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UV

Info about UV for sterilization.

Rough draft for now.

CAUTION: we're working with 120V power here. It can kill and/or set fires.  BE CAREFUL!

Precautions

  • Needs to be UV-C (200-300 nanometer(nM) wavelength). Common "Black Light" lamps are mostly UV-A or UV-B, and not useful for disinfection.
  • Hazardous to people and their eyes, like prolonged exposure to sunlight or a welding arc.
  • can damage plastics.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4699414/ - Effects of Ultraviolet Germicidal Irradiation (UVGI) on N95 Respirator Filtration Performance and Structural Integrity: UV exposure causes "small increase in particle penetration ", "little effect on the flow resistance", "pronounced effect on the strengths of the respirator materials." UV-C may cause up to 90% loss of strength, and varies widely with different makes and models.

Dosages

From an online search, consensus seems to be that total dose of applied energy (measured in milliJoules per square centimeter - mJ/cm2) is the key parameter. Bulb power output is typically measured in Watts; 1 Watt for 1 second is 1 Joule. Note that Watts here means the actual UV-C being generated, which will be much lower than the input electrical power to the bulb.
https://aem.asm.org/content/84/17/e00944-18 UVC LED Irradiation Effectively Inactivates Aerosolized Viruses, Bacteria, and Fungi in a Chamber-Type Air Disinfection System : Tested UVC LED's against a variety of viruses and bacteria. If I'm reading their figures 1 and 2 correctly, it takes 30 to 50 mJ/cm2 to inactivate airborne viruses whereas bacteria only take 3 to 5.
 https://www.nebraskamed.com/sites/default/files/documents/covid-19/n-95-decon-process.pdf  N95 Filtering Facepiece Respirator Ultraviolet Germicidal Irradiation (UVGI) Process for Decontamination and Reuse : Claims 3-5 mJ/cm2 is enough to inactivate viruses on surfaces, but as much as 1000 mJ/cm2(!!) may be needed to decontaminate N95 masks. The pdf contains detailed procedures as used in a hospital setting.

Design

Looking here at DIY options for those who don't have access to a commercial  UVC disinfecting device.

SmartPond

A "9 Watt UV Replacement Bulb" is available from Lowes and other retailers. Brand is SmartPond, model is 52287. http://www.smart-pond.com/. Specs I have found so far are not really clear. This bulb is intended for decontaminating pond water so it *should* be UV-C, but I have not yet seen specs to confirm that. Output is rated at 23uW/cm2, which isn't useful without knowing the expected working distance.
These bulbs have a starter built in to the square base, so they just need a ballast in series. Ballasts for similar-looking visible-light bulbs seem to work fine. These are said to work:
  1. Keystone CC579TP (currently using this one).
  2. Sola FCF-7/9-TP (untested)
  3. Philips - Advance LPL-59-TP-I (untested)
Socket: This bulb uses a G23 two-pin socket. Not easy to find, so a workaround is to pull the pins ouf of an old 4-pin PC disk drive power connector. They're a bit small but can be made to fit with a bit of pushing, and some shrink wrap and electrical tape for insulation.
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