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Innovations in fire system technology

Jan 26, 2005
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There is a vast array of fire detection systems and devices on the market today, ranging from the relatively simple to the most technically sophisticated. Modern automatic fire detection systems are available in two types – conventional and analogue – which, broadly speaking, are used in smaller and larger installations respectively.

Conventional systems use a two-wire radial circuit for each zone and are based on simple on/off switching technology first introduced in the 1970s. Although modern components and good system design can go some way to reducing potential problems, it is not uncommon for conventional systems to generate unwanted alarms due to transients, detector and circuit faults, and certain operating conditions.

A key development aimed at preventing such unwanted alarms has been the multi-criteria detector. Traditionally, detectors were designed to respond to particular fire phenomena such as heat or the presence of smoke. However, many manufacturers now offer multi-criteria devices, which typically contain both an optical sensing element and a thermal element. The fire alarm decision is taken by analysis of the responses from both elements, and this results in improved detection performance.

Despite such advances, conventional systems are still unable to match the performance of analogue technology and in some cases they may also work out more expensive. The purchase price of a conventional system may appear attractive, but the amount of cabling required for each detector and alarm spur can be substantial, so the installation costs can rapidly outweigh this initial advantage.

ANALOGUE SYSTEMS

For fire protection applications demanding both high reliability and performance, the more technically sophisticated and versatile analogue systems provide a clear advantage, despite a higher initial equipment cost.

Unlike conventional systems, analogue detection and alarm systems are not based on simple two-state binary detectors, but on ‘intelligent’ sensors within a software-based communications system. Each fire-detecting sensor or call point is electronically coded with a unique identification or ‘address’, and detectors and call points are wired in a single loop instead of the two-wire spurs used in a conventional system.

With typically up to four loops fed from a single control-and-indicator panel, the ‘analogue addressable’ system uses a low-power pulsed signal to interrogate each detector in turn, comparing the reply with data representing a normal, healthy condition within individually programmed limits. For the largest sites, several systems can be linked to form a complete local area network providing total coverage.

As well as dramatically reducing false alarms from transients or faulty circuitry, analogue addressable fire alarm systems can provide a far higher and more versatile degree of protection. Detectors can often be individually programmed for sensitivity or automatically switched between high and low alarm thresholds or even different detection modes – e.g. for night or day protection. The most sophisticated analogue systems can be interfaced with building management systems and can also be used to interact with other services such as ventilation or warden call systems.

The challenge for analogue addressable fire system technology has been to combine its advanced features with the simplicity of operation demanded by today’s building users and the straightforward installation procedures that help to make the contractor’s task much easier. Now appearing on the market is a new generation of fire detection systems that have succeeded in rising to this challenge.

ADVANCED FEATURES

The latest analogue addressable fire detection systems are generally available in single-, two- or four-loop versions, with each loop capable of accommodating typically up to 150 addresses (although EN54 places restrictions on the total number of devices connected to individual panels). In some cases, up to 63 panels can be networked together to form a single system capable of operating with over 32,000 devices.

Some new-generation systems have the ability to support highly complex sounder ringing pattern requirements. Multistage cause-and-effect programming is possible, whereby each addressable sounder or output interface can be programmed independently if required and can be set to respond to specific addresses, specific detection zones or specific panels on a networked system.

Three separate stages of programming per sounder are supported by some leading-edge systems, and each stage can be triggered differently. For example, if a single detector is triggered, the system can be programmed so that the sounder nearest to the detector operates immediately and continuously, while the remaining sounders in the affected zone operate in a pulsed mode, and the other sounders delay for a selectable period to allow the cause of the alarm to be investigated before global ringing commences.

SIMPLICITY OF OPERATION

At the heart of all fire systems is a control-and-indicator panel. Technology advancement has enabled major improvements to the manner in which the user interacts with the system. For example, systems are now available featuring large (120 x 90mm visible area) touch-screen displays. As well as providing detailed system-status information, such displays also act as multifunction keypads, and this versatility enables an extensive array of user and engineering facilities to be incorporated into the panel while at the same time making it easy to operate.

On more basic systems, the user is limited to a small number of dedicated pushbuttons, and consequently system interaction is restricted and complicated.

The touch-screen displays on the more advanced systems provide context-sensitive help information throughout their control menus to assist those who are unfamiliar with the system, so most users can add or remove devices or change device text via the panel without the need for a service engineer to visit the site. On some systems, the touch-screen display automatically reconfigures to suit the selected function – for example, if a ‘Change Device text’ menu option is selected, the touch screen would be automatically formatted as a full QWERTY keyboard to enable fast and simple text entry.

Most panels also incorporate conventional zone indication LEDs and system-status LEDs, which can readily be understood even by non-technical users.

STRAIGHTFORWARD INSTALLATION

On some of the latest fire detection systems, the installation and commissioning process has been greatly simplified by the use of spur-tolerant soft addressing. This technology allows the control panel to automatically scan the detection loops and allocate each device with an address number corresponding to its position on the loop, thus avoiding the traditional need for manual addressing of devices, which is not only time consuming but also a potential source of errors.

Another major innovation is the ability to utilise a spur isolator to connect a spur of analogue devices to the main loop. During the soft addressing process, whenever the panel detects a spur, it breaks from allocating address numbers to the loop-wired devices, allocates address numbers to each of the devices on the spur in sequence, and then continues to address the devices on the main loop.

ANCILLARY DEVICES

The range of ancillary devices available varies from one system to another, but typically it will include optical, ionisation, photo-thermal and heat detectors; callpoints in various styles; a choice of conventional and loop-powered sounders and beacons; low-cost passive repeater panels; and a wide variety of input and output interfaces.

Manufacturers of top-flight systems ensure that each of these components has been specifically designed to operate as part of the system, providing an assurance that the panel, the detectors, the interfaces and the ancillary devices are all fully compatible with each other and that the full range of system functionality is supported by each device.

CONCLUSION

The latest generation of analogue addressable fire detection systems offer a powerful combination of sophisticated features, simplicity of operation and ease of installation. While some of the advanced features of these fire detection systems have been designed with larger buildings in mind, the benefits of shorter installation time and lower wiring costs are expected to make the systems attractive for even quite small establishments.

ABOUT THE AUTHOR

Peter Cook is product marketing manager at Cooper Lighting and Security, with responsibility for product development and marketing of the company’s Menvier and JSB ranges of fire detection systems and emergency lighting. He has over 20 years’ experience with the company, having originally joined Menvier to work on its range of central battery systems for emergency lighting. Since the 1997 acquisition of Menvier by Cooper Industries Inc., his range of responsibilities has expanded to cover fire systems.