This article investigates the toxicology of gaseous products of pentafluoroethane (HFC-125) after the interaction of thermal decomposition with B-class flame together with hexafluoropropane (HFC-236fa) for comparison. For necessary analysis, gas chromatography, ion chromatography, and gas chromatography-mass spectrometry were employed during the interaction between the fire extinguishing agents (FEAs) and n-heptane flame in experiments. The results show that hydrogen fluoride (HF) output was proportional to the pool fire size and interaction time for the two FEAs. Moreover, further toxicology evaluations show that the thermolysis gaseous products of HFC-236fa with n-heptane flame interaction inflict much more harm on the lungs of laboratory mice than that of HFC-125 in pathology tests, thus indicating that besides the HF, other organic traces of gases, such as CF3CH=CF2, CF3CH2CF3, and so on, might have serious impacts on their toxicology. It is expected that these investigative results would be of great help to the further study of FEAs on the toxicology evaluation not only the fire suppression of HFC-125.