Among the fires that occur every year, the fires caused by wires and cables account for a large proportion. When the fire ignites the flammable insulation and sheath materials in the wires and cables, the fire accident will further expand, and the toxic gas emitted by the burning of wire and cable insulation and sheath materials will cause Cause casualties, and hinder the firefighters to extinguish the fire. A fire may cause the power line of the firefighting equipment to be burned, which cannot ensure the normal operation of the firefighting electrical equipment, delays the firefighting time, and causes greater loss of personnel and property. The selection of wires and cables should be safe, reliable, advanced in technology, economical and reasonable, prevent fires caused by wires and cables, reduce personal casualties and property losses caused by wires and cables in fires, and ensure that the power lines of fire-fighting equipment can still maintain their Integrity, what are the commonly used wires and cables in fire distribution lines?
1. What is flame retardant wire and cable?
Flame-retardant wires and cables are wires and cables that have the ability to prevent or delay the occurrence or spread of flames, that is, under specified test conditions, the wires and cables are burned, and after the fire source is removed, the spread of flames on the wires and cables is only within a limited range and can self-extinguishing. Flame-retardant wire and cable is not a non-combustible cable, it just adds a flame-retardant material to the insulation layer and sheath layer, so that the cable will not burn in a fire, and it will self-extinguish after a period of time when the external fire source disappears.
Flame-retardant wire and cable grades are divided into four grades: flame-retardant grade I, flame-retardant grade II, flame-retardant grade III, and flame-retardant grade IV according to flame-retardant performance. Each grade is divided into A and B according to the flame-retardant sample category Class, Class C, hereinafter referred to as ZA (flame retardant class A), ZB (flame retardant class B), ZC (flame retardant class C)
2. What is fire-resistant wire and cable?
The fire-resistant wire and cable is subjected to a fire-resistant test under the specified fire source and time, and has the ability to transmit power under the specified state, that is, to ensure the integrity of the line. Fire-resistant cables can maintain the normal operation of the line for a certain period of time, and are mainly used in important occasions where normal power transmission must be guaranteed even under fire conditions.
Fire-resistant cables must use copper conductors with a rated voltage of 0.6/1.0kV and below, and their insulation layer has fire-resistant properties, otherwise a fire-resistant layer should be set on the conductor or cable core. The refractory layer is usually wrapped directly by multi-layer refractory mica tape. The mica tape is an inorganic insulating material composed of glass fiber, mica powder, and silicate. The material can be sintered into a hard and dense insulator substance attached to the surface of the conductor after being exposed to fire, so as to ensure the normal operation of the line under fire conditions.
3. What is special wire and cable?
Special wires and cables refer to special wires and cables that have the characteristics of halogen-free, low smoke, non-toxic, high temperature resistance, radiation resistance, etc., and are used in special environments or for special purposes. At present, the main products are non-toxic, low-smoke wires and cables. The toxicity released by halogen-containing cables in fire is terrible.
If the toxicity of the gas concentration that can cause death in 30 minutes is judged as 1, then the toxicity index of polyvinyl chloride is 15.01, and the toxicity index of halogen-free polyolefin is 0.79. In the event of a fire, the intense, diffuse smoke disorients the victim and prolongs the time spent in the fire.
4. Classification of combustion characteristics of flame-retardant and fire-resistant wires and cables
According to the combustion characteristics of wires and cables, they can be divided into ordinary wires and cables, flame-retardant wires and cables, fire-resistant wires and cables, non-combustible wires and cables (mineral insulation), special wires and cables, etc. Ordinary wires and cables use organic materials as insulating layers and sheath tubes, which are easy to catch fire and spread in flames, and do not have the characteristics of flame retardancy, fire resistance, halogen-free and low smoke.
When ordinary wires and cables are used as distribution lines for fire-fighting electrical equipment, they should be laid in a non-combustible structure with the thickness of the protective layer not less than 30mm. This is the most common practice at present. Non-combustible wire and cable is also called mineral insulated wire and cable. It is usually a cable composed of copper core, copper sheath and magnesium oxide insulation and other all-inorganic materials. It has non-combustible, non-toxic and smoke-free properties in flames.
5. Misunderstandings about flame-retardant and fire-resistant wires and cables
The selection of flame-retardant and fire-resistant wires and cables in fire protection regulations is mostly principled and suggested, which is too simple and general. In addition, there are many types of flame-retardant and fire-resistant wires and cables, and the performance and labels of different manufacturers are different. Designers have many misunderstandings about flame-retardant and fire-resistant wires and cables.
The selection of flame-retardant and fire-resistant wires and cables must be flame-retardant. In actual engineering, if qualified flame-retardant wires and cables cannot be selected according to the specified flame-retardant level, the flame-retardant wires and cables may not necessarily be flame-retardant.
6. Common situations are: the flame retardant level does not meet the requirements, and the non-metallic content exceeds the standard; the flame retardant cable and the non-flame retardant cable are laid in the same pipeline; High-quality flame-retardant cables cannot achieve flame-retardant effects.