Fire-rated cable has been a very popular product type in the cable industry, third-party testing of fire-rated cable performance verification has a crucial role, TSTCABLES share with you about fire-rated cable flame retardant classification and related standards.
Fire-resistant cable, that is, under the specified test conditions, the specimen is burned, after the withdrawal of the test fire source, the spread of the flame is only within the limits of the residual flame or residual burning in the limited time to extinguish the cable, in the event of a fire, there is a possibility of being burned and can not be operated, but the spread of the fire can be prevented. In layman’s terms, the wire in case of fire, the ability to limit the combustion to a localized range, does not produce the spread, save a variety of other equipment, to avoid causing greater losses. At present, the cable industry is accustomed to flame retardant (Fire Retardant), halogen-free low smoke (Low Smoke Halogen Free, LSOH) or low halogen low smoke (Low Smoke Fume, LSF), fire-resistant (Fire Resistant) and other cables with a certain degree of fire resistance collectively referred to as fire-resistant cables. So what is the difference between these four types of fire cables? Let’s take a brief look.
First, the classification of fire-resistant cable
Flame Retardant Cable (Flame Retardant)
Flame retardant cable is characterized by delaying the spread of flame along the cable so that the fire does not expand. Because of its low cost, it is a large number of fire-resistant cable cable varieties used. Whether it is a single cable or a bundle of laying conditions, the cable is burned when the spread of flame can be controlled within a certain range, so you can avoid major disasters caused by the cable fire retardant, thus improving the fire level of the cable line.
Halogen-free, low-smoke, flame-retardant cables (LSOH)
Halogen-free low-smoke cable is characterized not only by excellent flame retardant properties, and constitute a low-smoke halogen-free cable materials do not contain halogen, low corrosion and toxicity of combustion, resulting in a very small amount of smoke, which reduces the human body, equipment and instruments damage, and is conducive to the occurrence of a fire in a timely manner to the rescue. Although halogen-free low-smoke flame retardant cables have excellent flame retardancy, corrosion resistance and low smoke concentration, their mechanical and electrical properties are slightly worse than ordinary cables.
Low Halogen Low Smoke Flame Retardant Cable (LSF)
Low Halogen Low Smoke Flame Retardant Cable has hydrogen chloride release and smoke concentration indicators between flame retardant cables and halogen-free low smoke flame retardant cables. Low Halogen (Low Halogen) cables also contain halogens in the material, but the content is lower. This type of cable is characterized not only by flame retardant properties, but also in the combustion of the smoke released is less, the release of hydrogen chloride is lower. This low-halogen, low-smoke flame-retardant cable is generally made of polyvinyl chloride (PVC) as the base material, and then processed with high-efficiency flame retardants, HCL absorbers and smoke suppressants. Therefore, this flame retardant material significantly improves the burning performance of ordinary flame retardant PVC materials.
Fire Resistant Cables
Fire-resistant cable is in the flame burning situation can maintain normal operation for a certain period of time, can maintain the integrity of the line (Circuit Intergrity). Fire-resistant cable combustion produced by the amount of acid gas smoke is small, fire-resistant and flame retardant performance is greatly improved, especially in the combustion, accompanied by water spray and mechanical strike vibration, the cable can still keep the line running intact.
Second, the difference between flame retardant cables and fire-resistant cables
The general public is very easy to confuse the concept of flame retardant cables and fire-resistant cables, although flame retardant cables have many advantages that are more applicable to the chemical industry, such as low-halogen, low-smoke fire-retardant, etc., but in general, fire-retardant cables can be used to replace the flame retardant cables, while flame retardant cables can not be replaced by fire-retardant cables.
The two principles are different, halogenated cable flame retardant principle is to rely on the halogen flame retardant effect, halogen-free cable flame retardant principle is to rely on the precipitation of water to reduce the temperature to extinguish the fire roasting. Fire-resistant cables rely on the fire-resistant layer of mica materials in the fire-resistant, heat-resistant properties to ensure that the cable in the fire also work properly.
The two structures and materials are different, the basic structure of fire-retardant cable is: insulation layer using fire-retardant materials; sheath and outer jacket using fire-retardant materials; wrapping and filling with fire-retardant materials.
The fire-resistant cable is usually between the conductor and insulation layer and then add a fire-resistant layer, so theoretically you can add a fire-resistant layer in the structure of the fire-retardant cable, the formation of both fire-retardant and fire-resistant cables, but in practice there is no need for this. Because the fire-resistant cable fire-resistant layer, usually using multi-layer mica tape directly wrapped around the wire. It can withstand prolonged combustion, even if the polymer is burned at the applied flame, but also to ensure the normal operation of the line.
The fire-resistant cable is usually between the conductor and insulation layer plus a fire-resistant layer, so theoretically you can add a fire-resistant layer in the structure of the flame-retardant cable, the formation of both flame-retardant and fire-resistant cables, but in practice there is no need for this. Because the fire-resistant cable fire-resistant layer, usually using multi-layer mica tape directly wrapped around the wire. It can withstand prolonged combustion, even if the polymer is burned at the applied flame, but also to ensure the normal operation of the line.
The main technical indicators of fire safety for cables are the flame resistance of CO 2 cables, the density of smoke and the toxicity of gases. Based on the above factors to develop the cable flame retardant standard system includes IEC standards, UL standards, etc., we come together to understand what are the important provisions of the level contained therein.
Third, the fire cable standards
1, fire cable IEC standards
In order to assess the cable’s flame retardant performance, the International Electrotechnical Commission formulated IEC60332-1, IEC60332-2 and IEC60332-3 three IEC standards, IEC60332-1 and IEC60332-2 were used to assess the single cable according to the tilt and vertical deployment of flame retardant capacity (the domestic counterpart of GB12666.3 and GB12666.4). IEC60332-1 and IEC60332-2 are used to assess the flame retardancy of single cables when they are arranged in an inclined and vertical position respectively (GB12666.3 and GB12666.4 in China). In contrast, the requirements for vertical burning of bundled cables are much higher in terms of flame retardancy.
IEC60332-1/BS4066-1 Flame Retardant Rating (Flame Test On Single Vertical Insulated Wires/Cables)
This is a standard for the flame retardancy of single cables. Test provisions, a 60cm long specimen fixed vertically in the front wall of the opening of the metal box, flame length of 175mm propane burner from the upper part of the specimen from the fixed end of the position of 450mm on the flame cone and the cable at an angle of 45 degrees in contact with the specimen if the specimen burns damaged part of the distance from the fixed end of the lower part of the test is not more than 50mm, the test passes.
IEC60332-3/BS4066-3 Flame Retardant Rating (Flame Test On BunchedWires/Cables)
This is a flame retardant standard for bundled cables. The test specifies that a bundle of 3.5m long cable specimens are fixed with wire in a trapezoidal test frame, and the number of specimens is determined by the non-metallic materials required for different classifications. The specimens are hung vertically on the back wall of the combustion furnace, and air is introduced into the combustion furnace through the air inlet on the bottom plate. Propane plane burner to 750 ℃ flame and specimen contact, the specimen in the mandatory blowing (air emissions 5m3 / min, wind speed 0.9m / s), must be in the vertical combustion within 20 minutes of combustion does not come up, the cable in the flame spread 2.5 meters within the self-extinguishing. iec60332 has a class A, B, C and D class points to assess the merits of flame retardant properties.
2、Fire-resistant cable UL standard
UL listed any cable after testing and verification if it meets a certain fire rating, can be printed on the cable UL identification word, fire rating and approval number.
Booster level – CMP level (air supply combustion test / Steiner sodium duct test Plenum FlameTest / Steiner TunnelTest)
This is the highest requirement of UL fire safety standards in the cable (Plenum Cable), the applicable safety standards for UL910, the test provides for the laying of a number of specimens in the device on the horizontal duct, with 87.9KW gas Bunsen burner (300,000 BTU / Hr) for 20 minutes. The qualifying criterion is that the flame must not extend more than 5 feet beyond the front of the Gas Bunsen burner flame. Optical density has a maximum peak value of 0.5 and a maximum average density value of 0.15. These CMP cables are typically installed in air return pressurization systems used in ventilation ducts or air handling equipment and are approved for use in Canada and the United States. FEP/PLENUM materials conforming to UL910 have better flame retardancy and lower smoke concentrations than low-smoke, halogen-free materials conforming to IEC60332-1 and IEC60332-3.
Trunk grade – CMR grade (Riser Flame Test)
Trunking Class-CMR (Riser Flame Test)
This is a UL standard for commercial grade cable (Riser Cable), applicable safety standard UL1666, the test specifies that multiple specimens are laid on a simulated upright shaft with a prescribed 154.5KW gas Bunsen burner (527, 500 BTU/Hr) for 30 minutes. The qualifying criterion is that the flame must not spread to the upper portion of a room 12 feet high. Trunking grade cable has no smoke concentration specification and is typically used for vertical and horizontal wiring use on floors.
Commercial Grade – Class CM (Vertical Tray Flame Test)
This is UL’s standard for Commercial Grade Cable (General Purpose Cable), which is governed by safety standard UL1581. The test involves laying multiple specimens on a vertical 8-foot-high support and burning them for 20 minutes with a prescribed 20KW strip torch (70,000 BTU/Hr). The passing standard is that the flame must not spread to the upper end of the cable and extinguish itself.UL1581 is similar to IEC60332-3C, except that the number of cables laid is different. Commercial grade cables do not have a smoke concentration specification and are generally only used for horizontal routing on the same floor, not for vertical routing on the floor.
General Purpose Class – CMG Class (Vertical Tray Flame Test)
This is the UL standard for General Purpose Cable (General Purpose Cable), and the applicable safety standard is UL1581. Commercial grade and General Purpose Cable have similar test conditions, and are recognized for use in both Canada and the United States. General Purpose Cable does not have a smoke concentration specification and is generally only used for horizontal wiring on the same floor, not vertical wiring on the floor.
Household Class – CMX Class (Vertical Wire Flame Test)
This is the UL standard for household grade cable (Restricted Cable), the applicable safety standards for UL1581, VW-1. The test specimen is required to be kept vertical and burned (30,000 TU/Hr) for 15 seconds with the test torch, then stopped for 15 seconds and repeated 5 times. Passing criteria are that the residual flame must not exceed 60 seconds, the specimen must not be burned more than 25%, and the surgical cotton padded on the bottom must not be ignited by falling objects.UL1581-VW-1 is similar to IEC60332-1, except that the burning time is different. This rating also has no smoke or toxicity specification and is intended for use only in home or small office systems where a single cable is laid. These cables should not be used in bundles and must be sleeved. Smoke density, halogen content and toxicity levels.
3、Fire-proof cable other standards
IEC60754-1/BS6425-1 Determination of halogen gas content (Emission Of Halogens)
This is the IEC and BS standards for hydrogen chloride (HCL) release concentration specification. Halogens contain fluorine, chlorine, bromine, iodine and the radioactive volatile element astatine, which are highly toxic. Experimental provisions, combustion furnace preheated to 800 ℃, a built-in 1.0 g sample pushed into the furnace, the use of air emission rate so that HCL dissolved in water, and then determine the halogen acid content of the aqueous solution. If the cable material combustion halogen acid (HCL) release less than 5mg / g, can be called halogen-free cable (LSOH), if the halogen acid (HCL) release more than 5mg / g but less than 15mg / g, can be called low-halogen cable (LSF). It is worth noting that the IEC60754-1 method can not be used to determine the HCL content of less than 5 mg / g of material, that is, can not determine whether the “halogen-free”. If you need to determine whether it is completely halogen-free, you can use IEC60754-2 method to determine.
IEC60754-2 Gas Acidity Measurement (Corrosivity)
This is a specification in the IEC standard for the corrosivity of combustion gases. The test measures the acidity of the halogenated acid gases produced by the material during combustion. It is determined by the pH value and electrical conductivity of an aqueous solution. The test specifies that the combustion furnace is preheated to 800°C, a quartz tube with a built-in specimen is pushed into the furnace, and a time clock is started. The PH value and electrical conductivity are measured every 1 minute for the first 5 minutes of combustion, and every 5 minutes for the next 25 minutes. Generally, the PH value of halogen-free cable materials will be greater than 4.3, and the electrical conductivity is less than 10μs; the lower the PH value, that is, the higher the acidity of the material’s halogenated acid gas. It is worth noting that when the HCL content is greater than 2mg/g and less than 5mg/g (i.e., in line with the requirements of IEC60754-1), the PH value of its aqueous solution is also less than 4.3, that is, it does not meet the requirements of IEC60754-2.
IEC 61034-1/ASTM E662 Emission of Smoke
This is the specification for smoke density in the IEC and ASTM standards. The experiment consists of a 3 m3 cube and a photometric system with a light source, the rectangle containing alcohol as a combustion source. A blower with a power of 10-15 m3/min ensures that the smoke is uniformly distributed over a windshield to prevent flame eddies on the trough, and a recorder connected to the light source notes the amount of light attenuation as the alcohol burns. Smoke density is measured in terms of light transmittance and if a light transmittance value of 60% can be achieved the cable material meets the low smoke standard, the higher the light transmittance the less smoke is released when the material burns.
ISO4589-2/BS2863 Oxygen Index (Oxygen Index LOI)
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 the 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 automatically at normal room temperature. At normal room temperature, the oxygen content of the air is 21%, and the oxygen index of general flame retardant cables is more than 33%.
ISO4589-3/BS2782.1 Temperature Index (Temperature Index TI)
This is the ISO and BS standard for the temperature index of the specification, the oxygen index of the material will fall with the temperature, when the temperature rises and the oxygen index of the material falls to 21%, the material will automatically burn, the temperature is known as the temperature index. For example, the oxygen index of coal at room temperature is 50%, but when the temperature rises to 150℃, the oxygen index will drop to 21%, and the material will burn immediately, and the temperature index of the material is 150℃. The temperature index of the material is 150℃. Generally, the temperature index of flame retardant cables is more than 250℃.
NES713 Toxicity Index (Toxicity Index)
This is the British naval engineering NES standard for cable materials for the combustion of gas toxicity specifications, toxicity is the structure of the organism caused by the destruction or dysfunction of a nature, toxicity index refers to the material combustion of all the gases produced by the toxicity of the total sum performance. The experiment stipulates that the combustion furnace is preheated to 800 ℃, the toxic substances contained in the cable material will be burned separately, and then use the airflow emission rate to collect each toxic gas, and then through chemical analysis to calculate the content of each toxic substance, this index is expressed in number of its toxicity. The greater the toxicity index, the higher the toxicity of the gases released by the material. Generally, the toxicity index of halogen-free cable materials are less than 5. It is worth noting that low-smoke halogen-free materials will also produce toxic CO when burned, if the material contains P, N, S, the generation of toxic gases is more, so halogen-free cables can not be called non-toxic cables, it should be called low-toxicity cables CM, CMR and CMP cables need to be through the stringent UL fire safety standards, the use of the cable material contains more halogen CM, CMR and CMP cables need to pass the strict UL fire safety standards, the cable materials used mostly contain halogens, CM and CMR cables are generally based on polyvinyl chloride (PVC), which contains chlorine; CMP cables are generally based on Teflon polytetrafluoroethylene (FEP), which contains fluorine. The toxicity of the gas produced by such halogen-containing cables is several times greater than that of halogen-free cables, which poses a great risk to fire safety and may lead to the death of most casualties at the fire scene, who are not burned to death but asphyxiated by the poisonous gas.
With China’s electric power industry, data communications industry, urban rail transportation industry, automotive industry and shipbuilding and other industries continue to expand the scale of the demand for wire and cable will continue to grow rapidly, the future of the wire and cable industry has great potential for development, and a full understanding of the wire and cable fire retardant standards and ratings for the relevant industry has become increasingly important.If you need high quality fire retardant cables, please feel free to contact us by email.
