The thermoplastics tend to be flammable. Combustible materials (fuel), oxygen, and spark sources are all necessary for the process of fire. Fire is a gas phase reaction in which high-energy combustible free radicals are made combining oxygen and the fuel to continue the fire cycle and can spread in a few minutes if plastics are not made to retard this process. Essentially, any or all of these elements must be influenced for the fire to stop or to get retarded, and that is exactly what the flame retardants do in plastics.
Plastics is used in many industries, such as textiles, furnishings, electrical and electronic switchgear and appliances, building, construction to name a few. This is the reason it must be formulated in a way that it can extinguish or retard the spread of heat, toxic gases, flame and smoke in case of fire. It allows people to safely evacuate from the vicinity of a fire, and minimizes the possibility of property damage and building damage.
Plastics contain flame retardants to strengthen their resistance to ignition, reduce the spread of flames, and prevent dripping which can increase the flammability of the material. To achieve these objectives, they use various chemistries to react with fire either chemically or physically. For instance, brominated flame retardants and synergists together trap the high energy gaseous free radicals to prevent the fire cycle to propagate and spread, nitrogen-based and phosphorus-based FRs quench such free radicals and dilute the fuel source (plastic) as well as create carbonaceous char layer that blocks non combusted plastic to add to fire, metal oxides through endothermic reaction brings the temperature of the plastics below their combustion temperature.