Flame Detector

What Makes a Flame Detector Different

A flame detector reacts to the radiation an open flame emits, ultraviolet, infrared, or both, rather than to smoke particles or a rise in ambient temperature. That gives it a response time measured in seconds instead of the minutes a smoke or heat detector can take to accumulate enough signal, and it works in spaces where smoke detectors are unreliable: engine rooms with constant airflow, exhaust and diesel fumes that would swamp a smoke chamber with false alarms, and open cargo areas too large or too ventilated for smoke to build a detectable concentration near any one sensor. The trade-off is that a flame detector only sees flame directly in its line of sight; it cannot detect a smouldering fire that has not yet broken into open flame, so it is normally installed alongside, not instead of, smoke or heat detection.

Main Components

Sensing element

UV detectors use a sensor tuned to the deep ultraviolet band flames produce; IR detectors watch one or more infrared wavelength bands, often comparing the flicker frequency, roughly 1-15 Hz, typical of real flame against steady infrared sources to reject false triggers. Combined UV/IR units cross-check both signals before alarming.

Optical window

A sealed, wide-angle lens that must stay clean; oil film, salt deposits or paint overspray on the window is the single most common cause of a detector going blind without anyone noticing.

Signal processing electronics

Filters out non-flame sources such as welding arcs, sunlight, hot machinery surfaces and lightning, using flicker-frequency analysis and, on dual-band units, the ratio between UV and IR signal strength.

Mounting and field of view

Fixed at a height and angle giving unobstructed sightlines over the protected area; detection range depends on flame size and typically extends tens of metres for a UV/IR unit rated for open deck or engine room use.

Selection and Sizing

• Detection technology matched to the fire risk; hydrocarbon fires suit UV/IR combination units, which reject more false alarm sources than UV alone
• Field of view and mounting height needed to cover the protected area without blind spots behind machinery or structure
• Response time and sensitivity setting appropriate to the space, since too sensitive in an engine room invites nuisance trips from hot work
• Housing rating suited to the environment, including explosion-proof certification where flammable vapours may be present, as in cargo pump rooms on tankers

Regulations and Class

SOLAS Chapter II-2 requires fixed fire detection in machinery spaces and other specified areas, with the detection system type-approved to the applicable performance standard for the technology and space it protects. Class rules require the detection system to report to a continuously manned or monitored central fire alarm panel, with detector function verified at scheduled fire drills and surveys. Detectors on cargo tank decks of tankers or in spaces handling flammable cargo also need to meet the relevant hazardous area (Ex) certification for the zone they are mounted in.

Typical Faults

What to Look for in a Supplier

• Marine type approval certificate valid for the specific area class, open deck, machinery space or hazardous area, the detector will serve
• Documented false-alarm rejection performance, not just raw sensitivity figures
• Ex-certified housing where the detector will sit in a zoned hazardous area
• Self-test or window-fouling indication that flags a blind detector before it is needed rather than after

A flame detector with a dirty window looks identical to a healthy one until the day it matters; window cleaning on the fire round schedule is worth more than any spec sheet number.