Risks related to new energy carriers

Context

It is clear that our mobility is currently undergoing a major change, in an attempt to combat global warming, air pollution and noise, that are are all caused by road traffic and that new forms of mobility can help to reduce.

Whilst there is a need to limit motorized traffic in favour of other modes of transport, it is also important to make the vehicles that will continue to be used cleaner, whether they are goods vehicles, public transport or private cars. For light vehicles and local goods transport, there is a shift towards widespread electrification of the fleet. Electrification also applies to public transport and, depending on technological progress, could extend to long-distance transport. For certain forms of public transport, hydrogen and natural gas – in gaseous or liquid form – are likely to replace diesel in the short term. Natural gas is already widely used as a transition fuel in public transport and other urban fleets (delivery, refuse collection). The transition is also beginning in rail transport.

What are the risks associated with new energy carriers (NEC) ?

The risk of fire is already present in tunnels and for many years has been the focus of significant research efforts, tunnel equipment upgrades and organisational efforts by tunnel operators and emergency services. New energy carriers do not necessarily increase risks in general, but they can generate new hazards, particularly in underground environments, which must be understood, prevented and dealt with as effectively as possible.

For the most common battery capacities, battery fires are no more powerful than the petrol vehicle fires we are familiar with, but they can pose difficulties for the emergency services trying to extinguish them, and therefore for the operator who needs to reopen the tunnel to traffic as soon as possible. Battery technologies are varied and rapidly evolving, and attention must be paid to the associated risks. Compressed or liquefied gases can cause explosions in the event of a leak or failure of safety systems.

CETU’s research activities on this topic

CETU has been involved in studying these phenomena for several years and significantly increased its efforts in 2022 with the launch of a dedicated strategic research programme. This programme addresses various issues.

The ‘New Energies and Technological Risks in Tunnels’ (NERTT) working group, led by the CETU, brought together operators, transport authorities, emergency services and technical experts. Its work resulted in a shared assessment of risks, published by CETU in January 2024, which is intended to foster discussions with local and national authorities.

Independent and collaborative research aims to improve our understanding of the triggers and consequences of explosive phenomena related to compressed or liquefied gases (natural gas and hydrogen). In particular, we are seeking to understand which parameters, related to the vehicle or the tunnel, influence the scale of events, and how best to assess their consequences for users, emergency services and the structural integrity of tunnels.

Work has also begun on a method for taking into account all hazardous phenomena associated with alternative propulsion systems within the general tunnel safety framework. A working group led by the CETU has brought together experts and engineering consultancies to work on integrating these factors into specific hazard investigations. An information document explaining how to adapt the current method is due to be published by the end of 2026.

Finally, a further working group led by the CETU has brought together tunnel operators and a representative from the DGCGC (Directorate-General for Civil Security and Contingency Management) to work on incorporating these phenomena into the operational management of an incident.

The rail sector is not to be excluded. The CETU has co-led a working group with EPSF (the French authority on rail safety) to analyse the potential risks associated with hydrogen trains, and is contributing its expertise to the transport of batteries or alternative-energy rail vehicles.

At the international level, the CETU chairs the PIARC working group dedicated to new energies in road tunnels, and regularly speaks on the subject at conferences and symposiums (ISTSS, ISAVFT, Interflam, ITACET, ITA COSUF, etc.).

Bibliographical references:

WILLMANN (C.), TRUCHOT (B.), New Energy Carriers and Additional Risks for User Safety in Tunnels, INTERFLAM 2019, London, 1-3 July 2019, pp. 1833-1844

WILLMANN (C.), TRUCHOT (B.), User’s safety in tunnels - additional risks of new energy carriers vehicles, 8th ISAVFT, Athens, 25-27 September 2019, pp. 450-464

Impact of new propulsion technologies on the operation and safety of road tunnels - Case studies, PIARC, 2022, 46p.

Impact of new propulsion technologies on the operation and safety of road tunnels - Technical report (2023), PIARC, 2023, 76p.

Nouveaux modes de propulsion en tunnel routier : risques et enjeux, shortly available in English.