The objective of this study was firstly to assess the magnitude of the chemical effect of DAP as fire retardant on the lignocellulosic material Olea europaea employing TGA. Therefore pyrolysis experiments of O. europaea before and after treatment with DAP 15% have been conducted using a TGA analyzer under nitrogen (N-2) flow. Secondly the objective was to investigate the effect of DAP at different temperatures based on the solid mass residue using infrared spectroscopy. Thus, mass residues obtained at 180, 260, 320, 400, 500 and 600 C respectively from TGA were examined by FTIR-ATR. Using the TGA curves of DAP and O. europaea (pristine) respectively, a calculated curve has arisen (0.85 x TG curve(O.europaea)(25-500 degrees C) + 0.15 x TG curve(DAP)(25-500 degrees C)) A comparison between this curve and the measured of the sample O. europaea + DAP 15%, showed that since they do not coincide, there is a chemical synergy between O. europaea and DAP. FTIR-ATR was employed to investigate the decomposition path of hemicelluloses, cellulose and lignin by detecting the characteristic peaks of the pyrolysis mass residues at different temperatures. Above 25 degrees C, several characteristic peaks gradually do not reappear. On the contrary, when DAP is present these characteristic peaks continue to appear shifting to higher temperatures implying its chemical effect on the lignocellulosic materials. This observation is verified by the shifting of the DIG curve of O. europaea treated with DAP towards lower temperatures and less pronounced peaks at the DIG curves. The combination of TGA and FTIR-ATR is a useful tool for the investigation of a fire retardant's effect on the thermal decomposition of lignocellulosic materials. (C) 2012 Elsevier BM. All rights reserved.