Hydrogen: Properties, Safety, Hazards

Hydrogen has fundamentally environmentally friendly properties. If it is burnt with air in combustion engines, emissions are very low or negligible if the combustion process is managed appropriately. During hydrogen combustion, emissions of nitrogen oxides (NOx) increase exponentially with the combustion temperature. With a low combustion temperature, nitrogen oxide emissions can therefore be significantly reduced with fuels produced on the basis of natural gas or mineral oil. Pollutant emissions can be completely avoided if hydrogen is used in low-temperature fuel cells. These include, for example, polymer electrolyte membrane fuel cells (PEMFC). Generating electricity from hydrogen and oxygen produces only demineralised water as a reaction product.

Compared to conventional power plants, emissions are up to 100 times lower when hydrogen is used in fuel cells with a higher operating temperature. Furthermore, hydrogen's status as a secondary energy carrier enables the flexible introduction of different renewable energies in the power and fuel sector. However, in order to assess the specific impact of hydrogen on environmental quality, the entire fuel chain must be considered. This extends from the primary energy to the end use.

How explosive is hydrogen? This question is often asked, as hydrogen is associated with explosions due to the oxyhydrogen experiment from chemistry lessons and some well-known accidents from the history of technology. The fire on board the Hindenburg airship in particular is often cited as an example of the explosion hazard of hydrogen. However, it has long been proven that there was no explosion at all and that the accident was not caused by hydrogen, but by an electrostatic spark. The most important thing is that hydrogen does not explode per se. This requires other factors - an oxidiser (e.g. pure oxygen, air or chlorine) in a certain volume ratio to hydrogen and an ignition source such as the spark resulting from an electronic charge. Pure hydrogen cannot burn.

If around 4% hydrogen is mixed into air at atmospheric pressure, this mixture can be ignited with an ignition source. However, there is no risk of explosion here. This is only the case from a hydrogen concentration of 18 %. As soon as around 75 % hydrogen is present, ignition and therefore explosions are no longer possible as the amount of oxygen is insufficient. As hydrogen is 14 times lighter than air and therefore volatilises quickly in the open air, the risk of hydrogen exploding is further reduced. Ventilation is therefore a decisive factor, especially in closed rooms. When handling hydrogen, care should also always be taken to keep it away from sources of ignition, including electrostatic discharge (ESD).

Hydrogen is a topic with many facets - from production, transport and storage to utilisation. With our expertise, know-how and many years of experience, we are an independent partner for safety and hazard prevention by being able to test, inspect and certify various aspects of hydrogen technology.

Hydrogen embrittlement is a phenomenon that has been studied for a long time and is also one of the typical hazards of hydrogen. This occurs when ionised hydrogen penetrates the crystal lattice of a metal. Accordingly, metals or metal alloys are affected by hydrogen embrittlement. Accelerated crack growth or material failure can be caused by hydrogen embrittlement, especially in the case of increased material stress. This is also referred to as "hydrogen-induced corrosion". Whether the respective material is susceptible to hydrogen embrittlement depends on several factors:

• Shape of the crystal lattice (e.g. spatial or surface centring)
• Metal surface quality (e.g. weld seams, fractures or defects)
• Load (e.g. temperature, pressure, tension or alternating load)

Therefore, the effects of ageing due to hydrogen should always be taken into account when selecting components. The risk of hydrogen embrittlement can be reduced or completely avoided by selecting the appropriate material. Stainless steel has proven itself for this purpose. It is also important to realise that hydrogen diffuses very quickly into other gases such as air. H+ ions can also form on catalytically active surfaces in pipework and storage tanks. This is ionised hydrogen: it is even smaller than the actual molecule, so it is able to diffuse easily into metals. In some types of steel and under special conditions, hydrogen embrittlement can occur for this specific reason.

Resistance or resilience to the phenomenon of hydrogen embrittlement is of fundamental importance, especially for the pipes of pipelines used to transport hydrogen. This is the only way to prevent hydrogen embrittlement and corrosion. The active electron of hydrogen can also jeopardise the joints (welds) between the pipes. Official standards or regulations regarding the safe transport of hydrogen have yet to be published. The main challenge is that the existing natural gas pipeline infrastructure and no special hydrogen pipelines should initially be used for hydrogen transport. This means that an individual assessment and personal experience or the involvement of an experienced expert are crucial in order to specifically rule out hydrogen embrittlement and other risks.

How dangerous is hydrogen? This question must be considered in a differentiated manner. Several aspects play a role here: Firstly, the danger of hydrogen should be compared with that of established energy sources. Secondly, the effort required to control these hazards and the risk-benefit analysis must be taken into account. Hydrogen can be explosive when mixed with oxygen in the right proportions and spreads quickly, but it also volatilises in a short space of time.

At the same time, the risk of hydrogen explosion should be taken seriously and reflected in appropriate safety precautions. One danger that should not be underestimated is the colourless and odourless nature of hydrogen. For this reason, hydrogen leaks often go unnoticed. These are even more risky in enclosed spaces. Hydrogen embrittlement, which leads to cracking, is also one of the typical dangers of hydrogen. However, these risks can be counteracted - with sufficient ventilation in closed rooms and the right choice of materials to prevent hydrogen embrittlement.