Below is list of detectors/devises used in the detection of fire briefly outlining their different applications uses.
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Types of Fire Detection Devices
Smoke detectors sense visible or invisible particles of combustion generated by burning, smouldering, or the incipient stage of combustion. A photoelectric smoke detector is the most common smoke detector used today. It detects smoke by using either the principle of light obscuration or light scattering. Its capability to detect smoke originating from fire is best utilized for fires that produce large particles during combustion.
Typical uses for photoelectric smoke detection: Office areas, Clean rooms, Raised floor spaces, Ceiling Voids, Atrium’s and corridors, Meeting rooms, Computer rooms, Telecommunications rooms, UPS/Electrical equipment rooms, Hotel rooms, Storage closets.
Advantages of photoelectric smoke detectors: Detects invisible products of combustion – It can detect fires that are in the incipient stage or detect other aerosol-type smoke products Quick detection – Provides for earlier detection than other types of smoke detectors or thermal detectors, Reliability, Large Area of Coverage making them very cost effective
Heat detectors are intended to minimize property damage by reacting to the change in temperature caused by a fire.
A heat detector is a fire alarm device designed to respond when the convected thermal energy of a fire increases the temperature of a heat sensitive element. The thermal mass and conductivity of the element regulate the rate flow of heat into the element. All heat detectors have this thermal lag. Heat detectors have two main classifications of operation, "rate-of-rise" and "fixed temperature". The heat detector is used to help in the reduction of damaged property. It is triggered when temperature increases.
Types of Heat detectors
Rate-of-Rise (ROR) heat detectors operate on a rapid rise in element temperature of 6.7° to 8.3°C increase per minute, irrespective of the starting temperature.
Fixed temperature heat detectors. This is the most common type of heat detector. Fixed temperature detectors operate when the heat sensitive eutectic alloy reaches the eutectic point changing state from a solid to a liquid. Thermal lag delays the accumulation of heat at the sensitive element so that a fixed-temperature device will reach its operating temperature sometime after the surrounding air temperature exceeds that temperature. The most common fixed temperature point for electrically connected heat detectors is 58°C. Technological developments have enabled the perfection of detectors that activate at a temperature of 47°C, increasing the available reaction time and margin of safety and more
Typical Heat detector installations are where the environment has too many airborne particulates due to excessive steam, moisture, dust, humidity or temperature, such as in attics, garages, warehouses, storage facilities, elevator machine rooms and electrical closets. Smoke detectors applied in those environments are cost prohibitive from a maintenance standpoint.
A flame detector is a sensor designed to detect and respond to the presence of a flame or fire, allowing flame detection.
Types of Flame detectors are: Ultraviolet (UV) detectors work by detecting the UV radiation emitted at the instant of ignition. While capable of detecting fires and explosions within 3–4 milliseconds, a time delay of 2–3 seconds is often included to minimize false alarms which can be triggered by other UV sources such as lightning, arc welding, radiation, and sunlight. UV detectors typically operate with wavelengths shorter than 300 nm to minimize the effects of natural background radiation. The solar blind UV wavelength band is also easily blinded by oily contaminants.
Near infrared (IR) array flame detectors (0.7 to 1.1 µm), also known as visual flame detectors, employ flame recognition technology to confirm fire by analysing near IR radiation
Carbon Monoxide Gas Detectors
A carbon monoxide detector or CO detector is a device that detects the presence of the carbon monoxide gas in order to prevent carbon monoxide poisoning.
Carbon monoxide is a colourless, tasteless and odourless compound produced by incomplete combustion of carbon-containing materials. It is often referred to as the "silent killer" because it is virtually undetectable by humans without using detection technology. Elevated levels of carbon monoxide can be dangerous to humans depending on the amount present and length of exposure. Carbon monoxide detectors are designed to measure carbon monoxide levels over time and sound an alarm before dangerous levels of carbon monoxide accumulate in an environment, giving people adequate warning to safely ventilate the area or evacuate. Some system-connected detectors also alert a monitoring service that can dispatch emergency services if necessary. While carbon monoxide detectors do not serve as smoke detectors and vice versa, dual smoke/ carbon monoxide detectors are also manufactured. Smoke detectors detect the smoke generated by flaming or smouldering fires, whereas carbon monoxide detectors detect and warn people about dangerous carbon monoxide build-up caused, for example, by a malfunctioning fuel-burning device. In the home, some common sources of carbon monoxide include open flames, space heaters, water heaters, blocked chimneys or running a car inside a garage
Optical Beam Detectors
Fire Beams or Optical beam smoke detectors work on the principle of light obscuration. The imaging detector uses the same technology as the optical detectors but with some differences. It uses ultra violet and/or infrared rays that are projected across a room to detect light scattering or absorbance. Fire Beams are usually installed in high ceiling applications such as conference halls, shopping malls and warehouses etc.
Aspirating Smoke Detectors
An aspirating smoke detector (ASD) is a system used in active fire protection, consisting of a central detection unit which draws air through a network of pipes to detect smoke. The sampling chamber is based on a nephelometer that detects the presence of smoke particles suspended in air by detecting the light scattered by them in the chamber. ASDs can typically detect smoke before it is visible to the naked eye. In most cases aspirating smoke detectors require a fan unit to draw in a sample of air from the protected area through its network of pipes
ASDs are suitable for environments where a highly sensitive rapid smoke detection capability is required. This makes them suitable in clean rooms; areas which contain goods easily damaged by fire, such as tobacco, electronic rooms and highly flammable liquid and gases. Often, normal point detectors will recognise the danger too late, as smoke often does not reach the ceiling quick enough for a fire to be detected in a timely fashion
ASD design corrects shortcomings of conventional smoke detectors by using a sampling pipe with multiple holes. The air samples are captured and filtered, removing any contaminants or dust to avoid false alarms and then processed by a centralized, highly sensitive laser detection unit. If smoke is detected, the systems alarm is triggered, and signals are then processed through centralized monitoring stations within a few seconds.
Unlike passive smoke detection systems, including spot detectors, ASD systems actively draw smoke to the detector through bore holes within a piping system that runs throughout the protected area. Furthermore, ASD systems incorporate integrity monitoring to ensure an alert is raised at any time the ASD’s ability to detect smoke is compromised. This is not the case with passive devices that are generally only electrically monitored with no ability to determine if smoke can actually reach the detection element.
ASD systems incorporate more than one level of alarm. This allows an ASD system to provide very early warning of an event, prompting investigation at the earliest smouldering stage of a fire when it is easily addressed. Other alarm levels may be configured to provide fire alarm inputs to fire systems as well as releasing suppression systems. ASD alarm sensitivities are configurable and can be programmed to levels ranging from thousands of times more sensitive than a conventional detector, to much less sensitive. The detectors work best in non-volatile environments. They can also be used in computer cabinets to alert users to the overheating of computer cables or individual computer components.