On March 14, 2019, during the tests on the Jerez track, the E-paddock, the structure used to host the vehicles of the MotoE World Cup, caught fire. In the fire all the bikes of the teams and prototype of Energica were destroyed (here you find the story of the incident). The clear cause of the fire is still under investigation but Dorna announced that no motorcycle was in charge at that time and that the cause was a short circuit that involved a recharging station. From there the fire spread over the entire E-paddock. Although the cause of the fire was not the motorbike, the event drew attention to the alleged danger of electric vehicles (EV - Electric Veichles), in particular the battery.
We want to start from this point to tackle the issue of the safety of electric vehicle batteries and to do so we asked for the support of Luca Parisi. Luca is a firefighter at the city of Trento, he is a national expert for firefight in confined space and for electric vehicles; at least he manages the website cfbt-it.orgabout the same matters. In addition to Parisi, we asked for the support of APT Group, the main Italian training and security center on safety (link).
As a starting point, it has to be clarified that we are talking about Lithium batteries and their various configurations. This type of battery represents the state of the art for the electric mobility; for those interested in the subject, we talked about them in this section (link).
Lithium batteries are not only installed on electrical veichles, they are everywhere, each of us has at least a dozen at home: mobile phone, computer, tablet, speakers, headphones, vacuum cleaner, drill and so on. The difference is the size and the quantity of energy stored, the larger the battery, the greater the damage in the event of an accident.
What is the danger of these batteries? Mainly, that when they catch fire they are very difficult to extinguish, hereafter we will see the reason. But this is not what we are mostly debating, the main point is about the possibility that the fire may develop from the battery. Now, this is a possible event, albeit rare, and when it happens it is because of a phenomenon that is called Thermal Runaway, which is a rapid and unstoppable increase in temperature due to a series of reactions.
Regarding the MotoE, the battery works at a temperature between 50 °C and 55 °C, at 60 °C the protection systems (the Battery Management System - BMS) takes action and the battery is safely disconnected. In general, a lithium battery is still stable up to 80 °C. However, if the temperature rises further, at about 130 °C, the first reactions that lead to the Thermal Runaway starts. If the heat of the battery is not dissipated, the temperature continues to increase, generating a series of reactions in which the battery itself produces the elements that feed the combustion, especially hydrogen. Furthermore, these reactions are predominantly exothermic, which means that they generate heat. It is the battery itself that produces the gases and heat that support the fire and that is why the burning of a lithium battery is very difficult to extinghish. As an example, the temperature increases from 1 °C/minute in the very early stages of the phenomenon to 100 °C/minute and more, just with dynamics inside the battery and without heat input from the outside.
A lithium battery can ignite for reasons that are mainly due to the poor quality of the components, due to damage caused by the impact with a foreign object or due to other external causes (for example exposure to strong heat sources). In the case of electric vehicles, the danger associated with strong mechanical shocks is the main cause; for this reason, the car batteries have a protective shield in the lower part to defend them from being hit by objects on the road.
From the burning mode of a lithium battery, it derives the extinguishing technique currently adopted all over the world: the cooling of the battery with water until the temperature is below the point where the gases and heat are no longer generated by the combustion. But the matter is not so simple because the hottest part is often the core of the battery. It is necessary first to cool down the external part and then the internal parts which takes time and needs a lot of water (for the battery of a Tesla it is estimated to need of 9000 litres of water). In addition, the water limits the spread of flames to the surrounding environment and prevents the risk of new fires. The case of a Tesla in the United States is emblematic: the fire that was generated due to a car accident was re-ignited twice after having apparently been extinguished.
To help firefighters, battery designers are developing various devices to allow an easy battery cool down. An example is the battery of FormulaE cars. Until the 2018 edition of the championship, the English company Williams Advanced Engineering designed and supplied the batteries to all participating teams. Their design includes a cavity, integrated into the body of the battery, filled with water and able to limit the heating of the battery for 10 minutes. This is enough time, in principle, for the rescue team to save the driver and connect the fire truck to two connections on the body of the battery to practically, flood it. None of them has ever been used during the 240.000Km total raced by FormulaE cars in the past seasons; only 2 battery failed and no thermal runaway occurred. It has also to be highlighted that this event has never affected any of the motorcycles produced by Energica as stated by Giampiero Testoni, the technical director of the company (here his technical note).
Some battery models consist of cells divided into modules separated by a layer of fire-resistant material, this in order to prevent the spread of the fire from a module to the adjacent one.
There are currently no general statistics on electric car fires but, as far as available, there is no higher EV fire risk than traditional vehicles (source National Highway Traffic Safety Administration).
It should be pointed out that the risk of lithium batteries is not so the self-ignition, which is unlikely, but the difficulty of extinguish them once they are involved in a fire due to external causes. Which is what happened to the MotoE in Jerez. For this reason it is necessary to develop adequate fire fighting techniques and properly train the personnel, both firemen and marshals on the circuit (as an example at the end of 2018 in the United States 1 firefighter on 4 was trained to suppress fire of an electric vehicle - source NFPA - National Fire Protection Association).
The manufacturers are also committed to developing safer batteries. Already a first step was done with lithium polymer batteries that do not contain those organic solvents that are the inflammable element of the classic lithium battery. But other developments are expected in the coming years.
Luca Parisi (http://www.cfbt-it.org)
ATP Group (http://www.aptgroup.it)
Motorsport Magazine - "MotoE: is it safe? ”Author Mat Oxley (link)
Williams Advanced Engineering (link)
NFPA - National Fire Protection Association (link)
United States Department of Energy - Sandia National Laboratories (link)