Fire alarms heat detectors

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. 

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. 

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. 

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. 

Heat is the most obvious choice of a characteristic by which a fire can be automatically recognized. In the section on fire suppression systems, the fusible links in the sprinkler heads represented one type of heat detector. Alloys have been developed that will have reproducible melting points. When the temperature at the detector site exceeds the melting point of the alloy, contacts are allowed to move so that the device can either make or break a circuit, just as with a manual alarm system. There are plastics which can perform in the same manner. Fixed temperature systems are very stable and not prone to false alarms, but are relatively slow to respond. There are several other versions of these fixed temperature detectors, including bimetalhc strips, where the differential rate of expansion of two different metals causes the strip to flex or bend to either make or break the contact. Others depend upon the thermal erqransion of hquids. 

Fire protection is provided in the HCF. B6580 and B6581 are provided with automatic fire-protection sprinkler systems, except in areas containing significant quantities of radiological materials where water sprinklers would exacerbate radiological hazards. The building also has a fully supervised alarm and evacuation system, which includes automatic smoke and heat detectors in certain areas. 

Heat sensors and/or smoke detectors may be part of the building safety equipment. If designed into the fire alarm system, they may automatically sound an alarm and call the fire department, they may trigger an automatic extinguishing system, or they may only serve as a local alarm. Because laboratory operations may generate heat or vapors, the type and location of the detectors must be carefully evaluated in order to avoid frequent false alarms. 

A device for the detection and notification of a fire event. Fire alarms can be activated by people or antomatic devices that can detect the presence of fire. These include heat-sensitive devices, which are activated if a specific temperature is reached a rate-of-rise heat detector, which is triggered either by a quick or a gradual escalation of temperature and smoke detectors, which sense changes cansed by the presence of smoke, in the intensity of light, in the refraction of light, or in the ionization of air. The arrangement and type of fire detectors for optimum performance is usually specified by fire codes or industry guidelines. 

All systems should receive a visual inspection each quarter. Test or inspect each antomatic system on an annual basis. Include all systems in the preventive maintenance plan. Test all snpervisory signal devices except valve tamper switches on a quarterly basis. Test valve tamper switches and water flow devices semiannually. Test duct detectors, electromechanical releasing devices, heat detectors, manual fire alarm boxes, and smoke detectors on a semiannual basis. Test occupant alarm notification devices to inclnde andible and visible devices at least annually. Maintain appropriate documentation on all tire-related system testing. 

BS 3116 Automatic fire alarms in buildings Part 1 1970 Heat sensitive (point) detectors Part 4 1974 Control and indicating equipment BS 4422 Glossary of terms associated with fire Part 1 1969 The phenomenon of fire Part 2 1971 Building materials and structures Part 3 1972 Means of escape Part 4 1975 Fire protection equipment Part 5 1976 Miscellaneous terms BS 4547 1972 Classification of fires... 

As indicated above, the spread of fire and smoke can be controlled by both passive and active means. On the one hand, the measures include separation of buildings com-partmentation fire walls fire doors fire and smoke shutters controls on air conditioning and pressurization of critical areas such as stairways and, on the other, detectors and alarms extinguishers hose reels and sprinkler systems. Smoke detectors generally detect fire more quickly than heat detectors. 

Automatic sprinklers are particularly effective for life safety because, they warn of the existence of fire and, at the same time, apply water to the burning area (Hisley, 2003). Standard sprinklers will typically detect a fire much later than a smoke or heat detector. Therefore, a combination of a detection/alarm system and suppression system is a dependable method of protection. 

Confinement of Smoke and Fire FIRE-DETECTION AND -ALARM SYSTEMS Heat Detectors Smoke Detectors Flame Detectors Gas Detectors... 

In this example a sensor (e.g. an automatic fire detector) is activated by combustion products such as smoke, heat or combustion gases. After activating the control unit (e.g. a fire alarm or detection system), it initiates programmed Controls of Fire Protection Systems (CFPS) or activates other actuators in the building. An actuator is for example a... 

Part B Fire Safety - the standard house with no floor area exceeding 200m must be fitted with smoke alarms to each level. A floor area greater than 200 m is considered to be a large house . If the kitchen cannot be isolated from the other rooms by a door, then a compatible interlinked heat detector must also be installed in the kitchen. 

Any of the above reasons tnay result in noise and an increase in temperature and must be corrected. Critical installations such as a refinery, a petrochemical plant, a chemical plant or a petroleum pipeline may require special precautions and control to avert any excessive heating of the bearings, which may become fire hazards. For these installations, bearing temperature detectors with a relay and alarm facility may also be installed in the control circuit of the switching device to give warning or trip the motor if the temperature of the bearing exceeds the preset safe value. 

When dealing with an entire fire detection system that utilizes more than one type of detector, a Detonator Module greatly expands the flexibility and capability of the system. An individual Detonator Module can accept multiple inputs from UV and IR controllers, other Detonator Modules, manual alarm stations, heat sensors, smoke detectors or any contact closure device. In the event of a fire, any of these devices will cause the internal fire circuitry of the module to activate the detonator circuit, sound alarms, and identify the zone that detected the fire. When properly used, a Detonator Module will add only one millisecond to the total system response time. See Figure 8 for an illustration of a fire detection system with a Detonator Module. 

Smoke detectors are primarily used where smoldering fires can be expected and where electrical equipment is located indoors. Examples of their use are in offices and sleeping quarters, computer rooms, control rooms, electrical switchgear rooms, etc. Their response is typically faster than that of heat detection devices. Smoke detectors are more susceptible to false alarms and usually multiple detectors are required to be in alarm before an extinguishing system is activated. 

Smoke detectors are particularly useful in those situations where the fire is likely to generate a substantial amount of smoke before temperature changes are sufficient to actuate a heat detection system and before a fire eye will detect a flame. Smoke detectors use a photoelectric beam between a receiving element and light source. If smoke obscures the beam an alarm is sounded. There are... 

Fusion detectors The simplest application consists of an electrical circuit which contains a switch that is held in either the open or closed condition by a piece of low melting point alloy. When this melts in the heat of a fire, the switch is released and the circuit condition changes, i.e. it is either made or broken Figure 25.7). A variation of this type of detector functions by the melting alloy running into a small cup to complete the alarm circuit. 

Normal heat and smoke detectors rely on the presence of convection currents caused by the fire to carry either the products of combustion or heat past the detector which is usually mounted at high level. If there is little heat from the fire then there can be a significant delay before the detector receives enough information from the fire to actuate the alarm. Carbon monoxide detectors overcome this problem since the carbon monoxide produced by the fire dissipates into the atmosphere of the protected area and... 

Laser detectors operate in a similar way to optical beam detectors. The laser beam is directed across the area to be protected and is deflected or obscured by either the heat, the flame or the smoke rising from a fire, thus changing the intensity of lighf at the receiver. This triggers the alarm. 

Automatic fire extinguishing systems such as sprinklers, drenchers or gas systems operate when the heat of the fire in the region of a detector head reaches predetermined levels and cause the seal in the detector head to fracture releasing the extinguishant. These systems can incorporate a facility to raise the alarm. 

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