In any automatic fire detection system, the detectors are the front line in the fight against fire. Detectors and call points initiate the alarm signals that activate the control panel. The panel initiates the alarm and shuts down building services that could cause the fire to spread and alerts the emergency services. Detection technology has advanced significantly in recent years, providing greater levels of protection and false alarm immunity than ever before and widening the choice of solutions for building owners and occupiers. This article outlines the key considerations when specifying different fire detection solutions.
The requirements demanded of any fire detection system are inherently simple. It should:
- Respond to a fire as quickly as possible to give the building occupants the greatest time to evacuate the building in an orderly manner.
- Not generate false alarms that will disrupt the everyday business carried on in the protected premises.
Modern electronics hardware and software technology has revolutionised the capabilities of the detectors themselves, the communication protocols between the detectors and the way in which the control panel reacts to the signals it receives from the detectors. Arguably, the intelligence now embedded in the detectors and the advances in detection chamber design have been the primary driver that has brought fire detection systems to their current level of sophistication and performance.
For example, today’s detectors feature adjustable sensitivity levels, automatic dust compensation, multiple pre-alarm and alarm thresholds, fault monitoring and loop isolation; all features controlled by embedded software in the device. Working in conjunction with the control panel, an automatic fire detection system is extremely versatile, configurable and controllable, capable of being configured for changing occupancy patterns, risk profile changes and environmental variables.
Which Detector Technology to Specify?
Detectors can be segmented into two main types: aspiration systems and point detectors. Given that the key criteria for any fire detection system is to provide cover throughout as much of the building as possible, the choice between aspiration and point detection is a critical one. It is often a finally balanced decision between the two types when planning a new installation. The environments for which both are suitable have become more closely aligned following recent advances in aspiration technology. Other key criteria include the required speed of response, the impact that a fire would have on the equipment and premises and the occupancy patterns of the protected building.
In an aspiration detector, networks of sampling pipes are connected to very sensitive optical detectors. Aspiration systems include sophisticated filtering that removes dust particles but allows the products of combustion through to the detection chamber, preventing false alarms without degrading the system’s ability to give very early warning of fire. The characteristics of a modern aspiration system make it suitable for protecting a surprisingly wide range of different facilities.
Aspiration systems were originally separate from the building’s main fire detection, installed to protect specific parts of the facility where enterprise-critical equipment such as the IT facility was housed. Latterly, aspiration systems are protecting a much wider range of locations, a fact recognised in the recent publication of EN54-20.
EN54-20 is a mandated standard under the Construction Products Directive (CPD), which introduces a new classification system for aspiration systems, defining Class A, B and C sensitivities.
Class A: Very High Sensitivity for Enterprise Critical Facilities
Across all businesses, fire not only has direct impact but also causes significant reputation damage. Twenty-five percent of data centres do not reopen following a major disaster; seventy percent of small firms that experience a major data loss go out of business within a year, and fifty percent of businesses report that IT downtime damages their reputation.
The newest aspiration technologies are capable of delivering ultra-high sensitivity along with false alarm immunity – essential for providing the earliest warning and service continuity in data centres and computer rooms, the heart of almost every modern business.
Class B Enhanced Sensitivity for Restricted Access Area
In facilities such as power plants, physical access is restricted because of the potential danger to life. Conversely, in clean rooms and laboratories, the disruption caused to the installed equipment and processes by people entering is not acceptable. As only the sampling pipes intrude into the protected space, routine maintenance is performed outside the area which means costs are reduced as there is no requirement to shut down the facility. Aspiration also extends protection to areas such as lift shafts and under-floor or ceiling ducts where access for point detector installation and maintenance is physically difficult or impossible. Lifts for example do not need to be deactivated for smoke detector testing when using aspiration and no specialist resource is required in order to minimise building disruption and cost.
Class B for Large Spaces such as Warehouses/Stadia
Aspiration detection is an effective option for protecting high racking warehouses. The 10.5-metre maximum installation height for point detectors may be too low, and beam detectors, which can be installed at heights up to 25 metres, may not have an unobstructed field of view. Large public areas such as stadiums are also affected by changes in airflow and smoke stratification which can cause issues for traditional smoke detection methods. Furthermore, aspiration detection solves the testing and maintenance issues associated with locating smoke detectors installed at high level.
Class B or Class C, Normal Sensitivity for Challenging Environments with High Levels of Dust & Dirt
The latest aspiration systems use sophisticated filtering techniques to remove particles larger than 20 microns but allow the products of combustion through to the remote detection chamber. This provides a very effective, false alarm free alternative to point detectors in dusty and contaminated applications such as food and drink manufacturing, pharmaceutical facilities, wood processing plants, flour mills and similar industrial facilities. Newer technologies are also impervious to high airflow and temperature extremes that can cause false alarms in point detectors.
Class C for Historic Buildings & Areas where Aesthetics are Important
The combination of discreet small-bore sampling pipes in the protected area and the remote aspiration detection unit provide an unobtrusive method of protecting heritage properties and high-end architectural buildings where aesthetics are important.
The trend toward ever-greater integration of the disparate systems to be found in a typical modern building has affected the requirements demanded of aspiration detectors, with multiple communication channels provided in the latest products to be brought to market. Integral IP connectivity enables remote interrogation and monitoring using TCP/IP protocols over LAN or WAN networks. Alerts can be automatically broadcasted to a number of different email addresses. The IP capability runs in parallel with the normal comprehensive communications with the fire control panel, which enables extensive fault monitoring. Modbus protocols can also be embedded, enabling seamless integration with building management systems without any additional hardware or software.
EN54-20 states that each ASD manufacturer must supply a specific software design tool that produces EN54-20 compliant designs based on the detector class selected. This software design tool is not to be interchangeable with other manufacturers. System Sensor’s FAAST and FAAST LT aspiration systems, for example, have device-specific Pipe IQ and PipeIQ LT design packages. The software generates the pipe design and layout, the BOM and exports the reports showing conformance to EN54-20. In addition to the design element, the software also includes a test and monitoring module for ongoing supervision once the system is installed. This system also features Acclimate mode, which, configured through PipeIQ, further reduces the device’s susceptibility to nuisance alarms, providing maximum protection from a device located in changing environments. During the first 24 hours of operation, the device monitors its environment. After the initial 24-hour period, the device adjusts the alarm point based on the particulate levels over a rolling one-hour period, adjusting the alarm level based on the stability of the environment being monitored.
The major advantage of point detectors in an intelligent fire system is that the source of the fire is identifiable to the exact location of a single detector.
In the past, point detectors were either thermal or smoke detectors. Thermal detectors responded either at a fixed temperature or to a temperature change; smoke detectors detected the presence of particles of combustion in the air. A point smoke detector offers the best combination of speed of response with immunity to false alarms for the majority of commercial applications.
The very first smoke detector, developed in 1941, was the ionisation smoke detector, which was the foundation of today’s multi-billion pound global fire detection industry. Ionisation technology is particularly effective in detecting the small particles of combustion produced by fast flaming fires, but it is less responsive to the larger particles produced by smouldering ones. In many countries, ionisation detectors are no longer approved, and the regulations surrounding the transportation and disposal of low-level radioactive materials have become more stringent and consequently more expensive. With increasing emphasis on environmental considerations, the use of products incorporating radioactive sources in commercial fire systems is now discouraged. The most widely used technology is now the optical detector, originally developed to improve the speed of response to slow-developing fires.
The most significant advancement in detector technology has been the development of multi-sensor devices, primarily designed to overcome the relatively poor performance of the optical detector in responding to fast fires with low particulate generation but significant heat rise. The photo-thermal detector was developed to address the inevitable balancing act between increasing the sensitivity of a detector so that it responds more quickly to an incipient fire and the consequent increase in the false alarm rate.
Originally crude units, in which two independent sensors, an optical and a thermal detector were mounted in a single housing, the availability of low cost embedded microprocessors enabling has enabled true composite units to be developed. Signal processing in the detector head itself resulted in the panel being presented with a single composite result from the raw data generated by the two sensors, improving the effectiveness of the device across the fire spectrum.
The multi-sensor detector concept has now been extended with the addition of further sensors, each one optimised to detect a specific product of combustion, typically carbon monoxide, heat and particulate matter. It is well known that every fire has a different profile during its development; the proportions change from one fire type to another, as does the time during which each element is produced, but in every case, to a greater or lesser extent, each of these three elements will be present. In cases where the fire is flaming, it will additionally produce a changing light signature as the result of the flame generation. Several manufacturers have introduced tri-sensor devices, in which the smoke and heat detectors are augmented by the addition of an infrared light sensor. Again, embedded intelligence in the head manages the inputs from the three sensors. Extending this principle even further, the latest multi-sensor detector to be launched is a quad sensor device, which combines optical, thermal, carbon monoxide and infrared detectors into a single device.
Without doubt, technology advances have been adopted to great effect by fire detector manufacturers that play a vital role in the life safety industry. The leading manufacturers share the common aim of increasing the protection levels and false alarm immunity provided to the users of the buildings they protect. New detection products currently in development will make their contribution as part of ever more efficient automatic detection systems in the future.
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