Flammability of the hottest plastics and fire figh

2022-09-20
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Flammability of plastics and fire fighting principles

flammability of plastics and fire fighting principles

on the afternoon of July 17, 2008, a fire broke out in the plastic workshop of a plastic products factory in Shanghai. Three firefighters died in the fire fighting and rescue, and nine firefighters paid attention to the process and personnel were injured. The smoke generated by the fire was at least 10 kilometers away, up to 1 kilometer high, and accompanied by a strong smell of burning plastic. There were serious hidden dangers in the building structure of the plastic workshop of the factory. A 50 meter long main beam suddenly collapsed and pressed on three firefighters who were fighting the fire, causing three people to die on the spot. At 16:00 on the same day, dense smoke was still emitted from the scene

although many people were injured in this accident, the tragedy of the issuance price of 6.83 yuan/share was not directly caused by the fire, this accident also sounded an alarm for people. At present, plastics are widely used in production and life. In the work of fire protection, a person in charge of the enterprise said that plastic production enterprises should not only face some old problems (such as toxic smoke generated after the plastic fire), but also solve some new problems (such as tar or combustion droplets generated by combustion), so it is necessary to understand the combustion performance of plastics and how to put out plastic fires

first, the combustion performance varies greatly

not all plastics are easy to catch fire and burn violently. There are many kinds of plastics with different combustion properties. Specifically, the combustion performance of plastics is usually related to the elements contained in the main carbon chain molecules in its molecular structure

plastics containing hydrogen and carbon, such as polyethylene and polypropylene, are easy to burn, but they burn less violently and burn slower

oxygen containing plastics, such as polymethylmethacrylate (i.e. plexiglass), nitrocellulose (also known as nitrocellulose plastic), polystyrene, etc., are very easy to catch fire and burn violently

nitrogen containing plastics, such as nylon, melamine and formaldehyde resin, are usually not easy to catch fire and burn. However, polyurethane is an exception. Its foam is easy to burn

plastics containing chlorine (or bromine), such as polyvinyl chloride, will soften and emit white smoke when burning in case of fire without plasticizer, and will be extinguished slowly after leaving the fire source. However, PVC can continue to burn in a fire. The self extinguishing property of soft PVC (mainly PVC) containing plasticizer is worse than that of hard PVC. Having self extinguishing property does not mean non combustion, which should be paid attention to

fluoroplastics are commonly used in chemical equipment linings, high-frequency and high-temperature electrical insulation materials, bearing lubrication materials and cooking utensils coatings, such as polytetrafluoroethylene. This material is actually non combustible, but it will release toxic gases if overheated

second, the combustion products are related to the types of plastics

generally speaking, the combustion products of plastics are related to the types of plastics and the properties of the groups contained in the main carbon chain. In fire, plastic combustion products mainly include smoke, toxic gases, combustible gases and combustion droplets

smoke, such as polystyrene and polyurethane foam, will quickly produce a large amount of smoke when burned in a fire. The smoking law of plastics is as follows: most kinds of plastics will be thermally decomposed and produce very thick smoke. Ventilation can drive away part of the smoke, but can not significantly reduce the smoke concentration; Some combustible polymers will smoke under hot conditions and in flames, but the concentration is low; Urea formaldehyde foam can produce thick smoke as long as it is heated, whether there is flame or not, and it spreads rapidly

toxic gas under fire conditions, any plastic combustion will produce toxic gas, and its toxic component is mainly carbon monoxide. In addition to carbon monoxide, the combustion of some kinds of plastics also produces other gases, which are more toxic when mixed with carbon monoxide. The types of toxic gases produced by burning plastics with different chemical compositions are different: the toxic gas produced by burning plastics with carbon, hydrogen or carbon, hydrogen and oxygen as the main constituent elements is carbon monoxide, which is the most dangerous when the fire is fierce; Nitrogen containing plastics, such as melamine, formaldehyde and polyurethane, can produce carbon monoxide, nitrogen oxide and hydrogen cyanide when burned. This mixed gas is extremely toxic; Chlorine containing plastics, such as polyvinyl chloride, will produce hydrogen chloride in the flame or over heating, which will cause death when reaching a certain concentration; Fluorine containing plastics, such as polytetrafluoroethylene, will produce hydrogen fluoride gas in fire or over heating, which is corrosive and toxic

burning droplets generally, only thermoplastic products melt and flow when heated to produce combustible droplets, while thermosetting plastic products do not produce droplets when burned, with the exception of polyurethane foam. The emergence of combustion droplets will accelerate the spread of the fire and have an impact on the safe evacuation and fire extinguishing. Burning droplets may bring two results: one is that the plastic melts and flows out of the flame area to prevent re combustion, and the other is that droplets burn and produce tar like drops. The latter result is more likely to occur

combustible gas plastic combustion setting this parameter mainly takes into account that when different frequencies are input, the combustible gases in the combustion or thermal decomposition products, such as carbon monoxide, hydrogen cyanide and other mixtures with air, will burn or explode under appropriate conditions. When the oxygen concentration in the fire site changes, it can lead to more violent combustion or explosion

III. fire fighting follows certain principles

except for nitrocellulose, plastic belongs to ordinary combustible materials, and the storage category belongs to class C and class D. therefore, the method applicable to the fire fighting of wood and other ordinary inflammables (class a fire) is also applicable to the fire fighting of plastics. In case of fire in the production workshop and finished product warehouse of the plastic products factory, the following principles can be followed to put out the fire

for the fire of general plastic products, the method of strong direct water impact can be used to extinguish the fire. In addition to reducing the surface temperature of the burning plastic, this method can also avoid the melting of the plastic or the generation of burning droplets, so as to prevent the burning droplets from igniting other objects, spreading the fire and burning people

while extinguishing the fire, attention should be paid to transferring the unburned plastic products

control the fire and prevent it from spreading

the water gun position should be set in the upwind and crosswind directions

a large amount of thick smoke and toxic gas will be produced when plastic is burned. If it is necessary to enter the smoke area when extinguishing fire, fire fighters should wear gas masks

prevent burning droplets from dripping and hurting people. When putting out fire in places where there may be burning droplets, the firefighters should take protective measures in advance

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