HYEX Safety founder and chief executive Olav Roald Hansen explains why a conventional approach to handling gas will not work for hydrogen and offers some best practice solutions
Safety is my speciality, so when we talk about hydrogen being the right choice for future maritime fuels my focus straight away turns to the safety implications of this decision. Clearly, there is a need for change as regards maritime fuel, not least in helping to reduce local pollution. This local focus is receiving much attention from politicians and industry leaders and it is at a local level where I expect we will see the most change in the short term.
Hydrogen is one of several solutions to this problem and it is anticipated to lead the way for certain types of vessels, notably those with temporary emissions requirements, for example, vessels entering fjords or city locations, where emissions need to fall, or be non-existent in some cases.
I am personally involved with projects on five hydrogen-powered vessels, two of which utilise liquid hydrogen and three which take a compressed gas approach.
When you work with hydrogen it is important to understand that it is very different to other gases with which you may be familiar. For instance, the flammability of hydrogen is very wide, while the ignition energy is very low; it has high reactivity and is very buoyant in gas form (not as vapor from liquid release). It is stored at very high pressure or very low temperature.
The implication of these properties is that incidents may be more likely to occur with hydrogen, partly because industry is still unfamiliar with its characteristics and partly because the infrastructure is still being developed to operate with it safely.
You have to be particularly careful with hydrogen indoors, because of its properties of high reactivity and ignition; outside is safer because of its high buoyancy, but even so, the reactivity of hydrogen means it is still possible for explosions to occur.
Liquid hydrogen represents a particular challenge and we have conducted a great deal of modelling to understand its characteristics in this state. A lot can be achieved with fairly simple models, although we also gain considerable insight using computational fluid dynamics.
This modelling has informed many of our conclusions with regard to the differences between hydrogen and other gases, which are of particular value for storage concerns; for instance, the established safety principles for ventilation, suppression, inerting and expulsion venting may not be adequate in the context of hydrogen.
In our experience, if it can leak, ignite and explode, it will, and it may be too late to take mitigating action once a leak begins. Hence it is important to work upfront, limit system complexity, limit pipe dimensions, gas volumes and pressures and use double containment measures to collect releases safely and direct them above deck. ‘Belt and braces’ is a good idea, providing the cost implications are acceptable.
Provided the extra safeguards have a limited/acceptable cost, they should be implemented.
This principle is called ‘as low as reasonably practicable’ (ALARP), ie implement risk reduction as long as the value of the reduced risk exceeds the cost of implementation. For hydrogen, uncertainties may be increased due to a lack of understanding, which would add an extra incentive to implement a belt and braces approach.
The IGF assessment typically requires proof of equivalent safety to conventional fuels and this is where hydrogen storage systems pose a significant challenge. Whether you have compressed or liquid hydrogen, either above or below deck, storage will remain the key challenge and focus for maritime use. Other parts of the system can be handled properly if you do a good job, but storage remains a technical hurdle at present. For the IGF assessment, it may be necessary to prevent all non-tolerable scenarios that are credible to fulfil the criteria.