Diploma thesis aims at application of analytical methods in the process of the fire investigation which were caused by various flame accelerators. The main aim of this diploma thesis is to evaluate suit ability of analytical determination of the fire-extinguishing water for the purpose of the fire investigation. In the experimental part, we determined flame accelerators in the samples, which were taken from fire-extinguishing water after subsequent extinguishing of the burning sample. The fire-extinguishing water was taken after burning of straw samples on which petrol – Natural 95 was poured. We determined volatile compound specific for petrol by GCxMS method. We defined several volatile compounds during the analysis – benzene and its alkylderivatives and derivatives of aliphatic compounds. On the basis of volatile products found in the samples treated by petrol, we can say that fireextinguishing water is suitable medium for analytical detection at the area of fire investigation.