Question 1

Your examiner asks: "What types of fire detectors are fitted on cargo ships under SOLAS Chapter II-2, and what are the conditions under which each type is most effective?"

Accepted Answer

Smoke detectors (ionisation or photoelectric): detect combustion particles — most effective for smouldering fires producing visible or invisible smoke before open flame. Heat detectors: either fixed-temperature (alarm at a set temperature, e.g. 57-96 degrees) or rate-of-rise (alarm when temperature rises faster than normal, e.g. 5 degrees per minute) — effective for fast-burning fires. Flame detectors: detect infrared or ultraviolet radiation from open flames — effective in machinery spaces with high background heat. Gas/carbon monoxide detectors: detect CO as an early indicator of smouldering fires. SOLAS II-2/7 requires automatic fire detection and alarm systems in crew accommodation, service spaces, control stations, and cargo spaces as appropriate. SOLAS II-2 Chapter 7 and the FSS Code Chapter 9 govern fire detection requirements. Key point for OOW orals: smoke detectors are the most sensitive for early detection of smouldering fires (which produce CO and aerosols before visible flames) — they are required in accommodation spaces. Heat detectors are more appropriate in galleys and machinery spaces where ambient temperatures and aerosols (cooking fumes, diesel exhaust) would cause false alarms from smoke detectors. Rate-of-rise detectors are faster-responding than fixed-temperature but can false-alarm in areas with rapid legitimate temperature changes (boiler rooms, hot work areas). Flame detectors are specifically required in unmanned machinery spaces. CO detectors as an early warning layer are increasingly specified in cargo hold monitoring systems. The FSS Code divides spaces into three categories: A (accommodation), B (service/machinery), and C (cargo) — each has specific detection requirements.

Question 2

Your examiner asks: "Describe the fire triangle and the four internationally recognised classes of fire relevant to shipboard operations. Which extinguishing media are correct for each?"

Accepted Answer

The fire triangle requires three elements simultaneously: heat (ignition source), fuel (combustible material), and oxygen. Remove any one element and the fire goes out. Classes: Class A — solids (wood, rope, bedding) — water, foam, dry powder; Class B — flammable liquids (fuel oil, paint, solvents) — foam, CO2, dry powder; Class C — flammable gases (LPG, acetylene) — dry powder, shut off supply first; Class D — combustible metals (magnesium, titanium, sodium) — specialist dry powder only; Class F (electrical equipment) — CO2, dry powder — NEVER water. Note: electrical fires are sometimes classed separately rather than as a fire class. The fire triangle (heat, fuel, oxygen) underpins all firefighting strategy: cooling removes heat (water); smothering removes oxygen (CO2, foam blanket); starvation removes fuel (shut off supply, remove combustible material). Note the tetrahedron model adds a fourth element — the chain reaction — which halite extinguishing agents (Halon, now banned under MARPOL Annex VI except for existing systems) interrupt. Electrical fires (Class F in some classifications) must never be fought with water or foam — both conduct electricity. CO2 is the correct agent for switchboard and electrical equipment fires. Class D fires (metals) react violently with water — specialist dry powder (not standard ABC powder) is the only safe option. At OOW level, the examiner expects correct extinguishing media for each class and awareness that using the wrong agent can be dangerous.

Question 3

You are OOW when the fire alarm activates in the unmanned engine room. The chief engineer is not on board. Describe the CO2 system release procedure and the safety precautions required.

Accepted Answer

Before CO2 release: confirm fire in engine room visually if safe; sound the CO2 alarm (pre-discharge alarm — minimum 20 seconds before release per FSS Code); verify all personnel are clear of the engine room; close all ventilation dampers, doors, skylights, and openings to the space; stop fuel supply and forced ventilation fans; account for all engine room personnel. Release: operate the CO2 system from the release station (typically outside engine room on the deck above) — pilot cylinder, then master valve. After release: do NOT re-enter the space until it is confirmed safe by gas detector. CO2 concentration to extinguish a fire in a machinery space is approximately 34% by volume — lethal to humans above 3-4%. FSS Code Chapter 5 (CO2 systems): the pre-discharge alarm is mandatory — its purpose is to give personnel time to evacuate the space. The minimum alarm period before discharge is not specified as a fixed time in the FSS Code but SOLAS II-2/10.4 requires an audible alarm that gives adequate warning — typically 20-30 seconds. The sequence of shutting ventilation, closing openings, and stopping fuel supply is critical: CO2 is effective only if the protected space can maintain sufficient concentration — if ventilation remains running, the CO2 is diluted and the fire may continue. Re-entry is the major post-fire hazard: CO2 is colourless and odourless. Residual CO2 in a space after fire suppression can remain at lethal concentrations for hours. Entry must be confirmed safe with a calibrated gas detector and BA (breathing apparatus) must be worn by the entry team regardless of detector readings until the space is fully ventilated. Multiple fatalities from premature re-entry after CO2 discharge are documented in MAIB and USCG investigation reports.