Karl-Heinz Knorr, b. 1964 in Bad Harzburg, is a physicist and since 1996 Chief Fire Officer of the Bremen Fire Department. He studied physics and technical electronics at Clausthal University of Technology and Southern Illinois University in Carbondale. Since 2016 he is also Vice President of the German Fire Brigade Association.
SPIEGEL: Mr. Knorr, burning electric cars make headlines, how dangerous is such a fire really?
Karl-Heinz Knorr: No more dangerous than the fire of a "normal" car. Because in an electric car is not more energy stored than in the full tank of a combustor. These vehicles burn but different. If the tank ruptures in a combustor, smother the fire with extinguishing foam. In an electric car, the thermal energy is not generated on the surface, but inside the battery. There is a danger here of a so-called "thermal runaway", in which the fire jumps from one cell to the next. Then, like a fire in a terraced housing estate without fire walls, a fire leads to the fire of the entire row. Such a battery fire is of course associated with heat and fire, but with 50 liters of gasoline that is also the case.
SPIEGEL: How do you extinguish a fire in a battery?
Knorr: This is a chemical process that you have to interrupt with intense cooling, otherwise it can start all over again. This works best with several thousand liters of water. This is an excellent coolant and you can also bring it very well with Tanklöschwagen on the highway or the highway. In contrast to the burner, you do not see with the naked eye whether the fire is really over. Therefore, after deleting with a thermal imager, we see if there are still hot spots. It is important, above all, that the towing companies also know about the risks of such cars and park them separately or in a water bath, so that the fire does not rekindle.
SPIEGEL: So, as after an accident in Tyrol, the subsequent storage and cooling of the wreckage is the real problem?
Knorr: For a limited period of time, the battery can theoretically flare up again 24 hours after the fire, at first small and harmless, a few minutes later intense again. The waste disposal companies must know this so that they do not push the car into a hall, but at best store it in a container with water. We therefore demand that towing companies be prepared for such cases. After 24 hours, however, the battery is no longer at risk.
SPIEGEL: Does the fire department need special equipment for such fires and toxins released as a result?
Knorr: You need more water, so on rural roads and highways, another tanker must be sent along. Otherwise, you do not need more equipment than another brand. As far as respiratory poisons are concerned, we also protect ourselves with "normal" car fires with respiratory protection, since only the smoke that develops when the upholstery and coverings burn is poisonous.
SPIEGEL: How often do electric cars burn?
Knorr: Rarely, the risk of fire is comparable to that of a combustor. High-quality batteries contain many safety systems that prevent auto-ignition. Of course, such a battery can cause a fire, because since there are cars, these also burn, for example, after accidents or technical defects. But a much bigger problem is the calorific value of normal cars, which has almost doubled in the last 25 years due to the many plastics. As a result, twice the energy is released in a fire today, which is particularly problematic in underground garages.
SPIEGEL: Even if tomorrow all people drive an electric car in Germany, so does not rise the risk of fire?
Knorr: No, the fact that a car burns during operation is no more likely in electrical engineering than in a gasoline car. You forget that, but already 50 milliliters of gasoline burn extremely hot and long, and in a tank stuck usually 50 to 80 liters – directly under the back seat. If you were to reintroduce this technology today, you would have a huge security discussion. But we have been used to these fuels for 70 years and even trust the layman to fill them at the filling station itself. So we drive all around and have no problem with it at all.