Nearly all plastics are based on hydrocarbons and are combustible. For use where safety is essential - such as aircraft, building/construction, public transport and increasingly in housings for electrical/electronics equipment - they must be rendered incombustible, or at least difficult to ignite and burn. Certain thermoplastics, such as PVC and modified PPO, are to some extent inherently resistant to burning, but may need to be supplemented by additives. John Murphy reviews the options.
Flame retardant (FR) additives work by breaking one of the links that produce and support combustion: heat, fuel and air. They may quench a flame by depriving it of oxygen or may absorb heat and produce water, so reducing the temperature. Increasingly, FR additives are used in combination, often with a synergistic effect. But experience has shown that fire itself is not the real hazard: far more dangerous to people are the toxic by-products generated during combustion, and dense smoke that prevents people from escaping in time.