Code of practice for storage and fumigation of bagged grain

Contents - Previous - Next

by Vern Watter

Proper storage practices permit good fumigation and help maintain a level of sanitation that prolongs the time between fumigations. They help pin-point the sources of infestation and try to eliminate sources of insect breeding.

Proper sanitation requires proper placement of stacks so that sweeping, inspection, and pesticide treatment can take place. The following should be observed:

Before bags are stored in any area, it should be cleaned of all debris and loose grain. All sweepings should be fumigated or immediately destroyed to avoid harboring an infestation. Floor cracks should be filled with cement or hard filler. Floors need spraying with a good residual pesticide to discourage insect migration for storage. Floors should dry before any material is placed in the area.

Walls should be checked for holes or cracks that could retain old grain. Moth webbing and old grain should be brushed clean and all holes and cracks should be filled with cement. Wall spraying with residual pesticides, of or appropriate type and formulation could be considered when practical to do so.

Overhead areas should be cleaned of dust and moth webbing and sprayed with residual insecticides.

Storage should be segregated:
Old and new stock
Good and bad stock
Different moisture levels
Different grains or varieties

Incoming grain should be checked for insect infestation and treated if infested. A regular programme of inspection maintenance and sanitation should be implemented.


Sanitation requirements for stored bagged grain.

All grain should be inspected on arrival and fumigated if infested.

Insects will live in spilled grain next to bags and along walls. This must be swept up daily and fumigated or destroyed.

Insects can live in grain dust on ledges and ceiling beams. These must be kept clean enough to discourage this infestation.

Tailings and siftings from equipment will contain many live insects. This should be fumigated or destroyed each day.

Weekly inspections should be made to locate possible infestations or grain that is no longer in good condition.

Where market demands permit, the oldest stock should always be shipped first.

Applications of residual insecticides should be made to the walls and other insect resting ares at least once per month.

If the storage area can be sealed enough for effective treatment, space treatments with Dichlorovos should be made twice per month.

All used bags should be fumigated before reuse.

All cleaning and bagging equipment should be fumigated once per month minimum.

Stock that can no longer be sold at regular prices and is more of an insect attractant than a value, should be disposed of at the least possible loss. Destruction may still be more profitable than keeping the material and increasing treatment costs.

Broken bags should be repaired and spills cleaned up as soon as foung.

A rodent trapping or poisoning program should be maintained wherever rodents are a problem.

Bird infestation in the godowns should be discouraged through use of hanging strips at doorways and other mechnaical deterrents.

Floor drains should be kept clean and treated to discourage cockroach infestations which can affect the odor and flavor of rice.

Code of Practice for Fumigation techniques

1. Preparation of area to be fumigated.

Check to be sure there is enough room on all sides and at the top to work. If bags are too close to walls or posts, the fumigation should not be attempted until it can be done safely and effectively.

Have the area around the stack swept clean so that a good floor seal can be achieved.

Measure the length width and height of the stack and calculate the volume to be fumigated.

Inspect to determine the type of insects causing infestation.

Calculate the dosage based on volume and species to be controlled

Consider potential reinfestation and include nearby stacks in fumigation if infested.

Consider safety of potentially exposed workers. Will there be other workers in this area during the fumigation? Can the fumigation be done at another time? Is there enough cross ventilation to provide a level of safety? Is gas monitoring equipment available if workers must be nearby? All safety feretions should be very safety taken into consider workers reservation.

Choose the proper fumigants.

Choose Methyl bromide if:

Less than 4 days are available

There is a heavy infestation of grain mites

Nearby electrical equipment could be damaged

Odor of chloropicrin is needed for safety reasons.

The price is advantageous

Choose Phosphine if:

Four or more days are available

Deep penetration is needed

Product may have high level of bromine from previous fumigations.

Damage to germination is a concern

The price is advantageous

Be sure that all needess equipment is on hand for sealing closing, leakage detection, safety equipment, ventilation

2. Equipment needed for fumigation of bagged grain.

Measuring tape to determine volume
Broom to clean floor
Ladder if stack is hard to climb
Polymer vinyl sheets or other gas proof sheets
Mending tape for sheets
Warning signs
Leak detectors
Instruments to measure concentration
Gloves if required
Adequate amount of fumigant
Label and labelling for fumigant or other instructions.
Clamps for rolled joints
Trays if phosphine is used
Scales if methyl bromide is used Fans if methyl bromide is used
Hoses if methyl bromide is used.

3. Proper placement of gas-proof sheets (tarps)

Most gas-proof sheets can be easily torn and must be handled with a degree of care.

The first step is to prefold the sheets so that they can be unrolled or unfolded easily. Many fumigators prefer to lay the sheet flat in a large open area and have one man on each side of the short direction of the sheet. Working together, they pick up an edge of the sheet about 1/4 of the way from the middle and bring it to the mid-point. Other sections are folded on top in accordian style until there is a stack on either side of the midpoint. The two sides are folded on top of each other and then one end of the folded area that is now about 1/2 meter1 meter wide is pulled on top for a distance of about 2/3 of the lenghth of the lower section. The sheet is then rolled tightly working from the folded end to the open ends so that air will be worked out. This tightly rolled sheet is then easy to transport and to lift on top of stacks.

The rolled sheet is placed on top of the stack and unrolled along the longest direction of the stack. The end of the folded sheet is pulled down so that is touches the floor and overlaps by at least 1.0 m. One side is then, pulled down until it too touches the floor and overlaps by 1 m. If this sheet is even on the floor it will facilitate other work. Sand snakes can then be used to anchor this area.

Next, pull the other edge down until it too touches the floor with a 1 m. overlap. If there is surplus sheet, it is better to gather it on the top in folds and hold it there with sand snakes. Surplus sheet on the floor makes sealing more difficult.

The corners are the hardest part to seal correctly since if they are not done corners, there will be too many folds on the floor and gas may leak. The corner is in effect a large triangle of material. Some try to roll this triangle and this has advantages outside where there are strong winds. However inside, the rolled corners will always result in gas loss at the floor.

The best way is to anchor one edge of the corner with a sand snake and then fold the surplus back along the other edge with an inside fold. This can be anchored with a sand snake and the sheet will then fold back down with two folded corners coming together at the corner. Along the floor there will be only large smooth sections that can be sealed with the sand snakes.

The major leaking point will be at the floor level snakes. The sand snakes should be pieced in a double row so that the second row will overlap the joints between sand snakes in the first row. At the corners, sand snakes should go around the corner rather than meet at the corner.

Floor level leakage also occurs when there is a floor joint, a crack, or a floor drain. These areas should be avoided when preparing for a fumigation but the problem can be partially Overcome by taping over these openings.

If a single gas proof sheet will not cover the stack, it will be necessary to join two or more sheets together. Just overlapping the sheets will not retain the gas for long enough. The sheets can be joined together and be reasonably gas tight by taking one meter of the edge of each sheet and rolling the two together into a tight seam. This rolled joint is then clamped with steel spring clamps every 1 meter or less. The rolled joint requires extra care for sealing at the bottom. The seam should be flattened and extra sand snakes used to get a better seal.

This is still not a strong seam. If it was placed horizontally the weight of the sheet would pull the seam apart after a few hours. The seams must run vertically or be gathered on top of the stack and weighted with sand snakes so that there is no pull against the seam.

If "Hanging seam" must be used such as when tall buildings are covered, another procedure is used. The two sheet edges are placed between two long boards, the combination is then rolled together several times and retained with C clamps every 1-2 meters.

If two sheets are not enough and only a small amount of additional sheet is needed, it should be placed in the middle. It is important of fold the middle sheet so that the combined sheets fit evenly and tightly. Lay the middle sheet on the floor and fold it in half. If the gap to be filled is 4 meters plus a meter on each side to roll, then we want a 6 meter sheet. Roll the folded side of the sheet until within 3 meters of the edge. This will open up to be a 6 meter wide sheet with a false seam down the center. Clamp the center false seam and then place the middle sheet in place and join with the other two sheets.

Clamps on rolled joints help prevent leakage Of gas during fumigation.

Many sheets

When many sheets are joined together, there could be a problem where two vertical seams meet at a horizontal seam. The seams must be staggered as shown in the illustration to avoid this.



4 Days 5g/ton

5g/ton = 5g/1.6 m Maize = 3.125 g/m
5g/ton = 5g/1.9 m Paddy = 2.631 g/m
7 Days 2g/tonne
2g/ton = 29/1.6 m maize = 1.25g/m = 35.49/1000 cu. ft. maize
2g/ton = 2g/1.9 m paddy = 1.05 g/m

Methyl bromide

24 Hours
9 lbs/100 ton = 28.8g/m = 1.81b/1000cu. = 28.8 oz/1000 cu. ft.
9 lbs/100 ton = 9 lb/5000 cu. ft. = 1.8 lb/100 cu. ft. = 140 OZ/62.5 m

Conversion factors

g/m phosphine x 658.8 = ppm
ppm3 10,000 = % by volume in air
g/m methyl bromide x 235.9 = ppm
oz/1000 cu.ft. = g/m = mg/liter (approximately)
Ib/1000 U9 bu x 12.87 = g/m
1 g/m phosphine = 659 ppm3 = 28.59/1000
cu. ft. 339/1165. n = .0077 m/sec
1 ft/hr = 28 m/hr = .47m/min = .0077 m/sec
1 picul = 60 kg
1 quintal = 100 kg
2.5 rai = 1 acre

4.1 Fumigation application - Phosphine

After the cubic content and/or the weight of the material to be fumigated is determined, the chart will give the rate in grams per unit. Various forms of phosphine will yield different amount of gas;

1 tablet = 1 gram
5 pellets = 1 gram 33 9 bags = 11 grams
1 mg PH3 Plate = 33 grams

The success of the fumigation depends on maintaining a sufficient concentration for a long enough periode of time. Aluminum phosphide releases gas slower than magnesium phosphide and bags of aluminum phosphide release gas slower than tablets which in turn release gas slower than pellets. Proper phosphine fumigations are for more than four days. It may be advantageous to use a combination of slow and fast release formulations or, if it can be done safely, to add part of the dosage after two days in order to prolong the period of moderate concentration.

When tablets or pellets are used in fumigation of bagged grain, they should be placed in a container so that the final dust can be disposed of safely. The containers must be large enough so that tablets are not piled on top of each other. Piled tablets are capable of sealing themselves so that the concentration in the center of the stack can reach the point of combustion. When spread out in a container this is not a problem.

Bags can be hung in a series on the side of a stack to help distrubute the gas. They too shou never be used touching each other.

Plates should be left standing on end on the floor with both sides open as they lean against the stack of bags or the pallets.

Gloves should be worn even though phosphine cannot be sorbed through the skin. There will be small amount of extremely toxic phosphis on the hands which could be! ingest edwhen eating or smoking after the fumigation if hand washing is not thorough.

Even though phosphine formulations are not supposed to normally give off significant amount of gas in the first hour, it is safer to cover the stack completely before the phosphine produce materials are opened and applied. Release depends on temperature, moisture, and formulations. Magnesium phosphide formulations have been measured to give of over 20 ppm in less than 30 minutes in mill fumigations. The manufacturer now suggests respiratory protection for any concentration over .1 ppm.

Respiratory protection should either be worn or readily available and in good working order depending on the like hood of its need.

After the gas releasing raterial has been put in place and gas-proof sheets replaced, warning signs should be placed on all sides of the area where someone might approach. A final check for leaks should then be made.

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.

1. Place a respirator around the neck.

2. Open all doors and windows.

3. Check the phosphine concentration using detector tubes and put on the respirator if the concentration is unsafe. If more than 0.1 ppm, send unprotected workers to another area

4. Remove the sand snakes, raise the corner of the sheets, the rolled joints on the vertical sides and quickly leave the area.

5. Leave for 30 minutes to one hour.

6. Return to open the sheet still further and again leave for a similar period.

7. Check on the safety of the area with detector tubes.

8. Remove the sheets, take away and fold for the next fumigation.

9. After a period of at least one hour, but preferably overninght, remove the spent residues and dispose of them in the recommonded manner (Set "Disposal of Spent Formulation")

10. Check tife success of the fumigation

11. Remove the warning notices.

12. Complete a written record of the fumigation in a log book and attach a record to the stack.

Disposal of spent formulation

Residues of pellets or tablets may be scattered on waste ground if amounts are small otherwise, they should be stirred into buckets containing warm water and detergent (30-6Og of detergent in 10-25) of water. When no further bubbles can be seen in the liquid, the buckets should be emptied on waste ground. Containers should be immersed in the liquid and then buried. Bags of aluminium phosphide should be buried. A gas mask should be worn or care taken not to inhale the fumes during disposal. Residues from tablets, pellets and bags must not be heaped together, otherwise there is a risk of fire explosion.

4.2 Methyl bromide fumigateer

Over the stack with sheets, join up, fold the corners and place the sand snakes in position.

Cheek sheeting, sand snakes and repair sheets with plastic tape if necessary.

Inert hose throgh tarp into expansion chamber.

Make final thorough check of the area around for possible hazards.

Send away all onlookers from the fumigation area.

Light halide lamps and put respirators on. Rubber gloves should not be worn.

Record the weight of the cylinder. Or select the proper number of cans.

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. Or add remaining cans of methyl bromide

5. Code of Practice on the Fumigation Techniques for Containers

The success of fumigations depends on many small details being done correctly. Safety of the fumigator, other possibly exposed persons and cargo need to be considered.

It is not enough to put the correct dosage into a container and shut the door. If the gas does not reach the insects in all parts of the container, they will not be killed. Gas can fail to reach the insects either through leakage or through poor circulation particularly with methyl bromide.

5.1 Examine the container carefully for any possible leaks around doors, hatches, or walls. These must be sealed before the fumigantion is complete.

5.2 Check the commodity and note whether suggested fumigant is appropriate. For example methyl bromide will not penetrate plastic bags. Chloropicrin is not legal on processed food going to the United States. Phosphine should not be used on starch vegetables like potatoes. Phosphine could also hurt copper, gold or silver but these are not likely to be in a container that needed to be fumigated. If the gas is inappropriate, the shipper should be contacted.

5.3 If methyl bromide is to be used, the tube should be taped to the roof of the interior of the container so that the gas will be discharged into the open space at the top where it will mix with the air before filtering down through the cargo. The hose can extend out through a corner of a door and the door carefully closed without normally pinching the hose.

5.4 Check the listed size of the container. Normally the cu. cap. is the most important figure since the entire space will be fumigated regardless of how full the container is.

5.5 Calculate the dosage from the cubic capacity a volume, the net weight of commodity or from a chart considering both items. Put the required amount of gas next to each container.

5.6 Several forms of phosphine can be used. Grain that has not been processed such as bulk maize could be probed wish tablets. Rice in bulk or in bags could be fumigated with Phostoxin prepac, Detia Bags FumiCel plates or similar brands. Plates should not be dropped into processed foods such as polished rice since the plates may break apart during release. They can be put in cotton bags and suspended from the top. Plates should never be placed between bags or stacked on top of each other as a fire could result.

5.7 Methyl bromide is often used froms 1 1/2 lb cans instead of cylinders because of the small dose. If the gas is released into the head space it will probably be effective but the fumigator can be injured utilizing these small containers. There is some leakage at the puncture point any time that the can is used. The leaks are worse if the seam on the can is punctured or if the gasket is old. Proper precautions are needed.

6. Code of Practice on the Fumigation Techniques of river Barges

6.1 Phosphine tablets.

Phosphine has the best chance of giving a good kill of all insects in bulk grain, but needs at least 4 days and a very good seal to maintain a lethal concentration. Even longer exposures may be necessary for resistant or tolerant species, or life stages.

Ideally the phosphine producing tablets should be added as the grain is placed in the barge if mechanical equipment is available so that the barge can be loaded in only a few hours. In most cases tablets will have to be probed into the grain mass after the barge is loaded.

If a four day exposure is contemplated, a dosage of 5 9. per tonne is suggested. The expensive fumigant can be reduced to only 3 9. per tonne if a 7 day exposure can be used.

For a four day exposure, it is best to probe the tablets to 3/4 of the depth of the hold. Longer exposures can permit shorter probes which can be done with less labour.

In a typical barge a minimum of 30 places would need to be probed. About 100 tablets would be used per probe but these should added a few each time the probe is withdrawn a few feet. Proper sealing is very important.

Any openings from the hold to the rope locker or other areas should be sealed on both the hold side before loading and on the other side to minimize the chance of leakage.

No one should be on the barge during the fumigation except possibly to take concentration readings.

After the fumigation, the tarps can be pulled back and the area should be kept secure from people until the concentration is below 13 ppm.

6. FumiCel and Fumistrips

The FumiCel and FumiStrip formulations of magnesium phosphide are a convenient new way of applying phosphine gas. These like the magnesium phoshide tablets release the gas faster than the older aluminum phosphide tablets but the kill many not be any quicker. Some insects must be exposed to the gas for a period of time and undergo at least one growth stage or molt before they succumb to the gas.

The FumiStrips can be used more effectively if they are fastened to the metal overhead rods so that they will be suspended in the air space instead of just being placed on the surface. They must never be used where two plates are touching each other.

The FumiCel plates release 33 g. of phosphine gas and the strips release 528 g. of phosphine gas. A combination of the two can permit right dosage and again 5 9. per tonne is suggested for a four day exposure. The manufacturer suggest that this be a static fumigation with the barge at anchor during this time.

As with any fumigantion, the quality of seal is very important. The type of fabric used in Thailand can, according to our tests, hold phosphine very well if the tarp is new or is adequately patched. It is important for the fumigator to carefully examine the tarp and and patch any obvious holes and it is important that they also monitor for leaks so that they can spot small hard to see holes or tears.

Compartment doors from the hold are best sealed with a section of plastic placed over the doorway. The door can then be shut on the sheet and the edges taped to the bulkhead. It can also be taped directly to the bulkhead over the door frame if there would be too many wrinkles in the tarp which could allow gas to escape.

Warning signs must be posted at all potential entrance points to the barge and no one should be on the barge during fumigantion unless readings show the air to contain less than 0.3 ppm.

Aeration with the tarps off should continue until gas readings are below 0.3 ppm even in the bottom of the hold and in the rope locker and other areas where the gas might linger. On warm windy days this should occur within a few hours but measurements are the safest way of knowing that the area is safe.


Fumigations are done either at anchor or innecessary because of previous infestation in a poorly cleaned hold but is needed more often due to infestation in the grain that is loaded.

Fumigations are done either at anchor or intransit. The high cost of demurrage when ships are held at anchor makes the in-transit fumigantion attractive but there are safety problems

Small leaks of gas can contaminate crews quarters, paint lockers and other areas and have resulted in some deaths. Intransit fumigation should only be done if a competent person has examined the ship and certified that a fumigation can be done without undue risk. A trained person then must accompany the ship and take gas readings throughout the fumigation so that any leakage will be discovered and appropriate actions can be taken.

Fumigation of bulk grain is very difficult because it is difficult to get even penetration of the gas. It is almost impossible to get good penetration of bulk grain with methyl bromide and penetration with phosphine can take from 7-14 days depending on the depth of the hold. In some tests conducted by USDA, adequate gas penetration was not achieved in the bottom of the hold unless ducts were installed prior to loading.

Fumigation in-transit is a valuable technique since there is no later point to provide reinfestation.

7.1 Methyl bromide.

Although methyl bromide does not have the penetraling and dispersing power of phosphine, it can kill insects in 24 hours if the gas reaches all areas.

Obviously the problem with methly bromide is due to the fact that it is 3.3 times the weight of air and moves very slowly if there are no fans to circulate the gas.

If the gas is released at only one point at the center of the barge as often happens, there will probably be failure to kill all of the insects. If the gas is released on top of the cargo at many different points, it will slowly drift down through the carge and above better distribution. Fans are still advised for recirculation of methyl bromide on barges. Although we believe this technique will work, research is needed to establish the exact size of fan and other details.

On some ship fumigations, methyl bromide is dispersed through tubing with several notches cut along the length. Unfortunately most of the gas will be lost at the first few openings and only a little gas will come out of the last openings.'

A "H" configuration as shown below can solve this problem. The main hose is attached to a 3 meter section of hose with a brass "T". Then perforated hoses are attached at the center with more brass "T" s. About four of these harnesses would be needed for the average barge and if they are made from a good quality plastic, they could be used many times. This would require releasing the gas into four hoses at four points instead of just one spot but this would not take much longer. The dispersion of the gas will be greatly improved if the harness is supported above the bags by fastening it to the metal curved ribs of the barge.

The use of a fan under the tarp for at least one hour after the introduction of the gas will greatly increase the dispersion of the gas.

It is inexpensive to check for gas leaks of methyl bromide with a halide leak detector, and this should be done on each treatment so that additional sealing can be done.

Since there can still be small undiscovered leaks, no one should be on the barge during the fumigation unless equiped with a gas mask. Signs should be placed to warn all persons to stay away during the fumigation period.

After 24 hours, the tarps can be removed and aeration can start but gas is likely to linger in lower areas and these areas should be checked before workers enter for unloading.


7.2 Ship fumigation while evacuated by personnel and crew.

If there is a possibility that gas can leak from the holds to an occupied or potentially occupied area, fumigations should only be done after the crew and all other persons have left the ship. The only persons remaining on the ship should be fumigation personnel that are equipped with respiratory protection and gas measurment devices.

Before the gas is introduced, the fumigator in charge should plan how the gas will be aerated to a safe level. This may mean placing fans in some areas if electricity is available or can be made available with protable generators.

If two days or less are available, only methyl bromide should be used since phosphine could not give an adequate kill in a short time.

Bulk grain cannot be adequately fumigated with methyl bromide unless perforated pipes are inserted deep into the grain in many areas to aid to distribution. This is a hazardous procedure that should only be attempted by trained personner wearing adequate respiratory protection equipment. Bulk grain should normally only be fumigated with phosphine and with an exposure time of at least 4 days.

Bagged grain can be easily fumigated with methyl bromide if a series of release points are used such as the "H" harness discussed in the barge fumigation section. Good control is still dependent on air circulation to in sure the gas stays evenly dispersed and can be readly evacuated. Fans must be used for at least one hour after gas release. This may mean gaining power through a portable generator.

After the gas been released at many points and the fans have run for at least one hour, the fans can be shut off and the seal can be checked for leaks. All leaks should be patched by persons wearing respiratory equipment. Exposure time should be at least 24 hours. After the exposure time is achieved, it is helpful if a new gas reading is taken to know if excessive leakage has occured. Tarps can be pulled back and aeration started. Fans placed near the bottom of the hold during loading can be started and will save hours of aeration time. Aeration is complete when the gas concentration in all areas is below 5 ppm. for methyl bromide or .3 ppm with phosphine.

7.3 Ship Fumigatiom-Bulk grain treated with Phosphine.

The only practical fumigant to penetrate large amounts of bulk grain is phosphine. It can do an excellent job if the gas penetrates to all areas in sufficient concentrations. Penertration is obtained through long exposures or through placing the tablets throughout the grain mass with probes.

Although many factors can influence the time required for phosphine gas to penetrate throughout a hold, some rough guidelines are:

Barges - Allow at least 4 days
Small freighters - Allow at least 7 days
Large ships - Allow 14 days and use ducts if possible

The large amount of phosphine required (58./tonne) should never just be placed on top of the grain. Particularly if the grain was loaded during wet weather, the release of the gas into the head space can be much faster than its penetration into the grain. The standard dosage could give over 1000 ppm if the gas was evenly dispersed and this would not be dangerous. However, a fast release could cause gas readings in the head space of over 17,900 ppm which could a fire or explosion. If the tablets are evenly probed into the grain mass, there should not be a problem.

For even distribution by probing, try to probe once per square meter. Probe as deep as possible, about 2-3 meters. Apply 4-5 tablets per meter is recommended but probably not practical under ship fumigation procedures. The purpose of placing only a few tablets each time the probe is withdrawn a little is not only to disperse the tablets for better gas distribution but also to seperate the tablets to avoid high concentrations of gas. All tablets should be at least 30 cm. under the surface of the grain.

After the probing, the hatch cover should be replaced and covered. The three tarps offer used can provide a reasonably good seal if they are in good condition. If there is leakage, additional sealing will be necessary. A trained person with gas measuring equipment and respiratory equipment must accompany the ship and the Captain must be prepared to take whatever precaution is necessary to protect the health of people on board.

Monitoring of the gas level should include areas adjacent to the holds as gas can leak into occupied or rarely occupied area and be dangerous.

7.4 Safety practice in intrainsit ship fumigation

The first step in any intransit ship fumigation is to examine the ship with the Captain or a designated ships officer to establish if the ship's holds can be safely fumigated intransit.

The holds should be examined for obvious points of leakage but unusualy conditions must be considered. There may be cross connections from the bilge to drains in the galley or other areas. Gas has been known to follow this path.

Smoke detectors draw air from the hold to a sampling point at the bridge in some ships. This could bring gas from the hold to the bridge and at least one fatality may have occured from this. It may not be safe to discontinue the use of the smoke detector but additional safeguards would be indicated.

Some crews like radios in their quarters and will rig elaborate antennas. They have been known to drill through a common wall between a hold and their quarters in order to get the antenna wire to a distant point. This can permit gas leakage into the crews quarters.

Doorways to the crews quarters are often left open even when they are next to a fumigated hold. Again leakage can occur.

Other areas are occasionally occupied by the crew and have been known to have high gas concentrations. Paint lockers and rope lockers may have hatches to the holds that are fumigated. We measured a very high concentration due to this on one ship.

Crews will sometimes sit on the hatch covers or sleep on the hatch covers and can be overcome by very small amounts of gas leakage.

All holds have vents and even though these may be well sealed at the time of sailing, the seals may deteriorate later.

A trained person must be on board the ship to measure the concentration and watch for unusual problems. He may be a ships officer or may be part of the fumigation crew. The key thing is sufficient training and equipment.

8. Flat Grain Storage Fumigations

Flat grain storage structures can be built quickly and at a low cost per ton of storage buth they have several problems. Even with aeration ducts and the fans running regularly, it is difficult to maintain uniform moisture in the grain.

Fumigation is even more difficult and most fumigators will agree that it is the most difficult type of fumigation to achieve 100% control. This is due to the tremendous amount of surface compared to the total amount of grain. The contrast would be silo fumigations where there is only a limited surface at the top compared with the total mass. It is the large surface area where the gas is lost on most fumigations. There is also gas loss through the metal walls as the gas can leak between the corrugated sheets where they overlap.

The problem is compounded by poor storage practice. The grain is rarely leveled so covering it with a tarp is difficult.

There apparently has been a tendecy in the past to take some short cuts from suggested procedures. The grain wasn't leveled first and the tablets were "walked in" rather than probed deeply into the grain. The grain was probably not covered with a tarp to hold the gas within the grain mass. Some tablets were placed within the aeration ducts and the fans were run for for about 15 min. Unfortunately all of these practices are wrong and could even be dangerous or could contribute to resistant insects.

The natural air currents in the grain would probably be up-ward so that very little of the gas would go below the point of application. It is very easy for the gas to escape through the roof vents and at the roof wall juncture.

The fans would have very little effect on the phosphine in the first 15 minutes since it would not reach its peak of release for 24-48 hours and the release is slow then.

Flat grain fumigations are done in many countries and can be reasonably successful but there is no substiture for the hard work it takes to do a good job.

8.1 Flat Grain Fumigation Techniques

The fumigation should be started by preparing the grain and the structure for the fumigation.

Two crews of workers should be selected. One will be the applicators and the others will spread a plastic sheet over the grain and tuck it in at the edges and pin together successive sheets.

There should be enough people on the application crew so that they can line up across the width of the grain and have no more than a meter between each worker. The line of applicators can then move across the grain probing phosphine into the grain every meter. This will give good horizontal coverage even if the tablets are probed only one or two meters deep.

The other crew will follow the applicators spreading out the plastic and joining sheets by overlapping and pinning with bamboo pegs. The two crews should be able to work fast enough to move through the area before appreciable gas has been released but gas measurements are still adviseable.

After the tablets have been probed and the grain covered, gas loss can be further reduced by sealing any roof vents with plastic bags and sealing doors and windows with plastic sheets or tape at the joints.

At least 7 days exposure should be used but the plastic should be removed within two weeks or sooner if the grain has a high moisture content. Sweating and mold can occur otherwise.

The people removing the plastic should be protected with gas masks if the concentration is above .3 ppm. The gas level can often be reduced below this at the end of the fumigation by merely leaving the doors and vents open for a day before the plastic removal.


Basic training

Groups to receive training
Subjects to be covered with each group and why
Suggested training techniques
Training materials available
How to prepare additional training material

Subjects to Study

Economic loss due to insects and molds
Important Insect species
Insect control through Integrated Pest Management
Non-chemical controls

Vertebrate pests and their control
Mycotoxins and their control
Warehouse practices and Sanitation
Government regulations

9.1 Training - Fumigation Detail

Commercial Pest Control Operators

Present Problems

Commodity pricing can cause fumigators to take some short cuts and avoid any costs that can be eliminated.

The gas-proof sheets are patched many times before they are replaced. Tape used to seal cracks is narrow 2" rather than 3". Insufficient time is spent in proper folding of tarps at the floor to get the best possible seal.

At least on export grain fumigations, an officer of the Dept. of Agr. monitors the dosage so that the correct amount will be applied. We can only speculate on dosages at other fumigations. The accent seems to be on the dosage rather than the concentration throughout the exposure. Fumigators do not return every few hours to take gas readings.

Leak detectors are not used even though this would not add substantially to the cost. Small leaks in the seal are probably often missed.

Fumigators sometimes do not have access to the many training meetings that occur in many other countries. Training is often in-house and may not be sufficient.

Most books and periodicals on fumigation are written in languages other than the local language. This makes home study impossible for many fumigators.

Most pesticides, equipment and safety materials must be imported at a high cost. Instructions will usually be in English and require explanation by informed professionals.

Exporters and others often specify the type of fumigant to use. They may not understand the limitations or safety problems of that choice.

Godown managers do not realize the importance of storage practices which makes good sealing impossible.

Ships and barges are often in poor condition making safe and effective sealing expensive time consuming and generally difficult.

Minimum standards for various types of fumigation should be printed in local language. Plant Quarantine should refuse to issue certificates for fumigations deemed by their officers to be possibly dangerous or ineffective.

Training sessions should be held in the local language.

Godown personnel should be trained to store properly

Exporters should be informed about the limitations of each fumigant.

Equipment should be developed that would permit recirculation of methyl bromide in barges or similar areas.

Leak detectors should be used on all fumigations and enforcement is suggested wherever a government officer is required to witness a fumigation.

Establish an import requirement that all pesticides, equipment and safety devices must be accompanied by adequate instructions in the local language.

Give government officers the right and duty to disapprove vessels that in their opinion might create a safety hazard for in-transit fumigation.

Stress to exporters and other purchasers of fumigation the high cost of infestation at the port of arrival compared with a modest increase in fumigation cost to do a better job acording to new standards.

Encourage fumigators to sell additional services with the fumigations. Residual spraying, space treatments, and even inspection services can be cost effective.

Set up a certification program for fumigation supervisors with written exams and recertification by exam or attendance at training sessions.

Restrict sale of dangerous fumigants to persons that have passed the writter exam.

Sponsor attendance by key Dept of Agr. Officers at fumigation training meetings in other countries.

Key subjects for commercial fumigators

Principles of fumigation. Gas movement, sorption, desorption, and aeration.

Principal fumigants and their advantages and limitations.

Safety in the use of fumigants

Respiratory equipment with practice in using each.

Gas leak devices with practical use on the job site or laboratory.

Gas monitoring equipment. Care and use. Calibration.

Techniques in fumigation under gas-proof sheets.

Techniques of container fumigation.

Techniques of barge fumigation with methyl bromide and with phosphine.

Techniques of ship fumigation in-transit or at anchor.

Use of fans to improve circulation of gas.

Information needed to pass written exams for fumigation supervisors.

Laws concerning fumigation in Thailand and Maritime regulations.

First Aid instructions for fumigant injuries.

How to handle fumigation requests that would be ineffective or dangerous.

Business aspects of fumigation including cost accounting.

Dosage calculation based on temperature, commodity, fumigant, time, and other factors. How to vary dosage and still obtain correct time/concentration.

Time/Concentration calculations in fumigation.

Fumigation techniques for flat grain storage.

Fumigation of perishable fruits, vegetables, and flowers.

Insect resistance and why past techniques won't work in the future.

Suggested Training Techniques

Lectures with slide series

Integrated pest management for stored grain

Inspection techniques

Principles of fumigation

Bagged grain fumigation

Barge fumigation

Shipping container fumigation

Rodents and their control


Techniques of tarp fumigation

Dosage calculations and concentration importance

Choosing the proper fumigant

Preparing the stack for methyl bromide

Sealing techniques and leak detection

Safety and respiratory equipment

Proper storage practices

Observation of sanitation

Sources of reinfestation

Other pests and inspection techniques

Dosage vs Concentration

Importance of expansion chamber for methyl bromide

Importance of a good seal

Concentration time graphs and charts

CT factors for 100% kill of Sitophilus species chart

Monitoring tests of typical fumigations

How to use the fumiscope

How to use the leak detector

How to put on gas mask and check. its function

Calculations important in fumigation

9.2 Training - Fumigation Detail

Warehouse - Godown - Bag Storage

Present Problems

Many facilities have serious insect problems particularly in old stock, floor sweepings, and grain residue in used bags, equipment, holes in the walls and other areas.

Residual pesticides are often rarely used and fumigation is used primarily at the time of sale. Loss in the meantime is probably close to 1% per month by weight and equally serious losses in quality occur.

Fumigations occasionally of only a few stacks of bags is probably worthless since reinfestation sometimes occurs even before the gas-proof sheet is removed.

Fumigations are often done by either the godown personnel or even by commercial fumigators with a less than effective floor seal. This translates into an ineffective fumigation.

Removal of infested floor sweepings is offer not done to eliminate this important source of reinfestation even though floor sweepers are employed. Education on this important step can improve grain quality at a very low cost by limiting reinfestation from spilled grain.

Training subjects for Godown and Warehouse Personnel

Importance of proper storage practices in fumigation and insect control.

Importance of sanitation in insect control to avoid reinfestation.

Inspection, isolation, and treatment of arriving grain.

Importance of an Integrated Pest Management program.

How to obtain initial control in an infested warehouse.

Fumigation specifications that will permit informed bidding.

Techniques of do-it-yourself fumigation.

Safety considerations in fumigations under gasproof sheets.

Residual insect control applications that can be profitable.

Space treatments - when and how they can be done profitably.

Use of gas leak detectors and monitoring equipment.

Advantages and limitations of various fumigation sites. Godown, barge, and ship.

Warehouse inspection techniques and their value. Economic advantages of grain handling with much reduced insect infestation.


Determine efficacy of present barge fumigations with monitoring lines checked every 4-6 hours on a Fumiscope or other device. Test insects will help evaluate control although there will probably be a good natural infestation. This test could then be repeated by making minor changes such as using pallets on the bottom and a higher expansion chamber on with multiple release points for the gas.

We can only speculate about present hazards. Gas testing for comparison with suggested Threshold Limit Values should be done on the following:

Intransit barge fumigations

Intransit ship fumigations

Godown tarp fumigations with nearby workers

Fumigated containers that may be stored below deck without aeration.

Tobacco sample room fumigations next to offices.

A demonstration godown should be selected and given the entire proposed program including fumigation of all stacks at one time and application of residuals followed by a space treatment. Godown personnel would also be taught how to inspect and monitor the control. This would then be visited by other interested parties to see that control is possible.

Try to obtain the total weight of grain bought per year by one godown and compare with the total weight sold. An attempt then should be made to determine the sources of the loss and evaluate the significance to a good pest control program.

The efficacy of various tarp treatments should be made by sampling before and after such typical fumigations as:

Fumigation tarp bunched at the bottom permitting leaks

Fumigation tarp held down with bags instead of sand snakes

Fumigation tarp not sealed to floor near walls or posts

Fumigation tarps properly sealed to smooth out tarp held with overlapping sand snakes.


Export grain must arrive insect free at the port of destination to receive a good price. Fumigations inside godowns are subject to reinfestation. Ship fumigations in transit can be hazardous and may not be effective due to the depth of the holds.

Barges are often used to transport grain from the godowns to the ship. They present a sealable area isolated from probable reinfestation but there have been problems in obtaining insect control during barge fumigations.

The 24 hour holding period of the barge at the dock is not long enough for effective fumigation with phosphine and there is strong reluctance to pay for longer demmurage. The tightly packed bags placed directly on the floor of the hold, impede fumigant circulation. There is no use of fans and only limited expansion chamber in the top. Although we saw multiple release points used in ships holds, we never saw more than one release point used on barges. This type of fumigation can be expected to be less than perfect.

Recognizing the success of recirculation of Methyl bromide in installations such as the Controlled Circulation Chamber for Orchids, we propose to test a modification of the barge fumigation procedure.

Instead of placing the first layer of bags on the bottom of the hold, rows of pallets should be placed with all 2 x 4 runners lined up with the ship so that air channels would run fore to aft.

The rope locker would be used as one plenum chamber. The door from the hold to the rope locker would be left open. A board would be sealed to the hatch opening and a hole in the board would be connected to a gas powered air pump. The air would then be ducted to the top of the hold and the tarp would be sealed around the duct as it is around the entire perimeter. The gas would be injected into the air stream where it would mix with air in the plenum created by the gas proof sheet held off the cargo by pipe hoops. The gas/air mixture would settle through the bags both by gravity and by the pull of the blower drawing air from the hold into the rope locker. The fan should run for the entire 24 hours and then again during aeration after the tarp had been removed. This will provide better safety for workers that must enter the hold to unload the bags by hand.

The pipe hoops may need to be lengthened to form,a larger expansion than normally exists and to allow for the loss of space taken up the pal lets.

Test lines should be placed at the top, middle, and bottom at the front, middle and rear as well as the rope locker and crews aren to evaluate the concentration. The fumiscope should be used for the readings.

The crew should not be allowed on board during the fumigation but could be on the dock if air sampling is done. There is always a hazard to the crew if they stay on a barge that is being fumigated but even a small leak will be serious during recircultion.

The size of the blower must be kept small enough to not put too much strain on the seal of the tarp put should be enough to assure proper circulation of the air gas mixture.

Contents - Previous - Next