A review of recent developments in the applications and actions of intumescent ®re-retardance is given. An attempt has been made to classify the main systems of importance such as melamine, ammonium polyphosphate, melamine phosphate, pentaerythritol phosphate, sodium silicate, vermiculite, expandable graphite and microbeads. They are de®ned in terms of the Berthelot number which is the product of heat of vaporization or decomposition and volume of gases evolved. In principle, only two kinds of gases are produced from this group, namely water vapour and ammonia (from melamine). The heats of decomposition are readily calculated from heats of formation. An important aspect which is not included in the Berthelot number is the ignition residue in the shape of glassy foam or a cellular enamel. # 2000 Society of Chemical Industry Keywords: intumescent;¯ame retardant; plastic; vermicular graphite; sodium silicate; intumescent paint; thermal insulation INTRODUCTIONThe term intumescence derives from medicine and means swelling under in¯ammation. Intumescent compounds and formulations are those which expand in the case of ®re under the in¯uence of heat. The number of intumescent compounds and formulations available is still much larger than cases of commercial applications. In recent developments intumescent agents for paints 1,2 are not only used as coatings but are also incorporated directly into plastic materials. Flame-retarded polyole®nes 3 and polyamides 4 are produced by this technology, for example melamine phosphates are added to glass-reinforced polyamides to meet a V-0 classi®cation in the UL 94 test, UL 94 is one of the most important UL standards relating to ®re safety test methods and requirements and contains several ®re tests for plastics.

No abstract