Researchers from Switzerland, Germany and France have examined in detail what happens when the battery module of an electric vehicle (EV) catches fire in an enclosed space.
A dry bang and then it starts: a battery module of an electric car is set ablaze in the Hagerbach test gallery. A video of the test (below) shows the energy contained in such batteries: meter-long flames hiss through the room and produce enormous quantities of thick, black soot. Visibility quickly approaches zero. After a few minutes, the battery module burns out. Ash and soot have spread throughout the room.
The experiment, financed by the Swiss Federal Roads Office (Astra), took place in December 2019 and the evaluation is now available. “In our experiment, we were thinking primarily of private and public operators of small and large underground or multi-storey car parks,” says project manager Lars Derek Mellert from Amstein + Walthert Progress. “All these underground structures are increasingly being used by electric cars. And everyone asks themselves: What happens if such a car catches fire? What are the health risks for people in the vicinity? And also: What effects does such a fire have on the operation of the plant?”
Mellert developed three test scenarios with the support of battery researcher Marcel Held and corrosion specialist Martin Tuchschmid from Empa. Other participants were experts from the Hagerbach AG test gallery and the French “Centre d’études des tunnels” (CETU) in Bron. Among other things, the researchers installed test surfaces in the fire chamber, on which the soot was deposited. After the test, these surfaces were chemically analysed and also stored in special rooms for several months to detect possible corrosion damage.
The Swiss researchers tested three realistic scenarios: A fire in an enclosed space, a fire in a room with a sprinkler system and a fire in a road tunnel with ventilation.
The first scenario involved a fire in a closed parking garage without mechanical ventilation. A parking area of 28 x 28 metres and a floor height of 2.5 metres was assumed. Such a parking floor would have an air volume of 2000 cubic metres. The fire of a small car with a fully charged battery of 32 kWh is assumed. For reasons of test economy everything was reduced to 1/8: A fully charged battery module with 4 kWh capacity in a room with 250 cubic meters of air volume was set on fire. The tests examined how the soot settles on tunnel walls, surfaces and on protective suits worn by firefighters present, how toxic the residues are and how the fire site can be cleaned after the event.
Scenario 2 deals with chemical residues in the extinguishing water used. The test set-up was identical to scenario 1, but this time the smoke from the battery was directed under a water shower similar to a sprinkler system with the aid of a metal plate. The raining soot water was collected in a collecting basin. The battery was not extinguished, but also burned out completely.
The third scenario dealt with the effect of a fire on a ventilation system. How far is the soot distributed in the exhaust ducts? Are substances deposited there that lead to corrosion damage? In the experiment, a 4 kWh battery module was again set on fire, but this time a fan blew the smoke at a constant speed (approx. 1.5 m/s) into a 160-meter-long ventilation tunnel. At a distance of 50, 100 and 150 metres from the site of the fire, the researchers had installed metal sheets in the tunnel where the soot was deposited. The chemical composition of the soot and possible corrosion effects were analyzed in Empa’s laboratories.
The results of the test have been available since the beginning of August. On the one hand, project Manager Mellert can give the all-clear: A burning electric car is no more dangerous in thermal terms than a burning car with a conventional drive. “The pollutant emissions of a vehicle fire have always been dangerous and possibly fatal,” says the final report. Completely independent of the type of drive or energy storage system, the primary objective must be for all persons to get out of the danger zone as quickly as possible. In particular, the highly corrosive, toxic hydrofluoric acid is often discussed as a particular danger in burning batteries. In the three tests in the Hagerbach tunnel, however, the concentrations remained below the critical range.
Conclusion: A tunnel ventilation system that is state of the art can cope not only with burning gasoline cars but also with electric cars. Increased corrosion damage to the ventilation system or the tunnel equipment is also not to be expected on the basis of the results now available.
Even the fire brigades do not have to learn much new facts on the basis of the tests. Firefighters know that the battery of an electric car cannot be extinguished but instead needs to be cooled with large quantities of water. So the fire can possibly be limited to a few battery cells, and part of the battery will not burn out. However, such a partially burnt out 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 already being practiced.
The extinguishing water becomes 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 bath. The analyses showed that the chemical load of the extinguishing water exceeds the Swiss limit values for industrial waste water by a factor of 70, and the cooling water is even up to 100 times above the limit value. It is important that this highly contaminated water does not run into the sewerage system without proper pre-treatment.
After the tests, the room was analysed and decontaminated by professional fire cleaners. The soot contains large amounts of cobalt oxide, nickel oxide and manganese oxide. These heavy metals cause severe allergic reactions on unprotected skin. It is therefore absolutely necessary to leave the clean-up of such a fire source to the fire brigade – it is too toxic for normal mortals.
More information: https://www.empa.ch/web/empa/
- ADAPTING SPACE BATTERY TECH FOR SAFER GRID BATTERY STORAGE
- AI DETECTION OF LITHIUM BATTERIES AND DANGEROUS GOODS
- RUGGED FLEXIBLE BATTERY DOESN’T CATCH FIRE
- BATTERY MONITORING DEAL TO ENHANCE SAFETY
Other articles on eNews Power
- Dialog extends PMIC deal with Renesas
- Turning a housebrick into a supercapacitor
- WattUp module for wireless charging
- Rocket tests perovskite solar cells in space