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Combustion properties vary greatly; not all plastics are easy to ignite and burn violently. There are many types of plastics, and their combustion properties vary. Specifically, the flammability of plastics is usually related to the elements contained in the main carbon chain molecules in their molecular structure. Plastics containing hydrogen and carbon, such as polyethylene and polypropylene, are flammable, but they do not burn very intensely and have a slow burning rate. Oxygen-containing plastics, such as polymethyl methacrylate (i.e., plexiglass), celluloid (also known as nitrocellulose plastic), and polystyrene, are highly flammable and burn violently. Nitrogen-containing plastics, such as nylon, melamine, and formaldehyde resins, are generally not flammable and do not burn easily. But polyurethane is an exception, as its foams are flammable. Plastics containing chlorine (or bromine), such as polyvinyl chloride, will soften when exposed to fire without the use of plasticizers, emit white smoke, and extinguish slowly after being removed from the heat source. However, in a fire, polyvinyl chloride can continue to burn. Soft PVC containing plasticizers (whose main component is polyvinyl chloride) has poorer self-extinguishing properties than rigid PVC. It should be noted that self-extinguishing does not mean non-flammable. Fluorinated plastics are commonly used for lining chemical equipment, as high-frequency and high-temperature electrical insulators, in bearing lubricants, and as coatings for cooking utensils. Materials such as polytetrafluoroethylene are actually non-flammable, but they release toxic gases when overheated. The combustion products depend on the type of plastic. Generally, plastic combustion products are related to the type of plastic and the nature of the groups contained in its main carbon chain. In fires, the combustion products of plastics mainly include smoke, toxic gases, flammable gases, and burning molten droplets. Smoke – materials such as polystyrene and polyurethane foam produce large amounts of smoke when burned in a fire. The smoking behavior of plastics is as follows: most types of plastics undergo thermal decomposition, producing dense smoke. Ventilation can help remove some of this smoke, but it cannot significantly reduce its concentration ； Some combustible polymers emit smoke under hot conditions and in flames, but at low concentrations ； Urea-formaldehyde foam plastic produces thick smoke whenever it is heated, whether in the presence of a flame or not, and the spread of this smoke is very rapid. Toxic gases: Under fire conditions, the burning of any plastic produces toxic gases, with carbon monoxide being the main toxic component. When certain types of plastic burn, in addition to producing carbon monoxide, they also generate other gases; when these gases mix with carbon monoxide, their toxicity increases. Plastics with different chemical compositions produce different types of toxic gases when burned: plastics whose main components are carbon, hydrogen, or carbon, hydrogen, and oxygen generate carbon monoxide as a toxic gas; this gas is the most dangerous when the fire is intense ； Nitrogen-containing plastics, such as melamine formaldehyde and polyurethanes, produce carbon monoxide, nitrogen oxides, and hydrogen cyanide when burned; this mixture of gases is highly toxic ； Chlorine-containing plastics, such as polyvinyl chloride, produce hydrogen chloride when exposed to flames or excessive heat; at certain concentrations, this gas can be fatal ； Fluorinated plastics, such as polytetrafluoroethylene, release hydrogen fluoride gas when exposed to fire or excessive heat; this gas is corrosive and toxic. Burning droplets: Under normal circumstances, only thermoplastic products melt and flow when heated, producing combustible droplets, while thermosetting plastic products do not produce droplets when burning – with the exception of polyurethane foam. The appearance of burning droplets accelerates the spread of the fire, affecting both safe evacuation and firefighting efforts. The burning of molten droplets can lead to two outcomes: either the plastic melts and flows out of the flame zone, preventing further combustion, or the droplets burn and produce tar-like droplets. The latter outcome is more likely to occur. Flammable gases: These are flammable gases present in the products of plastic combustion or thermal decomposition, such as carbon monoxide and hydrogen cyanide. Mixtures of these gases with air can burn or explode under appropriate conditions; changes in the oxygen concentration in a fire scene can lead to more intense burning or explosions. Fire fighting follows certain principles. Apart from cellulose nitrate, plastics are ordinary flammable materials; their storage category is Class C or Class D. Therefore, the methods used to extinguish fires involving wood and other common flammable materials (Class A fires) can also be applied to extinguish plastic fires. After a fire breaks out in the production workshop and finished goods warehouse of a plastic products factory, firefighting can be carried out according to the following principles. For fires involving ordinary plastic products, the method of using a strong stream of direct water to extinguish the fire can be employed. By using this method, in addition to reducing the surface temperature of the burning plastic, it is also possible to prevent the plastic from melting or producing burning droplets; this avoids such droplets from igniting other items and causing the fire to spread, which could result in injuries to people. While extinguishing the fire, care should be taken to move the unburned plastic products. Control the fire and prevent it from spreading. The water gun position should be located upwind and at the side wind. When plastics burn, they produce large amounts of smoke and toxic gases; if it is necessary to enter the smoke-filled area to extinguish the fire, firefighters should wear gas masks. Prevent burning molten droplets from falling and injuring people. When extinguishing fires in areas where burning molten droplets may be present, firefighters should take protective measures in advance.