Sylvania Engineering Bulletin - Germicidal & Short Wave UV 1962

8/13/2019 Sylvania Engineering Bulletin - Germicidal & Short Wave UV 1962

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GERM ICIDAL AND SHORT-WAVEULTRAVIOLET RADIATIONRadiant energy from tl're sun may be divided into tilreebroad bands: long-wave or infrared energy such as llcat.whjch is invisible; visible energy which produces light arrclcolor; and short-wave energy such as invisible ultr-aviolet. Asshorvn in Figure f . it is the ultraviolet radiation betlveerr120 and 300 nanometers that is germicidal in eflect;i.e.. itdestroys bacteria, rnold, yeast, and virus. Practically rrone

too

Figure 1

GERMICIDAL LAMPSGermicidal lamps are electricaliy the same as tluorescentlamps ol corresponding sizes and wattages and require

essentially the sar.ne auxiliary equipment. These lampscliftbr physically from fluorescent lamps in that theycontair.r no phosphor and are constructed with a specialtype of glass to permit maximum emission of germicidalultraviolet energy. The glass used in ordinary fluorescentlarrips filters out ali germicidal ultraviolet energy. The

of the solar ultraviolet energy below 295 nanometers canreach tlie earth's surface due to absorption in the ozor.rclayer ol tlie r-rppel atmosphere. Although the percentage olultraviolet ellergy in sunlight is small, there is still appre-ciable energy in the shorter rvavelengths. The germicidalelfectiveness of sunlight valies enorntously with the hour ofthe day and also with the seasons. Germicidal lamps.holvever, make ultraviolet energy available with control-lable limits regardless ol r.ratural environinental conditions.

300 400

physicai and electrical characteristics of the germicidal lampsare showr.r in Table I.The rnost practical method of generating gcrmicidalradiation is by passage of an elcctric discharge thror.tgh alow-pressure mercury vapor. About 95o/o of the ultravioletenergy is iadiated in the 253.7 nanometer lir.re. This is inthe wavelength region of greatest gcrrnicidal efficacl,.Typical spec,ral power distribution for the tubular geLrni-cidal lamps, Showing the principal radiation, is illustrated inFigure 2.

200Il.- EXTREME uv-----+- FAR uv-*- NEAR uv{ WAVELENGTH (NANOMETER UNITS)ELEcTRoMAGNET|c SPEOTRUM(enlorgement of ultroviolet region)

VISIBLEVIOLET RED

cosMrc nx/e aMMA -*t/, aavs/'t JLTRAOLET INFRARED ,/RADIO WAVES

X RAYS----r.SCHUMANN - I I BLAcK+G ER M lC IDAL+I l.- t_ I G H T ----r

l?HN'l VISIBLE

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=o(ttF=J=,lrj=o-Fzo0c 400

WAVELENGTH ( NANOMETERS)Figure 2. Principal radiation of the G30T8 lamp. When the weaker radiation is included, the total radiationbetween 250 and 600 nm is approximately 10 watts. The only other significant radiation in, or near, thevisible region falls between 1000 and 1750 nm; this amounts to less than 1/4 watt. The lower wattageGermicidal lamps have spectral radiant power distributions similar to the graph shown; approximatemultiplying factors are: Gi5T8 = 0.39; G8T5 = O.17;G4T411= 0.07.

TABLE I. GERMICIDAL LAMP DATAADescriptionRated Power (watts)BulbBaseNominal Lamp Length (inches)Nominal Arc Length (inches)Rated Life (hours)253.7 nm Output (watts) e253.7 nm Power Density at ^ \One Meter (microwatt per cmzl e

JApprox. Lamp AmperesApprox. Lamp VoltsApprox. Lumens

c4s11 b4

s11I nter.2114

40000.11.2 |

0.3510 112

c4T4l1414c

4 Pin Radio5 3/4

6d40000.68s

0.1 15215

G8T5o

T5Min. Bipin

1281126000

1.415 h

0.175740

G15T8i5T8

Med. Bipin1814

7500a235h

0.3056

100(U-shape) makes

G3OT830T8

Med. Bipin3632

75008.480h

0.35100250

lamp approxi-- The life and radiant power of these lamps are based onoperation with ballasts providing the proper operatingcharacteristics.The G4511 is classif ied primarily as an ozone producinglamp since it emits power at 184.9 nm capable ofgenerating ozone. The total power radiated at 184.9 nmis approximately one milliwatt. No starter is required forthis lamp, but a ballast is required.

Bent tube constructionmately one inch wide.Measured along U-shape.100 hour value.On line perperrdicular to plane of filament (C 2V).On line perpendicular to plane of U through larnpcenter.On line perpendicular to lamp axis through lamp center.

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The majority of gennicidal lamps operate most elficient_ly in still air at an ambient temperature of 7joF. These arethe conditions under which the ultraviolet output ismeasured and tabuiated. The ultraviolet output, and conse-quently the germicidal effectiveness, of these lamps de_creases at temperatures above or below this optimumtemperature. Lamps operating in a room at .+0oF produceonly about two-thirds to three-fourths as much ultravioletpower as aI 17oF . Il a lamp is cooled by air currents or bysubmersion in a iiquid, the ultraviolet output similarlydecreases. Typical maintenance information for the germi_cidal lamps is shown in Figure 3. Maintenance values forany particular iamp depend on several factors. The mostimportant are the number of hours that a lamp has beenoperated and the number ol operating hours per start. Dustcollecting on the tube and reflecting surfaces can easilydouble the loss as determined at the irradiated surface.

Figure 3. Typical maintenance data for germicidal lamps.

in damp areas. lt also has a gern.ricidal effect that isbeneficial, since it follows tlie air circulation and can get toareas shielded from direct ultraviolet radiation. Other usesfor the G4Sl l ozone lamps are in electric clothes dryers togive garments a clean, fresh smeil like sunlight drying and infood and beverage vending machines and refrigerators.Ozone is oxygen in the chemical form of 03. It consistsof three atoms of oxygen. It is a colorless gas-and boils at-1l2oC. Ozone gas is characteristically observed in natureafter electrical storms and has a freshness effect. It iscommonly experienced around sparkir.rg electrical ma_chinery. It is present in the air in varying concentrations,sometimes as high as one part in a rnillion, more usually lessthan one part per ten million. Ozone is unstable, quicklyreverting to ordinary oxygen. It is a powerlul oxldatior.ragent: the active oxygen ion will combine chemically withsubstances to change their character. This is one method ofcontrol of odors: char.rging an odorous substar.rce byoxidatior.r to another chemical composition with no notice-able odor.Ozone production is reduced as temperature and humid-ity are increased. The 184.9 nanometer radiation is ab-sorbed by the air, and ozone is produced only within a fewinches of the lamp. Continuous circulation of air near thetube is necessary for the ozone to be carried out into theroom where it will be most effective. The greater the aircirculation, the more widely the ozone will be dispersed,and more will be formed by the air passing near the larnp.The Council on Physical Medicine and Rehabilitation ofthe A.M.A. has set a human tolerable limitation of one partper ten million of ozone in the air of occupied rooms. Arule-of-thumb recommendation has been to use one 4-wattG4S 1 1 lamp per I ,000 cubic f'eet of inhabited space.

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SYLVANIA GERMICIDAL LAMPSSylvania germicidal lamps are availablc in four wlttagesand five bulb types. A complete description of all live lamptypes is inciuded in Table I. The E, 15, and 30 watt sizes aredesigned to operate witir standard fluorescent lamp equip_rnent of corresponding size. The U-shaped, 4 watt-larnpoperates with a normal 4-watt ballast, but requires an FS-5starter. The G4S11 4-watt lamp operates on either a normalstandard inductive ballast designed ibr 0.350 ampereoperation on 120 volt circuits, or a 35A/Al5 resistancelamp: no starter is required.In addition to the cnergy at 253.1 nanometers, theG4S 1 i lamp generates a con trolled amount of I g4.9nanometer radiatior.r which produces ozone gas lromatrnospheric oxygen (See Figurc 4). Ozone is a deodorantand. in tlie presence of water vapor, is bactericidal andfungicidal.

OZONEOzone has no odor. The odor associated with ozonc isnitrous oxide formed by the combination ol ozone andnitrogen. Nitrous oxide has a pungent acriti odor and aphysiologically irritating quality to certain tissue. Ozone isa powerful oxidizing agent which can neutralize objection-able odors such as stale tobacco smoke or tl-re mildew orlor

FzUOqUo=lcFloUFJUE 180 220 260 300 340 3BO 420 460 500 540 580 620WAVELENGTH ( N ANOI\4ETERS]Figure 4. Relative spectral power distribution of ozoneproducing bactericidal lamps.MEASUREMENT OF OZONE

A standard test method fbr ozonc uses potassium iodide.ln principle, oxidation causcd by ozone produces iodine. Inturn, this is detected by a starch test (See Relerence 9).Another ozone tcst makes use of the fuct that dihydro-acridine in an alcohol solution is oxidized by ozone intoacridinc which has an intense violet fluorescence onexposure to 365.0 nanometers, while the hydrated com-pound does not f-luoresce.

36b^4 4o4.iS.P

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NEED FOR GERMICIDAL LAMPS"Fresh air" always has been considered beneficial.Indoors, however, the air can be relatively stagnant or havepoor circulation, particularly during cold weather. Also, itcan be contaminated with germs from human beings. Undersuch conditions, air can be a means of carrying infectiousorganisms into the body.Bacteria and mold spores in the air can cause consider-able damage to products in a wide variety of industries.

This damage takes the form of spoilage and contamination.In addition to the costs resulting from such damage, thereare costs of added maintenance and refrigeration, plus theever-present threat to the health of consumers of theaffected products. Product sanitation obviously is of vitalimportance.SAFETY PRECAUTIONS

It is essential that adequate precautions be taken in anyapplication of germicidal lamps- Prolonged exposures orexposures to high intensities of ultraviolet radiation cancause temporary, but painful inflammation of the conjunc-tiva (inflammation of the outer membrane of the eye), aswell as histological effects in the cornea, iris, and lens oftheeye. In extreme cases, permanent harmful effects can occur.Reddening or even burning of the skin (erythema), similarto sunburn, will be caused by excessive exposure toultraviolet energy.The glass used in conventional eyeglasses affords ade-quate eye protection. However, care should be taken thatthe ultraviolet energy does not enter the eyes from the side,nor is reflected into the eyes from the back side of theglasses.Clear plastic face shields are available to protect the face.Welders' shields sometimes have been used. Such protectionshould include the ears, particularly when the wearer maybe exposed to a number of lamps. It is well to rememberthat when one is exposed to short-wave ultraviolet energy,the effects may not be felt until several hours afterward.Likewise, individuals vary greatly in their sensitivity toradiation. Children, for example, are much more sensitiveto ultraviolet than are adults.Where the concentration of germicidal energy is espe-cially high, protection of hands and arms may be necessary.Clothing and gloves will generally provide adequate protec-tion.Safe exposure limits for ultraviolet germicidal irradiationhave been set by the Council on Physical Medicine of theAmerican Medical Association. The general practice basedon these limits is given in Table II. Exposure is roughly theproduct of irradiation (microwatts per square centimeter)and time. The safe exposure time at 18 inches from a bareG30T8 germicidal lamp is about one minute.TABLE II. RECOMMENDED MAXIMUM SAFEEXPOSUR E TO GERM ICI DAL U LTRAVIOLET

lrradiance Uw cm-2

The near ultraviolet region of the spectrum in thevicinity of 330 to 380 nanometers is used for "black light"effects. This radiation does not produce erythemal effectsand is not considered hazardous.EXPOSURE TIME

A lethal exposure period of an organism is determinedby its susceptibility, the wavelength of radiation, thedensity of the radiant flux (watts per unit area), and thetime of exposure. Table III gives the amount of 253.7nanometer energy density in microwatt-seconds per squarecentimeter to destroy 90 percent of various commonmicroorganisms.The germicidal effectiveness is proportional to theproduct of intensity times time from one microsecond to afew hours.TABLE III. GERMICIDAL ENERGY

REOUIRED TO DESTROYCOMMON MICROORGANISMS EnergyOrganisms (pw-sec/cm2)

Bacillus anthracisS. enteritidisB. megatherium sp. (veg.)B, megatherium sp. (spores)B. paratyphosusB. subtilisB. subtilis sporesCorynebacterium diphtheriaeEberthella typhosaEscherichia coliMicrococcus candidusMicrococcus sphaero idesNeisseria catarrhalisPhytomonas tumef aciensProteus vu lgarisPseudomonas aerugi nosaPseudomonas f luorescensS. typhimuriumSarcina luteaSeratia marcescensDysentery bacilliShigella paradysenteriaeSpirillum rubrumStaphylococcus albusStaphylococcus aureusStreptococcus hemolyticusStreptococcus lactisStreptococcus viridans

YeastSaccharomyces el lipsoideusSaccharomyces sp.Saccharomyces cerevisiaeBrewers' yeastBakers' yeastCommon yeast cake

Mold Spores Color

452040001 300273032007100

1 200033702',t4030006050

1 0000440044002640550035008000

1 9700242022001 68044001 8402600216061 502000600080006000330039006000

1 30001 3000440004400060000

I 32000I 1 1000

1 70001 70005000

ExposureContinuous12 Hours7 Hours1 Hour

10 Minutes1 Minute

0.10.30.53.5

20210

Penicillium roquefortiPenicillium expansumPenicillium digitatumAspergillus glaucusAspergillus flavusAspergillus nigerRhizopus nigricansMucor racemosus AMucor racemosus BOospora lactis

GreenOliveOliveBluish greenYellowish greenB lackB lackWhite grayWhite grayWhite

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MEASUREMENT OFULTRAVIOLET RADIATIONAn ultraviolet meter developed by Ultra-Violet Products,Inc., measures 253.7 nm germicidal radiation directly.Visible light is not measured with this meter. Measurementsare calibrated in microwatts per square centimeter(pW/cm2). Figures 5A and 58 illustrate the meter. Interna-

tional Light, Inc., also manufactures and markets instru-ments that measure the germicidal region ol the spectrum.As lamps age, it is important to know when to replacelamps that have fallen below the standards normallyrequired for effective germicidal action. Since it is impos-sible to observe when this point occurs by looking at thetube, the use of a meter becomes imperative.

Figure 5A. The BLAK RAY@ UltravioletMeter is calibrated to measure short waveintensity in microwatts per square centi-meter.

Figure 5B. Detachable sensor cell makes readings as close as a one-quarter inch from the irradiatedsurface. The picture shows the measurement of short wave radiation on substances in laboratorydishes.


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APPLICATIONSThe more common applications of germicidal lamps fallinto two broad classifications, personal protection andproduct protection. Personal protection is the irradiation ofthe air in a room for the purpose of protecting theoccupants from airborne infectious diseases. Product pro-tection is the use of ultraviolet radiation in areas wherefood, pharmaceuticals, and other products are processedand stored to prevent contamination and spoilage by moids

or other microorganisms.Air Irradiation in Heating and Air-Conditioning Ducts:Germicidal lamps are used in heating and air-condition-ing ducts to reduce the quantity of live bacteria and tomake the air passing through the ducts equivalent, insofaras possible, to outdoor air in terms of freedom from livebacteria. The design of any system for air sterilizationdepends upon the sources of the contamination, the type ofspace, and the kind of occupancy of the space. Therequirements for theaters, restaurants, and stores are quitedifferent from those for schools and those for hospitalwards and operating rooms.Air being brought into a room or building can besterilized readily by properly placing lamps in the air-han-dling duct work. The size and shape of the duct, theultraviolet reflection characteristics of walls, and thenumber and arrangement of the lamps determine theefficiency. The essential feature of the geometry is to insurethat all the bacteria passing through the duct are subjectedto sufficient bactericidal irradiation.A simplified formula for calculating the number ofG30T8 germicidal lamps in such ducts for air temperaturesof 65o-70oF is as follows:CFMIt = t6-;-? where

N = approximate number of G30T8 lamps requiredCFM = cubic feet of air per minuted = smaller cross-sectional dimension of ductin inches

TYPICAL METHODS OF INSTALLING

More accurate calculations which may be required for largeinstallations require an allowance for air temperature andhumidity. For a relative humidity of 60% or less, if theduct air temperature is less than:60oF increase the number of lamps 1 l/2 times,50oF - increase the number of lamps 2 112 times,40oF - increase the number of lamps 4 times, and30oF - increase the number of lamps 6 times.At higher relative humidities, twice this number of lampsshould be used.

The basis of this formula is a 90% deactivation of thestandard test microorganism, Eschericia coli. It is assumedthat the duct walls have zero reflectance to 253.7 nano-metef energy.ExampleHow many G30T8 lamps would be required for 10,800CFM of air carried by a 60- by 75-inch duct?

Air temperature is 60oF, relative humidity 55%.r0.800\=2*xllr2

N = 13.5 or 14lampsAlthough there are a number of ways of installing germi-cidal lamps in air ducts, the best compromise is to place thelamps lengthwise on the duct wall. The lamps should bemounted on 4- to S-inch centers and grouped in thecenter-half of the duct walls, away from the corners (rectangularducts). Where mechanical conditions require it, the iampsmay be mounted end-to-end along the duct. Severalmethods of installing germicidal lamps in air ducts areshown in Figures 6,4, B, and C.

GERMICIDAL LAMPS IN AIR DUCTS

Figure 68. Figure 6C.Figure 64.

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Since gelnticidal larnps must be kcpt reasonably free ofdust lirr best results, tliey rnust be accessible lor cleaning.This rcquirer.neltt can usually be met by the use of hingedpanels c'rn the sides ot tlie bottom of the air duct.ln large ducts, gerrnicidal larnps rnay be assembled invertical frarnes, like rungs of a ladder, supportcd in thecenter of tlie chan.rber in wltatever series or ntultiplearrangemeut bcst lits local conditions and also providesaccess fbr cleaning and replacement.In very large ducts where the air speeds are relativelylow, the tubes should be placed in such a manner that theaverage distance measured perpendicular from the tubes tothe duct walls is maximum. The direction of air flow is notconsidered in this situation.It is sometimes desirable to courbinc the gcrmicidaltreatment of air with humidifying, filtering, and heating. Insuch cases, if possible, the lamps should be placed at a pointof average air temperature, away from the very hot air orthe very cold air. Further, the larlps should be placed afterthe air filtering, but befbre the humidification stage of thesystem. Placing the lamps alier liltering reduces lampmaintenance; placing them befbre hurnidilication increlsesgermicidal eff'ectiveness, since humidiflcation tends toINSTALLATION OF GERMICIDAL FIXTURES FOR

increase the resistance of bacteria and other microorganismsto germicidal energy.Irradiation of Air and Room Surfaces:Warm air in hospital rooms, offices, school rooms,cafeterias, and hallways normally rises toward the ceiling.The convection currents lorce cooler air down along thewalls to the floor where the air is warmed and again rises.The presence of such heat sources as radiators, floor lamps,and even human beings generally aids in the convection ofair-Due to this air movement in a roqm, germicidal lampscan be installed on walls, slightly above eye level, and stillbe germicidally effective. Air irradiated near the ceiling iscarried by convection to the lower portions of the roomwithout exposing human occupants to direct lamp radi-ation. The effect is similar to exchanging the air in theroom with air from the outside.Germicidal fixtures may be either recessed in the wall orsurface-mounted on the wall. These two methods areillustrated in Figures 7 and 8. Two types of fixtures may beused generally in occupied rooms: open and louvered types.Diagrams of these two types are shown in Figures 9 and 10.

AIR AND ROOM SURFACES IRRADIATION

Figure 7. RECESSED lN THE WALL.TYPES OF FIXTURES USED IN OCCUPIED

Figure 8. SURFACE IVTOUNTED ON THE WALL.ROOMS (TYPICAL PLACEMENT)

FIXTURE 10. LOUVER ED FIXTURE


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The open type fixture is satisfactory fbr rooms wherethe ceiling is at least 9 112 feel in height and where theoccupants do not stay for more than eight hours at a time.Where ceilings are less than 9 l12feet high and where theoccupants remain for prolonged periods as in hospital wardsand nurseries, the fixtures should be louvered.Any plan to install germicidal lamps for upper-airirradiation must take into account the ultraviolet reflec-tance characteristics of the ceiling. In areas with painted"white-coated" plaster ceilings and walls, an exposure ofmore than two to three hours may be unsafe unless properfinishes are used. The "white-coat" should be painted witheither a water-soluble or an oil paint.The number of lamps recommended in open-front or inlouvered fixtures for the irradiation of the upper air is givenin Table IV. This data is based on 90% upper-air deactiva-tion of a standard microorganism, Eschericia coli. Anannual fixture cleaning and lamp replacement is assumed.TABLE lV. Recommended Number of 15- or 30-WattGermicidal Lamps For lrradiation of Upper Airln Rooms (Open-front or Louvered Fixtures)

Room Widths (ft.)10-13 14-18 19-24 25-31RoomLength LamP Size(Ft.) 15W 30W 15W 30W 15W 30W 30W

formed, ultraviolet energy cannot eliminate it.The food industry represents a wide and varied lield ofapplication. Non-food products also offer a considerablenumber of applications.List of Products Protected by Germicidal Lamps:

Food ProductsSugar: granulated, syrupsBeverages: fruit juices, bottled drinks, beer, wineDairy Products: milk, cheeseBaked Goods: bread. cakesFruitNuts, Pies, PicklesVinegarVegetablesWaterMeats: processing, packaging, storing (coolers)

Non-Food ProductsBiologicals: vaccines, serums, toxoids, ointmentsPackaginglnstruments: medical. der.rtal, barber equipmentTextilesBottling OperationsStorage CabinetsPaper ProductsIndustrial Liquids: oils, dyesGlassesToothbrushes

Figure 11. Fixtures for germicidal lampsshould be of highly polished surfaces, andresistant to acid or alkaline fumes and moisture.ALZAK ALUMINUM REFLECTOR AND T-8 LAMPl; "V

10-1314-1 B19^2425-3132-3940-4849-58

222Jtr

32-39

30Vv

;61

PRODUCT PROTECTIONAlthough germicidal radiation was discovered I50 yearsago, it developed from a laboratory curio to an engineeringtool only during the last quarter of a century.Germicidal applications for product protection arenumerous. They range from the simple application ofgermicidai energy on products stored in storage cabinets tothe irradiation of harmful organisms in liquids. New fieldsfor the use of germicidal lamps exist wherever productsdesigned for human consumption are manufactured, orwherever a health hazard exists due to bacterial contamina-tion.All reflectors for industriai applications of germicidallamps should provide 60% to 70%reflectance for energy at253.7 nanometers. Materials should be of highly polishedmetal surfaces such as stainless steei, polished Alzakaluminum, decorative chrome plate, or Lurium@. Allfixture parts should be specially processed for resistance toacid or alkaline fumes and moisture (See Figure 11). Figure12 illustrates a simple fixture that can be used to providedirect germicidal irradiation. The relative radiant intensityis shown on a polar graph.Airborne microorganisms such as bacteria, yeast, andmoid spores, cannot thrive on the surfaces of foods, liquids,and pharmaceuticals if these surfaces are directly irradiatedwith sufficient amounts of ultraviolet energy. Mold spores,in general, are more resistant to ultraviolet energy thanairborne bacteria. Hence, high intensities of germicidaienergy are required for good control. If mold has already

RADIANT INTENSITY - "/" OF BARE LAMP

Figure 12. This illustrates a typical distributioncurve of a bare T-8 germicidal lamp in an Alzakalum inum ref lector.

1-131-13142-1425232-3-343-3-454-4-56

PARALLELTO LAMP PER PEN D IC U LARTO LAMP

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ULTRAVIOLET SAN ITATIONThere are three general methods for ultraviolet sanita-tion that can be used, either separateiy or in combination:L Upper-lir Irradiation:This hclps to provide an area of irradiated air in theupper portion ol the room. Normal air currents dilutethe lower contaminated air with the purilied air tomairrtain a low bacterial count at the breathing level.Upper-air irradiation permits continuous, safe occu-pancy ol a room (See Figure 13).2. Barrier-type Trradiation:This type of germicidal installation provides a narrowbeam of germicidal energy that can be directed to

Figure 13. The principle of upper-air irradiation is shown in a veter-inary hospital. Upper air in thezone irradiated by germicidal lampsis disinfected and displaced down-ward, diluting microorganism con-centration at the lower level.

SANITARY ENVIRONMENTGermicidal radiation can provide and maintait.r sanitaryconditions for objects previously made sterile. An 8-wattgerrnicidal lamp, for example, can be used eflectively instorage cabinets which liave a volume of one cubic lbot orless, such as those used lor storir.rg barbers' supplies, babies'

bottles, drinking glasses, and medlcal and dental instru-ments (See Figure 15). Similarly, a l5-watt germicidal larnpwill provide sufficient ultraviolet radiation lor a storagecapacity of 8 cubic feet and a 30-watt lamp for 20 cubicfeet or less. These systems provide effective intensities offrom 10 to 100 times those produced in the irradiation ofair for room ventilation. They are adequate for almostinstantaneous destruction ol bacteria introduced by thcopening and closing ol the cabinet door. The G4S11 andG4T4lI lamps are also useful fbr similar low volumesanitary applications. Lamps sl'rould always be positionecldirectly to the rear of the cabinet door so that when the:door is opened, the incornir.rg air will be intercepted by theenergy from the lamps.

prevent the passage of live microorganisms from oneplace to another. This method is iilustrated in Figure 14.Direct Irradiation:This is the most efficient way ol disinfecting, not onlythe air ol a room, but also the exposed solid surfaces.The limitation of this method is that germicidal intensi-ties are also irritating to the skin and eyes of bothindividuals and animals in the room. It is necessary toturn the germicidal lamps off when workers are onroutine duty or to protect them by goggles, masks,gloves, or other means. Germicidal lamps are used lorthe direct irradiation of various biological liquids, suchas serums, plasma, vaccines, toxins, etc.

Figure 14. Combination of upper-air aAdbarrier-type irradiation that disinfects the airin the hospital service room adjoining thenursery. lt consists of a 2-lamp fixture thathelps to prevent the circulation of airbornemicroorganisms into the nursery.

3.

ffim*m*,

Figure 15. TYPICAL SANITARY STORAGE CABINETS.


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MEAT STORAGEFreshly slaughtered beef must be "hung" in cold storagefor a short period of time to break down the connectivetissue changing it to a gelatinous mass. This change, knownas tenderizing, is due to enzyme action and can beenhanced by increasing the ambient temperature. Thecooler may be operated as high as 45oF (7oC) using asufficiently high relative humidity to reduce dehydration

losses. Temperatures of 45oF or above are conducive to theacceleration of the tenderizing process but, at the sametime, will also promote growth of molds on meat. Theinfected parts must be cut away, and this means a severeloss to the butcher.Properly installed germicidal tubes not only reducecontamination of stored meat by airborne bacteria, butthey reduce the bacterial growth on meat surfaces equiv-alent to a l0oF lowering of temperature below the40oF-45oF range. This retardation of bacterial growth issignificant since losses due to trimming, drying out,bacterial slime, and mold can range as high as 15 percent.Likewise, when aged meat is stored, the use of germicidallamps will result in a reduction of spoilage trim,

To obtain best results, install one l5-watt germicidaltube to cover 40 square feet of floor area, with a minimum,in case of small storage spaces, of two lamps. Ultravioletradiation must be directed on the meat surface, as well ason surfaces of the ceiling, walls, and floor. These germicidallamps should operate continuously. For worker protection,a switch should be installed to turn off the lamps when thestorage door is opened and while workers are in the storageroom.Slight air circulation is important. A small fan in theupper portion of the cooler will provide air circulationthrough the whole storage room. The fan should not bedirected on the germicidal tubes because cool circulating airwill reduce the ultraviolet output of the tubes.If reduced germicidal radiation is a problem when theambient temperature is low, the germicidal lamps can bejacketed with tubes of the same glass used to make thelamp. This jacket restores normal operating lamp temper-ature and jacketed tubes have two to three times thegermicidal ultraviolet output of an unjacketed tube at theusual meat storage temperatures.In the holding rooms a common usage is one l5-wattgermicidal lamp for each 40 square feet, or one 30-wattgermicidal lamp for each 100 square feet, above themonorail system. The usual mounting heights are 12 feet;atypical arrangement is illustrated in Figure 16.For cooling rooms, use 15 watts per 40 to 60 squarefeet, or 30 watts per 120 to 150 square feet of area. The

lamps should be mounted to irradiate as much of the meatsurfaces as possible.Two types of mold are mostly responsible for thedamage to the meat, namely Sporotrichum carnis whichproduces long white threads, and the Mucors together withThamnidium which form a greyish'white growth known aswhiskers. Mold formation is also encouraged by the highrelative humidity (r.h. 85 to 90 percent) which is adesirable condition to prevent'evaporation of the moistureand shrinkage of the meat. Mucors and other fungi arereadily destroyed by the 253.1nm radiation. It must be

borne in mind that careful handling, cleanliness, lowtemperatures, and similar methods are preventives ofproven value.Ultraviolet radiation of bactericidal wavelengths is pure-ly surface-effective. Its penetrating power is negligible. Inthe food industry, surface sterilization is important in theendeavor to prevent the infection not only of foodstuffsbut also of machines and tools.There is little possibility of introducing flavor ororganoleptic changes as a result of ultraviolet irradiationexcept with fats and oils. This is due to the generation ofhydrogen peroxide H2O2and its strong oxidizing action.

Figure 16. SANITARY STORAGE OF MEAT.

BAKERIESMold contamination is a major problem in bakeries.Humidity and the constant accumulation of fine dustmakes it difficult to prevent mold formation even withperiodic cleaning. Ultraviolet irradiation of walls andceilings to inhibit spore formation with localized treatmentof the conveyor and bakery products has proved effective.Germicidal irradiation of walls and ceilings in the fermenta-tion room can reduce the need for frequent cleaning ofthose surfaces and thus reduce maintenance costs. One15-watt germicidal lamp is commonly used for every 30 to40 square feet of ceiling area or one 30-watt germicidallamp may be used for every 75 to 100 square feet of ceilingarea.BIOLOGICAL SUPPLIES

Due to ever-increasing demands for biological supplies,pharmaceutical houses use large volume testing proceduresand mass production. These large-scale operations demandincreased sanitary control measures to insure that productsare free of contaminating organisms. Germicidal lamps playan important part in attaining sterile areas for the produc-tion and packaging of sterile material and in protectinglaboratory workers from infection.

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STERILIZATION OF LIOUIDSMicroorganisms absorb considerably less germicidalradiation when in very humid air, or in water, than when invery dry air. Waterborne E. coli, for example, may requirean 8 to 10 times greater exposure for a given kill than dryairborne bacteria. The ultraviolet absorption of water andminimum provisions for circulation during irradiation re-quire an additional multiplying factor of about 5, so thatthe exposures to produce any given disinfection of waterare 40 to 50 times greater than those required for dry air.Absorptive liquids decrease the germicidal intensitylogarithmically with the distance from the lamp. Minute

traces of iron compounds and organic compounds in liquidsdecrease the transmission of germicidal energy. Compoundsof calcium, magnesium, sodium, and aluminum sulfate in aliquid increase the transmission of germicidal energy, unlesstwo or more of the compounds form a precipitate.In each specific liquid, there is a critical distance fromthe germicidal lamp at which 90% of the ultraviolet energyhas been absorbed. Ten percent of the energy, or less,remain to be transmitted to the liquid beyond thatdistance. The distance for a 90% absorption, called the"effective depth of penetration" may vaty upward from afew thousandths of an inch in milk, and serums, orone-tenth of an inch in wines and syrups, to five inchesthrough drinkable water of high transmission and l0 feetfor some distilled water.The design of systems depends upon the particularrequirements. Immersion of the lamp directly in the wateris unsatisfactory because of the decrease in ultravioletoutput due to the cooling of the tube by the water. Whenthe lamp has to be immersed in the water, it should beinstalled inside a quarlz tube for satisfactory ultraviolettransmission. This avoids the cooling and consequent loss oflamp efficiency which would result if the water were incontact with the lamp wall. It also makes the cleaning andreplacing of the lamp easier. There must be a water-tightbond between the enveloping tube ends and the lamp endsfor satlsfactory operation.However, to avoid the extremes of water temperature,the germicidal lamp may be placed above the water surfaceand partially enclosed in a reflector. In this system, about25% of the ultraviolet output of the lamp should reach thewater surface directly; 50% Io 75% of the balance comesfrom the reflector.

The basic techniques for purifying water may beclassified by the way the germicidal lamps are used(immersed or offset) and by the water system (pressure orgravity). They combine in three basic types: IP (immersed-pressure), OP (offset-pressure), and OG (offset-gravity) asshown in Figure 17.

LP OP OGFigure 17. Basic Types of Water Disinfecting Devices\/,/

Figure 18. Suggested Dimensions and Ratings of SmallGravity Type Water Disinf ectorsAn Alzak or Lurium aluminum reflector on the uppercylindrical surface of the chamber nearly doubles thegermicidal radiation throughout the lower half of thechamber.Figure 18 illustrates practical dimensions for the gravityflow disinfectors which can be used with the 8, 15, and 30watt lamps. They will provide 90% disinfection, (with al0O% factor of safety) of drinking water, transmitting253.7 nanometer radiation effectively to a depth of at least5 inches if these rates of flow are not exceeded: G8T5, 100gallons per hour; G15T8,200 gallons per hour; and G30T8,500 gallons per hour. Where a compact and powerful sourceof germicidal energy is required, it is suggested that quartztubular high intensity mercury lamps be used.The continuous-flow capacity ratings of the three basictechniques are tabulated in Table V. The effective depth ofpenetration of Table V determined in a laboratory, fixesthe maximum depth of water to be processed in any device.The water may otherwise be distributed around or underthe germicidal tubes in any convenient way that willintercept all the energy from the tubes and reflectors.

*-'-rI

4t",."

TABLE V. 90% Disinfection of Liquids - Gallons per Hour*No. of G4T4t 2 3 lNo. of G8T5t 2 3No. of G15T8t 2No. of G30T8t 7 8 10800 1000 12001600 2000 24002400 3000 36003200 4000 48004000 5000 60004800 6000 72005600 7000 84006400 8000 96007200 9000 108008000 10000 120009600 12000 144002000 15000 190004400 18000 216009200 24000 28800

FOccoolOcoOPo

-d

1234F6789

1012151824

21426384

104125146167188209250313375500

235200 400 600400 800 1200600 1200 1800800 1600 24001000 2000 300012AO 2400 36001400 2800 42001600 3200 48001800 3600 54002000 4000 60002400 4800 72003000 6000 90003600 7200 108004800 9600 14400

42 8384 167124 250167 334208 416250 500292 584333 666375 750417 834500 1000625 1250750 15001000 2000

13 161600 20003200 40004800 60006400 80008000 100009600 1200011200 1400012800 1600014400 1800016000 2000015200 2400024000 3000028800 3600038400 48000

For cu. ft. per hour, multiply above by 0.13368; for cu. in. per hour, by 231.O; for cu. in. perminute, by 3.85.tAllows for 650/0 ol trare lamp eff iciency for lamp and reflector combination.*Based on standard microorganism, E. coli.


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ANTIOUING BOTTLESSome antique hobbyists use germicidal lamps to produceold apothecary glass. Exposure of preserve-type jars andbottles to germicidal radiation can change the color of the

glass and age the bottle. Certain impurities in the glass causethe color to change. The bottles thus become more valuableas a collector's item. Al1 glasses do not color, but exposureto the germicidal energy for a few hours will indicatewhether color changes will take place.Safety precautions must be adhered to at all time (See"Safety Precautions").CALCULATIONS IN THEULTRAVIOLET SPECTRUM

Many of the techniques and equations that are familiarin illumination engineering for lighting calculations can beused for the ultraviolet portion of the spectrum. Thevarious geometric equations are basic to all radiometriccalculations. Photometry parallels radiometry and is aspecial case of radiometry. In the specific case of photom-etry, terms from the luminous system are used. Thecorresponding radiometric terms can be used directly in thesame equations. Table VI gives the basic quantities usingthe new standard symbols. Many other symbols and unitshave been used in the past.When considering light, the radiant power (watts) isweighted, wavelength by wavelength, using the spectralsensitivity of the eye, i.e., the luminous spectral efficiencyfunction. If the appropriate constant of proportionality isused, the result is the lumen. In considering the ultravioletportion of the spectrum, one can weight the radiant powerby an appropriate factor for each wavelength, e.g., theerythemal response will lead to the unit of E-viton.Alternately, one may work directly with the power at aparticular wavelength or with the power in a particularwavelength band.

Several units of length are commonly used for wave-length. These includ., Ih. nuno-eter (,4m) equal to 10'9meters, the micron (1r) -e^qual to 10-b meters, and theangslrom (A ) equal to l0-l u meters.

Atmospheric attenuation over distances of several meterscan be entirely neglected for wavelengths above 300nanometers in the ultraviolet. It becomes appreciable below300 nanometers and increases rapidly with a decrease inwavelength. Atmospheric effects should be considered, evenfor distances of less than one meter, for wavelengths belowabout 230 nanometers. At a wavelength of 205 nanometers,a typical value of atmospheric transmittance for a onemeter path might be 0.1. Absorption and scattering are thetwo basic mechanisms of attenuatioir. -At a given wave-length the attenuation can easily vary by a factor of 100due to atmospheric conditions.The reflectance of metals is dependent on the method ofsurface preparation, impurities, surface conditions, andother factors. The difference for metals between polishedbulk material and evaporated surfaces can be quite large.Figure 19 shows typical values for specular surfaces. Thehigh value shown for aluminum is obtained for depositedfilms in vacuum. Even a very brief exposure to theatmosphere will significantly reduce this value.Transmittance values of materials are dependent onsample thickness since absorption losses vary exponentiallywith thickness. Figure 20 shows typical transmittancecurves of several common materials. The sample thicknessesare indicated, and surface reflection losses are included. Thecurves for materials such as quartz vary considerably withthe particular type. Transmittance values for glass oftenvary significantly with temperature, this effect is importantfor filters operating near hot sources.Measurement accuracy in the ultraviolet, particularly atthe shorter wavelengths, is considerably less than found inthe visible spectium. Also, the optical properties of thevarious system components are not as well known for theultraviolet region of the spectrum as for the visiblespectrum. Consequently, approximate calculations, basedon typical data, often are adequate. Examples of typicalcalculations are given below. Several methods are possiblefor solving each of the problems. The techniques used wereselected to demonstrate several types of calculations andare not necessarily the most direct. These examples areanalogous to lighting calculations as described in standardtextbooks on illuminating engineering.

SYMBOL DEFINING EOUATION OUANTITYA

TABLE VI. FUNDAMENTAL OUANTITIESRADIOMETBIC SYSTEM

uNlr ouANTtrYaPHOTOMETRIC (LUMINOUS) SYSTEM

UNITRadiant energy

Radiant fluxI ncident radiantflux density(irrad iance)Emitted radiantflux density(radiant exitance)Radiant intensity

Radiance

lou le

wattwatt meter-2

watt meter-2

watt sterad ian-1

watt meter-2steradian-1

Luminous f lux

lncident luminousflux density( illum i nation )Emitted luminousflux density(luminous exitance)Luminous intensity

Luminanced

lumenalumen Toot _(footcandle)

lumen foot-2

lumen steradian-l{candela)

alumen Toot _steradian-1(candela foot-2)

Luminous energy lumen seconddo'dt

-do-oAd0dA

dobd@

d2o "dA do cosdNotes: a) The prefixes "radlant" & "luminous" often are omitted if no confusion will occur.b) o is the solid angle of a differential source element expressed in steradians.c) 0 is the angle between a line of sight & the normal to area dAd) See Reference 6 for a complete discussion of this term & its various units

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/{7'-/' it./1__ _ _5__ -----rI:1- -l-'r.0

UzFUJUG

.4


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EXAMPLE 2: A parabolic trough reflector l2 inches long and with a focal length of 1-1/2 inches is located above the lampof Example 1. The reflector is specular Alzak aiuminum, and the lamp is located along the focai line of thereflector. What is the 253.lnm irradiance at point B?a) A quick check shows that point B is past the minimum inverse square distance for the reflector. Therefore, point B "sees"a reflector radiance equal to the lamp radiance times the reflector reflectance (0.6 from Figure l9).

Lrefl = 0.0193 x .6 = .0116 w in-2 sr-lb) If the reflector subtends the solid angle Ac,-r at point B and the solid angle is small, the reflector produces an irradiance of

EB = L.efl Ao = .oi tu (.6" - sl8"')-x = 324 x 10-6 w in-2c) The sum of tlie lamp irradiance plus the reflector irradiance is the total irradiance.

totai Eg = 63 x 10-6 + 324 x 10-6 = .39 x 10-3 w in-2 I |=-'">--- T

Iq8,,L--=EXAMPLE 3: Repeat Example 2 if the reflector linish is diffuse.a) The lamp is very close to the reflector. Consequently one-half of the lamp's radiant power is incident on tl're reflector.

0 = 112 x 1.43 = 0.715 wb) A good difluse Alzak surface will have a reflectance value close to the specular value;use 0.6. Since the reflector isshallow, neglect the interflections and curvature (these effects oppose and will tend to oancel), and assume it is aLambertian surlace. Thus,

Mre; =+{ff;t-.oosq5 w in-2, .00595Lretl = *" = .00 lt.lg * 1n-2 .r-l

c) The radiant intensity produced by the rellector isI = Lrefl x Aprojected = .00190 x (6" - 5/S") x 12" = .122 * rr-l

d) The irradiance at point B due to the reflector by the inverse square law is- .t22rR =-;= )r x 10-6 w in-lGa"y

e) The sum ol tlie lamp irradiance plus the reflector irradiance is the total irradiancetotalEg = 63 x 10-6 + 53 x 10-6 =.116 x l0-3 w in-2

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EXAMPLE 4: A relative spectral power distribution curve, R(I), is shown for blue fluorescent lamps. If a particular bluelamp,is rated at 1160 lm, determine the multiplier for the curue so that it is absolute in watts per micron(wli-l ).a) Choose a convenient scale for graphical work, say the l5 x 20 cm shown. Multiply the relative power curve R(tr) by theiumirtous spectlal efficiency function v(tr) at each wavelength. Then measure tlie area under this product curve;it turnsout to be 21.0 cm/ on the drawing size suggested.b) A unit length on the relative power scale is 10 cm and a unit length on the wavelength scale is 50 cm. Tirerefore, a unitarea on the graph scale is 10 x 50 = 500 cm2 on the drawing. The area under the product curve on the"graph scale is

21 .0 cm25oo cm2 = '042

c) If K is the multiplier to put the curve in absolute units, theno = 680 (tn*-t{ L*,nrt ('s-l) v(r) dr(p) = u60lm

1.11d) The final

K=

=

"f


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l.2.J.4.5.6.7

IiEFERENCESHuff, C., Smith, H., Boring, W., and Clarke, N., "Study of Ultraviolet Disinfection ol Water and Factors in TreatmentEfficiency," Public Health Reports, U. S. Publi. Health Service, Vol. 80, pp. 695, 705, August 1965.Kaufinan, J., "lntroducing SI Units," Illum. Eny.,Yol.63,p.537, Oct. 1968.l.F.S. Lighting Handbook,4th Edition. Pp. 25-15 to 25-17. Illuminating Engineering Society, New York 1966.I.E.S. Nomenclature and Definitions for lllumit:iling Engineering, U.S.A.S. Z7 .l 1967 .Koller, L., Ultraviolet Rodiatiott, John Wiley an,-l Sons, lnc., New York, 1965.Levin, R,, "Luininance A Tutorial Paper," Jotir. SMPTE,Yol. ll,p. 1005, Oct. 1968.Nicodemus, F.. "Radiometry," Applied Optic: and Optical Engineering, Ch.8, Vol.4, editor: R. Kingslake. AcademicPress. New York 1967.8. Nicodemus, F., "Optical Resource Letter on Radiometry," JOSA, Vol.59, pg.243, March 1969.9. Summer, W., Ulftaviolet and Infrared Engineering Interscience Publishers, Inc., New York 1962.10. Ultra-Violet Products, Inp., San Gabriel, California.

Acknowledgement: The author wishes to express hi,i appreciation to the following:Dr. L. J. Buttolph, Engineer on the staff of the Illuminating Engineering Society for his assistance insupplying information on germicidal lamp applications, including Figures 4,6,15-18, and Table III.Dr. Robert Levin of the General Er.rgineering Department, Sylvania Lighting Center, for his assistance inwriting the section on the calculations in the ultraviolet spectrum. and providing technical data.Ultra-Violet Products, Inc. of San Gabriel, California, for Figures 5A, 5B, 1 I , and l3

C. C. \{PELKASIliumination Engineering Dept.

watts Bulb Base Description or'fjl'l,', lll: t.,ll.Abbreviation Oty. r,,e4 s-11 , A-1000GERMICIDAL LAMPS STARTER REOUIRED

Producer (1)4 l-4 53/+, 4 Pin Radio Germicidal-UShape G4T4 I 1 12 40008 T-5 12" Min. Bipin Germicidal 24 600015 T-8 78" Med. Bipin Germicidal G15I8 24 750030 T-8 36" Med. Bipin Germicidal G30T8 24 75001. This lamp is.classified primarily as an ozonizing lamp and has limited germicidalaction. No starter required.

ffimil- G8T5ILl.i1t4{-.H#

G3OT8

G15T8

-t6-


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stAENERAL TELEPHONE & ELECTRONICsLIGHTING CENTER, DANVERS, MASSACHUSETTS 01923

Sylvania Engineering Bulletin - Germicidal & Short Wave UV 1962

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Transcript of Sylvania Engineering Bulletin - Germicidal & Short Wave UV 1962