Heat detectors

FIRE SIMULATOR predicts the effects of fire growth in a 1-room, 2-vent compartment with sprinkler and detector. It predicts temperature and smoke properties (Oj/CO/COj concentrations and optical densities), heat transfer through room walls and ceilings, sprinkler/heat and smoke detector activation time, heating history of sprinkler/heat detector links, smoke detector response, sprinkler activation, ceiling jet temperature and velocity history (at specified radius from the flre i, sprinkler suppression rate of fire, time to flashover, post-flashover burning rates and duration, doors and windows which open and close, forced ventilation, post-flashover ventilation-limited combustion, lower flammability limit, smoke emissivity, and generation rates of CO/CO, pro iri i post-flashover. 

A phonon/heat detector to measure the total energy deposit. This is a cylindrical... 

Smoke detectors are employed where the type of fire anticipated and equipment protection needs a faster response time than heat detectors. A smoke detector will detect the generation of the invisible and visible products of combustion before temperature changes are sufficient to activate heat detectors. The ability of a smoke detector to sense a fire is dependent on the rise, spread, rate-of-bum, coagulation and air movement of the smoke itself. Where the safety of personnel is a concern, it is crucial to detect a fire incident at its early stages because of the toxic gases, lack of oxygen that may develop, and obscuration of escape routes. Smoke detection systems should be considered when these factors are present. 

Thermal or heat detectors respond to the energy emission from a fire in the form or heat. The normal means by which the detector is activated is by convention currents of heated air or combustion products or by radiation effects. Because this means of activation takes some time to achieve thermal detectors are slower to respond to a fire when compared to some other detection devices. 

There are two common types of heat detectors - fixed temperature and rate of rise. Both rely on the heat of a fire incident to activate a signal device. Fixed temperature detectors signal when the detection element is heated to a predetermined temperature point. Rate of rise detectors signal when the temperature rises at a rate exceeding a pre-determined amount. Rate of rise devices can be set to operate rapidly, are effective across a wide range of ambient temperatures, usually recycle rapidly and can tolerate a slow increase in ambient temperatures without providing an alarm. Combination fixed temperature detectors and rate of rise will respond directly to a rapid rise in ambient temperatures caused by fire, will tolerate a slow increase in ambient temperatures without effecting an alarm, and recycle automatically on a drop in ambient temperature. 

Heat detectors normally have a higher reliability factor than other types of fire detectors. This tends to lead to fewer false alarms. Overall they are slower to activate than other detecting devices. They should be considered for installation only where speed of activation is not considered critical or as a backup fire detection device to other fire detection devices. They have an advantage of suitability for outdoor applications but the disadvantage of not sensing smoke particles or visible flame from a fire. 

Heat detectors are activated by either melting a fusible material, changes in electrical current induced by heat loads on bi-metallic metals, destruction of the device itself by the heat, or by sensing a rate of ambient temperature rise. 

Fire detectors generally fall within one of three categories heat, smoke, and flame. Heat detectors work by sensing the heat from a fire. Smoke detectors sense the combustion products from the fire. Flame detectors identify flame by sensing the IR or UV light it emits. 

Heat Detectors Smoke Detectors Flame Detectors... 

There are two common types of heat detectors. Fixed temperature detectors operate when the detection element is heated to a predetermined set temperature. Rate-of-rise detectors respond when the temperature rises at a rate exceeding a predetermined amount. 

Fixed temperature detectors are preferred because they require less calibration and maintenance. Heat detectors are normally more reliable than other types of detectors because of the simple nature of their operation and ease of maintenance. These factors tend to lead to fewer false alarms. The main disadvantage of heat detectors is that they are unlikely to detect fires in the incipient stage, where little heat is generated, but much smoke is likely.. Since heat detectors are inherently slower in operation than other types of detectors, they should be considered for installation in areas where high speed detection is not required. 

The most widely used heat detector is the automatic sprinkler head. 

One effect that a flaming fire has on the surrounding area is to rapidly increase air temperature in the space above the fire. Fixed temperature heat detectors will not initiate an alarm until the air temperature near the device exceeds the design operating point. The rate-of-rise detector, however, will function when the rate of temperature increase exceeds a predetermined value, typically around 12 to 15°F (7 to 8°C) per minute. Rate-of-rise detectors are designed to compensate for the normal changes in ambient temperature [less than 12°F (6.7°C) per minute] which are expected under nonfire conditions. 

There are several technologies of linear heat detectors, most designed to monitor air temperature and a few that detect radiant heat. This type of detection is wire or plastic tubing and can be used where other types of detectors are difficult to install. Generally, they are used to supplement other forms of detection in difficult areas, such as heavily congested areas, rim area of floating roof tanks, on pumps, etc. Linear types can be pneumatic, electrical, or optical. Electrical linear heat detectors come in three types that ... 

Heat detectors should be spaced to ensure prompt detection of heat given off by incipient fire conditions. Spacing considerations should include the degree of hazard, type of detector used, geometry of the protected area, effects of air handling equipment if it is indoors, or environmental factors (wind, temperature, etc.) if it is outdoors. See NFPA 72 for more information on spacing and installation requirements. 

Fire detectors—dry-pilot head and pneumatic rate-of-rise heat detectors are the most frequent devices used. A dry pilot head detection systems uses 165°F (74°C) V2-in sprinkler head with air pressure maintained in the piping. When the sprinkler opens the air is released resulting in the sprinkler valve opening. Other types of detectors include ultraviolet, infrared flame detectors, or thermostatic cable heat detection. 

Heat detector alarms for Kettle area annunciate (DCS, assumed fireball 1)... 

Heat detector alarms for kettle area annunciate... 

The catalyst preparation area is protected by an automatic water-spray sprinkler system that is actuated by associated heat detectors. Fixed fire water monitors surround this process area. The water for these fire protection systems is supplied through 8-inch underground water mains by three (two diesel and one electric) horizontal, centrifugal, 2500... 

At 11 09 A.M., a high-LEL detector in the catalyst preparation area sounded on the DCS. The lead outside operator was contacted by radio communications to investigate the problem. He said he was just leaving the Reactor No. 1 area and would go right to the catalyst preparation area. The thunderstorm had passed overhead and the rain was diminishing. At about 11 10 A.M., a whooshing noise (assumed to be the fireball) was heard by many and the heat detector for the automatic water-spray sprinkler coverage in this area alarmed in the control room. The lead outside operator did not respond when called on the radio. 

AM. Heat detector alarms for catalyst preparation area (Ketde No. 3 area) annunciate in control room. (DCS)... 

After heat detector alarms Control room operator tries to reach lead outside operator by radio, but there is no response. (Believe lead outside operator is critically burned.)... 

The effort to stop drug abuse and trafficking raises a number of important general civil liberties issues, including whether persons are being stopped without probable cause that they have committed a crime, whether racial or ethnic profiles are being used instead of specific evidence involving a particular individual, and whether the use of intrusive search techniques (such as use of aircraft or heat detectors) violates privacy. 

The rate of heat release of a fire is the driving force for a buoyant plume. When the plume hits the ceiling, it turns into a ceiling jet whose characteristics determine when heat detectors respond4 or when sprinklers are activated.5... 

Water, gas, electrical and drain lines are contained in chases which run vertically between floors on either side of the hall. Outside each laboratory there is a locked access panel in the chase, the key to which is kept in the laboratory. In an emergency any utilities to a single laboratory may be shut off from this chase. Of course, the building is equipped with the usual array of smoke and heat detectors and fire alarms. 

What are the differences between a photon detector and a heat detector ... 

A photon detector produces a current or voltage as a result of the emission of electrons from a photosensitive surface when struck by photons. A heat detector consists of a darkened surface to absorb infrared radiation and produce a temperature increase. A thermal transducer produces an electrical signal whose magnitude is related to the temperature and thus the intensity of the infrared radiation. 

Pneumatic detector A heat detector that is based on changes in the pressure that a gas exerts on a flexible diaphragm. p-ii junction diode A semiconductor device containing a junction between electron-rich and electron-deficient regions permits current in one direction only. 

The semiprep schematic in Fig. 7 is similar to the analytical-scale hardware except that the components tend to be larger and extra hardware is needed to collect fractions Peltier cooling is more difficult on a larger scale because it is relatively inefficient. Compressibility compensation is also more difficult because compression of a larger volume creates more heat. Detector flow... 

IR Detector. As with sources, detectors used in the ultraviolet and visible regions do not work in the infrared region. But infrared radiation possesses the property of heat, and heat detectors that transduce heat into an electrical signal can be used. Thermocouples and bolometers are used as detectors. A thermocouple consists of... 

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