Chemical tankers

Many of the changes in everyday life that have taken place during the last fifty years have resulted from developments in the chemical industry. A wide range of ordinary items are in fact derived from complex chemical processes, and are often derived from the by-products of the production of energy. Some perfumes and medicines are derived from coal: from oil and gases we obtain fertilizers and plastics, weed killers and detergents, clothing and paints.

The greatest advances made in the chemical industry have been made in the last 25 years and one result has been a rise in the demand for raw materials. This in turn has led to a great increase in the maritime transportation of chemicals and the development of specialized ships in which to carry them.

The ships that have been built in response to this demand are among the most complex ever constructed. The cargoes they carry often present tremendous challenges and difficulties from a safety point of view and many chemicals are also a far greater pollution threat than crude oil.

Yet despite this, chemical tankers are among the safest ships afloat. One reason for this is the action taken by the industry and governments to adopt and implement stringent regulations regarding both safety and pollution prevention.

The chemical trade

To most of us, chemistry seems to have little relevance to everyday life. In fact, the products of the chemical industry are all around us. Much of the food we eat is grown with artificial phosphate and nitrate fertilizers and protected with pesticide and herbicide sprays. Many of the clothes we wear are made of artificial fibres derived from various petrochemicals, which in turn may come from natural or petroleum gas. The same feedstocks can be used to produce weed killers, detergents for washing clothes and dishes, and anti-freeze for motor vehicle engines and artificial rubber. When we are ill we may turn to a patent medicine that comes from phenol, a derivative of coal. Almost every home contains toys, wire coating, packaging, records and other goods made from PVC, a versatile product that is derived from a combination of chemicals such as natural gas, oxygen, hydrochloric acid and common salt. And a modern world without plastics would be unthinkable.

The chemical industry has in fact transformed modern life and without it many of the products that we take for granted would never have been created. The raw materials for the chemical industry are almost as varied as its products and like any other raw materials have to be taken from where they are produced to where they are needed.

Much of this trade is carried out by ships, but the chemical trade is very different from other bulk shipping operations. In the first place, the tonnage involved is smaller. Crude oil is shipped in huge ships carrying up to half a million tons at a time. Chemicals are shipped in relatively small amounts. A crude oil tanker is usually dedicated solely to the carriage of crude oil. But a chemical carrier usually carries a variety of different products, all with different properties and, in many cases, presenting a multitude of difficulties and dangers.

The main chemicals carried in bulk can be divided into the following groups:

Heavy chemicals include substances that are produced in large quantities. Among the most common are: sulphuric acid, which is among the cheapest of all acids and can be produced from sulphur, air and water. It is also very versatile, being used for the production of phosphate fertilizer, explosives such as TNT, plastics such as rayon, purifying petroleum and removing oxides from metals and in storage batteries; phosphoric acid is used for the production of superphosphates and various other products, including detergents, paints, and foodstuffs: nitric acid is a basic ingredient of explosives, nitrate fertilizers and many dyes, and plastics; caustic soda is also shipped in liquid form. Others include hydrochloric acid, which is used in the steel reduction process and ore reduction, and ammonia.

Molasses and alcohols: molasses comes from either sugar beet or sugar cane and can be fermented into alcohols such as rum. Many alcohols are produced by the petrochemical industry, but some can also come from the fermentation of starch, such as ethanol. Alcohols of this type, including ethyl, methyl and propyl, are used in industrial processes (for example, to make cellulose acetate, which is a thermoplastic moulding compound used in the manufacture of telephones, buttons, films and many other products). Wines and some beers also come into this category and are being increasingly carried at sea in bulk quantities on ships that are in fact specialized chemical tankers.

Vegetable oils and animal fats: edible vegetable oils are derived from soya beans, groundnuts, cottonseed, sunflowers, olives, rape and other seeds. Coconut and palm oil can be used for cooking and also in the production of soap. Industrial oils come from linseed and castor seed. Some fats are extracted from animals including lard and fish oils. Oils and fats are in general esters of an alcohol (glycerol) and a variety of organic acids. Detergents and inorganics are common commodities which have been traded by sea for many years.

Petrochemical products form the most complex and probably the most versatile group of chemicals carried in bulk. They are all carbon compounds basically derived from oil or gas. They are extensively used in the production of fibre, artificial rubber and plastics and many are carried on liquefied gas carriers. Substances carried in chemical tankers include aromatics, such as benzene, which nowadays are derived mainly from oil but can be produced from coal. Other important petrochemicals include xylenes (used in the production of polyester fibres); phenol (previously known as carbolic acid) and styrenes. But the number of different products is enormous and is growing all the time.

Coal tar products: coal tar is derived from the carbonization of coal. It can be converted into numerous products, many of which can also be produced from oil (oil and coal are both fossil fuels composed of hydrocarbons). The derivatives include benzene, phenol (used for the production of Bakelite, the first 'plastic'), naphthalene and many more. Common products which are derived from coal include nylon, aspirin, antiseptics and herbicides.

Chemical hazards and problems

As might be expected in a trade where the products are so varied, the hazards presented by chemicals vary enormously. The identification and evaluation of these hazards is of vital importance not only to the operation of chemical tankers but also to their design and construction.

Hazard evaluation of chemicals is in itself a complex problem stemming from the combination of the flammability and toxicity characteristics of the chemicals themselves as well as from design and operation hazards.

We can distinguish between the overall hazard to the environment and the intrinsic hazards of the chemicals. In respect of the former, the hazard rating profile developed by the Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP), based on the release into the sea of noxious substances, falls into four main categories:

1	Damage to living resources
2	Hazards to human health
3	Reduction of amenities
4	Interference with other uses of the sea.

The main hazards and problems are listed below:

1	Cargo density	the specific gravity of chemicals carried at sea varies greatly. Some are lighter than water. Others are twice as dense. Those substances which have especially high density include inorganic acids, caustic soda and some halogenated hydrocarbons.
2	High viscosity	some lubricating oil additives, molasses and other products are very viscous, especially at low temperatures. As a result they are sticky and move very slowly, causing problems in cargo-handling and cleaning.
3	Low boiling point	some chemicals vaporize at a relatively low temperature. This can causes containment problems, since when a liquid turns into a gas it expands, creating growing pressure. It is necessary, therefore, to provide either a cooling system or to carry the chemical in specially-designed pressure vessels.
4	Reaction to other substances	some chemicals react to water, to air or to other products. Measures therefore have to be taken to protect them. Apart from the fact that an accident can lead to a dangerous reaction (such as the emission of a poisonous gas) many chemicals can be ruined if they are contaminated by other substances. Methanol, lubricating oil additives and alcohols can be spoiled by even a slight amount of water contamination. Too much oxygen can lead to a rapid deterioration in the quality of some vegetable oils. Other products can change into a different product completely.
5	Polymerization	some substances, such as petrochemicals, do not need to come into contact with another chemical before undergoing a chemical change - they are selfÄreactive and liable to polymerization unless protected by an inhibitor. This is a process whereby the molecules of a substance combine to produce a new compound. The process can be accelerated by catalytic factors such as heat, light and the presence of rust, acids or other compounds. Styrene, methyl methacrylate and vinyl acetate monomer are examples. Propylene oxide and butylene oxide are also liable to polymerization.
6	Toxicity	many chemicals are highly poisonous, either in the form of liquid or vapour or both. The problem is sometimes made worse by the fact that toxicity can be increased when vapours from one substance come into contact with those from another.
7	Solidification	some substances have to be kept at a high temperature, otherwise they solidify or become so viscous that they cannot easily be moved. Examples are some petrochemicals, molasses, waxes and vegetable oils and animal fats.
8	Pollution	while many of the factors listed above present problems for the ship and crew, a considerable number of chemicals are extremely dangerous to marine and other forms of life. Although crude oil is probably the best-known pollutant of the sea, many chemicals are in fact far more poisonous and present a much greater threat - a threat which can be much more longÄlasting, since some of the chemicals concerned can enter the food chain and ultimately threaten humans as well as marine life.

It can be seen from the above list that chemicals present many difficulties to the shipowners and crew. A further complication is the fact that most chemicals are transported in relatively small amounts. The ships which carry them are consequently much smaller than crude oil carriers but are expected to carry several different products at the same time. It is probable that these products will have different and usually incompatible properties.

The development of the chemical tanker

The chemical tanker is basically a development of the last forty years. The development of the chemical industry in the United States following the end of World War II led to a demand for ships in which to carry the industry's products. A number of T2 tankers, mass-produced during the war, were converted by installing special tanks, double bottoms and suitable structural and piping arrangements.

Chemical carriers are smaller in size than crude oil carriers, but are technically far more complex. These pictures show typical chemical carriers now in service. The 3,466 dwt Tina Jakobsen was built in Germany in 1980. An IMO Class 2 ship, she is fitted with 17 stainless steel tank.	The Bro Nora is owned by Sweden's Brostroms Shipping Company. She was built in Spain in 1997. The 5,811 dwt ship has 13 stainless steel tanks.
The Norwegian flagged Kristin Knutsen is owned by Jo Tankers and is built to IMO I, II and III standards. The 12,184-gt ship was built in 1998.	The C.T. Sun was built in 1980 and is owned by Sweden's Brostroms group. She has a deadweight tonnage of 6,275 and operates in the North Sea and Baltic.

For the next decade or so tankers used in the carriage of chemicals were nearly all conversions. As the trade developed these ships became more refined, with the addition of tank linings, cofferdams and other features. The range of products carried in the first chemical tankers was relatively limited and the products themselves were not technically too demanding. The products also all tended to be owned by one company.

By the 1960s the chemical trade was becoming more complex. The number of substances being transported at sea was increasing rapidly - as was the total tonnage - and the products were technically more complicated. At the same time a growing number of what came to be called 'parcel tankers' were making their appearance. These were tankers designed to carry a range of chemical products for a number of different owners.

These ships were of necessity more complex than the original first-generation chemical tankers and during the early 1960s the first purpose-built chemical tankers made their appearance.

By the mid-1960s the chemical tanker had developed into a ship that was different from any other type, including other tankers. The cargoes carried by chemical tankers were probably potentially the most dangerous substances afloat, to the ships, their crews and to the marine environment. All of this made it imperative for something to be done to ensure that the ships themselves were suitable for the task.

From the outside some chemical tankers may look much like other tankers but in fact they are far more complicated (and ton for ton more costly). A crude oil carrier can afford to be big and ponderous because it normally carries one type of oil from one loading port to one destination on behalf of one shipper. A chemical tanker by contrast usually carries many different cargoes for a number of different customers and consequently has to be very versatile.

Despite their relatively small size (most are well under 50,000 dwt) chemical tankers normally have many more tanks than a bulk crude carrier - thirty or more is common. This gives greater flexibility and since the amount of individual cargoes carried are usually small (most are under 500 cu m), the small size of the tank is not a disadvantage. The pipe work associated with the tanks is also extremely complicated, as are loading and unloading arrangements. All procedures involving the cargo have to be carried out with great care and precision, both to avoid cargo contamination and also to ensure that cargoes owned by different shippers are kept separate. Piping, monitoring and control equipment is all highly complex.

Ship construction also has to be of the highest possible standard. Tank cleaning is crucially important to cargo purity, so traditional stiffening inside the tanks is minimized. This enables the tanks to be cleaned more easily. The tanks have to be designed and constructed in such a way that stresses are avoided as far as possible since these can lead to fatigue cracks or damage to the tank coating. The design itself has to take into account the type of cargoes which are to be carried: some cargoes are more than twice as dense as sea water while others have to be carried at high temperatures to stop them solidifying. Both of these factors can affect the structure. Welding and other constructional features must be of the highest possible quality.

Chemical tankers make far greater use of cofferdams, double bottoms and similar devices than conventional crude oil tankers. To ensure that incompatible cargoes do not come into contact with each other, tanks are usually separated by a cofferdam - a space between the two tank walls.

Most chemical tankers have their tanks separated from the outer frame of the ship by a double bottom or double skin. If the ship is damaged in a collision or a grounding this space should protect the cargo tanks from damage.

The tanks of a chemical tanker are constructed of special. materials, all designed to carry certain products. The early chemical tankers generally had tanks made of stainless steel which resists corrosion from many products and could be cleaned relatively easily. But stainless steel is unsuitable for many chemicals and so different coatings were designed. Typical coatings in use nowadays include epoxy, phenolic resins, zinc silicate, polyurethane and rubber. Each one has advantages and disadvantages and so far no coating has been developed which is suitable for all chemicals.

As a result, most chemical tankers, especially parcel tankers, will have tanks lined with a number of different coatings (as well as some made of stainless steel) to enable it to carry as wide a range of products as possible.

Some of the coatings in use today are listed below:

 

Chemical tanker safety

The subject of chemical tanker safety was first raised at the international level in the mid-1960s. and it was agreed that the whole matter should be discussed by the International Maritime Organization’s Maritime Safety Committee (IMO's senior technical body) in March 1967.

The MSC duly did so and agreed that a new sub-committee be established dealing with ship design and equipment. It should 'consider as its initial task the construction and equipment of ships carrying chemicals in bulk.' The new sub-committee held its first session in January 1968 and agreed to prepare a code to cover the design criteria, construction and equipment of chemical tankers.

The Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk (BCH Code)

The new code was applied to ships built on or after 12 April 1972 and its purpose was given in a preamble which states: 'This Code has been developed to provide an agreed international standard for the safe carriage by sea of dangerous chemicals in bulk by prescribing the constructional features of ships involved in such carriage and the equipment they should carry with regard to the products involved.'

The Code was not, in its original form, concerned with pollution aspects. IMO was fully aware of the threat which chemicals posed to the marine environment, but had decided to consider this aspect in the context of a new international convention on marine pollution which was then being prepared. This was ultimately adopted in 1973 as the International Convention for the Prevention of Pollution from Ships (MARPOL), Annex II of which is concerned with the prevention of chemical pollution.

The basic philosophy of the code is to classify each chemical according to the hazard they present and to relate those hazards to the type of ship in which they are carried: the more dangerous the chemical the greater is the degree of cargo protection and survival capability required.

The hazards considered in the new Code were:

(a)	Fire hazard defined by flashpoint, boiling point, explosion limit range and auto-ignition temperature of the chemical.
(b)	Health hazard defined by: (i) irritant or toxic effect on the skin or to the mucous membranes of the eyes, nose, throat and lungs in the gas or vapour state combined with vapour pressure   (ii)  irrational effects on the skin in the liquid state   (iii)  toxic effect via skin absorption
(c)	Water pollution hazard defined by human toxicity, water solubility, volatility, odour or taste, and specific gravity.
(d)	Air pollution hazard defined by: (i) emergency exposure limit   (ii) vapour pressure   (iii) solubility in water   (iv) specific gravity of liquid   (v) relative density of vapour
(e)	Reactivity hazard defined by reactivity with: (i)  other chemicals   (ii) water   (iii) the chemical itself (including polymerization) Three ship types are specified in the Code.

•		Type I ships must be able to survive assumed damage anywhere in their length. Cargo tanks for the most dangerous products should be located outside the extent of the assumed damage and at least 760mm from the ship's shell.  Other cargoes, which present a lesser hazard may be carried in tanks next to the hull.
•		Type II ships, if more than 150m in length, must be able to survive assumed damage anywhere in their length; if less than 150m, the ship should survive assumed damage anywhere except when it involves either of the bulkheads bounding machinery spaces located aft. Tanks for Type II cargoes should be located at least 760mm from the ship's shell and outside the extent of assumed grounding damage.
•		Type III ships, if more than 125m in length, should be capable of surviving assumed damage anywhere in their length except when it involves either of the bulkheads bounding the machinery space. If less than 125m in length, they should be capable of surviving damage anywhere unless it involves machinery spaces. There is no special requirement for cargo tank location.

If the ship is intended to transport more than one substance, the requirements for ships' survival correspond to the most dangerous substance, but the cargo containment requirement need only conform to the specified minimum requirements for the chemicals taken individually.

Within the ship itself other factors vary according to the hazard prescribed, such as tanks, tank vents, tank environmental control systems, electrical instruments, vapour detectors and fire protection. The Code contains seven chapters, the first of which covers general matters such as application, definitions, surveys and certification.

The BCH Code was developed in a relatively short space of time and it was recognized in 1971 that it was far from being the last word on the subject. The preamble to the original version says that IMO intended to either extend the code or adopt other codes to cover hazardous gases in bulk (in the event a separate code was developed); that the subject of the cargo size limitations warranted consideration; and that the section on fire protection was incomplete; and that the section dealing with electrical requirements needed to be re-examined. Work on improving the Code came to be a continuous process. Between 1972 and 1983 no fewer than ten sets of amendments were adopted, enabling the Code to be improved in many areas and to keep abreast of technical developments.

The Bulk Chemical Code, like other instruments adopted by the Assembly, is only a recommendation. There was no obligation on governments to adopt it in whole or even in part. In practice, however, the vast majority of chemical. tankers constructed since the Code was adopted were built in accordance with its requirements.

Preventing pollution by chemicals: Annex II of MARPOL

The International Convention for the Prevention of Pollution from Ships, 1973/1978 (MARPOL 73/78)[1] is the most important international treaty dealing with marine pollution ever adopted. Its technical provisions are contained in five annexes dealing with different pollutants. Annex II deals with pollution by noxious liquid substances carried in bulk.

These substances are divided into four categories, graded A to D according to the danger they present to the marine environment.

1	Category A	Noxious liquid substances which if discharged into the sea from tank cleaning or deballasting operations would present a major hazard to either marine resources or human health or cause serious harm to amenities or other legitimate uses of the sea and therefore justify the application of stringent antiÄpollution measures. Examples are acetone cyanohydrin, carbon disulphide, cresols, naphthalene and tetraethyl lead.
2	Category B	Noxious liquid substances which if discharged into the sea from tank cleaning or deballasting operations would present a hazard to either marine resources or human health or cause harm to amenities or other legitimate uses of the sea and therefore justify the application of special anti-pollution measures. Examples are acrylonitrile, carbon tetrachloride, ethylene dichloride and phenol.
3	Category C	Noxious liquid substances which if discharged into the sea from tank cleaning or deballasting operations would present a minor hazard to either marine resources or human health or cause minor harm to amenities or other legitimate uses of the sea and therefore require special operational conditions. Examples are benzene, styrene, toluene and xylene.
4	Category D	Noxious liquid substances which if discharged into the sea from tank cleaning or deballasting operations would present a recognizable hazard to either marine resources or human health or cause minimal harm to amenities or other legitimate uses of the sea and therefore require some attention in operational conditions. Examples are acetone, phosphoric acid and tallow. As far as the safety side was concerned, the position of the BCH Code was ambiguous. Although only a recommended instrument, it provides for the issuing of a Certificate of Fitness. Several countries require that ships entering their ports should possess this Certificate, even if they come from countries where the Code has not been implemented. As far as these countries are concerned, the Code has in effect been given convention status.

On the pollution side, the situation was rather different. Annex II dated back to the early 1970s and by the end of the decade was becoming outdated as a result of continuing technical developments. MARPOL 1973 had not entered into force, but in 1978 IMO convened a conference on tanker safety and pollution prevention. This adopted a protocol to MARPOL, which made major changes to Annex I and in effect absorbed the parent convention.

At the same time, it was recognized that there were a number of technical difficulties connected with Annex II which had still not been solved. To give Governments and the industry time to solve these problems it was agreed at the 1978 conference that implementation of Annex II should be deferred for three years after the entry into force of Annex I. On both the safety and pollution front, therefore, there were problems which needed to be tackled by IMO.

The 1983 amendments to SOLAS

There was general agreement within IMO that the ambiguous position of the BCH Code should be ended by making the Code a mandatory instrument and that the simplest way of doing this would be by inserting an appropriate amendment into Chapter VII of the SOLAS Convention (which deals with the carriage of dangerous goods).

At the same time it was decided that the Code itself should be further improved by bringing it into line with another Code which had been developed by IMO to deal with the construction and equipment of ships carrying liquefied gases in bulk. This was adopted in 1975, four years after the BCH Code, and was regarded as more detailed and completes.

The result was the adoption in 1983 of a new code, the International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk (IBC Code). The Code contains the provisions of all ten sets of amendments to the original BCH Code, together with other improvements (such as a chapter on ships engaged in incineration at sea). It was agreed that the new Code would only apply to new ships (had it been made retroactive, owners of existing chemical tankers would have been faced with enormous conversion costs).

The new Code was adopted by the Maritime Safety Committee in 1983 and it was agreed that it would apply to ships of any size built on or after 12 July 1986. Existing ships would still be covered (voluntarily) by the original BCH Code.

Amendments to Annex II of MARPOL 73/78

While the MSC was working on the new IBC Code and the SOLAS amendments, IMO’s Marine Environment Protection Committee was tackling the problems associated with chemical pollution.

It had two principal objectives. The first was to amend Annex II of MARPOL 73/78 and remove the many problems associated with its implementation. The second was to modify the new IBC Code and the existing BCH Code so that they dealt with pollution aspects as well as safety.

A major problem with the implementation of Annex II arose from the original premise on which it was drafted, namely that the quantity of Category B or C chemicals remaining in a tank after unloading could be calculated using vertical and horizontal surface areas and the relevant physical properties of the substance at the temperature concerned, e.g. specific gravity and viscosity. Providing this calculated quantity was less than the upper limit established by the Convention this residue could be discharged into the wake of the ship with the proviso that the resultant concentrations in the sea did not exceed a certain limit. The application of the latter criteria required further calculations to establish a suitable speed and the under-water discharge rate for the chemical concerned. The operation of a chemical carrier with parcels of different chemicals and considerable variability of physical properties and ambient temperature conditions would mean that a member of the ship's crew would be employed virtually full-time in computing residue quantities and ascertaining discharge parameters.

Experience indicated that the complicated procedure described above could be circumvented if the efficient stripping of tanks to a relatively insignificant residue level during unloading was made mandatory. Those smaller quantities of residues could then be discharged overboard without limitation or rate of discharge, etc.

The main purpose of the amendments to Annex II adopted in December 1985 was to introduce new pollution control provisions based upon efficient stripping of tanks.

Another major problem of Annex II concerns reception facilities, the provision of which is crucial to the effective implementation of the regulations. Reception facilities for chemicals are more expensive and complicated than those designed for the reception of oily wastes, since the wastes they are required to deal with are much more varied. There is also little opportunity for recycling them (as can be done with some oily wastes).  As a result, governments and port authorities have been reluctant to provide such facilities, particularly as the Convention itself was ambiguous as to whether the facilities should be provided in loading or unloading ports.

There have been difficulties with some other aspects as well, such as developing monitoring equipment to ensure that chemicals are properly diluted before being discharged into the sea. Therefore certain operational procedures had to be developed to limit the discharge rate to minimize harm to the environment.

In 1983 the IMO Assembly had adopted procedures and arrangements for the discharge of noxious liquid substances which are called for by various regulations of Annex II and these were applied on a trial basis by a number of IMO Member States. These trials showed a number of difficulties in implementing Annex II, mainly associated with the problems already outlined in the previous paragraphs. They included:

1.   The requirements were too complex and put a heavy burden on the crew of the ship.

2.   Measures of control were very limited and compliance with the standards depended entirely upon the willingness of the crew.

3.   There is a general lack of facilities for the reception of chemical wastes. Although provision of facilities themselves did not present great difficulties because the amount is smal compared with oily wastes, treatment of wastes and ultimate disposal was (and still is) a problem.

The tests confirmed what many authorities had already suspected and much of MEPC's work has subsequently been directed towards improving tank unloading requirements and at the same time minimizing the need for reception facilities.

Years of work by the MEPC bore fruit in December 1985 when a special session of the Committee adopted the long-awaited amendments to Annex II. The amendments are designed to encourage shipowners to improve cargo tank stripping efficiencies, and they contain a number of specific requirements that will ensure that both new and existing chemical tankers reduce the quantities of residues to be disposed of.

As a result of adopting these requirements it was possible to adopt simplified procedures for the discharge of residues; furthermore, the quantities of categories B and C substances that will. be discharged into the sea have been reduced.

The IBC Code applies to all chemical tankers constructed after 1 July 1986. The BCH Code applies to other "existing" ships. The importance of the two codes is that they are concerned with carriage requirements, including the way the cargo is protected from the consequences of an accident. MARPOL's Annex II is concerned only with discharge requirements.

The two instruments are thus complementary: MARPOL is designed to prevent pollution resulting from routine operations, while the Codes help to reduce pollution resulting from accidents. Since then, work has continued on developing measures to implrove the safety of checmial carriage at sea. In 1992, IMO agreed to review all the provisions in Annex II of MARPOL, with the aim of simplifying the requirements to encourage more widespread implementation of the Annex. At the same time, it agreed to review the categorization system.The decision to completely review the Annex was influenced by a number of developments.

Firstly, improvements in ship technology meant that stripping of tanks had improved to the extent that only very minimum amounts of residues would be left in tanks after unloading and consequently the limits on the discharges of substances could also be drastically cut. As improvements in technology have enabled IMO to reconsider the amount of discharge permitted to enter the marine environment, they have also provided an opportunity to reconsider the number of defined pollution categories.

Another issue was increased understanding of the environmental impact of chemicals on the marine environment. In the existing product categorization, Annex II placed considerable emphasis on acute aquatic toxicity, tainting of fish and bioaccumulation with associated harmful effects, but it was being recognized that other properties were equally important - such as chronic aquatic toxicity, and the effect on wildlife or seabed of substances that would sink or persistently float on the surface.

The 1992 UNCED Rio Conference also influenced the review of Annex II. Chapter 19 of Agenda 21 adopted by the Conference included a programme on harmonization of classification and labelling of chemicals and the United Nations Committee of Exerts on the transport of Dangerous Goods and the Organization for Economic Cooperation and Development (OECD) have been acting as clearing houses for the development of harmonized hazard classification systems covering the physical and biological properties that affect safety and protection of the environment.

The work of these organizations in developing harmonized classification systems has a bearing on the work of the GESAMP Evaluation of Hazardous Substance working Group - and on the work of the Working Group on the Evaluation of Safety and Pollution Hazards (ESPH) - a working group of the IMO Sub-Committee on Bulk Liquids and Gases (BLG), which reports to the MEPC and MSC. The ESPH working group is dealing primarily with the assignment of pollution categories and carriage requirements for products in order to ensure their safe carriage and protection of the marine environment.

As instructed by the MEPC, the ESPH working group is considering whether the existing five product category system in Annex II (categories A, B, C, D plus "other liquid substances") could be simplified into a three-category system. The three-category system is based on the premise - in line with the development of the so-called precautionary approach[2]

- that no product should be permitted to enter the sea in unlimited quantities, as is the case with Category D and "other liquid substances" under Annex II. Therefore these two categories could be combined, creating a category for substances with limited restrictions.

A second category could combine current categories B and C, since ship technology now makes it easier for all ships to achieve minimum residue levels of 100 litres per tank - so there is no need to differentiate.

The third category would be equivalent to the existing Category A - in other words, substances considered highly environmentally hazardous and which should not be discharged at all. It is envisaged that the complete revision of Annex II will be completed by 2002. By then, hazard profiles for all noxious liquid substances carried in bulk on ships which come under MARPOL Annex II will have been re-evaluated and re-categorized. This is a mammoth task - some 300 substances are listed in the International Bulk Chemical Code. The MEPC is also looking into the whole issue of reception facilities and how to ensure adequate reception facilities are provided at ports.

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[1] Link to the Focus paper on MARPOL.

[2] The precautionary approach was introduced into the 1996 protocol to the Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter (LC), and is based on the premise that unless a substance can be proved to be harmless, it should not be dumped in the sea. Previously, the onus has been to prove something is harmful, to get its dumping banned.

[3] Each individual product is evaluated according to the hazards it presents.