UV fire detectors

The most important hardware items appeared to be the detectors themselves. The gas detection system gave frequent spurious alarms, and on both platforms the ultraviolet (UV) fire detectors were also prone to spurious activation from distant hot work for example, and had a limited ability to detect real fires. The tmreliability of these systems had a general effect on response time and would, overall, lengthen the time to respond. The second aspect which was related to hardware was fimction and performance testing of the emergency blowdown systems. It is critical that the workers believe the systems will work when required, and this can only be achieved by occasional use or at least fimction testing. 

These next scenes are not sequences of an explosion, but of a burning torch being thrown into an open cublicle with an open pan of gasoline on the floor. In the cubicle is a UV fire detector and a 10-pound bottle of Halon 1301, an extinguishing agent. 

Safety and security Temperature Toxic gases like CO, CO2, exhaust gases, smoke,. .. Combustible gases like CH4, C2H6 (gas detection via flame detection (Europe), fire detectors, caravans with gas detectors) UV sensors Radon sensing... 

Deluge systems should generally be activated by automatic means. Activation by manual means defeats the objective of installing a deluge system, and fire water monitors should be provided instead as they are more cost effective where manual means is relied upon. Most systems provided at petroleum facilities are typically activated by a heat detection. Usually a fusible plug pneumatic loop detection system or UV/IR detectors are placed around the equipment. This insures activation when operators are not present and only when a real fire situation is present. 

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. 

The IR/UV flame detectors are used to sense fires. Flame detectors that use only IR or UV can experience false alarms. The IR/UV detector is designed to recognize a different type of flame signature from the detectors while rejecting common false sources. When the conditions of any one of the several fire conditions are met the detector indicates a fire. IR/UV flame detectors generally have a cone of vision from 60 to 120-degree solid cone field of view. 

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... 

For incandescent fires, optical fire detectors should be used. These may be UV detectors, IR detectors, or closed-circuit TV (or a combination of these). The choice will depend partly on the type of flame that is anticipated. For example, methanol bums with a nearly invisible flame, so a fire of this material cannot be detected by CCTV. 

In Chapter 5.4, optical ultraviolet radiation sensors are described, including UV-enhanced silicon-based pn diodes, detectors made from other wide band gap materials in crystalline or polycrystalline form, the latter being a new, less costly alternative. Other domestic applications are personal UV exposure dosimetry, surveillance of sun beds, flame scanning in gas and oil burners, fire alarm monitors and water sterilization equipment surveillance. 

In a typical UV detector, the current is allowed to flow for a very short period of time before the voltage is reduced and the current stopped. Thus the output of the sensor tube is a series of voltage pulses, the frequency of which is proportional to the intensity of the UV sensed by the detector. The closer a fire is to the detector, the higher the output frequency, and the smaller the flame size that is needed to actuate the system. 

Applications. Ultraviolet detectors are ideally suited for applications where rapidly developing fire can occur in a relatively open area. UV detectors can be used to monitor ammunition assembly lines, gunpowder troughs, or open areas that are stocked with hazardous materials. These detectors are not typically affected by extremes of temperature or pressure, adverse weather conditions, high humidity, nor are they sensitive to solar radiation. 

In addition, smoke and various vapors can significantly absorb UV, making it difficult or impossible for the detector to "see" a fire. 

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. 

It responds well to a wide range of hydrocarbon fires and is blind to welding arcs except when very close to the detector. It can see through smoke and other contaminates that could blind a UV detector. It generally ignores lightning, electrical arcs and other forms of radiation. It is blind to solar radiation and resistant to most forms of artificial lighting. 

There are few models with automatic test capability. Testing is usually limited to hand held devices only 2 meters (7 ft.) from the detector or directly on the lens test unit. It can be ineffective if ice forms on the lens. It is sensitive to modulated emissions from hot black body sources. Most of the detectors have fixed sensitivities. The standard being under five seconds to a petroleum fire of 0.1 square meter (1.08 sq. ft.) located 20 meters (66 ft.) from the device. Response times increase as the distance increases. It cannot be used in locations where the ambient temperatures could reach up to 75 °C (167 °F). It is resistant to contaminants that could affect a UV detector. Its response is dependent on fires possessing a flicker characteristic so that detection of high pressure gas flames may be difficult. 

The use of two separate electrical or mechanical zones of detectors, both of which must be actuated before the confirmation of a fire or gas detection. For example, the detectors in one zone could all be placed on the north side of a protected area, and positioned to view the protected area looking south, while the detectors in the second zone would be located on the south side and positioned to view the northern area. Requiring both zones to be actuated reduces the probability of a false alarm activated by a false alarm source such as welding operations, from either the north or the south outside the protected area. However this method is not effective if the zone facing away from the source, sees the radiation. Another method of cross zoning is to have one set of detectors cover the area to be protected and another set located to face away from the protected area to intercept external sources of nuisance UV. If welding or lighting should occur outside the protected area, activation of the alarm for the protected area would be inhibited by second... 

Flame detector Senses either ultraviolet (UV) or infrared (IR) radiation emitted by a fire. 

The available types of flame sensing detectors are ultraviolet (UV), infrared detection (IR), combination of these, and monitored closed circuit television (CCTV). These devices operate on the detection of certain wavelengths of light emitted by flames. They are used when there is a potential for fires that rapidly produce flame such as flash fire. 

A fire occurs in four distinct phases. In the incipient phase, warming causes the emission of invisible but detectable gases. In the second phase, smoldering, smoke is formed so smoke detectors can be used. In the third phase, when the ignition temperature has been reached, flames and their emitted radiation (IR and UV) can be detected. In the fourth and last stage of the fire, heat is released the temperature of the space starts to rise, and the use of thermal sensors becomes feasible. 

If any one of these detectors sees UV radiation, it will fire all of the cannons. The circuitry was designed to indicate at any time if there was an electrical malfunction in the wiring to any of the cannon detonators. 

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