Hazards of Bulk Cargoes
High Density / Structural damage
Great care is required to avoid over stressing the vessel and doing structural damage. Carefully planning of the load and the discharge must be made, and at all times the maximum loading of the tank top must not be exceeded.
In addition, the maximum loading for each hatch must not be exceeded. Care must be taken to ensure that the peak height of an untrimmed cargo is not excessive thereby increasing the tank top loading.
In tween deck vessels, high density cargoes such as iron ore should be loaded in the lower hold only to avoid damage to the tween deck.
Shifting
Some cargoes may have a tendency to shift across the ship in heavy weather and so correct trimming of the cargo is required. Some cargoes such as grain may need extra measures to be taken to secure the surface. For example, bulk grain may be over stowed with bagged grain.
As a general rule all cargoes should be trimmed level or nearly level. and whenever possible spaces should be filled as fully as practicable without putting excessive stress on the structure.
Liquefaction
Some cargoes, particularly metal concentrates, may become semi‑liquid on top when loaded "wet". This is due to the vibration of the ship at sea causing the moisture in the cargo to migrate to the surface.
The surface may then act as a liquid and seriously affect the stability of the vessel. Examples of this are coal, duff and lead concentrates.
Gas Production
Explosive gasses such as methane and poisonous gasses such as carbon monoxide may be produced by some cargoes. For example coal
Self‑Heating
Some cargoes are liable to heat up on voyage. Temperatures should be taken and a log kept of each space. For example coal and steel swarf.
Corrosive
The cargo itself may be corrosive or the liquid draining out of the cargo into the bilge's may be corrosive. In some ships severe damage has occurred. For example coal and sulphur.
Dust Very dusty cargoes may be hazardous to humans and the environment and so measures may have to be taken to control the level of dust created e.g. stop load/discharge in high winds. For example alumina and phosphates.
Reactivity with other cargoes.
Two different bulk cargoes may not be compatible with each other and may have to be stowed well apart.
Oxygen depletion
Some cargoes will use up oxygen within the cargo space. The main example of this is rusting of steel swarf cargoes but some metal concentrate cargoes and some grain cargoes may also deplete the oxygen in the cargo space.
Merchant Shipping (Carriage of Cargoes) Regulations 1999
The MS (Carriage of Cargoes Regulations) 1999 contain a section about the carriage of solid cargoes in bulk.
Prior to Loading
The master is to have approved stability information containing comprehensive information on the ships stability and distribution of cargo and ballast for standard conditions.
The master is not to accept concentrate or other cargoes that might liquefy unless the moisture content is lower than its transportable moisture limit, If the moisture content is above the transportable moisture limit the master must satisfy the authorities that there is satisfactory stability in the event of a shift and that the ship has adequate structural integrity.
If loading a cargo with chemical properties that might create a potential hazard, for example coal, appropriate precautions for safe carriage are to be taken.
The owner is to ensure that the master is given the required information.
The master is not to accept cargo for loading unless he has been provided the required information and he has calculated that the stability would be sufficient.
Cargo Loading Manual
The owner is to ensure that the master is provided with a cargo loading manual that includes:
Loading and Unloading Plan
Before loading or unloading the master and terminal representative are to agree on a plan which:
• Ensures that the maximum permissible forces and moments on the ship are not exceeded.
• Includes the sequence, quantity and rate of loading or unloading.
Copies of the plan and its subsequent amendments are to be sent to the appropriate port State authority. (In the United Kingdom this will be the port or harbour authority who will keep the plans for at least 6 months)
Loading, Unloading and Stowage
The master is to ensure that bulk cargoes are loaded and trimmed reasonably level to the boundaries of the cargo space.
When bulk cargoes are carried in tween decks the master is to ensure that tween deck hatches are closed when the loading information indicates unacceptable stress of the bottom structure if they are left open.
The tween decks are not to be overloaded, and the cargo trimmed from side to side or secured by longitudinal divisions.
The master and terminal representative are to ensure that loading and unloading proceed according to the agreed plan. If the maximum permitted forces or moments are exceeded the master has the right to suspend operations and should inform the appropriate port State authority. The master and terminal representative are to take corrective action.
The master and terminal representative are to ensure that the unloading methods do not damage the ships structure.
The master is to ensure that ship's personnel continuously monitor cargo operations, check the ship's draft regularly and record draft and tonnage observations. If significant deviations form the plan are detected, cargo or ballast operations are to be adjusted to correct the deviations.
Code of Safe Working Practice for Solid Bulk Cargoes (BC Code)
This code is published by the IMO to promote safe carriage of solid bulk cargoes which are defined as any material consisting of a combination of particles, granules or larger pieces. generally uniform in composition, loaded loose.
They include coals, concentrates, fertilisers, animal foodstuffs, minerals and ores.
The topics covered by the code are summarized in the following sections.
Definitions
Cargo Distribution
To prevent the structure being over stressed, and to ensure adequate stability, the Master should make use of the ships stability information, capacity plan and loading calculators where applicable to determine cargo distribution. Where detailed information is not available the following should be taken into account:
Fore and aft distribution
Fore and aft distribution should avoid excessive longitudinal stresses, shearing forces and trim.
Maximum tonnage per hold
If no other information is available use the formula:
This figure may be increased by 20% in a lower hold when the cargo is levelled.
Peak Height
Where material is untrimmed or only partially trimmed the corresponding height of material pile peak above the cargo space floor should not exceed:
The material height in the tweendeck should not to exceed
Example
FERROAMNGANESE. SF = 0. 18 m3ltonne.
Tweendeck height = 4. Om
Height = 0.52m
High Density Materials
Should be loaded in the lower hold rather than the tweendeck but the consequences of an excessively high GM, such as racking stresses, must be considered.
A satisfactory condition can in general be achieved by loading approximately 1/3 of the cargo in the tweendeck.
Shifting divisions and bins
Should be erected when cargoes suspected of readily shifting are carried in tweendecks or partially filled lower holds.
Loading and Unloading
Prior to loading particular preparations should be made including:
Bilge wells and strainer plates
Should be prepared to facilitate drainage and prevent entry of cargo.
Precautions to prevent dust
Entering moving parts of deck machinery.
Ventilation systems
Shut down or screened and air conditioning on recirculate.
Safety of Personnel
Information
It is important therefore that the shipper informs the Master prior to loading as to whether a chemical hazard exists. The Master should also refer to Appendix B of the Code and ensure all relevant precautions are taken and an appropriate instrument for measuring the concentration of gas or oxygen should be provided.
Oxidation
Some bulk cargoes are liable to oxidation which may result in oxygen depletion, emission of toxic fumes, or self heating. Others may not oxidise but may emit toxic fumes, particularly when wet.
Dust Created by certain cargoes may constitute an explosion hazard, especially while loading, unloading and cleaning. This risk can be minimised by ventilation and hosing down rather than sweeping.
Flammable gases
Are emitted by some cargoes and all relevant precautions should be taken.
Carzoes Which May Lique
Shifting
These cargoes, listed in Appendix A may shift as a result of liquefaction at a moisture content above that of the Transportable Moisture Limit.
To prevent shifting
To prevent shifting and also decrease the effects of oxidation when the material has predisposition to oxidise these cargoes should be trimmed reasonably level on completion of loading irrespective of angle of repose.
Excess moisture content
Materials with a moisture content in excess of the Transportable Moisture Limit may be carried in approved specially constructed or speciallyfitted ships.
Test procedure
If the Master has doubts about the moisture content the following ship test may be used to determine the possibility of flow:
Half fill a cylindrical can (0.5 to 1.0 litre capacity) and strike it sharply on a hard surface 25 times at 2 second intervals from a height of about 0.2m. If free moisture or fluid conditions result then have additional laboratory tests done.
Weighing of wet and dry samples will provide information to obtain an indication of moisture content.
Chemical Hazards
Hazards
Hazards may be specified as in the IMDG Code by class unless they are hazardous only in bulk (MHB).
Segregation
Any necessary segregation is given in the Code. This may be applicable between different bulk cargoes or bulk/packaged cargoes.
Transport of Solid Waste in Bulk
Wastes are solid materials containing, or contaminated with one or more constituents which are subject to the provisions of the Code, applicable to materials of IMDG Classes 4.1, 4.2, 5.1, 6.1, 8 or 9 and, for which no direct use is envisaged, but which are carried for dumping, incineration, or other methods of disposal.
Transportation of wastes requires suitable documentation and will be classified according to its constituents with stowage and handling in accordance with previous section of the Code.
Wastes associated with radioactive materials are not considered as wastes for the purpose of this section.
Coal Cargoes
Guidelines for the carriage of coal cargoes are contained in Appendix B of the BC Code, modified by the 1996 amendment of the BC Code. Appendix G includes procedures for monitoring the gas content of coal cargoes.
Guidance is also given in MGN 60 (M)
Methane
Coal cargoes may emit methane which is lighter than air and is explosive in atmospheric concentrations between 5% and 16%.
Normally, all holds should be surface ventilated for 24 hours after departing the loading port. If the methane concentration is acceptably low at the end of this period the ventilators should be closed.
If the methane concentration exceeds 20% of the LEL, surface ventilation is to continue to reduce the concentration.
Self Heating
To control potential self heating, hatches are kept closed and surface ventilation limited to the minimum necessary to remove methane.
Self heating is indicated by an increasing concentration of carbon monoxide.
If the coal temperature exceeds 55*C at the time of loading, with the hatches open, expert advice should be obtained.
Trimming
Coal cargoes should be trimmed reasonably level to avoid gas pockets and prevent air permeating the coal.
GAS MONITORING
Two sample points should be provided for each hold, one to port and one to starboard.
Each point should have a hole at least 12mm in diameter as near as possible to the top of the hatch coaming, sealed with a screw cap to prevent the ingress of water and air. Measurement should be taken with a multi gas analyser capable of measuring methane oxygen and carbon monoxide.
Carbon monoxide monitoring will provide an early indication of self heating within the coal cargo.
