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The ammonium salts of orthophosphoric acid, MAP and DAP, have been known as additives for flame retardants for decades. They were used in coatings for construction parts mainly made from steel, wood, and other building materials. Because of their high solubility and low thermal stability, the applications for these products in modern architectural applications with higher standards is very limited. Ammonium polyphosphate (APP, FR, CROS 484) is the ammonium salt of polyphosphoric acid. In contrast to MAP and DAP, it has a polymeric structure with the general formula [NH3.HPO3]n. APP is recognized as a halogen-free, efficient and multi-purpose FR, which is used in many applications. Due to the environmental and toxicological concerns surrounding many halogenated products, FRs based on APP are finding a broader range of uses. Especially in construction & building APP is playing a mayor role as flame retardant additive in intumescent paints for structural steel fire protection. Intumescence in the result of a sequential chemical reaction between several chemical products activated by the heat of flames during fire. APP plays an important role in intumescent coatings: the reation between APP and other ingredients takes place at temperatures around 250 degree C to form a thermally insulating carboneous char. The char can be expanded up to 50 times the original thickness of the coating. This layer reduces the rate heating of the steel and prolongs its load bearing capacity. The intumescent behaviour of all paints has been tested by using a small scale test furnace consisting of a propane burner. Water based paints show in general a higher intumescence than solvent based paints. The intumescence and heat insulation was always better when coated APP grades were used in the paint formulation, because of their better humidity resistance. Coated APP grades therefore can contribute to more durable intumescent coatings, for longer and better performance especially under humidity and outdoor conditions. Coated APP grades also offer a higher thermal stability technology to improve the consistency of an intumescent foam is by means of ceramifying agents. The use of selected ceramifying agents increase the strength and resistance of the inumescent foam and at the same the adherence to the steel profile.