Question 1

You are loading a general cargo consignment. The cargo plan shows ammonium nitrate (Class 5.1) in Hold 2 and petroleum products in drums (Class 3) in Hold 3, which is adjacent. Is this acceptable under the IMDG Code?

Accepted Answer

Ammonium nitrate (Class 5.1, oxidiser) and petroleum products (Class 3, flammable liquids) require segregation of "away from" (separated by an intervening space or hold) at minimum. Adjacent holds sharing a common bulkhead do not satisfy "away from" — the cargoes must be in non-adjacent holds with at least one hold separation. Check the IMDG Segregation Table (Chapter 7.2): oxidisers and flammable liquids require at minimum "away from" and in some cases "separated from." This loading plan requires amendment. IMDG Code Chapter 7.2: segregation categories: "away from" (minimum separation of 3m horizontally in the same space, or in different compartments/holds); "separated from" (separated by a complete compartment or hold — i.e. at least one intervening space); "separated by a complete compartment or hold" and "separated longitudinally by an intervening complete compartment or hold." Ammonium nitrate as an oxidiser can cause catastrophic decomposition if contaminated with fuel oil (the Beirut Port explosion 2020, Texas City 1947 were both ammonium nitrate events). The segregation requirement between Class 5.1 and Class 3 is "away from" at minimum — adjacent holds sharing a bulkhead do not satisfy this. An OOW discovering an incorrect cargo plan before loading must stop operations and refer to the Chief Officer and master. The IMDG Segregation Table in Chapter 7.2.4 provides the complete matrix of segregation requirements between all classes.

Question 2

Your examiner asks: "State the nine classes of dangerous goods under the IMDG Code and give one example of each." Give a complete answer.

Accepted Answer

Class 1: Explosives (e.g. detonators, fireworks). Class 2: Gases — 2.1 Flammable (LPG), 2.2 Non-flammable/non-toxic (compressed air), 2.3 Toxic (chlorine). Class 3: Flammable liquids (petrol, acetone). Class 4: Flammable solids — 4.1 Flammable solids (matches), 4.2 Spontaneously combustible (wet fishmeal), 4.3 Dangerous when wet (sodium, calcium carbide). Class 5: Oxidising substances — 5.1 Oxidisers (ammonium nitrate), 5.2 Organic peroxides. Class 6: Toxic and infectious — 6.1 Toxic (pesticides), 6.2 Infectious substances. Class 7: Radioactive. Class 8: Corrosives (battery acid, caustic soda). Class 9: Miscellaneous dangerous goods (lithium batteries, dry ice). The IMDG Code (International Maritime Dangerous Goods Code, made mandatory under SOLAS VII/3) uses UN-based classifications. Key points for OOW orals: Class 4 has three subdivisions — 4.2 (spontaneously combustible materials including wet fishmeal which has caused numerous bulk carrier fires) and 4.3 (dangerous when wet — water reacts to produce flammable gases) are the most hazardous from a watchkeeping perspective. Class 9 (lithium batteries) has become increasingly significant — lithium battery fires in containers and car carriers have caused major incidents (e.g. Felicity Ace). The IMDG Code is updated biennially; the 2022 edition (Amendment 41-22) is the current edition. Segregation requirements between classes are specified in IMDG Chapter 7 — an OOW must understand that certain classes cannot be stowed in the same space (e.g. oxidisers and flammables).

Question 3

Your examiner asks: "What are shear force and bending moment in the context of a ship's hull, and why must they be checked during cargo loading?"

Accepted Answer

Shear force is the tendency of adjacent hull sections to slide vertically past each other due to unequal distribution of weight and buoyancy along the length. Bending moment is the tendency of the hull to bend — hogging (bending upward amidships, like a banana bowing up) or sagging (bending downward amidships). Both must remain within the limits defined in the vessel's Stability Booklet and Class Rules. Exceeding these limits can cause permanent hull deformation or structural failure. The loading computer calculates SF and BM for the proposed loading condition and shows whether limits are exceeded. An OOW assisting with cargo loading must ensure the loading computer output is checked at each stage of loading, not just at departure. Hull girder strength is a fundamental cargo ship safety concept. Hogging: amidships section is unsupported while ends are supported (bow and stern overloaded, cargo concentrated amidships insufficient) — the hull tends to bend upward amidships. Sagging: the opposite — heavy cargo amidships with buoyancy concentrated amidships — hull bends downward. Bulk carriers loading heavy ore in alternate holds and light grain in others create dramatic SF and BM values. Container ships with variable stack weights have complex SF/BM patterns. The loading computer (approved by class and flag) integrates weight, buoyancy, and hull girder stiffness to calculate SF and BM at each frame station. SOLAS II-1 Reg 5-1 requires approved loading instruments for bulk carriers — the equivalent applies to all cargo ships under class rules. At OOW level, the key point is to understand what the output means and when to refer to the Chief Officer if limits are approached.