How dangerous are burning electric cars?

https://www.eurekalert.org/pub_releases/2020-09/sflf-hda090120.php

News Release 1-Sep-2020
Swiss Federal Laboratories for Materials Science and Technology (EMPA)


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Crucial information for multi-storey and underground car parks

The trial, which was funded by the Swiss Federal Roads Office (FEDRO) and in which several Empa researchers participated, took place in December 2019. The results have just been published. "In our experiment we were considering in particular private and public operators of small and large underground or multi-story car parks," says project leader Lars Derek Mellert of Amstein + Walthert Progress AG. "All these existing underground structures are being used to an increasing extent by electric cars. And the operators ask themselves: What to do if such a car catches fire? What are the health risks for my employees? What effects does such a fire have on the operation of my plant?" But until now there has been hardly any meaningful technical literature, let alone practical experience for such a case.

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The results of the test were published in a final report in August 2020. Project leader Mellert reassures: In terms of heat development a burning electric car is not more hazardous than a burning car with a conventional drive. "The pollutants emitted by a burning vehicle have always been dangerous and possibly fatal," says the final report. Regardless of the type of drive or energy storage system, the primary objective has to be to get everyone out of the danger zone as quickly as possible. The highly corrosive, toxic hydrofluoric acid has often been discussed as a particular danger in burning batteries. In the three tests in the Hagerbach tunnel, however, the concentrations remained below critical levels.

Conclusion: A tunnel ventilation system that is state-of-the-art can cope not only with burning gasoline/diesel cars, but also with electric cars. Increased corrosion damage to the ventilation system or the tunnel equipment is also unlikely based on the results now available.

Even the fire brigades do not have to learn anything new on the basis of the tests. Firefighters know that the battery of an electric car is impossible to extinguish and that it can only be cooled with large amounts of water. So the fire can possibly be limited to a few battery cells, and part of the battery will not burn out. Of course, such a partially burnt wreck must be stored in a water basin or a special container so that it cannot reignite. But this is already known to the specialists and is being practiced.

The extinguishing water is poisonous

A problem, however, is the extinguishing and cooling water that is produced when fighting such a fire and storing a burnt-out battery in a water basin. The analyses showed that the chemical contamination of the extinguishing water exceeds the Swiss threshold values for industrial wastewater by a factor of 70; the cooling water is even up to 100-times above threshold values. It is important that this highly contaminated water does not enter the sewage system without proper treatment.

Professional decontamination mandatory

After the trials, the tunnel was decontaminated by a professional fire clean-up team. Samples taken subsequently confirmed that the methods and time required were sufficient for the clean-up after an electric car fire. But Mellert warns especially private owners of underground garages: "Do not try to clean up the soot and dirt yourself. The soot contains large amounts of cobalt oxide, nickel oxide and manganese oxide. These heavy metals cause severe allergic reactions on unprotected skin." So clean-up after an electric car fire is definitely a job for professionals in protective suits.