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/
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