Progress: Addressed, Not Adequately
DOT Relevance: 172 Subpart G
This key area pertains to the availability of appropriate information resources needed by first responders to potential emergencies (e.g., accidents) involving hydrogen stored and transported as a compressed gas in composite cylinders, which may be part of a hydrogen fueling infrastructure. Composite cylinders as used here refers to a broad range of pressure vessel types that include metallic or polymer shells (liners) that are reinforced by being hoop- wrapped or full-wrapped with high-strength carbon, fiberglass, or other fibers, which are generally resin impregnated. DOT special permits currently allow compressed hydrogen to be transported in certain specific types of composite packagings, as specified in the special permit language.
The emergency response information must be applicable to tube trailers and/or any other compressed hydrogen composite cylinder packaging. In particular, the emergency response information resources must apply to operations such as the transfer of hydrogen from tube trailers to stationary pressure vessels at vehicle fueling stations, temporary parking of tube trailers to provide the hydrogen source at a fueling station, delivery of hydrogen-filled composite cylinders to fueling stations, and the use of hydrogen mobile fuelers with composite pressure vessels.
This key area will be critical if hydrogen fueling infrastructures evolve that utilize hydrogen transported as a compressed gas in composite cylinders. Examples include hydrogen transported in tube trailers from central production plants to fueling stations (with the gas transferred to permanently installed high-pressure vessels at the fueling station, or, as is more common, parking of the tube trailer at the fueling station to serve as a temporary gas supply) and mobile fuelers (some of which utilize compressed hydrogen stored in composite cylinders). However, the economic viability of these infrastructure scenarios appears to be poor at this time, and so they are unlikely to be part of potential future hydrogen-fueled vehicle commercialization. The economic problems derive from the fact that, even with composite cylinders, the total quantity of hydrogen that can be transported in a tube trailer (or a mobile fueler) is such that the cost per unit mass or energy of hydrogen delivered to a fueling station would require the dispensed hydrogen cost to substantially exceed established goals.
As discussed below, emergency response resources applicable to accidents involving compressed hydrogen in steel pressure vessels (e.g., as used in tube trailers) are well developed for current applications, which are generally limited to restricted-access industrial sites and trained personnel. These same resources are probably appropriate and adequate for supporting current tests and demonstrations of hydrogen vehicles, which are few in number, have limited access, and are closely managed by trained personnel. A possible exception may be associated with current and future use of mobile fueling stations that store hydrogen in composite vessels. These units involve a relatively unusual combination of components (e.g., unlike tube trailers, they are not addressed specifically in the DOT ERG2004) and their application straddles two jurisdictions (i.e., DOT when they are transported on highways and OSHA/local AHJs when they are parked and operated as vehicle fueling stations).
Another issue may derive from the fact that current experience and emergency response information resources pertain primarily to applications such as tube trailers equipped with steel pressure vessels, which are designed, manufactured, tested, and marked consistent with DOT-3A or -33A specifications in 49 CFR 178.36 and 178.37, respectively. An accident involving a composite tube trailer in a fire situation, for example, may include special issues associated with the flammability or combustion product toxicity of the fiber materials or resins used in composite pressure vessel construction.
If hydrogen-fueled vehicles commercialize with a fueling infrastructure that involves tube trailers and/or the use of any other composite pressure vessels in DOT-jurisdiction applications, then new and specifically focused emergency response resources will be needed to enable first responders to deal effectively with potential accidents in environments such as public-access fueling stations. Moreover, these emergency response information resources will need to address any special emergency response requirements associated with the fact that the pressure vessels are of composite construction rather than steel construction.
Progress toward providing the technical basis to support development of emergency response information applicable to a potential hydrogen fuel infrastructure involving compressed hydrogen stored in composite cylinders is rated as Addressed, Not Adequately. This is because, although resources are currently available to guide emergency response to accidents involving compressed hydrogen packaging and transportation systems using steel pressure vessels, these were not developed with the anticipation that they would apply to public access situations such as fueling stations, and they do not include any special considerations that may be associated with composite materials (e.g., the previously mentioned potential flammability or combustion product issues).
The above-referenced currently available emergency response information resources include the DOT ERG2004. Compressed hydrogen is assigned ID Number 1049 and covered by Guide Number 115 (GassesFlammable, Including Refrigerated Liquids). Emergency response guidance pertaining to tube trailers that might transport hydrogen is also contained in literature produced by industrial gas companies (e.g., Safetygrams) and other sources.
In 2005, the NASFM and DOTs RITA established the Hydrogen Executive Leadership Panel (HELP). HELPs mission is to bring together emergency responders, government regulators, scientists, consumers and experts from the automotive and energy industries to facilitate a safe and orderly transition to hydrogen and other alternative fuel sources. HELP will focus on issues involved in training, educating, and mobilizing emergency responders to work with government, industry, and community groups to facilitate and ensure hydrogen transport, storage and distribution, and the safety of vehicles and environs.
ASME's Boiler and Pressure Vessel project team on hydrogen tanks is addressing high pressure gas storage in metal and composite tanks. The work plan includes a proposed new article KD-10 to Section VIII-3, a code case on composite tanks for Section VIII-3, and a revision to code case 2390 on metal lined composite reinforced circumferentially wrapped pressure vessels under Section VIII-3. Transport tanks may also be included in Section XII.
It is recommended that progress toward hydrogen-fueled vehicle commercialization should be monitored, and if there are indications that composite pressure vessels may be used as part of the fueling infrastructure beyond the pre-commercial demonstration phase (e.g., for tube trailer delivery of hydrogen to fueling stations), then work to develop appropriate emergency response information resources should be initiated. These resources should address any particular requirements associated with compressed hydrogen delivery and unloading at public-access fueling stations and any special issues associated with the use of composite rather than steel pressure vessels.
More research is also needed to develop emergency response resources applicable to mobile hydrogen fueling stations with composite pressure vessels, especially if the use of such mobile fueling stations increases.