For the material itself, people have been trying to improve the flame retardancy of materials, thereby reducing the possibility of fire risk. Flame retardancy of materials refers to the property of preventing, slowing down or stopping the combustion of combustible materials after being treated by special methods. The object of fire prevention is through some way, so that flammable objects will not be damaged rapidly when heated by fire.
It can be seen that the object of flame retardant is the material itself. The object of fire protection is other objects that need to be protected, such as by coating the steel surface with a layer of flame retardant coating to achieve steel fire protection. This shows that flame retardant and fire prevention are not the same thing.
Flame retardant in the process of burning the following effect to make the object to achieve flame retardancy: (1) capture free radicals; (2) absorption of heat; (3) coverage; (4) dilution; (5) dehydrating carbonization.
Brominated flame retardants are one of the largest flame retardants in the world at present. The main mechanism is to decompose rapidly at lower temperatures in the early stage of fire and quickly capture the free radicals H and HO in the combustion reaction, thus having high flame retardancy efficiency。
Polystyrene foamed plastics generally add brominated flame retardants. The decomposition temperature of this kind of flame retardant is about 200 degrees. The foam plate can not burn (and may burn) due to the effect of the flame retardant under the initial fire source, but after melting the oil, the combustible agent has been exhausted and does not have the flame retardancy. .
The combustion heat of polystyrene is 40.18kJ/g, which belongs to high combustion heat, with a flame temperature of up to 2210 degrees. The temperature and heat continuously process polystyrene around the flame. With the continuous expansion of the combustion range, many sundries may become the wick. The fire grew more and more, and gradually turned into a fire.
Thermosetting modified EPS is a single EPS particle coated with fireproof material and molded into lump sheet. The thermosetting modified EPS, after being attacked by the external fire source, first melts and even burns the EPS particles, but each particle melts in its own particle space, the volume is about the original 1/50, is absorbed by its fireproof material, and does not form a large amount of oil, and it can not cause the propagation of the flame. More importantly, the generated honeycomb inorganic substances not only prevent flame and heat transmission, but also prevent contact between air and adjacent foam. After the external finite fire source affects a certain depth, the combustion can not go further due to the lack of sufficient temperature and oxygen.
To sum up, the thermosetting EPS produces a certain thickness of honeycomb like inorganic material under the action of the limited external fire source, isolating the air and the external fire source, thus ending the combustion reaction. This is a typical fire protection structure from the microscopic level.
On the microcosmic point of view, the burning of most of the combustible material is not the combustion of the substance itself, but the combustion of the vapour in the gas or the liquid that is decomposed by the heat of the matter. If an object has a fireproof function, such as a composite plate, a heat source (such as a welding spark or slag) has a limited duration of heat, it can't quickly heat the flammable material through the inorganic material to reach the decomposition temperature, and it can not cause the combustion.
From the perspective of oxidants, the inorganic material layer of the composite board effectively cuts off the air. For example, the composite insulation board of 1200mm*600mm*30mm, covering an area of 1.44 square meters, accounts for 93% of the surface area, and the organic heat insulation board after the package almost does not contact with the air, and the combustion is almost impossible under the effect of welding and other small fire sources.
As a special composite plate, the heat preservation and decoration integrated system accounts for 5% of the external wall thermal insulation system. It has more than ten years of experience in engineering application. From the search results of Baidu, there are almost no reports of fire. It shows that the fireproof structure of the composite plate is effective. This is a successful example of a typical meso fire protection structure.
In the new design code for building fire protection in People's Republic of China, the first layer plastering thickness of the B1 level insulation material is 15mm, the other layers are not less than 5mm, and each layer is required to make a ring of fire isolation belt. Through the plastering layer, the inorganic fireproof isolation belt and the inorganic base wall, the 360 degree covers the surface of the organic heat insulation board, isolating the contact between the air and the insulation board so that the combustion can not be continued. Of course, when the external fire source is relatively large, it is necessary to have enough stability for the cover layer to be effective for a certain time, so the thickness of the plastering layer is required. This is the macro fire protection structure.