Hydrogen safety covers the safe production, handling and use of hydrogen, particularly hydrogen gas fuel and liquid hydrogen. Hydrogen possesses the NFPA 704's highest rating of four on the flammability scale because it is flammable when mixed even in small amounts with ordinary air. Ignition can occur at a volumetric ratio of hydrogen to air as low as 4% 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-energyignition, wide range of combustible fuel-air mixtures, buoyancy, and its ability to embrittle metals that must be accounted for to ensure safe operation.[1]
Hydrogen has one of the widest explosive/ignition mix range with air of all the gases with few exceptions such as acetylene, silane, and ethylene oxide, and in terms of minimum necessary ignition energy and mixture ratios has extremely low requirements for an explosion to occur. This means that whatever the mix proportion between air and hydrogen, when ignited in an enclosed space a hydrogen leak will most likely lead to an explosion, not a mere flame.[2]
There are many codes and standards regarding hydrogen safety in storage, transport, and use. These range from federal regulations,[3] ANSI/AIAA,[4] NFPA,[5] and ISO[6] standards. The Canadian Hydrogen Safety Program concluded that hydrogen fueling is as safe as, or safer than, compressed natural gas (CNG) fueling,[7]
The fire diamond hazard sign for both elemental hydrogen gas and its isotope deuterium.[8][9]
There are a number of items to consider to help design systems and procedures to avoid accidents when dealing with hydrogen, as one of the primary dangers of hydrogen is that it is extremely flammable.[10]
Inerting chambers and purging gas lines are important standard safety procedures to take when transferring hydrogen. In order to properly inert or purge, the flammability limits must be taken into account, and hydrogen's are very different from other kinds of gases. At normal atmospheric pressure it is 4% to 75%, based on the volume percent of hydrogen in oxygen it is 4% to 94%, while the limits of the detonation potential of hydrogen in air are 18.3% to 59% by volume.[1][11][12][13][14] In fact, these flammability limits can often be more stringent than this, as the turbulence during a fire can cause a deflagration which can create detonation. For comparison the deflagration limit of gasoline in air is 1.4–7.6%, and of acetylene in air,[15] 2.5–82%.
Therefore, when equipment is open to air before or after a transfer of hydrogen, there are unique conditions to take into consideration that might have otherwise been safe with transferring other kinds of gases. Incidents have occurred because inerting or purging was not sufficient, or because the introduction of air in the equipment was underestimated (e.g., when adding powders), resulting in an explosion.[16] For this reason, inerting or purging procedures and equipment are often unique to hydrogen, and often the fittings or marking on a hydrogen line should be completely different to ensure that this and other processes are properly followed, as many explosions have happened simply because a hydrogen line was accidentally plugged into a main line or because the hydrogen line was confused with another.[17][18][19]
The minimum ignition energy of hydrogen in air is one of the lowest among known substances at 0.02 mJ, and hydrogen-air mixtures can ignite with 1/10 the effort of igniting gasoline-air mixtures.[1][11] Because of this, any possible ignition source has to be scrutinized. Any electrical device, bond, or ground should meet applicable hazardous area classification requirement.[20][21] Any potential sources (like some ventilation system designs[22]) for static electricity build-up should likewise be minimized, e.g. through antistatic devices.[23]
Hot-work procedures must be robust, comprehensive, and well-enforced; and they should purge and ventilate high-areas and sample the atmosphere before work. Ceiling-mounted equipment should likewise meet hazardous area requirements (NFPA 497).[16] Finally, rupture discs should not be used as this has been a common ignition source for multiple explosions and fires. Instead other pressure relief systems such as a relief valve should be used.[24][25]
There are four main chemical properties to account for when dealing with hydrogen that can come into contact with other materials even in normal atmospheric pressures and temperatures:
The chemistry of hydrogen is very different from traditional chemicals. E.g., with oxidation in ambient environments. And neglecting this unique chemistry has caused issues at some chemical plants.[26] Another aspect to be considered as well is the fact that hydrogen can be generated as a byproduct of a different reaction may have been overlooked, e.g. Zirconium and steam creating a source of hydrogen.[27][28][14] This danger can be circumvented somewhat via the use of passive autocatalytic recombiners.
Another major issue to consider is the chemical compatibility of hydrogen with other common building materials like steel.[29][30] Because of hydrogen embrittlement, material compatibility with hydrogen is specially considered.[14]
These considerations can further change because of special reactions at high temperatures.[14]
The diffusivity of hydrogen is very different from ordinary gases, and therefore gasketing materials have to be chosen carefully.[31][32]
The buoyant forces and stresses on mechanical bodies involved are often reversed from standard gases. For example, because of buoyancy, stresses are often pronounced near the top of a large storage tank.[33][14]
All four of these factors are considered during the initial design of a system using hydrogen, and is typically accomplished by limiting the contact between susceptible metals and hydrogen, either by spacing, electroplating, surface cleaning, material choice, and quality assurance during manufacturing, welding, and installation. Otherwise, hydrogen damage can be managed and detected by specialty monitoring equipment.[34][16]
Locations of hydrogen sources and piping have to be chosen with care. Since hydrogen is a lighter-than-air gas, it collects under roofs and overhangs (typically referred to as trapping sites), where it forms an explosion hazard.[14] Many individuals are familiar with protecting plants from heavier-than-air vapors, but are unfamiliar with "looking up", and is therefore of particular note.[33] It can also enter pipes and can follow them to their destinations. Because of this, hydrogen pipes should be well-labeled and located above other pipes to prevent this occurrence.[10][16]
Even with proper design, hydrogen leaks can support combustion at very low flow rates, as low as 4 micrograms/s.[1][35][12] To this end, detection is important. Hydrogen sensors or a katharometer allow for rapid detection of hydrogen leaks to ensure that the hydrogen can be vented and the source of the leak tracked down. Around certain pipes or locations special tapes can be added for hydrogen detection purposes. A traditional method is to add a hydrogen odorant with the gas as is common with natural gas. In fuel cell applications these odorants can contaminate the fuel cells, but researchers are investigating other methods that might be used for hydrogen detection: tracers, new odorant technology, advanced sensors, and others.[1]
While hydrogen flames can be hard to see with the naked eye (it can have a so-called "invisible flame"), they show up readily on UV/IR flame detectors. More recently Multi IR detectors have been developed, which have even faster detection on hydrogen-flames.[36][37] This is quite important in fighting hydrogen fires, as the preferred method of fighting a fire is stopping the source of the leak, as in certain cases (namely, cryogenic hydrogen) dousing the source directly with water may cause icing, which in turn may cause a secondary rupture.[38][33]
Aside from flammability concerns, in enclosed spaces, hydrogen can also act as an asphyxiant gas.[1] Therefore, one should make sure to have proper ventilation to deal with both issues should they arise, as it is generally safe to simply vent hydrogen into the atmosphere. However, when placing and designing such ventilation systems, one must keep in mind that hydrogen will tend to accumulate towards the ceilings and peaks of structures, rather than the floor. Many dangers may be mitigated by the fact that hydrogen rapidly rises and often disperses before ignition.[39][16]
In certain emergency or maintenance situations, hydrogen can also be flared.[40][14] For example, a safety feature in some hydrogen-powered vehicles is that they can flare the fuel if the tank is on fire, burning out completely with little damage to the vehicle, in contrast to the expected result in a gasoline-fueled vehicle.[41]
Inventory management and facility spacing
Ideally, no fire or explosion will occur, but the facility should be designed so that if accidental ignition occurs, it will minimize additional damage. Minimum separation distances between hydrogen storage units should be considered, together with the pressure of said storage units (c.f., NFPA 2 and 55). Explosion venting should be laid out so that other parts of the facility will not be harmed. In certain situations, this translates to a roof that can be safely blown away from the rest of the structure in an explosion.[16]
Liquid hydrogen has a slightly different chemistry compared to other cryogenic chemicals, as trace accumulated air can easily contaminate liquid hydrogen and form an unstable mixture with detonative capabilities similar to TNT and other highly explosive materials. Because of this, 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.[1][42]
The main danger with cryogenic hydrogen is what is known as BLEVE (boiling liquid expanding vapor explosion). Because hydrogen is gaseous in atmospheric conditions, the rapid phase change together with the detonation energy combine to create a more hazardous situation.[43] A secondary danger is the fact that many materials change from being to ductile to brittle at extremely cold temperatures, allowing new places for leaks to form.[14]
Human factors
Along with traditional job safety training, checklists to help prevent commonly skipped steps (e.g., testing high points in the work area) are often implemented, along with instructions on the situational dangers that come inherent to working with hydrogen.[16][44]
As the zeppelin Hindenburg was approaching landing, a fire detonated one of the aft hydrogen cells, thereby rupturing neighboring cells and causing the airship to fall to the ground aft-first. The inferno then travelled towards the stern, bursting and igniting the remaining cells.
Despite four news stations recording the disaster on film and surviving eyewitness testimonies from crew and people on the ground, the cause of the initial fire was never conclusively determined.[citation needed]
A large LH2 tank ruptured and exploded, killing all 7 astronauts aboard the Space Shuttle Challenger
A faulty O-ring on the solid rocket booster allowed hot gases and flames to impinge upon the external LH2 tank, causing the tank wall to weaken and then burst. The thrust generated from the contents of the tank caused the LOX tank above to also rupture, and this mixture of LH2/LOX then detonated, destroying the orbiter in the explosion.
1999
Hanau, Germany
A large chemical tank used to store hydrogen for manufacturing processes exploded.
The tank was designed to lie on its side, but instead was laid upright. The forces towards the top of the tank caused it to rupture and then explode.[33]
Three reactor buildings were damaged by hydrogen explosions.
Exposed Zircaloy cladded fuel rods became very hot and reacted with steam, releasing hydrogen.[50][51] The containments were filled with inert nitrogen, which prevented hydrogen from burning in the containment. However, the hydrogen leaked from the containment into the reactor building, where it mixed with air and exploded.[52] To prevent further explosions, vent holes were opened in the top of the remaining reactor buildings.
On the way to an FCVhydrogen station, a truck carrying about 24 compressed hydrogen tanks caught fire. This caused the evacuation initially of a one-mile radius area of Diamond Bar. The fire broke out on the truck at about 1:20p.m. at the intersection of South Brea Canyon Road and Golden Springs Drive, according to a Los Angeles County Fire Department dispatcher.[54][55][56][57]
Leak in transfer hose.[66] This resulted in the temporary shutdown of multiple hydrogen fueling stations in the San Francisco area.[67]
June 2019
Norway
A Uno-X fueling station experienced an explosion,[68] resulting in the shutdown of all Uno-X hydrogen fueling stations and a temporary halt in sales of fuel cell vehicles in the country.[69]
Investigations determined that neither the electrolyzer nor the dispenser used by customers had anything to do with this incident.[70][71] Instead, Nel ASA announced the root cause of the incident had been identified as an assembly error of the use of a specific plug in a hydrogen tank in the high-pressure storage unit.[72]
An explosion caused significant damage to surrounding buildings. The blast was felt several miles away, damaging about 60 homes. No injuries from the explosion were reported.
The incident remains under investigation.[76][77][78][79] The company published a press release: Hydrogen Safety Systems Operated Effectively, Prevented Injury at Plant Explosion.[80]
A hydrogen tank at Global Tungsten & Powders Corp. exploded. A spokesperson for the company said five employees were taken to hospitals with non-life-threatening injuries.
OSHA and company officials are investigating the incident.
A pickup truck towing a trailer carrying full hydrogen tanks on US-23 in Delaware County Ohio explodes after crash. Three people were transported to a hospital with minor injuries.
An outdoor hydrogen tank exploded at the premises of HypTec in Austria, causing massive damage due to the pressure wave which could be felt 3 km away. The personnel at the site was indoor and only minor injuries to an employee occurred.
Standard for gaseous hydrogen systems at consumer sites
NFPA 50B
Standard for liquefied hydrogen systems at consumer sites
NFPA 52
Compressed Natural Gas Vehicular Fuel Systems Code
NFPA 57
Liquefied natural gas vehicular fuel systems standard[104]
Guidelines
The current ANSI/AIAA standard for hydrogen safety guidelines is AIAA G-095-2004, Guide to Safety of Hydrogen and Hydrogen Systems.[105] 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).[14] These documents cover both the risks posed by hydrogen in its different forms and how to ameliorate them. NASA also references Safety Standard for Hydrogen and Hydrogen Systems [106] and the Sourcebook for Hydrogen Applications.[107][102]
Another organization responsible for hydrogen safety guidelines is the Compressed Gas Association (CGA), which has a number of references of their own covering general hydrogen storage,[108] piping,[109] and venting.[110][102]
Propane is a three-carbon alkane with the molecular formula C3H8. It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel in domestic and industrial applications and in low-emissions public transportation. Discovered in 1857 by the French chemist Marcellin Berthelot, it became commercially available in the US by 1911. Propane is one of a group of liquefied petroleum gases. The others include propylene, butane, butylene, butadiene, isobutylene, and mixtures thereof. Propane has lower volumetric energy density, but higher gravimetric energy density and burns more cleanly than gasoline and coal.
A pipeline is a system of pipes for long-distance transportation of a liquid or gas, typically to a market area for consumption. The latest data from 2014 gives a total of slightly less than 2,175,000 miles (3,500,000 km) of pipeline in 120 countries around the world. The United States had 65%, Russia had 8%, and Canada had 3%, thus 76% of all pipeline were in these three countries. The main attribute to pollution from pipelines is caused by corrosion and leakage
Liquid hydrogen (H2(l)) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.
A hypergolic propellant is a rocket propellant combination used in a rocket engine, whose components spontaneously ignite when they come into contact with each other.
A substance is pyrophoric if it ignites spontaneously in air at or below 54 °C (129 °F) or within 5 minutes after coming into contact with air. Examples are organolithium compounds and triethylborane. Pyrophoric materials are often water-reactive as well and will ignite when they contact water or humid air. They can be handled safely in atmospheres of argon or nitrogen. Class D fire extinguishers are designated for use in fires involving pyrophoric materials. A related concept is hypergolicity, in which two compounds spontaneously ignite when mixed.
Liquefied petroleum gas, also referred to as liquid petroleum gas, is a fuel gas which contains a flammable mixture of hydrocarbon gases, specifically propane, n-butane and isobutane. It can sometimes contain some propylene, butylene, and isobutene.
A compressed-air vehicle (CAV) is a transport mechanism fueled by tanks of pressurized atmospheric gas and propelled by the release and expansion of the gas within a pneumatic motor.
Cryogenic fuels are fuels that require storage at extremely low temperatures in order to maintain them in a liquid state. These fuels are used in machinery that operates in space where ordinary fuel cannot be used, due to the very low temperatures often encountered in space, and the absence of an environment that supports combustion. Cryogenic fuels most often constitute liquefied gases such as liquid hydrogen.
A fuel tank is a safe container for flammable fluids, often gasoline or diesel fuel. Though any storage tank for fuel may be so called, the term is typically applied to part of an engine system in which the fuel is stored and propelled or released into an engine. Fuel tanks range in size and complexity from the small plastic tank of a butane lighter to the multi-chambered cryogenic Space Shuttle external tank.
A flash fire is a sudden, intense fire caused by ignition of a mixture of air and a dispersed flammable substance such as a solid, flammable or combustible liquid, or a flammable gas. It is characterized by high temperature, short duration, and a rapidly moving flame front.
In electrical and safety engineering, hazardous locations are places where fire or explosion hazards may exist. Sources of such hazards include gases, vapors, dust, fibers, and flyings, which are combustible or flammable. Electrical equipment installed in such locations can provide an ignition source, due to electrical arcing, or high temperatures. Standards and regulations exist to identify such locations, classify the hazards, and design equipment for safe use in such locations.
Mixtures of dispersed combustible materials and oxygen in the air will burn only if the fuel concentration lies within well-defined lower and upper bounds determined experimentally, referred to as flammability limits or explosive limits. Combustion can range in violence from deflagration through detonation.
The Hazardous Materials Identification System (HMIS) is a numerical hazard rating that incorporates the use of labels with color developed by the American Coatings Association as a compliance aid for the OSHA Hazard Communication (HazCom) Standard.
A bivalent engine is an engine that can use two different types of fuel. Examples are petroleum/CNG and petroleum/LPG engines, which are widely available in the European passenger vehicle aftermarket.
A combustible material is a material that can burn in air under certain conditions. A material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable material catches fire immediately on exposure to flame.
A dust explosion is the rapid combustion of fine particles suspended in the air within an enclosed location. Dust explosions can occur where any dispersed powdered combustible material is present in high-enough concentrations in the atmosphere or other oxidizing gaseous medium, such as pure oxygen. In cases when fuel plays the role of a combustible material, the explosion is known as a fuel-air explosion.
A flame arrester, deflagration arrester, or flame trap is a device or form of construction that will allow free passage of a gas or gaseous mixture but will interrupt or prevent the passage of flame. It prevents the transmission of flame through a flammable gas/air mixture by quenching the flame on the high surface area provided by an array of small passages through which the flame must pass. The emerging gases are cooled enough to prevent ignition on the protected side.
A hydrogen infrastructure is the infrastructure of hydrogen pipeline transport, points of hydrogen production and hydrogen stations for distribution as well as the sale of hydrogen fuel, and thus a crucial prerequisite before a successful commercialization of automotive fuel cell technology.
In fire and explosion prevention engineering, inerting refers to the introduction of an inert (non-combustible) gas into a closed system to make a flammable atmosphere oxygen deficient and non-ignitable.
Hydrogen transport involves the use of technology to transport hydrogen from the point of generation to the point of use.
↑ "Hydrogen". cameochemicals.noaa.gov. Retrieved Nov 29, 2020.
↑ "Deuterium". cameochemicals.noaa.gov. Retrieved Nov 29, 2020.
1 2 Utgikar, Vivek P.; Thiesen, Todd (2005). "Safety of compressed hydrogen fuel tanks: Leakage from stationary vehicles". Technology in Society. 27 (3): 315–320. doi:10.1016/j.techsoc.2005.04.005.
1 2 Lewis, Bernard; Guenther, von Elbe (1961). Combustion, Flames and Explosions of Gases (2nded.). New York: Academic Press, Inc. p.535. ISBN978-0124467507.
↑ "Hydrogen Lab Fire". H2Tools. Pacific Northwest National Laboratory. September 2017.
↑ "Fire at Hydrogen Fueling Station". H2Tools. Pacific Northwest National Laboratory. September 2017. The initial source of fire was likely a release of hydrogen from a failed weld on a pressure switch.
↑ "Small Fire in Fule Cell Test Stand". H2Tools. Pacific Northwest National Laboratory. September 2017. An electrical short circuit occurred, causing a small electrical fire.
↑ "Incorrect Relief Valve Set Point Leads to Explosion". H2Tools. Pacific Northwest National Laboratory. September 2017. Contributing cause was poor design of the venting system, which was installed in a horizontal position, causing inadequate venting and buildup of static electricity.
↑ "Fuel Cell Evaporation Pad Fire". H2Tools. Pacific Northwest National Laboratory. September 2017. One theory presented the possibility of a spark (caused by static electricity) being the source of the ignition that caused the fire. Due to the proximity of the fuel cell unit to a shrink-wrap packaging machine at the time of the incident, this seemed to be a plausible hypothesis.
↑ "Hydrogen Explosion Due to Inadequate Maintenance". H2Tools. Pacific Northwest National Laboratory. September 2017. As a corrective action, eliminate burst discs from hydrogen storage assembly. Redesign venting system for the pressure relief valves to prevent or inhibit moisture build up and allow moisture drainage.
↑ "Hydrogen Explosion at Coal-Fired Power Plant". H2Tools. Pacific Northwest National Laboratory. September 2017. Explore elimination of rupture disk PRDs and substitution of spring-style relief valves.
↑ "Gaseous Hydrogen Leak and Explosion". H2Tools. Pacific Northwest National Laboratory. September 2017. A GH2 leak occurred in an underground ASTM A106 Grade B, Schedule XX carbon steel pipe with a 3.5-inch diameter and a 0.6-inch wall thickness. The pipe was coated with coal tar primer and coal tar enamel, wrapped with asbestos felt impregnated with coal tar, coated with a second coat of coal tar enamel, and wrapped in Kraft paper, in accordance with American Water Works Association Standard G203. The source of the leak was an oval hole about 0.15 in x 0.20 in at the inner surface of the pipe and about 2-in in diameter at the outer surface of the pipe. Upon excavation of the pipe, it was noted that the coating was not present at the leak point. This resulted in galvanic corrosion over a 15-year period and the eventual rupture when high-pressure gas was applied to the thin pipe membrane. The pipe was 8 ft 9 in below the concrete pad.
↑ "Leak on Compressor at Fueling Station". H2Tools. Pacific Northwest National Laboratory. September 2017. This allowed greater movement of the shaft, which led to a shaft seal leaking hydrogen.
↑ M.S. Butler, C.W. Moran, Peter B. Sunderland, R.L. Axelbaum, Limits for Hydrogen Leaks that Can Support Stable Flames, International Journal of Hydrogen Energy 34 (2009) 5174–5182.
↑ "Emergency Response Handbook"(PDF). Piplines and Hazardous Materials Safety Administration - Department of Transportation. 2008. p.115. Archived from the original(PDF) on 3 June 2009. Do not direct water at source of leak or safety devices; icing may occur.
↑ "Hydrogen explosion in Austria". www.hydrogenfuelnews.com. August 8, 2023. Retrieved 2023-11-25. I live more than 3km away... and the blast made my windows shake
↑ Safety Standard for Hydrogen and Hydrogen Systems: Guidelines for Hydrogen System Design, Materials Selection, Operations, Storage, and Transportation. Washington, DC: Office of Safety and Mission Assurance, National Aeronautics and Space Administration. 1997-10-29. NASA TM-112540, NSS 1740.16.
↑ Sourcebook for Hydrogen Applications. Quebec, CA: Hydrogen Research Institute and the National Renewable Energy Laboratory. 1998.
↑ Hydrogen (4thed.). Arlington, VA: Compressed Gas Association, Inc. 1991.
↑ Standard for Hydrogen Piping Systems (1sted.). Arlington, VA: Compressed Gas Association, Inc. 1992.
↑ Hydrogen Vent Systems (1sted.). Arlington, VA: Compressed Gas Association, Inc. 1996.
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