Flame detectors are not low cost items, compared to smoke and heat detectors, but are vital where the risk is such that ignition will result in immediate flame that could spread rapidly causing risk to life, major damage, and costly shutdowns.
Because of the cost, clients have tended to use detectors with a long range and wide field of view to cover vast areas on a site with a relatively small number of devices. This has resulted in a requirement for larger and more complex extinguishing systems and release mechanisms to cover the greater areas of risk.
It is generally recognised that the most reliable flame detectors are those that monitor infrared radiation (IR). These detectors specifically look for the IR waveband of hot Carbon Dioxide. The first generation IR Flame detectors suffered from their inability to discriminate between the sun and a real fire. This shortcoming was overcome when – back in 1980 – Thorn patented the first “solar blind” IR detector. In addition, IR detectors do not react to vapour lamps, lightning, welding, angle grinding or similar activities, making them more reliable than Ultra Violet (UV) detectors that tend to react to these sources.
Because IR detectors essentially look for a hot CO2 plume, developers realised that hot “black bodies” could cause these detectors to react as if there was a fire. This was partially overcome by using “flicker analysis”, where detectors analyse the radiation for the characteristic flickering patterns that real flames have.
The risk of unwanted alarms due to black bodies was then reduced further by the introduction of dual and then triple IR channel detectors that measure the background radiation to minimise the influence of black bodies.
Triple channel IR detectors.
As described above, triple channel IR detectors more reliably detect fires while trying to provide better compensation for any black body radiation that could be present. This generally makes them more reliable, but sometimes specific, challenging site conditions cause problems.
Typically, a triple IR detector works by increasing the alarm threshold if a lot of background radiation is present. As the detector does not know where in the field of view the hot black body is sited, the sensitivity of the detector across its whole field of view is reduced.
This could mean that a detector might react more slowly than expected to a real fire. The opposite is also true, in that if there is a very large build up of black body radiation the detector could be so overwhelmed that an unwanted alarm occurs.

False alarm rejection.
The new FLAMEVision FV300 detector uses an IR array of 256 individual sensors that detect where in the field of view any build-up of IR radiation is occurring. The detector could be likened to a low-resolution infrared camera. The algorithms that analyse the IR image can be highly tuned to discriminate between flame and non-flame sources. They use image analysis; looking at the changes in the pixels on the array to identify the characteristics of a flame or a modulated black body and spectral analysis; looking at different IR wavelengths to distinguish between flame and non-flame sources. This discrimination is made easier by the use of the array as any IR sources within the field of view will form images on different parts of the array. The FV300 flame detector can then analyse and track each source separately thus reaching a decision on each individual source.
This means that if a large black body is detected the unit is able to compensate for it just in that area of the field of view while maintaining optimum sensitivity for all other areas. In addition the build up of black body radiation can be reported to the operator, not as a fire, but as something suspicious that might warrant investigation. The detector will send the co-ordinates of the suspicious object to the operator so they know the location of the problem in the field of view.
This inherent feature of the IR array, together with the ability to mask an area, results in a detector with an unrivalled false alarm rejection capability. Masking is where the operator can select an area of the field of view and instruct the detector to ignore any flames it might see in that area. This is especially useful were there is a process running that has a flame during normal operation. From the main control system the mask can be automatically turned on or off depending on whether the process is running or not.
FLAMEVision FV300 provides location information of single or multiple fire events in two ways; by referencing the IR sensing array cells that register alarms and sending co-ordinates to the main control system and secondly by superimposing a CCTV image with the fire location highlighted. This ensures that the most appropriate executive actions can be speedily deployed. This may involve isolating part of a plant rather than a costly and disruptive total shutdown. Frequently weather conditions can make it very difficult to see a flame on a CCTV picture (fog, mist, direct sun light etc), not forgetting that many flames burn invisibly, so highlighting the location of the fire helps the operator to react as quickly as possible should manual intervention be required. The detector can report four fire locations at any one time to the main control system. A visual image of what takes place in the array is represented in the Mesh diagram in Figure 2. In this case two fires have been identified.

Better site operation
Due to the fact that FLAMEVision FV300 reports where in the field of view the fire is, it is possible to identify the asset on fire among a multitude of other assets and to automatically release a “local” extinguishing system. This could mean that the whole plant does not have to be shut down. IR Array-based flame detectors like the FLAMEVision FV300 also identify the relative fire size and therefore can monitor the effectiveness of any extinguishant released. Knowing the location of a fire also allows the operator to mask out an area where there may be a flame during a process, hence eliminating unwanted alarms.
The range of the FLAMEVision FV300 is consistent across the field of view, unlike UV/IR or triple channel IR detectors where the range reduces as the target moves away from the axis. This makes design of the site fire detection layout much easier and could result in fewer detectors being required. In addition, as the presence of blackbodies in the field of view can be tracked, they will only affect the array cells in that part of the field of view. The unaffected array cells maintain their sensitivity and range. A sensitivity setting is therefore not required for these types of detectors.
Forensic audit of events
FLAMEVision FV300 is able to track and output information on the target sources over time and consequently store information about an incident prior to any alarm. This presents the benefit of a forensic audit of what took place in infrared terms prior to the alarm. Similarly, the tracking of hot IR sources allows maintenance staff to understand any hot body changes which take place from one maintenance period to another while giving facilities operators advance warning of a potential flame situation. The historical log can be viewed both as text information and graphically to help investigators quickly assess what caused a fire or unwanted alarm should one have occurred.
24-hour protection in exposed locations
The detection capability of FLAMEVision FV300 does not rely on the visual information provided by the CCTV output and is therefore not reliant on the weather, visibility and lighting conditions that can affect CCTV. IR will penetrate fog and driving rain so even with reduced visibility the location of a fire or fires will still be reported.
The ideal flame detection solution
Increased demand from clients for improved performance such as better range and consistency over the whole field of view, higher reliability and, more recently, the increased need for situational awareness of flame related events, has led to the evolution of existing technologies and the introduction of a number of new technologies. Some new technologies suffer inherent weaknesses such as the inability of video flame detection to operate well in adverse weather conditions. Triple channel IR flame detection technology has advanced to meet most but not all current clients’ requirements, in particular regarding situational awareness and blackbody rejection. Infrared array-based flame detectors such as the FLAMEVision FV300 can deliver some of the more-difficult-to-achieve clients’ demands including situational awareness without relying on CCTV to understand the IR picture of any alarm.
The use on site of a mixture of triple channel IR together with IR Array based flame detectors produces a flame detection solution which is not only robust but also able to accommodate most operators’ budgets.
Coincidence/voting systems
It has been common practice on many sites to shut down a process or release an extinguishing agent only if more than one detector signals a fire. This design is frequently called a “coincidence” or “voting system”. Typically in a risk area there might be a few detectors monitoring and the system is then programmed to take an action if two detectors trigger. This gives a reliable system and allows operators to take manual actions after one alarm before any automatic system kicks in after two alarms. But what is often forgotten is what happens if some of the detectors are in fault or have been isolated. For example if an area had three detectors and for some reason two are not operational, only one detector could trigger, therefore no automatic action could take place. Possible situations like this must be considered when designing safety systems. Fortunately the Tyco T2000 (MX addressable) system can monitor the condition of the detectors and if detectors in the risk area are not operational can automatically adjust the logic of the program to ensure automatic actions can still take place should a fire occur. This is often called “reduced voting”.
Offshore accommodation and other non-process areas
In offshore accommodation areas where smoke and heat detectors are required designers and safety consultants have always had to try and balance expenditure verses safety.
Typically following a risk assessment an accommodation area might be classed as a “zone two” hazardous location, so frequently an expensive, intrinsically safe fire detection system is installed. Occasionally designers try to cut costs by fitting conventional rather than addressable intrinsically safe detectors, but this gives very limited information and the emergency response team does not know the exact location of the fire. (In which space/room the fire might be).
For zone two areas EXN equipment can be used, and this has the advantage of being lower cost and does not require the use of safety barriers and complex safety calculations.
Until recently certified EXN fire detection equipment was not available but now ATEX and IECEx certified addressable detectors and callpoints that are also approved by the major marine classification societies are available from Tyco.
The use of EXN detectors have also proved popular on large car transporters/ferries where the car decks can be safely monitored for fire at a much lower initial and ongoing maintenance cost than intrinsically safe or flameproof equipment.
All addressable detectors (Standard, EXN or Intrinsically Safe) used with the Tyco T2000 (MX) fire detection panels are programmable, not only for sensitivity but also, uniquely, for the actual way they work.
As an example of this a combined optical smoke and heat detector situated near an incinerator can be programmed to work as a High Performance Optical (heat enhanced smoke) detector but automatically switched to heat detection mode when the incinerator is running.
This ability to switch operating modes greatly reduces the possibility of unwanted alarms and ensures all staff react as per their safety training when there really is an alarm rather than casually assuming it is a false alarm. In addition the use of combination detectors including Carbon Monoxide (CO) detection gives fast reaction to true fire situations while further reducing false alarm possibilities.

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