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INDUSTRIAL AND ENGINEERING CHEMISTRY
tory and the research laboratories of the Armstrong Cork Company to determine the effcct of boiling water on the tensile strength of cork composition. LITERATURE CITED
Benignus, P. G., and Rogers, D. F., “Mildewproofing Automotive Gaskets,” Monsanto Chemical Co., 1945. Berk, S., Am. SOC.Teeting Materials, Bull. 145, 73-76 (March 1947). ENQ.CHEM.,40,262-7 (1948). Berk, S.,IND. Brown, A. E., Modern Plastics, 23, No. 8, 189-195, 254, 256 (1946).
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(5) Cooke, T. F.,and Vicklund, R. E., IND.ENG.CHEM.,ANAL. ED., 18,59-60,1946. ( 6 ) Delmonte, J., “Technology of Adhesives,” New York, Reinhold Pub. Corp., 1947. (7) . . Federal SDec. Cork ComDosition, Gasket and Sheet, HH-C-576 (1936). (8) Kanagy, J. R., Charles, A. M., Abrams, E., Tener, R. F., J. Research Natl. Bur. Standards, 36, No. 5 , 441-54 (1946). (9) Kimberly, A. E.,and Scribner, B. W., Natl. Bur. Standards, M ~ E Pub. c . M-154,1937. (10) SOC.Automotive Engrs., Tech. Board, Progress R e p t . 2 (October 1946).
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RECEIVED
August 1, 1947.
Dispersal of Triethylene Glycol Vapor with Aerosol Bombs HENRY WISE’ Department of Medicine, University of Chicugo, Chicago 37, I l l . T w o units designed for the production of triethylene glycol vapor. by atomization are studied. The glycol aerosol is produced by the liquefied gas method with Freon-12 and carbon dioxide, respectively, as the propelling agent. Quantitative measurements of the concentrations of triethylene glycol vapor discharged show that the carbon dioxide bomb exceeds the Freon dispense in efficiency of glycol vapor production. The bactericidal effect of triethylene glycol vapor produced by atomization is’ demonstrated in the laboratory on moist airborne droplets containing beta hemolytic %treptococci, Group C. From the standpoint of air disinfection, the use of a single-discharge glycol atomizer will find only timited application under certain specific situations because of the rapid rate of disappearance of glycol vapor from the air.
T
HE successful dispersal of insecticides by aerosol bombs led to the suggestion by Goodhue and McGovran of adapting the liquefied gas method to the production of germicidal aerosols (1). Although propylene glycol aerosols were originally employed by Robertson and co-workers in the early laboratory experiments on air sterilization (8),further studies indicated that rapid killing effect of the glycol on air-borne bacteria could be accounted for only by the interaction of the microorganisms with vapor molecules and not with aerosol droplets (3, 8). In accordance with this hypothesis it was demonstrated that an increase in bactericidal activity was obtained when propylene glycol was dispersed as a vapor instead of an aerosol. This difference in germicidal potency between aerosol and vapor was even more pronounced with triethylene glycol (7), because of the much lower vapor pressure of this compound (6) and, consequently, the less rapid rate of evaporation of its aerosol particles. Thus, for the purpose of air disinfection the physical characteristics of glycol aerosols dispersed into air must favor a rapid production of glycol vapor molecules which are essential for effective collisions with air-borne bacteria. For a liquid with high boiling point such as triethylene glycol, the colloidal particles produced by the dispenser must be small enough t o allow rapid rates of evaporation at room temperatures. The following communication represents a study of two types of liquefied-gas aerosol bombs. They are self-contained units 1 Present
addresa, California Institute of Technology, Pasadena, Calif.
employing compressed Freon-12 (dichlorodifluoromethane) and carbon dioxide, respectively, as the propelling gases which force the liquid triethylene glycol under pressure through a narrow orifice. Observations were made on the physical properties of the aerosols formed, the concentrations of glycol vapor produced, and the bactericidal effect under experimentally controlled and natural conditions. Figure 1 shows a picture of the aerosol bombs used. The large pound-size container is the type generally employed for the production of insecticidal aerosols. It contains a mixture of triethylene glycol and Freon-12 under an initial pressure of approximately 100 pounds per square inch. The container must be kept upright during use, and a knob at the top of the cylinder controls a needle valve. When the knob is turned, a fine stream of liquid mixture is forced through the orifice (0.009 inch in diameter) a t a rapid rate and atomized a t the mouth of the discharge nozzle. The smaller unit utilizes compressed carbon dioxide as the propelling agent for the atomization of triethylene glycol. It consists of a steel cylinder, 65 mm. in length and 20 mm. in diameter, the upper end of which is provided with a sealed orifice. Attached to this outlet and extending almost to the bottom inside the cylinder is a narrow steel tube of O.OO&inch inside diameter (27 gage). When the seal is broken, the mixture of triethylene glycol and carbon dioxide i n the dispenser a t an initial pressure of 900 pounds per square inch escapes through the narrow tube a t a high velocity, and 1s atomized into a fine aerosol. This dispenser differs from the larger one in the much higher pressure used for the production of the dispersoid as well as in the absence of a needle valve to interrupt the process of atomization once the seal has been ruptured. The size of the unit has been designed, therefore, to contain enough triethylene glycol to saturate the air of an average size room (about 2500 cubic feet) temporarily with triethyIene glycol vapor after a single discharge. This aerosol bomb has a total capacity of 10 ml. and contains 0.2 t o 0.5 ml. of triethylene glycol and 0.4 to 1.0ml. of ethanol; the remaining volume is carbon dioxide. Ethanol is added to triethylene glycol in a volume ratio of two to one in order to increase the solubility of triethylene glycol in liquid carbon dioxide. PHYSICOCHEMICAL MEASUREMENTS
The measurements were taken in an air-conditioned chamber of 640 cubic foot capacity (IO). A centrally located fan circulated air gently within the chamber, and the formation of tri-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
ethylene glycol vapor was detected by the glycometer, a device developed in this laboratory for the quantitative measurement of glycol vapor concentrations in air (6).
Vol. 41, No. 3
time of discharge of a single unit did not exceed 50 seconds (reduced to 30 in a later design), and the glycometer responded immediately to the presence of glycol vapor in the air (Figure 2) The absolute quantity of vapor resulting from the discharge of such an aeroqol bomb had the same order of magnitude as that produced by heat vaporization of an equivalent amount of liquid triethylene glycol: This result may be explained by the extremely high pressure a t which the material in the carbon dioxide bomb is forced through the narrow orifice The large pressure gradient established at the moment the seal is broken, which represents a drop from 900 pounds per square inch inside the container to 14.6 pounds (atmospheric pressure’, produces aerosol particles of very m a l l size which vaporize instantaneouslv. BACTERICIDAL E F F E C T ON AIR-BORNE MICROORGAhISM +
Since the bactericidal effect of triethylene glycol on air-borne microorganisms is governed by the rclative number of glycol vapor molecules available for collision with the bacterial droplet (S), the efficiency of the aerosol bomb may be determined also by the rate of killing and the duration of this action on bacteria atomized into the glycol-treated atmosphere. The details of the experimental procedure followed have been described ekewhere ( I O ) . A broth suspension CODtaining a young culture of beta hemolytic streptococci Group C, was atomized into the experimental chamber into which the triethylene glycol from the aerosol bombs had previously been discharged. The number of air-borne bacteria was determined by 5-minute exposures on settling plates and on 5 cubic foot air samples in Folin bubblers ( 2 ) ; the concentration of glycol vapor in the air was measured with the glycometer (6). The data obtained verified the observations previously made on the absolute amount of vapor produced by each type of aerosol bomb. The Freon bomb produces sufficient yuantities of vapor to demonstrate a definite bactericidal effect on moist, air-borne microorganisms (Table I). However, the much higher concentrations of glrcol vapor which result from the carbon dioxide bomb show not only a more rapid killing of the bacteria but also a more prolonged effect (Table 11). Thus, even during the second test experiment (Table 11) in which the
Figure 1. Aerosol Bombs for Dispersal of Triethylene Glycol Vapor
The Freon bombs, containing from 5 to 35% by weight triethylene glycol, delivered an average of 10 to 15 grams of the glycol-Freon mixture per minute. (The delivery rate approached the lower value as the disperser became partially exhausted during use.) A surprisingly low concentration of glycol vapor resulted from the atomization of large quantities of material. Further investigation showed that most of the triethylene glycol was left behind in the disperser after all the Freon gas had been exhausted. The mixture issuing from a bomb filled with 25% triethylene glycol and 75% Freon by weight proved to contain less than 1 % triethylene glycol. The issuing fluid was collected in a ga5 trap of conventional design immersed in a dry ice-acetone bath. The Freon gas readily evaporated when the condensed aerosol was allowed to reach room temperature, and the quantity of triethylene glycol collected in the trap was subsequently weighed. The liquid material left over in the “empty” dispenser after exhaustion of the Freon gas could be recovered by turning the unit upside down and collecting the residual triethylene glycol which had remained in the container. illthough the relative inefficiency of this aerosol bomb for the delivery of triethy!ene glycol had thus been demonstrated, additional experiments were undertaken to determine the rate and quantity of vapor production following the discharge of the aerosol mixture. Several units, containing 10 to 30y0 triethylene glycol, were tested under varying atmospheric conditions, and the average maximum vapor density registered by the glycometer did not exceed 10% of thv theoretical glycol vapor concentration, calculated on the basis of triethylene glycol actually atomized. (Even in the case of heat vaporization of known quantities of liquid triethylene glycol, only 50% of the theoretical concentration can be recovered from the vapor phale owing to adsorption of the vapor on walls and other surfaces, IO.) After fairly rapid attainment of the maximum vapor concmtration, the rate of disappearance of vapor exhibited a steep concentration gradient (Figure 2 ) . Similar experimental measurements carried out n ith a carbon dioxide-triethylene glycol bomb indicated that the degree of vaporization of the aerosol has a different order of magnitude from that observed with the Freon-triethylene glycol disperser. The
TABLEI. EFFECT OF TRIETHYLENE GLYCOLVAPOR FROM FREON-12 BOMBO N AIR-BORNEHEMOLYTIC STREPTOCOCCI, GROUPC (Room temperature 7 5 O F.; relative hurnidity 34%; contents of bomb 35% glycol-65% Frk1n-12: glycol vapor concentbtion, 2.6 micrograms/lit,ri a t etart of bacterial sorav) YGSurvival of Streptococci ______ (Control = 100%) Slinutes after Introduction of Bacterial Spray Folin bubbler Settling pl&
11. EFFECT O R TRIETHYLENE GLYCOLVAPOR FROM CARBOKDIOXIDEBOMBOK AIR-BORKEHEMOLYTIC STREPTOCOCCI, GROUPC
TABLE
(Room temperature, 70° F.: relative humidity 40%. contents of h o m h , 0.3 C P . glycol, 0.6 cc. ethanol, 9.’1 cc. Cod % Survival of Streptococci(C~rltro1 = 100%) Minutes after Expt. l a Erpt. 26 Volin Settling Folin Settling Introduction of Bacterial Spray bubbler plate bubbler plate 27.2 64 5 59 3 During atomization 15.7 1 10.1 24.7 16 1 40.8 2 1.1 10.0 8 9 28.4 5 0.2 1.2 2.4 3.7 10 0 0 0 1.2 15 0 ... 0 R,licroorganisms dispersed into experimental room 10 minutes after discharge of t h e glycol-COz bomb. Glycol vapor concentration 3.6 micrograms/liter a t start of bacterial spray. b Microorganisms dispersed into experimental room 85 minutes after diecharge of the glycol-COS bomb. Glycol vapor concentration 0.7 microgramsfliter a t s t a r t of bacterial spray.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
635
hospital room have shown that, after the discharge of a carbon dioxide-triethylene glycol bomb, the glycol vapor is present in bactericidal concentrations only for a relatively short time. During this period no measurable reduction in the number of air-borne bacteria was observed. Various field experiments during the last few years in inhabited rooms and hospital 1%-ardshave verified the observations that the introduction of a single dose of triethylene glycol vapor is not a satisfactory method for air disinfection. In such 7'5 9'0 165 120 1% surroundings the rate of air exchange is so rapid TIME ( MINUTES 1 += that the concentration of triethylene glycol vapor Figure 2. Tracing of Glycometer Record Showing Rates of Formation after a short-term vaporization process and Disappearance of Triethylene Glycol Vapor from Experimental ishes quickly and bactericidal action is correChamber spondingly brief. The dried bacteria present in A contained 0.4 cc. triethylene glycol, 0.8 CD. ethanol, and 8.2 eo. carbon dioxide; B contained 35 % triethylene glycol and 65 % Freon-12. T h e time of disoharge for secondary reservoirs, such as textiles and dust each homh waa 30 seoonda. (Q), which may become air-borne during sweeping, bedmaking, etc., offer more resistance to the bacteria were introduced into the experimental chamber 85 minbactericidal effect of triethylene glycol vapor than the moist droplets. Under these conditions i t is necessary to maintain Utes after the triethylene glycol-carbon dioxide dispenser had the glycol concentration in the air near the saturation level with been discharged] a sterile atmosphere resulted within 10 to 15 minutes after the bacterial spray. No such effect could be the aid of automatic devices, such as the glycostat (6), in order expected after a single discharge from a Freon-triethylene glycol to reduce the number of air-borne bacteria by 60 to 70y0(4). bomb, since the glycol vapor concentration diminished to zero Therefore, from the standpoint of air disinfection, the intermittent introduction of triethylene glycol vapor by single diswithin one hour after the introduction of the vapor (Figure 2). charge of an aerosol bomb will find only limited application. It Similar bacterial experiments carried out with an aerosol of may prove useful when the source of infection has been removed pure Freon-12 or a mixture of carbon dioxide and ethanol indicated that these compounds make no contribution to the bacteriand an immediate attempt is made to protect a group of suscidal effect of the triethylene glycol vapor. The Freon gas receptibles from acquiring the infection by the air-borne route. leased at the time of atomization does not represent a hazard The degree of protection would, of course, be limited by the because of its nontoxic, nonflammable characteristics, although length of exposure t o the infected individual beforehand. Other the odor of the gas is perceptible in the air. situations where an aerosol bomb may find application are in certain spaces temporarily crowded with patients suffering from DISCUSSION O F RESULTS various kinds of upper respiratory infection, such as army dispensaries in winter. But even then the dispersal of glycol vapor The experimental data indicate that the process of atomization would have to be repeated at short intervals. A more satisby the liquefied gas method may be efficiently employed for the factory solution of this problem will be found in the maintenance production of triethylene glycol vapor provided three basic of glycol vapor at desired concentrations over long periods in requirements are fulfilled: (a)The propelling gas must be nonsurroundings where danger of infection by air-borne bacteria toxic, nonflammable] and relatively inexpensive. (b) The glycol exists. The applicability of an aerosol disperser of the carbon to be atomized must form a homogeneous solution with the inert dioxide type may become greatly enhanced if a larger unit is gas. Thereby the mixture which issues from the dispenser is designed for intermittent or continuous introduction of glycol uniform in composition and the distillation of one component a t vapor. a rate different from that of the other is prevented. Also, a high orifice pressure is required to yield the shearing force necessary for the instantaneous formation of aerosol droplets of small diameter; the physical characteristics of the propellant gas should exhibit, therefore, a high vapor pressure at room temperature. (c) The diameter of the nozzle should be reduced sufficiently to permit high orifice velocities without interference in the rate of discharge. The concentrations of triethylene glycol vapor produced by atomization with carbon dioxide bombs indicate that in a tightly enclosed space, the quantity of vapor formed by a single discharge may be sufficient to produce a bactericidal atmosphere lasting for relatively long periods. The experiments described were carried out under conditions highly favorable to the bactericidal action of glycol vapor, such as moderate humidities and temperatures, the use of moist droplets containing the microorganisms, an experimental chamber with no air exchange, and very slow air currents. I n such surroundings a glycol vapor concentration bactericidal to beta hemolytic streptococci, Group C, has been maintained for over 5 hours. However, it is unlikely that similar results can be obtained under natural conditions of inhabited r o o m because of the rapid rate of disappearance of glycol vapor from the air and the presence of desiccated, dust-borne microorganisms. Actual experiments carried out on a two-patient
ACKNOWLEDGMENT
The author is greatful t o 0. H. Robertson for his stimulating interest in this work and for his numerous suggestions made during the course of the investigation. prp'
LITERATURE CITED
(1) Goodhue, L. D., and McGovran, E. R., Science, 99, 511 (1944) (2) Lemon, H. M., Proc. SOC.Ezptl. Bid.Med., 54, 298 (1943). (3) Puck, T. T., J. Exptl.Med., 85, 729 (1947). (4) Puck, T. T., Robertson, 0. H., Hamburger, M., and Hurst, V., J . Infectious Diseases, 76, 216 (1945). (5) Puck, T. T., and Wise, Henry, J . Phys. Chem., 50, 329 (1946). (6) Puck, T. T., Wise, Henry, and Robertson, 0. H., J . Exptl. Med., 80,377 (1944). (7) Robertson, 0. H., Harvey Lectures, Ser. 38, 227 (1942-43) (8) Robertson, 0. H., Bigg, E., Puck, T. T. and Miller, B. F., J. Exptl.Med., 75,593 (1942). (9) Robertson, 0. H., Hamburger, M., Loosli, C. G., Puck, T. T., Lemon, H. M., and Wise, Henry, J . Am. Med. Assoc., 126, 993 (1944). (10) Robertson, 0. H., Puck, T. T., and Wise, Henry, J . Ezptl. M e d . , 84,559 (1946).
RECEIVED June 28, 1948. This work was undertaken for the Cornniission on Air-Borne Infeotions, Army Epidemiological Board. Preventive Medicine
Service, Office of the Surgeon General. U. S. Army.
