This article describes Ultraviolet radiation, how it is used, the danger to friendly cells and a home decontamination chamber to clean surfaces of the SARS-CoV-2 virus.
Dr. Art Hunter, Canadian Club of Rome Board of Directors, was the designer, developer, fabricator and first operator of this home decontamination chamber.
The first section below is a collage of material available on the Internet. Ultraviolet radiation was first discovered and used over 130 years ago and there are many products commercially available. The author sought a chamber that provided safe control of the flux density, exposure time, distance to the lamp and measurements so experiments and operations could be executed with ease and safety. Development of a low capital cost chamber was the only option.
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Ultraviolet (UV) radiation occupies the portion of electromagnetic spectrum from 100 to 400 nanometers (nm). The UV spectrum consists of three regions, as designated by the Commission Internationale de l’Eclairage:
- UV-A (315–400 nm)
- UV-B (280–315 nm)
- UV-C (100–280 nm)
For most people, the main source of UV exposure is the sun. Exposure from the sun is typically limited to the UV-A region, since the earth’s atmosphere protects us from the more harmful UV‑C and UV-B regions. Limiting our exposure time and using sunscreen lotions are two easy, effective methods for controlling overexposure to UV radiation. Only artificial light sources emit radiant energy within the UV-C band. Wavelengths below 180 nm (vacuum UV) are of little practical biological significance since they are readily absorbed by the air.
Because of its ability to cause chemical reactions and excite fluorescence in materials, UV light has a large number of useful applications in modern society. Listed below are some of the uses of specific wavelength bands in the UV spectrum:
- 5 nm: Extreme ultraviolet lithography
- 30–200 nm: Photoionization, ultraviolet photoelectron spectroscopy
- 230–365 nm: UV-ID, label tracking, barcode scanners
- 200–400 nm: Forensic analysis, drug detection
- 230–400 nm: Optical sensors, various instrumentation
- 240–280 nm: Disinfection, decontamination of surfaces and water (DNA absorption has a peak at 260 nm). Energy is absorbed by DNA and RNA strings which breaks the molecular bonds rendering the bacteria, germ, pathogen, mold or virus particle unviable.
- 270–360 nm: Protein analysis, DNA sequencing, drug discovery
- 280–400 nm: Medical imaging of cells
- 300–320 nm: Light therapy in medicine
- 300–365 nm: Curing of polymers and printer inks
- 300–400 nm: Solid-state lighting
- 350–370 nm: Bug zappers (flies are most attracted to light at 365 nm)
Adverse health effects associated with exposure to UVR are rated in severity according to wavelength and duration of exposure. The most significant adverse health effects have been reported at wavelengths below 315 nm, known collectively as actinic ultraviolet.
The effect of UV exposure is not felt immediately; the user may not realize the danger until after the damage is done. Symptoms typically occur 4 to 24 hours after exposure. It is important to note that UV radiation is harmful to both skin and eyes.
The effects on skin are of two types: acute and chronic. Acute effects appear within a few hours of exposure, while chronic effects are long-lasting and cumulative and may not appear for years. An acute effect of UVR is redness of the skin (called erythema), similar to sunburn. Chronic effects include accelerated skin aging and skin cancer.
The eyes are very sensitive to UV radiation. Prolonged direct exposure to UV-B and UV-C light can cause serious effects such as conjunctivitis and photokeratitis. Conjunctivitis is an inflammation of the membranes lining the insides of the eyelids and covering the cornea. Photokeratitis manifests as an aversion to bright light. The severity of these conditions depends on the duration, intensity, and wavelength. Symptoms may appear 6 to 12 hours after exposure and may subside after 24 to 36 hours with no permanent damage.
Unlike the skin, the eyes do not develop a tolerance to repeated exposure to UV. The absorption of UV-A radiation in the lens of the eye may produce progressive yellowing with time and may contribute to the formation of cataracts, causing partial or complete loss of transparency.
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The danger of UVC radiation is also to cells in humans, pets and plants. Further, UVC is classified as non-ionizing or no impact at the atomic level. However, the band just above UV is classified as X-RAYS which are classified as ionizing radiation where different materials (isotopes) can be formed with properties quite different from the base atom. Just exactly where this split takes place on the frequency spectrum depends on the material and its atomic structure and other environmental conditions. Hence, great care in the use of UVC is warranted. The safety precautions used in many of the products available for purchase are:
- reduce the radiation flux density
- reduce exposure time
- access control — clear the area of people, pets and plants
- containment of the dangerous radiation within a room or chamber
- use of interlocks to prevent inadvertent exposure due to human error or equipment failure
- adequate ventilation for possible isotope, ozone or outgassing to escape
- training of the equipment operators and clear written procedures
- use of personal protection equipment
- maintaining a log of equipment use, problems and outcomes.
A home UVC decontamination chamber has been developed by repurposing a used microwave oven. All the microwave generation electronic hardware was removed and discarded, the timer, door interlock and firmware was retained, the UVC lamp mounted, the door covered inside and out, and the entire unit mounted in another light tight box with other special interlocks.
The following PDF gives details of the design with many pictures during the chamber’s commissioning process.