Section 18.2 Cargo-Related Emergencies (Liquefaction, Cargo Shift, Fire in Cargo Hold)

Bulk carriers transport a vast array of commodities, some of which possess inherent hazards that can lead to serious emergencies if not properly managed. Understanding these cargo-specific risks is paramount for the Master and crew. The International Maritime Solid Bulk Cargoes (IMSBC) Code is the primary international reference for the safe carriage of solid bulk cargoes.

1. Cargo Liquefaction: This is one of the most dangerous phenomena for bulk carriers, primarily associated with fine-grained mineral ore concentrates (e.g., iron ore fines, nickel ore, bauxite fines, some types of coal) and other cargoes susceptible to moisture migration.

Mechanism: When a cargo with moisture content exceeding its Transportable Moisture Limit (TML) is subjected to the vibration and motion of the ship at sea, the interstitial water can migrate upwards. This reduces the friction between particles, causing the cargo to behave like a fluid (liquefy).

Consequences:

Rapid Loss of Stability: The liquefied cargo can shift suddenly and violently from one side of the hold to the other as the ship rolls, creating a massive free surface effect.

Listing and Capsizing: This can lead to a severe list, progressive flooding if hatch covers are breached or structural damage occurs, and ultimately, rapid capsizing of the vessel, often with little time for the crew to react or abandon ship.

IMSBC Code Requirements:

Cargo Information: Shippers are obligated to provide accurate cargo information, including the moisture content (MC), TML, and flow moisture point (FMP) for Group A cargoes (cargoes that may liquefy).

Testing: Procedures for sampling and testing cargoes for TML and MC are specified. The Master has the right to re-test if there are doubts.

Acceptance Criteria: Cargoes with MC exceeding TML must not be loaded unless the ship is specially constructed or fitted for carrying such cargoes (e.g., with dedicated dewatering systems, as per IMSBC Code section 7).

Key Preparedness and Response Aspects:

Prevention (Pre-Loading):

Strict Adherence to IMSBC Code: Ensure all documentation is correct and complete.

Verify TML and MC: Pay close attention to certificates. If in doubt, or if cargo appears excessively wet (e.g., “splatter test” on the bulkhead shows free moisture), insist on re-testing by an independent surveyor before and during loading.

Visual Inspection: Look for signs of excessive moisture during loading.

“Can Test”: While not a definitive test, the “can test” described in the IMSBC Code can provide an indication of potential liquefaction risk.

Weather Conditions: Avoid loading during heavy rain if the cargo is susceptible.

During Voyage (If Liquefaction is Suspected):

Signs of Liquefaction: Cargo surface flattening, free water forming on the surface, splattering against bulkheads, unusual ship motion or sluggish rolling.

Immediate Actions:

Consider heading for the nearest port or place of refuge.

Seek immediate expert advice (Company, P&I Club, Class).

If safe, try to reduce ship motions (e.g., alter course/speed to minimize rolling).

Ensure all crew are on alert and prepared for potential abandonment.

Do NOT enter the cargo hold.

Consider ballasting/deballasting strategies ONLY on expert advice, as this can worsen the situation if done incorrectly.

Training: Crew must be educated about the dangers of liquefaction, how to identify susceptible cargoes, and the importance of pre-loading checks.

2. Cargo Shift: While liquefaction is a specific type of cargo shift, other bulk cargoes can also shift, particularly those with a low angle of repose or if not properly trimmed during loading.

Causes:

Improper Trimming: Failure to level the cargo surface sufficiently, leaving large voids or high peaks.

Low Angle of Repose: Some cargoes (e.g., certain grains, some concentrates) naturally flow more easily.

Ship Motion: Heavy rolling or pitching can initiate cargo movement.

Insufficient Securing (for some cargoes): While most bulk cargoes are not “secured” in the traditional sense, proper stowage and trimming are key.

Consequences:

Listing: Similar to liquefaction, a cargo shift can cause a list, impairing maneuverability and potentially leading to progressive flooding or structural damage.

Structural Damage: The dynamic forces of shifting cargo can overstress the ship’s structure.

IMSBC Code Requirements:

Trimming Procedures: The IMSBC Code specifies trimming requirements for various cargoes to minimize the risk of shifting. Generally, cargoes should be trimmed reasonably level.

Angle of Repose: Information on the angle of repose is critical for assessing shift risk.

Key Preparedness and Response Aspects:

Prevention (Loading):

Strict Adherence to IMSBC Code Trimming Requirements: Ensure proper supervision during loading to achieve the required level of trimming.

Stowage Plan: Develop a stowage plan that considers cargo characteristics and minimizes void spaces.

During Voyage (If Cargo Shift is Suspected or Occurs):

Signs of Shift: Unexpected or increasing list, unusual ship motion.

Immediate Actions:

Reduce ship speed and alter course to minimize rolling and pitching.

If safe, inspect the cargo holds (externally at first).

Consider ballasting to counteract the list, but only after careful stability calculations and, if possible, expert advice. Incorrect ballasting can worsen the situation or overstress the hull.

Prepare emergency equipment.

Report to the company and seek advice.

Training: Crew, especially officers involved in cargo operations, must understand the principles of cargo trimming and the risks associated with different cargo types.

3. Fire in Cargo Hold: Many bulk cargoes are combustible or can self-heat, leading to fire.

Susceptible Cargoes:

Coal: Prone to self-heating and spontaneous combustion, especially lower-rank coals. Can also emit flammable methane gas.

Direct Reduced Iron (DRI) – HBI, HPI: Can self-heat and react with air and/or water, producing hydrogen (flammable gas) and intense heat. Some forms are highly reactive.

Sulphur (Bulk): Flammable and can create explosive dust clouds.

Seed Cake / Agricultural Products: Can self-heat or be susceptible to external ignition.

Woodchips/Sawdust: Combustible.

Metal Turnings/Swarf: Can self-heat and react with water.

Causes:

Self-Heating/Spontaneous Combustion: Inherent property of the cargo.

External Ignition Sources: Sparks from hot work, smoking, electrical faults.

Contamination: Contamination with other materials that can promote combustion.

Consequences:

Damage to Cargo and Vessel: Extensive fire damage.

Toxic and Flammable Gases: Risk to crew health and further explosion risk.

Structural Damage: Intense heat can weaken the ship’s structure.

Loss of Vessel: In severe cases.

IMSBC Code Requirements:

Cargo Declarations: Must state if the cargo is liable to self-heat or is flammable.

Specific Carriage Requirements: The Code details specific precautions for hazardous cargoes, including ventilation requirements, temperature monitoring, and fire-fighting procedures.

Prohibition of Smoking/Hot Work: Strict controls in and around cargo areas.

Key Preparedness and Response Aspects:

Prevention:

Adherence to IMSBC Code: Follow all specific carriage instructions for the cargo.

Temperature Monitoring: For self-heating cargoes (e.g., coal, DRI), regular temperature monitoring during loading and voyage is crucial.

Ventilation Control: Proper ventilation as per IMSBC Code (e.g., surface ventilation for coal to remove methane, but restricted ventilation if self-heating is detected to limit oxygen).

Inerting: Some cargoes (e.g., certain DRI) may require loading in an inert atmosphere or have inert gas capabilities onboard.

Hatch Cover Sealing: Ensure hatch covers are weathertight to prevent water ingress (which can exacerbate some self-heating reactions or damage cargo) and to assist in containing fire/gases if an incident occurs.

Detection:

Visual Inspection: Smoke or unusual smells from holds.

Gas Detection: Monitoring for flammable gases (e.g., methane, hydrogen) or toxic gases (e.g., carbon monoxide, hydrogen sulphide) as appropriate for the cargo.

Temperature Readings: Regular checks of cargo temperature.

Response:

Raise Alarm and Muster Crew.

Identify the Affected Hold.

Seal the Hold: Close all vents and openings to the affected hold to restrict oxygen supply (unless the IMSBC Code or expert advice dictates otherwise for a specific cargo, e.g., initial surface ventilation for methane from coal).

Boundary Cooling: Cool adjacent bulkheads and decks with water.

Fixed CO2 System: If a fixed CO2 system is fitted for cargo holds (common on many bulk carriers), prepare and use it according to procedures. This is often the primary means of fighting deep-seated cargo fires. Ensure personnel are clear before release.

Water Application (Caution): Applying water directly onto some burning bulk cargoes can be dangerous and counterproductive (e.g., some DRI reacts violently with water, coal fires can generate explosive gases if water is applied incorrectly). Always consult the IMSBC Code and seek expert advice before applying water to a cargo fire.

Seek Expert Advice: Immediately contact the company, P&I Club, and fire-fighting experts. The nature of the cargo dictates the correct fire-fighting strategy.

Consider Diversion: Head for the nearest suitable port.

Training: Drills for cargo hold fire scenarios, including use of fixed CO2 systems, boundary cooling, and understanding specific cargo hazards.

Managing cargo-related emergencies effectively relies heavily on understanding the specific properties of the cargo being carried, strict adherence to the IMSBC Code, diligent monitoring during the voyage, and well-rehearsed emergency procedures.