Ultraviolet light with wavelength shorter than 300 nanometers is extremely effective in killing microorganisms. The most effective sterilizing range of UV is within the C bandwidth (UVC - 253.7nm). This range is called the germicidal bandwidth. UVC, is not known to cause cancer or severe sunburns. It does not penetrate past dead cell layers of the skin, but it may cause eye irritations or burns after prolonged exposure. The links below offer detailed information on the nature of the ultraviolet light, science research, facts and conclusions for its effectiveness. Most importantly, the UV light can be utilized to improve the indoor air quality and introduce a healthier environment to live, work or study.
The Germicidal Nature of UVC Light
Ultraviolet rays have shorter wavelengths than visible light. A wavelength, the distance between the crests of two waves, is often measured in units called nanometers. A nanometer (nm) is a billionth of a meter, or about 1/25,000,000 inch. Wavelengths of visible light range from about 400 to 700 nm. Ultraviolet wavelengths range from about 1 to 400 nm and are beyond the range of visible light.
Ultraviolet rays with wavelengths shorter than 300 nm are extremely effective in killing microorganisms. The most effective sterilizing range for UV is within the C bandwidth (UVC). This range is called the germicidal bandwidth. UVC has been used in hospitals for decades to sterilize surgical instruments, water, and the air in operating rooms. Many food and drug companies use germicidal lamps to disinfect various types of products and their containers.
The cleansing mechanism of UV is a photochemical process. The contaminants that pollute the indoor environment are almost entirely based upon organic or carbon-based compounds. These compounds breakdown when exposed to high intensity UV at 240 to 280 nm. Short-wave ultraviolet light can destroy DNA in living microorganisms and breakdown organic material found in indoor air. UVC’s effectiveness is directly related to intensity and exposure time.
UV rays must strike the contaminants directly in order to penetrate the microorganism and breakdown its molecular bonds. This bond breakage translates into cellular or genetic damage with the germs rendered harmless by robbing them of the ability to reproduce
According to the Environmental Protection Agency (EPA), 10% of all colds are caught outdoors, 90% are caught indoors! We’ve all watched helplessly as a cold virus passed from one member of the family to another.
Perhaps you suffer from asthma or allergies and despite desperate attempts to dust more, keep the windows closed, clean your bedding, clothing, carpeting and furniture more frequently, your symptoms still persist.
The EPA states that indoor air can be up to 70 times more polluted than the outdoor environment. One reason for this is that the HVAC duct work is full of airborne germs, their particles and by products. These microbes are alive and thriving inside the furnace or air conditioning systems. The airborne germs adversely affect the air quality as they are blown past the furnace or air conditioning filter and circulated throughout the buildings.
In-duct and upper air UV air cleaners can be utilized to disinfect the indoor air.
UV Health Facts
Why is UV-B harmful while UV-C (germicidal UV) is not? - The difference has to do with the ability of UV rays to penetrate body surfaces. UVC has an extremely low penetrating ability. It is nearly completely absorbed by the outer, dead layer of the skin (stratum corneum) where is does little harm. It does reach the most superficial layer of the eye where overexposure can cause irritation, but it does not penetrate to the top of the lens of the eye and can not cause cataracts. UVC is completely stopped by the ordinary eye glasses and by ordinary clothing.
How much UV exposure is considered safe? The National Institute for Occupational Safety and Health (NIOSH) has established safe exposure levels for each type of UV. These safe exposure limits are set below the levels found to cause eye irritation, eye being the body part most sensitive to UV. For germicidal UV (253.7nm) the exposure limit is less than 0.2µW/cm² over 8 hours.
How can people be certain they are not overexposed to UV? When upper room UV is first installed it must be checked with a sensitive UV meter to make sure reflected UV is less than 0.2µW/cm² at eye level. UV air cleaners must be installed well above eye level - usually 7 feet above the floor. UV tubes (lamps) within the air cleaners should not be directly visible from within 30 feet. Safety is assured if UV measurements at eye level meet NIOSH standards.
What are the symptoms and signs of UV overexposure? UV overexposure causes an eye inflammatory condition known as photokeratitis. For 6 to 12 hours after an accidental overexposure the individual may feel nothing unusual, followed by the abrupt sensation of foreign body or "sand" in the eyes, redness of the skin around the eyes, some light sensitivity, tearing, and eye pain. The acute symptoms last 6 to 24 hours and resolve completely without long-term effects. Overexposure of the skin resembles sunburn but does not result in tanning.
What precautions are needed with overhead germicidal UV? Fixtures must be turned OFF when cleaning, inspecting or changing the lamps. Persons hypersensitive to sunlight may need to wear protective glasses, clothing or use sunscreen on exposed skin. No special protection is need for most people.
Illnesses from poor IAQ:
• Common Cold and Flu
• Eye Irritation
• Sinus Irritation
• Symptoms of Asthma
• Skin Irritation
• Respiratory Problems
• Chicken Pox
• Legionnaires’ Disease
Indoor Air Quality and people's health
Indoor Air Pollution - air pollutants
How UV light kills germs
UV Sterilization Study Results
UV light references