UVC Disinfection

Posted: October 14, 2020 in General Commentary, Uncategorized

“Once more unto the breach, dear friends, once more..”

W. Shakespeare

For purposes of furthering the exchange of ideas and information on methods of applying SSL (Light) to address the Pandemic we find ourselves in….

I offer the following, posed as FAQs.

Can UVC light be used to deactivate the virus that causes COVID?

Short answer is Yes. It has been shown that UVC radiation between 200nm and 260nm, at energy levels of at least 25mJ can be effective in deactivation of viral contaminants as well as other bacteria/germs present.

Is UV safe for human exposure?

The short answer here, in two parts:

Yes, exposure to UVC wavelengths shorter than 230nm are considered safe for human exposure.

No, exposure to UVC wavelengths greater than 230nm are considered hazardous to human skin and eye tissue, and should not be considered for use where humans or animals will be present when the light source in in operation.

Can LEDs be used for UVC disinfection?

Another two part answer here:

Yes, when the space is empty, LEDs can be utilized that generate UVC light, at intensities and power levels that will produce a disinfection effect against COVID and other viral contamination.

No, if the intent is to expose the human occupants to the LED UVC radiation. LEDs are limited to wavelengths of greater than 254nm, which is considered harmful to humans.

So, what are samples of sources that are safe for human exposure?

The following are currently the leading, commercially available, verified products that produce safe far UVC radiation at power levels required to attain the target 25mJ to 250mJ energy levels to realize a real disinfection result, that is safe for human exposure:

Ushio Care 222. This is an emitter source that includes band pass filters to eliminate harmful UVC radiation above 230nm.

Healthe is a downlight cylinder product, one of a couple of form factors offered, that combine a 222nm light source with conventional LEDs to provide both Circadian support as well as disinfection.

Air disinfection is another way to approach UVC application to disinfection, where human exposure is not exposed to the light itself. Apache has a wide range of products for this purpose.

These products represent the type of product and quality necessary to avoid issues like happened in China, when children were exposed to unfiltered UVC radiation of the wrong wavelength for 9 hours.

Other products, like the Kenall Indigo Clean products are effective against some bacterial contamination, but are not effective against viruses. As noted in prior articles, viruses are not living organisms, so are not deactivated by light in the UVB or UVA regions.

Is Light Disinfection the Best Solution?

This requires a three part answer:

Yes, when the surface or air being disinfected can be directly illuminated, at energy levels required (power and time) to produce the desired result. While chemicals are effective, they are more difficult to apply evenly and consistently than can be achieved by illumination. Further, chemicals that are effective against viruses can also to be toxic to humans if improperly applied or disposed of. Light disinfection appears to be a solution for spaces, like food service, that are difficult to continually re-disinfect using chemical processes.

No, when the surfaces are not exposed directly to UVC light, as UVC does not reflect from most surfaces, and when it does, the reflected power level is significantly reduced – making indirect exposure unreliable. Further, when surfaces are dirty or contaminated (could even be from a cleaning agent), the UVC light may not penetrate, thus will have minimal to no impact. 222nm energy has a hard time penetrating many surface contaminants that appear to be invisible, so some care must be taken to insure the irradiated surfaces are clean of contamination.

Best Solution is to use UVC light disinfection in concert with other methods, such as safe chemical disinfection, which can be found as List N products at the CDC web site. The combination means that surfaces are properly cleaned to start with, increasing the efficacy of UVC disinfection, while those hidden from direct light are also covered. Using UVC light alone is not a strong strategy.

Finally, is this my last word on this topic?

Short answer is No.

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