Abstract: It’s significant to understand the generation, transformation, and dissipation mechanism of energy of high pressure tanks in fire scenarios for the consequence assessment of explosion accidents. This study revealed the differences properties between high-pressure hydrogen storage tanks and nitrogen tanks under fire environments through comparative experiments. Fire tests were conducted using 6.8L - 30MPa type III tanks. The results show that fire can significantly weaken the pressure-bearing performance of the tanks, with the critical bursting pressure decreasing from 125.1 MPa at room temperature to 46.8 MPa in fire conditions (a reduction of 62.6%). The explosion of hydrogen tanks exhibited typical physical-chemical composite characteristics, forming a fireball with a diameter of 9 m. The peak shockwave pressure at a distance of 2 m reached 882.47 kPa, and the positive pressure duration was 168.11 ms. In contrast, nitrogen tanks only undergo physical explosions, with a peak shockwave pressure of 59.42 kPa and a positive pressure duration of only 2.17 ms. This study analyzed the energy conversion pathways during explosions of high-compressed gas tanks (H2 and N2) in open environments. A blast power assessment method for hydrogen storage cylinder explosions in unconfined spaces was developed. First, the physical explosion energy was calculated by determining the basic data such as the critical burst pressure, nominal volume and initial filling pressure of the high pressure tanks and comparing the applicability of five mechanical energy calculation models. Secondly, the mass of hydrogen was determined using the actual gas equation, and the total chemical explosion energy was derived by integrating the heat of combustion value of hydrogen. Finally, considering the contribution of mechanical and chemical energy to the shock wave intensity, the total explosion energy was converted into shock wave energy by the open space energy correction factor, followed by quantitative analysis and error verification with measured data. The research findings could provide crucial support for enhancing risk assessment of explosion accidents involving high-pressure hydrogen storage devices.