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 property damage.
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 (136.4°F).
Rate-of-Rise (ROR) heat detectors operate on a rapid rise in element temperature of 6.7° to 8.3°C (12° to 15°F) increase per minute, irrespective of the starting temperature. This type of heat detector can operate at a lower temperature fire condition than would be possible if the threshold were fixed. It has two heat-sensitive thermocouples or thermistors. One thermocouple monitors heat transferred by convection or radiation, while the other responds to ambient temperature. The detector responds when the first sensing element's temperature increases relative to the other.
Rate of rise detectors may not respond to low energy release rates of slowly developing fires. To detect slowly developing fires combination detectors add a fixed temperature element that will ultimately respond when the fixed temperature element reaches the design threshold.
Heat detectors commonly have a label on them that reads 'Not a life safety device'. This is because heat detectors are designed to respond to elevated temperatures, which may occur too late to safely alert individuals in the event of a fast-spreading fire. In contrast, smoke detectors are sensitive to the presence of smoke particles in the air, providing earlier warning of fire in many cases. Therefore, smoke detectors are more suitable for bedrooms or in hallways outside of bedrooms where early warning is crucial for life safety.
However, heat detectors are useful for areas like the kitchen, utility rooms (e.g., laundry room), garage, or attic, where smoke detectors may not be practical. In these areas, activities like cooking or the presence of dust and other particles could cause a smoke detector to trigger false alarms. A heat detector will provide a warning of a fire in these specific areas without being affected by non-fire related activities or particles. [1] This allows extra time to evacuate the building or to put out the fire, if possible.
Mechanical heat detectors are independent fire warning stations that—unlike smoke detectors—can be installed in any area of a home. Portability, ease of installation, and excellent performance and reliability make this a good choice for residential fire protection when combined with the required smoke detectors. Because the detectors are not interconnected, heat activation identifies the location of the fire, facilitating evacuation from the home. [2]
Each type of heat detector has its own set of advantages and limitations, making it important to select the appropriate device based on the specific requirements of the area being monitored.
A Fixed Threshold Detector triggers an alarm when a specific temperature threshold is reached or exceeded. This type of detector is generally less sensitive to rapid temperature fluctuations, making it more suitable for areas like large, industrial kitchens where ovens or other heat-producing equipment are frequently in use.
Example Use Case: If a Fixed Threshold Detector is placed above a large, closed oven, the detector is less likely to generate a nuisance alarm when the oven door is opened, releasing a transient heat surge. In this circumstance, the Fixed Threshold Detector would be the preferable choice.
A Rate-of-Rise Detector, on the other hand, is designed to respond to a rapid increase in temperature over a short period of time. This type of detector is more sensitive to sudden temperature changes, making it better suited for areas that contain highly combustible materials.
Example Use Case: If a room filled with highly combustible materials is protected by a Fixed Threshold Detector, a rapidly-spreading fire could exceed the alarm threshold before the detector is triggered due to a phenomenon known as thermal lag refers to the delay that can occur in temperature measurements, which could cause a delay in triggering the alarm system. In this case, the Rate-of-Rise Detector may be the preferred choice, as it would be more likely to detect rapid temperature increases and trigger an alarm in a timely manner.
A bolometer is a device for measuring radiant heat by means of a material having a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley.
A fire sprinkler system is an active fire protection method, consisting of a water supply system providing adequate pressure and flowrate to a water distribution piping system, to which fire sprinklers are connected. Although initially used only in factories and large commercial buildings, systems for homes and small buildings are now available at a cost-effective price.
A thermographic camera is a device that creates an image using infrared (IR) radiation, similar to a normal camera that forms an image using visible light. Instead of the 400–700 nanometre (nm) range of the visible light camera, infrared cameras are sensitive to wavelengths from about 1,000 nm to about 14,000 nm (14 μm). The practice of capturing and analyzing the data they provide is called thermography.
A smoke detector is a device that senses smoke, typically as an indicator of fire. Smoke detectors are usually housed in plastic enclosures, typically shaped like a disk about 150 millimetres (6 in) in diameter and 25 millimetres (1 in) thick, but shape and size vary. Smoke can be detected either optically (photoelectric) or by physical process (ionization). Detectors may use one or both sensing methods. Sensitive alarms can be used to detect and deter smoking in banned areas. Smoke detectors in large commercial and industrial buildings are usually connected to a central fire alarm system.
A security alarm is a system designed to detect intrusions, such as unauthorized entry, into a building or other areas, such as a home or school. Security alarms protect against burglary (theft) or property damage, as well as against intruders. Examples include personal systems, neighborhood security alerts, car alarms, and prisons.
A heating element converts electrical energy into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element. Unlike the Peltier effect, this process is independent of the direction of current.
A fire alarm control panel (FACP), fire alarm control unit (FACU), fire indicator panel (FIP), or simply fire alarm panel is the controlling component of a fire alarm system. The panel receives information from devices designed to detect and report fires, monitors their operational integrity, and provides for automatic control of equipment, and transmission of information necessary to prepare the facility for fire based on a predetermined sequence. The panel may also supply electrical energy to operate any associated initiating device, notification appliance, control, transmitter, or relay. There are four basic types of panels: coded panels, conventional panels, addressable panels, and multiplex systems.
A false alarm, also called a nuisance alarm, is the deceptive or erroneous report of an emergency, causing unnecessary panic and/or bringing resources to a place where they are not needed. False alarms may occur with residential burglary alarms, smoke detectors, industrial alarms, and in signal detection theory. False alarms have the potential to divert emergency responders away from legitimate emergencies, which could ultimately lead to loss of life. In some cases, repeated false alarms in a certain area may cause occupants to develop alarm fatigue and to start ignoring most alarms, knowing that each time it will probably be false. Intentionally falsely activating alarms in businesses and schools can lead to serious disciplinary actions, and criminal penalties such as fines and jail time.
A passive infrared sensor is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view. They are most often used in PIR-based motion detectors. PIR sensors are commonly used in security alarms and automatic lighting applications.
A carbon monoxide detector or CO detector is a device that detects the presence of the carbon monoxide (CO) gas to prevent carbon monoxide poisoning. In the late 1990s Underwriters Laboratories changed the definition of a single station CO detector with a sound device to carbon monoxide (CO) alarm. This applies to all CO safety alarms that meet UL 2034 standard; however for passive indicators and system devices that meet UL 2075, UL refers to these as carbon monoxide detectors. Most CO detectors use a sensor with a defined, limited lifespan, and will not work indefinitely.
Fire prevention is a function of many fire departments. The goal of fire prevention is to educate the public on the precautions which should be taken to prevent potentially harmful fires and how to survive these fires if they do occur. It is a proactive method of preventing fire-based emergencies and reducing the damage caused by them. Many fire departments have one or more Fire Prevention Officers, which may also be a routine duty of firefighters.
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.
A thermal cutoff is an electrical safety device that interrupts electric current when heated to a specific temperature. These devices may be for one-time use, or may be reset manually or automatically.
A flame detector is a sensor designed to detect and respond to the presence of a flame or fire, allowing flame detection. Responses to a detected flame depend on the installation, but can include sounding an alarm, deactivating a fuel line, and activating a fire suppression system. When used in applications such as industrial furnaces, their role is to provide confirmation that the furnace is working properly; it can be used to turn off the ignition system though in many cases they take no direct action beyond notifying the operator or control system. A flame detector can often respond faster and more accurately than a smoke or heat detector due to the mechanisms it uses to detect the flame.
An infinite switch, simmerstat, energy regulator or infinite controller is a type of switch that allows variable power output of a heating element of an electric stove. It is called "infinite" because its average output is infinitely variable rather than being limited to a few switched levels. It uses a bi-metallic strip conductive connection across terminals that disconnects with increased temperature. As current passes through the bimetal connection, it will heat and deform, breaking the connection and turning off the power. After a short time, the bimetal will cool and reconnect. Infinite switches vary the average power delivered to a device by switching frequently between on and off states. They may be used for situations that are not sensitive to such changes, such as the resistive heating elements in electric stoves and kilns.
The EN 54 Fire detection and fire alarm systems is a series of European standards that includes product standards and application guidelines for fire detection and fire alarm systems as well as voice alarm systems.
A thermal profile is a complex set of time-temperature data typically associated with the measurement of thermal temperatures in an oven. The thermal profile is often measured along a variety of dimensions such as slope, soak, time above liquidus (TAL), and peak.
Home safety is the awareness of risks and potential dangers in and around a home that may cause bodily harm, injury, or even death to those living there.
Thermopile laser sensors are used for measuring laser power from a few µW to several W. The incoming radiation of the laser is converted into heat energy at the surface. This heat input produces a temperature gradient across the sensor. Making use of the thermoelectric effect a voltage is generated by this temperature gradient. Since the voltage is directly proportional to the incoming radiation, it can be directly related to the irradiation power.
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