Thread by @eddericu

Introducing the LaminAir. *Safer indoor dining. Safer working in the office.* At least double-digit exposure reduction factors, while breathing 12 inches away from the device 🤯 🧵 (1)

First, what is exposure reduction factor (ERF)? It's a measure of how clean the air when using a device vs. not. If you get an exposure reduction factor of 20, that means the air is 20 times cleaner while using the device vs. not. (2)

N95s filter at least 95% of particles and offer great protection against many respiratory pathogens, smoke, airborne allergens, etc. (3)

N95s, in the worst case, let 5% pass through. If there's X amount of stuff in the air while not using the N95, and 5% are left over with the N95 on, that means that the exposure reduction factor is 20. E.g. X / (X * 0.05) = 1 / 0.05 = 20 (4)

... so it's a good goal to hit at least an exposure reduction factor of 20 when designing a device. How good is the LaminAir after going through a set of exercises? Pretty darn good! (5)

The exercises I did above were mostly inspired by OSHA respirator testing, and in 4 out of 6 exercises I did, the exposure reduction factor was 80 and above. Averaging those out in a conservative way (using harmonic mean) gave an overall exposure reduction factor of 36. (6)

To contextualize that overall ERF of 36, I show different exposure reduction factors next to the LaminAir, with the red horizontal line showing the lower bound for N95 (no leaks) and the green horizontal line showing the typical N95 performance (no leaks). (7)

Cloth masks give ERF of 2 (not that great for something as infectious as SARS-CoV-2). SmartAir's QT3 at 12 inches using their data gave a 2.5 (not that great). Universal masking with cloth masks gives a 4 (better, but still not that great). (8)

2 powerful CR boxes on max added to a classroom with only 200 CFM ventilation gave an ERF of about 5, using NIOSH research data on Effective DIY Air Cleaning. N95s with leaks usually give around an ERF of 10. (9)

An ERF of 10 means 90% of particles get filtered out, but you're still breathing in the remaining 10%. Combining layers of protection gets us even closer to N95 performance. 2 powerful CR boxes on max + universal cloth masking gave a 16.67 ERF, (10)

which translates to about 94% reduction, and 6% inhaled. Finally, the LaminAir, in my set of experiments, got a conservative ERF average of 36, which is a 97.3% reduction (3.6% inhaled). (11)

How have I been personally using the LaminAir? Given the performance, I've used it recently to attend a relative's birthday celebration two weeks ago. About 100+ people attended (so in light of wastewater/cases, someone there probably was infectious with COVID) (12).

Here's me right before eating lunch with my FloMask on. I had the LaminAir partly on my lap and on the table to save space. Louvers pointed to my face so I could get relatively clean air (13).

Right before and after that event, I also hung out with my family members for many hours. Three of them had sniffles. One of the three sounded different because of congestion. (14)

I had the LaminAir close to my face in times when the FloMask got too moist and I wanted to get a break while still hanging out with family. In the span of two weeks, I did not have any symptoms and felt great. (15)

Of course, people have different risk tolerances within the COVID-cautious community. If you're not comfortable doing indoor dining, you could combine the device with your fit-tested N95, and you should be getting an effect of universal masking with N95s (huge ERF). (16)

Interested in pre-ordering a device? Shipping in U.S. and Canada for now: My family is in the middle of moving to a new house so will be ramping up production not in January, but more likely Feb. and March. (17)breathesafe-llc.myshopify.com/products/lamin…

Much thanks to @ee_kelsey and @CleanAirStars. I got the inspiration from them to use the technology behind this device (laminar flow). They got high reductions of aerosol concentrations with reasonable short distances. (18)

...using different implementations but the same principles. They are (1) use HEPA, and (2) decrease entrainment. (19)

HEPA filtration gives great single-pass performance. When air passes through once, a huge chunk of aerosols are removed. (20)

Traditional pull configurations in a CR box are not great for personal protection because they pull in surrounding air (which could be dirty, shown in red) because of the swirl generated by the fan. (21)

Using push configuration, whee the fan pushes air TOWARDS the filter is better, because the exiting air becomes straight and laminar, instead of swirly. Straight (laminar) air pulls less air from surrounding air (which could be dirty). (22)

Slower air is better than faster air. Faster air means air molecules in the breathing area are more spread apart (i.e. less pressure) than in slower air. (23)

Surrounding air (higher pressure) will want to gravitate toward the breathing area (lower pressure), causing mixing. Dirtying up the concentrated clean air. Left: slow. Right: fast (24)

Finally, using a wide filter is better than a narrower filter. Wider filter with laminar flow means the sources of entrainment will be farther away from your nose and mouth (assuming you're breathing from the middle). That's it! I wish everyone a happy, healthy holidays. (25)

Again if you are interested in purchasing: (END)breathesafe-llc.myshopify.com/products/lamin…

One more thing that's important to know when it fails. Watch out for sources of wind / air currents, e.g. don't sit next to things that mix air well (like a box fan, CR box, etc.)

And if you're a researcher, scientist, engineer, or just a data nerd and are interested in the code, calculations, and assumptions being made, here's the most recent copy of the Jupyter Notebook, in HTML form: …safe-airgo.s3.us-east-2.amazonaws.com/images/laminai…