Hydrogen safety
Encyclopedia
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.
s and standards (RCS) for hydrogen
fuel cell vehicle
s, 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
.
/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.
(For comparison: Deflagration limit of gasoline in air: 1.4–7.6%; of acetylene in air, 2.5% to 82%)
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)
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 detector
s.
. 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.
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 react with steam, releasing hydrogen. Safety devices that normally burn the generated hydrogen failed due loss of electric power. To prevent further explosions, vent holes were opened on the top of remaining reactor buildings.
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
. 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.
Summary
Hydrogen is considered useful for cooling on power station generators because of its very high specific heat, however there are numerous reasons why Hydrogen safety is an important issue:- Colourless and odourless
- Low ignition energy
- High flame temperature
- Invisible flame in daylight conditions
- Negative Joule-Thompson Coefficient, meaning that a leak may self-ignite
- Small molecular size
- Wide range of Lower Explosive Limit to Upper Explosive Limit
Hydrogen codes and standards
Hydrogen codes and standards are codeCode (law)
A code is a type of legislation that purports to exhaustively cover a complete system of laws or a particular area of law as it existed at the time the code was enacted, by a process of codification. Though the process and motivations for codification are similar in common law and civil law...
s and standards (RCS) for hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
fuel cell vehicle
Fuel cell vehicle
A Fuel cell vehicle or Fuel Cell Electric Vehicle is a type of hydrogen vehicle which uses a fuel cell to produce electricity, powering its on-board electric motor...
s, stationary fuel cell applications and portable fuel cell applications
Portable fuel cell applications
Fuel cell applications are stationary fuel cell applications and portable fuel cell plications...
.
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
Hydrogen storage
Hydrogen storage describes the methods for storing H2 for subsequent use. The methods span many approaches, including high pressures, cryogenics, and chemical compounds that reversibly release H2 upon heating...
.
- Standard for the installation of stationary fuel cell power systems (National Fire Protection AssociationNational Fire Protection AssociationThe National Fire Protection Association is a United States trade association that creates and maintains private, copywrited, standards and codes for usage and adoption by local governments...
)
Guidelines
The current ANSIAnsi
Ansi is a village in Kaarma Parish, Saare County, on the island of Saaremaa, Estonia....
/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
- "Hydrogen-air mixtures can ignite with very low energy input, 1/10 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 (1 atm, 101 kPa) are 4.0 and 75.0. The flammability limits based on the volume percent of hydrogen in oxygen at 14.7 psia (1 atm, 101 kPa) 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 deflagrationDeflagrationDeflagration is a term describing subsonic combustion that usually propagates through thermal conductivity; hot burning material heats the next layer of cold material and ignites it. Most "fire" found in daily life, from flames to explosions, is deflagration...
to evolve into a detonationDetonationDetonation involves a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations are observed in both conventional solid and liquid explosives, as well as in reactive gases...
, even in the absence of gross confinement."
(For comparison: Deflagration limit of gasoline in air: 1.4–7.6%; of acetylene in air, 2.5% to 82%)
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.
- Hydrogen leaks can support combustion at very low flow rates, as low as 4 micrograms/s.
Liquid hydrogen
- "Condensed and solidified atmospheric air, or trace air accumulated in manufacturing, contaminates liquid hydrogenLiquid hydrogenLiquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.To exist as a liquid, H2 must be pressurized above and cooled below hydrogen's Critical point. However, for hydrogen to be in a full liquid state without boiling off, it needs to be...
, 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
Liquid oxygen
Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...
. 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 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 odorantHydrogen odorant
A hydrogen odorant in any form, is a minute amount of odorant such as ethyl isobutyrate, with a rotting-cabbage-like smell, that is added to the otherwise colorless and almost odorless hydrogen gas, so that leaks can be detected before a fire or explosion occurs...
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 detector
Flame detector
There are several types of flame detector. The optical flame detector is a detector that uses optical sensors to detect flames. There are also ionisation flame detectors, which use current flow in the flame to detect flame presence, and thermocouple flame detectors.-Ultraviolet:Ultraviolet ...
s.
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 acetyleneAcetylene
Acetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.As an alkyne, acetylene is unsaturated because...
. 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.
In a more recent event, an explosion of compressed hydrogen during delivery at the Muskingum River Coal Plant
Muskingum River Power Plant
Muskingum River Power Plant is a major coal-fired power station, owned and operated by American Electric Power. It is located on the west bank of Muskingum River, about north-west of the town of Beverly, Ohio, USA.-Units:...
(owned and operated by AEP
American Electric Power
American Electric Power is a major investor-owner electric utility in various parts of the United States. AEP ranks among the nation's largest generators of electricity, owning nearly 38,000 megawatts of generating capacity in the U.S...
) 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
Zircaloy
Zirconium alloys are solid solutions of zirconium or other metals, a common subgroup having the trade mark Zircaloy. Zirconium has very low absorption cross-section of thermal neutrons, high hardness, ductility and corrosion resistance...
cladded fuel rods became very hot and react with steam, releasing hydrogen. Safety devices that normally burn the generated hydrogen failed due loss of electric power. To prevent further explosions, vent holes were opened on the top of remaining reactor buildings.
See also
- Hydrogen embrittlementHydrogen embrittlementHydrogen embrittlement is the process by which various metals, most importantly high-strength steel, become brittle and fracture following exposure to hydrogen...
- Hydrogen economyHydrogen economyThe hydrogen economy is a proposed system of delivering energy using hydrogen. The term hydrogen economy was coined by John Bockris during a talk he gave in 1970 at General Motors Technical Center....
- Compressed hydrogenCompressed hydrogenCompressed hydrogen is the gaseous state of the element hydrogen kept under pressure. Compressed hydrogen in hydrogen tanks at 350 bar and 700 bar is used for mobile hydrogen storage in hydrogen vehicles...
- Liquid hydrogenLiquid hydrogenLiquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.To exist as a liquid, H2 must be pressurized above and cooled below hydrogen's Critical point. However, for hydrogen to be in a full liquid state without boiling off, it needs to be...
- Slush hydrogenSlush hydrogenSlush hydrogen is a combination of liquid hydrogen and solid hydrogen at the triple point with a lower temperature and a higher density than liquid hydrogen. It is formed by bringing liquid hydrogen down to nearly the melting point that increases density by 16–20% as compared to liquid hydrogen...
- Metallic hydrogenMetallic hydrogenMetallic hydrogen is a state of hydrogen which results when it is sufficiently compressed and undergoes a phase transition; it is an example of degenerate matter. Solid metallic hydrogen is predicted to consist of a crystal lattice of hydrogen nuclei , with a spacing which is significantly smaller...