Coronavirus and homemade tools

[DIYSwede]

Seems like some Chinese outlets whips out loads of discount ozone generators:



Advertised as a do-all, cure-all method "for use in the home, hotel room, conference centre, karaoke bar, car, RV" etc.
Specs for this particular unit is sparse, but it seems to be of the "Corona Discharge" type*,
pulls half an amp (at 220 VAC only) that equals 110W,
and thus cranks out a hefty 24 g/h of ozone - which could be detrimental to the stuff you're curing:

I've read in another forum thread from a dude working for a fire sanitizing company,
who'd just bought a really cheap car from a chain smoker:
He got the brilliant idea to borrow one 250 W Heavy Duty ozone generator from work,
and run it overnite in the car to rid it form the smell.

He got the car free of smell, all right - but all rubber parts within the compartment had petrified,
giving him a hell of a time to even get the unit back out, as all rubber seals had fixed the doors positively shut.
I never posted asking whether he scrapped the car or tried to refit everything "rubberish" inside.

My small unit pulls a mere 15 watts and gives plentiful of ozone for my 9 cubic meter hallway.

Two cents & YMMV

Johan

*Corona discharge units also "provide" Nitrous Oxide - which could lead to respiratory problems, established earlier in this thread:
https://en.wikipedia.org/wiki/Nitrous_oxide#Safety

[Jon]

Ford created a software patch to kill Coronavirus in NYC police vehicles, using the cars' heaters.

And that’s when an engineer at Ford realized: They didn’t need bleach to kill COVID-19 when the car’s own heater could do the job instead. And over the process of just 40 days, the auto company created a software patch that could upgrade the Interceptors to self-sterilize with the climate control system in just 15 minutes, no elbow grease required. (That patch is currently being installed on NYC police vehicles, and it’s offered to police officers free nationwide through dealers, though Ford is unsure how many have received the update to date.)

More: https://www.fastcompany.com/90510004...ar-heater-hack

[FEM2008]

New sterilization method seems to work on N95 masks. Research paper can be found here: https://pubs.acs.org/doi/full/10.102...stlett.0c00534
and FAQ here: https://docs.google.com/document/d/1...zKI0y0ijY/edit

[NeiljohnUK]

(Moved four politically-themed posts out of this thread and into Off-Topic. This is a good discussion, and I want to preserve its value.)


Similarly, here's the CleanKey. Stuff like this will be easy for our guys to make. I wouldn't mind an accompanying sleeve for it, so that it doesn't just go back in your pocket. 0:44 video:

The cleankey is a great idea, until a Police officer realises it also makes a usable knuckle duster, so not much good it the UK (banned it country), I've been making these out of 1/4" copper pipe offcuts and it does much the same thing, but it can't be mistaken as a weapon (hopefully). The broken s-biner lets it hang easily from a pocket or belt. Grip handle is ~1911 angle, later versions are P.08.

[Frank S]

The cleankey is a great idea, until a Police officer realises it also makes a usable knuckle duster, so not much good it the UK (banned it country), I've been making these out of 1/4" copper pipe offcuts and it does much the same thing, but it can't be mistaken as a weapon (hopefully). The broken s-biner lets it hang easily from a pocket or belt. Grip handle is ~1911 angle, later versions are P.08.

Still wont be of much use in the land of the round door knobs
People of today's time period are becoming far too FAUX germophobic because it is trendy

[Drew1966]

Simple. Elegant. Nice for most uses, but, as mentioned, no good for round doorknobs.

[NeiljohnUK]

Simple. Elegant. Nice for most uses, but, as mentioned, no good for round doorknobs.

Thankfully here we have lever type door handles, knobs are considered unsuitable for disabled users being hard to grip, and too easy to tie a ligature on.

[Altair]

Thanks NeiljohnUK! We've added your Antimicrobial Hand Tool to our Miscellaneous category,
as well as to your builder page: NeiljohnUK's Homemade Tools. Your receipt:

Antimicrobial Hand Tool by NeiljohnUK

tags: door, hand tools

[Jon]

The old concept of furnace filter plus box fan has evolved into a more effective variant, and been born again as a homemade tool for filtering COVID, with the backing of a group of aerosol scientists and HVAC industry leaders, the requisite COVID-era element of government conspiracy, and plenty of duct tape.



This COVID air filter build is being called a Corsi-Rosenthal box. It's essentially just a box fan duct-taped to MERV 13 furnace filters. A little more on its Wikipedia page, this Encycla page, and this CleanAirCrew FAQ. COVID aside, it's an inexpensive and highly efficient air filter that you can build in under an hour. HMT forum members have been building air cleaners with box fans and filters for years.

The Corsi part of Corsi-Rosenthal filters is Richard Corsi, an environmental engineering professor. The other half is Jim Rosenthal, the CEO of the HVAC company Air Relief Technologies. Corsi is on Twitter here, and Rosenthal is on Twitter here. The Corsi-Rosenthal box also has the approval of Bill Bahnfleth (Twitter is here), who is the chair of the Epidemic Task Force of ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers.

3M has also recently come out in support of Corsi-Rosenthal boxes; they ran their own tests and concluded "This Corsi-Rosenthal box movement is legit". Underwriters Laboratories also backs up the efficacy and safety of DIY air filters; see An Evaluation of DIY Air Filtration. Plenty of aerosol scientists have also jumped on board, including: Jose-Luis Jimenez, Kimberly Prather, Linsey Marr, Lisa Brosseau, Marwa Zaatari, and Eben Cross.

This group seems to be mostly united in their position that COVID is predominantly spread via the airborne route, and not via larger expelled respiratory droplets (they call these "ballistic droplets"). Thus, air filtration is reasonable, especially in colder seasons when ventilation is less practical. Airborne aerosols can stay suspended in the air for hours, like smoke, whereas expelled respiratory droplets arc downward to the ground in about 2 meters. Government COVID messaging worldwide was initially firmly droplet-based, and is now slowly backpedaling to an airborne position. Jose-Luis Jimenez (a highly-cited chemistry professor with a doctorate in Mechanical Engineering from MIT) has a good summary here laying out the reasons why COVID is primarily transmitted by airborne particles, and it's backed up by an article in The Lancet called Ten scientific reasons in support of airborne transmission of SARS-CoV-2. There is also a large COVID airborne FAQ written by many atmospheric chemistry and aerosol science professors and scientists here. Even more aerosol scientists in support of this are listed here: https://www.covidisairborne.org/



Some caveats:

1. There is strong backing to this position, but that alone doesn't mean that it's correct, especially in full. Science has many dueling factions.

2. The Corsi-Rosenthal box movement is popular on Twitter, but Twitter is not representative of any scientific field, and most scientists don't use it at all. There are often only a handful of heavily-cited scientists (whose volume of citations also does not make them correct) on Twitter for each field.

3. There is a tendency, especially during the pandemic, for a field to want to "own" COVID by ascribing its nuances to their own area of scientific pursuit. For example, this biases neurologists to look for a COVID link in the central nervous system, immunologists to focus on T cells, and aerosol scientists to point to air sanitation.

COVID positions are usually not complete without an element of government conspiracy, and the Corsi-Rosenthal box does not disappoint. Interestingly (and rarely), this position is neither politically left nor right. If COVID spreads primarily through expelled large respiratory droplets that arc down to the ground within 2 meters - they call this belief "droplet dogma" - then this shifts responsibility to individuals (mandating social distancing, handwashing, and homemade masks), whereas airborne acknowledgement shifts it to governments and corporations (mandating filtration of indoor public spaces). Mandating filtration of air in indoor public spaces has little impact on personal liberties, and thus little value as a political football. In fact, we already do this. Large HVAC installations are regulated in some places because they can spread Legionnaire's disease, so named because it was first discovered breeding and spreading via the air conditioning system at an American Legion convention in 1976.

Some graphic examples of this government spin, from Corsi-Rosenthal box advocates:





The key quantitative question is: How much reduction of COVID spread can we get from cleaning indoor air? We don't know, and it's difficult to model, but the tradeoff between reduction of spread and sacrifice of personal liberties seems like an easy win. A little more on modeling this reduction (ventilation + Corsi-Rosenthal boxes + UVGI) is here.

Furnace filter plus box fan is not a new idea, and we have plenty of entries in the homemade tool encyclopedia with early versions of it. You might have even experimented with it yourself. Here are a couple of builds by the guys on this forum:

By mr95gst:


By markfitz:


The cardboard-and-duct-tape construction of the Corsi-Rosenthal box is more rudimentary, and is intended to be built by people with minimal skills. The cube shape, which at first may appear gimmicky, is a reasonable way to maximize the filter surface area. It also incorporates a fan shroud to counter backflow around the edges of the box fan, which can be cut from the fan's cardboard package.

The construction of Corsi-Rosenthal boxes has recently started to shift from ad-hoc assembly to mass DIY manufacturing:



Here's a basic homemade tool for producing the fan shrouds in bulk:




This record player concept is clever, with the printed record label in the center and the tone arm switch:




Conceptually interesting, but unnecessary rotation is a red flag for gimmickiness.



Probably not practical, but this is an interesting take on connecting a CR box to a CO2 reader (these are used as proxies for measuring likely concentrations of coronavirus in the air). More info here. 3:49 video:

The cardboard and duct tape is endearing, but something like this would be more aesthetically acceptable to HMT members:



Another nice one, with more details here on GrabCAD:



Corsi-Rosenthal boxes use MERV 13 rated filters, which should filter out most of the aerosol drops in which coronavirus virions travel; around 1 micron in diameter. Yes, this means that you can also just filter coronavirus by putting a MERV 13 filter on your forced air furnace or air conditioner, although you should then rebalance it. They would be useful for pollen, wildfire smoke, and of course shop dust too. They're usually arranged in a cube shape, with the box fan on top, pushing air upwards, the filter flow direction arrows pointing into the cube, and some spacers on the bottom so that air can flow through the bottom filter (if it is built with a bottom filter, and not a cardboard bottom). The same concept can also be constructed with two or three sides, although the cube shape provides the greatest filter surface area, at the lowest noise level. Note how the airflow orientation pulls the sides of the cube together (the corners are also taped). Cost is under $100, and a child can build one.



A detailed assembly guide using a circular fan is here.

Analyses indicate that they're at least as effective as $1,000+ filters, and the filters should last at least 6 months, depending on use. The increased airflow and filter surface area may make them superior to most HEPA filters (equivalent to MERV 17-20), because although they have comparatively lower filtration efficiency for one pass, they have a higher flow rate and filter air faster (see CADR or Clean Air Delivery Rate). There's a good preprint on HEPA vs. Corsi-Rosenthal box efficacy here: Price-performance comparison of HEPA air purifiers and lower-cost MERV 13/14 filters with box fans, and another here: Characterizing the performance of a DIY air filter. Another nice UC Davis study is here: Testing Different Configurations of Do-It-Yourself Portable Air Cleaners. More analysis from Rosenthal is here, and also here from atmospheric chemist Eben Cross.



Here's a comparison of PM values for air before and after the Corsi-Rosenthal box:



Not all filters are performing equally; Rosenthal published an efficiency test here. People are making Corsi-Rosenthal boxes with the popular FilterBuy brand of filters on Amazon, but those aren't testing very well. Some more filtration test data:





I don't know if Corsi-Rosenthal boxes will be a transitional tool used only until we develop stricter indoor air filtration practices, or whether their utility will eventually make them more ubiquitous. They're far less controversial than masking or vaccination, and they're an easily constructed homemade tool that anyone can build.

[IntheGroove]

I probably won't build one but if I did I would make it blow-through instead of draw-through to keep all the badness inside...