Active protection systems detectors

Active fire protection—A fire protection system or device that requires moving parts, detectors, instruments, electrical or other power or utilities. 

The fire protection system consists not only of a deluge system activated by the ultraviolet sensors, but also of fusible link type fire systems. The deluge system has a trip mechanism from mercury checks activated by heat-activated-devices, a manual release on the deluge valve, a pneumatic remote trip station, and an electrical push button along with the electrical trip mechanism from the U/V detectors. The remote trip stations are located by escape routes so it is possible for the operator to trip the systems as he exits the building without exposing himself to further danger. 

Active fire protection systems (e.g. smoke or heat detectors, deluge sprinkler systems or foam systems). 

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... 

Active barriers are dependent on actions by the operators or on a technical control system to function as intended. The carpenter s control of the hammer movements in the example above is, in principle, such a barrier. It is very vulnerable to changes in behaviour of the carpenter. Several of the barriers against fires and explosions in the example above are of the active type. Process control is primarily maintained through the process control system, but the operator may intervene and take over the control. If gas is detected, shut-down is done automatically by the emergency shutdown system. Man is a very sensitive gas detector, and manual shut-down from the control room after a field operator has detected a gas leak but before it has been picked up by the gas detectors is not an uncommon event. Active fire-protection systems are both automatic (e.g. sprinkler systems) and manual (the fire brigade). Escape and evacuation is an active barrier. 

The preaction system. In libraries, museums, or other locations where special contents may be housed, the preaction sprinkler system must be used. Any operation of the sprinkler system in the absence of fire would be devastating to the building contents. Most fire safety professionals identify two events that must take place in order to activate the system. First, the heat of a fire will melt the fusible link in the sealed sprinkler heads. Second, a detector must open the deluge valve to admit the water. In the absence of either of these two events, the sprinkler system will not function. The biggest disadvantage of this system is the cost. However, when contents of great value must be protected, the expense of a preaction system may not be restrictive. 

Associated with each of these demands that may cause the hazardous event were various protective systems. These were either hardware (e.g., ventilation system, flammable gas detectors) or procedural (e.g., instructions on allowable maintenance activities). For any particular demand to lead to the hazardous event, all the protective systems designed to protect against that demand must have failed to perform. Again, this failure may be a hardware failure (e.g., the gas detector has drifted out of calibration) or a human error issue (e.g., the flammable gas detector alarm warned of a flammable leak but Ihe operator failed to take appropriate action). 

Optical detectors shall be used in more open configurations where ressure buildup due to the incipient explosion is limited. Optical etectors shall not be used where high dust concentrations limit the reliability of the suppression system. Both uv and ir detectors are available for optical detection. The use of daylight-sensitive sensors shall be avoided to avoid spurious activation. The sensor shall be mounted such that the angle of vision allows it to cover all the protected hazard area. The performance of an optical detector will also be affected by any obstacles within its vision, and this shall be overcome by the introduction of more detectors. Optical detectors shall be fitted with air shields to keep the optical lens clean. 

Pressure detection shall be used for closed enclosure applications. Threshold detectors provide an electric signal when a preset overpressure is exceeded. Dynamic detectors provide an electric signal to the control and indicating equipment (CIE). Typically they have both rate-of-rise and pressure threshold triggering points that can be configured specifically to the application conditions. Although this type of detector minimizes spurious activation of the isolation system (due to pressure fluctuations other than explosion pressure rise), care shall be taken to set up such detectors to meet appropriate detection response criteria for the particular application and protected enclosure geometry. 

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. 

In this model, OBPs participate in the selective transport of pheromone and other semiochemicals to their olfactory receptors. The selectivity of the system is likely to be achieved by layers of filters [ 16], i.e., by the participation of compartmentalized OBPs and olfactory receptors. It seems that OBPs transport only a subset of compounds that reach the pore tubules. Some of these compounds may not bind to the receptors compartmentalized in the particular sensilla. The odorant receptors, on the other hand, are activated by a subset of compounds, as indicated by studies in Drosophila, showing that a single OR is activated by multiple compounds [66]. If some potential receptor ligand reaches the pore tubules but are not transported by OBPs, receptor firing is prevented because the receptors are protected by the sensillar lymph. In other words, even if neither OBPs nor odorant receptors (ORs) are extremely specific, the detectors (olfactory system) can show remarkable selectivity if they function in a two-step filter. 

Other fire protection features have been incorporated into CNG refueling facilities such as methane detectors to warn of leaks from the dispenser, and automated fire suppression systems activated by ultraviolet/infrared detectors. Dry chemical is the preferred fire suppression material since water line protection from freezing is difficult in outdoor settings. The methane detectors can also be used to shut down the compressor and dispenser if desired. 

In addition, LNG storage and dispensing systems shall be protected by methane detectors that will sound an alarm and shut down the dispenser. A fire suppression system activated by infrared and ultraviolet flame sensors shall be included to protect the area where the vehicles are refueled. Additional measures such as automatically calling the fire department when the fire suppression system is activated should be considered. 

Signals to the Plant Protection and Instrumentation System (PPIS) and the NSSS Control Subsystem (NCS) are supplied by neutron detectors. During power operation, the neutron flux levels are monitored by detectors located in wells between the reactor vessel and the concrete cavity wall. These detectors are distributed symmetrically around the reactor vessel at about the core midplane. During low power operation, starting up, shutting down, and while shut down, the neutron flux levels are monitored by source-range detectors, located in selected side reflector elements near the bottom of the active core. 

Fusible links are made of low melting point materials designed to vent pneumatic systems as the fire melts the link. The depressurization can open fire deluge valves. Fusible links are very reliable, but they do require that the fire be well under way before they work, whereas otho- detectors, such as fire eyes, act more quickly. Depressurization of a fusible loop is considered to be a confirmed detection of a fire, and will automatically initiate appropriate shutdowns and activate fire protection equipment. 

An individual protective device that emits an audible alarm to notify others and assists in locating a firefighter in danger. The personal alert safety system (PASS) device includes a motion detector that senses movement and automatically sounds an alarm signal if no movement is sensed for 30 seconds in case a firefighter is incapacitated and cannot activate the alarm. Requirements for PASS devices are specified in NFPA 1982, Standard on Personal Alert Safety Systems (PASS) for Fire Fighters. Personal Factor... 

In the design of the detector system, the photoluminescence should be measured during enzymatic activity. This required the construction of a flow cell system that could be interfaced with both a UV-vis and fluorescence spectrometer. In addition, because ultimately the system will be handling very toxic materials, the complete system must be sealed to protect the operators. 

Under the manual detector positioning mode, only the safety limit switches are active in protecting the mechanical system. 

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