Fumigation of large structures

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Recently, phosphine generated from aluminium phosphide has been successfully applied for the fumigation of large buildings, such as warehouses, which can be rendered sufficiently gas tight to retain the vapours. Special attention must be paid to the possibility of reaction with copper and copper alloys, as discussed in Chapter 6.

ADVANCE PRECAUTIONS

Preliminary Inspection and Arrangements

The structure to be fumigated should be carefully inspected at the outset so that unusual features or potential problems can be taken into consideration before the fumigation is started. Such matters as sources of leakage, commodities that will absorb large amounts of fumigant, possible damage to commodities, arrangements for gas analysis, safety of personnel, etc. should all be noted so that appropriate arrangements can be made beforehand. In preparation for fumigation, a check list of the various duties to be performed should be made - a fumigator should never trust to memory or assume that essential things have been done. It is important to instruct the fumigation crew carefully, show them any special problems or hazards and inform them of emergency procedures in case of an accident.

Compliance with Official Regulations

The use of fumigants is often regulated by local or state governments. Regulations are designed to protect the health of those applying the chemicals and of the public in general. Regardless of whether the treatments are made regularly in permanent installations or are carried out once only in a particular place, it is necessary that all regulations be observed.

Advance Notice of Treatments

It is usually advisable to inform local fire departments of large-scale treatments, especially if an entire structure or building is to be fumigated. The police should also be warned if the work is being done in a built-up area.

Guards

If the fumigation is being done in a place accessible to the public or adjoining public thoroughfares, it is necessary to employ one or more guards to keep unauthorized persons from approaching the fumigation site or from interfering with the operation. The guards are employed to keep outsiders away while the fumigation is being prepared, during the gas application, during the treatment and until the entire fumigation area has been declared "gas free" after the treatment has ended.

Warning Notices

Regardless of whether guards are employed or not, properly worded warning signs should be posted on all sides of a fumigation site. These signs should have clearly printed letters at least 5 cm (2 in) high, with wording such as:

DANGER
FUMIGATION WITH POISON GAS
(name of particular fumigant)
KEEP OUT
BY ORDER

The date of application of the fumigant should be included on the warning notices for those treatments where there is a possibility that the notices may not be removed at the end of the fumigation, e.g. on freight containers, railway box cars or other transportation vehicles. Notices printed on cardboard are often available from the fumigant manufacturer or dealer.

Respirators

Fresh, unused respirator canisters, specifically designed for protection against the particular fumigant to be employed, should be provided for each operator likely to be exposed to any concentration of the gas. A minimum number is two canisters per operator. One is to be used during application of the fumigant and, if there is exposure to any fumigant during this operation, it should be replaced by a new one before the aeration process begins.

Careful checks of individual respirators, carried out under the supervision of the foreman or leader, should be made by all operators concerned. All precautions and procedures outlined in Chapter 3 (Respirators) should be carefully followed.

PREPARATIONS FOR FUMIGATION

Sealing

Particular attention must be given to the proper sealing of a structure, as this may constitute the difference between the success and failure of a fumigation. Brick or cement buildings in a good state of repair can usually be fumigated by sealing all external openings by any of the methods listed at the beginning of this chapter. Doors and windows should be firmly closed and almost invariably should be taped or caulked. If the entire building cannot be made gas tight, it may be covered with gas-proof sheets in the manner described in the previous section.

Circulating Fans

When methyl bromide is being used, artificial circulation should be provided by means of fans to prevent stratification of this heavy gas and to ensure even distribution. One 40 cm (16 in) fan is usually suffi cient for every 1 400 m (50 000 ft). Provision should be made to switch the fans on or off from outside the building.

Plan for Gas Discharge

All fumigations which are not strictly routine in nature must be carefully planned. If a particular operation is complicated or conducted on a large scale, it is well to have the duties and movements of each employee typed out on a specially drawn-up work sheet. When fumigating buildings, warehouses or ships with more than one floor or deck, it is advisable to include a plan on this sheet showing the location of each fumigant cylinder and gas outlet and all exits and entrances. When crews are fumigating large structures by releasing the fumigant from inside, it is sometimes advisable to place directional signs at strategic stairways, doors or turnings. Sometimes it is helpful to chalk arrows and other marks on the floor to indicate the direction and order of movements.

The work should be organized so that at no time will the operators pass through a room or space in which the gas has already been discharged. In buildings without basements, discharge should start on the top floor in order that the crew may work toward the prearranged exit on the ground floor. If there is a basement or cellar, a special plan may have to be made. Usually, the main floor may be omitted while one crew releases the fumigant in the upper floors and another works in the basement. The main floor is not treated until the others have been traversed and all operators, except those concerned with the final discharge, have left the building.

It is most important that operators should not be releasing fumigants inside a building for more than 30 minutes. It is better that a 15- to 20- minute period be allowed for each person. If the gas release cannot be done properly within that time by the available staff, more workers should be allocated to the crew during the preliminary planning.

In large operations, it is good practice to have the crew working in pairs; if an accident occurs to one person, the other can bring him into the fresh air or summon assistance. Each member should be fully acquainted with the role of the others in the team. When the discharge of the fumigant is to be done by operators moving inside the structure, a full rehearsal of the procedure should be carried out at least once before the actual fumigation is started.

Calculation of Dosage

All dosage recommendations are made on the basis of the volume (cubic content) of the structure. For regularly shaped square or rectangular buildings, dosages are calculated by multiplying length by width by height. If the buildings are irregular, the volume of each unit should be calculated separately, and then all added together. If the building has a peaked roof, the average between the height of the sidewall and the distance from the lowest floor to the top of the roof may be taken as the height dimension (third multiple) in calculating the volume of the structure.

No allowance should be made for space occupied by commodities, materials, machinery or furnishings. Dosage recommendations are given in Schedules P and Q.

Provision for Ventilation

If possible, some provision should be made in advance for starting postfumigation ventilation before the fumigators enter the buildings. If front and rear doors can be opened from the outside, a strong draught can be created to dilute the gas concentrations appreciably when ventilation is started.

When the roof ventilators are covered with plastic sheeting or kraft paper, they can be quickly and safely uncovered at ventilation time and the fans can be started.

Final Checks

When all preparations are completed, several checks should be made before the fumigants are applied.

1. Sources of ignition. All possible sources of fire should be eliminated. All pilot lights and gas and oil burners should be extinguished. It is particularly important that thermostaticallycontrolled, high temperature electrical equipment of any kind be disconnected during the fumigation. HCN is inflammable at the high concentrations that may be present during initial discharge of the gas. Methyl bromide may react in the presence of a flame or glowing wire to form hydrobromic acid, which may be corrosive or injurious to many materials.

2. Warning signs. Ascertain that the warning signs are properly placed on all possible entrances to the building, and, in large-scale operations, at strategic points on the approaches to the building.

3. Outside telephone. Locate a nearby telephone of ready and constant access which may be used in case of emergency.

4. Guards. See that the guards or watchmen are at their proper stations before gas discharge begins. They should prevent unauthorized persons from entering the building or interfering with the work of the fumigation crew.

5. Check on evacuation. As a final essential measure, the foreman fumigator, accompanied if necessary by senior crew members, should visit every floor and room of the structure calling in a loud voice a warning, such as: "Poison gas fumigation to begin everybody out." Failure to observe this precaution in the past has led to serious accidents, including at least one fatality. During the visit these operators will also have an opportunity to see if all other preparations are properly completed.

APPLICATION OF THE FUMIGANT

While the fumigant is being applied, all persons engaged in or associated with this operation should wear respirators (gas masks). The only permissible exception to this rule concerns the operators working in the open, or in some well-ventilated place, under conditions in which any gas that escapes from the equipment is immediately diluted and dissipated. The respirators should not be removed until the workers indoors have reached fresh air, the fumigant has been completely discharged, and all the valves and piping have been closed so that no fumigant can escape from the system.

During the application, unauthorised persons should not be allowed to approach or talk to the operators engaged in the discharge of the fumigant. The organization of fumigant discharge was also discussed earlier under "Plan for gas discharge". Special techniques for HCN and methyl bromide are given later in this chapter under the headings for each gas.

PRECAUTIONS DURING TREATMENT

During the course of the treatment regular checks should be made for leakage of the fumigant. This is necessary for safety and also to prevent a failure of the treatment. The sections dealing with the properties and uses of fumigants include descriptions of methods of leak detection.

When guards are posted during large-scale operations they should be on duty during the whole period of treatment.

FUMIGANT ANALYSIS

As an aid to effective fumigation, sampling tubes should be connected to strategic points throughout the structure. During the fumigation, samples may be drawn at intervals and analysed by one of the methods already described for the fumigant being used. If concentrations at any point fall below an established level, more fumigant may be introduced as required.

VENTILATION

The operators should wear respirators when they approach or enter the building.

Openings from Outside

In accordance with preparations made before fumigation, when airing begins, as many doors and windows as possible are opened from the outside. Ventilators and fans with readily accessible switches may be started. The operators should then withdraw from the immediate vicinity of the fumigated structure. At least 30 minutes should elapse before the fumigators enter the building to open more doors and windows and to start other ventilators. At the beginning of aeration, the building should be entered only for short periods of time. The process of ventilation may be divided into stages, with ample time given to each one. After being in the building for a short period, the operators should withdraw into fresh air, remove their respirators, and wait for 15 minutes or more before putting them on again and re-entering the structure.

Tests for Gas-free Condition

As soon as the crew foreman determines that the structure is properly aired, the appropriate chemical tests for residual fumigant, already described, may be carried out.

Particular attention should be paid to the retention of gas in highly sorptive material such as flours, meals and jute bags. This retention may be unduly prolonged by introducing cold air into a building that was warm during the fumigation. Serious accidents may result from closing such a building again and warming it up and causing the release of sorbed gas into the atmosphere. In cold weather, therefore, after the preliminary aeration, all doors and windows should be closed, the building heated to above 24C for two or three hours, and the aeration repeated. Under exceptional conditions, this process may have to be repeated two or three times before all material is safely free of gas.

After chemical tests have shown that both the structure and its contents are free from toxic concentrations, the building may be declared gas free and reoccupation permitted.

APPLICATION OF HCN

The materials from which HCN may be volatilized as a fumigant were listed in Chapter 6. The techniques for their practical application in building fumigation are described here.

Pot Method

The generation of HCN by the action of sulphuric acid on a cyanide salt is usually referred to as the pot method, although wooden barrels are often used as well as crocks or pots. This is not as convenient as the other two methods described below, which have largely replaced it, but it lends itself to emergency treatments.

Handling Chemicals

Sulphuric acid, 66 Beaume, is usually supplied in 45 1 (10 gall) carboys in wooden frames. It is advisable to divide this into smaller amounts in bottles; for this operation, a tilting frame is recommended. Acid should be poured slowly and with caution.

The sodium cyanide eggs, usually 25 9 (l oz) each, should be kept in tightly closed containers, away from heat and moisture, until they are needed.

Precautions

Sodium cyanide is a powerful stomach poison, which can also cause serious poisoning by being absorbed through cuts and exposed skin. All persons handling the dry sodium cyanide, and mixing the sulphuric acid in water before fumigation begins, should wear rubber gloves and tight fitting goggles.

Chemicals are made ready in the following proportions according to the systems of measurement used.

  Metric British U.S.
Sodium cyanide 1.0 kg 1.0 lb 1.0 lb
Sulphuric acid 1.5 litres 1.2 pints 1.5 pints
Water 3.0 litres 2.4 pints 3.0 pints

(Actually, it has been shown by chemical test that a 1 : 1.5 : 2 United States formula yields more gas than the one given. However, it has been observed that the smaller quantity of water used may result in a crystallization of the residue, which makes the emptying of the containers after fumigation more difficult (Back and Cotton, 1942).

Dosage

If properly generated according to the method given here, O.45 kg (1 lb) of sodium cyanide will generate 0.25 kg (8 oz approximately) of HCN gas. For many building fumigations at temperatures above 20C, the dosage of HCN gas recommended is 8 g/m (8oz/l 000 ft ).

Use and Placing of Generators

Earthenware crocks up to 18 1 (4 gall) capacity or clean, water-tight 227 l (50 gall) wooden barrels should be used as generators. For largescale operations in mills and warehouses, the barrels are safer to use. The generators may be set out in groups of three or four on each floor of the building, each in a galvanized iron washtub, if available. The tub should contain a pailful of water with several handfuls of washing soda to neutralize any acid that may leak or spill from the barrel. The generators may be conspicuously numbered in the order of their use, in accordance with the need for careful planning discussed previously.

Preparing for Generation

After the generators are set out in their final positions, the required amount of water is poured into each. Then the required amount of acid for each generator is measured into pails. Next, the acid is poured carefully and slowly into the water in the generators.

Caution: never, under any circumstances, pour water into sulphuric acid - always acid into water

The next step is to count the number of sodium eggs required for each generator and to place them in double-walled kraft paper bags or flour sacks. The bags or sacks are then carefully placed 30 or 60 cm (1 or 2 ft) away from the generator, where they can be easily seen and reached.

Generating the Fumigant

After the final preparation and inspection of the buildings have been made, the respirators, fitted with anticyanide canisters, are put on. Gas generation is started at the farthest point from the final exit (see previous sections for discussion of planning). As each generator is reached, the operator carefully lowers the bag with cyanide into the acid, without allowing any liquid to splash on his person. Then he moves quickly to the next generator and repeats the same procedure at each station until he reaches the final exit.

Cleaning Generators

After the fumigation is finished and the structure has been thoroughly ventilated, the residue must be emptied and the generators cleaned. Sometimes the chemical reaction is incomplete and therefore it is advisable to wear a respirator while handling the generators and emptying them. The residual material should be taken to properly approved sites for disposal. The empty generators should then be thoroughly washed with fresh water and the liquid disposed of in the manner already suggested.

Special Pressure Generators

Special generators made of acid-resistant metals are available from some manufacturers of sodium cyanide. They permit the generating of HCN outside a structure. The acid is placed at the bottom of the metal generator and the sodium cyanide, preferably in egg-shaped form, is suspended above in a metal basket. The lid of the generator is then tightly clamped down with thumbscrews. When the charge of HCN is to be released, the basket of sodium cyanide eggs is plunged into the acid and the generated gas flows through a rubber hose into the fumigation space. This method is especially suitable for releasing HCN into fixed installations.

Liquid HCN

If liquid HCN is available in steel cylinders, this is one of the most convenient ways of applying it on a large scale. This method is commonly used in countries where HCN is manufactured, or where it may readily be shipped. (Note that a time limit is set for the return of cylinders see Chapter 6).

The cylinders are always discharged from the outside of the structures being fumigated. This feature adds to the convenience and safety of the method. For fumigation of buildings and ships, the HCN must be forced under pressure through piping. For this purpose, air compressors are connected to a special valve on the head of the cylinder to drive the liquid through a siphon tube out of the discharge valve into the lines (see Figure 20).

Some premises, which are regularly fumigated with HCN, have a permanent piping system of copper tubes and the necessary connexions. When buildings are fumigated occasionally, a temporary piping system made of rubber hose is used.

The manufacturers and suppliers of liquid HCN in cylinders supply comprehensive and detailed manuals covering all aspects of its application, together with full instructions for the installation of piping systems.

Absorbed HCN

The use of HCN absorbed in porous materials such as cardboard discs, which has already been described, is a convenient method of dispensing the gas. The hermetically sealed cans hold a standard amount of HCN, usually 0.5 or 1 kg (1 or 2.25 lb) approximately. Some brands are available with small amounts of added warning agents, such as chloropicrin.

The use of HCN discs must be carefully planned according to the system already described.

Cooling. The discs should be precooled for several hours before treatment begins. This can be done by immersing the cans in tubs of water containing ice, by placing them in a refrigerator overnight, or by surrounding them with dry ice. The use of dry ice is especially suitable during hot weather.

Protection of floors. To prevent floors or floor coverings from being marred, the discs may be emptied onto sheets of corrugated or ordinary wrapping paper of about 1 m (1 yd ).

Openinq cans. The cans are quickly opened with the special can opener, as illustrated in Figure 21. Respirators must always be worn when cans of discs are opened or distributed.

Distributing cans. In the fumigation of large buildings with two or more floors or many rooms, it is advisable to open the cans at the points of distribution and immediately cap them with the fibre caps that act as protection for the cans during shipment. When fumigation is started, this provision enables the operator to empty the cans and scatter the discs.

Scattering the discs. The fumigating crew of not less than two men should work according to a prearranged plan and proceed toward the final exit in the manner already described.

In hot weather, HCN evolves rapidly from the discs and the operators may have to move quickly to avoid working in poisonous atmospheres.

Disposing of discs. Under normal conditions, the used discs are free of HCN by the time the structure is opened for ventilation. Nevertheless, all discs should be carefully gathered and burned in the open, or taken to an approved disposal site.

APPLYING METHYL BROMIDE

Liquid methyl bromide should not come directly in contact with painted surfaces. This can be avoided by volatilizing the spray in the free air or by discharging the liquid into metal pans or cons with a large surface area.

The fans provided for methyl bromide fumigation should be operated for 15 to JO minutes at the beginning of a fumigation. Once equal distribution has been attained, the gas/air mixture remains in equilibrium almost indefinitely and the methyl bromide does not stratify during the period of fumigation. However, if gas analysis at any time indicates unequal distribution, or any additional fumigant is discharged during treatment, the fans should he operated again for as long as is considered necessary.

Direct Discharge from Cylinders

Methyl bromide cylinders may be placed, according to dosage requirements at strategic points throughout the structure so that the valves may be fully opened by the operators, wearing respirators, as they retreat toward the final exit.

In large operations, or in structures with high ceilings or roofs, stand pipes (curved copper tubing directed upward) are often attached to the cylinder outlets. In this technique, a short "T" is fitted to the top of the pipe to discharge the gas laterally and prevent contact with the ceiling.

Hot Gas Method

Methyl bromide may be discharged from outside the building by passing it through a heat exchanger after it leaves the cylinder. This is the method already described for the fumigation of buildings under tarpaulins.

Recirculation Method

Another method, applicable in low structures that are not covered by tarpaulins, is the use of plastic ducts similar to those used in the fumigation of grain by the recirculation technique. To prevent the collapse of plastic ducts at bends, short metal ducts of the same diameter are introduced into the line wherever it is necessary to change direction. A fan draws air from the ground floor and forces it through the duct back into the building through an upstairs window. Methyl bromide is introduced through tubing on the intake side of the fan and is thus distributed throughout the building.

Pressure Method

For discharging methyl bromide into flour mills or other tall buildings from the outside, the fumigant may he forced through the lines by compressed air. The liquid flows through flexible copper tubing of 9 or 12 mm (0.375 or 0.5 in) outside diameter. At the outlet end, each tube is pinched to give an aperture of 2 mm (0.08 in) width. The outlets are directed laterally or upward, but never downward. Some manufacturers add nitrogen or another inert gas above the liquid in the cylinder in order to supplement the natural vapour pressure of the fumigant. This combination is usually sufficient to start the methyl bromide through the lines, even in tall buildings. When the cylinder is half empty, additional pressure up to 10.5 kg/cm(50 lb/in2) may be provided from a compressor in order to complete the discharge.

APPLYING PHOSPHINE

A number of formulations for generating phosphine are available for the fumigation of large structures. When tablets or pellets of aluminium phosphide are used, they are distributed on trays or thick paper at intervals throughout the building. Similarly, magnesium phosphide plates are laid out to give an even dispersion of the required dosage. If there are one or more storeys, the operators start at the top floor and work downward toward the final exit. As suggested in Chapter 6, under normal conditions evolution of the phosphine is delayed and it is not necessary to wear respirators if the distribution can be completed in a few minutes. If there is a possibility of considerable delay, or under conditions of high temperature and humidity, respirators should be worn at the discretion of the official supervising the fumigation.

For small structures, where the work can be completed in a few minutes, sachets may be employed by suspending them evenly on thin rope as from a washing line.

At the completion of the fumigation and aeration, the residual powder from the tablets or pellets or the used plates or sachets must be carefully collected and safely disposed of, as described in Chapter 6.

Mill fumigation

Methyl bromide and phosphine are effective in the fumigation of modern concrete, stone or brick mills that can be made sufficiently gas tight to retain the fumigant. HCN may be satisfactory for mills which allow more leakage, such as ones with frame or sheet metal construction. number of special measures must be carried out when mills are fumigated in order that the fumigant may penetrate all parts of the machinery and equipment. These are especially important with HCN because it does not penetrate well into accumulations of flour, meal or other sorptive materials.

PREPARATIONS FOR HCN FUMIGATION

The following is a summary of the more important measures to he taken (Cotton, 1958):

1. Before stopping the mill. Shut off the source of grain fed to the mill. Then continue to run the machinery until 811 parts of the milling system are empty. At the same time, remove elevator bootslides so that stock may be pulled out and not carried forward. Use a rubber mallet or a similar device that will not damage the equipment to hammer all parts of the machinery from which accumulations of flour, meal or dust can be dislodged.

2. After stopping the mill. All machines, ducts, bins and conveyors in the entire mill should be thoroughly cleaned. All infested material collected in cleaning the mill should be removed to the fumigation chamber and fumigated or the debris should be taken outdoors and buried. All doors to conveyor boxes and bins, and those leading to enclosed machinery, should be opened as widely as possible to aid gas penetration. It is especially important to open the "dead" spouts into which the fumigant penetrates with difficulty.

3. Machinery piping system. Fumigation of the various units of the mill and its machinery is assisted by the installation of a special piping system equipped with nozzles which automatically deliver equal quantities of fumigant to each unit. An installation of this type leads to a considerable saving of fumigant. Also, it may eliminate the necessity of dismantling and cleaning the machinery, and labour costs may thus be greatly reduced. The manufacturers of liquid HCN supply information on the planning and installation of such systems.

PREPARATIONS FOR METHYL BROMIDE AND PHOSPHINE FUMIGATION

These two fumigants penetrate well into accumulations of sorptive mill products and trash lying in a mill. Therefore, if methyl bromide is used, the cleaning programme required before HCN fumigation can be delayed until after the fumigation is completed. In fact, this is recommended because the insects are killed where they are and the debris does not need to be moved to a special fumigation chamber.

All doors or vents to bins, conveyors and machinery should be opened as already outlined for HCN fumigation. Further information on the biology and control of insects in flour mills is given by Hill (1978).

Local fumigation

Local fumigation is the treatment of isolated insect infestations in buildings. In mills, the term is applied particularly to the fumigation of individual machines and enclosed equipment that harbour insects. The popular term "spot fumigation" applies to this type of treatment as well as to treatments of isolated outbreaks in stored grain, which are discussed in Chapter 10.

The fumigants used for this work are pure compounds or mixtures that evaporate slowly and do not diffuse quickly from the treated locality into the main space of the building. Some of the more common formulations are given in Schedule R and in Chapter 7. Although these vapours diffuse slowly, they kill insects only when the equipment is fairly tightly enclosed. It is usual to apply the fumigants during weekends or at night after the mill has been shut down. They should be applied regularly every two or three weeks. A regular programme of local fumigations may keep insect populations at a low level throughout the year. This contributes to the production of goods free from infestation. However, only in exceptional circumstances does such a programrne eliminate the need for occasional general fumigations. Local fumigation may be done by alert and competent mill employees who are assigned to this work and specially trained for it. (See also White et al, 1957; Cotton, 1961, 1963; Hill and Armstrong, 1952; Hill, 1978.)

PREPARATIONS

Before local fumigants are applied, the mill should be run dry. The milling stock should not be removed until after treatment. All vents from milling machinery to the outside should be closed and other steps taken to reduce draughts in the mill system as much as possible. Dead spouts and filled suction lines should be cleaned.

PRECAUTION

In all applications of local fumigants, the operators should wear industrialtype respirators fitted with the proper canisters. Care should be taken not to spill liquids on skin or clothing.

METHODS OF APPLICATION

There are two principal methods for the application of local fumigants in mills: hand application and injection by automatic applicators.

Hand Application

When the fumigants are applied by hand, the dosages for each locality may be poured from the shipping drums into litre or quart bottles, which are then placed individually beside each particular point of application. It is best to use bottles graduated in millilitres or fluid ounces so that the correct dosage may be applied at each station. The operators should work in pairs.

With hand applications, the usual procedure is to start at the top of the building and work quickly downward from floor to floor as the liquids are poured or dashed into the individual units. After each application, the opening is tightly closed. The empty bottles may be abandoned and picked up when the building is finally aerated after fumigation. Windows should be left open during application but closed on each floor as the team works downward.

When application is completed, all doors or other entrances should be closed and locked. Warning signs should be posted at all possible entrances and a guard placed on duty; these and other precautions should be generally the same as for all building fumigations.

If possible, the mill should not be opened until 24 hours have elapsed from the time of application. If only one night i allowed for treatment, exposure may be shortened to 12 or 16 hours. At the end of exposure, all doors and windows should be opened to provide as much ventilation as possible. Appropriate tests for lingering fumigant should be made with detector tubes or other suitable equipment to ensure that gas concentrations are below the threshold limit value before the building is reoccupied.

Automatic Injection

This type of application is confined to treatments of milling machinery. The fumigant is discharged in equal, predetermined dosages from special equipment operated by compressed air, which are supplied by the fumigant manufacturers or blenders (Figure 35). The liquid is injected through small holes specially bored at selected points in the milling machinery. Because this is essentially a machinery fumigation, the building may be fully ventilated during treatment.

Automatic injection in mills is a specialized treatment and details of dosage, location of injection points and other technical considerations are determined after an inspection of the premises has been made by representatives of the companies supplying the fumigants and the applicators.

A similar type of treatment has been used For the control of insects in the wooden linings of railway box cars (Dawson, 1962; Schesser, 1967).


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