Offshore flame detection
Dr Eliot Sizeland presents an innovative flame detection solution for offshore helidecks.
The Civil Aviation Authority publication CAP 437 ‘Standards for Offshore Helicopter Landing Areas’ has become an accepted worldwide source of reference. The latest edition, 8.2 July 2021[1], maintains its position as one of the go-to documents for helicopter safety offshore.
The requirements set out in the publication relate to fixed and mobile installations, whether they are operating in the oil and gas or renewable energy sectors. CAP 437 requires new build Normally Unattended Installations (NUIs) be fitted with deck integrated fire fighting systems (DIFFS), and existing NUI’s be retro-fitted with an alternative automatically activated fire fighting system
DIFFS on NUIs should be integrated with platform safety systems such that pop-up nozzles are activated automatically in the event of an impact of a helicopter on the helideck where a Post-Crash Fire (PCF) is a foreseeable outcome. The overall design of a DIFFS should incorporate a method of fire detection, typically optical flame detection, and be configured to avoid spurious trips. The system should also be capable of remote override. This article discusses the latest advances in optical flame detection for this application.
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.
Dr Eliot Sizeland is vice president of business development at Fire & Gas Detection Technologies Inc.
REFERENCES:
[1] UK Civil Aviation Authority, Safety Regulation Group, CAP 437 ‘Standards for Offshore Helicopter Landing Areas’, Edition 8, amendment 02 July 2021
[2] FlameSpec IR3-HD manual, document number F101V0020.06, published June 2021
[3] NFPA 409, 2016 edition