Most thermoplastics are flammable, burning easily when heated to a high enough temperature. Plastics, being hydrocarbons, combust through a process that begins with heat which pyrolizes their long-chain structure into volatile hydrocarbons, hydrogen, and hydroxyl-free radicals. These elements formed during decomposition are high in energy and react with oxygen, releasing heat and causing fire to spread.
Flame retardants are added to polyolefins, polycarbonate, polyamides, polyester, and other polymers to increase resistance to ignition, reduce flame spread, suppress smoke formation, and prevent a polymer from dripping. The primary goal is to delay the ignition and burning of materials, allowing people more time to escape the affected area A secondary consideration is to limit property damage.
Plastics containing flame retardants are found in homes, office buildings, cars and mass-transit vehicles, furnishings, fibers, household appliances, and many other applications. In general, their use is mandated by regulations in building codes or industry specific standards. Additional examples of plastic products that require flame retardants include construction fabrics, banner films, ceiling insulation, roofing and siding, carpet backing, automotive fabrics, components in trains and planes, tent materials,, stadium seating, mattress covers, television and computer housings, electric wiring, power cable, and conduit for tunnels.
For a fire to begin, fuel, oxygen, and a source of ignition must be present. Flame retardants work by interfering with one or more of these fundamentals, either physically or chemically. Those having a physical effect either cool the substrate below its combustion temperature, form a solid or gaseous protective layer that excludes oxygen, or add inert gases that dilute the fuel in its gaseous phase. Those that act chemically interrupt the process by reacting with elements in the gaseous phase or shield the polymer by forming a carbonaceous surface layer. The most commercially viable flame retardants include brominated and chlorinated types, phosphorus based types, and metallic oxides.