ULTRAVIOLET AIR SANITATION

Destruction of Microorganisms

FREDERIC W. ROBINSON Hanovia Chemical & Manufacturing Company, Newark. N. J.

MPROVEMENT in our methods for sanitation, especially of food and water supplies during the past haif century, has brought with it marked reduction in sickness and in

the death rate from diseases affecting the intestinal tract. This steady improvement in health standards has perhaps

contributed to an almost entire neglect of sanitation in the air we breathe. It is bighly significant, therefore, to find from authoritative statistics that as high as 85 per cent of the deaths from infections and parasitic diseases are caused by microorganisms whose normal portal of entry is the upper respiratory tract.

The recent high rate of comuieroial development of air- conditioning equipment and improved methods of air bac- teriology have served to focus attention on the subject of air

I

EFFECT OF ULTRAVIOLET ON ORGANISMS SPRAYED

COLLECTED FRO= THE Ant ON THE O'THER SIDE imo THE AIR ON ONE SIDE OF L.4m BARRIER AND

Lamps alternately turned off and on.

if the aims and p&poses of ultraviolet air sanitation are 6rst defined. Air sanitation is closely analogous to water sanitation; its purpose is s u b stantially the s a m e t o make the air in confined spaces more safe under the particular circumstances of its use, and to guard against the possibility that air-borne organisms may cause clinical infections. Such applications may vary greatly in their technical details according to the type of problem presented. Most cases will fall into one of the following cate- gories.

Infection by Sedimentation Inhibited

In hospital opcrating room the primary objective is to reduce the risk from pathogenic organisms set- tling from the air on the surfaces of open incisions, on instruments, or on the hands of the operating person- ne1 from which they might be trans- ferred into open wounds. Protec- tion of perishable foodstuffs against contamination from air-horae organisms is a further example.

Meleney (U) , Hunt (8, Beck (a), Hart (6, 7), and others have clearly recognized the lack of adequate air sanitation in the hospital operating room. One may quickly determine hy exposing blood agar plates how many bacteria may be expected to find their way hy sedimentation on to an area of any given size during any given time in the operating room.

Hunt (8) reported that in a modern operating room using every reasonable precaution to ensure asepsis, but without ultraviolet, considerable numbers of bacteria may be col- lected from the air by sedimentation. A 10O-mm. blood plate exposed for 1 hour and incubated for 36 hours showed eighty-six colonies, seventy-six colonies, and seventy-eight colonies, respectively, on successive days. In another case thkty colonies were found. R. G. Urquhart (3) found an average of forty-eight colonies in a series of exposures of 45 minutes each (Figure 1). These figures are in close agree- ment with conditions found in other institutions. Hunt estimated, from a survey of other publications and from his own experience, that 10 per cent expresses conservatively the

FLOOR &ASD T Y P ~ OF LAMP

23

24 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 31, NO. 1

48

17 I 5 I 2

I. 2 . 3. 0 0 0

I I - r A

i

6

(Above) A , Four ultraviolet tubes two positions B. Four ultraviolet tubes: four positions 1. Supply table 2. Instrument table 3. Operating table 4. Operating room (Numerals above circles indioate number of oolonies)

(Right) Colony Counts (Average) : 1. Without ultraviolet ray 2. With four ultraviolet tubes in two positions 3. With four ultraviolet tubes in four positions

average morbidity from operative wound infections a t the present time. Fortunately most of these are mild and super- ficial and last but a few days. Whether mild or severe, if some of these infections may be prevented by better air sani- tation, the patient should have the benefit of this added pro- tection.

In a typical case (3) with a properly engineered installation of four small ultraviolet fixtures using a total of 120 watts of electrical current, a reduction of between 80 and 90 per cent in the number of bacteria collected by sedimentation was shown. No inconvenience to the operating personnel results; the fixtures are mounted on the walls a t ceiling height or about 14 feet from the floor where the operating room is of the amphitheater type, and the entire air contents of the room thus come under the influence of the ultraviolet.

The quartz low-pressure discharge tubes used for this pur- pose emit approximately 95 per gent of their total ultraviolet output in the wave length 2,537 A., which is a t the peak of the bactericidal efficiency curve as shown in Figure 2.

It is important to use lamps of the filter-jacketed type. The filter jacket screens out all radiations shorter than 2,200 A. and by this means prevents the production of ozone which otherwise would result.

The very purpose of air sanita.tion makes it necessary to avoid excessive ultraviolet intensities. The amount of ultra- violet which may fall on the patient during the course of the operation should be kept sufficiently low so that no reac- tion will be caused in the tissues exposed.

It is recommended that plain glass spectacles or cellophane

FIGURE 1. EFFECT OF ULTRA- VIOLET ON BACTERIAL CONTAMI- NATION OF AIR IN A HOSPITAL

OPERATING ROOM

14

Blood agar plates exposed an avera e of 45 minutes on o erating and sappyy

tabyes.

Courtesy, Department of Surgery, State of Connecticut Tuberculosis Sanatoria 6

visors be issued to the operating personnel, either of which has been found to give adequate protection to the eyes.

Prevention of Cross Infection

In infants' nurseries, school rooms, and hospitals for con- tagious diseases the primary objective is to prevent cross in- fection through interchange of nasopharyngeal flora.

I00

80

60

40

20

2400. 2600 2800 3000 ULTRAVICCET WAVELENGTH IN ANGSTROMS.

FIGURE 2. BACTERICIDAL EFFICIENCY CURVE FOR B. coli (6)

In the study of diseases whose normal portal of entry is the nasopharynx, it is difficult to determine the bacterial con- tamination of the air. In that case one should know the total number of bacteria present in the air, and this, as Wells (I?') showed, may be many times greater than the number which may be collected by sedimentation. In one experiment

JANUARY, 1939 INDUSTRIAL AND EEGINEERING CHEMISTRY 25

welve out of fifteen plates remained negative when exposed for 15 minutes in air containing twenty-five B. coli per cubic foot. The use of an air centrifuge or other adequate method of assay seems almost impera- tive, therefore, in studying air contamination in rela- tion to respiratory infec- tions.

I n many cases in this categofy, sanitation of the air is rendered more difii- cult by the fact that long exposures of the eyes would result in severe cases of con- junctivitis. This may he prevented by the use of in- direct fixtures so arranged that (a) the eyes are effec- tively guarded at all times, and (b) adequate air sanita- tion is still provided.

In the Mar lboro S ta t e Hospital, Marlboro, N. J., a group of patients has been living 24 hours a day under ultraviolet air sanitation for 4 months without the de- velopment of any subjective symptoms. Several impor- tant studies in air sanitation 8s applied to rooms under more or less permanent oc- cupancy were reported by Wells (16, 16) and Vonder Weidt (14) xhicb demon- strate that great improve- nient in air sanitation re- sults when ul t raviolet is employed in a well-designed installation.

The technique of ultra- violet air sanitation in its relation to isolation wards for contagious diseases is under study by McKhann (10). He found that a light barrier set up in the cor- ridor between wards may be made practically imper- vious to air-borne bacteria carried by ordinary venti- lating currents. McKhann sounds a note of warning which is important in all air sanitation problems in- volving more or less per- iiianently inhabited rooms, hospi ta l wards, school rooms, hospi ta l reception rooms, etc. He points out t.hat, since the ultraviolet equipment must be so in- stalled as t.o protect the eyes of those in the room (cotn- iiionly, indirect lighting fix-

tures above eye level), the radiation serves tu dilute the contaminated air with sterile air, and thus reduces but never completely elimi- nates the contamination so long as infectors remain in the room. With sui table design, however, installa- tions with indirect lighting of this type may he made to show a degree of air sanitation equivalent to one hundred to five hun- dred or more complete turnovers of air per hour (16). Widespread applica- tion of this principle in the rooms where perishable food products are packed is an obvious and logical antici- pation, but on the basis oi present knowledge there is no basis for the belief that foodstuffs other than clear fluids may themselves he effectively and eeonomi- cally sterilized by iiltra- violet. For the past ten years it has been known that by painstaking irradia- tion the growth of mold on bread may be inhibited by from 24 hours to several days, but so far, huyers have not been found will- ing to pay a premium for stale bread. The process is therefore definitely limited by its lack of economic ad- vantage.

Sterilization of Air S u p p l y

Compressed-air systems are employed, for example, in the operation of bone drills, in 6lling sterile bio- logical solutions into con- ta iners , or in pumping milk.

Sanitation in Air- Conditioned Systems

1x1 air-conditioned sys- tems there are two types of cross infection to be guarded against-that which may arise within the room where an infector is located and the transfer of air-borne organisms from one room to another. The ability of ultraviolet rays to destroy bacter ia was determined many years ago. Domes and Blunt (4)

26 INDUSTRIAL AND ENGINEERING CHEMISTRY VOL. 31, NO. 1

made one of the earliest studies of this subject in 1877. Barnard and Morgan (1) in 1903 showed that the most effective rays were those between 2,265 and 3,287 4. wave length, In 1922 Klemperer and Kempner (9) showed that ultraviolet was able to free the air of bacteria; by eliminat- ing the possible effects of ionization and ozone, they were able to show that this effect is due to a direct action of the ultraviolet on the bacteria. In September, 1925, a patent was granted to Napier (13) covering the withdrawal of air from a room and destruction of bacteria in the air by ultra- violet before its reintroduction.

borne bacteria, he may refer to the presentation of this subject by Wells and Wells (17) whose experimental work laid a solid foundation for the whole subject of air sanitation.

In conjunction with air-conditioning systems, ultraviolet air sanitation offers profound benefits. Since, with the excep- tion of a few special cases, the economics of air conditioning demands a recirculation of a large part of the air, usually 50 to 90 per cent, the possibility of distributing air-borne organisms from one person to another can hardly be disregarded. In fact, this has in some instances prevented the installation of air-conditioning equipment.

INSTALLATION OB EQUIP- MENT USED TO’ DESTROY AIR-BORNE BACTERIA IN A MIDWESTERN HOSPITAL

Obviously in the sterilization of air supply, where all of the air is under control, it should not be difficult by the use of quartz ultraviolet discharge tubes to ensure complete sterility and to calculate the engineering design accordingly. In inhibition of infection by sedimentation and in the prevention of cross infection, however, since the bacterial contamination arises largely in the same chamber (from the noses and throats of the people in the room) in which the infected person is confined, complete sterility of the air becomes a hypo- thetical concept and possibly is not essential.

While it is pertinent, therefore, to differentiate sharply between air conditions where one or more sources of con- tamination are contained within the chamber, and other con- ditions where this is not the case, the problem remains always to make the air in question as safe as possible for the purpose it serves. This constitutes the whole problem as far as it concerns us here.

Unfortunately many misleading and sometimes entirely erroneous statements on this subject have been broadcast in the public press, and ultraviolet sterilization has been held out as a panacea in many and varied instances where its value is as yet unproved. As early as 1914 the treatment of freshly killed meat with ultraviolet was advocated by Monvoisin et al. ( l a ) in order to sterilize the surface, but up to the present time no economic advantage of this process has been shown. Such promiscuous statements are to be deplored, since they natu- rally tend to retard the sound application of a principle which seems to hold great promise of benefit to the public health. Living microorganisms have been captured even in the stratosphere, and organisms characteristic of the respiratory mucosa have been recovered from the air in an airtight metal chamber 48 hours after inoculation. Should one be inclined to doubt the possibility of clinical infection resulting from air-

By the use of adequately designed ultraviolet installations mounted in the air ducts, satisfactory air sanitation has been provided in railway cars (16). Here the rate of circulation corresponds to twenty turnovers of air per hour. The rate of destruction of bacteria is dependent upon the rate of circula- tion; if the total rate of circulation is conspicuously lower than twenty turnovers per hour, some additional provision for ultraviolet radiation in the room would be essential for ade- quate air sanitation.

’

Literature Cited Barnard and Morgan, Brit. Med. J., Nov. 14, 1903. Beck, W. C., Arch. Surg., 33, 876-89 (1936). Conn. State Tuberculosis Sanatoria, Dept. of Surgery, personal

Downes, A,, and Blunt, T. P., PTOC. Roy. SOC. (London), 26,488

Ehrismann and Noethling, 2. Hyg. Infektionskrankh., 113, 597

Hart, Deryl, Diseases of Chest, 111, No. 6,14,28 (1937). Hart, Deryl, Modern Hospital, 46, No. 6, 79-81 (1936). Hunt, E. L., New Engl. J. Med., 209,931-3 (1933). Klemperer, G., and Kempner, L. R., “Die Therapie der Gegen-

McKhann, C. F., Steger, Adelbert, and Long, A. P., Am. J .

Meleney, F. L., Surg., Gynecol., and Obstet., 60,269 (1935). Monvoisin, Barrat, and Robin, British Patent 22,669 (Nov. 17,

Napier, F. L., U. S. Patent 1,553,098 (Sept. 8, 1925). Vonder Heidt, L. C., Modern Hospital, 51, No. 2,69-71 (1938). Wells, W. F., Ibid., 51, No. 1, 66-9 (1938). Wells, W. F., and Wells, M. W., Am. J. Pub. Health, 28, 343-50

Wells, W. F., and Wells, M. W., J. Am. Med. Assoc., 107, 1698-

communication.

(1877).

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wart,” 1922.

Diseases Children, 55, 579-99 (1938).

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RECEWED August 26, 1938.