The letter is written in a formal report/letter style.

Dear Superintendent (Technical Superintendent / Fleet Manager),

Subject: False activation of HIPER MIST smoke detection system above the incinerator and proposal for an additional activation layer.

We report that the HIPER MIST (water-mist fire fighting) system on board has repeatedly activated on the space immediately above the incinerator unit, sited in the engine room. The activation is false because it is triggered not by a genuine fire but by the high temperature and combustion products / smoke normally produced by the incinerator during burning of sludge and solid waste. Under normal incinerator operation the combustion gases and radiant heat raise local temperature and particulate/optical smoke to the detection threshold of the adjoining detectors, causing spurious activation of the mist system above the unit.

To stop these false alarms while retaining genuine fire protection, we propose to add a second, independent layer of confirmation before the HIPER MIST system discharges above the incinerator. We recommend a cross-zone / AND logic arrangement in which the mist system is not released on a single smoke or heat signal, but only when BOTH (1) the fire/smoke detector above the incinerator AND (2) a second independent detector (for example a rate-of-rise heat detector or an optical smoke detector sampling a different location) confirm the same event, with a short delay. We also recommend adding a per-zone isolator, a time delay (confirmation window) of 5-10 seconds, and an incinerator-running interlock: when the incinerator is confirmed to be in burner operation (combustion temperature and burner running signal), the fast-actuating release above it is inhibited and only a local/annunciated alarm is raised, while the system remains fully armed for a real fire elsewhere.

We further propose a maintenance item to tune/relocate the detector heads in the space, check the incinerator insulation and flue duct lagging, and improve ventilation so that normal stack/combustion heat and flue products do not reach the detectors. This will reduce nuisance trips at source.

Such an arrangement does not reduce fire safety: it adds a confirmation stage so that a real fire in the space will still cause discharge, but random false activation from incinerator heat is prevented. Approval of the class society and flag administration will be sought where the system is part of the statutory fire control system before the modification is effected, and a full risk assessment and test will be carried out.

We request your approval and the drawings/vendor support required to implement the additional activation layer at the next port stay.

Regards,

Second Engineer Officer