Discussion on Allowable Hydrogen Leakage Rates of High-Pressure Hydrogen Storage Cylinders in GB and ISO Standards

Hydrogen storage cylinders for vehicles are critical components in hydrogen energy vehicles, with their safety being a key factor for application. Various countries and organizations have introduced a series of technical specifications and standards to regulate the airtightness tests and hydrogen leakage rates of such cylinders. This paper compares the qualification criteria for hydrogen leakage rates in various standards for the first time, focusing on aspects such as test subjects, cylinder volume, airtightness test temperature and pressure, and acceptable hydrogen leakage conditions. The study then discusses the rationale for the permissible hydrogen leakage rate of 6 Nml/L/h for high-pressure hydrogen storage cylinders as specified in ISO standards and China’s GB standards. The paper analyzes the average hydrogen concentration in confined spaces under various application scenarios when the hydrogen leakage rate of storage cylinders is 6 Nml/L/h at a steady state. It is found that the maximum permissible hydrogen leakage rate stipulated in existing standards (6 Nml/L/h) cannot meet the requirement of maintaining hydrogen concentrations below 1% (the safety boundary for determining the permissible hydrogen leakage rate of 6 Nml/L/h) in some application scenarios. In certain cases, it may even exceed the lower flammability limit of hydrogen at 4%. Additionally, this study calculates and provides permissible hydrogen leakage rates for hydrogen storage cylinders under Chinese application scenarios. The results indicate that the permissible leakage rates in these scenarios should be significantly lower than the maximum allowable leakage rate specified in existing standards. This research suggests that the permissible hydrogen leakage rate regulations should comprehensively consider factors such as cylinder capacity, environmental space, and ventilation rates in different application scenarios, thereby establishing regulations suitable for practical usage conditions.