Linear Heat Detection Systems

WHY LINEAR HEAT DETECTION ? - More than 60% of businesses that suffer a major fire NEVER recover, and with 80% of Industrial fires identified as undetected overheat situations which progress to the combustion stage, then why not detect the overheat BEFORE the fire ignites.

Fire Buys "TH" digital linear heat detection - for many applications not only rapid FIRE DETECTION but potentially - FIRE PREVENTION.  (flash fire risk applications excluded).

Linear Heat Detection:

The monitoring and signalling of abnormal local temperature rise, overheat or fire conditions at point of risk- by a small diameter current carrying cable  . This is an Internationally tried, tested and approved detection concept that does not rely upon favourable air flows, is not susceptible to adverse environmental conditions (dirty, dusty, damp or corrosive) can be installed and operate continuously with limited maintenance in areas of limited access and surveillance.

Product Categories

Linear detection products and systems fall into one of four categories - ANALOGUE, DIGITAL, FIBRE OPTIC, ELECTRONIC PNEUMATIC.

Fire Buys has detailed application experience in ALL the above mentioned categories , and has carefully evaluated the claims made by each in respect of speed of response , sensor cable recoverability , site adjustment of alarm levels , multi kilometer zone runs etc.

What is indisputable , is that ALL overheat and incipient fire conditions are initially , LOCALISED events . As such , only a very small length of the heat sensitive cable - which forms the basis of all such systems - will be exposed to the event .

With some systems operating on a temperature / length relationship , the alarm temperature in this case would be significantly greater than that offered by a system which was not length dependant!  Similarly , multi kms zone length claims offer no advantage when the linear heat detection system forms part of a total "protection" package - ie the zone definition being determined by the extinguishing system limitations , local / International fire system design standards or by fire doors / barriers located within the risk area. Even where installed as an independent detection system ,some systems reliability may be dependant upon a "loop" connection to its dedicated interface / control unit - effectively increasing by 100% the zone length of sensor cable  required by non loop configuration systems .

Whilst the Company is able to offer systems of all operating characteristics , it is a belief -based upon FACT not theory - that the DIGITAL systems provide the most cost effective and responsive solution to the majority of risks being protected by linear heat detection .

The specified digital linear detection system can be simply integrated into any existing or proposed Central fire alarm (detection + extinguishing) control system - either directly or via a dedicated interface device (with volt-freecontacts or RS232 communication port options - dependant upon interface). And operated with limited maintenance and ease of repair / replacement  .

System suitability for operation within corrosive environments and/or hazardous/intrinsically safe classified areas is achieved by way of specification of correct outer extrusion and/or use of zener barriers/galvanic isolators.
 

Definitions

• Analogue: A multi-conductor or co-axial cable which exerts a defined change in electrical resistance of internal polymers when subjected to changes in ambient/surface temperatures. System monitoring through an associated electronic interface unit provides fault indication of open and short circuit conditions on the sensor cable. The same unit allows for site re-calibration based upon post installation alterations to maximum ambient temperature conditions and changes to zone lengths of sensor cable . Compatibility is achieved with central fire alarm control panels via electrical current increase or volt -free fire and fault relay contacts. Optional mechanical or corrosion resistant extrusions/metal braiding to suit the environment in which it is installed. Mechanical or fire damage to the sensor cable is repaired via section (not total length) replacement.
  
   
• Digital: A "switching " cable where a change in state of internal insulation - caused by temperature rise to a pre-defined level - allows a short circuit or "hot junction" to occur between two twisted steel or copper covered steel (depending upon manufacturer) conductors. The "twist" provides evenly distributed tension between the conductors which assures the detector actuates once its designated alarm temperature is reached and the associated internal conductor insulation breakdown has occurred. The "twist" also adds a measure of protection from induced electrical interference such as EMI and RFI which could affect monitoring circuitry. Identification of the exact point of alarm along a zone length of digital sensor cable can be achieved via the systems "alarm point location " feature. Mechanical damage to an installed run of sensor cable is signalled by loss of a small monitoring current that passes through the cable and an end of line resistor fitted across the conductors at the remote end of the sensor cable. Mechanical or fire damage to the sensor cable is repaired via section (not total length) replacement. Australian standards AS1670 requires maximum spacing of 7.2 metres between parallel runs, with a maximum distance to adjacent walls of 3.6 metres.
  
   
• Fibre Optic: A site programmable system (via laptop computer) consisting of electronic control unit and associated fibre optic sensor cable (one or more optical fibres incorporated in a hermetically sealed stainless steel tube) to 8kms zone length, which may be designed with a "fibre break & recovery " feature that allows the system to continue operation even after mechanical damage. This is achieved through a loop design where the system switches automatically to monitoring from both ends in the event of fibre damage (USA class A designation). Temperature measurements and locations along the optical fibre are achieved by launching laser pulses down the fibre and analysing the back scattered signals. Specific bands are compared to determine temperature and location of each measurement point calculated from the time of flight from laser emission. This information allows the control system to produce a real time graph on a monitor. The system alarms if there is a significant increase in optical loss or break of the sensor element.
  
   
• Electronic Pneumatic: Designated as an electronic pneumatic device, this fully supervised, maintenance free and fully restorable (even after direct exposure to flame) system consists of a combination of 2mm diameter capillary stainless steel tube (the detection cable and associated electronic control panel. The product operation is based upon the fundamental principles of thermodynamics, heat transfer and electro mechanics, resulting in a rate of rise technology detector for "point of risk"/localised protection, that has built in sensitivity switching that requires no special tooling or training. The sensor 'wire", whilst being all metal, has the flexibility of a plastic cable - thereby offering ease of installation with no special tooling requirements or minimum bend radius restrictions. It is suitable for a wide range of 'short - medium zone length applications.

Applications

Traditional installations for LINEAR HEAT detection system, include - but are not restricted to - Cable trays, Transformers, Conveyors, Floating roof tanks - rim seal protection, off-shore oil rigs, Warehouses , Cool rooms, Road & Rail tunnels, Metro stations (under platform / electrical cupboards / escalators), Airport terminals and hangars. This list has been extensively increased during the 60 years that linear heat detection has been under development and manufacture to also include:

Hospitals (service ducts), Shopping precincts (escalators / lifts / multi storey car parks), Various military and aerospace applications, listed buildings, On and off road vehicles (engine bay protection of HGV's, earth movers, combine harvesters), Marine craft (leisure craft - engine bays, ferry - car and storage decks), Restaurants (cooker hoods) and Perimeter fencing protection.

Any area where the installation and operational benefits of this small diameter "detector and cable in one" detection device - which can be installed at the precise point of risk (not most convenient roof / ceiling height - can be utilised to the full benefit of the end user and the protection of life and capital investment.

Installation

Easily and rapidly installed when using manufacturers approved and economically priced sensor cable support devices, installed at the recommended 1 to 1.5 m spacing. Ensures correct sensor cable location for the risk to be protected and continuous uninterrupted operation of the system during its anticipated minimum 10 year lifetime.

Note- Detailed research has been carried out by the product/systems manufacturers in conjunction with end users, as to the most effective and efficient positioning and mounting of linear heat sensor cables for the specified risk/s. This considers avoiding "post installation" obstruction to routine operation and maintenance of the area/s being protected. And to the correct specification of clips/fixings - to maintain continuous protection and minimise the risk of mechanical damage to the sensor cable.

It is therefore recommended that professional advice/guidance be sought prior to installation in these areas.