> > > >

1945 Theatre Catalog, 4th Edition, Page 521 (495)

1945 Theatre Catalog, 4th Edition
1945 Theatre Catalog
1945 Theatre Catalog, 4th Edition, Page 521
Page 521

1945 Theatre Catalog, 4th Edition, Page 521

. Patron Protection with Ultraviolet light

Air-Duct Installation of Germicidal Tubes

Described for Sanitizing Air

About ten years ago Dr. Harvey C. Rentschler, head of Westinghouse Lamp research, became interested in the question of general sanitation of the air. He reasoned that, if food supplies, such as meat, milk, and water, are brought under the supervision of boards of health, resulting in a much better control of epidemics traceable to food, some comparable control ought to be applied to the air we breathe.

The method of air treatment that offered the greatest possibility was by radiation with ultraviolet light known to have bactericidal effects. Very little was known of the various groups of ultraviolet wavelengths or the effects of these groups. In fact, the general impression was that there was only one kind of ultraviolet. Analysis of visible light proves that it is made up of wavelengths representing different colors. In a similar manner, ultraviolet comprises several groups of wavelengths. One group, just shorter than the visible violet (3900 to about 3300 angstroms), is chemically active. It affects photographic plates and, in common with still shorter wavelengths, causes duorescent and phosphorescent materials to glow. A second group, measuring 3300 to 2850 angstroms, is biologically effective causing tanning, increasing vitamin D, and preventing rickets. The bactericidal wavelengths, 2850 to 2000, reach maximum effectiveness at about 2600 angstroms. Below 2000 angstroms, the wavelengths are rapidly absorbed by the air, especially the oxygen, thus producing ozone.

An electric discharge through mercury vapor at pressures measured by a few microns of mercury produces radiation which is very largely in the bactericidal region. The amount of electric power to produce this group of radiations is small so that it becomes practical and economical to use germicidal ultraviolet radiation for purifying air and thus protecting persons and products from airborne infection. The quantity of radiae tion required to kill various bacteria and mold spores was determined by an extensive series of tests using phototubes sensitive to different groups of ultraviolet wavelengths to measure the radiation reaching culture plates. The meter used gave an audible click for each unit quantity measured. For sim> plicity, the units were called ffclicks" and, on the standard meter, each is equivalent to 220 microwatt seconds to the square centimeter.

These tests on the scientific fundamentals formed the basis on which the number of Sterilamp ultraviolet lamps is determined for practically all types of installations. The number of and arrangement of Sterilamps specified is




Sterilamp Specialist (Retired), Lamp Division of the Westinghouse Electric Corporation

based on the scientific facts accumulated over years of research.

Modern air-conditioning systems proe vide air which is at the proper temperature and humidity and free from dirt. But air in occupied rooms, at times, is highly contaminated with bacteria which may cause respiratory and other diseases.

Adding Sterilamps to air-conditioning systems assures the delivery of air not only at the desired temperature, humidity, and cleanliness, but also virtually free from all disease-producing germs. Properly installed, Sterilamps can attain an efficiency of .98 per cent in the destruction of these disease-producing agencies.

Air-conditioning ducts must be constructed, equipped, and maintained so that there is no chance of damage due to fire and smoke originating within the duct.

Since ordinary glass enclosures around ultraviolet lamps would absorb much of the radiant energy and prevent irradiation of the air, it was necessary to con in Theatres

sider the temperatures generated by the lamps. Tests made on 30-inch Sterilamps showed that, at the warmest point directly over an electrode, there was an average temperature of only 156 degrees, with an average temperature over the entire active discharge portion of the tube of 122 degrees, and an ambient temperature of 70'degrees. In View of this, the Underwriters Laboratories, Inc., under the date of July 28, 1942, made the following statement:

Inasmuch as these lamps are of the cold cathode gas-tube type and so have no hot parts to cause ignition in the event of breaking and do not operate at a temperature high enough to ignite combustible materials, it is judged that the installation of Sterilamps in air ducts of air-conditioning systems does not constitute a fire hazard.

Locating Sterilamps in the plenum chamber, where the filtering equipment or the cooling coils are usually housed, should be given the first consideration. When there is an obstructionless length of at least three feet between the filter bank or cooling equipment and the fan opening, maximum efficiency at minimum cost is obtainable with such an installation. The comparatively large cross-section area of the plenum chamber reduces air velocity and makes possible the use of fewer lamps to provide the required amount of radiation. Simi lNSIDE THE AlR-CONDlTlONlNG DUCT of a large chemical plant, a workman installs for germs u trap-SM lamps. Ultraviolet light from the lamps will kill 98 per cent of the bacteria in the air passing through the duc'. thus purifying the air the workers breath and thereby lessening the possibility of contaminating products. The same principles of installing Sterilamps in ducts can be easily applied to theatre air-conditioning systems.
1945 Theatre Catalog, 4th Edition, Page 521