Explain the cargo hold fire detection system used on ships; maintenance procedures; and steps taken when a fire is detected in the cargo hold.

(Refer to the detailed answer for 6a68b2de3478942caa0b55d9 and 679d0c29bc2c89ff76a298c4 for the system description and testing.)

System: A bulk carrier's cargo holds are protected by a fixed smoke-sampling (aspirating) fire detection system wired to a detector cabinet/control panel on the bridge. Sample pipes (small-bore) run from each hold to a manifold in the cabinet; a suction fan draws a continuous air sample from each hold; the sample passes through an optical/ionisation smoke detector; when smoke is drawn into the sample, the detector actuates and raises an alarm identifying the affected hold, with audible and visual alarms at the ship's bridge/engine room.

Maintenance procedures:

• Daily: verify the control panel indicates normal/no fault; observe no blocked sample flow alarms.
• Weekly/periodic: test the suction/aspirator flow on each sampling line (flow meter) and confirm air is drawn from the holds; clean the filters; complete a functional test by releasing test smoke (or introducing clean air or a test detector) at a sample point in a hold and confirming the corresponding alarm is raised at the cabinet; test the audible/visual alarm; log the result.
• Periodically (per manufacturer/ FSS): calibrate the detector; replace the filter elements; service the fan(s) and pump; check the sampling pipes for damage/blockage or contamination; purge/clean the pipes; quarterly/6-monthly system check and annual service by the technician; keep a record.
• Check standby batteries and power supplies, and the changeover to emergency supply.
• Ensure the system has been type-approved and is maintained in accordance with the maintenance schedule and the maker's manual.

Steps when a fire is detected in a cargo hold:

1. Treat any alarm as real: confirm on the panel which hold, and the master and duty officer are informed; the general alarm may be sounded as appropriate.
2. Use all available means to verify (e.g. view the hold through the hatch/vent, look for smoke/heat, monitor temperature gauges, use the gas/O2 measurement where safe, and confirm via a second sampling). Do not open the hatch if the hold may contain a fire or generate an explosive atmosphere.
3. Commence the emergency organisation - the Master takes charge of the fire response; all personnel follow the muster list; the crew man the fire boundary/control and mobile teams as required.
4. Close all ventilation and hatches to the affected hold to starve the fire of air (unless the cargo needs a different action such as CO2 injection); ensure the hold is sealed and do not open it (opening can cause a serious air supply leading to an explosive flare-up).
5. If the ship is fitted with a fixed fire-extinguishing system for the holds (e.g. CO2 steaming or water mist/foam), operate it to flood the hold as the situation demands - releasing CO2 if the cargo allows; this reduces oxygen. (Not all holds have a gas system; if no gas, use boundary cooling and sealed smothering.)
6. Use boundary cooling: cool the surrounding structure (decks, bulkheads and the ship side) with fire hoses/water spray to prevent the fire spreading to adjacent holds/accommodation.
7. Assess whether the cargo is one that reacts with water (dangerous goods); follow the IMDG/emergency schedules.
8. Monitor temperature/CO/gas and decide whether to proceed to the refit/port, notify the company and port State (through the Master), and where necessary abandon or fight externally; consider calling for shore assistance (firefighting tugs) if needed.
9. Record the incident, and carry out after-actions: gas-free/entry checks before opening, inspect the hold, and report the fire in accordance with the accident/incident procedure.