Is there a real danger of Tuberculosis?
The air in buildings often contains potentially health-threatening bacteria and viruses, particularly for people who have impaired immune systems. 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, as described in more detail below. Germicidal UV Lamps are not only effective for the control of tuberculosis transmission, but also for other microbial disorders such as Influenza, Morbillivirus (causing measles), and aerosolized bioterror agents.
Tuberculosis is an infectious disease that can be contracted by breathing air containing the tuberculosis bacterium. When an infected person coughs or sneezes, they release these bacteria into the air in the form of an aerosol. To learn more, read our blog post on Mycobacterium Tuberculosis.
What technological methods can be used to control Tuberculosis transmission, and how do they work?
According to the Rensselaer Polytechnic Instituteopen_in_new, reducing the risk of airborne tuberculosis transmission can be done in three ways: dilution, filtration, and purification by ultraviolet germicidal irradiation (UVGI):
- Dilution doesn’t destroy bacteria but spreads it over a larger volume of air. New air is introduced into a room by natural ventilation (opening windows or doors) or mechanical ventilation (such as air conditioning units).
- Filtration reduces the concentration of harmful microorganisms in a room by trapping them in a filter and removing them from the circulated air.
- Purification (UVGI) neutralizes harmful bacteria like Mycobacterium Tuberculosis by destroying its DNA structure and preventing it from multiplying. Read our Benefits of UV-C blog post to learn more about the cost and efficiency of upper room UVGI when compared to dilution, filtration, and other disinfection methods.
Air treatment using UVGI requires that persons in the treated space be shielded from excessive exposure to the UV rays. This can be done by placing the UV source in the ductwork of a ventilation system (our AeroLogic® line), in a freestanding disinfecting system, or in an open location within a room (our Hygeaire® line).
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When installing UVGI in an open location, to prevent undue human exposure to the UV rays, it is important to ensure that UV-C wavelengths are 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 CDC and NIOSH have recommended, in their paper Environmental Control for Tuberculosisopen_in_new, that UVGI purification be used as a supplement to other preventative methods, in high-risk settings.
How is control of Tuberculosis achieved using upper room UVGI?
Disinfection with upper room UVGI is achieved by a UV-C lamp in a specially-designed fixture that directs the UV radiation to the upper room area (like our Hygeaire®). The UV lamp used for UVGI is a shortwave, low-pressure tube that produces ultraviolet wavelengths lethal to harmful microorganisms. Approximately 95% of the ultraviolet energy emitted from germicidal lamps is at 254 nanometers, (see Figure 1) the region of germicidal effectiveness designed to control the transmission of bacteria, mold, and viruses including Tuberculosis.
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.
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 ultraviolet fixture.
Any advice for those wishing to use UVGI to control Tuberculosis transmission?
The CDC offers guidelines on the use of UVGIopen_in_new to prevent disease transmission. Such guidelines offer little advice to the room designer seeking to properly place UVGI systems. The designer needs to know whether the room is suitable for upper room UVGI, how many fixtures to use, and where they should be located. The suitability of a room for upper room UVGI is determined by the ceiling height and the UV reflectance of the surfaces in the upper room.
Upper room UVGI should not be used in rooms with ceiling heights less than 8 feet. All upper room surfaces likely to be UV irradiated should have a reflectance at 254 nanometers of less than 5%. A low UV reflectivity finish must be used on upper surfaces such as the ceiling to ensure that UV radiation levels in the occupied space of the room do not exceed occupational eye and skin safety standards.
To determine the appropriate number of fixtures, a simple guideline is that 30 watts of UV lamp power are required for each 200 square feet of floor area. As for location, manufacturers of UVGI equipment provide information on the area over which their equipment can be expected to damage Tuberculosis bacteria and control transmission (see Figure 4).
Such information can be used to determine the number and positioning of the equipment necessary to cover the entire upper room effectively by overlaying the coverage area of the individual fixtures on the floor plan of the space to be treated.
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-C distribution from this fixture in terms of the blue pattern visible on the walls.
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 to control the transmission of many viruses and bacteria, including Tuberculosis. 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.
Originally published as the Rensselaer Polytechnic Institute articleopen_in_new, Controlling Tuberculosis Transmission with Ultraviolet Irradiation, 2003.
Learn More & Shop Hygeaire®
Made in the USA from U.S. and imported parts (since the 1940s), our Hygeaire® UV-C Indirect Air Fixtures are constructed corrosion-resistant stainless steel, aluminum, and the highest quality materials. They use germicidal lamps to project UV rays across upper room air in occupied spaces. Models can be mounted on the wall or ceiling in residential, commercial, and industrial applications.
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