Pipe gallery is an underground urban pipeline integrated corridor, a tunnel space built underground in the city, which integrates various engineering pipelines such as power communication, gas, heat supply, drainage, etc., and is an important infrastructure and lifeline to ensure the operation of the city.
The pipe gallery is complex, and it is difficult to arrange fire-fighting equipment, but it is also a very important part of the city, which makes many fire-fighting equipment buyers particularly headache.
There are many combustibles in the pipe gallery, mainly including cables, optical cables, and pipelines. Since cables are composed of protective layers, insulators, and conductors, PVC and rubber are mostly used. Easy to scorch and ignite.
Due to interphase short circuit, short circuit to ground, poor contact and line overload between cables and optical cables, it is very likely that cables will catch fire. When densely laid cables catch fire in the pipe gallery, the heat generated by the fire will not be diffused in a short time, which will lead to a rapid rise in the temperature in the pipe gallery. The wires and cables in the pipe gallery are stacked and arranged in a centralized manner. If the upper wires and cables are on fire, PVC, rubber and other materials will quickly spread the flame to the lower cables, optical cables and wires in case of high-temperature melt dripping; In contrast, once the lower cable catches fire, the hot gas and thermal radiation will soon affect the upper line, so it will be particularly difficult to deal with, the fire is difficult to control, and will cause significant losses.
Pipe gallery fire has the following characteristics:
The fire is fierce and burns rapidly. Due to the structural nature of the pipe gallery, the front and back are connected, and the cables and optical cables are set in dense places. Once the fire breaks out, the fire will quickly spread to the adjacent areas, and the fire will spread rapidly along the cable trend.
Fighting difficulties. Cable burning produces a large amount of toxic gas, the internal space of the pipe gallery is narrow, various communication equipment are affected by shielding, and communication is inconvenient, which makes it difficult for firefighters to extinguish the fire with internal skills.
There is a risk of electric shock. In the pipe gallery with dense wire and cable layout, the high-voltage cable may still have residual voltage after power failure, which is dangerous for electric shock.
At the same time, the internal structure of the pipe gallery is complex, and the installation of fire-fighting facilities is complex, which is incompatible with some large-scale fire-extinguishing devices, and the installation works are time-consuming and laborious. For electrical fires in closed environment, automatic fire extinguishing system is adopted. At present, the general fire extinguishing measures are: ultra-fine dry powder fire extinguishing system, gas fire extinguishing system, aerosol fire extinguishing system, water spray fire extinguishing system. The gas fire extinguishing system generally adopts carbon dioxide fire extinguishing system and pipe network heptafluoropropane fire extinguishing system. Due to the pressure drop and large evaporation caused by long-distance transportation, this kind of fire extinguisher reduces the effective injection amount. Therefore, in order to ensure the fire protection of the whole pipe gallery, a large number of carbon dioxide or heptafluoropropane storage stations need to be set up. However, due to large land occupation, high cost, difficult and expensive construction, it is generally not used.
Considering the difficulty of pipe gallery fire, the following feasible and effective fire extinguishing methods are listed for comparison:
Automatic water spray fire extinguishing system
The automatic water spray system is a fire extinguishing system composed of containers, water, deluge valve groups, filters, and water spray nozzles. When the automatic water spray fire extinguishing system is adopted, the comprehensive pipe gallery project needs to be equipped with fire pump rooms, relevant fire pipelines, some electrical equipment, and some automatic control systems.
Advantages: real time monitoring and effectively reducing the temperature of the fire scene.
Disadvantages: the reserved main fire-fighting pipes in the comprehensive pipe gallery and the pipe positions of fire-fighting pipes in each fire-fighting zone increase the section size of the comprehensive pipe gallery.
Aerosol automatic fire extinguishing system
The aerosol automatic fire extinguishing system is a fixed fire extinguishing system, using strontium nitrate as the main oxidant and potassium nitrate as the auxiliary oxidant. The oxides of strontium nitrate are strontium oxide, strontium hydroxide and strontium carbonate.
Advantages: these three substances will not absorb moisture in the air and form conductive and corrosive electrolytes and electrolyte liquid films, thus avoiding damage to the equipment, but the price and maintenance cost are expensive.
Disadvantages: the product is gas-solid two-phase flow, so the pipe network design of combined distribution cannot be carried out. At the same time, it must be connected to the network to start, and the starting current takes up too much space. It is easy to cause pollution and damage to electrical equipment.
Suspended heptafluoropropane system
There are three types of hanging heptafluoropropane: temperature control, electric control and electric temperature control. Similar to the fire extinguishing mechanism of halogenated alkyl series fire extinguishing agents, it belongs to the category of chemical fire extinguishing. Fluorine containing free radicals are generated through the thermal decomposition of fire extinguishing agents, and react with H, oh, O2 active free radicals that produce branched chain reaction in the process of combustion reaction, so as to effectively inhibit the chemical reaction in the process of combustion to implement fire extinguishing.
Advantages: unlike the pipe network type, the hanging heptafluoropropane needs heptafluoropropane storage station, and does not need a long pipeline to connect. The pressure caused by long-distance transmission is insufficient. At the same time, unlike the cabinet heptafluoropropane, the pressure is insufficient, and the spraying is uneven. It also has the advantages of heptafluoropropane, low toxicity, no pollution and so on. It has the advantages of rapid fire extinguishing, high efficiency, hanging, small volume, easy maintenance, and sufficient supply.
Disadvantages: under the high temperature of the fire extinguishing site, fluorine-containing halothane extinguishing agent will produce a large amount of hydrogen fluoride (HF) gas, which will be combined with gaseous water to form hydrofluoric acid (white fog). Hydrofluoric acid is a highly corrosive acid, which has a strong acid corrosion effect on skin, leather, paper, glass and precision instruments. The longer the fire scale and spraying time, the higher the HF concentration produced by FM200 fire extinguishing system, the stronger the acid corrosion effect on precision instruments and equipment, and the stronger the corrosion effect on human skin. At the same time, because FM200 produces "white fog" during spraying, it is corrosive and more harmful in the process of gas evacuation.
And the superfine dry powder fire extinguishing system:
Superfine dry powder particles are thinner than ordinary dry powder. They are non-toxic, harmless, non irritating to human skin, non corrosive to protectors, non decomposing, non hygroscopic, non caking under normal conditions, and have good fluidity, dispersion and electrical insulation. The average particle size is less than 10 microns, which is 6-10 times the fire extinguishing efficiency of ordinary dry powder. The ultra-fine dry powder fire extinguishing device is driven by nitrogen, with temperature control and electric control startup, double insurance, fast response, and good total flooding effect. Its fire extinguishing efficiency is a fire extinguishing method with obvious advantages in fire extinguishing speed and efficiency among the fire extinguishing agents identified in the world at present.
advantage:
(1) There is no need to lay a large number of pipelines, and the cost is low;
(2) Steel material, beautiful appearance design, fast connection structure, convenient installation, simple maintenance, 5 years maintenance free;
(3) It belongs to water and pressure free fire fighting, which will not cause secondary damage to the protectors and the site;
(4) There are various control modes, which can realize temperature control startup, on-site manual startup and fire alarm linkage startup;
(5) Vertical spray, no space, simple control, good fire extinguishing effect;
(6) Quick start and instant fire extinguishing.
