Hydrogen safety

Hydrogen safety covers the safe use and handling of hydrogen. Hydrogen poses unique challenges due to its ease of leaking, 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 extremely low temperatures.

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.
*Standard for the installation of stationary fuel cell power systems (National Fire Protection Association)

Guidelines

The current ANSI/AIAA standard for hydrogen safety guidelines is AIAA G-095-2004, Guide to Safety of Hydrogen and Hydrogen Systems [cite web
url= http://aero-defense.ihs.com/document/abstract/GFEIHBAAAAAAAAAA
title= AIAA G-095-2004, Guide to Safety of Hydrogen and Hydrogen Systems
format= PDF
publisher= AIAA
accessdate = 2008-07-28] . 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). [cite web
url= http://www.hq.nasa.gov/office/codeq/doctree/canceled/871916.pdf
title= Safety Standard for Hydrogen and Hydrogen Systems
last= Gregory | first= Frederick D.
date= Feb. 12, 1997 | format= PDF |work= |publisher= NASA
accessdate= 2008-05-09 ] These documents cover both the risks posed by hydrogen in its different forms and how to ameliorate them.

Ignition

* "Hydrogen-air mixtures can ignite with very low energy input, 1/10th that required igniting a gasoline-air mixture. For reference, an invisible spark or a static spark from a person can cause ignition."
* "Although the autoignition temperature of hydrogen is higher than those for most hydrocarbons, hydrogen's lower ignition energy makes the ignition of hydrogen–air mixtures more likely. The minimum energy for spark ignition at atmospheric pressure is about 0.02 millijoules."

Mixtures

* "The flammability limits based on the volume percent of hydrogen in air (at 14.7 psia) are 4.0 and 75.0. The flammability limits based on the volume percent of hydrogen in oxygen (at 14.7 psia) are 4.0 and 94.0."
* "Explosive limits of hydrogen in air are 18.3 to 59 percent by volume"
* "Flames in and around a collection of pipes or structures can create turbulence that causes a deflagration to evolve into a detonation, even in the absence of gross confinement."

(For comparison: Deflagration limit of gasoline in air: 1.4–7.6%)

Leaks

* "Leakage, diffusion, and buoyancy: These hazards result from the difficulty in containing hydrogen. Hydrogen diffuses extensively, and when a liquid spill or large gas release occurs, a combustible mixture can form over a considerable distance from the spill location."
* "Hydrogen, in both the liquid and gaseous states, is particularly subject to leakage because of its low viscosity and low molecular weight (leakage is inversely proportional to viscosity). Because of its low viscosity alone, the leakage rate of liquid hydrogen is roughly 100 times that of JP-4 fuel, 50 times that of water, and 10 times that of liquid nitrogen."

Liquid hydrogen

* "Condensed and solidified atmospheric air, or trace air accumulated in manufacturing, contaminates liquid hydrogen, thereby forming an unstable mixture. This mixture may detonate with effects similar to those produced by trinitrotoluene (TNT) and other highly explosive materials"

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. [http://www.almc.army.mil/alog/issues/MayJun00/MS492.htm] )

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 ventillation, 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 microsensors 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.

Accidents

Hydrogen has been feared 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 the gases except acetylene. However this can be mitigated by the fact that hydrogen rapidly rises and disperses before ignition. Unless the escape is in an enclosed, unventilated area, it is unlikely to be serious. Hydrogen also usually rapidly escapes after containment breach. Additionally, hydrogen flames are difficult to see, so may be difficult to fight. An experiment performed at the University of Miami attempted to counter this by showing that hydrogen escapes while gasoline remains by setting alight hydrogen- and petrol-fuelled vehicles. [ cite web
url= http://www.evworld.com/article.cfm?storyid=482
title= Hydrogen Car Fire Surprise
date= January 18, 2003 |work= |publisher=
accessdate= 2008-05-09 ]

In the LZ 129 Hindenburg disaster, 2/3 of passengers and crew survived. The skin of the Hindenburg may have contributed to the actual blaze. Of the 62 passengers, 27 died. Of the 27 dead, 25 jumped to their deaths from the stricken airship in panic. The other 2 that died did so due to the fire spreading to the diesel powered engines. The hydrogen combustion itself was above, and mostly away from the gondola.

In a more recent event, an explosion of compressed hydrogen during delivery at the AEP Muskingum River Coal Plant caused significant damage and killed one person. [ cite web
url= http://www.washingtonpost.com/wp-dyn/content/article/2007/01/08/AR2007010800350.html
title= "Ohio Power Plant Blast Kills 1, Hurts 9"
last= Williams | first= Mark
date= January 8, 2007 |work= | publisher= Associated Press
accessdate= 2008-05-09 ] [ cite web
url= http://www.eei.org/meetings/nonav_2007-04-29-cs/Citations_Accident_Review.pdf
title= Muskingum River Plant Hydrogen Explosion January 8, 2007
date= November 11, 2006 | format= PDF |publisher= American Electric Power
accessdate= 2008-05-09 ]

ee Also

*Hydrogen embrittlement
*Hydrogen economy
*Compressed hydrogen
*Liquid hydrogen
*Slush hydrogen
*Metallic hydrogen

References

External links

* [http://www.hysafe.org/ Hysafe]
* [http://www.hydrogenandfuelcellsafety.info Hydrogen and fuelcell safety]
* [http://www.ehammertraining.us/energy/h2_login/login.cfm DOE-Hydrogen safety for First Responders]
* [http://hazmat.dot.gov/pubs/erg/erg2008_eng.pdf First Responders - Emergency Response Guidebook - Guide 115]