【 Weak current College 】 civil buildings fire analysis and intelligent leakage application of fire-alarm system

Civil building contains two most, public gathering areas and housing. Public gathering area means shopping malls, markets, hotels, theaters, stadiums, dance halls and other places, to provide a comfortable shopping, accommodation, entertainment environment also because you want to use a large number of electrical equipment, facilities, increasing the risk of electrical fires; and people's standard of living is increasing rapidly, will also use more updates of electrical home appliances, and these appliances direct contact of the vast majority are the only use common sense and do not have electrical expertise of ordinary people, not regulated power customary and mobile extension socket abuse also enable domestic electrical fire incidence has been increasing.
First, there is a fire of some statistics
Based on reliable data and statistics, only the first half of 2007 the total national town, death fire 95336, injured 488 898, direct property losses of nearly $ 5 b, visible fire resulting in bodily injuries and economic loss is very high. The State Department has developed the production safety accident reports and studies dealing with regulations, such as a series of prevention and assistance measures, the competent authorities of all levels on fire prevention has also been given great importance given by the national fire trend steadily down. However noteworthy that, due to electrical failure was caused by the fire on a yearly basis, according to preliminary statistics, about 10 years ago by 4-5 times the number of fires which occurred more than a quarter. In electrical accidents in the fire, the electrical equipment accounted for 10 per cent, line 52.0 percent, electrical equipment and apparatus 36.4 percent (including lighting apparatus 10.6%), other 1.6 per cent; heavy, oversized electrical fires, their causes short-circuits accounted for 52%, overload or 4.6 percent, bad 12.6 percent, overheating 18.5 percent, leakage 1.8 percent, 0.5 percent, lightning strike, electrical fault accounted for 10 per cent.
Second, the results from the fire statistics to see China's electrical safety standards
From electrical accidents and fires caused by the statistics known. China's electrical safety system has not been thoroughly penetrated into the base, some on electrical safety, work in dereliction of duty, and does not strictly follow the rules for using electricity for the operation of phenomena also occur from time to time, these are causing the root cause of electrical fires. As China's economy continues to grow, electricity consumption is also growing rapidly, therefore by electrical accidents caused by the fire, there is also a rising trend.
Most of the electric fire accidents are due to electrical equipment running artificially raised in violation of the rules of operation, for example forgot to disconnect the electrical power supply, the electric heaters on drying clothes, etc., these are not normative power lead to the typical cases of fire; the use of, the provisions do not conform to the manufacturing of electrical equipment and installations is another electric fire dangers, for example, incandescent (or other heat large light source) and electric heaters, etc. due to overheat and ignite combustibles; there are around a large part of the reason is because the wire overload, over current protection device characteristics of poor or shorted wire protection switch, fuse, caused a power circuit and grounding, are supposed to pay attention to the electric fire hazard.
In sum, the electric fire causes and prevention has several noteworthy:
1. a public gathering areas most serious electrical fire hazards are electrical devices, circuit temperature is too high, on the one hand, in engineering design because there is no good off the wire selected is too small or too low temperatures cause lines, electrical lines of deficiency, spark or transformer grounding wire? contacts, power distribution, bus and cable tray, fuses, etc. are present because of poor people as the construction of the local temperature increases are fire hazards, the supervision and inspection in fire or electrical device detection process can be used by help of thermal infrared imager and other testing equipment for thermal and heat, you can use ultrasonic detector to find electrical wiring, equipment received and brand impact of virtual phenomenon, and so on, you can use infrared devices such as a nod to measure specific parts of the body temperature.
2. Construction and installation are not standardized, cause electrical equipment failure. The exposed wires, cables, connectors, the phenomenon is most common with lights, common mobile socket, power distribution unit Cabinet air conditioner, advertising lights, power cable connector exposed. Suspended ceiling, decorative wall cable shaft, counters, cabinets, concealed inside the outlet the power supply cable connector exposed also prevalent;
3. Electrical equipment and fuel companies did not take effective measures, increased risk of electrical fires, for example, some electrical device installed directly on the combustible components, or electrical equipment using flammable objects such as boxes, in everyday life, the most common is the air switch, leakage breaker, ballasts, lighting control switch, outlet directly installed on wooden boards, etc.;
4, electric line laying protective measures are not in place:
(1) ceiling-mounted parts electrical lines laid in the most serious problems. For example, a wooden ceiling luminaire wiring not wearing protective tube; downlead suspended ceiling or in the cable harness into ceiling-mounted luminaire does not take protective measures; ceiling luminaire wiring through pipe protection are not in place of phenomena occurred from time to time, and some have even wear hose wire but still have the exposed part or distribution extension protection tube are not introducing a junction box or apparatus;
(2) wire, cable in the wall, metal components, combustible components do not take protection measures, and some wires, cables, do not wear metal protection pipe laying in flammable decoration dissection or wear within. wooden curtain walls, stairs, walls between the cable access distribution box wear steel pipe mouth did not do proper protection measures:
(3) indoor electrical line laying position. Electrical line laying position and heat source too close distance, such as: a flashlight (especially heat high lights) power cable attached to the heating pipe laying. or power covered wire near the radiator, metal pipe laying, winding in metal tubes, etc.;
5, the mobile extension socket problems, especially, whether it is a public place or a family, mobile extension socket problems are more and more, many bad socket does not use qualified insulated and sheathed, mobile extension socket threaded wire using, electricity, water-proof measures need to be takenPlaces (such as restaurants, shops selling flower beds, washing machine, fish tanks, etc.) do not use waterproof mobile extension socket, etc.;
6, Terminal wire crimp is not normative. Air switches and breakers of terminals and neutral line bus terminals, the Terminal crimping multiple wire or stranded conductors without Terminal crimping, crimp terminals crimping weakly happens from time to time;
7, management measures are not in place. Warehouse stacked vertically below the luminaire combustibles; generator and fire boilers and other combustibles in a room with reset; distribution Cabinet stacked debris around; lighting and too close to combustibles distance around; cable ditch legacy are combustible debris, etc.;
8, a lot of fire power equipment, facilities and other reasons due to the construction itself exists to varying degrees of fire hazards. Design and calculation errors in the selection of fire power equipment or wires overheating or fire sporadically in fire inspection also often find fire distribution box Terminal temperature thermal or electrical equipment have been destroyed to no effect, as well as air switch shell burnt, wire connector outside insulation ageing, breaker crimp is corrosion causing bad, etc., such fire-fighting, fire protection circuit, not only in fire, does not have the effect, become the cause of the fire should be attention to;
9, shaft, 7 ㈠ with not take fire blocking measures, tall buildings cable well in each floor office fire sealing has been made, the transformer naked bus and other electrical equipment through the fire wall cavity is not implemented, such as fire sealing makes the flame through shafts or other pathway yanran, resulting in greater loss.
You can say, our country's security of electricity will also need to do a lot of work. According to the fire department fire statistics, it is not difficult to see from electrical faults caused by the fire is on the rise: this required in the manufacture of electrical equipment, appliance or electrical installation, maintenance, you should strictly follow the rules for the construction operation, doing every procedure, every detail perfect. Fire hazard mostly because of violation of fire regulations and fire protection technology standards, and therefore to determine whether a safety factor not only pose a fire hazard in the fire chief on the laws and regulations, but also in fire protection technology standards have also been based on.
In everyday life, and high-pressure distribution transformer system contacts are professionally trained and experienced professionals, due to the high-voltage thrown in, electrical accident frequency much lower than with the general population exposure to a wide range of low-voltage systems (AC220/380V). Therefore, low-voltage electrical installations for fire prevention measures in the electrical engineering design, construction and daily use and maintenance has become particularly important. People in a century of electricity, and gradually perfected on different voltage level of protection for low-voltage equipment of protected content are over current protection, ground fault protection, overvoltage and less voltage protection, earthing and equipotential bonding, insulated or quarantine measures and special places and special equipment for protection. These measures not only effectively protect the personal safety can also fire prevention electrical failure.
3. used for fire prevention measures leakage protection
Residual current protection related knowledge: in the low-voltage distribution system, any of the electrical equipment is a node, the device current is a vector, at any time into the outflow of vector and should be zero, that's familiar to Kiel-g's first law, as long as the device's current does not "leak", then the device insulation is reliable. If the device or the power supply line insulation fault occurs. then current will return to the Earth, the current transformer is an exciting role, the current mutual inductance coil and switch tripping mechanism connections. the transformer excitation of the differential current exceeds a limit, switch will action, as protection switch trip depends on fault current has nothing to do with the voltage.. This switch is called a residual current protection switch. Thus the residual current protection and earthing protection. in order to make the current in the insulation failure to complete the circuit, requires protection of electrical equipment must be grounded,
For normal work of used appliances and the laying of lines, residual current protection switch should not, if there are residual current circuit, regardless of the existence of this current is flowing through protection line (PL) of the PCT or protection switch and no electrical devices but there fault current line (e.g. for wires insulation damage through the metal protection pipe flow to the Earth's residual current), residual current protection switch should be timely action, cut off the circuit. Therefore, the fault-current protection switch to prevent grounding current fire of electrical installation system can also play a large role.
Residual current under what conditions can cause a fire? in General, when the fault free release of energy to be ignited flammable objects when the open flame and thereby cause a fire. The majority of electrical fires are caused by ARC, after extensive tests and practical experience shows that several hundred Ma small current can create arc, applied residual current protection switch for fault current protection can effectively prevent electrical line of fire.
4 short circuit arc of fire prevention
Short circuit arc of fire in the majority of the grounding caused, AC220V, 300-500mA of current is enough to produce the arc, residual current protection switch (RCD) timely and effectively cut off the power switch, or you can send a signal. as soon as possible in identifying, avoiding the occurrence of fire. At the same time, using the residual current protection switch can also be hidden on ground fault played a preventive role, for example due to improper construction results in neutral and Earth wire received wrong, or the construction of the cable insulation damage inadvertently make RCD alert or action, this is because the leak current line by PE by Earth return to power, the total incoming Department current vector and is not zero, the RCD action occurs or signals, only exclude ground fault, eliminating the risks, protect switch to reset.
In order to effectively avoid personal electric shock accident and ground fault arc fire, in accordance with the standards, IEG in building sets two-or three-level RCD.
(1) configuration levels of the programme: RCD at the end of the loop on setting 30mA or 10Instantaneous RCD 0mA, and set when the rated current for 5 times the maximum operation time for the front end to power 0.04s; gas line Office, should be set to delay action 300 ~ 500mA smart choice-RCD, its action is not the smallest 0.15s action time as 0.05s.
(2) configure the third-level programmes: RCD and configuration levels comparison of RCD, its extra III RCD General fixed delay type (such as in 1s delay, 1 △ n take 1A), the level of the RCD is scoped to the zero sequence transformers, generally used for fire signal system, the only alarm not actions (such as needs can also be scoped to the breakers actions), to large buildings often require the installation of three-level RCD.
5. set the leakage of the causes of fire alarm system
Building power Office installation with residual leakage protection function of the circuit breaker or into line circuit breaker and residual current protection independent of the remaining switches use is effective in preventing electrical short fire. In the sustainable development of China's economy today, because people on safety specifications in-depth knowledge of electricity, making the electrical failure caused personal injury accident gradually, but each year by the electrical accidents caused by the increase in the number of fire, and fire-on-year decline in the number is in sharp contrast to the trend. In the 1980s, the RCD as preventing electrical fires a measures to promote, my many provinces, including some in developed economies are not enough attention, some construction units and designers even believe that installation is optional or RCD protection is not necessary to use some favour! RCD's designers also due to various reasons only has designed a two-level, allowing the building to memory is not being blank line fire protection district, so there is a certain line of fire danger, and our current promotion "people-oriented" humanity is alien to a harmonious society.
RCD applications standardize in countries in fact, such as the low-voltage distribution design code GB50054-95 no. 4.4.21 bar: "in order to reduce the ground fault caused by electrical fire danger and installation of leakage current protector, the rated current shall not exceed 0.5A"; and if the senior civil building design fire protection standard "GB50045-95 (2005 Edition) new section 9.5.1:" fire hazard in high-rise buildings, personnel are crowded, and other places to set current fire alarm system "; the building design fire protection standard of section 11.2.7 GB50016-2006 provides a desirable set leakage fire alarm system.
It must therefore be fully aware of the power set at RCD protection feature is important for preventing electrical fires, as one of the initiatives for low-voltage electrical equipment unceasing development, residual current protection for some technical problem has been overcome, the leakage current fire alarm system in the civil architecture of lay the Foundation. The doctrine of "complementary" buildings》 intelligent leakage fire alarm system, "a chapter as the new system be replicated on the ground that the system will monitor, analysis, alarm and control integrated and unified management, due to the central computer involvement instantaneous analysis and manipulation of data. The system consists of multiple monitoring subsystem, proprietary software, computer network, the full realization of a teleoperation, telemetry and remote control, to timely implement electrical fault alarm and cut off the power to effectively prevent the occurrence of electric fire, thereby protecting the whole low-voltage electrical system. At present, the "intelligent leakage fire alarm system" as a new advanced protection measures have been Fire Department, construction drawing examination centers and fire engineering workers, as a pre-alarm system, its better than the automatic fire alarm systems and fire protection system that can advance warning and to take emergency measures, to minimize the loss of the user to a minimum, result in engineering design should strictly follow the specifications set "leakage" of fire alarm system.
China electrical fires in all types of fire in a considerable proportion of electrical fires high characteristics, is also a need to formulate an electrical fire in the special laws, at the prevention of the occurrence of electrical fires. United States and Japan and other developed countries have laws and regulations relating to the electrical specialist, such as the United States national electrical safety code (NFPA70), Japan's electric utilities Act, etc.
The advantage of foreign management system in the following areas, for reference: (1) electrical safety regulations drawn up a detailed, comprehensive, easy-to-Manager of operations; (2) the specification of legally binding, in accordance with the law on electrical design, installation sector qualification certification, particularly in the electrical safety of staff and regular examination of qualification license thousands raised the level of the professional skills and competence; (3) the management bodies, regardless of where they are established inspection, electrical installation and construction does not leave gaps; (4) use the units (including industrial building, civil construction and residential) electrical safety awareness and a stronger insurance awareness, promote electrical safety management; (5) the product quality is preventing electrical fires determinants, Japan electrical supplies ban Act implementation and continuous improvement to ensure electrical safety, fire prevention success stories. Therefore, to formulate the relevant national electrical safety standard, and this specification should have a higher legal force, it is mandatory that all industries should accordingly draw up specifications for various types of the child and the rules and regulations, such as electrical wiring, electrical equipment, such as design specifications for fire prevention, fire safety design specifications for electrical equipment, as designers, builders, and audit, inspection and electrical units of power of norms and standards of conduct.