. (2021) Inward and outward effectiveness of cloth masks, a surgical mask, and a face shield, Aerosol Science and Technology, 55:6, 718-733, DOI: 10.1080/02786826.2021.1890687

Face shields are rated as the poorest protective layers.

medrxiv.org/content/10.110…
Salimnia et al. (2021). A laboratory model demonstrating the protective effects of surgical masks, face shields, and a combination of both in a speaking simulation

An experimental study evaluating little to no contribution of face shield.

pubmed.ncbi.nlm.nih.gov/33485923/
Bagtasa (2021). Efficacy of face shields to ambient aerosols in local indoor and outdoor setting. 2021: Proceedings of the 39th Samahang Pisika ng Pilipinas Physics Conference

Evaluating that face masks are the ones doing the work, not face shields.

proceedings.spp-online.org/article/view/S…
Wendling et al. (2021) Experimental Efficacy of Face Shield and the Mask against Emitted and Potentially Received Particles, J. Environmental Research and Public Health

One of the flawed studies conducted by medical professionals. Fails on equipoise.

pubmed.ncbi.nlm.nih.gov/33671300/
A visualization of TU Delft shows what happens to the emissions in the first place when the face masks are interfering:

If the face mask are already directing the emissions to the sides and the back instead to the front, what's the use of Wendling's setup?
Verma et al. (2020). Visualizing droplet dispersal for face shields and masks with exhalation valves

A visualization experiment by the Florida Atlantic University showing that face shields are poor source control... They don't stop aerosols at all.

aip.scitation.org/doi/10.1063/5.…
Most of these studies were derived from hospital settings, therefore they perceived sporadic (i.e. cough, sneezes, speaking) emissions as the high risk scenarios, and focused only for that scenario.

Here is what happens at different angles of approach:
If the cough is coming from behind, the wearer of the face shield is practically screwed:
Here is what happens when you walk in an indoor space (close spaces, crowded places) saturated with airborne particles while donning a face shield:
Faster accumulation of airborne particles if you're looking side-to-side while walking:
A face shield provide a place for retention of airborne particles:
If there's wind potentially carrying SARS-CoV-2 coming from behind:
Similar scenario, only at an oblique angle:
As Dr. Jimenez has said, face shields are useless against Covid-19, now that the understanding that it is airborne. When face shields are coupled with face masks, face masks are the ones doing the work while face shields do nothing.

There are in-fact, other atmospheric consequences of face shields that lead to the increase in infectivity of SARS-CoV-2.

This is the extended abstract of the conference paper that I'll be presenting two weeks from now.
If one insist on doing RCTs on face shields in public settings, despite these studies and despite the fact that face shields are physical items, not medicine, maybe for truthfulness sake, include the Pontresina Case
thelocal.ch/20200715/only-…

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More from @JoshuaCAgar

Joshua C. Agar Profile picture
Dec 21, 2023
Our study that developed CO2 monitors that informed occupants of the relative risk that they may be subjected to due to airborne diseases transmitted through shared room air transmission has been published. #CovidIsAirborne

doi.org/10.3389/fbuil.…
Image
Using a multivariate method, the ventilation rates of different indoor spaces are determined and used for the subsequent computations using the Wells–Riley model to derive the respective infection risk, particularly of COVID-19. Image
"Infection risks are determined to be higher in indoor spaces with low ventilation rates. However, having high ventilation rates does not mean low infection risks as smaller spaces will also have higher infection risks."
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Read 7 tweets
Joshua C. Agar Profile picture
Dec 12, 2023
Part of the PowerPoint presentation to be presented on Thursday:

How aerosols move Image
Conservation of Mass
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Infection risk modeling

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Read 4 tweets
Joshua C. Agar Profile picture
Apr 23, 2023
High humidity also attributes to high infection rates and deaths due to Covid-19.

Shown below are the trends derived from the correlation between Covid-19 deaths and relative humidity. 60% RH is the Goldilocks Zone: lesser or greater than that results in the increase of the risk Image


Why 60%?

It has to do with two things: (1) lessening evaporation rates due to inhomogeneous mixing and (2) rate of condensation which attributes to the increase of pore pressure within the mask.royalsocietypublishing.org/doi/10.1098/rs…
Countries above the tropics experience case surges during their winter season when relative humidity is low. The hot and humid respiratory emissions will mix with the cold and dry indoor air resulting in higher evaporation rates,
Read 7 tweets
Joshua C. Agar Profile picture
Feb 5, 2023
When used in physical settings, the Cochrane method and RCTs are mere pretentious eminence-based assertions masquerading as empiricism (A thread).

It is important to note that the interventions mentioned are physical in nature, not clinical and medicinal. (1/n)
We have two studies that use the Cochrane method:

The first one is the study headed by Derek Chu (funded by WHO) in 2020, which has determined, using the Newcastle Ottawa Scale & Cochrane method, the effectiveness of face masks in stopping transmission. (2/n)
The second one, headed by John Conly, uses the Cochrane method whose results are being interpreted as "evidence" against face masks.

In fact, the study pointed out the inadequacy of the study design due to the high risk of bias when dealing with physical interventions. (3/n)
Read 7 tweets
Joshua C. Agar Profile picture
Nov 3, 2022
Testing the filtration efficiency (how much they reduce Covid-19 risk) of mask. #COVIDisAirborne

KN95 Mask
Copper/Cloth Mask
Surgical mask (the one bought from any vendor). This assumes observance of fit.
Read 4 tweets
Joshua C. Agar Profile picture
Nov 1, 2022
With no regard to the limits on occupancy and social distancing, here are the reproduction numbers from scenarios where a symptomatic infector within a 40-student DepEd classroom, even though the 1000-ppm CO2 ventilation requirement was satisfied. #COVIDisAirborne Image
With no regard to the limits on occupancy and social distancing, here are the reproduction numbers from scenarios where an asymptomatic infector within a 40-student DepEd classroom, even though the 1000-ppm CO2 ventilation requirement was satisfied. #COVIDisAirborne Image
This is why masking is important: to prevent outbreaks such as this.

Whoever cooked up this bad idea should be responsible. Remember the names of the IATF members who supported this folly. Never forget what they did, along w/ JoeyCon & Fr. Austriaco who advocated mass infection.
Read 5 tweets

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