Triple IR Flame Detectors

Triple IR (IR3) flame detectors are arguably the most used optical flame detector for hydrocarbon fires today.

A triple IR detector has three sensors, each sensitive to a different IR wavelength. The IR radiation emitted by a typical hydrocarbon fire is more intense at the wavelength accepted by one sensor, typically 4.5 microns, than the other two which monitor adjacent spectral bands (guard bands) for false alarms. “With other sources of radiation (e.g., heaters, lamps, sunlight) this is not the case, as. the intensity at 4.5 micron is no greater than the intensity of at least one of the guard bands. Electronic circuitry in the detector translates the information received into data that can be analysed for flame flicker analysis, threshold energy signal comparison, and mathematical ratios and correlations between various signals.

Triple IR detectors are virtually immune to false alarms and can have extremely long detection distances to some fire types. There are, however, wide performance variations from brand to brand as no two triple IR detectors are the same.

The presence of exhaust (combustion) gases from helicopter engines is known to cause false alarms for some IR3 detectors, a special configuration, immune to these false positives, has been developed by FGD.

False alarms offshore are a genuine concern for production and safety. Should a helicopter engine downdraft induce a false alarm on approach to a helideck, the firefighting system could activate automatically and create a safety concern for all onboard the aircraft.

The special FlameSpec configurations have been independently tested and approved by Factory Mutual (FM). The table[2] shows the response data for one such configuration.

A typical helideck installation

A typical helideck suppression system is activated by a standalone control system mounted close to the DIFFs skid in an ATEX-approved enclosure.

This system automatically monitors the helideck via three flame detectors, located at 120-degree intervals around the perimeter of the helideck.

One such flame detector has an embedded HD camera which can be viewed remotely from a control room or shore-based facility. This feature has been found to be particularly suited to remote NUI facilities.

Many operators have noted the benefit of having video and data of events stored quickly to non-volatile memory locally for post incident investigation. Recordings start one minute before detection and continue for up to four minutes.

Summary

In this article, we have presented an innovative solution to help reduce false alarms from triple frequency infrared flame detectors in applications where exhaust gases from helicopter engines can exist. We have also discussed how the use of an integral HD CCTV camera can provide a live video feed with real-time incident status to operators who can make informed decisions and direct responders accordingly.