With reference to equipment supplied to detect and combat hold fires in dry cargo ships:

For a dry cargo ship carrying dangerous goods (per SOLAS Ch. II-2 and the FSS Code), the cargo holds are protected by a fixed smoke-detection (smoke sampling/aspirating) system monitored from the bridge. The arrangement:

• A control cabinet/panel on the bridge houses the smoke detectors (optical/ionisation) and the sampling manifold.
• Small-bore sampling pipes run from each cargo hold to the cabinet; a suction fan draws a continuous air sample from each hold.
• The sample passes over the detector; if smoke is present, the detector actuates and the panel identifies the affected hold, raising audible and visual alarms on the bridge (and a remote alarm in the engine room/crew accommodation).
• The system is designed to detect a fire in the cargo (including a dangerous-goods fire) at an early stage, giving the bridge early warning.
• The panel shows the zone/hold, the alarm state, and provides for testing and reset; the system is powered from the main and emergency supplies.
• For dangerous cargo, the detection is supplemented by the requirement to monitor the cargo (temperature, gas) and to have the appropriate firefighting response (e.g. CO2 or water mist for the holds, and the emergency schedules from the IMDG Code).

The response to a hold fire depends on the cargo and its quantity:

• On detection, the bridge confirms the alarm, sounds the general alarm, and the master takes charge; the crew muster and the fire party is deployed.
• The hold is sealed (hatches closed, ventilation closed) to starve the fire of air; the hold is not opened (opening can cause a flare-up).
• If the ship is fitted with a fixed fire-extinguishing system for the holds (e.g. CO2 or water mist/foam), it is operated to flood the hold - the quantity of the extinguishing medium is based on the hold's gross volume (e.g. CO2 at 30% of the gross volume for cargo spaces), so it is sufficient regardless of the cargo quantity; the system is designed for the largest hold.
• Boundary cooling: the surrounding structure (decks, bulkheads, ship side) is cooled with water to prevent the fire spreading to adjacent holds.
• The cargo quantity affects the response: a full hold has less free space (so the fire is more confined and the CO2/water mist is more effective in the void), while a partially loaded hold has more air space (so the fire may develop more freely and the extinguishing medium must fill the larger void); the response is adjusted accordingly - e.g. for a partially loaded hold, more CO2 may be needed to fill the void, and the fire may be more difficult to smother.
• For dangerous cargo, the IMDG emergency schedules are followed (e.g. the correct extinguishing agent, the need to avoid water on certain cargoes, the evacuation and the reporting); the ship may need to proceed to a port and call for shore assistance.
• The fire is monitored (temperature, gas) and the response is adjusted; after the fire is extinguished, the hold is gas-freed and inspected before entry, and the incident is reported.