FIRE SAFETY & DISASTER RECOVERY
Compared to a straight forward single sensor detector, the decision of which Multisensor detector to choose, is more complicated; and that is before all the different modes and settings available are taken into account.
CHOOSING THE
RIGHT DETECTOR The choices and decisions concerning which detector types to use are initially made during fire system design but are also sometimes re-visited and even modified during commissioning and/or maintenance. They are not always well recorded nor is the rationale behind them.
Multisensor detectors could be a
universal solution for the protection of all life safety and property protection risks, providing the appropriate compliant sensitivity modes are selected to meet and maintain the evacuation strategy.
System Designers and Engineers
need to understand how the technology in the device works and more importantly the appropriate fire engineering application of such devices.
The decision of which detector to use, is made when the fire protection system is designed. There should be reviews at regular intervals, ideally as part of the maintenance schedule, as the circumstances under which the system was first commissioned may have changed and technology will have moved on. This is especially important as there is (as yet) no legal requirement in the UK to replace fire detectors after a specified number of years in service.
FALSE ALARMS According to the National Office of
Statistics, over 300,000 false alarms were raised in the UK in 2014/15. Overall, the number of false alarms is slowly declining year-on-year, the exception being Scotland, which has seen a slight increase for the first time in years. The FIA quotes the estimated cost of false alarms in the UK as being in excess of £1 billion a year. In addition to the cost, false alarms take up the time and resources of the emergency services,
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who may not be available to respond to a genuine alarm at the same time.
The fire protection industry has made great progress in developing detectors that can recognise if a signal warrants an alarm or not; Multisensor detectors are part of the solution.
Multisensor detectors are extremely efficient in detecting real fires and ignoring false alarms if the modes are set correctly. Reputable detector manufacturers work with System Designers and Installers to ensure they are aware of the settings and how to configure them correctly.
MODES AND SETTINGS The decision on when to alarm
is continually improving; specially developed algorithms and communication protocols interconnect detectors and allow information and verification exchanges. The suitability of a detector can no longer be solely based on sensor technology.
“OVER 300,000 FALSE ALARMS WERE RAISED IN THE UK IN 2014-15.”
Algorithms embedded within detectors or control panels are used to change the sensitivity to fires. Each detector comes with a choice of modes and settings suited to different environments. In addition to different levels of sensitivity, these settings can include a ‘minimum time to alarm’, ‘day/night’ sensitivity switching and single point alarm confirmation.
Algorithms are used to improve the performance of Multisensor detectors. They can also be used to combine the responses from a number of detectors to make an ‘intelligent’ system decision. Algorithms can be highly tailored and are usually designed to improve the performance of a detector in a specific environment.
Detector modes and algorithms have to be matched carefully with the potential fire risk when the system is being designed. Extreme care has to be taken not to be overly concerned
with avoiding false alarms at the risk of missing a genuine alarm. There are many fires that produce smoke but little heat or carbon monoxide, especially at ceiling height where the detector is most likely installed.
Well-designed Multisensor detectors in carefully selected modes can detect more fires than many single-sensor detectors. Algorithms will increase the accuracy of the detector and help to filter out most false alarms if correctly applied. Algorithms that are just designed to filter out false alarms can have dangerous consequences if they override the original sensor reading. This can be avoided by applying the ‘and/or’ logic in algorithms, to allow the most likely fire phenomenon (most often smoke) to set off the alarm.
The range of modes, settings and algorithms is developed and programmed by the detector manufacturer. It is the responsibility of the System Designer and Installer to apply the correct setting for the environment in which the detector is installed. This means they need to be aware of the different algorithm settings and modes. Manufacturers have a duty to make information about specific modes and settings available to ensure the safest and most suitable setting is applied always in every environment.
WHAT NEXT? Multisensor detectors have come
a long way since their introduction to the market. System Designers and Installers need to be aware that Multisensor detectors are not always the best solution for every fire protection system, the technology also varies depending on the manufacturer and model. Manufacturers have a duty of care to make information about the sensors and algorithms available to Engineers involved in the design, installation and maintenance of fire protections systems. They have to make information readily available and offer regular training to the industry so that we can professionally protect life and property into the future.
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