Scrutable

I have just been shown (on Facebook...) a link to this UK company, which makes a product called "ProtectivAir". As far as I can tell this works a bit like a "live" gas boiler: as you breathe air in, it is passed under a UV light which kills all the viruses and other pathogens within. It is being pimped

Not knowing anything about the biology here, I went to look at their site for evidence of efficacy in controlled trials, but found none. Does this sound plausible as a solution? What would the next steps be to test it?

UV light does kill stuff, I think flow rates and dwell times are important here. I imagine it’s a couple of orders of magnitude more expensive than a paper filter too.

UV is used to kill viruses. Here is an evaluation of one specific system: https://www.cambridge.org/core/journals ... ore-reader. I presume it uses 254nm wavelength UV-C. Shorter wavelength seems to be safer: https://www.nature.com/articles/s41598- ... 7ffc3c986f - 222nm. Despite that study, I'm not exposing myself to any UV-C until long term exposure studies are done.

The specific product you mention, ProtectivAir, says on the product page on its website:

This technology has been confirmed in tests at Public Health England, Porton Down. To view report click here

and I took a look at the report. It states in the executive summary:

The aim of the study was to assess the protective effects of aerosolised, UV-inactivated virus against subsequent influenza A infection in ferrets, which are the standard animal model for human influenza infection. Control groups of ferrets were exposed to infectious virus aerosol challenge, formalin-inactivated virus, or mock exposure.

so it seems that an unnamed device (hopefully the ProtectivAir) was used to render a virus inactive, and the purpose of this was to see if ferrets exposed to it were protected against a later exposure to a subsequent virus. So the device's ability to sterilise air was not directly studied.

Millennie Al wrote: Sun Mar 29, 2020 3:56 am so it seems that an unnamed device (hopefully the ProtectivAir) was used to render a virus inactive, and the purpose of this was to see if ferrets exposed to it were protected against a later exposure to a subsequent virus. So the device's ability to sterilise air was not directly studied.

Apparently doing initial testing with ferrets this is standard, but if I was an NHS worker I'd like to see a few more tests before I took off my N95 and replaced it with this device...

I did some digging. The company that makes it has only one medical-type person on the board of directors (link goes to Archive.org, as it seems there is no longer a "Meet the Team" page on the company site) --- an immunologist named John Maudsley, who is also the owner of a company whose mission is "curing [sic] cancer" with vaccines.

And by an amazing coincidence, local (just 4 minutes drive) to where he lives (Kenilworth) is the registered office of the Cancer Vaccines Charitable Trust. The person who I saw pimping the device on Facebook is from Redditch, half an hour from Kenilworth, and organised an event in January 2019 to promote the "cure cancer with vaccines" ideas.

The numbers are all very small (e.g., the charity turns over about £3,000-£5,000 per year), but my quackometer is starting to twitch a little bit here.

UV is good as a tool for sterilising surfaces - eg in the biological safety hoods that you see in many articles discussing vaccine development, these hoods will have a UV lamp for killing off any nasties between uses. But you don't tend to use harsh UV in the presence of humans, so it might be a bit tricky in a hospital ward.

Also UV doesn't go round corners, so it's best for flat surfaces!

Wiki.

UV treatment of drinking water and wastewater is well established. Most office water coolers have it, though how effective those are I am sceptical. Here, for example, are some commercial gadgets that can clean tens of litres of drinking water per minute, designed for private water supplies, although I can't find figures on their anti-virus effectiveness. They are small enough that if (if!) they could treat air effectively at the same flow rate, I could see them being viable as luggable PPE.

You can also get room air purifiers, although these seem less established. Production of ozone and other oxidants is a side-effect of zapping air with UV, so not ideal for breathing air. Here is some recent research on inactivation of airborne viruses using vacuum ultraviolet photocatalysis for a flow-through indoor air purifier with short irradiation time.

AMS wrote: Sun Mar 29, 2020 1:49 pm UV is good as a tool for sterilising surfaces - eg in the biological safety hoods that you see in many articles discussing vaccine development, these hoods will have a UV lamp for killing off any nasties between uses. But you don't tend to use harsh UV in the presence of humans, so it might be a bit tricky in a hospital ward.

Also UV doesn't go round corners, so it's best for flat surfaces!

It looks as if the UV is in a belt-worn cartridge through which inhaled air passes ProtectivAir Sterilizes Inhaled Air Using UV Light

What sort of size is the virus compared to the UV wavelengths being discussed? All I have is a vague recollection that poliovirus is about 40nm. What is the effect of this on effectiveness of irradiation with particular wavelengths of UV light?

jimbob wrote: Wed Apr 01, 2020 7:17 am What sort of size is the virus compared to the UV wavelengths being discussed? All I have is a vague recollection that poliovirus is about 40nm. What is the effect of this on effectiveness of irradiation with particular wavelengths of UV light?

According to this article they’re about 120 um in diameter.

FredM wrote: Wed Apr 01, 2020 3:03 pm

jimbob wrote: Wed Apr 01, 2020 7:17 am What sort of size is the virus compared to the UV wavelengths being discussed? All I have is a vague recollection that poliovirus is about 40nm. What is the effect of this on effectiveness of irradiation with particular wavelengths of UV light?

According to this article they’re about 120 um in diameter.

"Coronavirus virions are spherical with diameters of approximately 125 nm"

I don't think being sub-wavelength has much to do with it. UV can do things like ionize and break water molecules or create ozone from oxygen, just generally creating reactive species which are bad for lifeforms. This is in addition to directly messing up RNA or DNA.

Got me nanometres mixed up with micrometers - schoolboy error.

shpalman wrote: Wed Apr 01, 2020 3:32 pm

FredM wrote: Wed Apr 01, 2020 3:03 pm

jimbob wrote: Wed Apr 01, 2020 7:17 am What sort of size is the virus compared to the UV wavelengths being discussed? All I have is a vague recollection that poliovirus is about 40nm. What is the effect of this on effectiveness of irradiation with particular wavelengths of UV light?

According to this article they’re about 120 um in diameter.

"Coronavirus virions are spherical with diameters of approximately 125 nm"

I don't think being sub-wavelength has much to do with it. UV can do things like ionize and break water molecules or create ozone from oxygen, just generally creating reactive species which are bad for lifeforms. This is in addition to directly messing up RNA or DNA.

Yep - UV range photons have enough energy to cause chemical reactions, particularly in anything containing double bonds/aromatic rings, which are important parts of the DNA bases A C G and T (U in RNA). So basically it's driving chemical degradation. It's also why lots of plastic degrade in sunlight.

DNA and RNA have a broad absorption maximum at about 260 nm.

UV can be used used to disinfect a flow water through a pipe, and it is also possible to buy UV pens to disinfect glasses of water, so the idea of using it to disinfect a flow of another liquid (in this case, air) is not implausible but there are issues.

I don't know the system in question, but it might operate with a HEP filter which removes particles of diameters down to a specified low limit, which in itself is pretty good at removing infectious particles. If it doesn't operate with pre-filtering with a HEP filter, you have the problem of what is in particles that are sufficiently opaque to UV to mean that things inside the particles can remain viably infectious. I don't know how opaque to UV atomised droplets that are produced when people cough or sneeze are.

Suggested reading:

Wikipedia: Ultraviolet germicidal irradiation
Wikipedia: Ultraviolet germicidal irradiation - Disadvantages
Wikipedia: Ultraviolet germicidal irradiation - Air Disinfection

They should go belt & braces; gamma irradiation plus extreme heat - plasma heat.
Make it like domestos - killing 99% but then go a bit more. Maybe use Domestos for the first stage, then the plasma, then the gamma. Maybe acid then alkali? Or is that overkill?