Question

review of related literature about development of fire response system

Answer 1

Answer)

The progress on fire detection technologies has been substantial over the last decade due to advance in sensor, microelectronics and information technologies, progress in fire detection technologies over the last decade, including various emerging sensor technologies (e.g., computer vision system, distributed fiber optic temperature sensor, and intelligent multiple sensor), signal processing and monitoring technology (e.g., real-time control via Internet) and integrated fire detection systems.

For example, techniques are available now for measuring almost any stable gaseous species produced prior to or during combustion .The distributed fiber optical temperature sensors have been introduced to provide fire protection for those applications with difficult ambient conditions such as tunnels, underground railways and stations. More than one fire signature detected by a multiple sensor, such as smoke, heat and CO signatures, can be processed at the same time through an intelligent algorithm to intelligently discriminate between fire and non-threatening or deceptive conditions. In addition, fire detection systems are integrated with other building service systems to reduce false alarms, speed building evacuation and assist in fire fighting . Advances in fire detection technology has effectively reduced the loss of property and life by fire.

For example, electrical fires occurring at a Bell Canada switching station in Toronto, 1999 and at the CDNX’s operation center in Vancouver, 2000, disrupted nationwide communications, knocked out stock trading operations, shut down police service, merchants, businesses and federal agencies in various degrees, and caused loss of many millions of dollars. One such disaster, the 1998 Swissair crash near Peggy’s Cove in Nova Scotia, killed all 229 people on board, because the fire, caused by faulty electrical wiring, occurred in an inaccessible space and was not properly detected and located.

Fire detection technology still faces challenges related to reducing false alarms, increasing sensitivity and dynamic response, as well as providing protections for highly expensive and complex installations to better safeguard the public and meet evolving regulations. Development in fire detection technology, including emerging sensor technology, fire signal processing and monitoring technology and integrated fire detection system.

Emerging Sensor Technology

Heat Detectors

The distributed fiber optic temperature sensor is considered as one of the new and promising heat detection technologies for fire protection applications . Optic fiber has been widely used for the transmission of information, and it can also be used for sensing changes in temperature, strain and tensile force subjected to the fiber optic cable, as the variation of these physical parameters alters the refractive indices and geometric properties of the optical fiber and then perturbs the intensity, phase, or polarization of the light wave propagating within the optical fiber. Unlike the conventional thermal detectors, the distributed optical fiber sensor uses the entire optical fiber as the sensing medium. Temperature measurement can be made at any and every point along the fiber cable. The measured temperature is in the range of -160 to 800oC, which is limited only by the durability of the fiber, or more specifically, its primary coating. In comparison to conventional thermal detectors, the optical fiber sensor cable responds much more quickly to temperature fluctuations due to its low mass. The fiber cable itself is strong, resilient, flexible for different geometry and can be directly placed near or into protected facilities. It is also immune to all kinds of interference emissions. Conceivably, the location, size, and development of a fire can be determined with higher spatial and temperature resolutions and unmatched flexibility in measurement locations. The distributed fiber optic temperature sensors based on Rayleigh and Raman scattering were introduced for fire detection in the late 1980's . They have been used to provide fire protection for those applications with difficult ambient conditions such as tunnels, underground railways and stations, conveyor lines, steelworks and petrochemical plants.

Smoke Detectors

Smoke is produced much earlier than other fire signatures during the stages of fire growth and development. The rapid detection of smoke at very low levels can maximize the probability for successful fire suppression, escape and survivability. Smoke can be sensed from the interaction of the particles with a beam of light or electromagnetic radiation. The mass concentration, volume fraction and size distribution of the smoke are identified as key parameters for smoke detection. A smoke detector must be capable of responding to smoke from both smoldering and flaming combustion, because the smokes from these fires are significantly different in structure and composition. Smoke from a smoldering fire tends to have bigger particles of combustion products than those generated from flaming combustion. The detector may be located at the sensing location (spot detector) or at a remote location with the smoke pumped to the detector.

An optical smoke detector has been considered as a replacement for the ionization chamber smoke detector . It detects a fire when smoke particles interact with a beam of light passing through it.

The multi-criteria sensing detectors that combine smoke sensing with other types of sensing have been considered as an effective method that is able to provide a wide range of detection capability and at the same time, reduce nuisance alarms without sacrificing smoke detector sensitivity.

Flame Detectors

The fire, itself, is a source of radiation, and it can be detected by the recognition of radiation produced in the burning zone. Currently there are two types of flame detectors based on the measurement of the range of flame radiation: infra-red detector and ultra-violet detector. Infra-red detectors (IR) detect fires when a characteristic flame flicker produced by fire is received, while ultra-violet detectors (UV) detect fires when any ultra-violet radiation produced by flaming combustion is detected.

CCTV (Closed Circuit Television) technology has great advantage for use on sensing and monitoring a fire. Compared with other types of fire detectors, the video cameras cannot be fooled by visible, or emissions from common background sources, eliminating false alarm problems.

Another automatic CCTV detection technique is the machine vision fire detection system (MVFDS) that is a combination of video cameras, computers, and artificial intelligence techniques,another benefit of the video sensor system is that it can be used as a multi-function sensor in the building service system. Video sensor systems have been used not only for fire detection but also for building security, improving response rate and energy saving for HVAC systems by identifying occupant numbers and their locations, monitoring electrical power switchboards and control panels and lighting level sensing and control.

One drawback of the video fire detection system is that its visibility decreases rapidly with the increase in smoke concentration. Thermal cameras that image the infrared radiation emitted from hot surfaces are capable of overcoming the drawback of the video sensing system in smoke filled environment. They can locate the fire origin, burning wall or people in danger through the smoke. Thermal cameras have been used for fire fighting for many years.

Gas Sensors

Since gases are produced in all stages of combustion, a specific gas signature could be used for reliable fire detection. The measured CO, CO2,H2, O2, and smoke density generated by open cellulose fires (wood), smolderingpyrolysis (cellulosic) and cotton fires, open plastic fire (polyurethane), and liquid n-heptane and methylated spirit fires. The result showed that there were large differences in the chemical composition of the smoke involving different types of fires. Of the four warning gases, the best was carbon monoxide that presented in all six types of fires. Its concentration was high in relatively slow burning fires and low in faster burning fires. There were also large differences in the oxygen concentrations involving six types of fires in which the oxygen concentrations changed significantly when involving faster burning fires, such as liquid fuel fires, while the change in the oxygen concentration was hardly detected when involving smoldering fires. Based on test results, gas sensors can be used not only for fire detection but they can also be used to provide information on whether the fire is flaming, smoldering, or intermediate.

Since electronic equipment and components emit a complex range of chemical vapours when heated, these emitted chemical vapours can be used for the early fire detection in electronic equipment. Bell Labs developed an HCl detector to detect HCl generated by the pyrolysis or combustion of PVC cable insulation. It does not respond to common nuisance signals, such as cigarette smoke, steam or dust. However, in order to detect non-HCl-producing fires occurring in electronic facilities, other types of fire detection devices are required.

The use of Fourier Transform Infrared (FTIR) spectrometers for fire detection has been studied for many years. FTIR can examine the entire spectrum from about 2.5 µm to 25 µm, and quantify the presence of multiple species of interest to provide early fire warning with low false alarms.

Signal Processing and Monitoring Technology

With the introduction of artificial intelligence techniques, the effectiveness of fire detection technology is significantly enhanced. Fire signal received by the sensor is processed by the microcomputer-based technology (software algorithms) and compared with known information and data base of generic fire signatures, and then an output response based on the total quantity of available information is generated. More than one fire signature detected by multiple sensors, such as smoke, heat and CO signatures, can be processed at the same time through an intelligent algorithm. The intelligent algorithms used for fire detection, including cross-correlation, algorithmic comparison, neural networks and fuzzy reasoning. Some new fire detection algorithms, such as the Hidden Markov Model based on a signal classification principle , are also being developed. Advance in artificial intelligent techniques and semiconductor technology allows the fire detection system to accurately and intelligently discriminate between fire and non-threatening or deceptive conditions.

Currently there are two types of intelligent fire detection systems: one is where the fire signal processing and decision making are carried out in the detector and the other is where the fire identification and decision making are carried out in the panel. For medium to large fire detection systems, intelligence in the panel is a cost-effective selection.

Integrated Fire Detection System

The integration of a fire detection system with other building systems on a commonbackbone will allow the building systems to communicate with each other. The fire messages will be released not only from fire detection systems but also from other building systems. They will have priority at all times in the network. The decision-making components of the integrated system will assess the conditions and then determine what actions are required based on the sensor data. The appropriate commands will be sent to the system’s transducers and control devices. Once a fire occurs in a building, fire detection and alarm systems in buildings will be able to activate various fire safety systems, such as smoke control, and various pressurization and smoke exhaust systems .

The integrated systems have the potential for reducing false alarms, speeding building evacuation and assisting in fire fighting. These changes will increase the level of protection to life and property and create new markets for fire detection, alarm and fighting systems . As these technologies mature, changes to building pract ices may also result.

Another push to integrate the fire detection system with other building systems is that the new generation of the building is expected to add the capability to learn about the building’s circumstances and its occupants’ needs and change the behaviour of its control systems accordingly. For example, the building will use sensors to identify how a particular person tends to react to particular circumstances and to learn different behaviours from different people.