Hydrogen safety covers the safe production, handling and use of hydrogen - particularly hydrogen gas fuel and liquid hydrogen. The main concern in working with hydrogen is flammability.
Contents
- Summary
- Hydrogen codes and standards
- Guidelines
- Ignition
- Mixtures
- Leaks
- Liquid hydrogen
- Prevention
- Incidents
- References
Hydrogen possesses the NFPA 704's highest rating of 4 on the flammability scale because it elemental form of H2 hydrogen gas flameable when mixed even in small amounts with ordinary air; hydrogen gas and normal air can ignite at as low as 4% air due to the oxygen in the air and the simplicity and chemical properties of the reaction. However, hydrogen has no rating for innate hazard for reactivity or toxicity. The storage and use of hydrogen poses unique challenges due to its ease of leaking as a gaseous fuel, low-energy ignition, wide range of combustible fuel-air mixtures, buoyancy, and its ability to embrittle metals that must be accounted for to ensure safe operation. Liquid hydrogen poses additional challenges due to its increased density and the extremely low temperatures needed to keep it in liquid form.
Summary
Hydrogen codes and standards
Hydrogen codes and standards are codes and standards (RCS) for hydrogen fuel cell vehicles, stationary fuel cell applications and portable fuel cell applications.
Additional to the codes and standards for hydrogen technology products, there are codes and standards for hydrogen safety, for the safe handling of hydrogen and the storage of hydrogen.
Guidelines
The current ANSI/AIAA standard for hydrogen safety guidelines is AIAA G-095-2004, Guide to Safety of Hydrogen and Hydrogen Systems. As NASA has been one of the world's largest users of hydrogen, this evolved from NASA's earlier guidelines, NSS 1740.16 (8719.16). These documents cover both the risks posed by hydrogen in its different forms and how to ameliorate them.
Ignition
Mixtures
(For comparison: Deflagration limit of gasoline in air: 1.4–7.6%; of acetylene in air, 2.5% to 82%)
Leaks
Liquid hydrogen
Liquid Hydrogen requires complex storage technology such as the special thermally insulated containers and requires special handling common to all cryogenic substances. This is similar to, but more severe than liquid oxygen. Even with thermally insulated containers it is difficult to keep such a low temperature, and the hydrogen will gradually leak away. (Typically it will evaporate at a rate of 1% per day.)
Prevention
Hydrogen collects under roofs and overhangs, where it forms an explosion hazard; any building that contains a potential source of hydrogen should have good ventilation, strong ignition suppression systems for all electric devices, and preferably be designed to have a roof that can be safely blown away from the rest of the structure in an explosion. It also enters pipes and can follow them to their destinations. Hydrogen pipes should be located above other pipes to prevent this occurrence. Hydrogen sensors allow for rapid detection of hydrogen leaks to ensure that the hydrogen can be vented and the source of the leak tracked down. As in natural gas, an odorant can be added to hydrogen sources to enable leaks to be detected by smell. While hydrogen flames can be hard to see with the naked eye, they show up readily on UV/IR flame detectors.
Incidents
Hydrogen has been portrayed in the popular press as a relatively more dangerous fuel, and hydrogen in fact has the widest explosive/ignition mix range with air of all gases except acetylene. However this is mitigated by the fact that hydrogen rapidly rises and disperses before ignition, and unless the escape is in an enclosed, unventilated area, it is unlikely to be serious.
Demonstrations have shown that a fuel fire in a hydrogen-powered vehicle can burn out completely with little damage to the vehicle, in stark contrast to the expected result in a gasoline-fueled vehicle.
In a more recent event, an explosion of compressed hydrogen during delivery at the Muskingum River Coal Plant (owned and operated by AEP) caused significant damage and killed one person. For more information on incidents involving hydrogen, visit the US DOE's Hydrogen Incident Reporting and Lessons Learned page.
During the 2011 Fukushima nuclear emergency, four reactor buildings were damaged by hydrogen explosions. Exposed Zircaloy cladded fuel rods became very hot and reacted with steam, releasing hydrogen. Safety devices that normally burn the generated hydrogen failed due to loss of electric power. Catalytic hydrogen recombiners, mandatory in other countries, were not installed. To prevent further explosions, vent holes were opened in the top of the remaining reactor buildings.