Progress: Not Addressed
DOT Relevance: 173 Subpart D
UN SCETDG has approved entry UN 3468, Hydrogen in a metal hydride storage system, to the Dangerous Goods List in the UN Model Regulation for the Transport of Dangerous Goods. This entry has been adopted by the US DOT and is included in the Hazardous Materials table in 49 CFR 172.101. Packaging instructions for UN 3468 require approval by the Associate Administrator prior to first shipment (49 CFR 173.214). The Hazardous Materials table also includes entry NA 9279, Hydrogen absorbed in metal hydride, which includes no packaging instructions and requires a special permit for transport. Without any guidance on packaging, the OHMS must individually review and issue an approval or special permit for each system design and manufacturer/offeror for all metal hydride-based hydrogen storage systems.
This discussion applies to both entries, UN 3468 and NA 9279. Systems which are appropriately identified by these entries can be divided into two broad groups that really only differ in where and how they might be used and transported. This section will discuss Micro systems and Item 18.3 will discuss Portable systems. Micro systems are ones that are expected to be transported both as stand-alone storage containers and as storage containers connected to and in use with fuel cell systems. It is anticipated that Micro systems will be approved for transport and use with all modes of transport including the passenger cabin of aircraft. Portable systems are not expected to be transported or used within the passenger cabin of aircraft. Micro systems will likely have a maximum size limitation applied to them. Current proposed size limitations have been arbitrarily chosen and will likely be revised as a natural safety or application-based limit becomes apparent.
Today travelers expect to be allowed to carry and use a host of electronic devices while traveling by road, rail, ship, and air. These devices include laptop computers, cellular phones, PDAs, video games, DVD players, cameras, video recorders, and others. Many devices combine several functions into a single device. As the number of functions a device performs increases, as their overall performance is enhanced and as customer expectations rise, the power and energy requirements for the devices become greater. This has lead to a widening gap between device power and energy demand and the ability of current battery technology to meet demand. One technology that is expected to be able to provide better power and energy capabilities in these applications is hydrogen fuel cells. Fuel cells are similar to batteries in that they convert chemical potential energy into electrical power and energy. However unlike batteries, the fuel and oxidant are supplied from external sources and the by-products exhausted. With hydrogen fuel cells, the fuel is hydrogen and the by-product is water.
Currently there are a lot of development activities being carried out by various companies and organizations around the world on these technologies. Advanced prototypes and early entry products are starting to leave the laboratory environments and enter the marketplace. The number of products and designs available are expected to increase dramatically over the next few years. Without packaging instructions being included in the hazardous materials regulations and without at least a template or set of guidelines for use by the OHMS for evaluating these systems, the effort required to review and approve or issue special permits for each may be burdensome.
Micro systems have additional complexities in their review since it will also need to consider the implications of when they are attached to or detached from a fuel cell appliance. This becomes even more critical in light of their expected transport and use within the passenger cabin of aircraft in todays environment of heightened concern of potential terrorism.
This item has been assigned a criticality of high. Without packaging instructions being developed for metal hydride-based hydrogen storage systems, there is no set of consistent minimum requirements to manufacturers and offerors follow. The absence of packaging instructions requires that OHMS personnel review and approve each system from each offeror and manufacturer. This could present a burdensome work load on the OHMS if this technology is found to be able to meet current expectations leading to many requests for approval.
While it is considered critical that packaging instructions be developed for systems identified by UN 3468 and NA 9279, it is also recommended that the packaging instructions be designed so as to not prohibit new and innovative designs. This technology is relatively new and is evolving. New advanced materials and designs are expected. The packaging instructions should therefore be performance-based and avoid being too prescriptive, while ensuring a minimum level of safety.
The hazardous materials table currently includes two listings: NA 9279, Hydrogen absorbed in metal hydride and UN 3468, Hydrogen in a metal hydride storage system. Currently these identifications can only be used with approval from the OHMS after review and approval of the packaging. No packaging instructions have been adopted in either the US regulations or the UN Model Regulations. The OHMS has issued several special permits for metal hydride hydrogen storage systems that are identified by either one or both of these identifiers.
Progress on developing consensus standards that might be used as packaging instructions include:
Proposals have been submitted to ICAO and the UN SCETDG for approval of metal hydride hydrogen storage systems of limited size being transported aboard aircraft, both cargo and passenger, including within the passenger cabin. ICAO has approved part of the request to allow transport aboard cargo aircraft. These proposals have included introducing system level tests of the systems and/or reference to ISO 16111 to approve packaging.
ASME's Boiler and Pressure Vessel project team on hydrogen tanks is addressing metal hydride vessel design in a code case to Section VIII-1.
It is recommended that the OHMS develop a minimum set of design and test criteria for packaging of systems that meet the UN 3468 and NA 9279 hazard descriptions and that meet the micro system definition used in this report. These criteria should be provided to potential manufacturers and offerors for use in their design and testing of the storage systems and would help ensure consistency in application of rigor in determining the minimum level of safety. It is preferred that these criteria be performance-based. Ideally they would be based on the ISO and IEC standards underdevelopment by international expert committees (ISO 16111 and IEC 62282-6-1).
To help ensure that the standards being developed for metal hydride-based hydrogen storage systems meet the need of OHMS, it is recommended that the OHMS assign personnel or contractors to actively participate on the applicable development committees. These would include ISO TC 197 working group 10, IEC TC 105 working group 8, the CGA Hydrogen Fuel Technology committee and ULs 2265 technical committee.
From experience obtained from systems approved under these guidelines, they could, at an appropriate future time, be refined and used as a basis for a New Rule Making Proposal for conversion into regulations and incorporated into 49 CFR 173.