Bulk
cargoes
The carriage of grain
General Cargoes
The carriage of timber on deck
Containerization
Cargo stowage and securing
The prevention of infestation
The Code of Safe Practice for Solid Bulk Cargoes
General precautions
Bulk cargoes having an angle of repose less than or equal to 35 degrees
Bulk cargoes having an angle of repose greater than 35 degrees
Safety of personnel
Cargoes which may liquefy
Sampling and test procedures for cargoes which may liquefy
Appendices to the Code
Materials possessing chemical hazards
Bulk cargoes which are neither liable to liquefy nor possess chemical hazards
The carriage of grain
General Cargoes
The carriage of timber on deck
Containerization
Cargo stowage and securing
The prevention of infestation
The Code of Safe Practice for Solid Bulk Cargoes
General precautions
Bulk cargoes having an angle of repose less than or equal to 35 degrees
Bulk cargoes having an angle of repose greater than 35 degrees
Safety of personnel
Cargoes which may liquefy
Sampling and test procedures for cargoes which may liquefy
Appendices to the Code
Materials possessing chemical hazards
Bulk cargoes which are neither liable to liquefy nor possess chemical hazards
During
the last hundred years shipping, like other forms of transport has undergone
great changes. Until the end of the last century most goods at sea were carried
in packaged form. Grain, for example, was carried in sacks and cotton in
bales. Very few liquids were carried at all, but those that were - including
oil - were usually carried in barrels. Cargoes in fact were carried in much
the same way as they always had been.Today everything has
changed. Oil is the major commodity carried at sea in bulk; so are grain,
coal and other minerals. Containerization is now common and the general cargo
ship has in many trades been replaced by specialized vessels such as container
ships, ro-ro ships and car carriers among others.
Virtually all liquids
transported by sea - such as crude oil and finished petroleum products - are
carried in bulk, and tankers now form by far the greatest percentage of the
world fleet of merchant ships. The second biggest group consists of solid
bulk cargo carriers. The goods carried in this way include coal, grains,
ores, concentrates, fertilizers and animal feeds. From the shippers' point
of view bulk carriage has numerous advantages. A bulk cargo can be loaded
and unloaded far more quickly than one that is unitized, thereby leading to
great savings in time and money. However, there are a number of dangers in
the carriage of bulk cargoes which include the following:
1. Improper weight
distribution resulting in structural damage. This can be caused by putting
too much weight on the inner bottom of the ship or by wrongly distributing
the cargo between holds, leading to excessive stresses on the ship's structure.
2. Improper stability
and cargo shift. Another result of improper loading can be excessive
stability. This leads to the normal rolls of the ship becoming shorter but
much more violent. Apart from being extremely uncomfortable for those on
board, this can in turn lead to damage to the ship's structure.
Stability of the ship
can also be affected by the cargo shifting during the course of the voyage.
This can occur because the cargo is inadequately trimmed (levelled-off) or
improperly distributed. In some cases cargoes can liquify as a result of
vibration and the motion of the ship and then slide or flow to one side of
the cargo hold. This usually happens when the cargo consists of finely-grained
material, such as fine coal and ore concentrates, which are damp when loaded.
However it occurs, a shift of cargo can lead to the ship listing and ultimately
capsizing.
3. Spontaneous heating.
Some cargoes carried in bulk have a tendency to heat spontaneously during
the course of a voyage. The result can be a fire or explosion.
4. Chemical hazards.
These hazards include the emission of toxic or explosive gases, oxygen depletion,
spontaneous combustion or severe corrosion.
Measures to counter
these problems have been adopted at both a national and international level.
Back to top
Grain has been transported by sea for many thousands of years - it was an important feature of commerce in the Mediterranean in ancient times - and nowadays, is generally carried in bulk. However, grain has one great hazard when carried at sea in bulk; it tends to shift within the cargo space of the ship. Because of this danger and the great amount of grain transported by sea, special rules governing its carriage in bulk have appeared in various international instruments including the International Convention on the Safety of Life at Sea.
Back to top
General cargoes, even if not classed as dangerous, can pose dangers to ships or those on board, if certain precautions are not observed. If the cargo is to be discharged in generally the same condition as when loaded, further common sense considerations apply. In order to plan stowage, the responsible officer should have information on the nature, mass and stowage factor of the individual cargo. Where large items of cargoes are concerned, information on the dimensions of the cargo is required. Such information will then be used to distribute the cargo in such a way as to ensure adequate stability and workable trim at all stages of the voyage and to have the cargo gear rigged so as to ensure that heavy items can be lifted without the possibility of a stow collapsing and endangering the ship; of items of machinery or steel shafts falling and penetrating the ship's shell-plating; or of shifting deck-cargoes causing fractured deck piping and ventilation trunks.
In addition to those
safety matters, the cargo officer must take into account commercial considerations
and separate tainting from taintable cargoes or sweating cargoes from those
that may be damaged by moisture and that heavy items are not placed on frail
packages or packaged liquids on bagged cargoes. For some cargoes ventilation
must be encouraged or sometimes it must be restricted but the different climatological
conditions in which a ship is expected to operate must always be taken into
account. In all cases, the drainage of liquids to the hold bilges or wells
should be facilitated.
The securing of breakbulk cargoes is most conveniently done by planning stows to occupy the spaces from side to side, incorporating, where appropriate, built-in anchors of dunnage or using locked stows. Heavy items are individually lashed and for some cargoes, known to have given rise to difficulties in the past, IMO has published a Code of Safe Practice for Cargo Stowage and Securing (resolution A.714(17)). For the securing of freight containers a wide variety of standardized fittings are available. On open-top container ships, the need to secure cargoes is greatly diminished as all containers are placed within cells. The securing of containers on general cargo ships can cause problems unless special fittings have been provided.
Barge carrying ships
have specialized arrangements to secure the barges and if problems arise,
they stem from the cargoes within the barges. Ro-ro ships have fittings to
secure lorries, although these are not always used.
Back to top
Timber is often carried on the decks of ships and sometimes cause the combined centre of gravity of ship and cargo to rise, which adversely affects stability, a situation made worse when the deck cargo absorbs rain and seawater during the voyage, especially when freezing occurs and ice accumulates on deck. However, there is usually an increase in buoyancy and the timber also gives the ship greater protection against the rough sea conditions. Thus, ships which carry timber deck cargoes may be granted reduction of the freeboard applicable under the 1966 International Convention on Load Lines except in the North Atlantic zone in winter where icing can be a problem.
The
Code of Safe Practice for Ships Carrying Timber Deck Cargoes gives further
information and guidance on this subject. It was adopted by IMO in 1973 and
amended in 1978 and 1990. Like the BC Code and contrary to the International
Grain Code, it is not a mandatory instrument but is intended to serve as guidance
to Governments who can implement it if they desire, either in whole or in
part. The Code is intended to apply to ships of 24 metres (79 feet) in length
and over. Timber deck cargoes are defined as cargoes of timber, including
logs, and sawn timber whether loose or packaged, which are carried on an uncovered
part of a freeboard or superstructure deck.Back to top
Since first introduced in the 1950s, containers have revolutionized the carriage of general cargoes which presented great advantages both in ease and speed of handling, cargo security, and together with other factors have transformed both ships and ports.
In many countries the
traditional cargo berths, located in the centre of urban areas, have lost
trade because they do not provide the space needed for container operations
as berthing facilities in many cases have moved downriver, to where there
is more land available and the water is deep enough to accommodate container
ships that have steadily increased in size. Usually ports have been developed
with a close eye on land transport as well, for one of the major advantages
of containers is that they enable an integrated transport system involving
road, rail and sea elements to be established, the link being the port and
the common feature the container itself.
More
recently another innovation has affected the shipment of cargoes, especially
on short-sea routes: the trailer on board ship. The special-purpose roll/on-roll/off
ship offers many of the advantages of the container ship, including speed
and security. A container on a trailer can be driven straight onto a ship
in one port and off again when it reaches its destination. There is no cargo
handling involved and consequently no extra costs or loss of time. Both developments
offer economic benefits and both raise problems.In view of the rapid
increase in the use of freight containers for the consignment of goods by
sea and the development of specialized container ships, in 1967 IMO undertook
to study the safety of containerization in marine transport. The container
itself emerged as the most important aspect to be considered.
In the 1970s IMO and the International Labour Organisation began work on guidelines for training in the packing of cargo in freight containers. These were published in 1978 as a short guide which emphasized the effect upon the contents of the containers of sea itself. The movement of the ship in adverse weather can result in pitching, rolling and other movements greater than anything found ashore. The guidelines were revised in 1984.
Experience had by then
shown that probably the greatest problem associated with ro-ro ship safety
concerned cargo stowage. A survey carried out by the Norwegian classification
society, det Norske Veritas, showed that 43% of ro-ro losses could
be attributed to faults in this area. The danger is even greater in the case
of ro-ro ships than on pure containerships, because containers are generally
carried on trailers: a loading error can result in the container and the trailer
both falling over or becoming dangerously unbalanced. In 1983 IMO therefore
adopted a resolution on elements to be taken into account when considering
safe stowage and securing of cargo units and vehicles in ships and two years
later, it adopted another resolution on securing arrangements for the transport
of road vehicles on ro-ro ships. It contained guidelines intended to apply
to commercial vehicles, including semi-trailers and road trains, with a total
mass (including cargoes) of up to 40 tons, and articulated road trains of
not more than 45 tons but does not apply to buses.
The
resolution stipulates that given adequately designed ships and properly equipped
road vehicles, lashing of sufficient strength will be capable of withstanding
the forces imposed on them during the voyage. The side guards often required
for vehicles can obstruct proper securing and the guidelines take this difficulty
into account. They cover securing points both on the deck of the ship and
on the vehicle, as well as lashings and stowage.Back to top
In 1991 the IMO Assembly
adopted the Code of Safe Practice for Cargo Stowage and Securing. Its purpose
is to provide an international standard to promote the safe stowage and securing
of cargoes by:
drawing the attention
of shipowners and ship operators to the need to ensure that the ship is
suitable for its intended purpose;
providing advice to
ensure that the ship is equipped with proper cargo securing means;
providing general
advice concerning the proper stowage and securing of cargoes to minimize
the risks to the ship and personnel;
providing specific
advice on those cargoes which are known to create difficulties and hazards
with regard to their stowage and securing;
advising on actions
which may be taken in heavy sea conditions; and
advising on actions
which may be taken to remedy the effects of cargo shifting.
The Code is based
on a number of general principles:
All cargoes should
be stowed and secured in such a way that the ship and persons on board are
not put at risk.
The safe stowage and
securing of cargoes depend on proper planning, execution and supervision.
Personnel commissioned
to tasks of cargo stowage and securing should be properly qualified and
experienced.
Personnel planning
and supervising the stowage and securing of cargo should have a sound practical
knowledge of the application and content of the Cargo Securing Manual, if
provided.
In all cases, improper
stowage and securing of cargo will be potentially hazardous to the securing
of other cargoes and to the ship itself.
Decisions taken for
measures of stowage and securing cargo should be based on the most severe
weather conditions which may be expected by experience for the intended
voyage.
Ship-handling decisions
taken by the master, especially in bad weather conditions, should take into
account the type and stowage position of the cargo and the securing arrangements.
Back to top
Infestation by insects and rodents is a threat which all ships face. It can have serious consequences for a variety of reasons. Pests can damage equipment and spread disease and infection, contaminate food in galleys and stores and cause damage to cargoes. Although pesticides can be used to eliminate or control infestation, very few pesticides are suitable against all types of pests and if improperly used can themselves present dangers.
In 1971 IMO adopted
recommendations on the safe use of pesticides in ships. It has been revised
several times since then. It gives guidance on the prevention of infestation,
the use of insecticides, pesticides and fumigants.
Back to top
The dangers associated with the carriage of cargo in bulk have been known for a long time and the 1960 International Conference on the Safety of Life at Sea recommended that IMO draw up an international code of safe practice dealing with this subject. Work began immediately and in 1965 the first Code of Safe Practice for Solid Bulk Cargoes was adopted.
The Code has been updated
at regular intervals since then and is kept under continuous review by the
Sub-Committee on Containers and Cargoes. The practices contained in the Code
are intended as recommendations to Governments, ship operators and shipmasters.
Its aim is to bring to the attention of those concerned an internationally-accepted
method of dealing with the hazards to safety which may be encountered when
carrying cargo in bulk. The Code does not deal with the transport of grain,
which is covered by the International Code for the Safe Carriage of Grain
(International Grain Code).
The Code of Safe Practice
for Solid Bulk Cargoes deals with three basic types of cargo: those which
may liquefy; materials which possess chemical hazards; and materials which
fall into neither of these categories but many nevertheless pose some dangers,
as stated above.
The Code highlights
the dangers associated with the shipment of certain types of bulk cargoes;
gives guidance on various procedures which should be adopted; lists typical
products which are shipped in bulk; gives advice on their properties and how
they should be handled; and describes various test procedures which should
be employed to determine the characteristic cargo properties.
Back to top
It is of fundamental importance that bulk cargoes be properly distributed throughout the ship so that the structure is not overstressed and the ship has an adequate standard of stability.
Loaded conditions vary
according to the density of the cargo carried. General cargo ships are normally
constructed so that one ton of cargo occupies about 1.39-1.67 cubic metres
of space when loaded to full bale cubic and deadweight capacity. The ratio
of volume of cargo to its mass is known as the stowage factor. When the high
density bulk cargoes with a stowage factor of about 0.56 cubic metres per
ton or lower are carried, it is particularly important to pay attention to
the distribution of weight in order to avoid excessive stresses on the structure
of the ship. Since hull arrangements vary, it is not possible to establish
overall rules applicable to all types of ships.
It
is essential that the master be provided with loading information sufficiently
comprehensive to enable him to load the ship without overstressing the structure.
This applies to localized stresses on the structure as well as on the bending
stresses. The master must also be able to calculate the stability of his
ship for the anticipated worst conditions during the voyage.Generally speaking,
high density cargoes should be loaded in the lower hold spaces rather than
the 'tween decks[2]. Particular care should be taken when a ship has a high GM.
In order to prevent cargoes from shifting the considerations dealt with below
under the heading Bulk cargoes having an angle of repose greater than 35 degrees[3]
should also be taken into account.
The Code gives various
precautions to be followed when information on the physical properties of
the cargo is not available.
The Code lists other
general precautions such as the need to protect machinery and the interior
of the ship from dust and to ensure that bilges and service lines are in good
order and not damaged during loading.
Back to top
When a bulk cargo is emptied on to a flat surface, such as the hold of a ship, it forms a cone whose angle of repose varies according to the type of cargo. This angle is the one formed between the horizontal plane and the cone slope.
Cargoes with a low angle
of repose are particularly liable to dry-surface movement aboard ship. To
overcome this problem, the Code states that such cargoes should be trimmed
reasonably level and spaces in which they are loaded should be filled as fully
as is practicable, without resulting in excessive weight on the supporting
structure.
Special provisions should be made for stowing dry cargoes which flow very freely, in a similar manner to grain.
Securing arrangements,
such as shifting boards or bins, should be used whenever the amount, location
or properties of the cargo could cause excessive heeling through cargo shift,
taking into account the density of the cargo.
Back to top
Generally speaking, high-density cargoes, such as most iron ores, have a high angle of repose, i.e. above 35 degrees.
The Code states that
high density cargoes should be loaded entirely in the lower holds of the ship
unless this results in the ship being too "stiff"[4]
or in the cargo weight on the bottom structure being excessive. It should
be trimmed sufficiently level to cover evenly all of the tank top, to reduce
the pile peak height and equalize weight distribution. In some circumstances
the pile peak may be allowed to extend through the 'tween-deck hatchway but
the Code says that the importance of trimming as a means of reducing the possibility
of a shift of cargo can never be over-stressed. This is particularly true
for smaller ships of less than 100 metres in length.
Trimming also helps
to cut oxidation by reducing the surface area exposed to the atmosphere.
It also helps to eliminate the "funnel" effect which in certain
cargoes, such as direct reduced iron (DRI) and concentrates, can cause spontaneous
combustion. This occurs when voids in the cargo enable hot gases to move
upwards, at the same time sucking in fresh air. This effect is obviously
not desirable, since it escalates the process of spontaneous combustion.
The Code goes on to
list various considerations which should be taken into account when cargo
is loaded in the 'tween-decks to reduce "stiffness".
Back to top
After listing various regulations adopted by the International Labour Organisation, which should be taken into account during cargo handling operations, the Code gives details of other dangers which may exist. Some cargoes, for example, are liable to oxidation which may result in the reduction of the oxygen supply, the emission of toxic fumes and self-heating. Others may emit toxic fumes without oxidation or when wet. The shipper should inform the master of chemical hazards which may exist and the Code gives details of precautions which should be taken.
Health hazards can arise
because of dust, and some cargoes can create dust or emit flammable gases
which create a danger of explosion.
Back to top
These include concentrates (materials obtained from a natural ore by a process of purification, by physical or chemical separation and removal or unwanted constituents), some coals and other materials with similar properties.
One purpose of this
section of the Code is to draw attention to the latent risk of cargo shift
and describe precautions which should be taken. Concentrates and similar
finely-particulate materials may appear to be in a relatively dry granular
state when loaded and yet may contain sufficient moisture to become fluid
under the stimulus of compaction and vibration. In the resulting semi-fluid
state, the cargo may flow to one side when the ship rolls but not completely
return when the ship rolls the other way. As in the case of cargoes liable
to shift, this can result in the ship reaching a dangerous heel or eventually
capsizing.
The stability of the
ship is also likely to be affected by "free surfaces"[5]
of liquids in the cargo spaces. General cargo ships should only carry bulk
cargoes which have a moisture content below the transportable moisture limit
(TML), which is 95% of the flow moisture point (FMP) unless they are fitted
with special arrangements to restrain the cargo.
Cargo ships in which
internal structural boundaries are sufficient to limit cargo shift may also
carry cargoes whose moisture content exceeds the transportable moisture limit.
All ships which carry cargoes of this type should carry evidence of approval
of the flag State. The Code stipulates the data which should be included
in submission for approval.
To prevent possible
increases in the liquid content of concentrates, cargoes containing liquids
(other than canned goods or the like) should not be stowed in the same compartment
as cargoes which may liquify. Precautions should be taken to prevent water
entering holds; this is even more important where contact with seawater could
lead to serious corrosion problems for hull or machinery. In this connection
masters should be aware of the possible danger of using water to cool combustible
materials such as coal at sea, as this may well bring the moisture content
to a flow state or create other hazards. Water, if used, is most effectively
applied in the form of spray or mist.
Back to top
The Code strongly recommends that, prior to loading cargoes of this type, masters should obtain a certificate stating the flow moisture point, the transportable moisture limit of the cargo together with its actual moisture content.
The Code gives details
of the various sampling procedures and tests which should be used before transporting
concentrates and similar materials. These include the selection of samples
for laboratory tests to determine the transportable moisture content of concentrates;
and the selection of samples to determine the flow moisture point and the
moisture content at the time of loading. Procedures concerning the issuing
of certificates by Administrations are also given including a recommended
test procedure to be used by laboratories.
Back to top
A list of cargoes which may liquefy is contained in appendix A to the Code. The stowage factor is generally low (from 0.33 to 0.57 cubic metres per ton) and it is emphasized that the list of materials is not exhaustive. It includes concentrates derived from copper, iron, lead, manganese, nickel, and zinc ores, various pyrites, fine-particulate coal, coal slurry and various other substances.
Back to top
Appendix B gives an extensive list of materials of this type ranging from aluminium dross to zinc ashes. Some of the classified
materials
listed also appear in the International Maritime Dangerous Goods (IMDG) Code
when carried in packaged form, but others become hazardous only when they are
carried in bulk - for example, because they might reduce the oxygen content
of a cargo space or are prone to self-heating. Examples are woodchips, coal
and DRI.The various types listed
include: flammable solids; flammable solids or substances liable to spontaneous
combustion; flammable solids or substances which, in contact with water, emit
flammable gases; oxidizing substances; poisonous substances; radio-active
substances; or corrosives.
Such materials should be carefully segregated from other dangerous goods carried in packaged or unitized form. The Code describes how this should be done.
Each
entry includes either the United Nations number[6] and IMO class[7] or the MHB (materials hazardous in bulk) classification and a
BC number; the relevant MFAG (Medical First Aid Guide) table number[8]; approximate angle of repose and
stowage factor; Emergency Schedule number; separation and stowage requirements;
and properties, observations and special requirements.Back to top
These cargoes do not normally have special hazards and are covered in Appendix C. The list ranges from alumina to zircon sand as well as many of the more commonly-carried bulk cargoes such as clay, cement, iron ore, pig iron, sand and sugar. The list includes the angle of repose of each material, its approximate stowage factor, and the properties and special requirements connected with each one.
IMO Resolution A.713(17)
Despite the efforts
of IMO and its Member Governments, the number of bulk carriers sinking during
the late 1980s and early 1990s, sometimes without trace, began to cause serious
alarm. As a result, resolution (A.713(17)) which contains interim measures
designed to improve the safety of ships carrying solid bulk cargoes, was duly
adopted.
Owners are encouraged
to fit vessels with equipment to monitor the stresses on the ship's structure
during the voyage and during cargo operations. They are also encouraged to
install equipment required by the Global Maritime Distress and Safety System
(GMDSS), which enters into force on 1 February 1992.
The impact of this resolution
was immediately beneficial. The number of bulk carrier losses dropped from
around one a month to just two within the next year. It is significant that
the resolution did not introduce any new measures but simply stressed the
importance of implementing existing standards.
Back to top
[1] For ships with a small list the metacentre may be
considered to be the point on a line drawn vertically through the ship which
is intersected by a line drawn vertically from the centre of buoyancy when
the ship is rolling. If this point is below the centre of gravity the ship
will roll over. The term GM means the vertical distance from the metacentre
(M) to the centre of gravity (G).
[2]
A 'tween-decker is a ship with more than one deck, thus providing space
between the two adjacent decks.
[3] These
sections of the Code are currently under revision, the aim being to develop
new criteria for shifting of cargoes.
[4] i.e. having a large metacentric
height.
[5] When
a cargo space contains a liquid, the metacentric height of the ship is reduced
by an amount depending mainly on the width of the free surface of the liquid.
The effect is independent of the amount of liquid in the cargo space.
[6] The
UN Committee of Experts on the Transport of Dangerous Goods numbers each
dangerous substance, with the exception of MHB.
[7] Substances
included in the IMDG Code are arranged in different classes according to
their properties (e.g. explosives, flammable liquids, corrosives, etc.).
[8] The
Medical First Aid Guide is intended for use in conjunction with the IMDG
Code. Poisons are divided into groups and given individual numbers.
Back to top