Basics

Safer than petrol

All too often misunderstood, hydrogen gas raises safety concerns that aren’t always founded. Here, Linde – with a proud hydrogen pedigree – sets the record straight.

Hydrogen fuel cell mobility – based on green hydrogen – provides a promising alternative drivetrain solution for the zero-emission world we are thankfully heading toward. But it also provides cause for some undue concern.

If hydrogen is to realise its potential, would-be buyers of hydrogen fuel cell vehicles (FCVs) need reassurance that they will not be driving to work in a ticking time bomb. With over 100 years’ experience of working with the gas, Linde is best positioned to allay such fears.

The entire hydrogen economy as we know it uses Protium – the lightest and most abundant isotope of the gas in the universe. Far from being an explosion waiting to happen, the inherent properties of this gas actually offer safety benefits over other flammable fuels like gasoline and natural gas – as long as it is handled responsibly.

How danger disappears into thin air

Hydrogen doesn’t like to hang around, as Thomas Knoche, head of projects in Linde’s Hydrogen Solutions and Advanced Customer Applications division explains: “Hydrogen is very light; much lighter than air in fact, and so will disperse extremely quickly. This means that unless the rising gas is somehow confined, it rapidly dilutes into a non-flammable concentration.”  So, while the gas is indeed flammable, it needs to be contained before a fire could break out – and that is much easier said than done.

That said, if certain conditions are met, hydrogen can, like any flammable fuel, combust. However, it needs an oxidiser such as oxygen to be present in a concentration of at least 10% pure or 41% air. It also needs an ignition source. Even when alight, a hydrogen flame burns with relatively low radiant heat compared to a hydrocarbon fire, i.e. the levels of heat emitted near the flame. This greatly reduces the risk of the fire spreading.

The most prominent concern among sceptics is Hydrogen explosion. Avoiding leakages and installing a tight hydrogen system nullifies this risk completely. “An explosion cannot occur in a tank or any enclosed location that contains only hydrogen,” explains Knoche. “This differs from gasoline for example, where a tank contains not only the gasoline but a layer of air – so all you need is an ignitions source to light this flammable cocktail”.

However, those involved in hydrogen technology don’t simply rely on these properties for safety. Assessing hazards, defining risks, implementing safeguards – in short mitigation measures for any risks, no matter how small and where, must be put in place when using the gas. Take the FCVs for example.

“The hydrogen in vehicles is stored in tanks under very high pressures,” explains Knoche. “This design makes them very robust under mechanical impacts, for example during a collision.” So confident was Toyota in this fact that it once ran demonstrations where it loaded its ‘Mirai’ hydrogen fuel cell car with two full tanks of hydrogen and dropped it from 10m before shooting the tanks with military-grade rifles. The result? A harmlessly dissipating gas – which would be picked up by on-board sensors anyway.

Linde’s expertise can ensure the right level of safety regulation for building refuelling stations.

Regulating refuelling: Hydrogen codes and standards

The Mirai is indeed one of very few OEM hydrogen FCVs roaming the roads today. Its birthplace: Japan, where conservative regulations governing the handling of hydrogen risk obstructing the country’s ‘hydrogen vision’. After all, it’s not just the cars, but the refuelling stations that make up the necessary infrastructure.

Currently in Japan, hydrogen is regulated as an industrial gas. This stipulates, for example, that certain high-grade steel must be used in construction of the stations; massive safety distances must be adhered to; only supervisors with hydrogen-handling experience can be employed etc. As such, the stations become prohibitively expensive forcing the government to relax these rules – a hard public message to convey.

“We know from our collaboration in hydrogen international codes and standards, that Japan started very conservatively and that the US also err on the side of caution with prescriptive standardisation methods,” explains Knoche. “In Germany, we are much more flexible –  but you are also responsible for the risk mitigation. We run detailed risk analyses which can then inform the ISOs related to hydrogen.”

What does that mean? It means that the true experts are trusted with defining the right safety codes and practices. As mentioned, with over a century of experience handling the gas, Linde certainly qualifies as an expert. It also means that Linde can install hydrogen refuelling stations on very small footprints – contributing to a safe hydrogen vision.