Aircraft Carriage, Hydride Systems (30.1)

Aircraft Carriage, Hydride Systems (30.1)

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 and stand-alone systems and systems coupled to appliances. This section will discuss stand-alone systems that are being transported when not coupled to an appliance; Item 30.2 discusses aircraft carriage of systems coupled to an appliance.

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.

Hydride-based hydrogen storage systems may be transported onboard aircraft as either cargo or in passenger baggage, especially with micro systems. When transported by individuals within baggage, the systems may or may not include any original overpacking supplied by the manufacturer. For allowance onboard cargo-only aircraft, modifications to appropriate entries of the hazardous materials table, 172.101, will need to be made. Exceptions or packaging instructions may need to be included in 49 CFR 173. Packaging instructions and container specifications were discussed in Items 18 and 27 of this report.

For allowance onboard passenger aircraft, in addition to what is required for cargo-only aircraft, further consideration needs to be given to the potential hazards and risks. As cargo onboard passenger aircraft, the hazards are essentially the same as for cargo-only, however with greater potential risk of loss of life if an accident was to occur. When carried onboard passenger aircraft by passengers there is even more risk due to lesser control over packaging. Here it may be appropriate to apply limitations on individual system size or capacity and limits on amounts that can be carried by individual passengers. This allowance may require modification to the language that is required to be posted by commercial airlines, 175.25(a)(1). The language currently forbids carrying onboard aircraft of hazardous materials with several cited exceptions, such as certain smoking materials, fuel cartridges for use with micro fuel cell systems may need to be included. Section 175.75 lists quantity limitations aboard aircraft, the appropriateness of these limitations with respect to hydride-based hydrogen storage systems need to be reviewed.

Paragraph 175.75(a)(2) allows up to 25 kg (55 lb) net weight of an allowed hazardous material to be carried aboard an aircraft; for a UN 3468 material, does net weight refer to hydrogen or the hydride material? The weight of hydrogen may only be a few percent of the total hydride weight, thus 25 kg (55 lb) of hydrogen could translate into several hundred kilograms of hydride material. In addition 175.75(b) places no quantity limitation on ORM-D materials, limitations may be appropriate if non-rechargeable hydride-based systems are shipped under ORM-D exceptions.

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.

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.

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.
  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 and IEC 62282-6-1).

The language required to be posted by commercial airlines, 175.25(a)(1) needs to be reviewed for any appropriate changes if hydride-based hydrogen storage systems are allowed to be carried aboard aircraft by passengers. The quantity limitations of 175.25(a) and (b) need to be reviewed for appropriateness and possible revision if hydride-based hydrogen storage systems are 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 group 8, and ULs STP 2265.