The current code, known as NFPA 2, provides fundamental safeguards for the generation, installation, storage, piping, use and handling of hydrogen in compressed gas or cryogenic (low temperature) liquid form.

To benchmark the number of sites that readily accept hydrogen, the Sandia team focused on geographic areas where hydrogen-fueling sites are being actively developed. There are 9,710 retail gasoline stations in California. In a recent draft Public Opportunity Notice (PON), the California Energy Commission (CEC) identified primary and secondary priority locations for fueling stations. Of the 9,710 total sites in California, there are 343 designated retail gasoline stations in these primary and secondary priority locations.

The Sandia team took a sample of the locations and evaluated each of these sites for readiness to integrate hydrogen. The assessment is based solely on compliance to the prescriptive requirements of the applicable hydrogen code—i.e., NFPA 2.

A key factor in the codes that Sandia examined was the separation distances required for fueling infrastructure, including fuel dispensers, air intakes and tanks and storage equipment. The code defines required distances between such components and public streets, parking, on-site convenience stores and perimeter lines around the site.

Under the previous code, virtually no hydrogen fuel cell stations could be sited at existing stations. The reason, said Chris San Marchi, manager of Sandia’s hydrogen and metallurgy science group, is simple: Those codes were developed via an “expert opinion-based process” and not the risk-informed process developed by Sandia researchers and now used in the code. The previous code was developed for flammable gases in an industrial setting, which carries different risks compared to hydrogen fuel at a fueling station.The distances set forth in the code, therefore, were much larger than they need to be, San Marchi said.

The risk metric used to develop the new NFPA code, he added, was that the stations accepting hydrogen fuel needed to be proven as safe as or safer than gasoline-only stations.

GH2 reference station: 100 kg GH2 storage, 3 bank cascade and tube trailer with 1 compressor and associated pre-cooler equipment (70 kg/day capacity, 1 dual hose dispenser); 18,000 ft2 (672 m2) station site with 5,500 ft2 (11 m2) of open space. Click to enlarge.		LH2 reference station: 3500-15,000 gallons (13,250-56,780 liters) (910-1300 kg) LH2 storage (200-300 kg/day capacity, 1-2 dual hose dispensers); 18,000 ft2 (1,672 m2) station site with 15,000 ft2 (1,394 m2) of open space. Click to enlarge.

All fueling facilities are susceptible to fire due to the presence of flammable liquids and gases; according to the NFPA, more than 5,000 fires and explosions a year occurred at conventional gasoline stations from 2004-2008.

If you have a hydrogen leak at a fueling station, for example, and in the event that the hydrogen ignites, we need to understand how that flame is going to behave in order to maintain and control it within a typical fueling station.

—Chris San Marchi

A scientific understanding of how such flames and other potential hazards behave is necessary to properly determine and mitigate safety risks, San Marchi said.

Sandia researchers at the Combustion Research Facility for years have studied and modeled the intricate workings of the combustion engine and, more recently, hydrogen behavior and its effects on materials and engine components, San Marchi said. The knowledge gained by Sandia’s work on the physical behavior of hydrogen and risks associated with hydrogen fuels provided the scientific basis to revise the separation distances in the NFPA 2 code for hydrogen installations.

Some gas stations still may not be able to accept hydrogen under the new code because gas station lot sizes vary greatly, and many smaller sites—particularly those in dense, urban areas—cannot be properly configured, he said. For example, he said, the required distance between a high-pressure tank carrying hydrogen and the property boundary would be too great for a “skinny” station or a wedge-shaped lot. While larger lots naturally work better in the current environment, San Marchi said, there are opportunities to develop risk mitigations that could allow even wider deployment of hydrogen fueling stations.

One of Sandia’s next objectives is to work with all parties to look closer at the underutilized performance-based parts of the NFPA 2 code, rather than the prescriptive-based elements that focus on rigid distance requirements.

While the prescriptive sections of the code are typically implemented, there are also sections of the code that allow for the use of more risk analysis to optimize the fueling facility, San Marchi said. If station developers and others take a more performance-based approach, he said, more existing fueling facilities will be able to integrate hydrogen systems and support the developing fuel-cell electric vehicle market.

Sandia is also in the process of developing a risk-informed approach for shortening the separation distances for liquid hydrogen storage at fueling stations, as current efforts only examined separation distances for gaseous hydrogen. Liquid hydrogen is attractive because it takes up less space than gaseous hydrogen and allows fueling stations to accommodate larger numbers of fuel-cell electric vehicles. However, there are additional issues associated with the low temperatures required for liquid systems installed on small properties.

We need to do more experimental and modeling work to understand and evaluate the science and physics of liquid hydrogen. By evaluating the risks quantitatively, we believe we can shorten the separation distances required in the code for liquid hydrogen just as we did with gaseous hydrogen. That could then lead to even more fueling stations that can accept hydrogen and support the continued growth of the fuel-cell electric vehicle market.

—Chris San Marchi

Sandia’s hydrogen safety, codes and standards program is a diverse portfolio of activities funded by the Department of Energy’s Fuel Cell Technologies Office to provide the technical basis for developing and revising safety codes and standards for hydrogen infrastructure, including the NFPA 2 code.

This work is aligned with Hydrogen Fueling Infrastructure Research and Station Technology (H2FIRST) (earlier post), a new project established by the Department of Energy’s Office of Energy Efficiency and Renewable Energy.

Resources

• A.P. Harris, Daniel E. Dedrick, Chris LaFleur, Chris San Marchi (2014) “Safety, Codes and Standards for Hydrogen Installations: Hydrogen Fueling System Footprint Metric Development,” Sandia Report SAND2014-3416