Hydrogen is a highly flammable gas and its mixtures with air burn over a very wide range of concentrations, making it particularly dangerous in terms of explosion or fire hazard. This gas is also characterised by a very low molecular weight, which makes it more likely to diffuse in the air than higher molecular weight gases such as methane, propane or butane.
Examples of hydrogen explosions and fires
Here are some examples of explosions and fires caused by hydrogen ignition:
- Tanker explosion during hydrogen unloading: hydrogen ignited and exploded at the Duferco Farrell plant, during the unloading of a tanker belonging to Air Liquid. At the time of the incident there was approximately 23 m3 of hydrogen in the tank of the vehicle. The driver of the tanker was taken to hospital with injuries, including second degree burns. The tanker burnt down completely over a period of several hours, posing hazard to the storage tanks, which stored between 45 and 55 m3 of hydrogen. 
- Hydrogen explosion during a tanker truck unloading: the incident took place at a power station site when the yellow tank (see graphic below – the left side) was being filled with hydrogen pumped from a tanker truck (the right side). The investigation showed that a malfunction of the safety plate resulted in the release of approximately 17 kg of hydrogen gas over a period of 10 seconds, which subsequently ignited. Electrostatic discharge was one of the probable ignition sources. The explosion caused death of the tanker driver, who died running to his vehicle to turn the flow of hydrogen off. Ten power plant workers were also injured in the incident. The infrastructure of the plant was also affected by the incident. 
- Explosion at a hydrogen generation plant: the 7 April 2020 explosion caused extensive damage to surrounding buildings. The explosion, which occurred at the OneH2 Hydrogen Fuel plant in Long View, North Carolina, was perceptible within a radius of several miles. 
- Explosion at a hydrogen refuelling station: On 10 June 2019, a refuelling station explosion occurred in Norway. Following the incident, the station operator also suspended operations at its other locations. Following the incident, Toyota and Hyundai halted sales of hydrogen-powered cars. 
Incydent rozpoczął się, gdy pękła płytka bezpieczeństwa (zaznaczona na czerwono) w jednym ze zbiorników wodoru na terenie elektrowni.
The roof (highlighted in red) was not designed for safe hydrogen ventilation and allowed the build-up of the explosive gas.
Explosion during hydrogen loading and unloading
During loading and unloading of a hydrogen tanker, electrostatic discharge may occur and cause sparks and ignition of the hydrogen-air mixture. In addition, as hydrogen flows through pipes and valves, friction can occur between hydrogen particles and metal surfaces and it can also result in electrostatic discharge.
These are some of the reasons why hydrogen refuelling stations should be equipped with earthing control systems. It is important that both this equipment and other equipment located in an an explosive atmosphere zone are ATEX certified for Group IIC gases. The Earth-Rite RTR system is currently the only earthing control system provided with such a certificate.
Hydrogen – a gas you can not smell
Another important factor that makes hydrogen particularly dangerous is the fact that it is colourless and odourless, making it difficult to detect in the event of a leak or an accident. An explosive hydrogen-air mixture can form in the event of a hydrogen leak, increasing the risk of explosion or fire.
Hydrogen can even penetrate through thick metal walls
One of the key characteristics of hydrogen challenging the technology is its ability to penetrate physical barriers. A hydrogen atom can become bound to the surface of a material (adsorption), either physically or chemically, and subsequently it can penetrate the material structure through absorption. Then, through diffusion, hydrogen is able to penetrate even thick metal shielding and escape outside of the tanks .
Hydrogen is more dangerous than other gases
All these factors make hydrogen more dangerous than methane, propane, butane or dozens of other gases in terms of the risk of explosion or fire during tanker loading and unloading. This is why the use of appropriate procedures and safeguards, such as earthing control systems or leak detection are extremely important, as they minimise the risk of hazardous situations.
The risk of hydrogen explosion is four times higher than that of natural gas
SGN – a natural gas distributor operating in the British Isles – is currently implementing the H100 Fife project, intended to introduce hydrogen for commercial use in households. The project involves investigation of the safety of this fuel in terms of explosion and fire hazards. The company, however, refused to present the results of its studies, photographs and video recording from the tests, invoking project protection.
This is how SGN justified its decision: we believe that premature disclosure of any information or reports could be unnecessarily detrimental to the funding and viability of the project, as well as its objective, which is to explore low-carbon heating alternatives to natural gas. 
At the same time, SGN indicates in one of its analyses that hydrogen is up to four times more likely to ignite, more likely to leak and more explosive than natural gas. 
The most famous hydrogen explosion in history
In 1937, the ‘Hindenburg’ zeppelin set off on a tour around Europe. An explosion occurred on board of the zeppelin while flying over the city of Manchester in England, which quickly engulfed the entire structure. The explosion and fire killed 36 people, including 13 passengers and 23 crew members. Many valuable possessions were on board, including paintings and monuments of German culture.
Experiments led to a conclusion that static electricity was the most likely cause of the disaster. The Hindenburg zeppelin had impressive dimensions: it was 245 metres long and 41 metres in diameter. There were 16 tanks inside the craft, which contained as much as 200,000 cubic metres of hydrogen combined.
How to reduce the risk of hydrogen explosion and fire
The following steps can be undertaken to minimise the risk of hydrogen ignition caused by electrostatic discharge:
- Electrostatic earthing: Ensure that all tanks, pipelines and equipment involved in hydrogen storage, transport and handling are earthed to avoid the build-up of static electricity.
- Detection: hydrogen can escape through the smallest openings and even diffuse through the metal walls of tanks. This is why, it is important to monitor its presence.
- Humidity control: Monitor and control humidity levels in areas where hydrogen is stored or processed. High humidity can help dissipate static electricity.
- Temperature control: Ensure that temperature is controlled in the vicinity of hydrogen-related processes, as high temperatures can increase the risk of electrostatic discharge.
- Source elimination: Avoid using materials able to generate electrostatic charges, such as plastics and synthetic textiles.
- Use the appropriate materials: Use grounding and conductive materials which help dissipate static electricity.
- Staff training: Ensure that the staff involved in processes using hydrogen are trained in the safe handling of electrostatic charges and are familiar with the relevant safety procedures.
- Monitoring and testing: Regularly monitor and test hydrogen-related processes in order to detect possible leaks or static build-up and take appropriate precautions.
In summary, it is crucial to ensure that appropriate safety procedures are in place and that regular checks are carried out, to avoid the risk of hydrogen ignition caused by electrostatic discharge.
 Nowe materiały do magazynowania wodoru oparte na skandzie, itrze i glinie: synteza i właściwości fizykochemiczne, Agnieszka Starobrat, Doctoral dissertation comprising a part of MISDoMP in 2015–2020, supervised by: prof. dr hab. Wojciecha Grochali at the New Functional Materials Technology Laboratory, CeNT UW and prof. dr hab. Jacek A. Majewski at the Institute of Theoretical Physics of the Faculty of Physics, University of Warsaw
 H100 Hydrogen Characterisation Final Report, Report Number 0431389-02, 14 maja 2019