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COVID-19 devices meant to sterilize your person and airline seat

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Patrick

Tue Jul 14 2020, 12:22AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

We all know the UV spectrum has some hazards associated with it.

There products dumped into the "COVID-19" crisis and are UV based. do we have any independent data on hazard vs effectiveness? My classes were canceled so i dont have access to the college lab. but id like to put together a method to test them.

klugesmith

Tue Jul 14 2020, 06:49PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Do you mean UVC exposure levels to kill viruses, injure human skin and eyes, or damage upholstery and paint? I think the numbers have been well known for decades. At work they are practicing with a mobile robot bearing a germicidal lamp head, to make rounds at night when no people are in the building.

Patrick

Wed Jul 15 2020, 02:01AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

klugesmith wrote ...

Do you mean UVC exposure levels to kill viruses, injure human skin and eyes, or damage upholstery and paint? I think the numbers have been well known for decades.

yes like this one here:

Dont LEDs suck for this purpose, and the mercury ones are too dangerous right ??

klugesmith

Wed Jul 15 2020, 06:42AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

I would guess the LED's suck for that, but had never heard of LED's at UVC wavelengths.

What makes plain old germicidal lamps dangerous? Risk of cuts from glass shards if they break?
T5's with bi-pin ends and clear non-fluorescent tubes have been in use for many decades.

Very efficient source of 254 nm, which is close to the most potent wavelength for damaging DNA.
No more mercury than a fluorescent lamp of the same size.
One application in 1970's and 1980's was EPROM erasers, which used ordinary germicidal lamps.
Of course the light can burn your skin, or the surface of cornea if your eye is exposed.

This site gives some numbers for UVC exposure to kill germs.

Left as an exercise for you is safety limits for UVC exposure to people.

I think a variant is "ozone" lamps, with differently formulated tube to let out the 185 nm.
That's in a wavelength range called Vacuum UV, because it doesn't take much air to block it.

Patrick

Wed Jul 15 2020, 11:42PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I was thinking in terms of:

1) if its low power enough to be eye safe, will it still clean a airline chair in 30 seconds ?
2) if it can sterilize at a distance and fast (assuming LEDs can), wont it be powerful enough to be dangerous to health ?

klugesmith

Thu Jul 16 2020, 04:51PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

I agree that handheld personal UVC sterilizers are silly. Like selling snake oil.
Looks like it takes 20 mJ/cm^2 to get 90% reduction of some kinds of virus.
Safety rules (see TLV) limit human exposure to 3 mJ/cm^2 cumulative in any 1000 seconds (?).
I think the first consequence of overdoing it would be temporary conjunctivitis in sensitive people.

A personal sterilizer, like for an armrest you are about to touch, might work if it were very intense, and well shrouded and/or required operator to wear protective glasses. How about paper test strips that change color when exposed to enough UVC to sterilize things?

Patrick

Sun Jul 19 2020, 08:19PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

klugesmith wrote ...

I agree that handheld personal UVC sterilizers are silly. Like selling snake oil...
... How about paper test strips that change color when exposed to enough UVC to sterilize things?

yes, this is the conclusion I came to as well, it doesn't look like these companies have put a lot of thought into reality.

klugesmith

Tue Jul 21 2020, 03:31PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Just heard of an emerging technology that might get a boost from Covid abatement.

Couple of companies are making excimer lamps that are efficient radiators of UV light at 222 nm. They claim that that wavelength is good for killing bacteria and viruses, but much safer than 254 nm for people. Its depth of penetration is so shallow that it doesn't reach live cells in skin or eyes. (As wavelengths go down and photon energies go up, they interact more strongly with matter & are stopped sooner. That trend eventually reverses, somewhere between deep UV and soft x-rays.)

Those companies have dreams of occupied rooms being continuously irradiated with 222 nm to reduce the spread of pathogens.

Looks like it won't be easy for you or me to buy a 222 nm lamp to play with.

Patrick

Tue Jul 21 2020, 07:37PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Excellent... i will consider some experiments.

klugesmith

Fri Jul 31 2020, 04:13AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Came to work for the first time in a week, to attend to some lab things.
Had to leave the room while new mobile surface-disinfecting robot made its rounds.

Then remembered we can't easily post pictures here. The one I saw (safely, from the other side of a plain glass window) is a lot like the ones on this maker's page:

As far as I can tell, the lamps are 254-nm germicidal tubes in about T8 x 36 inch size, driven very hard.

The operator monitored coverage using some special yellow paper post-it notes, that change color when irradiated enough to kill germs. I want to get one & see how it reacts to an old UV-EPROM eraser light.

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