Linear Detection System Comparison
LINEAR HEAT DETECTION is the most effective method of detecting over-heat and fire conditions within a number of heavy Industrial risk areas. The point of risk installation is not reliant upon favourable airflows it operates with limited maintenance in adverse environmental conditions and within areas of limited access and surveillance.
During the past decade, the " heavy Industrial" reference list of installations for linear detection has been complimented by an increasing number of light Industrial, commercial and even domestic project installations. Included within such a list are:
- Multi -storey car parks
- Road / Rail Tunnels
- Warehouses (bulk, rack storage and freezers)
- Railway Stations (incl: Metro systems)
- On + Off road vehicle protection
- Shopping Malls
There are various types of Linear Detection categories which are designed and manufactured with very different operating concepts.
There can be no system which is totally re-settable or recoverable in a real fire situation. Independent statistics prove that the size of ALL overheat/incipient fire conditions would only ever expose a short length of installed sensor cable to the alarm condition. It does not matter what the risk or application is. Therefore if some cable is damaged surely it would make more sense to replace this section of cable. There is no material which is immune to some change in characteristics after exposure to an overheat or fire situation. All cables should be replaced or repaired.
This system is advertised as a non-electrical system which is safe for use within any environment. However this system has a high maintenance due to the risk of potential failure from a mechanical pump to maintain air pressure within the sensor tube. Also there is a high incidence of false alarm signals as a result of the sensor tube rupturing from environmental corrosion or mechanical damage. The length of the tube has to be restricted in order to maintain air pressure at specific levels.
A system which is internationally proven and certified for its ability to be the most flexible of all linear detection concepts. A great advantage of this system is that it only requires a minimum length of cable exposed to the over-heat condition for the cable to respond. It is one of the simplest to integrate with any central fire alarm control panel. Also it can be connected to optional interface units which can increase the ability of the cable to attain a pre-specified alarm temperature location, pre-alarm signal and ambient temperature rise alarm. One interface unit is able to continue to provide detection with a break in the communications or linear sensor cable. All optional interface units have solid state volt free contact outputs facility and alarm point location as standard.
This works by responding to an average resistance. That is a high temperature rise over a short length of installed linear sensor cable or a lower temperature rise over a longer length of installed cable which will have the same resistance change. Therefore unless an EXACT length of sensor cable in an alarm condition can be specified an analogue system cannot give an accurate alarm temperature. This system must be used with a dedicated electronic interface unit.
An expensive system which is only practical to use in applications where temperature monitoring is required. Therefore the cost rules this system out when it comes to wanting to detect an over-heat or detect a fire. It has been seen that sometimes when sharp bends in the fiber have been caused through installation it can create repeated numbers of false alarms which in turn creates a further cost. The same occurs when there are minimal levels of vibration on the cable.
MEASURING POINT SYSTEM
This is cable which has added hybrid electronic detection circuits along its length. These are added at various regular intervals of 1, 2, 4 or 8 meters acting like point detectors at these intervals. The cable itself has to be thicker in order to incorporate the electronic devices and is unable to detect along the whole length of the cable making it less sensitive.
The most sensitive of all smoke detectors. It has site adjustable sensitive levels of air sampling which works via small bore pipes into which air sampling holes have been drilled in areas of potential risk locations. However this system relies on smoke in order to provide detection which comes after an over-heat AND will only provide sensitive detection where pipework runs and hole locations have been correctly located......as much guess work as a science !.