Question 1

You are carrying a cargo of bagged rice from Bangkok to Rotterdam. Your examiner asks: "What is ship's sweat and cargo sweat, and how do you manage ventilation to prevent condensation damage?"

Accepted Answer

Ship's sweat: moisture condenses on the cold steel of the ship's structure (hull and deckhead) and drips onto the cargo — occurs when the dew point of the air inside the hold is higher than the steel temperature. This typically happens when the ship moves from a warm humid region to a cold region (e.g. tropics to North Atlantic). Cargo sweat: moisture condenses directly on the surface of the cargo — occurs when the cargo is cooler than the dew point of the incoming ventilation air. This typically happens when the ship moves from a cold to a warm humid region. Rule: ventilate when the dew point of outside air is lower than the dew point of air inside the hold (Three Degrees Rule — ventilate if outside dew point is at least 3 degrees below cargo dew point). Do NOT ventilate when this condition is not met or when rain or spray could enter. Condensation damage is a significant cause of cargo claims on general cargo and container vessels. The Three Degrees Rule is the practical industry standard for ventilation decisions: ventilate when the outside dew point temperature is at least 3 degrees Celsius below the inside hold dew point — this ensures that introducing outside air will reduce rather than increase the moisture content inside the hold. A sling psychrometer or whirling hygrometer measures wet and dry bulb temperatures from which dew point is calculated using humidity tables (published in admiralty meteorological publications). An OOW keeping cargo watches must monitor external conditions and adjust ventilation decisions accordingly. The OOW's ventilation decisions must be logged — cargo claim investigations check the ventilation record against the meteorological log to assess whether appropriate action was taken. Rice, sugar, coffee, and cocoa are all hygroscopic cargoes particularly susceptible to condensation damage.

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

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.