From ancient times people have realized that early detection of fire has a positive effect in the fire control. The earliest recorded examples of fire protection can be traced back to the Roman Empire and the catastrophic fires that started in Rome. As a result, Emperor Neron had adopted regulations that required fireproof material for walls and buildings restoration to be used. The second recorded case of adopting fire protection regulations occurred in the year 1666, after the great fire of London, which destroyed more than 80% of the city. The fire of London spurred interest in the development of the first equipment for fire suppression in the form of hand pumps and fire hydrant installation for water supply.
Progression of Fire Detection Devices
The first generation of fire detection devices (1849-1940) was based on thermal detectors. But the start of fire alarm systems development began with the invention of the telegraph by Samuel F. B. Morse in 1844. The first practical fire detection systems using telegraph, was developed in U. S. by Dr. William Channing and Moses G. Farmer in 1852. Two years later, he applied for a patent for his electromagnetic telegraph fire protection system intended to be used in cities. In Europe in 1848, the first fire alarm device was developed by C.A. von Steingel, which was operated by the firemen and used button switches and different kinds of bells to give prearranged audio signals. The first telegraph device was created three years later in Berlin and as fire alarm telegraph equipment, used a cable connection, to alert total of 37 fire stations. The development of the first temperature sensors started with the introduction of bimetallic sensors in the 19th century. The working principle of these sensors was based on the unequal expansion between the two metal stripes. These relays were reliable and durable, and are still considered ideal for many industrial applications.
Fire smoke detectors are most critical and front end components of any fire detection & alarm system. These front end sensors have also evolved over the time and it’s their advancement, which has contributed to making conventional fire alarm system, intelligent & smart-because without these smart, fast, reliable and addressable front line sensors, no fire alarm systems could have been made smart or intelligent. The evolution of these frontline sensors can be divided into four generations based on their development, improvement, and merging with the electronic technology industry.
The first generation of smoke detectors started in 1930, when the first electronic smoke detector was actually made by Swiss physicist named Walter Jaeger–leading to the invention of the first electronic device for smoke detection. Later he developed the first patented smoke detector in the early 1940s.
The second generation of smoke detectors was developed between early 1960s until 1975, where americium 24, a radioactive source for ionization, was used for application in the electronics industry. In 1964 an ionization smoke detector with a 24V power supply was developed by Alert. However these detectors were to be made in accordance to international rules, and also were needed to have an appropriate radioactivity label for their functioning. After detectors were used, they were to be properly disposed as a radioactive waste.
A year after the discovery of ionizing smoke detectors, Duane Pearsall developed a photoelectric smoke detector. Major changes in smoke detectors’ technology occurred during the 70s and 80s in last century. These photoelectric smoke detectors operate on the light beam interruption principle, having a light source, usually white light or more often low-power laser, and a photoelectric module. A beam of light sent through the detector in normal conditions of cleanliness bypasses photocell usually at approx. 90 degrees. When smoke particles obstruct the light beam, there is a break-ray, which focused on the photo-electric cell changes the physical variables of the set limits thus triggering alarm.
The third generation of smoke detectors (1975-1990) is characterized by an increased interest in smoke detectors. In this period, there were a number of key changes in the detectors’ design, including the replacement of the filament as a light source with a light emitting diode and the use of silicon. With the development of electronics and integrated circuits, there is a decrease in the volume of the detector components, which directly contributes to physical size reduction of the detector, a decrease in energy consumption and an improved reliability. In 1982, first analogue addressable detectors were introduced.
The fourth generation of smoke detectors (1990-present) is characterized by the use of multiple detectors in a loop, and application of algorithms. Development of microelectronics has enabled the application of many different functions. This was particularly important for all types of detectors which, through the utilization of microelectronics, can be produced as intelligent components. In this way, some basic evaluation and decision-making functions can be integrated in the detector. In 1996 a first multi detector (temperature and smoke) was developed as a detector that uses smart “OR” and “AND” logic. Major changes in smoke detectors technology, were introduced by the development of smart detectors. Such smoke detectors provided option to regulate the alarm threshold via a central control panel.
During this time, along with optical smoke detector, flame detectors were also developed. Flame detectors are solutions for almost all applications where fire may occur due to large losses of complex equipment such as oil and gas pipelines, offshore platforms, automotive manufacturing facilities, aircrafts, ships, ammunition factories, nuclear plants, and where the risk of staff injury is high. These systems use devices that match the radiation energy & are sensitive to ember, charcoal, or actual fire of sufficient intensity to activate the detector and trigger the alarm. In order to reduce false alarms due to a possible misidentification of real alarms due to any transient conditions a 2-3 seconds delay is often included in the design these flame detectors.
The first & second generation of the sensors were “Analogue”. However, from 3rd and 4th generations of sensors/ detectors the shift began towards solid state sensors and later to “Addressable” type intelligent systems in which a detector compares its current sensor value with the configured threshold to make the alarm decision, which is then transmitted to the panel when the sensor is interrogated.
Conventional Systems
Conventional systems are hardware-based and use analog technology. These systems are made up of zones (“Area/ Wide Area Zoning”) which are formed by using multiple devices, both initiating and notification devices connected to the main control panel. Conventional systems are analog in nature i.e. they use electrical currents to communicate with the control panel. Initiating and notification devices are designed to dramatically increase the current in the circuit (the amount of electricity flowing through the wires) any time the environmental conditions (heat or smoke) in the area of the sensor exceed a predetermined threshold. This change in the current is communicated to the control panel to trigger the alarm. Since the conventional system relies on individual circuits to communicate with the control panel, the information the panel can receive is limited to the number of devices it can support.
The information is also limited, in the sense that it only tells the panel whether a device has been activated or removed, not which device or where. In a Conventional Fire Alarm System, physical cabling is used to interconnect several call points and detectors, the signals from which are wired back to the main control unit. Single device or set of devices connected in a loop represent one individual “Zone” (Area/ Wide Area Zoning) & the incidents are indicated at the Fire Alarm Control
Panel either with an indicator lamp, a text display or in some cases both.
Addressable Systems
Instead of relying on changes in the electrical current running through a circuit in a conventional system, with an addressable system digital technology transfers information from the connected devices to the main control panel as binary code – combinations of ones and zeros. The alarm signal starts as an analog signal created by variations in voltage within the signalling device based on changes in the coverage. In the new age of addressable devices, this analogue signal is converted into a digital or binary signal using a digital signal converter or in built processors. Depending on the device and the types of information it is designed to convey, an addressable device can transfer a wide variety of critical information to the control panel — as opposed to the single triggering signal that conventional systems provide.
Because they use digital technology, addressable systems offer a much broader range in the types of information that the control panel can receive from the devices. While all addressable systems provide the location of every device on the system to the control panel, newer, “analog addressable” systems provide even more information, such as how much smoke or heat the detector is sensing. This information allows the control panel to make “intelligent” decisions such as when or when not to go into alarm mode.
The most important type of information that addressable systems transmit is exactly where the fire is occurring in a building (“Pointed/ Focussed Zoning”). Because the exact location of each device in an addressable system is programmed in, fire-fighters know before they even arrive precisely where in the building the fire is occurring, which allows them to respond more quickly to a fire. With a conventional system, unless the area in which the system is protecting is a single room, the firefighters will have to spread out to locate the fire.
Intelligent Fire Panels, on the other hand, give every detector a uniquely identifiable address & they literally become a zone in themselves although much smaller, thus when a fire is detected, the main control panel tells you exactly which device is going off, to point out exact location of incident (Pointed or Focussed Zoning). Such pointed zoning is extremely useful in case of large and complex buildings or area.
One big advantage of intelligent type systems is that the data output of detector is sensitive to the local environment, which is very useful to know when the device is approaching an alarm condition by integrating multiple types of information e.g., in case of a fire, thee multiple sensors can have information of intensity of heat, density of smoke, types of gases, occupancy level, illumination level etc., before raising the alarm. This “Pre-Alarm” can be signalled at the panel and can therefore be investigated to check if there is a real fire, or if it is caused by other signals, for example steam or dust from building work. This can avoid the inconvenience and expense of evacuating a building or calling out the fire brigade unnecessarily because of a nuisance alarm. The Pre-Alarm Threshold is typically set at 80% of the alarm threshold.
Conventional Vs. Addressable (Intelligent/ Smart)
Conventional fire alarm systems have indeed been around a long time and have proven their reliability & credibility yet in today’s digital world, people often think of analog devices or systems as old fashioned or with out-dated technology. Many businesses today still use them. And, while newer technologies now exist, conventional systems still remain a good option in some settings.
Conventional systems are highly reliable, cost-effective, and affordable for small remain just one or two zones could cover the entire area. However, more and more small businesses are beginning to consider addressable systems — when it comes to the time to replace their systems for additional benefits that the newer technology provides.
Prabhat Khare possesses a BE (Electrical) degree from IIT Roorkee (Gold Medalist). Now, he is the Director of KK Consultants.
