In the buildings with thick smoke and flames, people outside dare not enter, and people inside cannot escape, except for one kind of people, that is, firefighters. They can rush into the smoky and burning buildings and rescue residents from death.
Firefighters are also human. Why can they walk through the fire site that ordinary people can't enter? The important reason is the special clothes they wear - fire fighting clothes. Fire fighting clothing has many special functions, such as fire prevention, heat resistance, waterproof and ventilation, resistance to the corrosion of chemical substances such as acid and alkali, and also has a certain anti-static effect. Moreover, the generous and thick fire clothes can also ensure that firefighters are comfortable and flexible. What is the secret of such a special fire suit?
Modern firefighters do not wear single-layer clothes, but are divided into several layers: the outermost reflective layer, the middle waterproof layer, the inner thermal insulation layer, etc.
The reflective layer of the fire suit is actually a metal aluminum coating on the surface of the clothes. It is this thin metal coating that can reflect most of the heat radiation in the fire scene. PTFE [(c2f4) n] is usually used as the waterproof layer of Fire clothing. This is a kind of plastic with excellent performance. It will not be soaked or expanded in water.
Moreover, it can also withstand the extreme low temperature of - 269.3 ℃ and the high temperature of 250 ℃, and is not afraid of strong acids and concentrated alkalis. Even aqua regia, which is particularly corrosive, has nothing to do with it. In addition, polytetrafluoroethylene has good dielectric properties, which is neither affected by electromagnetic frequency nor changed with temperature. Therefore, it has won the reputation of "king of plastics".
The insulation layer inside the fire suit is also very important. It is usually made of flame retardant fiber. This is a kind of synthetic fiber, which has two characteristics: high temperature resistance and strong flame retardancy. The synthetic fiber commonly used in the thermal insulation layer of Fire clothing is aromatic polyamide fiber, also known as aramid fiber. Its molecules contain amide groups and benzene rings composed of acyl and imino groups. If the position of amide group in benzene ring is in meta position (i.e. meta aramid), the covalent bond of benzene ring has no conjugation effect and is easy to move freely. Therefore, the macromolecular chain presents a flexible structure and the chemical structure is particularly stable. When the temperature of meta aramid fiber exceeds 400 ℃, its surface fiber will carbonize. This layer of coke can play a continuous heat barrier role, so as to delay the carbonization speed of fiber and play an excellent heat defense effect.
Other synthetic fibers, such as polyester, acrylic and vinylon, can also be made flame retardant by adding flame retardant. Most flame retardants are compounds with phosphorus as the central element. Its function is to decompose into nonvolatile glassy substances at the combustion temperature, wrap them on the surface of fiber polymers and form a dense protective layer to achieve the purpose of flame retardancy.
It is with the layers of protective "shields" of reflective layer, waterproof layer and thermal insulation layer that firefighters can rush into the fire site and rescue people without hesitation.