(a) Briefly describe the cargo hold fire detection system on a bulk carrier, and how does the system function to detect and alert the crew to the presence of a fire? (10)
(b) Give reasons why fire detectors in cargo holds differ from those in machinery spaces. (5)
(c) Describe how to verify that each is in working order. (5)
Structured for DG Shipping MEO Class II examination scoring criteria.
(Refer to the detailed answer for 6a68b2de3478942caa0b55d9.)
A bulk carrier's cargo holds are protected by a fixed smoke-detection (smoke sampling/aspirating) system controlled from a cabinet on the bridge. Small-bore sampling pipes are run from each hold to a manifold; a suction fan continuously draws an air sample from each hold back to the cabinet. The sample passes over an optical or ionisation smoke detector; if smoke is present in a hold, the sample is smoke-laden, the detector actuates, and the control panel identifies the affected hold(s) and raises audible and visual alarms on the bridge (and often a remote alarm in the engine room / crewwatch). The system provides early warning of a fire (including of a dangerous-cargo fire) so the master and crew can act before the fire becomes unmanageable.
(Refer to detailed answer for 6a68b2de3478942caa0b55d9(c).) Summary: cargo holds are large unoccupied/low-occupancy spaces with dusty and possibly flammable atmosphere, needing aspiration across a large volume; machinery spaces are occupied, hot, oily, with localised sources and need fast local heat/smoke detection; false alarms from engine heat/smoke would be common in machinery spaces so heat/flame detection is preferred there, while holds need smoke sampling over a large volume; the hold system is monitored/aspirated from the bridge.
(Refer to the same.) Test the aspirator/flow per sampling line, inject test smoke at a sample point and confirm the correct zone alarm; test audible/visual alarms and panel indication; inspect pipes for damage/blockage; carry out quarterly/annual servicing per manufacturer; for machinery space detectors, apply heat smoke to each point detector and confirm the correct zone; check the power supply (normal/emergency). Record all tests.