In addition to the obvious risks of fast flaming fires developing in the processing plants themselves, there will also be internal hazardous areas, ‘mission-critical’ control centres and general office areas, all of which will require a specific approach. 
To address these different types of risk, the major detector manufacturers are continually developing new detection methods and improving existing technologies in order to provide better performance.  By optimising the detection technology as closely as possible to the specific type of risk, the objective is to achieve the most reliable and rapid detection of an actual fire without initiating an unacceptably high number of nuisance alarms. 
The ultimate goal, that of instantaneous detection of a real fire, combined with zero false alarms arising from environmental disturbances, is unlikely ever to be realised; however, today’s fire detectors perform significantly better than those available only a few years ago. 
Looking at trends
Probably the most important trends, apart from the improved functionality of detection devices, are the move away from ionisation detectors on environmental grounds, the introduction of increasingly complex multi-sensor detectors and significantly enhanced functionality within the system, enabling the fire detection to be more closely characterised to the protected areas.
The established techniques employed for oil and gas plant fire detection can be separated into internal and external categories.
- External protection:
* UV and/or IR flame detectors
* Linear heat detection
* Video smoke detection
- Internal protection:
* UV and/or IR flame detectors
* Linear heat and smoke detection
* Video smoke detection
* Ionisation or photoelectric smoke detectors
* Rate of rise and fixed temperature thermal detectors
* Multi-sensor multi-criteria detectors, typically a combined smoke and thermal device
* Gas detectors: these are considered unsuitable as a stand-alone fire detection technology, but some manufacturers are starting to incorporate carbon monoxide (CO) detectors into multi-sensor devices
Where are the risks?
In areas where there are risks of explosion due to the continuous or intermittent presence of inflammable substances, it is necessary to install fire detection products that are suitable for such applications.  These products carry an ATEX approval for use in hazardous areas and are categorised either as Explosion Proof or Intrinsically Safe. 
Products suitable for such areas have ratings that define the type of hazardous area in which they may be used; a thorough review of the area must be undertaken before any such products are used.  Installations in such areas require special consideration of the wiring, terminations, fixings etc and considerable expertise is needed in planning and carrying out the installation.
Explosion Proof products have been designed to contain an explosion within the housing resulting from the ignition of any inflammable substances that have entered it, whereas Intrinsically Safe products are designed so that insufficient energy is available to ignite any hazardous substances present.  The use of a Zener barrier/galvanic isolator is required at the beginning of an intrinsically safe circuit to limit the energy on the loop, so that faults in the wiring cannot produce enough energy to ignite any inflammable substances present. 
UV and IR flame detectors
Fire, particularly the type of hydrocarbon and petrochemical fire most likely to be found in an oil and gas plant, have well-defined characteristics, radiating across the IR, visible and UV spectra with clearly defined peaks at specific wavelengths and exhibiting a low frequency flicker, typically 1 - 10Hz. 
Radiation detectors, operating in either the UV or infra-red spectra, are an effective detection method both outdoors and inside.  They respond rapidly, provide effective cover in large areas and are unaffected by wind, rain or sunlight.  They require a clear line of sight to operate effectively.   Various stand-alone and combined detectors are available, with the latest devices being either combined UV/IR detectors or multiple IR detectors optimised to different frequencies. 
Such devices are generally immune to sunlight, changes in the background environment, heat and light sources such as halogen lights, arc welding and lightning and can operate over a range of up to 60m with a 90/90 cone of vision.
Linear smoke and heat detectors
Infrared beam detectors are ideal for protecting large internal open spaces.  They are unsuitable for external use as the operating principle relies on the products of combustion collecting at the ceiling level and attenuating the reflected signal. 
Testing and routine maintenance of beam detectors mounted at high levels has always presented a problem because of the difficulty of access, the cost of erecting high-level platforms and the disproportionately high labour costs incurred in carrying out a routine test. 
A recent development from one manufacturer incorporates an optical filter that is introduced into the optical path during testing, attenuating the beam and causing the unit to go into alarm.  Unlike other methods, this test process provides a complete check of every component in the alarm path without the need for high-level access.
Linear heat detectors may be used in areas where fire detection through heat detection is appropriate and where the installation of a cable detector may be more appropriate than the use of point detectors.  Examples would be the protection of long tunnels, or detection of heat within pipes used to carry inflammable substances such as methane gas. 
Linear heat detectors consist of a cable that is run in one continuous circuit and, depending on the type of linear heat detection used, they can provide an indication either at a point or over a wider area.  Some linear heat detection systems are inherently Intrinsically Safe.
Video detecters
Video smoke detection is an alternative method of protecting open areas, both indoors and outdoors, day and night.  Using standard closed-circuit television cameras as sensors, the system uses sophisticated image recognition and processing software to identify the distinctive characteristics of smoke and flame patterns, differentiating between smoke and haze or dust. 
In indoor applications, the video smoke detector can detect smoke at an earlier stage than conventional detectors because the smoke particles can be identified before they rise to the ceiling.  As a non-obtrusive means of detection, video is particularly applicable in hazardous, explosive, or radioactive areas.
Smoke detection: optical or ionisation
The smoke detector offers the best combination of early detection and low false alarm rates for most indoor “commercial” applications where value and performance have to be closely considered. 
Optical smoke detectors offer a combination of early detection and false alarm immunity at cost-effectives prices; recently, the majority of detector manufacturers have concentrated their development efforts on migrating the features and benefits, such as automatic drift compensation, adjustable sensitivity and multi-sensor technology from their more sophisticated addressable product ranges into new conventional devices to improve the performance in smaller installations. 
Early smoke detectors were of the ionisation chamber type, very good at detecting small particles of combustion, but susceptible to false alarms caused by changes in humidity, air pressure, temperature and air velocity. 
The characteristics of the ionisation detector theoretically make it more effective than a photoelectric device in responding quickly to fast, flaming fires, although nowadays it is becoming harder to obtain approval for an ionisation detector, and the regulations surrounding the transportation of radioactive materials are becoming more stringent and therefore more expensive. 
A greater understanding of the dynamics and properties of a developing fire have enabled manufacturers to produce different types of detector to provide optimised detection for the markedly different fire hazards to be found throughout a modern oil and gas plant. 

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