In case of fire, the PVC mixture is easy to decompose and escape a large amount of highly toxic and corrosive HCl gas after heating, which will produce a large amount of highly toxic smoke, which will cause great loss of life and property and bring great difficulties to rescue work. In order to avoid and reduce the fire and the secondary damage caused by the fire ten years later, a large number of studies have found that change can effectively solve the problem in the outer layer of the material and process used in the product.
The main characteristic of halogen-free low smoke flame retardant wire and cable is that the amount of smoke released during combustion is very small, and all materials do not contain halogen. In a fire, the discharge of toxic substances in the cable is terrible. The toxicity index of PVC and halogen-free polymer is 15.01 and 0.79 respectively if the toxicity of the concentration of gas that can cause death is determined as 1 at 30 minutes. In case of fire, there is fierce debate over the direction of the victims, thus prolonging the retention time in the fire. According to the relevant data, when the light transmittance is 70%, the human naked vision ability to distinguish objects is only about 5 m. the light transmittance of the smoke emitted during the combustion of 15% PVC is less, that is, the smoke that people smoke here is only about 2 m, and the distance between naked eyes is about 2 m. Another feature of this kind of smoke is that it propagates abnormally fast together with the hot air flow, reaching a speed of more than 20 m / min. Therefore, the key to the safety of using LSZH wires and cables is to ensure. This section is quoted from code for fire protection of wires and cables of civil buildings (dgj08-93-2002j10166-2002).
For this reason, advanced countries in the world have launched halogen-free flat wire flame retardant materials and alternative production of PVC, as well as the formulation of relevant standards, civil wires in Europe and Japan are fully promoted. China has also formulated corresponding standards, such as GB / t19666-2005 "general rules for flame retardant and fire resistant wires and cables" GA306. 1-2001 "flame retardant and fire-resistant cables: classification and requirements of plastic insulated and fire-resistant cables", JB / t10491-2004 "XLPE insulated wires and cables with rated voltage of 450750V and below", and Shanghai has formulated series of standards such as "code for engineering construction" (dgj08-93-2002j10166-2002). Low smoke and halogen-free cables have been widely used in airport, subway, large-scale buildings and government projects 。