Commercial intumescent flame retardants and intumescent compounds were tested as flame retardants for polypropylene. Their routes of decomposition were followed up by thermal gravimetric analysis, differential scanning calorimetry as well as thermal mechanic analysis and described by chemical formula, balances of weight, and heats of formation. These investigations showed that the combination of ammonium polyphosphate, polyols, and melamine exerted intumescence at 400 degrees C and melamine was no blowing agent but reacted to melamine polyphosphate. Further they made clear that bisethylenediamine phosphate exerted intumescence at 350 degrees C and degraded to piperazine phosphate. Intumescent flame-retarded building parts exemplified the advantage of intumescent flame retardance by the time delay until they still fulfilled their function. F15 classification was achieved for thick walled intumescent polypropylene pipes and thin walled electrical boxes consisting of a flame-retarded glass reinforced bismaleinimide core and an intumescent polyolefine shell in furnace fire tests. The difference in temperatures inside and outside of the building parts was calculated and compared with measurements in fire tests. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012