What to check on a Smoke Detector.
2 models from fike in Smoke Detector. Below: the full model list.
What distinguishes this detector type
Point-type smoke detectors used on board fall into two working principles. Optical (photoelectric) detectors shine an infrared beam across a sensing chamber and measure light scattered by smoke particles; they respond well to the dense, visible smoke typical of smouldering cable insulation, upholstery or slow-burning solids. Ionisation detectors use a small radioactive source to ionise air in the chamber and measure the drop in current when smoke particles interfere with that ionised flow; they respond faster to the fine, largely invisible particles thrown off by fast-flaming fires with little visible smoke, such as burning fuel or paper. Multi-criteria detectors combine a smoke sensor with a heat or CO sensor and vote between them to cut false alarms, at the cost of a slower response in a genuine fast fire.
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Main components
Sensing chamber
The optical or ionisation element itself, protected by an insect screen and a light trap or ionisation chamber housing. This is the part that ages: dust and salt-laden air gradually raise the baseline signal until the head drifts into false alarm territory.
Detector base and loop wiring
Plugs into a fixed base wired into an addressable or conventional loop back to the fire panel. Addressable bases carry an individual address so the panel reports the exact detector, not just the zone.
Fire panel interface
Processes the analogue signal, applies drift compensation and raises alarm, pre-alarm or fault at the bridge panel and any repeater panels.
Selection and placement
Type selection follows the fire risk of the space, not a fixed rule for the whole ship:
- Machinery spaces and areas with oil mist: heat detectors or multi-criteria units, since smoke detectors alone false-alarm on normal engine room haze.
- Accommodation, control rooms, cable trunks: optical smoke detectors are the default.
- Galleys and spaces with cooking fumes or steam: heat detectors or specially rated smoke detectors to avoid nuisance alarms.
- Coverage area per detector, ceiling height and beam obstructions all affect spacing and must follow the fire detection system's approved layout drawing, not a generic ceiling grid.
Regulations and class
SOLAS Chapter II-2 requires fixed fire detection and alarm systems in specified spaces depending on ship type, and the detectors themselves must meet the applicable IMO performance standard for shipborne fire detection equipment. Class rules require the system to be tested and the individual detector heads to be functionally tested at survey intervals set by the classification society, with sensitivity drift checked against the manufacturer's data. A detector that has drifted out of its calibrated window is treated as a fault, not left in service on the assumption it "still works".
Typical faults
| Fault | Cause | Consequence |
|---|---|---|
| Nuisance alarms | Dust or salt build-up in the chamber, insect ingress, wrong type for the space | Crew starts isolating or ignoring zones, defeating the system's purpose |
| No alarm on test | Corroded base contacts, broken loop wiring, detector not seated | Real fire in that space goes undetected until it is visible or smelt |
| Ground fault on loop | Chafed cable at a bulkhead penetration, moisture ingress in a junction box | Panel may isolate part of the loop, dropping several detectors at once |
| Sensitivity drift flagged by panel | Ageing sensing element, contamination | Detector due for cleaning or replacement before it fails outright |
What to look for in a supplier
- Type approval certificate matching the specific detector model, not just the product family.
- Compatibility confirmed with the existing fire panel's protocol - addressable loops are not interchangeable between panel manufacturers.
- Traceable batch and manufacture date, since sensing elements have a service life independent of whether they have triggered an alarm.
- Availability of the matching base, since heads and bases from different ranges of the same maker are not always compatible.
When a detector keeps false-alarming, replace or clean it rather than isolating the zone on the panel - an isolated zone is a zone with no fire protection at all, and it is easy to forget it was ever isolated.
