Since hydrogen is both inexhaustible and non-polluting, it has a role to play in the transition to a low-carbon emissions economy – or even a zero-emissions economy in the case of renewable hydrogen. But can this energy-carrying gas explode? What risks are involved in using hydrogen, and what solutions exist to limit these risks in the field of transportation?
Hydrogen: A brief reminder of the basics
With its simple atomic structure, hydrogen is the lightest atom in Mendeleev's periodic table. It is the most abundant chemical element in the universe. As well as being colorless and odorless, H2 or dihydrogen, consisting of two hydrogen atoms, is a highly energetic molecule. The combustion of 1 kilogram of H2 releases approximately three times more energy than the same mass of petroleum fuel.
Understanding the properties of hydrogen to ensure its safe use
Like any fuel, hydrogen presents a risk of ignition or explosion in contact with air and a spark or source of heat. Its extreme lightness – it is 14 times lighter than air – and speed of diffusion give it the disadvantage of being able to escape through the slightest gap but also the advantage of dissipating rapidly into the atmosphere, thus limiting the risk of fire in open areas.
Due to its small atomic size, hydrogen can diffuse into metal and modify the crystal lattice, causing the embrittlement of metallic materials, known as the hydrogen embrittlement phenomenon. It is therefore important to select appropriate materials for the design of safe hydrogen systems.
Hydrogen vehicles: Innovatively designed to ensure safety
The interest in low-carbon energies has prompted manufacturers to develop systems that enable hydrogen to be produced, transported, stored, and used in complete safety. For example, in hydrogen vehicle tanks, everything is designed to avoid or control gas leaks and to reduce the risk of ignition in the event of an accident:
- Heavy-duty sealing: A polymer liner surrounded by a thick layer of high-strength composites seals the fuel tank and can withstand impacts of 5,000 joules.
- Fully controlled system: Vehicles are embedded with strategically placed sensors to check for leaks in the system and a circuit breaker to cut off the gas flow if a leak is detected.
- Fire precautions: Valves allow the hydrogen to be safely evacuated out of the vehicle and thus avoid overpressure in the tank.
A battery of tests to ensure the safety of hydrogen vehicles
Hydrogen systems are subject to strict safety standards, requiring them to undergo a whole series of tests to verify their resistance to extreme temperatures, chemicals, falls, shocks, and so on. They even undergo ballistics testing to test their resistance to ultra-powerful impacts.