Hydrogen Vehicle Fueling FAQs

Both stationary and portable hydrogen refueling systems are in use. Dispensers are permanently installed in service stations capable of generating hydrogen through natural gas reformation, an electrolyzer powered by electricity supplied by the grid, or renewable sources such as solar or wind power. Stationary installations may also be supplied with hydrogen through deliveries from tanker or tube trailer trucks. There are platform and vehicle-mounted refueling systems also in use to refuel road tours and to temporarily fuel fleet operations based in a certain geographic location.

NIST Handbook 44 requirements form the basis for type evaluation under the National Type Evaluation Program and for routine inspection and test procedures for measuring equipment for commercial hydrogen vehicle refueling systems. Specifically, NIST Handbook 44 Section 1.10 General Code and Section 3.39 Hydrogen Gas-Measuring Devices Code provides specifications, tolerances, and other technical requirements for hydrogen measuring devices.

NIST Handbook 130 requirements in Section 2.32 Method of Sale Regulation of IV. Uniform Regulations - B. Uniform Regulation for the Method of Sale of Commodities specifies the kilogram (kg) as the unit of measurement for sales of gaseous hydrogen vehicle fuel and for related labeling and advertising requirements. NIST Handbook 130 also includes fuel quality standards and references to test methods.

The legal metrology requirements in the NIST Handbooks 44 and 130 were developed by the U.S. National Work Group (USNWG) for the Development of Commercial Hydrogen Measurement Standards. The startup of the USNWG was sponsored by the U.S. Department of Energy (DOE) and NIST OWM. This group is comprised of stakeholders from private industries, standards organizations, and state and federal government. Broad participation was sought so as to include hydrogen dispenser and component manufacturers, fuel suppliers, standards developers, and weights and measures device type evaluation laboratories and regulators in developing its recommendations. The recommendations developed by the USNWG adhered to the weights and measures standards development process through the National Conference on Weights and Measures (NCWM) and for inclusion in the NIST Handbooks 44 and 130.

Industry pre-market practice has been to dispense hydrogen in mass units of measurement. Because the hydrogen is delivered in a compressed gaseous form, volume measurement would not be suitable due to the dependency on pressure and temperature of the gas. To ensure accuracy in the amount of hydrogen fuel delivered, mass units have been the preferred method of delivery in the weights and measures and hydrogen communities.

The corresponding international standard developed by the International Organization of Legal Metrology (OIML) in Recommendation (R) 139 “Compressed gaseous fuel measuring systems for vehicles” also recognizes mass as the basis for dispensing compressed gases. The most current version of OIML R 139 is available at: http://www.oiml.org/en.

The NIST Handbook 44 Section 3.39. Hydrogen Gas-Measuring Devices Code, paragraph T.2. Tolerances specifies that hydrogen dispensers fall within the Accuracy Class 7.0. These devices are required to meet a performance of ± 5.0 % for acceptance tolerance and ± 7.0 % for maintenance tolerance.

The NIST Handbook 44 Section 3.39. Hydrogen Gas-Measuring Devices Code, paragraph N.4 describes three official methods for testing the measurement performance of a hydrogen dispenser: the gravimetric test, master meter transfer standard test, and PVT (pressure volume temperature) test.

Multiple organizations in the fuel standards community worked to fully develop a hydrogen fuel quality standard.  There has been a concerted effort to harmonize these standards among the different organizations. The vehicle fuel quality standard recognized and required by many weights and measures jurisdictions and other enforcement agencies is included in the NIST Handbook 130 Section IV. G. Uniform Fuels and Automotive Lubricants Regulation, Section 2. Standard Fuel Specifications, paragraph 2.20. Hydrogen Fuel.

This standard specifies that hydrogen fuel meets the requirements of the most current version of Society of Automotive Engineers (SAE) Standard J2719, “Hydrogen Fuel Quality for Fuel Cell Vehicles.” The SAE J2719 Standard is aligned with the corresponding International Organization for Standardization (ISO) standard for hydrogen fuel quality (ISO/DIS 14687-2 Hydrogen fuel - Product specification - Part 2 Proton exchange membrane fuel cell applications for road vehicles). SAE J2719 references the specific ASTM sampling and testing methods that are necessary to ensure that hydrogen fuel meets the designated 99.97 % purity standard and that all remaining constituents are within allowable limits.

U.S. device type evaluations are carried out by the National Conference on Weights and Measures National Type Evaluation Program, NCWM NTEP, whose laboratories use NCWM Publication 14. A set of general evaluation criteria (i.e., checklist) based on the General Code in Section 1.10 and device-specific design requirements in Section 3.39 of NIST Handbook 44 were developed for inclusion in the NCWM Publication 14, “Measuring Devices Technical Policy, Checklists, and Test Procedures.” Fueling dispenser checklists are typically developed by the NCWM National Type Evaluation Technical Committee (NTETC) Measuring Sector.