Packaging Instructions for Portable Metal Hydride Hydrogen Storage Systems (18.3)

Packaging Instructions for Portable Metal Hydride Hydrogen Storage Systems (18.3)

Criticality: High
Progress: Not Addressed
Score: 40
DOT Relevance: 173 Subpart D

Description of Key Area

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 Portable systems and Item 18.2 discussed Micro 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. In most instances portable systems will be stand-alone; however there may be specific applications where the portable systems will be attached to a fuel cell appliance during transportation.

Today electronic appliances are ubiquitous and there is ever greater demand to un-tether them from the grid, i.e., to use them without always having a cord running to a grid-connected electrical outlet. Today this is accomplished by the use of batteries. However a gap has been developing between application power and energy demand and the ability of current battery technology to meet demand. Hydrogen fuel cell technology is expected to be able to provide better power and energy capabilities in these applications. 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. Another advantage of hydrogen fuel cells is that they do not need electricity to be recharged as batteries do. This advantage can provide tremendous benefits under certain circumstances such as what was experienced by emergency responders on the Gulf Coast after hurricane Katrina in 2005 when there was no operational electrical grid to recharge batteries for radios and other equipment.

Portable metal hydride-based hydrogen storage systems will find use in many applications, not all of which will be with fuel cells. Since these systems can provide a very compact, low-pressure storage option for hydrogen gas, they may be used in laboratories which need hydrogen for equipment, such as gas chromatographs. They may be used as exchangeable fuel tanks on mobility devices such as wheel-chairs, scooters, golf carts, etc., which may be propelled by either fuel cells or internal combustion engines. Portable systems are expected to be used with portable generators for backup power and for auxiliary power units (APUs), which is an example of an application where they might be connected to an appliance and operating while being transported.

Currently there are a lot of development activities being carried out by various companies and organizations around the world on these technologies. Entry level products have started entering 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.

Discussion of Criticality

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.

Discussion of Progress

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:

  1. The ISO technical committee for hydrogen technologies (TC 197) has a working group drafting a standard for transportable reversible metal hydride hydrogen storage systems (ISO 16111). This document is currently in the approval stage as a committee draft (CD) for advancement to the draft international standard stage (DIS). In parallel to the CD approval, the document is being considered for publication as a technical specification; with possible publication of the TS much earlier than possible for the International Standard. Once the international standard is approved, the technical specification will be withdrawn. This document only considers stand-alone containers.
  2. CGA has also considered developing a standard for portable metal hydride hydrogen storage systems. This effort is early in development and the expected publication date is unknown.

Proposals have been submitted to ICAO for approval of metal hydride-based hydrogen storage systems to be transported aboard aircraft. ICAO approved transport aboard cargo aircraft. It is expected that future requests to ICAO for transport in the cargo space of passenger aircraft will be made once a published document on system design and testing is available for reference. The OHMS granted special permit DOT-E 13598, issued to Jadoo Power Systems, that allows up to 90.7 kg (200 lb) to be transported aboard cargo aircraft.

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 portable 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 ISO 16111, underdevelopment by an international committee of experts.

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 and the CGA Hydrogen Fuel Technology 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.