Hydrogen safety
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.
Hydrogen possesses the NFPA 704's highest rating of 4 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-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
- For over 40 years, industry has used hydrogen in vast quantities as an industrial chemical and fuel for space exploration. During that time, industry has developed an infrastructure to produce, store, transport and utilize hydrogen safely.
- Hydrogen gas is an extremely high-powered fuel. It burns with incredible speed and can produce incredible force and is used mostly for applications that require vast amounts of instantaneous power - such as rocketry and spaceflight. For instance, it was used to power the Space Shuttle.
- Liquid hydrogen is sometimes used as an extremely condensed hydrogen fuel.
- Gaseous hydrogen can be used as a coolant for electric generators in power stations. This is because of its high thermal conductivity and low "windage", so reducing frictional and turbulence losses.
- Hydrogen is also used as a feedstock in industrial processes including production of ammonia and methanol.
Hydrogen codes and standards
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
Guidelines
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 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."
- "The limits of detonability 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."
Leaks
- Hydrogen is odorless, colorless and tasteless, so most human senses won't help to detect a leak. By comparison, natural gas is also odorless, colorless and tasteless, but industry adds a sulfur-containing odorant called a mercaptan to make it detectable by people. Currently, all known odorants contaminate fuel cells. However, given hydrogen's tendency to rise quickly, a hydrogen leak indoors would briefly collect on the ceiling and eventually move towards the corners and away from places where people might be exposed to it. For that and other reasons, industry often uses hydrogen sensors to help detect hydrogen leaks and has maintained a high safety record using them for decades. Researchers are investigating other methods that might be used for hydrogen detection: tracers, new odorant technology, advanced sensors and others.
- 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 hydrogen, thereby forming an unstable mixture. This mixture may detonate with effects similar to those produced by trinitrotoluene and other highly explosive materials"
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. More recently Multi IR detectors have been developed, which have even faster detection on hydrogen-flames. Chemo-chromic indicators can be added to silicone tapes for hydrogen detection purposes.Incidents
Hydrogen is extremely flammable. However this is mitigated by the fact that hydrogen rapidly rises and often disperses before ignition, unless the escape is in an enclosed, unventilated area. Demonstrations have shown that a fuel fire in a hydrogen-powered vehicle can burn out completely with little damage to the vehicle, in contrast to the expected result in a gasoline-fueled vehicle.Ahlhorn disaster. On the 5th of January 1918, a fire detonated a hydrogen zeppelin inside a hangar in Germany. The resulting blast was felt 40km away, and destroyed several neighbouring hangars and zeppelins within.
Hindenburg disaster. May 6th, 1937. As the zeppelin Hindenburg was approaching landing at Naval Air Station Lakehurst, a fire detonated one of the aft hydrogen cells rupturing neighbouring 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 4 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.
In January 2007 an explosion of compressed hydrogen during delivery at the Muskingum River Coal Plant 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 accident, three reactor buildings were damaged by hydrogen explosions. Exposed Zircaloy cladded fuel rods became very hot and reacted with steam, releasing hydrogen. The containments were filled with inert nitrogen, which prevented hydrogen from burning in the containment. However, the hydrogen leaked from the containment to the reactor building where it mixed with air and exploded. To prevent further explosions, vent holes were opened in the top of the remaining reactor buildings.
In February 2018, on the way to an FCV hydrogen 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, a suburb of Los Angeles, CA. The fire broke out on the truck at about 1:20 p.m. at the intersection of South Brea Canyon Road and Golden Springs Drive, according to a Los Angeles County Fire Department dispatcher. The National Transportation Safety Board has launched an investigation.
In August 2018 a delivery truck carrying liquid hydrogen caught fire at Veridam in El Cajon CA.
In May 2019 leaking hydrogen led to an explosion at AB Specialty Silicones in Waukegan, Illinois, that killed four workers and seriously injured a fifth.
Also in May 2019 a hydrogen tank exploded killing 2 and injuring 6 in Gangneung, South Korea at the Gangwon Technopark.
In June 2019 Air Products and Chemicals, Inc. in Santa Clara CA. The hydrogen transfill facility had an explosion during the loading of a tanker truck that was being fueled. This resulted in the temporary shutdown of multiple hydrogen fueling stations in the San Francisco area.
In June 2019 Uno-X fueling station in Norway experienced an explosion, resulting in the shutdown of all Uno-X hydrogen fueling stations and a temporary halt in sales of fuel cell vehicles in Norway. Based on preliminary investigation findings neither the electrolyzer or the dispenser used by customers had anything to do with this incident. Therefore the electrolyzer division will now return to business as usual. June 27, 2019 Nel ASA announces the root cause of the incident has been identified as an assembly error of a specific plug in a hydrogen tank in the high-pressure storage unit.
In December 2019 a gas explosion at an Airgas facility in Waukesha, Wisconsin injured one worker and caused 2 hydrogen storage tanks to leak.
On 7 April 2020 an explosion at the Hydrogen Fuel plant in Long View, North Carolina, 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 is under investigation.The company published a press release:.
On 11 June 2020 there was an explosion at the Praxair Inc., 703 6th St. Texas City, Texas, a hydrogen production plant.