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Health and Indoor Air Quality

Indoor Air Quality - IAQ, UV And People's Health

    UV facts

Health and Indoor Air Quality

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 some cases allergy or asthma symptoms can be triggered by the airborne microorganisms that are spread by the HVAC system.

In-duct and upper air UV air cleaners can be used to disinfect the indoor air and kill or inactivate the pathogenic microorganisms. A specialized application of germicidal UV on the coiling coil can also help by eliminating microbial growth from the coil and drain pan.

UV Facts - Germicidal UV Light

About Ultraviolet (UV) Light Used for Air Disinfection
by Edward A. Nardell, M. D. Harvard Medical School

What is UV or ultraviolet light? Ultraviolet light is part of the spectrum of electromagnetic energy generated by the sun. The full spectrum includes, in order of increasing energy, radio waves, infrared, visible light, ultraviolet, x-rays, gamma rays and cosmic rays. Since UV is not visible, it is technically not "light", but use of the term "ultraviolet light" is so widespread that, it will be used here. Most sources of light generate some UV. For air disinfection, UV is generated by electric lamps that resemble ordinary fluorescent lamps.

What is germicidal UV? This is UV of a specific type (253.7nm wavelength) known to kill airborne germs that transmit infections from person to person within buildings. Germicidal UV is aimed at the upper room air so that only airborne microbes are directly exposed. Room occupants are exposed only to low levels of reflected UV - levels below that known to cause eye irritation. Germicidal UV has been used safely and effectively in hospitals, clinics and laboratories for more than 60 years. UV does not prevent transmission of infections (e.g. colds) by direct person to person contact.

Is UV harmful? We are all exposed to the UV in sunlight. UV exposure can be very harmful, or harmless, depending on the type of UV, the type of exposure, the duration of exposure, and individual differences in response to UV. There are the following types of UV based on the wavelength measured in nanometers (nm):

UV-V ultraviolet with wavelength below 200nm is known as Vacuum UV or UV V.

UV-C (200 - 280nm) - Also known as "shortwave" UV, UVC or C-band UV includes germicidal (253.7nm wavelength) UV used for air disinfection. Unintentional overexposure causes transient redness and eye irritation, but does NOT cause skin cancer or cataracts.*
Click here for Ultraviolet Safety Study
* Never expose eyes or skin to UVC light from any source. Prolonged UV exposure can cause burns and temporary loss of vision or blindness.

UV-B (280 -315nm) - A small, but dangerous part of sunlight. Most solar UV-B is absorbed by the diminishing atmospheric ozone layer. Prolonged exposure is responsible for some type of skin cancer, skin aging, and cataracts (clouding of the lens of the eye).

UV-A (315 - 400nm) - Longwave UV, also known as "blacklight", the major type of UV in sunlight, responsible for skin tanning, generally not harmful, used in medicine to treat certain skin disorders.

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 it 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 irradiance limit is set to 0.2W/cm. See sidebar for UV exposure details →

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 0.2W/cm 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 needed for most people.

UV light Next UV Topic - Indoor Air Pollution


Ultraviolet Light
"Germicidal ultraviolet light installed in HVAC systems has gained great popularity over the last several years. Unfortunately, many of the claims by over-zealous manufacturers and distributors are exaggerated
and some just blatantly false. While there is no one cure for indoor air quality problems, ultraviolet light technology does provide benefits and can be part of an overall Indoor Air Quality improvement plan."
Indoor Air Quality Association
Uv light fights allergy, asthma, mold
UV Exposure Level
The American Conference of Governmental Industrial Hygienists (ACGIH) Committee on Physical Agents has established a TLV (Threshold Limit Value) for UV-C exposure to avoid skin and eye injuries. For 254nm UV, this TLV is 6mJ/cm over an eight-hour period.

The TLV function differs by wavelengths because of variable energy and potential for cell damage. This TLV is supported by the International Commission on Non-Ionizing Radiation Protection and is used in setting lamp safety standards by the Illuminating Engineering Society of North America. This TLV is interpreted as if eye exposure in rooms is continuous over eight hours and at the highest eye-level irradiance found in the room. In those highly unlikely conditions, a 6mJ/cm dose is reached under the ACGIH TLV after just eight hours of continuous exposure to irradiance of 0.2 W/cm. Thus, 0.2W/cm is widely interpreted as the upper permissible limit of irradiance at eye height.

Safety of Upper-Room Ultraviolet Germicidal Air Disinfection for Room Occupants

Health and Indoor Air Quality
UV In The Light Spectrum
Ultraviolet Light - UV - UVC, UVB, UVA

The shortwave UV, also called UV-C or UV C band, is the germicidal UV, utilized in air cleaners and water purifiers.


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