Part 3: Hydrogen Safety –differently dangerous

By Andy Crook, GotBoost AAT AAE FIMI

In his final article exploring the role of Hydrogen in future mobility, Andy considers the unique safety challenges ahead

The public perception of hydrogen safety is based on historical events, such as the Hindenburg and the Challenger space shuttle disaster. Neither of these are representative of the use case of hydrogen for personal or public mobility.

The Space Shuttle for example used cryogenic Hydrogen/ Oxygen mixtures, the explosion from the ruptured tanks contained many times more fuel than any land-based vehicle.

For widespread hydrogen uptake, the public must perceive that its use presents no greater danger than current fossil fuels. This requires a new safety culture, not based on previous industrial experience, codes and practice, but new hydrogen safety and engineering practices.

The three main areas are safe handling, safe working environments and the knowledge and skills required to work safely on hydrogen vehicles.

Safe Handling and Storage

One of the primary safety concerns revolves around the storage tanks and re-fuelling of hydrogen vehicles. Hydrogen is stored at high pressure (typically 700 Bar in cars and 350 Bar in HGV’s and Buses). The carbon fibre (class IV) tanks are designed to withstand severe impact and temperature extremes. These tanks are subjected to rigorous testing, including gunfire, puncture, and fire exposure.

Hydrogen fuel stations also employ advanced technologies to manage risks. Nozzle attachments are designed to create a secure connection to the vehicle, preventing leaks. Additionally, sensors monitor for any sign of hydrogen release, automatically shutting down the system if a leak is detected.

Safe Working Environments

When repairing or inspecting Hydrogen vehicles the working environment must be considered, the main hazards are:

Chemical – Flammable and/or explosive atmospheres

Physiological - frostbite, respiratory ailment and asphyxiation

Mechanical – Overpressure and embrittlement

The level of risk must be assessed, and appropriate precautions taken to mitigate that risk. These include, but are not limited to, gas monitors, leak and fire detection, alarms, forced ventilation and safe working practices. The correct PPE (anti-static footwear, and fire-retardant overalls for example) and knowledge of Dangerous Substances and Explosive Atmosphere Regulations (DSEAR) zones and safe distance calculations.

Knowledge and Skills

As we have seen with Electric Vehicles, there is an obvious need for training to bridge the skills and knowledge gap. At every level, from Hydrogen awareness to research and development, the focus should be on the safety and the differences between hydrogen and fossil fuels.

In conclusion, while safety considerations are inherent to the introduction of any new technology, the use of hydrogen for over 100 years in industry has demonstrated that a proactive and comprehensive approach to managing these concerns through robust safety protocols and training can allow hydrogen to play a critical role in the automotive future. Hydrogen is not more dangerous it is differently dangerous.

What Makes Hydrogen Differently Dangerous?

Hydrogen is the most abundant element in the universe and, as discussed in the previous two articles, it could offer compelling alternatives to fossil fuels as an energy vector. However, its properties present some significant differences to the fossil fuels we are used too.

Properties of Hydrogen

It is the smallest and simplest molecule. A hydrogen molecule consists of two hydrogen atoms (H2) bonded together, making it the simplest diatomic molecule. Each hydrogen atom has only one proton in its nucleus and one electron, resulting in the molecule's extremely small size. This simplicity and small size influences many of hydrogen's physical and chemical properties.

Hydrogen's molecular size makes it prone to leakage through the smallest openings. This necessitates the use of specialised materials, fittings, valves, and seals in hydrogen systems.

Hydrogen can be absorbed by metals under certain conditions, leading to embrittlement and cracking. This phenomenon affects the integrity of metallic components exposed to hydrogen, requiring careful material selection and system design to mitigate risks.

Hydrogen is 14 times lighter than air, causing it to rise and disperse quickly into the atmosphere when released. This can be a double-edged sword; while it may reduce the duration of exposure in the event of a leak, it also poses a risk for accumulation in enclosed spaces, leading to potential explosive atmospheres.

Hydrogen has a low density, especially in its gaseous state, which necessitates high-pressure or cryogenic storage methods.

Given its colourless, odourless, and tasteless nature, hydrogen leaks can be difficult to detect without appropriate sensors. Leak detection systems are essential for hydrogen safety.

Wide Flammability Range

Hydrogen has a wide flammability range in air, between 4% and 75% by volume, making it flammable over a much wider range of mixture concentrations than fossil fuels. It requires much less energy to ignite a stoichiometric hydrogen mixture in air, (around 10 times less than that required for petrol or natural gas). This necessitates careful handling and storage to prevent accidental ignition.

Combustion Characteristics

Hydrogen burns with a nearly invisible flame in daylight, which can make detecting a hydrogen fire more challenging. Hydrogen has a higher combustion energy per unit mass than most other fuels, which can result in intense fires with a significant release of energy.

Hydrogen Production & Demand

The age-old chicken and egg of supply and demand is that production at scale (supply) requires a low-cost fuel (to create the demand), however green hydrogen currently costs approximately three times more than hydrogen made from fossil fuels. Without incentives in place or legislation (a minimum % of Hydrogen in the UK gas network) to kick-start production, the Hydrogen Economy in the UK will remain a pipe dream (pun intended).

In conclusion, while the properties of hydrogen present some unique safety challenges compared to conventional fuels, these risks can be effectively managed through robust engineering controls of safe storage and handling, appropriate working environments, and comprehensive safety training.

By embracing a new safety culture specifically tailored for hydrogen, its viability as a clean energy vector for transportation can be realised. Continued research, investment in green production methods (hydrogen from renewable sources), and public education will be crucial for widespread adoption of hydrogen for mobility. With a proactive approach to addressing the 'differently dangerous' nature of hydrogen, it has potential as a sustainable fuel for the future.