Fire Detection Systems

Fire Detection Systems covers flame, smoke and heat detectors, manual call points, beacons and sounders, and the fire and gas or fire alarm panels that run them.

On a rig these devices sit on one approved system with a cause and effect logic. A used detector or panel is only useful if it matches that system's protocol, approvals and hazardous area marking.

How a fire detection system works offshore

Detectors watch for one or more products of a fire. The panel decides, under its voting logic, whether an input is a pre-alarm, a confirmed fire or a fault. A confirmed fire raises the general alarm and can stop ventilation, close fire dampers, isolate fuel and release deluge, foam or gas suppression. Two-out-of-N voting between detectors in one area is common because it cuts spurious releases without losing coverage.

Detector types

Type	Senses	Suited to
UV/IR flame	Ultraviolet plus one infrared band	Drill floor, well test area, enclosed modules
Multi-spectrum IR (IR3)	Three infrared bands of a hydrocarbon flame	Open hazardous areas with sunlight and hot surfaces
Optical smoke	Light scattered by smoke particles	Accommodation, control rooms, switchboard rooms
Ionisation smoke	Change in ion current from smoke	Older installations; being replaced
Aspirating smoke	Air drawn through pipes to a central sensor	Equipment rooms, cabinets, high air flow spaces
Heat (fixed or rate of rise)	Temperature or its rate of change	Galleys, engine rooms, dirty spaces
Linear heat cable	Temperature along a cable run	Cable trays, conveyors, roof spaces

UV detectors respond to arc welding and can be blinded by smoke and oil film. IR3 detectors resist sunlight and hot-work false alarms better but cost more. A hydrogen flame is hard to see in the infrared, so hydrogen risks need a UV or specific hydrogen flame detector.

Key specifications

Parameter	Why it matters	Typical classes or units
Cone of vision and range	Sets how many detectors cover an area	Degrees and m (ft) for a reference fire
Response time	Decides how soon suppression starts	Seconds to a reference fire
Ex marking	Decides which zones it may sit in	Ex d or Ex e, IIC, T4 to T6
Output	Decides panel compatibility	4 to 20 mA, relays, addressable loop
Self-test	Proves the optics are clean	Automatic optical integrity check

Standards and approvals

EN 54-2 and EN 54-4 cover control panels and power supplies. EN 54-5 covers heat, EN 54-7 smoke, EN 54-10 flame and EN 54-11 manual call points.
FM 3260 is the North American approval standard for flame detectors.
The FSS Code, Chapter 9, governs fixed fire detection and alarm systems, with Marine Equipment Directive (wheelmark) approval common for vessel equipment.
DNV-OS-D301 and ABS rules set detection layout and performance for classed offshore units.
IEC 61508 SIL certificates matter when a detector initiates a safety function such as deluge release.

A used detector must keep the approvals the class society accepted for your system. A unit with the same model number but a different firmware or option code may not carry the same certificate.

Failure modes and inspection

Contaminated windows on flame detectors. Salt, mud and paint cut sensitivity. Check that the optical self-test passes after cleaning.
Ageing UV tubes. Test with the maker's test lamp at the stated distance.
Dust and insects in smoke chambers. Test with approved aerosol and check the drift compensation reading.
Panel batteries. Check capacity against the standby and alarm load calculation.
Loop faults. Measure loop resistance and insulation, and check isolators.

Documentation

Ex certificate and type approval for each device model.
Panel software version, configuration file and cause and effect chart.
Last function test report showing each detector address tested.
Battery date codes and standby calculation.

Integration and compatibility

Addressable detectors speak the panel maker's loop protocol. Mixing makers on one loop rarely works and rarely keeps its approval. Conventional and 4 to 20 mA detectors are easier to swap, but check the alarm current and fault thresholds. A replacement panel brings a new configuration, so plan for reprogramming, a full cause and effect test and a class survey.

Ionisation detectors and radioactive sources

Ionisation smoke detectors contain a small americium-241 source. Moving, storing and disposing of them is regulated as radioactive material in many countries. Optical, multi-criteria or aspirating detectors are the usual replacements, so treat surplus ionisation heads as a liability rather than spares.

Recertification and refurbishment

A used panel or detector goes back into service after a bench check, a function test against its specification and a configuration check against your system. Flame detectors may need a factory check if the self-test fails. Choose surplus spares of the exact model and firmware on your approved device list.

For the gas side of the same panel, see gas and H2S detection. For the systems the alarms release, see deluge and sprinkler systems.

FAQ

Frequently asked questions

Which flame detector suits a drill floor?

A multi-spectrum infrared (IR3) or UV/IR flame detector suits most drill floor duties. IR3 units tolerate sunlight, hot surfaces and nearby welding better, which cuts false alarms. Where hydrogen fires are possible, add a detector that can see a hydrogen flame.

Can I add a different brand of detector to my addressable fire panel?

Usually not, because addressable devices use the panel maker's own loop protocol. Even a compatible device may fall outside the system's approval. Conventional and 4 to 20 mA detectors are more interchangeable, provided the alarm and fault currents match.

How do I test a used flame detector?

Test it with the maker's own test lamp at the stated distance, after cleaning the window and confirming the optical self-test passes. Record the response for each output. A detector that fails the self-test after cleaning needs a factory check.

Are ionisation smoke detectors still allowed offshore?

They may remain installed under many rules, but they contain americium-241 and their transport and disposal are regulated. Optical, multi-criteria or aspirating detectors are the usual replacements. Avoid buying ionisation units as spares.

What records should come with a used fire and gas panel?

Ask for the software version, the configuration file, the cause and effect chart and the last full function test report. Add the type approval, battery date codes and the list of approved loop devices. Without the configuration file, plan to reprogram from scratch.

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