Dry Bulk Cargo Hazards

Dry bulk cargoes — grain, coal, iron ore, nickel ore, bauxite, fertilisers, and hundreds of other materials — appear inert but carry serious hazards. More than 100 seafarers have died in bulk carrier casualties directly attributable to cargo hazards in the past two decades.

Answer in Brief

The four main hazard categories for dry bulk cargo: (1) Liquefaction — cargo flows like liquid after vibration, causing sudden list; (2) Self-heating and spontaneous combustion — particularly coal; (3) Oxygen depletion and toxic gas emission — in enclosed holds; (4) Shifting cargo — leading to dangerous list. The IMSBC Code (International Maritime Solid Bulk Cargoes Code) regulates all of these.

Hazard 1: Liquefaction

What it is: Certain fine-grained cargoes with high moisture content can liquefy during the voyage. Vibration from the ship’s engines and sea conditions causes the solid cargo to behave like a liquid — it flows.

The danger: A hold of liquefied cargo shifts to one side. The ship develops a severe list. In minutes, the list can become uncontrollable, leading to capsize.

Cargoes at risk: Nickel ore, iron ore fines, bauxite, some mineral sands, coal fines, fluorspar.

Prevention:

• Cargo must be tested for moisture content (Transportable Moisture Limit — TML) before loading
• Actual moisture content must be below TML
• Shipper must provide a Certificate of Moisture Content
• Master has the right to reject cargo if moisture content exceeds TML
• If doubt exists: use the can test (fill a can with cargo sample, seal, shake — if water appears on surface, cargo is unsafe to load)

Warning signs: Cracking sounds from cargo holds, list developing without obvious cause.

Hazard 2: Self-Heating and Spontaneous Combustion

What it is: Coal, certain sulphide ores, and other materials can oxidise and generate heat internally. If heat accumulates without ventilation, fire can start within the cargo — even without external ignition.

Cargoes at risk: Coal (particularly high-volatility coal), charcoal, sulphide concentrates.

Prevention:

• Follow IMSBC Code requirements for ventilation of coal holds
• Coal requires surface ventilation — do not ventilate if cargo temperature > ambient temperature (risk of condensation and increased oxidation in some conditions)
• Monitor hold atmosphere: O₂ concentration, CO concentration (CO increases indicate active combustion)
• Coal additionally emits methane — explosive when mixed with air in 5–15% concentration range. No naked flames, no electrical sparks near coal cargo holds.

If fire detected: Water is NOT appropriate for coal cargo fire — creates explosion risk (steam). CO₂ or boundary cooling are the approaches. Seek expert guidance immediately.

Hazard 3: Oxygen Depletion and Toxic Gas Emission

What it is: Some cargoes consume oxygen in enclosed spaces, creating an atmosphere that is immediately dangerous to life. Other cargoes emit toxic gases.

Oxygen-depleting cargoes: Direct-reduced iron (DRI), coal (during oxidation), wood pellets, some ores.

Toxic gas-emitting cargoes:

• Ammonium nitrate: Can emit toxic nitrogen dioxide
• Timber: Can emit CO₂ and CO in enclosed spaces
• Sulphide concentrates: Hydrogen sulphide (H₂S) — extremely toxic at low concentrations

Prevention:

• Treat all bulk cargo holds as enclosed spaces — never enter without atmospheric testing
• Test for O₂ content (minimum 20.8% for safe entry)
• Test for toxic gases specific to the cargo
• Permit-to-Work system for hold entry
• Minimum two persons — one entering, one supervising topside with rescue equipment

The IMSBC Code requires: Specific ventilation, monitoring, and entry precautions for each Group A (liquefaction risk), Group B (chemical hazard), and Group C (no special hazard) cargo.

Hazard 4: Cargo Shifting

What it is: Even non-liquefying cargo can shift during heavy rolling, creating a list. Particularly risky with:

• Concentrates (high density, fine grain)
• Grain (angle of repose can be exceeded)
• Any cargo loaded unevenly

Prevention:

• Trim the cargo (level surface after loading — no peaks or valleys)
• Grain requires fitting of feeder boxes or bagging, or longitudinal shifting boards (SOLAS grain loading requirements)
• Maintain adequate GM throughout the voyage
• Monitor for list development — investigate any unexplained list immediately

The IMSBC Code

The International Maritime Solid Bulk Cargoes (IMSBC) Code (mandatory under SOLAS chapter VI) classifies all bulk cargoes and specifies:

• Individual schedules for hundreds of cargoes with specific requirements
• TML testing methods
• Atmosphere monitoring requirements
• Ventilation instructions
• Emergency procedures

Every bulk carrier Chief Officer must have access to the IMSBC Code and understand the schedule for every cargo being loaded.

Questions about specific bulk cargo hazards, IMSBC Code requirements, or cargo hold safety? Chat with SailorGPT