Last Updated on October 19, 2018
The air in buildings often contains potentially health-threatening bacteria and virus, particularly for people who have impaired immune systems. Tuberculosis is an infectious disease that can be contracted by breathing air containing the tuberculosis bacterium. To reduce the risk of transmission of disease, the air can be disinfected and purified by ultraviolet germicidal irradiation (UVGI) which is produced by Germicidal UV Lamps. In addition to controlling tuberculosis, Germicidal UV Lamps are applicable for controlling other microbial disorders such as influenza, measles, and aerosolized bioterror agents.
How is tuberculosis spread?
Tuberculosis is spread when a person who has tuberculosis disease coughs or sneezes, thereby releasing the bacteria into the air in the form of an aerosol. Persons inhaling these bacteria may become infected.
What technological methods can be used to reduce the risk of infection, and how do they work?
Purifying the air through UVGI destroys the infectious agents in the air because exposure to ultraviolet (UV) radiation damages the deoxyribonucleic acid (DNA) of bacteria and virus, including that of Mycobacterium tuberculosis. This DNA damage stops the infectious agent from replicating. Air treatment using UVGI requires that persons in the treated space be shielded from excessive exposure to the UV radiation. This can be done by placing the UV source in the ductwork of a ventilation system (AeroLogic®), in a freestanding disinfecting system, or in an open location within a room (Hygeaire®). When installing UVGI in an open location, to prevent undue human exposure to the UV radiation, it is important to ensure that the UV radiation is restricted to the portion of the room that is above standing head height. The UVGI technology has long been used in laboratories and healthcare facilities, but it is also applicable for use in spaces where people congregate. The Centers for Disease Control and Prevention (CDC) has recommended that UVGI purification be used as a supplement to air dilution, in high-risk settings.
How air purification is achieved using upper room UVGI?
Upper room UVGI is achieved by using a UV-C lamp in a specially designed fixture that directs the UV radiation to the upper room area (Hygeaire®). The UV lamp used for UVGI is a shortwave, low-pressure tube that produces ultraviolet wavelengths lethal to microorganisms. Approximately 95% of the ultraviolet energy emitted from germicidal lamps is at 254 nanometers, (see Figure 1) the region of germicidal effectiveness most destructive to bacteria, mold, and virus.
The lamp also emits some visible short wavelengths that appear as blue light. UVGI lamps are based on conventional fluorescent lamp technology, except they have a special glass to emit UV and have no phosphor coating to produce visible light. Like conventional fluorescent lamps, UVGI lamps are available in linear and compact forms, both of which require ballasts to operate.
Figure 1. Spectral power distribution of the low pressure UV-C Wavelengths
The Hygeaire® fixtures used for upper room UVGI are designed to shield the lamp from direct view of persons in the occupied space and to emit the UV-C radiation in a wide, flat, slightly inclined distribution such as that shown in (see Figure 2). This is usually accomplished by placing the UV source inside an aluminum or stainless steel box and passing the UV rays through a series of wide horizontal louvers (see Figure 3). UVGI fixtures are available in forms suitable for wall and corner mounting and for suspension from the ceiling (Hygeaire®). The amount of UV radiation emitted from the fixture is low, relative to the amount emitted by the UVGI lamp, because of the absorbing effect of the louvers in the fixture.
Figure 2. Distribution of UV radiation from a Hygeaire® wall-mounted UVGI fixture
Figure 3. Cross-section through a wall-mounted Hygeaire® fixture (Manufactured by Atlantic Ultraviolet Corporation®)Figure 4. Example of the coverage area of the Hygeaire® Model LIND24-EVO from Atlantic Ultraviolet Corporation®
What does an upper room UVGI Hygeaire® installation look like?
Figure 5 shows a Hygeaire® upper room UVGI installation in the main room of St. Agnes Shelter for the Homeless, New York City. The ceiling height is 12 feet. Eleven UVGI fixtures, of the type shown in Figure 6, are mounted on the wall, approximately 8 feet above the floor. Figure 7 suggests the UV radiation distribution from this fixture in terms of the blue pattern visible on the walls.
Figure 5. Main room of the St. Agnes Shelter for the Homeless
Figure 6. Wall-mounted UVGI fixture used in the St. Agnes Shelter for the Homeless (Atlantic Ultraviolet Corporation® Hygeaire® Model LIND24-EVO)
What is the future of upper room UVGI?
Upper room UVGI is likely to become a common feature of buildings. Upper room UVGI is an effective method for cleansing the air of many types of virus and bacteria, including some of those suggested as weapons for bioterrorism. The technology is well-developed. It can be easily retrofitted in many buildings. It has been shown to be effective in the laboratory and is currently undergoing an extensive test of its effectiveness for preventing the spread of tuberculosis in representative environments. Estimates of its cost-effectiveness for this purpose support the use of Upper Room UVGI.
Figure 7. A wall-mounted Hygeaire® UVGI fixture used in the St. Agnes Shelter for the Homeless (the distribution of ultraviolet radiation from the fixture is indicated by the pattern of blue light on the nearby walls)
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