3.2.1. Introduction
3.2.2. Checking the effectiveness of treatments
3.2.3. Safety considerations
3.2.4. Requisites for effective fumigation
3.2.5. Fumigation using phosphine
3.2.6. Fumigation with methyl bromide
3.2.7. Application equipment
3.2.8. Construction of stacks for fumigation
3.2.9. The measurement of gas concentrations to determine efficacy of fumigation
3.2.10. Post-treatment action
Summary
Fumigation provides an effective method of controlling all developmental stages of Prostephanus truncatus, the Larger Grain Borer (LGB), in shelled bagged maize. Of the available fumigants phosphine is easily applied; the gas distributes much more readily than the only other fumigant, methyl bromide, for which specific application equipment is essential. The principal disadvantage of phosphine is the relatively long, five-day exposure period, now generally recommended. Using methyl bromide, a satisfactory fumigation can be achieved in periods as short as 24 hours. Complete control, by fumigation, of all developmental stages of P. truncatus and any other insect pests present in shelled maize, can only be expected if the recommended techniques are properly applied.
It is strongly recommended that a routine procedure is adopted to measure the gas concentration in fumigated stacks. Measurement of the gas concentration remaining in a stack shortly before the end of the exposure period will provide a good indication of effectiveness of the fumigation.
3.2.3.1. Fumigation should only be carried out by trained staff; a minimum of two must he involved, one designated in charge. Adequate labour must be available to handle sheets and sandsnakes, and to assist with fumigant distribution procedures so as avoid accidents or damage.
3.2.3.2. All fumigants must he kept in a securely locked store. A register of stocks held and issued should he maintained. Respirators, with appropriate canisters, should he available and checked regularly. Where methyl bromide is frequently used, it is preferable to provide operators with a personal respirator, for which they are responsible. During the application of methyl bromide, gloves must not he worn due to the danger of skin blistering, should fumigant become trapped under the gloves. Gloves should he worn when handling aluminium phosphide formulations.
3.2.4.1. Good quality sheets without holes or tears must he used for fumigation. Operators must be trained in careful handling of sheets, and he aware of the need for proper folding and stowage after use.
3.2.4.2. Fumigation must be carried out on sound unbroken concrete floors in which the expansion joints are filled with bitumen or mastic compound, to prevent leakage of fumigant into the ground. Badly broken floors should either he repaired; or a gas-proof sheet laid on the floor before stack construction.
3.2.4.3. Leaking roots must be repaired, particularly when phosphine is used, to prevent accidental wetting of aluminium phosphide formulations which can provide a fire hazard.
Dunnage should be used to prevent moisture uptake through the floor. Dunnage should be laid on a clear floor to the size of the stack to be built, without projecting beyond the edges of the stack. Dunnage should be clean, level, and free from projecting nails and splinters.
Ensure that all dunnage is laid in the same way - so that when you inspect, you are able to see right under the bags. Where pole dunnage is used, the poles should he placed close enough together so that the centre of the bag does not touch the floor.
If stacks have been built on dunnage, away from wall and pillars, and free from roof or roof trusses, good stacking will allow:
· efficient use of available space
· easy cleaning of the store
· easy inspection of both store and produce
· efficient pest control
· easy auditing of stocks-on-hand
3.2.4.4. Stack construction should take account of the likely need for fumigation. Stacks constructed in the open must he on gas-proof sheeting unless a sound concrete plinth is provided. In windy conditions fumigation sheets should be secured with ropes to prevent billowing leading to excessive fumigant loss.
Stacks should always he built for operational convenience. They should be:
· clear of walls (not less than one meter);
· clear of roof trusses (not less than a meter below each truss);
· clear of pillars;
· built so they are safe to walk upon and will not collapse causing damage to adjacent walls or stacks.
The eventual size of the stack is determined by factors such as available floor space, taking into account the need for gangways, the distance between floor and roof or roof trusses, availability and size of fumigation sheets, etc. If space permits, it is possible to stack bagged grains such as wheat, maize and paddy up to 30 layers without causing damage as a result of compaction to the grain in the bottom layers.
3.2.4.5. Where a pre-fumigation survey reveals live insect pests on the floor or walls of a store, arrangements should be made for application of a suitable contact insecticide (preferably a mixture containing a synthetic pyrethroid and an organophosphorus compound), to prevent stack re-infestation after the fumigation. Ideally, all stacks within a store should be fumigated at the same time, although this may be impractical in many situations. Surface spraying of stacks awaiting fumigation with contact insecticides will provide partial protection against cross infestation, or against re-infestation following fumigation, but this cannot he relied on.
3.2.4.6. Floors must be swept to remove spilled grain which is re-bagged for inclusion with any damaged bags in the stack to be fumigated.
3.2.4.7. Sufficient sandsnakes must be available for the entire perimeter of the stack, allowing for overlapping, and for the provision of at least double rows at each corner. Where sandsnakes smaller than those recommended in Section B.3 are used, they should be laid in a double row around the stack, with overlapping, and with three provided at each corner.
3.2.4.8. Fumigation sheets should he of sufficient dimensions to cover the stack leaving a one-metre margin on the floor on all tour sides. Sheets must be examined for holes and tears, and any damage repaired before they are used.
3.2.5.1. Preparation:
A minimum of equipment for application is required, hut respirators should be available in case of accidents. After determining the dimensions, stacks should be sheeted, and sandsnakes placed in readiness around the perimeter, hut off the fumigation sheet.
3.2.5.2. Application of phosphine:
Fumigant should he applied at the rate of 2 g of phosphine per tonne of maize (1.3 g per cubic meter which is the same as 0.2 mg per litre), for a minimum exposure period of 120 hours.
3.2.5.3. Application of tablets or pellets:
One operator should he responsible for checking that the correct application rate of tablets or pellets is used, and that tablet tubes are completely emptied before discarding. Empty containers should be collected and counted; this provides an additional check on the rate of phosphine applied. Tablets or pellets are best laid on trays (well separated to avoid the risk of fire), rather than directly on the floor, to make residue collection easier. Where stacks are constructed on pallets, trays can be placed under the pallets on both sides of a stack. Where stacks are built directly on the floor, trays of fumigant can he placed on the stack top immediately prior to final sheeting arrangement.
3.2.5.4. Use of sachet formulations:
Sachet formulations can be distributed around the stack and tied, at head height, to maize bags using the cords provided. One operator should distribute sachets, checking to ensure the correct application rate.
3.2.5.5. Final sealing arrangements:
Sheeting arrangement at floor level should now be completed, and sandsnakes put in place against the stack to form a gas-tight seal. A final inspection should be made by the operator-in-charge to establish that sealing of the sheeting is satisfactory, and sandsnakes are properly laid. Warning notices must he placed on, or near the stack. Instructions must he given to the storekeeper to prevent interference with the stack at any time during the exposure period.
3.2.5.6. Checking fumigation effectiveness:
Before the fumigation is terminated on the fifth day (120 hours), the concentration of phosphine in the stack should be checked using methods described in Section 3.1.5.3. A concentration of phosphine of not less than 150 ppm (ca 0.2 mg per litre), indicates that satisfactory control of insect pests can be expected.
3.2.5.7. Airing procedures:
At the end of the fumigation an airing period is necessary to remove fumigant remaining in the stack. For operators, wearing respirators the steps include:
· All persons not directly involved in the airing procedure must leave the store and not re-enter until given permission to do so by the operator-in-charge.· Doors must be opened, preferably at opposite sides of the store, to ensure through ventilation.
· For stack airing to commence, both ends of the fumigation sheet must be lifted to allow the escape of gas. This is carried out by first removing sandsnakes, then, two operators, on the stack top, lift the ends of the fumigation sheet onto the top of the stack using a rope attached to the sheet corners.
· Where only one or two sheets are used for fumigation, it may be possible at this time, to drop them completely to the floor.
· Final removal and folding of fumigation sheets must wait until the end of the airing period, and until tests have shown that it is safe to enter the store without respirators.
3.2.5.8 Duration of the airing period:
In large stores, where there is good ventilation, residual phosphine can be expected to escape from stacks, not exceeding 200 tonnes, in about two hours, particularly if the fumigation sheet is completely removed. Where ventilation is poor, and for larger stacks, a much longer airing period, preferably overnight, may be necessary. Entry to stores, in which fumigated stacks are being aired must not be permitted to other personnel until the operator-in-charge indicates that it is safe to do so, preferably after checks have been made using detector tubes. Warning notices should not be removed until this time.
3.2.5.9. Disposal of spent aluminium phosphine residues:
Powder residues from tablet or pellet formulations of phosphine should be deactivated in water containing a little detergent, the mixture can he safely discarded into drains, or into a hole dug in waste ground. Sachet formulations should be safely discarded by burial, and not left where they may be accessible to children or animals.
3.2.6.1. Exposure period:
Effective control of P. truncatus, and other insects pest in bagged maize, can be achieved with methyl bromide in exposure periods of 24 or 48 hours, provided the fumigant is well distributed, and the stack is well sealed.
3.2.6.2. Stack preparation:
Bags in the top layers must he lifted to form channels or pits to accommodate a piping system for distribution of fumigant as described in Figure 3.3. When the piping system has been laid, sheets can be put over the stack, great care being taken when working on top of the stack to avoid the pits and channels. Additional sandsnakes should be placed over sheet at the point where the piping system enters the stack to ensure minimal leakage of fumigant at this position.
3.2.6.3. Connecting the piping system and cylinder:
All pipe connections and unions must he tightened thoroughly to ensure that joints are gas-tight. It is recommended that cylinders are connected to the piping system through a fitment which includes a pressure gauge and that methyl bromide is discharged from cylinders at a pressure of not less than 80 pounds per square inch (or metric equivalent) to overcome the back pressure in the piping system. In tropical climates the internal pressure in methyl bromide cylinders is usually sufficient to deliver the fumigant without the need for external pressurization. Where, however, a pressure gauge is not available, and the internal cylinder pressure is likely to be low because of cool climatic conditions, or because only a small quantity of fumigant remains, standing cylinders in the sun for 1-2 hours will usually increase the pressure sufficiently to allow satisfactory discharge of fumigant. A filter, containing glass wool, and situated in the piping system where it joins the cylinder, will help prevent the blockage of nozzle outlets with rust or other dirt particles.
3.2.6.4. Sate application and use of respirators:
During application of methyl bromide all personnel not directly involved must leave the store. At least two operators, must, however, he present when the gas is released into the stack, and both must wear respirators equipped with the appropriate canister.
3.2.6.5. Application of methyl bromide:
For fumigations lasting 24 hours, the application rate of methyl bromide should be 32 g per cubic metre (which is the same as 32 ml per litre). Where the exposure period is 48 hours the application rate can be reduced to 20 g per cubic metre. The quantity of fumigant applied should be measured as accurately as possible, hut may have to be rounded-up to the nearest 0.5 kg, depending upon the accuracy of the weighing scale used. The required dose of methyl bromide is measured during delivery, by weighing the cylinder on a platform scale or other suitable balance.
3.2.6.6. Checks for leakage:
During the delivery of methyl bromide, checks should be made for leaks from the piping system and cylinder connections. Halide leak detector lamps, provide very good indications of leakage. Severe leakage of methyl bromide from pipe connections may he visible as liquid, and delivery may need to he suspended whilst the leakage is rectified. On completion of the application, the piping system should he disconnected from the cylinder. In tropical climatic conditions, there is unlikely to he any residual fumigant in the piping system, hut care should he taken during disconnection, by an operator wearing a respirator. The free end of the piping system should be pushed under the adjacent sheet margin. Gas loss from beneath fumigation sheets, at floor level, can be checked with detector lamps. Minor losses of methyl bromide at this position, causing pale green colouration to the detector lamp, can be expected immediately after application due the slight increase in pressure within the stack. Bright green, or intense blue colourations indicate that unacceptable levels of leakage are in progress and adjustment to the fumigation sheet and/or sandsnakes is essential. This should be undertaken by operators wearing respirators.
3.2.6.7. Checking the gas concentration:
The concentration of gas remaining in the stack should be measured before the end of the treatment to obtain an indication of the effectiveness of the fumigation. For effective fumigation in treatments of 24 hours duration, methyl bromide concentrations of the order of 10 mg per litre should be detectable at the top, middle, and bottom of a stack. In treatments of 48 hours duration, concentrations of the order of 5 mg per litre should be detectable at these positions.
3.2.6.8. Procedure for airing of stacks:
At the end of the fumigation period, stacks must be opened to allow escape of residual methyl bromide. Respirators must be worn by all operators involved in the ventilation procedure which includes:
· Staff not involved in the airing procedure must leave the store and not re-enter until permission is given by the operator-in-charge.· Door must be opened, preferably on both sides of the store, to allow thorough ventilation.
· Partial un-sheeting of the stack should commence by first by removing sandsnakes, then operators, on top of the stack, should pull both ends of the fumigation sheet onto the stack top, using ropes attached to the sheet corners.
· Where only one or two sheets are used in a fumigation, it may be relatively easy to drop these completely to the floor at this time.
· Final removal of fumigation sheets and folding must wait until the end of the airing period, and until tests have shown that it is safe to enter the store without respirators. If halide leak detectors can be used, the safety of operators may be monitored indicating the concentration of methyl bromide present during stack opening procedure. Detector tubes may alternatively he used for checking the safety levels of fumigant in the store.
3.2.6.9. Duration of airing:
The time for airing to he completed will vary according to the size of stack, and the degree of store ventilation. Most of the methyl bromide can be expected to have aired off from stacks not exceeding 200 tonnes in approximately two hours provided there is a good through ventilation. However, longer periods may be necessary for large stacks, or for stacks in confined spaces. In such circumstances low concentrations of gas can often be detected in the outer layers of stacks twenty four hours after the un-sheeting operation. Overnight airing of stacks is a safer option, particularly where leak detection equipment is not available.
3.2.7.1. Phosphine:
A minimum of equipment is necessary in connection with the application of phosphine, although respirators with appropriate canisters should he available. Where sachet formulations are used, these can he hung from the sides of stacks or placed on the top. Tablet or pellet formulations can he placed directly on the floor hut removal of spent residues for disposal is then a problem. Cardboard or paper trays make removal of residues easier; these can he seated under pallets or. if this is not possible, trays can he placed on top of the stack.
3.2.7.2. Methyl bromide:
Since methyl bromide is more than three times heavier than air, the most effective method of obtaining good fumigant distribution is a branched piping system, terminating in nozzles (discharging into pits or channels) placed on the stack top. Nylon piping (internal diameter 7 mm, external diameter 10 mm), has proved to he very suitable for the delivery system. Very small apertures (about 1 mm), cut into the heat-sealed ends of piping, are effective in causing vaporization of methyl bromide, and aiding distribution.
The design of piping systems should he branched, so that fumigant is distributed from the centre of the system, and provides equal pressure and gas discharge at each outlet. The number of outlets required is dependent on the size of stack to he fumigated hut as a general rule one nozzle is allowed for every 8 square metres. For a stack comprising 100-200 tonnes of maize, two outlets are usually sufficient. A 500-tonne stack will require about eight outlets. The smallest piping system should he T-shaped, and larger systems are conveniently designed in an H-arrangement with an equal number of outlets in each arm. No more than six outlets should he used for one arm of an H-arrangement. For very large stacks, (eg, those of more than 750 tonnes), fumigant is best applied at more than one point, into separately laid piping systems. Very long, un-branched piping systems should not be used, since these will result in uneven distribution of methyl bromide, most of which will be discharged from outlets nearest to the cylinder. Weighing scales are essential for the accurate metering of fumigant into stacks, and should preferably he of the platform type.
Wherever possible, stacks should he constructed taking into account the probable need for fumigation. The dimensions of stacks should also he designed to accommodate the size of fumigation sheets available. All stacks must he constructed with a space of at least one metre on all four sides to allow proper sheeting for fumigation. Where stacks are built on wooden pallets, these should he laid with the open sides facing in one direction, to aid gas circulation beneath stacks, and to allow easy placing of aluminum phosphide formulations. When methyl bromide is to he used, stacks should be flat-topped rather than sloping, to make the construction of pits or channels easier. Pits provide an area into which methyl bromide can vaporize helping to retain fumigant in the upper layers of a stack, and should he four hags deep and four hags wide. Channels have the same functions, and should he of similar dimensions to pits, hut run the length of the stack. Very large stacks may accommodate two channels for separate piping systems. Channels should be closed at the ends, rather than open. in order to retain methyl bromide, which may otherwise fall rapidly to ground level from the ends of the stack. In constructing pits and channels, the stack edges must not be made unsafe by removal of too many bags, since this could provide a serious hazard to those involved in subsequent piping and sheeting operations.
Figure 3.3 Methyl bromide piping system
Figure 3.3b Preparation of a stack for fumigation with methyl bromide
3.2.9.1. Phosphine:
Since phosphine distributes very readily within maize stacks, the efficacy of a treatment can usually he determined by taking measurements at one location only. To sample the concentration of fumigant in air, a single nylon capillary tube can be inserted during the preparations of a stack for fumigation, or, a gas sample can be withdrawn during the treatment, by means of a syringe needle inserted through the fumigation sheet.
Gas detector tubes similar in design to those used for safety purposes (but covering a different concentration range), can be used to measure fumigant concentrations, or alternatively, a meter designed to measure phosphine can be employed. Gas can be drawn through capillary tubing into a meter, or into detector tubes, by means of a hand-held pump. A sample taken using a syringe and needle, which is inserted through the fumigation sheet, can he injected directly into a phosphine meter.
3.2.9.2. Methyl bromide:
Methyl bromide does not distribute as easily as phosphine in maize stacks and in order to determine the efficacy of fumigations with methyl bromide, gas concentrations need to be measured at more than one location within a stack. This is best achieved by inserting nylon capillary tubing at top, middle and bottom positions on the outside edges during stack construction. The middle surface sampling position should preferably be on the opposite stack face to the other sampling positions, in order to establish satisfactory fumigant distribution across the stack. Although not normal practice, if capillary lines were not inserted in a stack prior to fumigation, it may be possible to withdraw gas samples using a syringe inserted through the sheet as described for phosphine.
Warning signs should be removed. When the treatment has involved the direct addition of phosphide or methyl bromide preparation to the grain, a cautionary notice, in the local language(s), should be placed on all access hatches to a store which contains treated grain stating:
FUMIGATED WITH PHOSPHINE (METHYL BROMIDE)
(Date of Completion of Treatment)
PHOSPHINE MAY BE EVOLVED FROM RESIDUAL POWDER WHEN THIS GRAIN IS DISTURBED
These notices should he removed or cancelled when the treated grain is unloaded. Residues of tablets or pellets, where they can be collected. and spent sachets, blankets, or plates should he disposed of in accordance with manufactures' recommendations.
3.2.10.1. Record Keeping, Including Assessment of Effectiveness of Fumigation
The Fumigator-in-Charge must maintain a written record of each fumigation. The record must include:
· the names of all personnel engaged either on grain handling or fumigation work during the application of fumigant, and the nature of their duties;· the location of treatment;
· type of storage-bag, bulk, container;
· type and tonnage of commodity treated*;
· volume of enclosure*;
· results of gastightness test*;
· the date and time of commencement of fumigant application*;
· the dosage used (expressed preferably in grams per m3 or tablets, pellets, or sachets per tonne) and exposure time*;
· length of airing period*;
· time of issue of declaration of clearance*;
· a declaration that the actual dosage applied was equal to the target dosage, and that all packaging materials that had contained the fumigant formulation had been cleared and accounted for prior to supervised disposal;
· when sampling lines were installed, records of all measurements of concentrations obtained from within the fumigation enclosure;
· details of any incidents or accidents.
* Items marked with an asterisk should be recorded on stack/bin cards.
1. All fumigations must be carried out under the supervision of fully trained personnel.
2. All areas where a fumigation will take place, must be inspected before the fumigation to ensure that it can be carried out safely and effectively.
3. Where there is any doubt about safety, or the ability to make a complete seal between the floor and sheet, fumigation should not take place.
4. Store managers and operational personnel must be informed well in advance and in writing when the fumigation will take place.
5. In the case of small stores when operations commence, all personnel not concerned with the fumigation procedures will be cleared from the store. In larger stores, they will be confined to an area considered safe by the fumigation Officer-In-Charge/Supervisor.
6. Stacks to he fumigated should have one metre of clear space on all sides and at least one metre over the top, clear of roof-trusses.
7. The floor around the stack to be fumigated must be clean and free of spilled grain before sheeting up.
8. Unsafe stacks must be rebuilt and made safe.
9. Only fumigation sheets of a type and quality recommended by the appropriate National Plant Protection Services should be used.
10. Approved sheets used during fumigation should always be in a good state of repair.
11. Stacks to be fumigated should be completely covered by the sheet, with at least one metre of sheet on the floor all round the stack.
12. Where more than one sheet is used to cover a stack, they should be joined by rolling or folding at least one metre of the two sheets together along the whole length of the join.
13. The join must be held firmly in place with fumigation clamps and/or sand snakes.
14. Sheets must he sealed to the floor with sand snakes of a suitable weight and width to give at least 15 cm. ground contact. The ends of each sandsnake must overlap when laid in position. A double row should be used on each corner of the stack.
15. Phosphine generating formulations such as pellets and tablets, must be laid on trays or other suitable containers to aid the complete removal of residues at the end of the fumigation (exposure) period.
16. Aluminum phosphide tablets when placed on trays must be separated from one another and not placed in piles. Piling the preparation is a dangerous practice, and must he avoided.
17. Dosages: Phosphine will be applied at a rate of not less than 1.3 grains of phosphine per cubic metre of space under fumigation for a period of not less than one hundred and twenty hours. (5 days). Tins dosage equates to 2 grams of phosphine per to line of bagged maize. Methyl bromide will be used for quarantine fumigations only when it has comparative advantage over the use of phosphine. Methyl bromide will be applied at 32 grams per cubic meter of space under fumigation for a fumigation (exposure) period of not less than 24 hours. Dosage should be reduced to 20 grains per cubic meter if a 48 hour exposure period is possible.
18. Whilst a stack is undergoing fumigation in small stores, they must not remain locked.
19. In large stores where stacks are under fumigation and it is necessary to work, the working area must be given the maximum ventilation possible. Regular checks should he made using approved gas detection apparatus as an indicator of excessive leakage, or potential hazard. If gas is detected in quantities greater that the TLV values for phosphine or methyl bromide, the store must be evacuated immediately. In public places, watchmen must he employed to keep people away from the fumigation area.
20. With fumigations using phosphine generating formulations a check for leaks should be made 4, 12 and 24 hours after insertion of the preparation and final sealing. Any leaks found should be sealed. Immediate, and periodic checks should be made when using methyl bromide.
21. After the prescribed fumigation period under gas (5 days for phosphine; 24 or 48 hours for methyl bromide) removal of the gas and aeration should commence. Final reading of gas concentrations should be taken at this stage, and recorded.
22. In small stores, by-standers or any other non-concerned personnel should be evacuated from the vicinity of the store prior to ventilation.
23. The fumigation must be recorded in a register by the Fumigator-in-Charge giving date, fumigant used, dosage, period under gas, type of commodity and any other treatments that may have been carried out. A fumigation certificate must be issued giving details of the fumigation.
24. Personnel carrying out fumigations will at all times wear protective clothing appropriate for the work they are carrying out. They must also observe all safety measures that are necessary to protect themselves and others during a fumigation.
25. All stages of the Larger Grain borer (LGB) in stacks of bagged maize can be effectively controlled by fumigation with phosphine or methyl bromide.
26. An application rate of phosphine of 2 g tonne-¹ are effective in controlling LGB during a five-day exposure period in maize with a temperature varying from 21° to 22°C. It is recommended that this application rate and exposure period be used for controlling LGB infestations in maize under all temperature conditions.
27. Monitoring of phosphine concentrations in stacks during treatments will greatly assist in determining the effectiveness of the fumigation treatment. It is recommended that, in all fumigations, a concentration of no less than 0.2 mg l-¹ (ca 150 ppm)** should remain in a fumigated stack five days after fumigant application.
1 gm phosphine = 1 tablet (3gm) » 700 ppm.
28. To ensure effective control of LGB using phosphine, only good quality fumigation sheets without holes or tears should be used. Where sheets have to be joined, leakage should be reduced to a minimum by careful attention to folding and, at ground level, sandsnakes with a minimum contact width of 15 cm should be used. Sufficient sandsnakes must be provided to allow overlapping all round a stack, and with a double row placed at stack corners.
29. Methyl bromide applied at the rate of 32 g m-3 and employing an exposure period of 24 hours, provides an effective control of all stages of LGB, in well sealed stacks of bagged maize in which the temperature range is 27° to 22° C. It is recommended that this application rate is employed for all stacks fumigated for 24 hours, the fumigant being applied to the top of the stack through a branched piping system terminating in jets. Where, however, the exposure period can be extended to 48 hours, the application rate can be reduced by one third to 20 gm-3 without risk of compromising the efficacy of insect control.
30. Methyl bromide can be used effectively to control LOB in maize contained in either jute or woven polypropylene (WPP) bags. There is evidence to suggest that more effective control may be attainable in the upper layers of bag stacks of WPP bags owing to the slower downward penetration of fumigant through bags of this type than through jute bags.
31. All commercial and quarantine fumigations should he certified by a fumigation inspector. The declaration should clearly state that the fumigation was carried out in compliance with these Guidelines, and that the minimum gas concentration stipulated for both phosphine and methyl bromide at the end of the required exposure period was in fact achieved.
32. Phosphine:
· Estimate the weight or volume of the commodity and calculate the dosage to be applied at the appropriate rate.· Partly cover the stack with the fumigation sheets.
· Open the appropriate number of tins of aluminium phosphide preparation. Wearing rubber or plastic gloves, insert the calculated dosage of aluminium phosphide. Distribute hags evenly over the top of the stack. Tablets or pellets should be put out on trays to allow recovery of the residues.
· Close the sheeting, seal the joints and coercers and put the sand snakes in position.
· Erect a safety barrier and put out warning notices.
· Check and dispose of the empty containers. The entire contents of non-resealable tins or lubes should be used.
· Clean the gloves in detergent solution.
· After four hours check for leaks by detector tubes. Seal off any leaks,
· Inform appropriate staff and leave for a minimum five days (depending on temperature), preferably longer.
The following description of termination of the phosphine fumigation presumes that the sheets are required for another fumigation. If they are not required, and if the grain is thoroughly dry, the sheets may be left in position. If the stack has been a long time under sheets it may be safe to assume that no gas remains.
· Place a respirator around the neck.· Open all doors and windows.
· Check the phosphine concentration using detector tubes and put on the respirator if the concentration is unsafe.
· Remove the sand snakes, raise the corners of the sheets, the rolled joints on the vertical sides and quickly leave the area.
· Leave for 30 minutes to one hour.
· Return to open the sheet still further and again leave for a similar period.
· Check on the safety of the area with detector tubes.
· Remove the sheets, take away and fold for the next fumigation.
· After a period of at least one hour, but preferably overnight, remove the spent residues and dispose of them in the recommended manner.
· Check the success of the fumigation.
· Complete a written record of the fumigation in a log book and attach a record to the stack.
33. Methyl bromide:
· Estimate the volume or weight to be fumigated and calculate the dosage to be applied at the dosage rate appropriate for the commodity and (the temperature). Ensure that there is sufficient methyl bromide in the cylinder.· Prepare the stack for fumigation and make channels or pits in the lop of the stacks for placing piping system outlets.
· Calculate the number of outlets required and choose a suitable piping layout.
· Place the piping, arrange the jets and connect up to the filter, cylinder fittings and cylinder.
· Cover the stack with sheets, join up, fold the corners and place the sand snakes in position.
· Check sheeting, sand snakes and pipe couplings and repair sheets with plastic tape if necessary.
· Make final thorough check on the area around for possible hazards.
· Send away all onlookers from the fumigation area.
· Put up warning notices, inform management and others concerned and issue appropriate instructions.
· Light halide lamps and put respirators on fitted with appropriate canisters. Rubber gloves should not be worn.
· Pressurize the cylinder to 80 to 100 psi (550 to 690 kN/m2) with a foot pump or compressor.
· Record the weight of the cylinder.
· Open the cylinder valve and check for any leaks. Introduce a small quantity of methyl bromide, about 10 percent of the full dose, by opening the side valve for a short period.
· Check and seal off any leaks around the stack. The halide lamp will indicate whether there is any need for a respirator to be worn.
· Re-open the side valve and introduce the methyl bromide until the scales indicate that the full dose has been given.
· Repeat the check for leaks.
· Uncouple the cylinder after blowing out the lines with the pump.
· Leave for not less than 24 or 48 hours.
· It is desirable to measure the concentration achieved. A gas monitoring meter and gas sampling lines are therefore needed.
On termination of the methyl bromide fumigation:
· Open all doors and windows.· Wearing a respirator, remove the sand snakes open up the stack at the corners and at the rolled joints on the vertical sides and quickly leave the area.
· Return 30 minutes to one hour later, still wearing the respirator, and open up the sheet still further.
· One to two hours later return with a halide lamp, wearing the respirator if necessary, remove the sheet from the stack, check for any damage, repair if necessary and fold it for next fumigation.
· Leave for several hours or overnight.
· Check with the halide lamp or detector tubes and leave for further ventilation, if necessary.
· When the area is clear of gas, remove the piping and jets.
· Remove the warning notices.
· Check the effectiveness of the fumigation.
· Check all items for damage and repair before storing or using again.
· Complete a written record of the fumigation and attach the record to the stack.
