The lithium ion batteries that power electric vehicles, but also the smartphones we use every day, they are generally safe but in some circumstances they can become flammable.
In an electric vehicle, lithium-ion batteries are grouped in the form of several cylindrical cells forms and packages. This distribution allows you to better balance the charge between the cells and manage heat more efficiently. To ensure correct operation of vehicles, and above all an adequate safety standardthere is a need for specific measures – from cooling systems to thermal insulation – that are able to prevent, or contain, the overheating of lithium ion batteries.
While petrol cars can catch fire due to fuel leaks, collisions or engine malfunctions, electric cars can catch fire due to a chemical reaction that takes place inside damaged batteries and leads to overheating in temperature and a consequent “thermal runaway”.
If the overheating of the batteries is not (or cannot) be counteracted, a more or less large (and more or less serious) fire can slowly break out.
This can occur, for example, if: exist manufacturing defects which can cause thermal runaway; batteries are exposed to prolonged exposure extreme temperatures; a strong collision or impact damages the batteries to the point of compromising their structure, with the internal parts of the various cells which may come into contact inappropriately; an external object penetrates the battery modules altering their state.
The last two cases, in particular, could be the origin of the flames that escaped from the bus that crashed from an overpass between Mestre and Marghera. The strong impact of the electric vehicle with the ground may have damaged the lithium-ion batteries and caused a subsequent thermal runaway. However, the prosecutor of Mestre, Bruno Cherchi, told journalists that “there are no particular flames or a fire in the technical sense of the crashed bus”. There was instead “a gas leak from the lithium batteries that make up the truck” and the judiciary is investigating this. The batteries, in any case, were secured and seized.
In one of the amateur videos shot shortly after the accident, in which a father pulls his daughter out of a bus window, smoke can actually be seen coming out of the front of the vehicle but there is apparently no trace of flames.
For the Provincial Commander of the Venice Fire Brigade, Mauro Luongo“complicating the rescue operations were the batteries which caught fire with the impact. The batteries have critical issues when they are hot, we had to wait for them to cool down to remove them”.
Mestre, the fire brigade commander: “The extraction of people from the bus was complicated”
Massimo Fiorese, CEO of the company The Spa Line to which the crashed bus belongedclaims instead that “the bus did not catch fire, it only made a few flames. Being electric, if it had caught fire completely it would have been an even worse tragedy”.
The way the flames spread, in fact, is another key difference between fires caused by an electric car or a petrol car. In the first case the flames spread quite slowly, while in the second they envelop the vehicles in a few moments, accompanied by strong explosions. When batteries catch fire, they also generate intense fires that last a long time and which can be potentially toxic.
Furthermore, in the case of batteries, it is not uncommon to see new flames breaking out even when it seems that the fire has been put out. This could be one of the reasons why those on the Mestre bus were immediately removed and made safe by the Venice firefighters.
There are no studies capable of certifying, with extreme certainty, whether fire risks associated with electric vehicles are higher (or lower) than those of petrol cars. Even the statistics don’t help: the former are present on the road in significantly fewer numbers than the latter.
However, it seems universally recognised, especially among rescuers, that greater difficulty in extinguishing flames generated by lithium ion batteries. In this case, in fact, a generous flow of water is not only insufficient but could even make the situation worse. This is due to chemical reaction which occurs when lithium ion batteries come into contact with water: flammable hydrogen gas is produced which can fuel the flames.
In 2021, firefighters in Austin, Texas, said they put out an electric car on fire with 40 times the normal amount of water, precisely because of the lithium ion batteries in its engine. The vehicle in question was a Tesla, i.e. an electric car produced by the company of which Elon Musk is CEO.
There is a site, called “Tesla Fire”, which collects all the episodes of Tesla cars burning due to their batteries: the “confirmed” cases would be 204 in the last ten years. The data is significant as the company led by Musk is the second car manufacturer in the world by number of electric vehicles produced.
The overall number of cars that catch fire every year, in the United States alone, is much higher: there are approximately 117 thousand according to data collected by National Fire Protection Associationa non-profit organization that aims to reduce deaths due to fires of all types.
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