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Introduction of flame-retardant fire-retardant cables
Introduction of flame-retardant fire-retardant cables At present, the cable industry is accustomed to refer to fire-retardant cables such as Flame Retardant, Low Smoke Zero Halogen (LSOH), Low-Smoke Low-Fume (LSF), Fire Resistant, and other fire-resistant cables. 

◎Flame Retardant 

Flame retardant cable is characterized by retarding the spread of flame along the cable so that the fire will not expand. Because of its low cost, it is a large variety of cables used in fire protection cables. Whether it is a single cable or a bundled cable, when the cable is burned, the spread of the flame can be controlled within a certain range. Therefore, it is possible to avoid a major disaster caused by the ignition of the cable and increase the fire protection level of the cable line. ◎Low-smoke halogen-free flame retardant cable (LSOH) 

The characteristics of low-smoke halogen-free cables are not only excellent flame-retardant properties, but also the materials that make up the low-smoke halogen-free cables contain no halogen, have low corrosiveness and toxicity when burned, and produce a very small amount of smoke, thereby reducing the amount of smoke. Damage to equipment and equipment is conducive to timely rescue in case of fire. Although low-smoke halogen-free flame-retardant cable has excellent flame retardancy, corrosion resistance and low smoke concentration, its mechanical and electrical properties are slightly inferior to ordinary cables. ◎ Low-halogen low-smoke flame-retardant cable (LSF) 

The low-halogen low-smoke flame-retardant cable has a hydrogen chloride emission amount and a smoke concentration index between the flame-retardant cable and the low-smoke halogen-free flame-retardant cable. Low Halogen cables also contain halogens, but at lower levels. The characteristics of this type of cable are not only flame-retardant, but also emit less smoke and emit less hydrogen chloride. This low-halogen, low-smoke, flame-retardant cable is generally made of polyvinyl chloride (PVC) as a base material, and is equipped with high-efficiency flame retardants, HCL absorbents, and smoke suppressants. Therefore, this flame-retardant material significantly improves the combustion performance of ordinary flame-retardant PVC materials. Fire Resistant Cable (Fire Resistant) 

The fire-resistant cable can maintain normal operation for a certain period of time under the condition of flame combustion, and can maintain the circuit integrity. Fire-resistant and flame-retardant cables generate less smoke of acid gas and fire-retardant flame-retardant performance. Especially when burning, with the water spray and mechanical shock and vibration, the cable can still maintain the complete operation of the line. The main technical indicators of cable standards and grade cables related to fire safety are the flame retardancy of CO2 cables, the density of smoke, and the toxicity of gases. The US fire protection standards are more concerned with the first two issues, but Europe and the United States have a completely different view of fire safety. The traditional American concept believes that the root cause of fire is the production of carbon monoxide (CO) poisonous gas and the subsequent release of heat from CO to CO2 in the combustion process. Therefore, controlling the heat release during the combustion process can reduce the risk of fire. Since European tradition, it has been convinced that the release of halo acid (HCL), gas corrosion, smoke concentration, and gas toxicity in combustion are the major factors that determine whether people can safely escape from the fire scene. 

IEC flame retardant rating In order to assess the strength of the flame retardant cable performance, the International Electrotechnical Commission respectively developed three standards IEC60332-1, IEC60332-2 and IEC60332-3. IEC60332-1 and IEC60332-2 are used to evaluate the flame retardant ability of a single cable when it is tilted and placed vertically (domestic to GB12666.3 and GB12666.4). IEC 60332-3 (GB12666.5-90 corresponding to the domestic) is used to evaluate the flame retardant ability of the bundled cables in the vertical combustion, compared to the requirements of the flame retardant ability of the bundled cables in the vertical combustion. Flame retardant rating of IEC60332-1/BS4066-1 (single wire or cable vertical burning test) 

This is a flame retardant standard for a single cable. The test stipulated that a 60cm long sample was vertically fixed in a metal box opened in the front wall. The flaming length 175mm propane burner was brought into contact with the cable at a 45 degree angle from a position 450mm from the upper fixed end of the sample. If the burned part of the specimen does not exceed 50mm from the lower part of the fixed end, the test passes. 

◎IEC60332-3/BS4066-3 flame retardant rating (bundle wire or cable vertical burning test) 

This is the flame retardant standard for bundled cables. The test stipulates that bundled 3.5m long cable specimens shall be fixed on a trapezoidal test stand with wire, and the number of specimens shall be determined according to the non-metallic materials required for different classifications. The sample is hung vertically on the back wall of the burner and air is introduced into the burner through the air inlet on the bottom plate. The propane surface burner is contacted with the sample with a flame of 750°C. When the sample is forced to blow (air discharge 5m3/min, wind speed 0.9m/s), it must be burned within 20 minutes of vertical combustion, and the cable spreads in the flame. Within 2.5 meters self extinguishes. IEC60332 is divided into Class A, Class B, Class C and Class D to assess the flame retardant performance. 

Fire-resistant grade fire-resistant cable refers to the normal operation that can be maintained for a certain period of time in the case of flame combustion, that is, to maintain the circuit integrity. In order to assess the strength and weakness of the cable's fire resistance performance, the International Electrotechnical Commission and the British Electrotechnical Commission established two standards, IEC60331 and BS6387, respectively. In contrast, BS6387 is much higher than IEC60331 in terms of fire resistance requirements. 

◎ IEC60331 flame retardant grade Place the sample line above the gas burner and connect it to the rated voltage supply. For 3 hours of combustion, the temperature for the fire is controlled between 750°C and 800°C. After 3 hours. The fire source and the power supply were turned off. After 12 hours, the sample line had to be restarted and the integrity of the cable loop was restored. 

◎ BS6387 flame retardant test BS6387 requires horizontal burning test, water spray test and mechanical shock vibration burning test. 

Horizontal combustion experiments were A grade 650°C/3h, B grade 750°C/3h, C grade 950°C/3h and S grade 950°C/3min. Class A indicates that at 300°C, a 300 volt level is applied for 3 hours without breakdown; Class B indicates a 300 volt application at 750°C for 3 hours without breakdown; Class C indicates a 300 volt application at 950°C No puncture when burned for 3 hours; S class means applying 300V at 950°C. Level Burning for 3 minutes without breakdown Water Spray Burning Experiment Divided into Class W, indicating burning at 300V for 15 minutes and then spraying with water 15 Minutes without impact shock combustion test divided into X grade 650 °C/15min, Y grade 750 °C/15min and Z grade 950 °C/15min, X grade represents 650 °C under 300V applied while burning while mechanical shock every 30 seconds Vibration does not breakdown for 15 minutes; Y indicates that the application of 300 volts at 750 °C while the combustion side of the mechanical shock vibration every 30 seconds for 15 minutes without breakdown; Z level indicates the application of 300 volts at 950 °C while burning side of every 30 Second mechanical shock shock for 15 minutes without breakdown. The highest level model required by BS6387 is CWZ. 

Smoke Density, Halogen Content and Toxicity Grade ◎ IEC 60754-1/BS6425-1 (determining halogen gas content) 

This is a specification for the release concentration of hydrogen chloride (HCL) in the IEC and BS standards. Chlorine, Chlorine, Bromine, Iodine, and Astatine, which are highly volatile elements, are highly toxic. The experiment stipulates that when the combustion furnace is preheated to 800°C, a 1.0 g sample is pushed into the furnace and HCL is dissolved in water using the gas discharge rate, and the halogen acid content of the aqueous solution is determined. If the cable material burns when the amount of halogen acid released is less than 5mg/g, it can be called halogen-free cable (LSOH). If the amount of halogenated acid (HCL) is greater than 5mg/g and less than 15mg/g, it can be called Low-halogen cable (LSF). It is worth noting that the IEC 60754-1 method cannot be used to determine the material with an HCL content of less than 5 mg/g, ie it cannot be judged whether it is "halogen-free". The need to determine whether complete halogen free can be measured using the IEC 60754-2 method. 

◎ IEC60754-2 (Toxicity test) 

This is the specification for corrosiveness of combustion gases in the IEC standard. This test measures the acidity of the halogen acid gas produced by the material during combustion. It is determined by the pH and conductivity of the aqueous solution. The experiment stipulated that the combustion furnace was preheated to 800°C, a quartz tube with a built-in sample was pushed into the furnace, and the timing was started. The pH and electrical conductivity were measured every 1 minute for the first 5 minutes after the sample was burned, and every 5 minutes for the next 25 minutes. General halogen-free cable materials will have a pH greater than 4.3 and a conductivity of less than 10 μs. The lower the pH, the higher the acidity of the halogen acid gas of the material. It is worth noting that when the HCL content is greater than 2 mg/g and less than 5 mg/g (ie, in compliance with the requirements of IEC 60754-1), the pH of the aqueous solution is also less than 4.3, ie it does not meet the requirements of IEC 60754-2. 

◎IEC61034-1/ASTME662 (Smoke Density Test) 

This is the specification for smoke density in the IEC and ASTM standards. The experiment consists of a 3m3 cube and a photometric system with a light source. The rectangular tank contains alcohol as a combustion source. A blower with a power of 10-15m3/min ensures that the smoke is evenly distributed on a windshield to prevent flame turbulence on the groove. When the alcohol is burned, the recorder connected to the light source records the light attenuation. The smoke density is measured by light transmittance. If the light transmission value of 60% can be achieved, the cable material reaches a low smoke standard. The higher the light transmittance, the less smoke is emitted when the material is burned. 

◎ISO4589-2/BS2863 (oxygen index test) 

This is the specification for the oxygen index in the ISO and BS standards. It means that at room temperature, when the oxygen content of air is greater than this oxygen index, the material will burn immediately. The higher the oxygen index value, the more flame-retardant the material is. If the oxygen index of a material is 21%, it means that the material will burn spontaneously under normal room temperature. At normal room temperature, the oxygen content of air is 21%, and the oxygen index of general flame-retardant cables is greater than 33% to 42. %. 

◎ISO4589-3/BS2782.1 (Temperature Index Test) 

This is the specification for the temperature index in the ISO and BS standards. The oxygen index of the material will decrease as the temperature rises. When the temperature rises and the oxygen index of the material falls to 21%, the material will automatically burn. This temperature is This is called the temperature index. For example, the oxygen index of coal at room temperature is 50%, but when the temperature rises to 150°C, the oxygen index will drop to 21%, and the material will burn immediately, and the temperature index of the material is 150°C. The general flame-retardant cable temperature index is between about 250°C and 300°C. 

◎ ES713 (Toxicity Index Test) 

This is the gas toxicity specification in the United Kingdom*Engineering NES standard for the burning of cable materials. Toxicity refers to a property that causes damage or dysfunction to the structure of organisms. Toxicity index refers to the toxicity of all gases produced when the material is burned. The summation performance experiment stipulates that the combustion furnace is preheated to 800°C, the toxic materials contained in the cable material will be burned separately, and then each poisonous gas will be collected using the gas flow discharge rate, and then the content of each toxic substance will be calculated through chemical analysis. It is based on the number of its toxicity. The greater the toxicity index, the more toxic the gas released from this material. General halogen-free cable materials have a toxicity index of less than 5. It is worth noting that low-smoke halogen-free materials also produce toxic CO when burned. If the materials contain P, N, S, more toxic gases are generated, so halogen-free cables cannot be called non-toxic cables. For low toxicity cables. CM, CMR and CMP cables need to adopt strict UL fire protection standards, and the cable materials used contain halogens. CM and CMR cables generally use polyvinyl chloride (PVC) as the substrate, while PVC materials contain chlorine; CMP cables generally have special characteristics. Fluorine-polytetrafluoroethylene (FEP) is the substrate, while FEP materials contain fluorine. The halogen-generated gas produced by these halogenated cables is several times more toxic than halogen-free cables, and there are many hidden dangers in fire safety. This may cause most of the casualties of the fire scene to be not burned but suffocated by poisonous gas. 



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