Frequently Asked Questions
Fumigation is a controlled process in pest control whereby a fumigant is released into an enclosed space in a gaseous state in sufficient concentration and duration to eliminate all life stages of the target pest. Pest Control Operators (PCOs) are required to be licensed by the authorities before they are permitted to carry out fumigation using any of the approved fumigants in the country. In Singapore, 2 types of fumigants are approved for use: a) Methyl Bromide and b) Hydrogen Phosphide. Only licensed fumigators are authorised to carry out fumigation in accordance with the Hydrogen Cyanide (Fumigation) Act Chapter 132 and the Hydrogen Cyanide (Fumigation) Regulations Chapter 132 Section 2. A permit has to be applied and approved by the National Environment Agency (NEA) 24 hours before the fumigation takes place.
Fumigation requires the use of fumigants which in sufficient concentration are highly toxic and lethal to humans and animals. A fumigation treatment can only be carried out by persons specially trained and licensed to apply the fumigants. Entering a fumigated area requires the use of an appropriate respirator or a self-contained breathing apparatus. During fumigation, the fumigant is released into a tightly sealed enclosure and it remains in a gaseous state for a required period of time in sufficient concentration to kill all life stages of the target pest.
Pesticide treatment is not fumigation. Pesticides are mixed with the required diluents mainly water to form a chemical solution of sufficient concentration which is then sprayed on the target areas to kill targeted pests on contact or to leave a residual effect on the surfaces. Common treatment methods include thermal fogging for mosquitoes, ultra-low volume fogging or residual spraying for stored product pests, cockroaches and bedbugs.
Insect pests or other pests found living in or around the product, may hide in hard to reach cracks and crevices in the storage facilities. None of the pesticide formulations which are sprayed in such places will be effective in containing the pests. It is only the fumigant which has the ability in its gaseous state to penetrate such inaccessible spots and eradicate the pests. When a pest population warrants a treatment, fumigants are the best tool to penetrate into structures and commodities without leaving a dangerous residue. However, fumigants can be hazardous and deadly and require a specialized team to apply the fumigant and carry out the fumigation process.
Fumigants only control existing infestations in the cargo. They do not provide any residual protection against subsequent re-infestation. Any timber that has been treated by Methyl Bromide must be shipped within 21 days of treatment. During this 21-day period, it should be kept isolated to prevent cross infestation between fumigated and unfumigated cargo. Similarly, for stored food products, fumigated commodity must be kept apart from infested unfumigated stock to prevent cross contamination from stored product pests.
- Quarantine Pre-shipment Fumigation for ISPM 15 compliance - Fumigant used: Methyl Bromide
- Stored Food Products (e.g. tobacco, milk powder, spices, flour) - Fumigant Used: Hydrogen Phosphide
ISPM 15 refers to the ‘International Standards for Phytosanitary Measures Publication No. 15: Guidelines for Regulating Wood Packaging Material in International Trade’. ISPM 15 was developed and endorsed by The United Nations Food & Agriculture Organisation (FAO) to address the global spread of timber pests by regulating the movement of timber packing and dunnage in international trade. ISPM 15 describes phytosanitary measures to reduce the risk of introduction and spread of quarantine pests associated with solid timber packing material.
Methyl bromide is absorbed by oils, fats and finely ground materials. It is also known to react with materials containing sulphur, including food stuffs and proteins to produce objectionable discoloration and odours which may persist even after prolonged aeration.
Methyl Bromide fumigation should be carried out for packing materials such as wooden crates, skids and other packing materials. The maximum thickness of the packing wood must not exceed 200 mm.
The dosage to be administered is 48 grams per cubic meter. The WPM is placed on a smooth uncracked cement or concrete floor and covered with tarpaulin sheets which must be certified gas -proof to contain the gas and sealed with sandsnakes. Gas monitoring lines for measuring gas concentration is to be placed at different locations within the sealed enclosure. The total cubic area of the enclosure is measured and the required dosage of methyl bromide is released into the enclosure. Gas monitoring is then carried out during the exposure period. After 24 hours the fumigation covers are removed and the cargo is aerated until the gas concentration drops below 5ppm.
Methyl bromide is listed as a compound that may be absorbed through the skin as well as by the respiratory system. High concentrations of methyl bromide on humans may bring about death through pulmonary injury and associated circulatory failure. The onset of toxic symptoms maybe delayed and the latent period may vary between 0.5 to 48 hours, according to the intensity of the exposure and the personal reaction of the patient. Contact of the human skin with the liquid or strong concentrations of the gas may cause severe blistering.The threshold limit for an 8-hour daily exposure to Methyl Bromide should not exceed 5 ppm. Studies indicate that daily exposure to concentrations of 20 to 100 ppm can quickl y bring about severe neurological symptoms. Exposure for only a few hours to concentrations of 100 to 200 ppm may cause severe illness or death.
Against insects, Methyl Bromide exerts its principal toxic effect on the nervous system. As in humans, the onset of poisoning symptoms may be delayed and with many species of insects’ definite conclusions as to the success of the treatment should be delayed for at least 24 hours.
The insects absorb fumigant through their respiratory system as they breathe through small openings in their skin. Insect breathing depends on several factors including temperature and humidity. The higher the temperature the faster they breathe and take in Methyl Bromide. Their metabolism is temperature dependent. Conversely the lower the temperature the more inactive they become. Their respiration is affected by the humidity in their environment. The drier it is, the slower they breathe to conserve body water.
For the purpose of monitoring Methyl Bromide concentrations within the fumigation enclosure to check the efficacy of the treatment as well as to detect any serious leaks in the air within the risk area for protecting personnel during fumigation and subsequent aeration, the devices to be used are:
- Riken FI-21 – for measuring MB gas concentration within the fumigation enclosure
- Riken GH 202F/Riken SP-220 -for measuring MB gas concentration in the surrounding area
In Singapore, Methyl Bromide is supplied in liquid form in 20 kg & 50 kg steel cylinders. To discharge the fumigant, the liquid from the cylinder is passed through a heat exchanger or vaporizer which is a special container with copper coils immersed in water heated to 65 C. This causes the liquid Methyl Bromide to be immediately vaporised by the heat and converted into a gaseous form.
Respiratory protection must be in the form of a full-face gas mask with an AX filter or a self-contained breathing apparatus.
Prolonged contact of liquid Methyl Bromide with the skin produces severe blisters similar to those caused by burns or extreme chilling. Great care should be taken to avoid spilling liquid Methyl Bromide on clothes, gloves or footwear. Since there is no sensation produced by such contact, Methyl Bromide may be maintained in contact with the skin for extended periods without an awareness that this has occurred.
As soon as possible after Methyl Bromide is spilled on clothing or footwear, it should be removed and thoroughly aired. If it has remained in contact with the skin so that blisters form, the blisters should be left intact and the area covered with a sterile dressing. If liquid Methyl Bromide is spilled on any part of the body, although it will evaporate quickly, the parts touched should be washed with soap and water immediately.
There is no known antidote for Methyl Bromide poisoning. Also, because the onset of symptoms maybe delayed for as long as 45 hours, there are no specific procedures to bring about immediate recovery. However, there are certain well-defined symptoms which, except in cases of exposure to high and rapidly fatal concentrations, may serve as preliminary warnings of initial poisoning. If, on experiencing these symptoms, the fumigator immediately abstains from further contact with Methyl Bromide and places himself under medical supervision, there is every prospect of complete recovery.
If the affected individual is seriously poisoned, it is advisable for all other members of the crew to place themselves under medical observation immediately.
A blood bromide level should be obtained immediately on any individuals suspected of being exposed to methyl bromide.
- nausea and vomiting
- loss of appetite
- abdominal pain
- double or blurred vision
- impaired, slurred speech
- unusual fatigue
- mental confusion
- Make sure the fumigation enclosure is air tight
- Wear protective chemical suits, plastic gloves and full-face gas mask fitted with AX filter if the gas concentration is unknown or if it exceeds the threshold limit value of 5ppm
- The area surrounding the fumigation enclosure should be well aerated
- No work should be carried out within 6 m of the fumigation area
- The ambient air should be monitored to determine if the gas concentration level is within the acceptable threshold limit value
- A first-aid kit equipped with the proper materials should be readily available at the fumigation site
- Do not eat, drink, smoke in an area where fumigation is carried out
- To display danger sign boards at the fumigation area indicating skull with cross bones with the information on ‘AREA UNDER FUMIGATION. DO NOT ENTER’
At relative humidity of over 75% and temperature of 25°C, maximum release of phosphine occurs in 45 hours. The minimum phosphine concentration at end state should not drop below 300 ppm on the last day of fumigation after 72 hours of exposure period.
To calculate the amount of phosphine required, 2 key factors need to be established:
- the total cubic volume of the cargo i.e. the length, breadth and height of the stack.
- the dosage stipulated by the client
Using the cubic metre of the stack, the number of hydrogen phosphide plates to be used is derived by multiplying the total cubic volume (cbm) by the dosage (2g) and dividing the outcome by 33g to determine the number of plates required. (Each hydrogen phosphide plate contains 33 g of phosphine)
- cbm x dosage / 33g
Phosphine ranks as one of the most toxic fumigants for stored product insects. It is a slow acting poison that is effective at very low concentrations with sufficient exposure time. Usually, exposure time of 4 or more days are required to control insects, depending on the temperature. Ideal temperature wld be more than 20⁰ C. The exposure time however cannot be shortened by increasing the dosage; in fact, high concentrations can have a narcotic effect on insects thereby reducing mortality and increasing the chances of resistance in insects and consequently causing the effectiveness of phosphine to be reduced considerably by development of resistance in insects.
Some stages of insects are considerably more tolerant to phosphine than others. The eggs and pupae are usually hardest to kill while larvae and adults succumb more easily. Hence the need for a sufficient exposure period to ensure that all life stages are killed.
- Drager X-AM 5000 – to measure the gas concentration within the fumigation enclosure. This is critical to enable the fumigator to monitor if the gas concentration is maintained above the required levels to ensure the efficacy of the treatment. Should the concentration drop below the stipulated threshold of 300 ppm, sufficient top-up of the fumigant must be applied to raise the concentration and extend the exposure time.
- Drager PAC 7000 – to measure the gas concentration within the fumigation risk area is kept below the TLV of 0.1 ppm.
Disposal of phosphide plates is done by placing the spent plates in a cylindrical metal basket and immersing the container into a drum of water and leaving it to soak for 24 hours or more until all reside gas in the used plates has been liberated. The plates can then be discarded as general waste. The waste water used for treating the spent plates must conform to local government regulations on the treatment of waste water before in can be discarded in the sewage or waterway.
For aluminium phosphide pallets, the residue powder (aluminium hydroxide) from the tablets, should be slowly added to a drum of water with detergent as a wetting agent and stirring it into the water until a slurry is formed and the residue sinks.
For purposes of safety the disposal procedure should be carried out in the open air, where any generated phosphine can rapidly disperse and workers carrying out the process are protected with the appropriate respiratory equipment.
Phosphine reacts with certain metals, particularly copper, copper compounds, silver and gold to cause corrosion. High humidity and temperature appear to favour the reaction.
As a result of this reaction any copper-containing equipment, especially electrical apparatus, may be severely damaged. During fumigation of buildings with phosphine, special attention should be given to electric motors, electric wiring, switches, fire alarm systems, electronic systems or other pieces of equipment that contain copper.
If equipment that is liable to damage cannot be removed from the area being treated some protection may be afforded by coating copper materials with a thin layer of paraffin, spraying with a light lubricating oil.
Phosphine is very toxic to all forms of animal life, hence exposure of human beings even in small amounts should be avoided. Poisoning can result from ingestion or inhalation; however, the gas is not absorbed through the skin. The threshold limit value-time weighted average (TLV-TWA) for an eight-hour daily exposure in a five-day week is set at 0.3 ppm. A concentration of 2000 ppm is known to be lethal to humans.
For personal protection against the vapours of phosphine at concentrations above the threshold limit, a respirator with an A2B2 filter must be used. Such respirators however will give protection up to 0.5 percent phosphine by volume in air. Above this concentration, air must be supplied by a self-contained breathing equipment. The Drager PAC 7000 must always be available on hand with the Fumigator to keep a tab on the level of phosphine concentration to decide on the appropriate respiratory device to be used.
1. Chemical gloves should be worn when tablets or pellets are being dispensed by hand.
2. Respirators i.e. full faced gas masks with an A2B2 canister or self-contained breathing apparatus need to be worn when phosphine plates, tablets or pellets are being dispensed
3. The Drager PAC 7000 must always be available on hand with the Fumigator to keep a tab on the level of phosphine concentration in the surrounding area.
4. Do not smoke or touch food at any time during the application of the fumigant
5. Any spaces adjoining or close to structures undergoing treatment with phosphine should be kept continuously aired by leaving windows open or by providing artificial ventilation by means of fans or blowers.
6. All persons working in any place near the fumigation area must be notified that fumigation is in progress. No work should be carried out within 6m of a fumigation zone. Warning notices should be posted to prevent exposure of employees or the public at large to the gas.
7. When the fumigation is completed and aeration of a structure is undertaken, full precautions must be undertaken to ensure that no person is exposed to residual vapours of the fumigant.
Should a person become exposed to phosphine as a result of inattention, negligence, failure to follow proper procedures or some other reason and as a result, symptoms consisting of fatigue, ringing in the ears, nausea, or pressure in the chest appear, he should immediately go into the open fresh air. Symptoms of poisoning by a small quantity of phosphine will normally disappear when a person is removed to the fresh air. However, despite the seeming insignificance of even mild cases of poisoning with symptoms as described above, first aid measures are necessary before and until the arrival of a doctor.
A. Remove patient from exposure area into open area with fresh air. Keep at rest.
b. If the patient is unconscious, place in semi-prone recovery position or otherwise maintain the airway.
c. If patient is conscious but has difficulty in breathing, treat in a seated position and give oxygen if available.
d. Allow patient to recline with the legs slightly elevated.
e. If breathing stops, immediately ventilate the patient artificially.
f. If the heart stops, begin cardiopulmonary resuscitation-CPR. Under no conditions should an affected person resume work during the next 48 hours, particularly work dealing with fumigation, as it takes time for the body to eliminate the poison completely. Complete abstinence from alcoholic beverages after any poisoning is strongly recommended.
According to the amount of phosphine inhaled, symptoms may occur immediately or several hours after exposure. Slight or mild poisoning may result in fatigue, ringing in the ears, nausea, pressure in the chest and uneasiness. All these symptoms will normally disappear in fresh air.
Greater quantities will quickly lead to general fatigue, nausea, gastrointestinal symptoms with vomiting, stomach ache, diarrhoea, disturbance of equilibrium, strong pains in the chest and dyspnoea (difficulty in breathing).
Very high concentrations rapidly result in strong dyspnoea, cyanosis (bluish-purple skin colour), agitation, ataxia (difficulty in walking), anoxia (subnormal blood oxygen content), unconsciousness and death. Death can be immediate or occur several days later due to oedema and collapse of the lungs, paralysis of the respiratory system or oedema of the brain. Disturbances of kidney and liver functions (haematuria, proteinuria, uraemia, jaundice) and cardiac arrhythmia may occur.