Aircraft Carriage, Hydride Systems in Appliances (30.2)

Aircraft Carriage, Hydride Systems in Appliances (30.2)

Criticality: High
Progress: Not Addressed
Score: 40
DOT Relevance: 175

Description of Key Area

The carriage by aircraft of hydride-based hydrogen storage systems is considered critical for commercial success by many potential manufacturers of the hydrogen storage systems and fuel cell appliances and devices powered by them. This area covers both rechargeable and non-rechargeable type hydrogen storage systems, micro and portable systems, stand-alone systems, and systems coupled to appliances. This section will discuss systems transported while coupled to an appliance. Stand-alone systems, not coupled to an appliance, are discussed in Item 30.1 of this report. The discussion of Item 30.1 is applicable to systems coupled to an appliance as well as for stand-alone systems.

As has been previously discussed, hydride-based hydrogen storage systems can be divided into two broad categories, rechargeable systems and non-rechargeable systems. The rechargeable systems contain a reversible hydride-forming material and are refilled by applying hydrogen; they will most likely be identified by UN 3468 or NA 9279 with a 2.1 flammable gas hazard classification. Non-rechargeable systems will likely contain a mixture of hazardous materials that are not normally allowed within a single package since they are capable of reacting together to produce a flammable gas. These systems will require exceptions to a number of clauses in current regulations and may require either new hazardous materials table entries or ORM-D exceptions. Each of these two categories can be further divided into micro and portable systems, with the difference being the intended use of the appliance they fuel. Micro systems are primarily intended for use with low-power fuel cell appliances for use in consumer electronics, such as cellular phones and laptop computers. It is considered essential that these systems be able to be carried and used by travelers in the passenger cabin of aircraft and upper size limitations will likely be imposed. Portable systems are not intended to be used in fixed, stationary locations but it is not expected that they need to be carried or used in the passenger cabin of aircraft.

For micro systems, it is considered critical for commercial success that they be able to be carried and used in the passenger cabin of aircraft. For portable systems, it is not deemed critical that they be carried and used in the passenger cabin of aircraft; however there are situations where it may be important to be able to have them transported by passenger carrying aircraft while coupled to an appliance. An example would be for systems used with a fuel cell that powers a mobility device such as a wheelchair.

Standards being developed for hydride-based hydrogen storage systems, such as ISO 16111, consider the systems up to a shut-off valve. The standards are written to ensure that systems will not pose a hazard: by leaking hydrogen at a rate that could create a flammable fuel-air mixture; from overpressurization in fire conditions, etc. Either through the standards or regulations, overpacking and requirements for restraining the systems during transport may be imposed. When the systems are coupled into an appliance, the testing found in the standards may not be sufficient. When coupled to an appliance, the shut-off valve will likely be open and thus hydrogen will be able to pass out of the storage container into the appliance. In this situation, hydrogen leakage and overpressurization testing to ensure safety must include the coupling and fuel cell appliance. The robustness of the coupling between the storage system and appliance must also be tested against potential abuse the combined unit may experience in transport and use.

In addition to modifications that might be required discussed in Item 30.1 of this report, other modifications might be appropriate in 175.10(a) which is written specifically for battery power mobility devices. It might be appropriate to either modify them to include fuel cell powered devices or to include new paragraph(s) under 175.10(a) for fuel cell powered appliances.

Discussion of Criticality

This item has been assigned a criticality of high. It is expected that many manufacturers will seek allowance of hydride-based hydrogen storage systems aboard aircraft. DOT-E 13598 currently allows up to 90.7 kg (200 lb) of UN 3468 material aboard cargo-only aircraft. Allowance will be sought to allow micro systems to be carried in carry-on baggage within the passenger cabin of aircraft. There is currently no allowance for systems to be carried into or used within the passenger cabin of aircraft.

Consideration must be given to size and quantity limitations to systems to be allowed within passenger baggage, carry-on and checked, and that allowed as cargo on passenger and cargo-only aircraft. Packaging instructions and container specification must include appropriate testing to ensure safety of the systems allowed aboard aircraft. The testing for systems to be allowed to be transported while coupled to an appliance must include the coupling and appliance to ensure safety of the complete unit.

While it is considered critical that appropriate packaging instructions be developed, 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

Hydrogen as a compressed gas, UN 1049, is allowed on cargo-only aircraft with a 150 kg (331 lb) net limit. UN 3468, Hydrogen in a metal hydride storage system has been included in ICAOs dangerous goods list and forbidden from carriage on either cargo-only or passenger aircraft. At the recent ICAO Dangerous Goods Panel meeting in Oct/Nov of 2005, the panel accepted a proposal from the US panel member to allow cargo-only carriage, with a 100 kg (220 lb) limit. This new ruling is to become effective in January of 2007. Carriage aboard passenger aircraft has not been allowed. US DOT special permit E 13598 allows up to 90.7 kg (200 lb) of UN 3468/NA 9279 material be carried aboard cargo-only aircraft.

An informal and then a formal proposal were made to the UN SCETDG by the representative from Japan, to allow micro fuel cell systems and the fuel cartridges to be carried aboard aircraft. The original informal proposal requested a new entry in the Dangerous Goods List (DGL), with a hazard class 9. The formal proposal submitted for consideration at the July 2005 meeting of the UN SCETDG was revised and instead requested a new DGL entry with a flammable gas hazard, class 2.1. This proposal was withdrawn without consideration. It is anticipated that a new proposal will be submitted requesting modification of UN 3468 to include systems coupled with fuel cell units as well as the stand-alone systems.

Progress on developing consensus standards that might be used as a basis for 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. IEC TC 105 has drafted and is currently reviewing a draft publicly available standard for Micro Fuel Cell Systems (IEC PAS 62282-6-1). This document includes sections on fuel storage containers and complete integrated fuel cell appliances with fuel containers. This standard is expected to reference ISO 16111 for metal hydride-based hydrogen storage container design and testing. IEC document 62282-5 for Portable fuel cell appliances may also be appropriate for considerations for fuel cell appliances that do not qualify as micro, such as might be used on mobility devices.
  3. UL is developing a consensus standard (UL 2265) on micro fuel cell systems. An effort is being made to keep UL 2265 consistent with IEC 62282-6 and its development is therefore trailing that of IEC 62282-6.


It is recommended that the OHMS develop a minimum set of design and test criteria for packaging of hydride-based hydrogen storage systems as previously recommended in Items 18 and 25 of this report. Consideration should be given to the impact of onboard aircraft carriage. 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. Size and quantity limitations need to be considered for allowance aboard passenger aircraft, particularly for inclusion in passenger baggage, checked as well as carry-on. 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, IEC 62282-6-1 and IEC 62282-5). Systems coupled to appliances must include the appliance standard, and may therefore have further restrictions imposed.

New exceptions or modifications of existing exceptions in 175.10(a) may need to be developed for hydride-based hydrogen storage systems coupled to an appliance allowed aboard aircraft.

To help ensure that the standards being developed for 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 groups 7 and 8, and ULs STP 2265.