Hydrogen: Properties, Applications, and Hazards. The Most Comprehensive Overview

Introduction

Hydrogen (H₂) holds a special place among all the elements of the Periodic Table. It is the lightest substance in the Universe, a powerful energy carrier, and a key element of all organic life. However, the uniqueness of hydrogen also has a downside: the risks associated with it are equally unique. Invisible, odorless, extremely volatile, and explosive over an exceptionally wide range of concentrations — this gas demands special treatment at all stages, from production to disposal.

In this article, I have compiled and systematized the maximum amount of information on hydrogen: from the physicochemical fundamentals to the practical aspects of industrial safety and current trends in hydrogen energy. The material will be useful both for technical specialists working with hydrogen in production and for anyone who wants to gain a deeper understanding of the nature of this unique substance.

Physical Properties of Hydrogen

Under normal conditions, hydrogen is a colorless, tasteless, and odorless gas, indistinguishable in appearance from air. It is the lightest of all known gases: its density at 0 °C is 0.0899 kg/m³, which is about 14 times lighter than air. It is this property that determines its behavior during leaks: hydrogen rises rapidly upwards at a speed of about 20 m/s, which is why the best protection against its accumulation indoors is reliable ventilation at the upper points of the volume.

The thermal conductivity of hydrogen is no less remarkable. Among all gases, it possesses the highest thermal conductivity: 0.174 W/(m·K) at 0 °C and 0.1 MPa. This property is used, in particular, for cooling powerful turbine generators at thermal and nuclear power plants.

The main physical parameters of hydrogen are summarized in the table:

Parameter	Value
Density at 0 °C and 0.1 MPa (gas)	0.0899 kg/m³
Relative density (air = 1)	0.0695 (~14 times lighter)
Boiling point	–252.8 °C
Melting point	–259.2 °C
Critical temperature	–240 °C
Critical pressure	1.28 MPa
Thermal conductivity (0 °C, 0.1 MPa)	0.174 W/(m·K)
Specific heat of combustion	120–140 MJ/kg
Dissociation energy of the H₂ molecule	436 kJ/mol

Cryogenic risks deserve special attention. Liquid hydrogen exists only at temperatures below –253 °C. At this temperature, it is extremely light (density of about 70.8 kg/m³) and fluid. Upon contact with skin or ordinary structural materials, it causes instantaneous frostbite and makes metals brittle.

Chemical Properties of Hydrogen

The molecular formula of hydrogen is H₂, and its molar mass is approximately 2.02 g/mol. Under ordinary conditions, molecular hydrogen is relatively unreactive: its molecule is very stable (dissociation energy of 436 kJ/mol), and without heating or a catalyst, it reacts only with fluorine.

In most compounds, hydrogen exhibits an oxidation state of +1, less frequently –1 (in metal hydrides). It dissolves well in some metals — Ni, Pt, Pd — which can lead to the dangerous phenomenon of hydrogen embrittlement.

Key chemical reactions involving hydrogen:

• Reaction with oxygen: 2H₂ + O₂ → 2H₂O with the release of 143.3 MJ/kg of heat. At 550 °C and above, the reaction is accompanied by an explosion.

• Oxyhydrogen gas: a mixture of two volumes of hydrogen with one volume of oxygen (stoichiometric ratio 2:1). It explodes from the slightest spark.

• Reaction with halogens: in light, H₂ explodes upon contact with chlorine (in a 1:1 ratio), and in the dark — with fluorine.

• Reducing properties: at high temperatures (>550–600 °C), hydrogen actively removes oxygen from metal oxides, reducing them to pure metals. This property is widely used in metallurgy.

• Ammonia synthesis: on appropriate catalysts, hydrogen reacts with nitrogen to form ammonia NH₃ (the Haber process).

Industrial Applications of Hydrogen

Hydrogen is not just a laboratory gas but the backbone of several key industries. According to 2024 data, about 97 million tons of hydrogen were produced and consumed worldwide. The main consumers are the gas chemical industry, oil refining, and metallurgy.

The chemical industry is the largest consumer of hydrogen. The main areas are the production of ammonia (NH₃) for mineral fertilizers and methanol (CH₃OH) for plastics, explosives, and pharmaceuticals. These two products account for the lion's share of global hydrogen consumption.

Oil refining is the second largest consumer. Hydrogen is used in hydrocracking and hydrotreating processes to remove sulfur and improve the quality of gasoline and diesel fuel.

Metallurgy is one of the fastest-growing sectors of hydrogen consumption. Here, hydrogen performs a dual function: as a reducing agent for metal oxides (in powder metallurgy) and as a protective atmosphere during high-temperature treatment of metals and alloys. Of particular interest is the technology of direct reduction of iron from ore using hydrogen — the so-called "green steel."

Other important applications of hydrogen include:

• Food industry: hydrogenation of liquid oils for the production of margarines and confectionery fats.

• Glass production: creating a reducing gas atmosphere over the tin bath in the manufacture of polished flat glass.

• Energy: cooling of powerful turbine generators at thermal and nuclear power plants due to the exceptionally high thermal conductivity of hydrogen.

• Space industry: highly efficient rocket fuel (liquid hydrogen paired with liquid oxygen).

• Analytical equipment: carrier gas in chromatographs and flame in flame ionization detectors (FID).

Russia is among the top five producers of hydrogen, with an output of around 5.5 million tons per year.

Methods of Hydrogen Production

On an industrial scale, hydrogen is produced by several fundamentally different methods, each with its own technical and economic characteristics and carbon footprint.

Steam methane reforming (SMR) is the dominant technology, accounting for about 70% of global hydrogen production. The process involves the interaction of methane with steam at high temperatures (700–1000 °C) in the presence of a nickel catalyst. In Russia, more than 99% of all hydrogen is produced using SMR technology. The cost per kilogram of hydrogen produced by SMR is about 4–6 times lower than by electrolysis. The main disadvantage is significant CO₂ emissions: about 9 kg of carbon dioxide per 1 kg of hydrogen.

Water electrolysis is the decomposition of water into hydrogen and oxygen under the action of an electric current. In Russia, this method accounts for less than 1% of the hydrogen produced. The main advantage is the high purity of the resulting product. The disadvantage is the high cost: specific electricity consumption in traditional electrolysis is about 50 kWh per 1 kg of hydrogen.

Coal gasification is the reaction of coal with steam and oxygen at high temperatures. The technology is widespread in countries with large reserves of cheap coal (China, South Africa) but has the highest carbon footprint among all methods.

Methane pyrolysis is the thermal decomposition of methane into hydrogen and solid carbon without air access. A promising technology that allows the production of hydrogen without CO₂ emissions.

Special attention should be paid to so-called "green" hydrogen — hydrogen produced by electrolysis using renewable energy sources (solar, wind). Research in this area is actively underway in Russia. In 2025, ITMO scientists created a new type of reactor for water electrolysis: the use of magnets and nanoparticles accelerated the process by a factor of 6 and reduced energy consumption by 15% (from 57.3 to 48.8 kWh per 1 kg of hydrogen). In parallel, scientists at the Boreskov Institute of Catalysis of the Siberian Branch of the Russian Academy of Sciences are developing an energy-efficient method for producing green hydrogen from ammonia using photocatalytic processes occurring at room temperature.

Storage and Transportation of Hydrogen

The storage of hydrogen is one of the key technical problems of the hydrogen economy. The small size of the H₂ molecule and its high volatility create serious difficulties.

Main methods of hydrogen storage:

• Compressed (compressed) hydrogen: storage in steel or composite cylinders at pressures from 200 to 700 atmospheres. The most common method for small volumes. Disadvantage: 15–20% of the energy contained in the hydrogen itself is spent on compression.

• Liquid hydrogen: storage in special cryogenic tanks at temperatures below –253 °C. Provides high storage density (about 70.8 kg/m³) but requires complex and expensive cryogenic equipment. The liquefaction process is also very energy-intensive.

• Metal hydride storage: hydrogen is chemically bound with alloys based on magnesium, titanium, and other metals, forming solid hydrides. The advantage is safer storage at significantly lower pressures (10–30 bar) compared to gas cylinders. However, this technology requires active temperature management over a wide range.

Fire and Explosion Hazard of Hydrogen

From an industrial safety perspective, hydrogen is one of the most dangerous gases. Its fire and explosion hazard characteristics are impressive and require an extremely serious attitude.

Gaseous hydrogen is classified as a flammable explosive gas. Explosive mixtures of hydrogen with air belong to the most dangerous category — IIC, Group T1 according to GOST 12.1.011-78.

The flammability limits of hydrogen are extremely wide:

Mixture	Lower Flammability Limit	Upper Flammability Limit
Hydrogen + Air	4 % vol.	75 % vol.
Hydrogen + Oxygen	4.1 % vol.	96 % vol.

For comparison: for methane, this range is only 4.4–17 % vol., which is about 5–6 times narrower. This means that hydrogen is capable of igniting and detonating in virtually any proportion with air — from trace amounts to almost complete displacement of oxygen.

The minimum energy required to ignite a hydrogen-air mixture is only 0.017 mJ — about 10 times lower than for hydrocarbons. This is enough for even a weak electrostatic discharge from a person's clothing to serve as an ignition source.

The auto-ignition temperature of hydrogen is 510 °C.

In a confined space, hydrogen accumulates near the ceiling, and the equalization of its concentration in the overhead area without external influence can take several hours. Moreover, a hydrogen-air mixture burns with a nearly colorless flame that is practically invisible in daylight, creating an additional hazard for personnel.

Cryogenic spills of liquid hydrogen deserve special attention. Although gaseous hydrogen is significantly lighter than air, in large quantities, very cold gaseous hydrogen (after liquid evaporation) can have approximately the same density as air and temporarily remain low above the ground until it warms up. Thus, an explosion or fire is possible only within the volume of a cloud that constitutes a combustible air-hydrogen mixture.

The propagation speed of a blast wave in an oxyhydrogen mixture (2H₂ + O₂) can reach 2,864 m/s.

Hydrogen Safety in the Workplace

Given the high fire and explosion hazard of hydrogen, working with it requires strict compliance with special protective measures. According to GOST 3022-80 and GOST R 51673-2000, the following safety requirements are regulated:

• Concentration control: installation of pre-explosion concentration sensors with an alarm at 10% of the Lower Flammability Limit (LFL) in rooms where hydrogen leakage is possible.

• Ventilation: forced exhaust ventilation in the upper zone of rooms, as hydrogen is lighter than air and accumulates under the ceiling.

• Grounding: all equipment must be reliably grounded to dissipate static electricity.

• Personal protective equipment: when working in a hydrogen environment, it is necessary to use an isolating gas mask (oxygen or hose type).

• Personnel training: mandatory training in working with pressurized gas and actions in emergency situations.

• Cylinder operation: must be carried out in accordance with the rules for the design and safe operation of pressure vessels.

Special attention should be paid to the problem of hydrogen embrittlement. The exact mechanism of this phenomenon is not yet fully understood, but the generally accepted explanation links it to the recombination of atomic hydrogen into molecular form at dislocations and nanopores, which is accompanied by a sharp increase in pressure and the subsequent initiation of cracks in the metal. High-strength steels, as well as titanium and nickel alloys, are most susceptible to hydrogen embrittlement.

Detection of Hydrogen Leaks

Timely detection of leaks is a critically important element of the hydrogen safety system. Modern gas analyzers and hydrogen sensors allow this task to be solved with high accuracy.

In recent years, significant progress has been made in this area by Russian scientists. At Tomsk State University, a new generation of gas analyzers has been created, characterized by small size, low cost (around 300 rubles per sensor), and the ability to determine both low and high levels of pre-explosion concentrations of hydrogen. These sensors are highly sensitive, selective, and fast-acting.

Gas analyzers of this type are capable of monitoring hydrogen leaks in the containment of a nuclear reactor at a nuclear power plant, in rooms with batteries, during the transportation of cylinders, in the chemical industry, and other areas.

To detect hydrogen leakage, specialized leak detectors are also used, intended for enterprises whose activities involve the production, storage, transportation, and use of hydrogen.

Conclusion

Hydrogen is a unique substance that combines colossal industrial potential with equally colossal danger. On the one hand, it is an indispensable reagent for the chemical and oil refining industries, a promising energy carrier for the "green" energy of the future, and a key element in many technological processes. On the other hand, it is a gas that demands an extremely serious attitude towards safety issues at all stages of handling.

Understanding the physicochemical properties of hydrogen, the mechanisms of its fire and explosion hazard, methods of safe storage, and leak detection is not just of theoretical interest but a practical necessity for everyone working with this gas in production.

Russia, possessing significant natural gas reserves and a developed scientific base, has all the prerequisites to remain among the world leaders in both traditional hydrogen production and the development of promising "green" technologies. At the same time, the key success factor will always be the strict compliance with safety requirements, based on a deep understanding of the nature of this unique element.