US3587978A - Space fumigation system - Google Patents

Abstract

THE FUMIGATION OF ENCLOSED SPACES, AND PARTICULARLY TOBACCO WAREHOUSES, IS ACCOMPLISHED BY THE INJECTION AT PREDETERMINED INTERVALS OF A SOLUTION OF A DIALKYL HALOVINYL PHOSPHATE OF OF PYRETHRUM IN A TRICHLOROETHANE, UTILIZING AN AUTOMATIC DISPENSING SYSTEM INCLUDING MEANS FOR SUPPLYING INSECTICIDE SOLUTION, A SOURCE OF COMPRESSED AIR, AN INSECTICIDE DISTRIBUTION CONDUIT PROVIDED WITH A SERIES OF SIPHON MEMBERS EACH FITTED WITH A PNEUMATIC ATOMIZING SPRAY NOZZLE AND CONNECTED TO THE COMPRESSED AIR SUPPLY TO FORM A SIPHON SPRAY SYSTEM FOR DISTRIBUTION OF THE INSECTICIDAL LIQUID IN FINELY DISPERSED CONDITION.

Description

United States Patent [72] Inventors Jesse Douglas Rollow, Jr.

' 6106 Cromwell Drive, Washington, D.C.

20016; Constant Roosevelt Ray, 2204 Colwyn Road, Richmond, Va. 23229 (21] Appl. No. 784,800 [22] Filed Dec. 18, 1968 [45] Patented June 28, 1971 [54] SPACE FUMIGATION SYSTEM 7 Claims, 4 Drawing Figs.

[52] U.S. Cl 239/550, 21/58, 222/4, 222/204, 239/70, 239/424 [51} 1nt.Cl B05b 1/14 [50] Field of Search 21/2,58, 106, 107, 108, 109; 2391266, 268, 550, 551; 222/4, 482, 565, 204

[56] References Cited UNITED STATES PATENTS 762,014 6/1904 Wittbold 239/550 928,038 7/1909 Fusch 21/108X 1,056,094 3/1913 Gilman 239/550X 1,658,220 2/1928 Binks 239/550X 2,473,684 6/1949 Howard. 21/108 3,062,454 11/1962 Cocks 239/550X 3,137,446 6/1964 Senichi Masuda 239/551X 3,370,571 2/1968 Knapp 43/132X Primary Examiner-Morris O. Wolk Assistant Examiner-Joseph T. Zatarga At!orney-Hugo E. Weisberger PATENTED JUN28 IBM 3, E387 9 i3 2 INVENTORS JESSE DOUGLAS ROLLOW JR. cowsmm R. RAY

ATTORNEY SPACE FUMIGATION SYSTEM BACKGROUND OF THE INVENTION The control of insects and other pests within large enclosed spaces such as buildings, bins, and the like, in which there are stored commodities susceptible to insect attack is a matter of great economic importance. It is customary in the storage of tobacco leaves, and'especially flue-cured tobacco, to store this product for periods of as much as seven or eight years in tobacco warehouses. Such stored tobacco is subject to serious insect infestations, of which the most familiar examples are those of the cigarette beetle, Lasioderma serricorne (F), and the tobacco moth, Ephestia elutella (Huebner). Early efforts to control these two pests utilized mainly pyrethrum, applied either as a powder by dusting within the storage space, or in the form of an aerosol together with a highly refined volatile hydrocarbon oil as a carrier.

More recently it was found that tobacco, grains, and other stored commodities could be protected against insect damage by fumigation of the storage areas with the vapors of a dialkyl halovinyl phosphate, the preferred compound for this purpose being dimethyl 2,2-dichlorovinyl phosphate (DDVP), also sold under the designation Dichlorvos. DDVP is known to be particularly effective against the cigarette beetle and the tobacco moth and it had been proposed in prior art to apply this compound as a thermal aerosol either alone, or in percent solution in a light oil, from an automatic generator suspended above hogsheads of tobacco, utilizing an automatic timer and solenoid valve, set to release a concentration of about 0.5 grams per 1,000 cubic feet daily in the late afternoon just preceding the peak flight activity of the insect. In addition to the use of such carriers as deodorized kerosene, DDVP is also applied in the form of an aqueous emulsion ofa solution of the insecticide in a halogenated aliphatic hydrocarbon such as carbon tetrachloride or tctrachloroethylene (perchloroethylene), and a process of this type is described in U.S. Pat. No. 2,968,59l. These previously employed halogenated solvents have not been entirely satisfactory, how ever, owing to the large differential in vapor pressure between the DDVP and the solvent, problems in maintaining the DDVP in solution, and the tendency of the solvent to condense and to wet the tobacco leaves directly or by penetration into the hogsheads. Accordingly, there has existed a need for a suitable solvent which would be free from these drawbacks and which would not cause actual or potential damage to the tobacco or other commodities.

As indicated previously, it has been customary to apply DDVP either by direct air pressure spraying ofits solutions, or as an aerosol or mist by means of mechanical or thermal fog generators. Thus in one system developed by the US. Department of Agriculture, an automatic dispensing unit applies a metered amount of the insecticide at a specific time for a repeated number of discharges. The system consists of a pressurized cylinder controlled by a solenoid valve energized by a central clock timer. Another known system is that disclosed in US. Pat. No. 3,209,950, wherein a metered amount ofinsecticide is dispensed from an aerosol type container in which it is stored under pressure together with a fluorocarbon propellent, the dispensing being regulated by the action of a solenoid valve and a clock mechanism. These systems, in which the highly toxic insecticide is constantly maintained under considerable pressure, have the major disadvantage that leakage may occur, thereby endangering operators or other persons entering the warehouse between application sequences. They also require periodic changes or renewals of pressure supply cylinders or aerosol bottles. Moreover in the case of the aerosol bottles the discharge pressure may drop below the ef' fective level as the container contents near exhaustion. Finally, as is the case with most pressurized systems, they are cumbersome in operation and expensive to maintain. There has accordingly existed a long-felt need for a liquid dispensing system and particularly an insecticide dispensing system in which the liquid or the insecticidal solution would be distributed from a central supply source and dispensed in spray form at a plurality of points of application, the liquid or the insecticidal solution being at ordinary atmospheric pressure, and with suitable means provided for automatic dispensing and spraying.

GENERAL DESCRIPTION OF THE INVENTION In accordance with the present invention, there is provided a novel system for the distribution and dispensing ofliquids, such as insecticidal solutions, within an enclosed space. The system will be described with particular reference to its application in warehouses for the storage of tobacco, but it is to be understood that such description is for purposes ofillustration only, and that the principles of the invention are applicable to all types of installations for dispensing not only insecticidal solutions, but other volatile or siphonable liquids.

In accordance with another aspect of the invention, there is provided a novel insecticide composition and process of applying the same, said insecticide comprising a solution of a dialkyl halovinyl phosphate or of pyrethrum in a trichloroethane. This insecticidal solution dimethyl volatility characteristics which enable it to be successfully utilized in the dispensing system of the invention, and at the same time, the dispensing system, operating as it does with the insecticidal solution at atmospheric pressure, is especially suited for handling this type of volatile insecticide.

The novel insecticidal composition of the present invention comprises a solution of a dialkyl halovinyl phosphate or of pyrethrum in a trichloroethane. The trichloroethane is preferably l,l,l,-trichloroethane (methyl chloroform), CH C-Cl;,, a colorless liquid, insoluble in water, boiling point 75 C., specific gravity 1.325. This solvent possesses very favorable volatility characteristics, forming a persistent mist, but with no tendency to condense on the tobacco or other commodity being treated. Alternatively there may be employed as a solvent, the compound l,l,2-trichloroethane (vinyl trichloride), CH-Cl -CH Cl, a colorless liquid, boiling point ll3.7 C., specific gravity 1.4432, but the volatility characteristics of this solvent are less favorable.

The preferred dialkyl halovinyl phosphate is dimethyl 2,2- dichlorovinyl phosphate. However other compounds of this class which may be employed include: diethyl-2,2-dichlorovinyl phosphate, dimethyl 2-chlorovinyl phosphate, di-sec-butyl 2,2-dichlorovinyl phosphate, dimethyl 2,2-dibromovinyl phosphate, dimethyl l,2-dibromo-2,2-dichloroethyl phosphate, and dimethyl l,2-dibromo-2-chloroethyl phosphate.

The concentration ofDDVP or equivalent insecticide of the same type lies in the range ofabout 10 percent by weight up to the limit of solubility, preferably between about 10 percent and about 20 percent. A minor portion of the trichloroethane may be replaced by a diluent, such as, for example, a highly refined volatile hydrocarbon, e.g. deodorized kerosene. The clear solution is characterized by rapid evaporation of the solvent, with both the active ingredient and the trichloroethane vaporizing promptly upon leaving the spraying nozzle, and with complete avoidance of clogging difficulties.

It has been found, in accordance with the present invention, that the addition to the DDVP-trichloroethane combination of from about 0.01 percent to about 1 percent by weight of an alkali metal or alkaline earth metal salt of an alkyl carboxylic acid having between about four and about l2 carbon atoms serves to minimize corrosion of metal nozzles and to stabilize the solution. Samples of such acids include butyric, octoic, and lauric acids. The preferred acid is one containing eight carbon atoms, and may be either straight chain or branched in structure, for example octoic acid. Examples of alkali metals include sodium and potassium, while examples of alkaline earth metals include calcium and barium. The preferred additive is calcium octoate, in an amount of from about 0.25 to about 1 percent, and preferably about 0.5 percent by weight.

In accordance with the practice of the invention, the dialkyl halovinyl phosphate solution, prepared as described, is in jected into the space to be fumigated in the form of a fog or mist of finely divided particles, preferably using the spraying system described more fully below. The preferred practice involves application of dosage rate of the dialkyl halovinyl phosphate, for example DDVP, at a level of 0.5 grams per 1,000 cubic feet, daily. The insecticide is applied each afternoon during the twilight hours when the insects are flying. The system is designed so that the recommended dosage is applied during a period of approximately 1 to 8 minutes each day. Particle size of the fog or mist is of importance, although not critical, and will advantageously lie predominantly in the range of about 1 to about 40 microns, preferably from about 1 to about 15 microns.

Where pyrethrum is employed as the active insecticidal ingredient, it is in solution in a concentration of about 1 percent by weight in a trichloroethane solvent. A suitable formulation is a solution of 1 percent pyrethrum, 50 percent 1,1,1- trichloroethane, and 49 percent Ultransene (deodorized refined kerosene), all by weight, lf desired, a small amount of a synergist, such as piperonyl butoxide, may be included.

1f the insecticidal solutions of the invention are to be applied in emulsion form, a suitable surface-active agent may be incorporated therein, in accordance with conventional practice. There may also be incorporated suitable antioxidants and other types ofstabilizers.

DESCRIPTION OF THE PREFERRED EMBODIMENT The practice of the invention and the operation of the novel space fumigation system will be more readily understood by reference to the accompanying drawings, which are illustrative ofa presently preferred embodiment, and in which:

FIG. 1 is a vertical sectional view through a storage warehouse or chamber, showing the general organization of the pneumatic insecticide-spraying system;

H6. 2 is a view, partly in section, showing the arrangement of the compressed air and liquid supply lines, siphon tube and spray nozzle mounting; and

H6. 3 is a sectional view ofa siphon spray nozzle.

FIG. 4 is a front elevation of the exit portion of the spray nozzle showing the liquid discharge orifice surrounded by the annular air discharge nozzle.

Referring now to the drawings, a building structure to be fumigated, such as a tobacco warehouse, is depicted diagrammatically at 10. The warehouse has walls 11, roof structure 12, and floor 13. Positioned on the floor in the interior of the warehouse 10 are hogsheads 14 of tobacco, shown generally. The space fumigation system comprises a supply tank 15 for holding insecticidal solution, which is kept filled from a central source, not shown, via inlet 16. Extending in a horizontal position from outlet 17 of the supply tank is a conduit 18, which may be made of any suitable material, such as stainless steel or a plastic such as polypropylene or polytetrafluoro ethylene (Teflon). At selected intervals there extend vertically upward from conduit 18, a plurality of siphon conduits 19, through which the liquid is induced to rise by the action of the compressed air as described below. These siphon members may be of any suitable height, depending upon the specific gravity and the flow rate of the liquid being dispensed. In a typical installation the liquid conduit 18 may range in inside diameter from about three-eighths inch to about 1 inch, depending upon the flow rate and the number ofspray nozzles to be supplied. The siphon conduits are of a height sufficient to provide a siphon action for the liquid being used, and their height will typically range from about 3 inches to about 12 inches.

At its upper end, each siphon member 19 is connected to the liquid inlet portion 28 ofa siphon-type pneumatic atomizing spray nozzle 20, an embodiment ofwhich is shown in more detail in FIGS. 3 and 4. The spray nozzle comprises a body portion 20 provided at its lower end with an inlet 28 which may be threaded and which leads to a liquid discharge nozzle 29 which terminates in a narrow liquid discharge orifice 30. The liquid discharge orifice 29 is provided with a screw plug 31 to permit cleaning or insertion of a needle control attachment when necessary. At the upper end of body member 20 there is an air inlet 21 which connects with a plurality of air ports 33, the air being first forced through an intermediate gasket 34 which is provided with a multiplicity of openings which serve to distribute the compressed air so that it surrounds liquid orifice 30 in a chamber provided by cap 35, which has in its center an opening 36 of a diameter sufficient to form an annular air nozzle 37. The flow of air through air nozzle 37 induces a flow of liquid through liquid orifice 30, and forms a fine spray or mist, which is transmitted to the space surrounding the spray nozzle.

Increasing air pressure at any given liquid pressure decreases liquid particle size, and decreasing air pressure increases liquid particle size. It will further be apparent that the spray particle size will be dependent upon the relationship between the inside diameter of the liquid orifice, and the outside diameter of the liquid orifice in its relation to the diameter of the annular air nozzle opening. For the insecticidal solutions of the invention, the liquid orifice size will advantageously range from about 0.016 inch to about 0.100 inch inside diameter; the outside diameter will advantageously range from about 0.050 inch to about 0.150 inch. The air nozzle diameter will correspondingly range from about 0.064 inch to about 0.180 inch inside diameter.

There is connected to the airinlet portion 21 of each spray nozzle 20 a flexible conduit 22, a multiplicity of which leads from an air supply pipe 42 which has dimensions similar to those of the liquid supply conduit. The liquid supply conduit 18 is suspended from roof 12 by hanger members 40, as shown in FIG. 1, while the air supply conduit 42 is suspended from the roof 12 by hanger members 41, at a height which places it at approximately the same level, or near the level of the spray nozzles 20. The respective conduits and fittings therefor, when of plastic material, provide low cost, flexibility, high tensile strength, resistance to corrosion, and ease ofinstallation.

Compressed air or other gas is supplied to the system at any desired pressure, for example between about 10 and 50 lbs. per sq. inch, preferably 30-35 lbs. per sq. inch, from a compressor and compressed air storage tank shown generally at 44. The system is rendered substantially automatic by the inclusion in the air supply line leading from compressor 44, of a solenoid valve 45 of any suitable type, which is actuated by a timer 46. The solenoid valve serves to turn the air supply on and off electrically, being normally closed and open when actuated by the timer. The timer 46 is preferably of a type which will provide time intervals between 1 second and '60 minutes, and which will stop the solenoid valve at a preselected time. There may also be included in the air supply line an air filter 47, and an air pressure regulator and gauge 48.

In the operation of the fumigating system, a supply of insecticidal solution, such as a solution of DDVP or pyrethrum in 1,1,l-trichloroethane, is maintained in supply tank 15 and flows through conduit 18 into siphon members 19. The insecticide is dispensed by means of compressed air supplied to the spray nozzles at selected time intervals and at any desired rate. For example, the system may be adjusted to dispense approximately 0.5 grams daily of DDVP per 1,000 cubic feet of storage space in approximately 2 minutes during the twilight hours which correspond to maximum flight activity of the insects. The timer is set for the required time and turned on at dusk. 1t stops automatically and remains inactive until the following evening.

The following examples illustrate the composition and method of the invention, but are not to be regarded as limit- EXAMPLE 1 An insecticidal solution of i,l.l-trichloroetharle containing 20 percent by weight of dissolved dimethyl 2,2-dichlorovinyl phosphate was prepared, in which there was incorporated 0.5 percent by weight of calcium octoate. Utilizing the dispensing system described above, with air pressure at 35 lbs. per sq. inch, and adjusting the spray nozzles for a particle size of ll microns, the solution was sprayed into the interior of a tobacco warehouse containing stored tobacco at a rate of 0.5 grams DDVP per 1,000 cubic feet of storage space for a period of 2 minutes. Tests showed that 98 percent of the sprayed particles had a particle size below l5 microns. Destruction of cigarette beetle and tobacco moth infestations was virtually complete.

EXAMPLE 2 b. a conduit for distribution of said liquid connected to said container and having connected therewith a plurality of upward extending siphon conduits;

c. a plurality of pneumatic atomizing spray nozzles for dispensing said liquid mounted at the upper ends of said siphon conduits; and

d.' a source of compressed gas connected by means of an air conduit to each of said spray nozzles whereby to draw said liquid into said spray nozzles and to expel the liquid therefrom in finely dispersed form.

2. The system of claim I in which said liquid and air conduits are suspended in substantially horizontal position by means of hanger members.

3. The system of claim 1 in which said liquid is at substantially atmospheric pressure.

4. The system of claim 1 which further includes a solenoid valve positioned in the gas supply source to initiate or stop the flow of gas to said spray nozzles.

5. The system of claim 4 which further includes timing means for periodically actuating said solenoid valve at predetermined periods of time.

6. The system of claim 1 in which said system includes a body ofan insecticidal solution.

7. The system of claim 6 in which said siphon conduits are of a height sufficient to provide siphon action for said insecticidal solution.

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