Linear Heat Detection

FAQ's - Linear Heat & Fire Detection Systems

 

Q - As linear heat detection systems rely on abnormal temperature rises to generate an alarm , wouldn't it be better to specify a smoke detection system ?
A - Where it is a typical office type risk - ie paper fires and / or a clean environment , then smoke detection should be specified . However , where the risk is within a dirty , dusty , damp , corrosive environment and areas of limited access and surveillance , smoke detection of ANY design should NOT be used ! Linear detection - as a combined cable and detector in one - has been designed to monitor for abnormal temperature rises at the exact point of risk - not the most convenient roof / ceiling height , and is therefore not reliant upon favourable airflows to take the heat to the detector ( as with point type temperature monitoring detectors ). Back to FAQ Index

Q - Which is the better linear heat detection system - "analogue"or "digital".
A - Incipient Fire and / or Overheat conditions will ALWAYS be localised events. The fastest response to such an alarm condition will therefore be from a linear heat sensor cable that has a fixed alarm temperature level regardless of whether 1% or 100% of its installed length is subjected to the condition ( ie DIGITAL) . Other Linear heat sensing systems which specify - the longer the length of sensor cable heated , the lower the alarm temperature - ( ANALOGUE)  will not be as sensitive as digital, and because the short length exposure alarm temperature is above the analogue sensor cable destruct temperature, the theoretical "recoverability" feature will not be witnessed in an actual installed/ operational state.  Back to FAQ Index

Q - What are the advantages (if any) with fibre optic type linear heat detection systems ?
A - Fibre optic technology in the field of linear heat detection may appear to offer many advantages - long zone lengths , fast response , accurate alarm point location , recoverability ( stainless steel protected sensors only) etc . In practice however, price is prohibitive, installation and repair complicated ( requiring specialist knowledge and tools ), loop configuration may be required - involving excessive lengths of sensor ( and increased cost ) .Integration with some existing fire control systems difficult or again requiring special training. Operating history also limited when compared with other linear heat detection operating concepts . Sharp bends in DTS type fibre optic systems can result in incorrect reading/ assessment by the system associated control unit .

Zone lengths up to 5000m, fast response and accurate alarm point location can already be offered by digital linear heat detection at a fraction of the price of a fibre optic system.Back to FAQ Index

Q - Will linear detection systems operate if connected directly to a new or existing central control panel or does it require its own dedicated control panel ?
A - This depends upon the linear detection system selected AND the central control panel !

With "analogue" linear detection, a manufacturer supplied dedicated interface must always be used.

With "digital" linear detection, it is dependant more upon the existing central control panel - typically whether it will monitor and signal the short circuit alarm principle of the sensor cable as an alarm and not fault condition, and whether the panel zone card will operate with the electrical resistance values specified for the heat sensor cable selected.  Compatability with Central Control systems is assured where an interface unit is specified with the digital linear heat sensor cable .Back to FAQ Index

Q - Can I integrate the Linear detection system with an addressable central fire alarm control panel ?
A - Interface units supplied by both analogue and digital linear heat detection operating systems , provide alarm and fault output contacts. The digital linear detection interface unit ZI-01 can be loop powered , or via a dedicated 24vdc supply with its volt-free contacts signalling to a panel manufacturer supplied Zone Monitoring Unit ( ZMU) or similar device. RS232 Communication options are available on the ZI-01 interface unit.Back to FAQ Index

Q - What is the maximum length of sensor cable I can use on a zone ?
A - This is dependant upon the linear detection system specified - especially where analogue linear detection has been selected, as this systems maximum zone length is reliant upon the maximum ambient temperature specified (because of the systems temperature/length/resistance operating relationship). Digital linear detection is not so restrictive, with zone lengths exceeding 1000m not uncommon.
Maximum zone length calculations should follow tried and proven linear detection system design practices and whether extinguishing zones are to be associated with the linear detection zones. They should not be based solely upon price considerations. Back to FAQ Index

Q - Should the linear heat sensor cable always be installed in direct contact with (or very close to) the equipment/risk it is protecting ?
A - Unless it is the surface temperature of a specific piece of equipment that is considered to generate the major risk, there should always be a clear airflow around the heat sensor cable (except at regular sensor fixing/ support points).
In most cases , the possible "heat sink" effect from a piece of equipment that the sensor cable is in direct continuous contact with , will have an adverse affect on the linear detection system alarm response times.
Remember also to verify that the selected sensor cable location does not present an obstruction to site engineers access for routine maintenance or repair of the site installed equipment being protected by linear detection. If it does , the heat sensor cable might be moved to allow the repair / maintenance to be effected, and not replaced. Resulting in loss of protection. Back to FAQ Index

Q - Can DIGITAL Linear detection systems signal exactly where the alarm condition has occurred along the heat sensor cable ?
A - YES. Using manufacturer supplied interface units, the "alarm point location "can be identified and displayed accurately ( to 0.2% accuracy on the ZI-01 unit). Particularly important when one considers that this detection concept is able to warn of an overheat condition (pre-combustion). Hence there would be no visible flame to assist with identifying the origin of the alarm - thus providing the end user with a fire PREVENTION capability (in certain applications).Back to FAQ Index

Q - Does the linear heat sensor cable need replacement after an alarm ?
A - Only the fire/overheat damaged Section requires replacement. Even where linear detection systems using stainless steel tubing are installed, we would suggest that a) direct flame exposure would still damage the sensor cable and b) the linear heat detection system would not be the only replacement consideration after a local fire had been detected and extinguished Back to FAQ Index

Q - What are the maximum and minimum temperatures in which I can install linear heat sensor cables ?
A - Proline type "TH" digital linear heat sensor cables will currently operate continuously within a -40C/-40F to +70C/158F ambient temperature range. Back to FAQ Index

Q - Is there any recommended minimum temperature allowance between the specified maximum normal ambient and minimum alarm temperature ?
A - International standards recommend a minimum of 11C / 20F between maximum specified ambient and the linear detection system alarm temperature.
Please remember that local hot spot temperatures should also be considered in alarm temperature selection - for example …….
1) steam pipes
2) heaters or halogen lighting
3) Reflected sunlight off of a floating roof ( "black body "temperature ) on a Middle East storage tank project , where temperatures around the installed linear heat sensor cable have been recorded at 75C - although the project maximum ambient was only specified as 55C. Back to FAQ Index

Q - Is Linear Heat detection suitable for installation within designated hazardous areas ?
A - All linear heat detection systems supplied by Proline Protection Systems Ltd are suitable for use on hazardous sites. Any control or interface unit MUST be installed within a designated "safe ", with the associated interconnecting cabling and heat sensor cable installed within the hazardous area. System approved zener barriers or galvanic isolators will be supplied within the control or interface unit - providing the hazardous area application is defined at the enquiry / quotation stage. Back to FAQ Index

Q - Are linear detection systems suitable for use within sub zero temperatures and/or corrosive environments ?
A - YES, but care should be taken by the customer to specify environmental conditions at the intial quotation request stage - to ensure appropriate sensor cable extrusions are specified. Back to FAQ Index

Q - Why should I specify manufacturers approved fixings/clips for the sensor cable. They are sure to be more expensive than locally produced/supplied equivalents ?
A - Manufacturer approved fixings are not always the more expensive. They should ALWAYS be specified because they have been designed with correct sensor cable location in relation to the risk in mind - to maximise system sensitivity, and to promote continuous uninterrupted operation of the system - which would not be the case where cheap, unsuitable or less effective fixing devices had been selected. The decision should NOT be left to the installation contractor - many of whom have little experience with linear detection system design and operation.
In certain cases, failure to specify manufacturer approved fixings would invalidate system warranties. Back to FAQ Index

Q - What is the recommended maximum spacing between clips and why ?
A - 1 to 1.5m. This minimises sensor cable "sag" - something which if excessive could increase the potential risk of mechanical damage to the sensor cable.
For larger open risk areas (ie. warehouse/aircraft hanger roof) where regular fixing points may not be available, sensor cable can be supplid complete with stainless steel tensioning wire wrapped around it. This dramatically increases the spacing between fixings. Back to FAQ Index

Q - Do I have to use linear detection manufacturers supplied junction/termination boxes ?
A - In general terms - NO! As long as the specification of the junction / termination boxes meet end user/site minimum specifications. Only on "analogue" linear heat detection systems should the manufacturers supplied remote end of sensor cable terminations (ie. heat shrink cap)- ALWAYS be specified and used. Back to FAQ Index

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