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1945 Theatre Catalog, 4th Edition, Page 512 (486)

1945 Theatre Catalog, 4th Edition
1945 Theatre Catalog
1945 Theatre Catalog, 4th Edition, Page 512
Page 512

1945 Theatre Catalog, 4th Edition, Page 512

Ultraviolet Air Sterilization in Theatres

Summary of the Basic Findings of Science;

Notes on

Men of science have long recognized the fact that bacteria-laden air, arising from common occupancy of enclosed spaces, constitutes a universal hygienic hazard, since such diseases as colds, influenza, measles, whooping cough, scarlet fever, and diptheria may be transmitted by air-borne germs.

To curb possible cross infection and epidemic spread, investigators determined that ventilation equivalent to 100 complete changes of air an hour is necessary to secure any marked reduction in the transmission of air-borne contagion. Since the installation of an air-conditioning and ventilation system to meet such a terrific load is engineerineg impracticable and economically inexpedient, other solutions were sought.

As early as 1877, 'it was demonstrated that the sunis rays are a powerful sanitizer, and that is due to the invisible, ultraviolet rays. Practical difficulties beset the efforts to develop a lamp which would make possible a practical application of this fact of nature. It was not until the mid-thirties that light scientists and engineers learned to control the infra-red (heat) waves, the visible radiation, and the excessive ozone production and, thereby, to develop a practical generator of the germicidal ultraviolet rays. The obstacles were overcome largely through the perfection of a special glass, capable of transmitting approximately 80 per cent of the radiation at about the 2537 A.U.* point, the very peak of ultravioletis bactericidal power.

The installation of germicidal lamps presents a clinically-proved and economical means of making safe the air in a confined space. The germ-killing capacity of a properly installed system is equivalent to from 100 to 500 complete changes of air an hour, an efficiency far in excess of anything than can be accomplished by mechanical ventilation.

Lamps Useful in Many Places

Germicidal lamps, now being made available to theatres, follow the successful application of the device to other fields. In hospitals, the lamps are used over operating tables to throw a barrier of germ-killing ultraviolet light around the patient. Nurseries are equipped to prevent transmission of infection from one infant to another and from nurse to

* A. U.. abbreviation for Angstrom unit, named for the great Swedish physicist, A. J. Angstrom (18144874), is the unit of wavelength, approxi' mately l/250,000,000 inch. Indicative of the spread and arrangement of the radiant energy spectrum, let it be said that ultraviolet ranges from 136 to 3.800 A. U.. visible light from 3,800 to 7,200 A. U.. infra-red (heat) from 7,200 to 4,000,000 A. U.. and Hertzian waves and the radio bands from 4,000,000 A. U. In the ultra,violet band, the following areas are recognized: x-rays to 1.000 A. U.. ozone formation from 1,000 to 2.000 A.U.. germicidal from 2,000 to 2,800 A. U.. fluorescent excitation from 2,500 to 4,400 A. U. and tanning and antirachitic portion from 2.800 to 3.800 A. U.

infant. Business ofiices, stores, and factories are supplementing air-conditioning with germicidal-lamp conditioning. The lamps are also aiding in the prevention of contamination in blood-plasma laboratories, in penicillin-producing plants, in food and beverage processing.

Possible Usetin Decoration

In devising lights to give a definite result, there is no way of achieving the end of having a single, exclusive wavelength ethere is always a spread. Accordingly, with lamps designed to furnish light in adjoining bands of the spectrum, there would, by the very nature of things, be some overlapping.

The utlization of fiuorescence involves the so-called black light, which, within the range of 2,500 to 4,400 A.U., causes the characteristic glowing. The peak in this range is around 3,600 A.U. On the other hand, the germicidal band ranges from 2,000 to 2,800 A.U., with the peak at just above 2,500 A.U. Thus, it will be noted that in these two types of lamps there is an overlap between 2,500 and 2,800 A.U. where the germicidal lamp has also properties of iiblack light?

When germicidal lamps are used in units, and some of the light hits the wall above the point of fixture attachment, there is the possibility that the interior decorator might deve10p a decorative scheme which would take advantage of this tfextra added" property.

Extreme care must be used in selecting colored or patterned material for areas subject to ultraviolet irradiation. In the same way that the actinic rays of the sun cause fading, so the germicidal lamp, being much richer in such active rays, will also induce a fading. Accordingly, the decorator must know his fabrics, and select for use in these places only those that are definitely colorfast.


In appearance, germicidal lamps are generally slender, rod-shaped glass tubes. A faint blue light is given off when the lamp is in operation, but the rays dealing death to air-borne microbes are invisible.

Commercially available in various lengthsewith 30-inch size the most economical for theatre use--the lamps may be used singly or in groups of as many as four in series and wired on a special transformer.

The lethal power comes from a high concentration of ultraviolet rays, produced by an electrical discharge between the electrodes through a mixture of inert gases and mercury vapor in a tube which will transmit the bactericidal wave lengths of natural sunlight.

About 80 per cent of the radiant-energy output of these lamps is confined.


Use of Certain Commercial Units

Ozone Charcteristics

Radiation of wavelengths shorter than 2,000 A.U. forms ozone from the oxygen in the air. The amount is controlled by the transmission properties of the glass envelope of the lamp, and also by the 2537 A.U. radiation, that decomposes the ozone and converts it back to fiordinary" oxygen. Humidity is also an important factor, as the higher the humidity the less the concentration of ozone.

Ozone is also destroyed by the absorption on or contact with various surfaces, by oxidizing vapors and gases, and, to a slight extent, by spontaneous decomposition.

The amount of ozone produced by a cold-cathode lamp is rarely above 0.04 to 0.15 part to one million parts of air. Incidentally, ultraviolet lamps produce only pure ozone, and never any nitrous oxide (laughing gas) or the poisonous nitric oxide.

The maximum amount of ozone permissible for human tolerance, according to the National Bureau of Standards, is, for prolonged exposures, 0.5 part to one million parts of air. So, the amount of ozone that is generated by a germicidal lamp is well below the tolerated peak.

While ozone is a powerful oxidizing agent, it should be noted that, in all the duct installations supervised by the men of Westinghouse, there has been no observed oxidation (rusting) of the duct work from this cause.

The production of ozone might be thought by some to be objectionable, but this is probably a mere matter of personal opinion, as most people find it pleasant. Actually, the ozone can be beneficial, since it makes the air sweetsmelling and tends to keep down any molds which might cause a musty odor.

Destruction of Bacteria

It is beyond the scope of this article to describe in detail the experiments conducted in establishing the principles of ultraviolet lightis germicidal power, but, here are a few of the considerations which are important.

In the first place, the method by which the bacteria are killed is interesting. Under the influence of ultraviolet light --and just a few seconds are sufficient to start the process-the bacteria start to swell, and, as the internal pressure becomes greater, vescicles are formed on their surface. Continuing the exposure, the bacteria continue to swell, until the internal pressure is so great that they actually explode.

While this process has actually been observed, photographing it has been almost impossible. Since the action is the same on microscopic animals-but those considerably larger than bacteriaeand

1945 Theatre Catalog, 4th Edition, Page 512