Hydrogen has unique physical and chemical properties which present benefits and challenges to its successful widespread adoption as a fuel.
- Due to the small size of its molecules, hydrogen can diffuse in or even through materials. Since this increases the probability of leaks, only a few materials are suitable for use in combination with hydrogen.
- The number of connections shall be minimised (e.g. welded and screwed connections), and any connection techniques and sealing materials used shall be suitable for this purpose.
- Besides this, diffusion of hydrogen in certain materials can lead to negative changes in the material properties. This phenomenon is known as ‘hydrogen embrittlement’. The high coefficient of diffusion in the air also offers a safety advantage. In an open area, the hydrogen gas will mix with air quickly and thus be diluted. The risk of explosion is therefore reduced.
- Hydrogen gas is fourteen times lighter than air and rises at a speed of almost 20 m/s, 6 times faster than natural gas which means that when released, it rises and disperses quickly. If hydrogen is released in a closed room, it will accumulate at the highest point. There is a risk of an accumulation of hydrogen at the top of a closed room. This risk is relevant in service areas of the establishment and under roofs over the hydrogen delivery installation.
- Hydrogen is also odorless, colorless, and tasteless making it undetectable by human senses. For these reasons, hydrogen systems are designed with ventilation and leak detection. Natural gas is also odorless, colorless, and tasteless, but a sulfur-containing odorant is added so people can detect it. There is no known odorant light enough to “travel with” hydrogen at an equal dispersion rate, so odorants are not used to provide a detection method. Many odorants can also contaminate fuel cells.
- A detection system shall be installed there where ventilation is difficult or cannot be guaranteed to a sufficient extent.
- The location of the hydrogen delivery installation shall be chosen such that any hydrogen that escapes is blown in a safe direction (the prevailing wind direction). An option to ensure this can be a flare.
- Hydrogen gas requires very little energy to ignite. Furthermore, a mixture of hydrogen gas and air can be ignited along a very wide area (volume fraction of 4 % to 75 %). To prevent static charges accumulating in the constructions, materials that conduct electricity well are used and potential equalisation shall be ensured.
- Note: Friction of garments can even suffice to generate this small level of energy.
- The self-ignition temperature is 585 °C.
- Since hydrogen has a colourless, hardly visible flame and has hardly any heat radiation a hydrogen fire cannot be easily detected by people. A flame can be detected using special thermal imaging cameras and/or UV measurement. When applying flame detection, external influences on the equipment, such as sunlight or welding activities in the environment, should be taken into account.
- Hydrogen is unlikely to cause asphyxiation. With the exception of oxygen, any gas can cause asphyxiation in high enough concentrations. Because hydrogen rises and disperses so rapidly, it is unlikely to cause asphyxiation. Hydrogen is non-toxic and nonpoisonous. It will not contaminate groundwater. It is a gas under normal atmospheric conditions, and a release of hydrogen does not contribute to atmospheric or water pollution. Hydrogen can be used as safely as other common fuels we use today when guidelines are observed and users understand its behavior.
