Question 1

Your chemical tanker is carrying methanol in Cargo Tank 3. What are the key safety requirements for carrying methanol under the IBC Code?

Accepted Answer

METHANOL UNDER IBC CODE — CM REQUIREMENTS: Methanol (UN 1230) is a CHAPTER 17 IBC Code product — an individual chemical with specific carriage requirements. IBC Code lists requirements in the COF (Certificate of Fitness) and the ship's cargo data sheet. KEY METHANOL REQUIREMENTS: (1) TANK TYPE: IBC Code requires type 2 or type 3 tank (independent tank) — methanol can be carried in IMO Type 2 independent tanks; (2) VAPOUR PRESSURE: methanol vapour pressure at 45°C is approximately 40 kPa — within Pressure/Vacuum (P/V) valve normal range; (3) FLAMMABILITY: methanol is highly flammable — flashpoint 11°C. Treat as flammable liquid at all times. Inert gas or dry air padding required (IBC requirement for specific tank type); (4) TOXICITY: methanol is toxic by inhalation, skin absorption, and ingestion. IMO IBC: toxic vapour detector required. PPE: chemical splash suit, SCBA, gloves, goggles for any exposure risk; (5) REACTIVITY: methanol is incompatible with: strong oxidising agents; strong acids; chlorine compounds. Do not stow adjacent to incompatible cargoes without IBC Code buffer tank or compatibility check; (6) FIRE: methanol produces an almost invisible flame in daylight. Use dry powder, CO2, or alcohol-resistant foam. Water dilutes but does NOT extinguish methanol fire effectively; (7) HEATING: methanol does not require heating. At normal temperatures, it remains pourable; (8) CARGO DATA SHEET: IBC Code Chapter 17 methanol data sheet specifies all handling requirements. The vessel's MSDS/SDS for methanol must be on board; (9) COF: the vessel's Certificate of Fitness must authorise methanol carriage. Check column heading requirements. IBC Code (International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk): made mandatory by SOLAS II-2/54 and MARPOL Annex II. Chapter 17 lists individual products and specifies: tank type, fire protection, vapour detection, cargo pump type, inhibitor requirements, maximum filling limit, temperature requirements, and more. Methanol hazards — invisible flame: one of the most dangerous aspects of a methanol fire. In daylight, the methanol flame produces no visible light — the fire can be burning on deck without anyone seeing it. Heat is the indicator. Several accidents have involved personnel walking into invisible methanol fires. Water on methanol fire (option C): water will dilute methanol and reduce the flammability — but a large methanol fire on a tank deck cannot be extinguished by water alone. The correct agent is alcohol-resistant AFFF foam, CO2, or dry powder. Adding water to a burning methanol pool can cause rapid vaporisation and vapour spread. Certificate of Fitness (COF): the COF is issued by the classification society on behalf of the flag state. It lists the specific products the vessel is authorised to carry. Carrying a product not on the COF is a SOLAS violation. The COF also specifies the column requirements (tank type, fire protection, etc.) for each product — the CM must check the COF against the cargo before loading. IBC Code ongoing applicability (option D): incorrect. The IBC Code applies to the operation and management of chemical cargo, not just the ship's construction. Chapter 3 sets requirements for cargo operations, fire safety, and personnel protection that apply every voyage.

Question 2

As Chief Mate on a product tanker, explain the purpose and operation of the inert gas system before cargo discharge.

Accepted Answer

INERT GAS SYSTEM (IGS) — CM KNOWLEDGE: PURPOSE: The IGS prevents flammable hydrocarbon vapours from reaching an explosive concentration in cargo tanks. A hydrocarbon-air mixture is flammable between approximately 1-10% hydrocarbon concentration (LEL to UEL). The IGS keeps O2 concentration below 8% (SOLAS requirement: below 8% O2 by volume) — at this level, the vapour cannot ignite regardless of hydrocarbon concentration. SYSTEM COMPONENTS: (1) SOURCE: combustion gas from the ship's boiler or dedicated inert gas generator (IG generator using gas turbine or diesel exhaust). Typical O2 content of flue gas: 2-5%; (2) SCRUBBER: removes corrosive components (SO2, H2S, soot) from the flue gas before it enters tanks. Water is the scrubbing medium; (3) BLOWER (FANS): propel the scrubbed gas into the distribution main; (4) DECK WATER SEAL: the critical safety device between the blower and cargo tanks. Prevents backflow of hydrocarbon gas to the machinery space if fans fail. Always maintained wet; (5) P/V BREAKER: secondary protection against overpressure/underpressure in tanks; (6) O2 ANALYSER: continuous monitoring of O2 content in the IG supply and individual tanks. PRE-DISCHARGE PROCEDURE: (1) Check O2 content of all cargo tanks — must be below 8% by volume; (2) Ensure IG pressure positive in tanks before beginning discharge (tank pressure > atmospheric); (3) Start IG supply to replace vapour volume as cargo is discharged; (4) Monitor O2 levels throughout discharge; (5) Never open tank in oxygen-enriched atmosphere without gas-free certificate. IGS SOLAS requirement: SOLAS II-2/4.5.5 — inert gas systems are required on crude oil tankers over 20,000 DWT and product carriers over 40,000 DWT. Failure to maintain the IGS is a detainable deficiency under PSC. The flammability triangle: three elements required for fire — fuel (hydrocarbon vapour), oxygen (above 10-11%), and ignition source. The IGS removes oxygen below 8%, eliminating one corner of the triangle. O2 below 8%: at this level, even if there is 100% hydrocarbon vapour in the space, the mixture cannot ignite. This is the safety principle of the IGS. The deck water seal: critical safety device. If the IG fans fail, backflow of hydrocarbon vapour toward the boiler (ignition source) must be prevented. The water seal provides a physical barrier. If the seal runs dry — the IGS is compromised. The CM must ensure the water level is maintained. CO2 confusion (option C): the IG system uses boiler flue gas (N2 + CO2 + water vapour — low O2), NOT pure CO2. The CO2 fixed fire system is separate and is used for firefighting in cargo holds on other vessel types. IGS during discharge (option B): during discharge, as liquid cargo leaves the tank, the vapour space increases. If the tank is not kept under positive IG pressure, air could be drawn in through vapour venting points and create a flammable mixture. IGS must run continuously throughout discharge.

Question 3

Your crude oil tanker is 4 hours from the terminal. As Chief Mate, what pre-arrival preparations do you coordinate?

Accepted Answer

PRE-ARRIVAL CRUDE TANKER — CM PREPARATIONS: (1) SHIP-SHORE COMMUNICATIONS: make contact with the terminal. Confirm: berth availability; cargo order; hose/arm connection details; cargo plan and loading/discharge sequence; free flow/simultaneous operations restrictions; emergency shutdown procedures; (2) CARGO PLAN: prepare/review the loading or discharge plan — cargo sequence, tank allocation, ullages, API gravity, temperatures, transfer rates; (3) STABILITY: calculate stability at all stages of the cargo operation. Ensure GM remains positive throughout. Identify the critical condition (minimum GM stage); (4) TANK CONDITION: check all cargo tank O2 levels — below 8% required. Note temperature and pressure of cargo and tank atmosphere; (5) MANIFOLD PREPARATION: inspect manifolds — blank flanges removed, drip trays clear, manifold valves operational; manifold pressure rating confirmed compatible with terminal pumps; (6) MOORING PLAN: confirm berth orientation; prepare appropriate mooring lines; (7) PUMPROOM INSPECTION: access pumproom — check bilge level; inspect pump seals; ensure cargo pumps ready for operation; (8) CARGO HEATING: if heated cargo — ensure steam coils operational and steam supply available; (9) DECK EQUIPMENT: cargo deck valves operated (any seized valves to chief engineer); hose handling equipment ready; (10) ISGOTT SHIP-SHORE SAFETY CHECKLIST: complete the ISGOTT pre-arrival section of the Ship-Shore Safety Checklist (Part A — ship's responsibilities) before the terminal vessel inspector arrives; (11) HOT WORK SUSPENDED: ensure all hot work is completed and stopped before entering port limits; (12) EMERGENCY SHUTDOWN: brief the duty officer on the ESD procedure and agree a shore contact name. ISGOTT (International Safety Guide for Oil Tankers and Terminals): the industry reference document for tanker terminal operations. The Ship-Shore Safety Checklist in ISGOTT: completed jointly by the vessel and the terminal before cargo operations begin. Part A covers vessel systems; Part B covers terminal systems. Both must be completed and signed. CM role in pumproom (option D): the pumproom is a critical space on a tanker — it contains all cargo pumps, stripping pumps, ballast pumps, valves, and pipework. Pumproom entry has caused numerous casualties (enclosed space, H2S accumulation, flooding). The CM has direct responsibility for cargo operations, which includes ensuring the pumproom equipment is operational. Chief engineer: responsible for maintenance of the cargo pumps as machinery, but the CM is responsible for the cargo operation, which requires those pumps. The Manifold safety: manifold flanges must be compatible between ship and shore hose/arm flanges. The pressure rating of the shore supply must not exceed the ship's manifold rated pressure. MARPOL Annex I: on a crude oil tanker, any oil discharge or spill must be reported. The pre-arrival preparation includes ensuring all drain plugs are in drip trays and that the manifold area is ready to contain any hose drips. Cargo heating: for high-viscosity crudes, the cargo may need to be maintained at 40-60°C or above throughout the voyage. The CM must check that the heating system is functional before arrival at the discharge port.