3.1.1. Is fumigation appropriate?
3.1.2. The need for fumigation and timing of treatments
3.1.3. Action before fumigation
3.1.4. Integrated commodity management
3.1.5. General safety considerations in fumigation
Fumigation is a versatile technique that can be applied in a wide range of situations. The details of the procedure required to ensure a successful fumigation vary greatly with different circumstances. There are a number of important generalizations that can be made, however, to help management assess a particular situation and decide what fumigant to use and what preparations and precautions are required to ensure both the safety and efficacy of the process.
Fumigation should be undertaken only when management is satisfied that a need to carry out pest control exists, that fumigation is the appropriate process, and that the fumigation may be safely and effectively carried out.
Fumigation is a precise operation, requiring considerable expertise and cannot he undertaken without proper preparation. It is important that management realises this, and ensures that due planning is carried out before fumigation is required.
An essential requirement for fumigation is an enclosure that will retain the fumigant at sufficiently high concentrations over the exposure period. Barges and lighters, shipping containers, and whole warehouses or godowns may he used providing they are adequately sealed. Gastight sheeting is commonly used to enclose bag stacked commodities. Bulk storage also may be constructed so that they are gastight (Refer Chapter 3.2, 3.3; TDS #14, #15).
Fumigation is usually the preferred method of pest control in warm and humid climates, where pests must he eliminated without moving the infested commodity. Often, fumigation of commodities in the export trade may he mandatory for quarantine or contractual reasons. Fumigation is useful where a rapid kill of pests is required and for effective removal of pests from structures into which clean commodities are to he brought. In situations where there is a choice between fumigation and use of contact pesticides (e.g. organophosphate compounds, pyrethroids), the residues left by fumigation may be considered more acceptable.
Fumigation must not he used when:
· trained operators are not available;
· the enclosure in which the fumigation is to he carried out cannot be sealed to an adequate standard;
· workers and other persons cannot he reliably excluded from the enclosure and risk area; and
· fumigant cannot he safely aired from the enclosure after the exposure is complete.
The need for pest control in a given situation is influenced by three main factors:
· acceptability of the observed level of pests;
· suitability of the environment for multiplication of the pests; and
· how long the commodity is to he retained before being passed to control of other parties.
In effect, an assessment must he made whether there is an immediate requirement for control, whether a treatment should he applied to avoid an anticipated pest problem, or whether action is not needed. To make such an assessment an action level needs to be defined. These considerations lead to three possible decisions:
· immediate treatment of an existing problem;
· immediate treatment of an anticipated problem; or
· no action.
3.1.2.1. Action Levels for Treatment:
An infestation which is initially at levels low enough to escape detection by normal sampling may quickly build up to damaging and unacceptable proportions. High populations of insect pests not only cause direct losses through their feeding, hut may cause indirect damage through their production of metabolic heat and moisture that lead to increased moisture migration and production of conditions conducive to moulding. Thus, if infestable commodities are to be stored for more than about 6 weeks under humid, tropical conditions, a precautionary fumigation is often advisable before infestation becomes obvious, and before the infestation sets up conditions that may make subsequent storage difficult.
Any commodity taken in for longer term storage should he treated immediately as it may he assumed that it will have become at least lightly infested in transit and it was probably not stored in previously insect-free conditions. Grain may he infested in the field and contaminated with pests from harvesting and handling machinery and during transport. Infested materials brought into store are a potential hazard to disinfested commodities already in store, as they provide a source of cross-infestation.
In commercial trade within a country, an infestation level of one live insect per kilo at time of sale can he taken to he the maximum tolerable in human foodstuffs to be consumed soon after purchase. If this standard is to he met, a low level of infestation, less than 20 insects per tonne, is acceptable if 6 or fewer weeks storage remain. Higher levels may he acceptable in human food that will he milled or processed before consumption.
Export markets may stipulate their own phytosanitary requirements, and a fumigation at export is often required to meet these specifications.
3.1.2.2. Choice of Fumigant:
· requirement for short treatment time;
· effect of fumigant on the commodity, and existing residue levels;
· target organisms;
· economic advantages and availability of particular materials;
· training of fumigators;
· environmental safety considerations.
Phosphine generally requires long exposure periods, whereas methyl bromide provides a rapid fumigation that can be completed in less than 4 days, often within 24 hours. The presence or absence of certain tolerant insects may influence both the choice of fumigant and the length of the exposure period. The target organisms may he tolerant and require longer exposure.
Fumigants can affect the commodity; or the nature of the commodity itself may affect the efficiency of a fumigant. Methyl bromide and phosphine may reduce seed viability, and methyl bromide can taint some products. Sorption of methyl bromide in oilseeds and other high oil content materials can reduce or even stop penetration of this gas into a bulk.
3.1.2.3. Personnel:
A basic requirement is that sufficient personnel trained in fumigation practices are available to carry out all necessary operations in a reasonable time. The fumigator-in-charge should be experienced in fumigation practice and all fumigators should possess a current certificate of competency as fumigators or have an equivalent qualification. Persons without experience should he trained in advance of operations and should work only as fumigators' assistants.
The Fumigator-in-Charge should he responsible for safe and effective conduct of the fumigation. He should organize and supervise the work of the other fumigators and must be present at all significant stages of the work. He should also undertake:
· the planning of the fumigation and the procurement of materials and equipment;· the thorough instruction of subordinates with respect to safety precautions, the maintenance and correct use of protective equipment, the general work plan, and the individual tasks;
· the performance of tests for the fumigant gas and the issuance of clearance certificates; and
· supervision of the recovery and safe disposal of contaminated fumigation materials.
3.1.2.4. Materials and Equipment:
Adequate supplies of the appropriate fumigant or fumigant-generating materials should he available before commencement of the fumigation. The formulations used should be clearly labelled and give full instructions and warning notices in local language(s).
Equipment should include: personal safety equipment such as gloves, respirators and respirator canisters, and fumigant detection apparatus; and appropriate fumigant release apparatus such as scales, heat exchanger, distribution lines, nozzles, tablet dispensing apparatus, and flash proof circulation tans. A high level of supervision is required to ensure that this equipment is kept in good working order. Unless the storage is already suitably sealed for fumigation, there may he a requirement for fumigation sheeting and sealing materials. Efforts to seal enclosures should he continued until the appropriate standard is met. Equipment should be available to monitor fumigant concentrations throughout the fumigation.
Figure 3.1 Deciding on the most appropriate fumigation treatment
¹ Combinations of carbon dioxide with phosphine or methyl bromide can have advantages in certain circumstances. The use of carbon dioxide requires longer exposure periods and a high level of gastightness of the fumigated enclosure
|
When and when not to use phosphine as a fumigant Phosphine is the fumigant of choice: · when a commodity is required in not less than 5** days; · when Trogoderma granarium or Prostephanus truncatus are present and use of methyl bromide is not mandatory; · when oilseeds*, expeller cake, and meals must be treated; · where germination is important; · where commodities have been treated previously with methyl bromide; · where taint may he a problem if methyl bromide is used, e.g. on flour; Phosphine should not be used: · where resistance is known to exist in an insect population; · in unsealed enclosures; · at temperatures below 15°C; · where a rapid treatment is required, i.e. less than 5-7 days; · areas immediately adjacent to workspaces and habitations; · where there is no trained, qualified, and properly protected fumigation team. ** Exposure periods longer than 5 days may sometimes he necessary * Residue data not yet available. |
|
When and when not to use methyl bromide as a fumigant Methyl bromide should be used: · when a treatment must be completed within 4 days or less; · for most quarantine treatments; Methyl bromide use should be avoided:* · on seed required for planting or malting; · on very absorbent materials, such as expeller cake or oilseeds; · in areas immediately adjacent to workspaces or habitations; · on materials previously fumigated with methyl bromide more than once; · where there is no trained, qualified, and properly protected fumigation team; · in unsealed enclosures; * There may, however, he occasions when methyl bromide must be used to fulfill quarantine or contractual obligations, where it would not otherwise be the fumigant of choice. The use of methyl bromide is currently under discussion based on the Montreal Protocol regarding its ozone depletion characteristics. Further use may be restricted on some instances and certain circumstances. |
3.1.3.1. Notification of Authorities and Persons Concerned:
3.1.3.1.1. Fumigation of a Building or Enclosed Space:
A fumigator intending to treat a building or other enclosed space outside the premises of an approved fumigation company shall deliver an appropriate notice in writing 24 hours before the fumigation commences, to:
· the nearest Police Station and Fire Brigade;· every tenant or occupier within the fumigation enclosure and risk area, who must acknowledge receipt by signing the duplicate copy which shall he retained by the fumigator;
· the authority concerned with plant quarantine matters;
· the division of the Health Department that deals with occupational health matters;
· other health authorities as appropriate.
3.1.3.1.2. Fumigation of a Ship:
The fumigator in charge, when intending to fumigate a ship or other vessel, shall deliver a notice in writing before the fumigation commences to:
· the appropriate Port Authority;· the appropriate Police Station and Fire Brigade; and
· the master or other person in charge of the vessel, who must acknowledge receipt by signing the duplicate copy which shall be retained by the fumigator.
3.1.3.2. Fumigation Warning Signs:
The fumigator in charge of fumigation of any building, vessel, or enclosed space shall, before the application of the fumigant, affix to each door and other means of access to the fumigation enclosure, a notice with a white background on which there shall be printed, in the local language(s), the message 'DANGER KEEP OUT', followed by the words 'FUMIGATION WITH [Name of Fumigant]' in capital letters not less than 10 cm (3 inches) high, in a contrasting colour to the background.
The fumigator's name and telephone number should he clearly shown at the foot of the notice. All warning notices should he suitably illuminated at night.
|
3.1.3.2. FORM OF NOTICE OF IMPENDING FUMIGATION Schedule No. 1 Notice of Intention to Conduct a Fumigation1 TO: __________________________________2 Please take notice that it is may intention to fumigate3 _____________________ by means of4 __________________on _________________commencing at ______________o'clock a.m./p.m. Date ____________________Signed_________________ Notes to Occupier: 1. You are required to vacate the area before fumigation as instructed and not return until advised that the area is safe for re-entry. 2. You are require to acknowledge receipt of this notice by signing the duplicate hereof. Date ____________________Signed _____________________ Notes on the form: 1 The design and wording of this form should take into account the relevant requirements of local legislation 2 This form should be sent to the appropriate authority, the nearest Police Station and Fire Brigade, and every tenant or occupier within the fumigation and risk area who must acknowledge receipt by signing a duplicate copy which shall be retained by the fumigator 3 Here state name of number and location of building, vessel, or oilier enclosed space intended to be fumigated 4 Here insert name of fumigant to be used |
|
3.1.3.2. FORM OF NOTICE TO BE AFFIXED TO PREMISES UNDERGOING FUMIGATION DANGER-KEEP OUT POISON GAS FUMIGATION WITH [NAME OF FUMIGANT USED]
Fumigator:_________________________ Contact Address: ____________________ Telephone: _________________________ Date of Fumigation: __________________ |
|
3.1.3.2. FORM OF CLEARANCE NOTICE FOLLOWING COMPLETION OF FUMIGATION Certificate of Clearance1 [Name of fumigant used] Fumigation To the Officer-in-charge of the grain store at _________________I, being the Officer-in-charge of the fumigation of _____________________, here by declare that I am satisfied that the risk area is free from danger arising from the use of the fumigant. I make this declaration after having examined the area and tested for fumigant in the atmosphere in the working spaces and cell top spaces/over grain spaces. Signature of fumigator __________________________ Date: ________________Time:___________________ The above Certificate of Clearance was handed to me at ______________________________ on _____________________________Signature of officer in charge of the premises:________________________________________________________________ Note on the form: 1. The design and wording of this form should lake into account the relevant requirements of local legislation. |
3.1.3.3. Precautions and Test of Equipment:
No person shall commence a fumigation until the following conditions apply:
· The fumigator has by personal inspection ascertained that all portions of the fumigation enclosure and risk area have been vacated.· All tires and naked lights within the fumigation enclosure have been put out. For flammable fumigants, there should he no smoking or carrying of matches and cigarette lighters inside the risk area.
· All liquids and foods that are not required to be included in the fumigation and might he affected by the fumigant are removed from the fumigation enclosure.
· All cracks, crevices, or openings in or between walls and ceilings or roof and floors and all fireplaces in the building, vessel, or other enclosed space about to be fumigated have been sealed to prevent the escape of fumigant from the fumigation enclosure.
· Fans as required are in position and tested for efficiency. For flammable fumigants, it is essential that fans and their switches, if any, used within the fumigation enclosure comply with the requirements of hazardous locations and are flash proof.
· The nearest operable telephone outside the fumigation area has been located and its number noted.
3.1.3.4. Testing for Gastightness:
Wherever possible, all enclosures to be fumigated should be assessed for gastightness before fumigation. Standards of sealing required are described elsewhere giving operational procedures for specific applications, which also cover methods of sealing. If necessary, enclosures should be further sealed until the appropriate standard is met.
To he fully effective, both in terms of benefit cost ratios and in meeting an acceptable level of pest control, fumigation operations, clearly, must be integrated into overall storage operations. Because fumigation disinfests, but does not confer residual protection, reinfestation may commence as soon as a fumigation enclosure is opened. Every action must be taken to prevent this and to enhance the effectiveness of Fumigation.
3.1.4.1. Adjuncts to Fumigation:
3.4.1.1.1. Store Hygiene:
The basic requirement for good store hygiene is essential to the success of any pest control operation. Store hygiene includes:
· Daily sweeping of the store environment to remove spillage which must be either fumigated immediately or disposed of, preferably by burning (not retained within the store);· Regularly cleaning the structure of the store;
· Spraying the fabric of the store with residual insecticides following cleaning to control insects prior to fumigation;
· Routine inspection of all stocks;
· Routine disinfestation of all incoming stocks;
· Segregation of all infested stocks; and · Simultaneous fumigation of all stocks within a store to prevent cross infestation (but is dependent on availability of sufficient number of fumigation sheets).
3.1.4.1.2. Gas-Proof Surface:
Where commodities are stored in bag-stacks these should be built on a gas-proof surface. This can be done by the use of a gastight plastic floor sheet or specially sealed flooring, such as good quality, sound concrete. Any cracks evident in concrete floors should be immediately repaired.
3.1.4.1.3. Access:
Provision must be made for adequate access to bag-stacks so fumigation can be undertaken. A minimum requirement is a space of 1 metre away from walls, other stacks and below any structure supporting the roof of the storage.
3.1.4.1.4. Stock Management:
Stock rotation and control: the principle of first in-first (FIFO) out is a very effective way of avoiding an unacceptable increase in pest numbers.
3.1.4.2. Investigation of Failures:
The assessment of whether a treatment succeeded and investigation of failures, should be an integral part of fumigation management. Remedial action can then be planned to avoid new and further failures, and optimise procedures.
Fumigation must be deemed to have tailed if measurements of fumigant concentration throughout the fumigation interval do not confirm that an adequate concentration x time (Ct) product has been attained, even though no live insects are found immediately after fumigation.
In cases where a natural infestation was evident at the time of treatment, some evidence of the efficacy of the fumigant may be obtained by inspecting the treated commodity following the fumigation and ventilation. Visual inspection of insects from half kilo grain samples, taken according to standard sampling procedure, will he required. Such inspection will give an estimate of the mortality of adult stages, but detection of any surviving immature stages generally requires incubation of grain samples. These should be held in ventilated containers at 25-35°C for six weeks before being re-examined.
This particularly concerns application of the fumigant and subsequent opening of the enclosure for airing. These are the operations during which the greatest risk occurs of accidental exposure to harmful concentrations of fumigant. Because of the risk of accidental exposure, protective equipment must he worn as appropriate and he available for rescue purposes.
3.1.5.1. Monitoring; Health of Operators:
It is essential that the employer initiate a compulsory program of monitoring of the health of fumigation operators. Advance warning of the development of medical conditions incompatible with work as fumigation operators will enable measures to be taken to lessen the risk of occupational health problems developing in the operators.
3.1.5.2. Fumigation Personnel:
3.1.5.2.1. Minimum Number of Persons:
There should never be fewer than two people present during the introduction and removal of a fumigant, irrespective of how small the dosage or how restricted the extent of the fumigation. One of these people should always be designated as the Fumigator-in-Charge and be appropriately qualified (Refer TDS #10). In emergencies, where a person becomes incapacitated in a fumigation enclosure or risk area, the rescue team must include one person who does not enter the enclosure or risk area. It is this person's sole duty to seek further assistance in the even of the rescuers also succumbing.
3.1.5.3. Use of Safety Equipment:
3.1.5.3.1. Respirators:
All fumigation procedures must be carried out using techniques which minimise the risk of exposing pest control operators, other workers, and the general public, to toxic gases.
Although it is not general practice for operators applying phosphine to wear respirators, a full face mask with appropriate gas canister should be available at all times in case of accidents. Respirators may he especially necessary during large-scale phosphine applications in poorly ventilated stores, and should be worn during the unsealing of sheets at the start of the gas ventilation period.
During the application of methyl bromide and the removal of sheets to ventilate stacks, respirators with appropriate canisters must he worn by all operators involved. At least two staff should be involved in these operations, one being designated in charge.
There are no visual means to indicate when the useful life of respirator canisters has expired. If proper fumigation procedures are followed operators should never be exposed to dangerous concentrations of fumigant, and canisters should therefore have a long useful life. Where, however, exposure to an unusually high level of fumigant occurs, such as the fracture of methyl bromide piping or cylinder connection, the canister involved should he discarded immediately and not used again. All canisters should he re-closed with their original seal when not in use. As a general rule, canisters should not be used for longer than one year.
However, the latest regulations advise that, where canisters such as type AX (for organic vapours with boiling points of less than 65°C) are used for protection against methyl bromide, they should be discarded after a single use. This is because, after use, desorption of fumigant can occur within the canister, allowing methyl bromide to move through the adsorbent. This may then be inhaled directly on the next occasion the canister is used.
3.1.5.3.2. Gas detector tubes:
The safety of operators working in stores can he assessed using detector tubes, into which gas is drawn, Using a handpump. A stain is produced in the graduated portion of the detector tube when fumigant is drawn in, the length of the stain indicating the gas concentration present in air. Fumigant concentrations at the level of the occupational exposure standard (OES), can be measured with these tubes although the accuracy can vary. Detector tubes have fixed shelf life and should not he used once the expiry date has been reached. Tubes must he kept refrigerated.
3.1.5.3.3. Estimation and Detection of Fumigants:
In a well-conducted fumigation the fumigant concentration achieved within the enclosure is measured from time to time during the exposure period. Fumigant concentration should be monitored in workspaces close to enclosures under gas. After a fumigation it is necessary to check that the fumigant has been aired off adequately. It may also he necessary to check residue levels in the treated commodity. The information on fumigant concentrations during a treatment provides a check on whether the intended dosage and distribution were, in fact, achieved. The other data are required for safety and sometimes for legal or contractual reasons.
Industrial hygiene standards for worker exposure to fumigants have been established. These are based on a time weighted average concentration for a normal 8-hour workday and a 40-hour workweek, to which all workers may he repeatedly exposed, day after day, without adverse effect.
The concentration to which workers can he exposed continuously for a short period of time without suffering from (1) irritation, (2) chronic or irreversible tissue damage, or (3) narcosis of sufficient degree to increase the likelihood of accidental injury, impair sell rescue, or materially reduce work efficiency-provided that the daily TLV-TWA is not exceeded-is defined as the Threshold Limit Value-Short Term Exposure Limit (TLV-STEL).
Daily Threshold Limit Values - Time Weighted Averages (TLV -TWA)*
|
|
ppm (v/v) |
g/m3 |
|
Phosphine |
0.3 |
0.0004 |
|
Methyl bromide |
5 |
0.019 |
* American Conference of Governmental Industrial Hygienists (1988). Ceiling limit that should not he. exceeded during any part of the working exposure
A Short Term Exposure Limit is defined as a 15 minute time weighted average exposure which should not he exceeded at any time during a workday, even if the 8- hour time weighted average is within the TLV. Short term exposures should exceed three times the TLV-TWA for no more than a total of 30 minutes during a workday and UNDER NO CIRCUMSTANCES should they exceed five times the TLV-TWA provided that the TLV-STEL is not exceeded.
The current OES¹ values are as follows:
¹ Occupational exposure standard, which is equivalent or synonymus with Threshold Level Value. (TLV) in some countries.
Phosphine:
0.3 parts per million (ppm), 0.4 mg per cubic metre, per 10 minute reference period. Phosphine can sometimes be detected by its smell at this limit, hut no reliance can he placed on this as a safety factor.
Methyl bromide:
5 parts per million (ppm), 8-hour time-weighted average, and 15 ppm, 10 minute reference period. Methyl bromide is not detectable by smell at gas concentrations normally used for fumigation purposes. 2% chloropicrin is often added to methyl bromide as a tear gas. to provide operators with a warning that fumigant is present in the workplace. The sweet-smelling ester amyl acetate has also been used as a warning agent. Halide leak detector lamps also provide good indications of the presence of methyl bromide. The functioning of these detectors is the colour changes occurring, in the presence of halides, to gas flame burning within a copper ring. These changes vary from. pale green, at the lowest level of detection (ca. 10 ppm), to intense blue at the highest (> 1000 ppm). It is important to note that these detectors do not give clear indications at the level of the OES (5 ppm) for methyl bromide, and cannot be relied upon to give precise information of safety levels at, or near to, the OES.
3.1.5.4. Protective Clothing:
As well as appropriate breathing apparatus, operators releasing all fumigants except carbon dioxide should wear completely buttoned boiler suits (coveralls or overalls) and, protective gloves2 and footwear.
² Gloves should not be worn when applying methyl bromide.
3.1.5.5. Safety Harness and Ropes:
When fumigators are required to enter fumigation enclosures that have difficult access, safety harnesses and lifelines must he worn.
3.1.5.6. Detection Equipment:
Appropriate detection equipment, e.g. halide lamps, conductivity meters, and detector tubes, should he on hand for the fumigants proposed for use. The equipment should he tested regularly and maintained in good working order at all times.
3.1.5.7. Lighting:
Adequate lighting, including approved design torches, should be available for all fumigations. The lighting equipment should he suitable for use in flammable atmospheres, including those generated from grain dust.
3.1.5.8. FIRST AID PROVISIONS
3.1.5.8.1. Instruction in First Aid:
All fumigators and their assisting personnel should he instructed in first aid and other emergency procedures specific to fumigation.
3.1.5.8.2. Medical Kit:
A first aid kit including items specific to fumigation should he available at all times. Advice on the content of this kit should he sought from the appropriate government health authorities.
3.1.5.8.3. Recovery of Affected Personnel:
Protective clothing and self-contained breathing apparatus must he used when recovering affected personnel from areas where fumigants are present. The affected personnel should he moved to fresh air, placed in a restful position and kept warm while awaiting medical attention.
3.1.5.9. METHODS FOR SAFE STORAGE AND HANDLING OF GAS CYLINDERS:
Cylinders of poisonous gases are potentially dangerous, because of their contents and because they are generally under high pressure. Fortunately, the risk of mishap can he virtually eliminated if a few simple rules are followed.
3.1.5.9.1. Move and store cylinders correctly:
3.1.5.9.2. Keep Cylinder Cool:
This rule should he printed on every cylinder label. Pressure will rise within the cylinder should it become heated by, for example, being located near a burner, heater, or oven, or left in full sunlight.
· Store full and empty cylinders apart to avoid confusion and interruptions to fumigation procedure.
· Keep cylinders upright at all times during use and transport.
· Do not drop cylinders or otherwise subject them to severe physical forces.
· Protect cylinders from being accidentally knocked over.
· Protect cylinders stored in the open against rusting and extremes of weather. Cylinders should not he stored in conditions likely to encourage corrosion.
3.1.5.9.3. Take extreme care with poisonous gases:
Know and understand the properties and hazards associated with each gas before using it. Only personnel familiar with and trained in the use of poisonous gases for fumigation should he allowed to handle them. Personnel handling these gases should have available, for immediate use, canister gas masks or self-contained breathing apparatus of a design approved by the appropriate authorities. Fumigation personnel should he regularly trained in the use of this equipment.
3.1.5.9.4. Use gas in strict accordance with the suppliers' requirements and instructions:
Make sure that suppliers' instructions are available and understood by everyone using gases during fumigations. In releasing a fumigant gas, use equipment and an application process that have been approved by the gas supplier. Follow the instructions fully; do not take shortcuts.
3.1.5.9.5. Read the label on the gas cylinder:
Many cylinders look alike. The gas name label is the only way to tell what gas is inside the cylinder. Do not deface the label. The use of the wrong gas could he, at best, extremely inconvenient and, at worst, disastrous.
3.1.5.9.6. Avoid leaks:
All compressed gases (other than air) can create a hazard if they leak into the atmosphere. Even small leaks are dangerous in a confined space, as the concentration can build up over a period of time. the danger applies not only to poisonous and flammable gases, but also to gases such as carbon dioxide which is not only toxic, hut also in sufficient quantity in a confined space will produce an atmosphere deficient in oxygen.
Test for leaks as follows:
· attach and tighten regulator, hose and equipment;
· shut off control valve on equipment;
· open cylinder valve and screw in regulator control knob to pressurise system;
· close cylinder valve and watch pressure gauges;- if pressure is retained, there is no leak is present;- it pressure drops, a leak is present; it should he located by going over the equipment and hoses with soapy water and a brush, and corrected.
3.1.5.9.7. Be prepared for emergencies:
Make sure the gas supply can he turned off quickly in an emergency. Keep appropriate emergency equipment close at hand. Make sure that emergency telephone numbers - fire brigade, doctor, ambulance-are readily available.
3.1.5.9.8. Fumigant cylinders:
Methyl bromide is delivered from cylinders ranging in content from 18 to 100 kg of the fumigant. The cylinder valves should he checked with a halide lamp when taking the cylinder out of store. The amount of methyl bromide applied should be determined by weighing the cylinder before and after application. The cylinder should he placed on a portable platform scale capable of weighing at least 150 kg or it may he suspended from a spring balance attached to a tripod. Alternatively, the exact amount of methyl bromide required may he transferred by weighing from a large cylinder to a small cylinder. The small cylinder can then he taken to the stack. This avoids moving the balance, hut the small cylinder must he pressurized to ensure effective delivery.
Cylinders may have a single outlet closed by a wheel valve (A in figure la), with a dip tube to the bottom of the cylinder, or two outlets (figure 1b), of which one outlet has no dip tube and is used for pressurization of the cylinder. The other outlet is for delivery, has a key valve, B, and a dip tube to the bottom of the cylinder. As shown in figure 3.2, the cylinders need a delivery fitting that incorporates a Schrader valve, C, a gauge, D, a wheel valve, E, additional to the wheel or key valve on the cylinder, and a filter, F. The filter contains glass wool to prevent dirt and rust from getting to the nozzles. The size of the connecting joint varies with the manufacturer and the fitting must have an adapter suitable for the cylinder (some cylinders have a 3/8 inch (1 cm) male thread.) However, apart from the special connection to the cylinder, the rest of the line couplings should he a standard 10 mm.
To assist in applying the fumigant, the pressure should he raised to 80 to 100 p.s.i. (550 - 690 kN/m²). This may he achieved by means of a heavy duty car foot pump, although it is preferable to use a compressor. Cylinders with a single outlet can he pressurized through the delivery valve, hut not while delivery is taking place. With cylinders having two outlets, the pressure can he kept at a constant level throughout the entire application. The pressure should not he allowed to fall below 40 psi. (275 kN/m².)
The opening of the valves should he carried out by two persons wearing respirators and using a halide lamp to detect leakage. All other personnel should stand at a distance. A rapid release of large quantities of methyl bromide can take place if valves are faulty or Joints are loose. In this case, the valves must he closed tightly and the sources of leakage attended to. With valve E closed (figure 1), valve A or B should he opened and the pressure checked and increased if necessary. Valve E should then he opened cautiously and a small amount of methyl bromide (about 10 percent of the dose) introduced into the stack. Valve E should he then closed and the whole system checked for leaks. Joints should be tightened, if necessary, and any leakage around the stack sealed off.
In the event of an emergency where gross leakage occurs due to breakage or disconnection of a delivery pipe, the main cylinder valve should be turned off and the team should withdraw. After a period of ventilation, an operator, wearing a respirator, should check that the area is clear with a halide lamp or detector tubes before carrying out the necessary repairs.
When the gas tightness is satisfactory, the required dose should be applied. After closing valve A or B, the lines should be cleared by applying compressed air through the side valve, C, and the cylinder should then be disconnected.
Figure 3.2. Methyl bromide cylinders and fittings.
Figure 3.2. Methyl bromide cylinders and fittings.
