Fire tests with lithium-ion battery electric vehicles in road tunnels

Alternative propulsion technologies, including battery-electric vehicles, are becoming increasingly prevalent. Whilst such vehicles remain a small overall proportion of the vehicle fleet, the combined impact of government policy and technological advances in alternative fuels is expected to accelerate the increase in their numbers in coming years.

As a result of these changes, the nature of tunnel safety risk (including the risk of fire) is expected to change over time. The risk implications associated with such vehicles thus requires more detailed consideration. This entails evaluation of incident consequences with particular attention being paid to the impact of fire characteristics and toxic emissions on tunnel users and to the need for specific emergency intervention strategies.

In the past, concerns were voiced with respect to the fire safety of the new energy storage device (battery) and the possibility of more difficult firefighting conditions. This resulted in a series of investigations concerning the safety aspects of batteries and battery electric vehicles. However, most of the tests performed merely dealt with battery cells or battery packs. To date, publicly available tests involving actual vehicles remain relatively rare. In 2018, the Austrian Government commissioned a research project concerning the effect of incidents with battery electric vehicles on tunnel safety. This project encompassed fire tests of passenger cars, simulations for heavy duty vehicles, and the impact of incidents with such vehicles on the safety of tunnel users and the tunnel structure.

In a series of fire tests, the heat-release and production of (toxic) substances has been evaluated. The burning behaviour of vehicles with different energy storage technologies (i.e. Li-ion batteries, Diesel) was monitored and compared to each other. The heat-release rate and emission of (toxic) substances was measured, and different fire-fighting methods were applied during each test.

This paper will focus on the aspect of full-scale fire tests of passenger cars performed in a road tunnel. It should be emphasized that the battery-electric vehicle fire tests presented here were the first of their kind under real road tunnel conditions. This concerns the fire behaviour, but also some new approaches to fighting a BEV fire. All previous tests reported in journals were either carried out in fire halls or only concerned individual battery modules.