Section 4.1 Understanding Cargo Groups (A, B, C) and Schedules

The IMSBC Code categorizes solid bulk cargoes based on their primary hazards to facilitate understanding and the application of appropriate safety measures. This grouping is fundamental to how the Code is structured and used.

1. The Three Main Cargo Groups:

1. Group A Cargoes:
   1. Definition: These are cargoes which may liquefy if shipped at a moisture content exceeding their Transportable Moisture Limit (TML).
   2. Mechanism of Liquefaction: Certain fine-particled mineral cargoes (like concentrates, some fine ores, mineral sands) can appear solid and stable when loaded. However, during a voyage, the compaction and vibration from the ship’s motion and engine operation can cause the moisture within the cargo to migrate. This reduces the friction between particles, allowing them to behave like a fluid. The cargo can lose its shear strength, effectively transforming from a seemingly solid state to a viscous liquid state.
   3. Consequences of Liquefaction: If liquefaction occurs, the cargo can shift rapidly and violently with the ship’s rolling motion. This can lead to a sudden loss of stability (due to the large free surface effect of the liquefied cargo), development of a severe list, and potentially the rapid capsize of the vessel with little or no warning. Numerous bulk carrier losses have been attributed to cargo liquefaction.
   4. Key Requirement: The shipper must provide a certificate stating the cargo’s TML and its actual moisture content. The moisture content must not exceed the TML unless the ship is specially constructed or fitted for carrying liquefiable cargoes (as per Section 7 of the IMSBC Code) and specific precautions are taken.
   5. Examples: Mineral concentrates (e.g., copper, lead, zinc, nickel), iron ore fines, bauxite fines (some types), fluorspar, manganese ore fines, coal slurry.
2. Group B Cargoes:
   1. Definition: These are cargoes which possess a chemical hazard that could give rise to a dangerous situation on a ship. These hazards are diverse and specific to the cargo.
   2. Types of Chemical Hazards:
      1. Self-heating and Spontaneous Combustion: Some cargoes (e.g., certain types of coal, direct reduced iron (DRI), petroleum coke, fishmeal) can oxidize or undergo biological activity, generating heat. If this heat is not dissipated, the temperature can rise to the point of ignition.
      2. Emission of Flammable Gases: Some cargoes (e.g., certain coals, DRI) can emit flammable gases like methane or hydrogen, which can form an explosive atmosphere in the cargo hold if not properly ventilated.
      3. Emission of Toxic Gases: Some cargoes (e.g., certain metal sulphide concentrates, some fertilizers if contaminated or decomposing) can emit toxic gases (e.g., hydrogen sulphide, ammonia, carbon monoxide).
      4. Corrosivity: Some cargoes (e.g., sulphur, some fertilizers, salt) can be corrosive to the ship’s steel structure if moisture is present.
      5. Oxygen Depletion: Some cargoes (e.g., ores, concentrates, forest products, DRI) can deplete the oxygen content in the hold atmosphere through oxidation or other chemical processes, creating a suffocation hazard for anyone entering the space.
      6. Reactivity with Water or Air: Some cargoes may react dangerously with water or air, producing heat or hazardous gases.
   3. Key Requirement: The shipper must provide detailed information on the chemical properties and hazards of the cargo, and the Code specifies precautions for stowage, ventilation, temperature monitoring, gas monitoring, personnel entry, and emergency response.
   4. Examples: Coal, Direct Reduced Iron (DRI – various forms A, B, C), Ammonium Nitrate Based Fertilizers (ANBF), Sulphur (bulk), Petroleum Coke (calcined and uncalcined), Metal Sulphide Concentrates, Wood Pellets, Seed Cake.
3. Group C Cargoes:
   1. Definition: These are cargoes which are neither liable to liquefy (Group A) nor to possess chemical hazards (Group B) as defined by the Code.
   2. Primary Hazard (Generally): While not chemically hazardous or prone to liquefaction in the same way as Group A, Group C cargoes can still pose risks, primarily related to shifting if not properly stowed and trimmed, especially if they have a low angle of repose. Shifting of a large volume of dense cargo can lead to a list and compromised stability.
   3. Other Considerations: Some Group C cargoes can be very dusty, requiring precautions during loading/discharge. Some may be dense, requiring careful attention to tank top loading limits and longitudinal strength.
   4. Key Requirement: Generally require proper trimming to minimize the risk of shifting. The shipper should provide information on the angle of repose if it is less than 35 degrees, or if the cargo is otherwise prone to shifting.
   5. Examples: Iron ore (lump/pellets, not fines prone to liquefaction), bauxite (lump, not liquefiable fines), cement, salt (rock salt), sand, gravel, alumina, sugar (raw, bulk), scrap metal (depending on form, some scrap can be Group B).

2. Individual Cargo Schedules:

The IMSBC Code contains individual schedules for a large number of commonly shipped solid bulk cargoes. Each schedule provides specific information and requirements for that particular cargo.

1. Structure of a Schedule: Typically includes:
   1. Description: A brief physical description of the cargo.
   2. Characteristics: A table listing key properties such as angle of repose, bulk density, stowage factor, size, class (if dangerous goods), and group (A, B, A & B, or C).
   3. Hazard: A detailed description of the potential hazards associated with the cargo (e.g., liquefaction, self-heating, gas emission, corrosivity, oxygen depletion, shifting).
   4. Stowage and Segregation: Specific requirements for how and where the cargo should be stowed (e.g., “away from heat,” “clear of living quarters,” “on deck only” for some hazardous cargoes), and segregation requirements from other incompatible cargoes or substances.
   5. Hold Cleanliness: The required standard of cleanliness for the cargo holds before loading.
   6. Weather Precautions: Precautions to be taken during loading/discharge in adverse weather (e.g., protecting cargo from rain if it’s moisture-sensitive or could become liquefiable).
   7. Loading: Specific instructions for loading, including trimming requirements, and precautions against dust or over-stressing the tank top.
   8. Precautions: General safety precautions for handling the cargo.
   9. Ventilation: Specific ventilation requirements during the voyage (e.g., “mechanical ventilation,” “surface ventilation only,” “no ventilation”).
   10. Carriage: Instructions for care of the cargo during the voyage (e.g., temperature monitoring, gas monitoring).
   11. Discharge: Any specific precautions for discharge.
   12. Clean-up: Notes on cleaning up residues.
   13. Emergency Procedures: Guidance on actions to take in case of an emergency (e.g., fire, spillage, liquefaction). This often refers to the Emergency Response Procedures for Ships Carrying Dangerous Goods (EmS Guide) if the cargo is also classified under the IMDG Code.
2. Using the Schedules: Before loading any listed cargo, the Master and Chief Officer must consult the relevant individual schedule in the IMSBC Code. This provides the authoritative guidance for safe handling and carriage.

3. Cargoes Not Listed in the IMSBC Code (Solid Bulk Cargoes N.O.S.):

If a shipper intends to load a solid bulk cargo that is not specifically listed by its Bulk Cargo Shipping Name (BCSN) in the IMSBC Code, it is considered a “Solid Bulk Cargo N.O.S.” (Not Otherwise Specified).

1. Procedure: The Code outlines a strict procedure for such cargoes:
   1. The shipper must provide detailed information concerning the properties and hazards of the cargo to the competent authority of the port of loading.
   2. The competent authority of the port of loading must assess this information and establish preliminary suitable conditions for carriage.
   3. This assessment and the proposed conditions for carriage must then be agreed upon by the competent authorities of the port of discharge and the Flag State of the vessel. This is often referred to as a “Tripartite Agreement.”
   4. The Master must be provided with a copy of this agreement and the agreed conditions for carriage before loading commences.
2. Master’s Responsibility: The Master should not load an unlisted cargo unless this procedure has been followed and the necessary approvals and conditions for carriage are provided.

Analysis for the Master (Cargo Groups and Schedules): A fundamental understanding of the Group A, B, and C classifications is the first step in risk assessment for any bulk cargo.

1. Immediate Red Flags: Knowing a cargo is Group A immediately alerts the Master to the critical importance of moisture content and TML. A Group B classification signals the need to investigate specific chemical hazards.
2. The Schedule is Key: The individual cargo schedule in the IMSBC Code is the primary reference document. It should be treated as the definitive guide for that specific cargo.
3. Beyond the Group: Even within Group C, cargoes can vary widely in their handling characteristics (e.g., density, angle of repose, dustiness). The schedule provides this detail.
4. “A and B” Cargoes: Some cargoes may be listed as “Group A and B,” meaning they possess both liquefaction potential and chemical hazards (e.g., some metal sulphide concentrates). These require adherence to precautions for both groups.
5. Dynamic Nature of the Code: The IMSBC Code is amended regularly (typically every two years) to include new cargoes, update existing schedules based on new information or incidents, and refine safety procedures. The Master must ensure the vessel carries the latest edition of the Code and any applicable amendments.
6. Training: Deck officers must be trained in using the IMSBC Code, understanding the group classifications, and interpreting the individual schedules. This is vital for your consultancy and bulkersguide.com – providing clear explanations and training materials on navigating the IMSBC Code would be highly valuable.

The grouping system and individual schedules within the IMSBC Code provide a structured and systematic approach to managing the diverse risks associated with solid bulk cargoes. For the Master, proficiency in using the Code is a non-negotiable aspect of ensuring the safety of the voyage.