If Hydrogen is expected to be highly valuable, some improvements should be conducted, mainly regarding the storage safety. To prevent from high pressure hydrogen composite tanks bursting, the comprehension of the thermo-mechanics phenomena in the case of fire should be improved. To understand the kinetic of strength loss, the heat flux produced by fire of various intensities should be assessed. This is the objective of this real scale experimental campaign, which will allow studying in future works, the strength loss of composite high-pressure vessels in similar fire conditions to the ones determined in this study. Fire calibration tests were performed on metallic cylinder vessels. These tests with metallic cylinders are critical in the characterization of the thermal load of various fire sources (pool fire, propane gas fire, hydrogen gas fire) so as to evaluate differences related to different thermal load. Radiant panels were also used as thermal source for reference of pure radiation heat transfer. The retained thermal load might be representative of accidental situations in worst case scenarios, and relevant for a standardized testing protocol. The tests performed show that hydrogen gas fires and heptane pool fire allow reaching the target in terms of absorbed energy, regarding the results of risk analysis performed previously. Other considerations can be taken into account that will led to retain an hydrogen gas fire for further works. Firstly, hydrogen gas fire is the more realistic scenario: Hydrogen is the combustible that we every time find near an hydrogen storage. Secondly, as one of the objectives of the project is to make recommendations for standardization issues, it?s important to note that gas fires are not too complex to calibrate, control and reproduce. Finally, due to previous considerations, Hydrogen gas fire will be retained for thermal load of composite cylinders in future works.