4.3 Container Cargo, Bulk Cargoes & IMDG Code Awareness

4.3 Container Cargo, Bulk Cargoes & IMDG Code Awareness

Modern merchant shipping encompasses specialized cargo systems governed by comprehensive international safety codes. General Purpose ratings work across diverse vessel types: container carriers transporting thousands of standardized boxes, bulk carriers moving mineral ores and agricultural grains, and general cargo ships carrying hazardous chemicals. Understanding container handling systems, the liquefaction hazards of solid bulk cargoes under the IMSBC Code, and dangerous goods classification under the IMDG Code is essential for deck watchkeeping, personal safety, and successful completion of the DG Shipping GP Rating exam.

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1. Container Cargo Handling, Dimensions & Securing Systems

Intermodal containers are manufactured to strict International Organization for Standardization (ISO) specifications, enabling intermodal transfer across ships, trucks, and rail.

Standard Container Specifications

• Twenty-foot Equivalent Unit (TEU): The standard statistical measurement of container capacity based on a $20\text{-foot}$ container.
• High-Cube Containers (HC): Feature an increased height of $9\text{ ft } 6\text{ in}$ ($2.90\text{ m}$), offering 12% more internal cubic volume. They are marked with black and yellow chevron warning stripes around the top corner castings and height warning decals on the doors.

Below Deck vs. On Deck Securing Systems

                 CONTAINER SECURING CONNECTIONS

                      [ TIER 3 CONTAINER ]
                       INTERMEDIATE LOCKS
                      [ TIER 2 CONTAINER ]
                       INTERMEDIATE LOCKS
                      [ TIER 1 CONTAINER ]
                          BASE LOCKS
                      [ HATCH FOUNDATION ]

 Approved upper-tier corner fitting
             |
        LASHING ROD
             |
         TURNBUCKLE
             |
 Deck or lashing-bridge securing eye

 Rods run diagonally outside the stack, from the specified corner
 fittings to their anchors. Follow the Cargo Securing Manual for
 tiers, geometry, fittings and tightening. Bridge fittings, where
 specified, connect adjacent stacks at the top corner fittings.

Below Deck (Cellular Holds)

• Holds are fitted with vertical structural steel angles known as cell guides.
• Containers slide down between the cell guides and are held rigidly along their corner posts.
• Cell guides restrain container movement, but fit the stacking cones, twistlocks or other securing fittings required by the Cargo Securing Manual. Below-deck stowage does not remove those requirements.

On Deck Securing Hardware

Containers on weather deck pontoon hatch covers are stacked 4 to 9 tiers high. They must resist extreme wind, wave impact, and dynamic rolling accelerations using specialized securing hardware:

1. Twistlocks: Forged steel locking devices inserted into container corner castings:
   • Semi-Automatic Twistlocks (SATLs): Feature a bright yellow lower body and release handle. They are inserted manually into container bottom corner castings on the quay before hoisting. When lowered onto the container stack, internal spring-loaded cones automatically lock into the corner casting below. Unlocking is achieved from deck level using a long aluminum lashing pole.
   • Manual Twistlocks: Require a crew member to physically turn a lever handle ($90^\circ$ left or right) to lock and unlock.
2. Bridge Fittings: Heavy, screw-tightened steel clamps fitted into adjacent top corner castings to clamp two adjacent container stacks together athwartships, preventing the stacks from racking or separating independently during heavy rolling.
3. Stacking Cones: Placed between corner castings to prevent lateral sliding where twistlocks are not utilized.
4. Lashing Rods & Turnbuckles (Bottle Screws): High-tensile solid steel rods with head knobs that fit into corner castings. Short rods (approx. 2.5 m) secure the second tier; long rods (approx. 5.0 m) secure the third tier. Turnbuckles with pelican hooks connect the rods to deck D-rings, tightened with tommy bars and locked with locknuts.
5. Lashing Bridges: Elevated steel walkways spanning athwartships between container bays on large modern vessels. They allow ratings to secure lashing rods to the 2nd, 3rd, and 4th tiers safely without climbing precariously onto hatch covers.

Trainee GP Rating Safety During Lashing & Unlashing

Deck lashing operations represent high-risk working environments. GP ratings must follow these non-negotiable safety rules:

1. Never Walk Under Suspended Loads: Never walk or stand beneath a moving container, shore gantry spreader, or ship crane. Crane operators have significant blind spots.
2. Mandatory Personal Protective Equipment (PPE): Always wear a high-visibility vest or boiler suit, hard hat with chinstrap fastened, protective safety eyewear, heavy-duty leather rigger gloves, and steel-toed non-slip safety footwear.
3. Twistlock Orientation Inspection: Verify that all twistlock handles face the correct uniform direction (locked vs. unlocked) per the ship's Cargo Securing Manual (CSM). An incorrectly oriented twistlock can jam a container or tear open corner castings.
4. Safe Handling of Lashing Poles: Keep both feet planted firmly on the deck or lashing bridge. Grip the aluminum lashing pole with both hands. When unlocking twistlocks aloft, stand clear of the fall line to prevent dropped twistlocks from striking you.
5. Fall Arrest & Working Aloft Precautions: When working on container tops, hatch coamings, or outer outboard lashing platforms, mariners must wear an approved full-body safety harness connected via an energy-absorbing lanyard or self-retracting lifeline (inertia reel) to a certified jackstay or engineered anchor point.

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2. Solid Bulk Cargoes & The IMSBC Code

The maritime transport of solid bulk cargoes is governed by the IMSBC Code (International Maritime Solid Bulk Cargoes Code), mandatory under SOLAS Chapter VI.

The Three IMSBC Cargo Groups

                         IMSBC CARGO GROUPS

 GROUP A                     GROUP B                    GROUP C
 Moisture hazards            Chemical hazards           Neither A nor B
 - Iron ore fines            - Coal                     - Iron ore lumps
 - Nickel ore                - Direct reduced iron      - Quartz lumps
 - Bauxite fines             - Ammonium nitrate         - Cement clinker
 - Copper concentrate                                   - Steel scrap

 A: Liquefaction or dynamic separation may impair stability.
 B: Fire, harmful gas, oxygen depletion or other chemical danger.
 C: Physical hazards such as overload and shifting still require control.
 Coal is normally A and B unless properly classified as B only.

Group A (Moisture Hazards)

• Definition: Cargoes with moisture-related hazards that may liquefy or undergo dynamic separation. They may look dry when loaded. Dynamic separation forms a liquid layer of water and fine solids above the solid cargo; its free surface can impair stability. A cargo may have both Group A and Group B hazards.
• Physics of Liquefaction: Ship motion and vibration can compact moist cargo and raise pore water pressure. This reduces effective contact and friction between particles, lowering the cargo’s shear strength until it can behave as a fluid. The resulting slurry may move to one side with a roll and not fully return, progressively causing a dangerous heel.
• Catastrophic Consequence: Moving slurry creates a free-surface effect and cargo shift. The resulting heel can become too large for the ship to recover, causing sudden capsize. Trimming alone does not make an excessively wet Group A cargo safe.
• Common Group A Cargoes: Iron ore fines, nickel ore, bauxite fines, copper concentrates, lead concentrates, and zinc concentrates.
• Critical Statutory Moisture Parameters:
  • Moisture Content (MC): The actual percentage of water present in a cargo sample.
  • Flow Moisture Point (FMP): The moisture percentage at which a flow state develops under standardized laboratory vibration testing.
  • Transportable Moisture Limit (TML): The cargo-specific moisture limit determined by an approved laboratory method. For the applicable flow-table or penetration method:

$\text{TML} = 0.90 \times \text{FMP}$

Other approved methods, including Proctor/Fagerberg methods, determine TML from their own criteria. Use the certified TML for the cargo; do not apply the 90% formula to every Group A material.

• The Onboard "Can Test":
  • A practical screening check performed by ship's officers and ratings at the loading berth under IMSBC Code Section 8.
  • A cylindrical can (approx. 1 liter capacity, such as a metal coffee tin) is filled half-full with a fresh sample of the bulk cargo.
  • The can is brought to a height of approximately $20\text{ cm}$ above a solid steel deck or hard surface and tapped sharply onto the surface 25 times at 1-second intervals.
  • Result: If free moisture, wet sheen, or liquid slurry appears on the top surface of the sample, the cargo is dangerously wet and suspect. The cargo fails the test; loading must be stopped immediately and certified laboratory moisture testing demanded.

Group B (Cargoes Possessing Chemical Hazards)

• Definition: Materials possessing inherent chemical hazards that can endanger the vessel or crew through fire, explosion, toxic gas emission, or oxygen depletion.
• Key Group B Cargoes and Hazards:
  • Coal: Emits flammable, explosive methane gas ($CH_4$, explosive range 5% to 15% in air); absorbs oxygen from the hold atmosphere creating a lethal asphyxiation hazard; undergoes self-heating leading to spontaneous combustion, which generates deadly carbon monoxide ($CO$).
  • Direct Reduced Iron (DRI): Pure metallic iron pellets that react vigorously with water/moisture to generate flammable hydrogen gas ($H_2$) and intense heat, capable of igniting hold fires and melting electrical cabling.
  • Ammonium Nitrate Fertilizers: Powerful oxidizing agents that support combustion and decompose under heat to release toxic nitrogen oxide ($NO_x$) fumes, with extreme risks of explosion.
• Safety Controls: Follow the individual IMSBC schedule for gas and temperature monitoring and ventilation. Never blow air through the body of self-heating coal. Methane-emitting coal requires surface ventilation; a steadily rising carbon monoxide level requires closing the hold, stopping ventilation and seeking expert advice immediately.

Group C (Neither Group A nor Group B)

• Definition: Cargoes classified as neither Group A nor Group B. Their carriage still requires control of physical hazards such as overloading and cargo shift.
• Examples: Iron ore lumps, cement clinker, dry silica quartz, scrap metal, and marble granules.
• Hazards: High density can cause localized structural overloading of double bottom tank tops if poorly distributed; cargo shifting can occur if not properly trimmed.

Carriage of Bulk Grain & The International Grain Code

Regulated under the International Code for the Safe Carriage of Grain in Bulk (International Grain Code):

• Hazard: Bulk grain (wheat, corn, barley) settles during voyage vibrations, creating void spaces under the deckhead. If the vessel rolls beyond the natural angle of repose, the grain surface shifts violently to the low side, creating a permanent listing moment.
• Precautions: Follow the approved grain loading manual and trim as required for the selected loading condition. Partly filled grain surfaces must be level as required by the Code; prevent shift by approved overstowing or securing unless the stability calculation allows for it. Saucers and bundling in hatch openings are arrangements for filled, trimmed compartments. Heel due to assumed grain shift must not exceed $12^\circ$; for ships constructed on or after 1 January 1994, use the angle of deck-edge immersion instead if it is smaller.

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3. IMDG Code (International Maritime Dangerous Goods) Awareness

The maritime transport of dangerous goods in packaged form is governed by the IMDG Code (International Maritime Dangerous Goods Code), mandatory under SOLAS Chapter VII and MARPOL Annex III.

The 9 IMDG Hazard Classes

                          THE 9 IMDG CLASSES

   Class 1: EXPLOSIVES (Div 1.1 - 1.6)
   Class 2: GASES (2.1 Flammable, 2.2 Non-Flammable/Non-Toxic, 2.3 Toxic)
   Class 3: FLAMMABLE LIQUIDS (Flashpoint <= 60 deg C)
   Class 4: FLAMMABLE SOLIDS (4.1 Solids, 4.2 Spont. Combustible, 4.3 Dangerous When Wet)
   Class 5: OXIDIZERS & PEROXIDES (5.1 Oxidizing, 5.2 Organic Peroxides)
   Class 6: TOXIC & INFECTIOUS (6.1 Toxic Substances, 6.2 Infectious Pathogens)
   Class 7: RADIOACTIVE MATERIAL (White-I, Yellow-II, Yellow-III)
   Class 8: CORROSIVE SUBSTANCES (Acids and Alkalis)
   Class 9: MISCELLANEOUS DANGEROUS GOODS (Marine Pollutants, Li-ion Batteries)

1. Class 1: Explosives: Substances or articles designed to produce an explosive or pyrotechnic effect. Subdivided into 6 divisions (1.1 mass explosion hazard down to 1.6 extremely insensitive articles; e.g., dynamite, ammunition, distress flares).
2. Class 2: Gases:
   • Division 2.1: Flammable Gases (e.g., propane, butane, acetylene, LPG). Red label with flame.
   • Division 2.2: Non-Flammable, Non-Toxic Gases (e.g., compressed air, nitrogen, $CO_2$, argon). Green label with gas cylinder.
   • Division 2.3: Toxic Gases (e.g., chlorine, phosgene, hydrogen sulfide). White label with skull and crossbones.
3. Class 3: Flammable Liquids: Liquids, mixtures of liquids, or liquids containing solids in solution/suspension that give off flammable vapors at a closed-cup flashpoint of $60^\circ\text{C}$ or below (e.g., gasoline, diesel, crude oil, paints, thinners, acetone). Red diamond label with flame.
4. Class 4: Flammable Solids & Water-Reactive Substances:
   • Division 4.1: Flammable Solids (e.g., matches, sulfur, red phosphorus). Red and white vertical stripes.
   • Division 4.2: Spontaneously Combustible Substances (pyrophoric and self-heating materials like white phosphorus, activated carbon). Top half white, bottom half red.
   • Division 4.3: Dangerous When Wet (emit flammable gases like hydrogen or acetylene in contact with water; e.g., calcium carbide, sodium metal). Blue label with flame.
5. Class 5: Oxidizing Substances & Organic Peroxides:
   • Division 5.1: Oxidizing Substances (substances yielding oxygen to stimulate combustion in other materials; e.g., ammonium nitrate, calcium hypochlorite). Yellow label with burning ball.
   • Division 5.2: Organic Peroxides (thermally unstable compounds undergoing exothermic decomposition; e.g., benzoyl peroxide). Top half red, bottom half yellow.
6. Class 6: Toxic & Infectious Substances:
   • Division 6.1: Toxic Substances (liable to cause death or serious injury if swallowed, inhaled, or absorbed; e.g., cyanides, arsenic, pesticides). White label with skull and crossbones.
   • Division 6.2: Infectious Substances (pathogens and biological cultures; e.g., medical clinical waste). White label with biohazard symbol.
7. Class 7: Radioactive Material: Substances containing radionuclides emitting ionizing radiation (e.g., medical isotopes, uranium hexafluoride). White-I, Yellow-II, or Yellow-III diamond labels with radiation trefoil.
8. Class 8: Corrosive Substances: Substances causing severe destruction of intact living tissue or chemical corrosion of ship steel and aluminum (e.g., sulfuric acid, hydrochloric acid, caustic soda, battery acid). Top half white with liquids corroding hand and steel, bottom half black.
9. Class 9: Miscellaneous Dangerous Substances & Articles: Substances presenting hazards during maritime transport not covered by other classes (e.g., marine pollutants, dry ice, asbestos, lithium-ion batteries). White label with 7 vertical black stripes in top half.

Hazard Communication & Safety Documentation

• Placards & Labels: Diamond-shaped hazard placards measuring $250 \times 250\text{ mm}$ must be displayed on all four exterior sides of freight containers; package labels measure $100 \times 100\text{ mm}$.
• UN Number: A unique 4-digit number assigned by the United Nations Committee of Experts (e.g., UN 1203 for Motor Gasoline, UN 1005 for Anhydrous Ammonia). Displayed on an orange rectangular panel or inside the hazard diamond placard.
• Proper Shipping Name (PSN): The standard chemical or technical name identified in the IMDG Code. Commercial brand names or trade names must never be used on statutory shipping papers.
• Safety Data Sheet (SDS): A 16-section hazard-information reference that can support emergency response. It does not replace the required dangerous-goods transport information identifying the cargo, its hazards and the shipper’s declaration.
• The EmS Guide (Emergency Schedules):
  • Provides emergency response schedules for crews:
    • Fire Schedules (F-A to F-J): Detail fire-extinguishing tactics (e.g., use water spray, do not use water, evacuate space).
    • Spillage Schedules (S-A to S-Z): Detail containment and cleanup actions (e.g., wash overboard with plenty of water, collect in dedicated drums, use breathing apparatus).
• Medical First Aid Guide (MFAG): Companion guidance providing specific clinical diagnosis, antidotes, and resuscitation treatments for chemical accidents at sea.

Stowage & Segregation Principles

Incompatible dangerous goods must be segregated under the applicable IMDG entry and segregation table. For packages stowed conventionally, the four terms mean:

• 1: "Away from": At least 3 m horizontally, projected vertically; the same hold or deck may be used.
• 2: "Separated from": Different compartments or holds below deck; an intervening fire- and liquid-resistant deck can provide vertical separation. On deck: at least 6 m horizontally.
• 3: "Separated by a complete compartment or hold from": An entire intervening compartment or hold horizontally, or a complete intervening compartment vertically between two decks, at least one resistant to fire and liquid. Otherwise use longitudinal separation. On deck, or between on-deck cargo and an upper compartment: at least 12 m horizontally.
• 4: "Separated longitudinally by an intervening complete compartment or hold from": An intervening complete compartment or hold longitudinally; vertical separation alone is insufficient. On deck: at least 24 m longitudinally. Between under-deck and on-deck packages: at least 24 m longitudinally, including a complete compartment.

Freight containers and other cargo transport units use their own applicable IMDG segregation provisions; do not apply these package distances as a universal container-stowage table.