Steve Scorfield Technology Manager System Sensor Europe
From the fire detection point of view, a high risk environment such as an oil or gas plant provides a number of different challenges. Such facilities are generally large and spread out, with both internal and external areas requiring fire detection and protection. 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.
Probably the two most important trends, apart from the improved functionality of detection devices, is the move away from ionisation detectors on environmental grounds and the introduction of increasingly complex multi-sensor detectors.
Fire detection techniques
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
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, responding rapidly, providing effective cover in large areas and being 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 detectors
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 versus ionisation technology
The smoke detector offers the best combination of early detection and low false alarm rates for most indoor applications. Recently, the majority of detector manufacturers have concentrated their development efforts on migrating the features and benefits of their more sophisticated addressable product ranges into new conventional devices to improve the performance in smaller installations. The latest generation of conventional detectors, launched in the last year or two, features automatic drift compensation, adjustable sensitivity, multisensor technology and other advances, such as remote interrogation and test - very different from the original 'onoff' switch. Some modern conventional detectors include a remote programming unit that enables the engineer to read/ write the last maintenance date, read the optical chamber contamination level and the thermal element value, select the required alarm threshold and test the device - all from ground level, saving time during commissioning and routine maintenance.
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. End of life disposal, which typically has to be undertaken by the original manufacturer, is a further significant and increasing cost. In some countries, ionisation detectors are completely banned; consequently, no new ionisation detectors have been introduced for the last five or more years from any major manufacturer.
Originally, there was a significant cost differential between the ionisation and the optical smoke detector. Today, however, complex ASICs (Application Specific Integrated Circuits) and advanced volume manufacturing techniques enables photoelectric detectors to be produced cost effectively; they have become the preferred technology by a clear and growing margin. The photoelectric detector operates at the other end of the smoke detection spectrum to the ionisation detector in that it detects large particles of smoke more effectively than small ones. Photoelectric devices are relatively immune to environmental changes, although they can be fooled into reacting to particulate contamination arising from sources other than fire. The latest generation of multi-sensor, multi-criteria detectors offer similar performance and an environmentally acceptable alternative to the ionisation detector. The majority of manufacturers offer Intrinsically Safe versions of their smoke detectors, enabling the fire system to continue coverage into Hazardous Areas of the site.
Multi-sensor detectors
Historically, only a few manufacturers produced composite detectors. Early units comprised of independent smoke and thermal detectors in a common housing; both were connected to the control panel and an alarm signal generated if either unit exceeded its alarm threshold. However, this approach did not match the performance of an ionisation detector.
The multi-sensor detectors, now manufactured by all the major suppliers, are very different. Whether conventional or addressable, the devices use signal processing embedded in the head to enable an alarm signal only if the composite output of the two detectors justifies the decision. Multisensor detectors provide effective protection against both slow and fast developing fires. They are true multi-criteria units; the output levels from both the optical chamber and the thermistor are continually monitored by the onboard processor, using algorithms developed specifically for the task. An alarm signal is only enabled in the detector once the processor is satisfied that an incipient fire has been detected. By using a combination of inputs, the incidence of nuisance alarms is reduced while, at the same time, the response time to an actual fire is not impaired and can actually be improved.
Multi-sensor detectors including gas
It has long been known that gas detection can be an effective sensing technology in a fire detector. Recently, the implementation of a fire detector containing a CO sensor has become possible, due to the introduction of electro-chemical cell technology. However, as a single sensor solution, CO detectors are unable to meet all of the criteria of a general-purpose fire detector; gains in false alarm elimination are lost in fire detection performance. CO detectors are not suitable as stand-alone fire detectors for two main reasons: the electrochemical cell is not fail safe, since it can become very insensitive without any noticeable change in its clean air performance (although technology is improving in this area). Additionally, not all fires produce sufficient quantities of CO for successful fire detection to be guaranteed using a single element CO sensor.
Research has shown that a multi-sensor incorporating at least one gas element, a photoelectric sensor and a heat sensor offers substantial performance advantages. Suitable technology has started to evolve and combination smoke-heat-CO detectors have been launched on the market with some success; they claim enhanced performance with respect to false alarm elimination.
High-sensitivity systems
In areas such as telecoms facilities, computer suites, control rooms and other high-value environments where there is substantial cost for downtime or where a significant investment in installed equipment has been made, it is imperative that any fire is detected at the very earliest time. Given that such environments will normally be temperature and humidity controlled, with dust filtered out of the atmosphere, it is possible to increase the sensitivity of the smoke detector dramatically without running the risk of frequent nuisance alarms.
Traditionally, the technique used to achieve very high-sensitivity coverage in a specific area has been the aspiration system. A dedicated network of pipes is installed in the protected areas and air is sucked through them to a remote detection chamber that contains a large, highly sensitive optical smoke detector using a laser as the light source.
An ultra-sensitive photoelectric point smoke detector that uses a laser instead of an infrared light-emitting diode (LED) as the light source is now available. The laser detector is a very sensitive and extremely stable sensor that provides up to 100 times more sensitivity than a standard LED device. It has a significant number of advantages over the aspiration system approach. The source of smoke is identifiable to a single detector rather than, as is the case with an aspiration system, a general area. As one detector within an addressable fire system, the laser detector is fully supervised and can be mixed on a loop with all other types of smoke and heat detector. It is interchangeable into the same base as any other addressable sensor on the loop, enabling the fire protection system to be upgraded at minimal cost for those areas within the building that require the highest levels of protection. The sensitivity of each detection point can be set to that required in the area protected, rather than needing to have an even greater sensitivity for the whole system, as is necessary in an aspiration detector due to smoke dilution. An aspiration detector sucks in air from all the holes in the piping and during a small fire condition, will suck in clean air through most of the holes. Where the system has occasional particulate occurring, false alarms would be more prevalent from the aspiration system.
Modules
Fire systems are increasingly required to communicate with other systems and equipment within the site, so that an alarm can be used to initiate process shutdown and also to control and supervise sounders, strobes, door releases, break glass call-points and other ancillary devices. There are no European harmonised standards for modules, so national standards, where they exist, need to be considered.
Conclusions
As an important part of the life safety industry, the world’s fire detector manufacturers are constantly improving their products to increase the levels of protection afforded to the users of the sites they protect. An example of the benefits of applying advanced technology, the latest devices provide increased functionality and better protection than ever before. 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.
Two real-life examples illustrate the importance of the issue of coworker reporting in the classified arena. These case studies place the subject in a context directly related to espionage and its consequences.
Espionage cases are statistically rare, but spies have been caught as a result of supervisor and coworker reporting. A famous case described widely in the media was that of Jonathan Pollard, a naval intelligence analyst arrested for espionage on behalf of Israel, whose arrest was the result of a supervisor's suspicion, followed by a coworker's report. Pollard's supervisor began to develop doubts about him, not only when he was caught lying about his dealings with another government agency but also when he was repeatedly late in completing work assignments. He was also requesting so many Top Secret documents that kit was becoming a burden on the clerk who had to log them in. For these and other reasons, the supervisor perceived Pollard as an undesirable employee and resolved to get rid of him. He did not suspect a security problem, however, until a coworker reported seeing Pollard take a package of Top Secret material out of the building late on a Friday afternoon. Investigations confirmed that Pollard was regularly removing and compromising large quantities of highly classified documents.
In another case, the colleagues of Navy spy Jerry Whitworth observed him monitoring and copying sensitive communications without authorization, saw classified papers ink his personal locker, and knew he took classified materials home. However, they assumed he was doing it only to keep his work current. Coworkers may not have known about his 42 bank accounts; his 44 credit accounts; the large cash payments he made on loans, cars, and computers; and other suspicious signs.
In 1983 alone, Whitworth spent $130,000 when his salary was $23,000. However, his colleagues did see Whitworth and his wife turn up at the dock to meet the USS Enterprise in a rented Rolls Royce, a luxury they themselves could never afford.
None of these coworkers reported Whitworth's activities before his arrest as part of the John Walker spy ring. Their failure to inform security personnel about Whitworth's security violations and lavish spending habits allowed the Walker ring to continue for several years, causing significant damage to national security.
Pollard and Whitworth both exhibited egregious and observable in their flagrant breaking of security rules. The Pollard case illustrates how alert supervisors and coworkers can make a difference when they report suspicious behavior. The Whitworth case shows the tragic results of colleagues not reporting that behavior.
