Detectors suppressed systems

To reduce the chance of false activation of the suppression system by vibration, a flexible pressure detector standoff is often used. Also, two detectors in series may be employed to reduce further the possi-bihty of false activation. 

Typical applications for these high speed IR detectors are characterized by strictly controlled, dark environments where a flash fire could originate. While simple high speed infrared systems have been available for several years, modern sensor and filter developments, coupled with state-of-the-art electronics, have resulted in systems tailored for the munitions industry. These systems are more selective within the electromagnetic spectrum, fast in response, and extremely flexible in application to suppression systems. 

To initiate an explosion suppression system, a detector is used to sense either an overpressure generated by, or a flame of, an incipient explosion. It is important to locate the detector in a position that ensures sufficient time for the suppression system to sense and activate the devices to extinguish the explosion. 

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. 

Many states now require lire suppression systems for public service stations and for some private fleet refueling facilities. Most of these systems are dry chemical using infrared detectors and work as effectively on methanol vehicle fires as gasoline vehicle fires. No special requirements are necessary for these systems when used at a methanol refueling facility. All fire suppression systems should be checked after installation for proper coverage using a fraction of the dry chemical that would normally be used (this is called a puff test ). The puff test not only shows the coverage that will be obtained, but tests the components of the fire protection system. 

All refueling systems of significant size should consider the incorporation of a fire suppression system. The current systems using dry chemical should be effective on hydrogen fires, though fire suppression professionals should be consulted when choosing which type of system to use. Special sensors may be required since the infrared detectors used for petroleum fuels may not sense hydrogen fires as efficiently. 

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. 

Pressure sensors are not suitable as explosion suppression systems in large obstructed areas, but the basic ultraviolet (UV) detection system available today as a fire detector is capable of being used as an explosion detector, providing the exploding fireball is in the cone of vision of one of the detectors within the first 75 milliseconds. The extinguishing agent used must make... 

Explosion suppression systems comprise explosion detectors, pres-... 

A suitable locking mechanism must ensure that the production plant can be started up again only if the explosion suppression system is fully operational. The alarm center must be designed so that, if work is performed within the protected vessel, the detectors can be made inoperable and secured against inadvertent triggering. 

Explosion suppression is detecting an explosion at an early stage and suppressing it with a suitable suppressant. Explosion suppression relies on early detection of an explosion and rapid injection of the suppressant. A typical explosion pressure at the moment of detection is 0.035-0.1 barg. Suppressant extinguishes the flame within 0.08 sec. An explosion suppression system normally includes explosion detector, control unit, suppressor, and a suitable suppressant. 

Is the product dusty or hazardous Even if the product is water wet, consideration should be given to the fact that the product may be toxic, flammable or hazardous in other ways. This would entail a hazard analysis review of what if situations. For example. What if the product escapes from the confinement of the dryer, or what if air gets into the dryer from the surrounding environment Some drying processes may require the addition of a fire or explosion suppression system. One such system uses an infra-red detector to sense a cinder combined with a sonic detection device to sense the shock wave of a deflagration. 

A typical suppression system operates on the basic principle shown in Figure 56.17. The detector 1 placed inside the dryer casing detects the pressure wave, before the outburst of... 

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. 

Features for fire prevention were the mechanical properties of some metal material containers and radioactive material form to prevent or reduce the release, and smoke detectors and sprinkler fire suppression systems to prevent or delay ignition of combustible materials. In addition, administrative operating procedures, hazardous material handling training and packaging requirements could also help prevent or mitigate a fire caused by an electrical wiring short or overheat. 

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