Technical profile: Shipboard fumigation
July 01, 1995
by Teresa Acklin
Contributed by suppliers, technical profiles feature new technology, products, specific applications or proprietary concepts. This material was prepared by the International Maritme Fumigation Organization Ltd. (IMFO), London, a group formed recently by independent companies involved in providing shipboard fumigation services.
The use of fumigants on board ships has been well known for many years. Initially, fumigation mainly involved the use of hydrogen cyanide to treat the empty vessels when they became rat infested.
The acute toxicity of hydrogen cyanide and the many deaths of workers involved caused it to be replaced in many countries by methyl bromide. Methyl bromide's speed of action and efficacy have made it the fumigant of choice for this application, but recently, questions have developed about its environmental impact (see story on page 12). The future of methyl bromide may be uncertain, and no foreseeable alternative exists for shipboard rodent control, other than to reconsider hydrogen cyanide.
Methyl bromide also has been widely used for the fumigation of both bulk and container cargoes in transit. This use is being replaced by the fumigant phosphine, which is produced from either aluminum or magnesium phosphide. Although phosphine is a much slower-acting fumigant than methyl bromide, it has the great advantage, if used correctly, of leaving no detectable residues.
Phosphine is now widely specified in many international contracts. Members of the International Maritime Fumigation Organization Ltd. (IMFO) recognized the enormous difference between standards of fumigation provided to the international trade and have set out to achieve the following objectives:
to ensure that safety is not compromised for commercial expediency. Phosphine is a dangerous and highly toxic gas, which is often used in a way that can endanger people not directly involved in the fumigation;
to provide systems that will ensure total eradication of all stages of the insect life cycle so that resistance to fumigants will not be increased;
to provide environmentally friendly systems and procedures, which will minimize both pesticide use and subsequent residues; and
to provide the client with the necessary information so that he can understand precisely what he is likely to get in terms of efficient insect control and residues in relation to what he is paying. The client must request fumigation on the basis of a specific technical requirement and be assured he is provided with what he requests.
For many years, the use of fumigants and other pesticides on board ships has been subject to recommendations laid down by the United Nations International Maritime Organization, which has more than 100 countries as signatories to the agreement. These recommendations are currently being reviewed to reflect today's increasingly widespread use of phosphine and to provide a sound basis for safe practice.
Recognizing that the general practice worldwide is to ignore the vast majority of the U.N. recommendations, IMFO members ensure that they not only are followed, but in fact enhanced. For example, IMFO members not only will provide safety equipment and instruction, but will ensure that these are written down in a very simple, straightforward and usable form. It is recognized that despite the number of times a ship has been fumigated, the ship's conditions and the crew itself both will change.
Also, it is simple to arrange for the powdery residues remaining after fumigation, as well as the phosphine gas itself, to be disposed of at the port of discharge by trained fumigators. This step must be organized correctly to increase safety and reduce the risk to crew and dock workers. Through IMFO, this option can be provided economically and reliably.
Fumigants are very effective at eradicating insects, but they work on the basis of concentration and time. Thus, the first objective of the fumigator is to get fumigant to all parts of the cargo.
Methyl bromide generally sinks relatively rapidly to the bottom of the hold, whereas phosphine generally does not. Convection currents and other air movement within the hold sometimes help and sometimes interfere with gas distribution.
To overcome the relatively poor distribution of the fumigants, the rates of application need to be increased. For example, surface application of phosphine will take at least several days to penetrate a few meters into the cargo; application probed into the cargo will penetrate and distribute more quickly and fully.
To enhance efficacy, the practice of probing tablets or pellets deep into the cargo using vacuum probes was developed. But this has the disadvantage of leaving the powdery residues mixed with the cargo.
To dispose of the residues safely and rapidly at discharge, the aluminum or magnesium phosphide must be in some sort of retrievable packages. Therefore, ideally a re-circulation system can be used to create a controlled air movement in the hold during the fumigation. The fumigant is then distributed quickly and evenly, and the powdery residues can be easily removed at the end of the fumigation.
There are many other options; some are effective and some certainly are not. By making use of the well established scientific facts regarding distribution, concentration and time, fumigation can be used predictably.
IMFO currently has members in Europe, North America and Africa and representatives in many other locations. Member companies must conform to strict requirements and often are accepted on a probationary basis, working as a representative under the control of other members.
The potential advantages resulting from a group of independent expert companies working together but also competing with each other, as well as multi-national fumigation and pest control companies, appear to be significant. For example, research and development work in a wide range of conditions is currently under way. Potential beneficiaries are not only traders, but buyers of the goods, end users, insurers, dock workers, the ship owners and their crews.