NEWSHEET 22
Which Line Type Overheat Detection System - 2008
There is an acknowledgement by many of those responsible for identifying the origins of life and investment threatening fires that - with the exception of specific Petro-Chemical type gas ignition "flash fires"- the majority of Industrial fires are overheat conditions which - if undetected - progress to the combustion stage.
To those businesses unfortunate enough to have suffered from a fire, the direct financial costs associated with repair / replacement of flame or smoke damaged equipment -whilst potentially high- can represent only a small percentage of the difficult to quantify "consequential losses". With more than half of those businesses affected by fires suffering long term loss of market share or profitability. The emotional affect on those individuals directly involved and the damage to the environment should also be recognised.
"Fire Detector" manufacturers constantly seek to develop and introduce new and further improved methods of preventing(or minimising) possible damage caused by a fire. Point type (heat/smoke) and line of sight type (beam /flame) detectors provide a suitable means of protection throughout many Industrial sectors and their respective applications. But as with everything, they were not developed for - nor capable of -being a suitable means of protection for ALL risk applications.
LINE TYPE HEAT SENSING (LHS) is not a new concept, but historically its application has been somewhat restricted by specifiers and consultants to what was once referred to as its "traditional" risk protection of cable trays, conveyors, fuel storage tanks etc.
As a detector and cable combined, capable of installation within almost ANY environmental condition, with "point of risk" installation and a simple integration with a site Central Fire Protection Control Panel, the features and benefits offered by such a system allow rapid detection of abnormal temperature conditions within a much more diverse range of applications.
Whether road/rail tunnel,car park,on or off-road vehicle, marine craft,fuel pipeline, freezer warehouse (bulk or rack storage),escalator/elevator,listed building,thatched (straw) roof or protection of expensive domestic property against forest fires.......linear heat detection provides the solution to what might otherwise be a costly high maintenance and less reliable/possibly troublesome (ie. false alarms) alternative.
Detection without reliance on favourable airflows provides many end users with the possibility of a fire PREVENTION system by detection of the pre-combustion overheat condition.
Within areas where air pressure may prevent smoke from reaching a ceiling mounted point type detector (ie corridor) and where the presence of individuals may not be guaranteed to visually detect a fire, linear heat detection can be utilised as the wiring for manual call point zones - adding a further fire detection capability in an area where call point cable costs would have been incurred anyway.
The two most commonly specified LHS operating concepts are "DIGITAL" and "FIBRE OPTIC".
The FM approved and UL listed Digital "TH" system offers a fixed level alarm temperature -regardless of length exposed - and can be designed without concern of any adverse affect that local high ambient temperatures might have to desired "zone" lengths, or RFI /EMI might have to its operation. Multi kms of a single zone sensor cable can be directly addressed from a central control panel loop or can have an economic optional interface included which provides alarm point location (of particular benefit in overheat- no visible flame conditions), local colour coded LCD display, volt free output contacts and RS232 /RS485 serial links. A 5000m length of sensor cable can be site programmed (ZI-03) so that any section of that 5kms is dedicated to up to 50 alarm outputs. Allowing any central panel to take the necessary correct and local "executive" action/s in a fire situation in terms of local extinguishing, ventilation, smoke extraction zone operation. For other larger risk areas, a single interface (ZI-05) can provide alarm point location, fire over-ride fault, pre-alarm, multiple simultaneous fire condition signalling and display for up to 128,000metres of "TH" sensor cable.
The FM approval testing on the "Zense" fibre optic LHS system will provide the required International certification for a more "sophisticated" and increased information output system. This offers market leading reliability, spatial and sampling resolution of 1 metre as standard, temperature accuracy of +/-0.75C, a 7 seconds measurement time with temperature recording and optional application specific graphical data visualisation and user interfaces. All via a "manufacturer" supplied single or double ended standard multi-mode GI50 or 62.5m fibre optic cable connection to a maximum length of 4 kms.
Whilst other LHS concepts are available,detection by hybrid circuits built into a cable at regular intervals during its manufacture, pneumatic and/or resistance averaging systems do not provide the more operationally beneficial features and benefits of the systems described above. These Include detection at ANY and ALL points along the sensor cable length without reliance on any minimum length exposure which prevents the pre-specification of ACCURATE alarm temperature levels - because length exposure in a fire condition cannot be guaranteed! Recoverability - a "feature" sometimes marketed as being beneficial to a linear heat detection system installation is, in practice many times not an option - unless large percentages of the installed resistance averaging sensor cable will be exposed. Not conducive with the proven very localised conditions associated with incipient fires and overheat conditions that would be found in any risk area.It should be considered that regardless of LHS system specified, section replacement after a fire is all that would be required. It is also suggested that site repairs following a severe overheat or fire situation, would inlvolve much more than simply the replacement of a short length of small diameter heat sensing cable?
Every type of fire detector has been designed for specific risks or groups of applications. None are capable or suitable for all risks - including linear heat detection. But as an integral part of an installed or proposed total fire protection system it is able to enhance the total detection capability of a Central Fire or Building Management Control system. Within areas where overheat detection could prevent the onset of a fire or where, because of environmental conditions, the end user would otherwise witness an initial product/system purchase and installation budget price spiral beyond recognition because of repeated operating maintenance costs or detector false alarm charges during the systems operating lifetime.
After more than 30 years of specialising in LHS products (all operating concepts), their application and International market development -ensuring conformity with recognised and accepted fire industry standards- the above comments are made with some degree of experience.
Brian Cummins
Chief Executive Officer
PROLINE PROTECTIONSYSTEMS LTD
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