When it's urgent: Electric cars in underground parking garages

Electric vehicles have become an integral part of our everyday lives. They roll quietly through cities, promise a clean future, and contribute to the energy transition. But despite all the enthusiasm for this new technology, there is a downside that hardly anyone likes to talk about: fires in underground garages and parking structures.

While combustion engine vehicles have been taken into account in fire protection concepts for decades, modern electric cars with their significantly higher fire load are challenging these familiar assumptions. The problem is that most underground garages were built long before electric cars were even a topic of discussion – and they are simply not prepared for these new risks.

A burning car is always dangerous. But with electric cars, the situation is even more dramatic. While a combustion engine can usually be extinguished relatively quickly, an electric car fire generates enormous temperatures that can last for hours. The cause lies at the heart of the vehicle—the battery.

What many people don't know is that the fire load of a lithium-ion battery is not simply equal to the electrical storage capacity specified in the brochure. Rather, the chemical reactions in the event of a fire release many times more energy. Studies show that the heat released is eight to ten times higher than the stored electrical energy. In other words, in the event of a fire, a 100 kWh battery becomes a heat source of almost 1,000 kWh – in addition to the burning vehicle itself. By comparison, a 60-liter tank in a combustion engine has a fire load of approximately 600 kWh.

For underground garages and parking structures, this means that even a single electric vehicle can generate temperatures that push concrete and steel to their limits and render escape routes impassable in a very short time.

At Merkle CAE Solutions, we have virtually “set fire” to around fifty underground parking garages in recent years. Even a rough estimate shows that few of the existing underground parking garages would be designed to withstand the stresses of a burning electric vehicle.

Existing building regulations (e.g., the Model Garage Ordinance in Germany) are still based on conventional combustion engine vehicles. These typically define a “design fire” with a specific heat release rate—but this is based on the behavior of gasoline and diesel cars.

Our numerical fire simulations—in accordance with the guidelines for engineering methods in fire protection—allow us to understand in detail how smoke, heat, and visibility develop, what forces act on the supporting structure, and when the fire department can still intervene—or when it can no longer do so. This turns an abstract danger into a concrete picture: we can see where the smoke first rises, which areas become impassable, and which components suffer the most.

The results speak for themselves:

• Even a single burning Tesla or SUV can generate temperatures that exceed the design limits of concrete and steel.
• Layers of smoke form within minutes, leaving people with no chance of escape.
• Even powerful smoke extraction systems and sprinklers reach their limits, as the heat continues to build up for hours and cannot be easily cooled down.

What is particularly treacherous is that while the all-clear can be given after a short time with combustion engines, the fire in electric cars flares up again and again – often to the point where even the water used to extinguish it is hardly sufficient.

Electric mobility is advancing inexorably. But it would be negligent to leave yesterday's infrastructure to face tomorrow's risks alone. Underground parking garages urgently need to be retrofitted.

This includes new fire protection concepts specifically designed for electric vehicles: more powerful smoke extraction systems, better material protection linings, sprinkler systems with sufficient water supply, and clear operational plans for the fire department. Equally important are simulations in the planning phase that highlight risks at an early stage, as well as training for emergency services, who need to be prepared for the specific dangers of battery fires.

Electric vehicles are here to stay. But we mustn't pretend that an electric car fire is the same as a combustion engine fire. The fire load is 1.5-2 times higher, the duration significantly longer, and the impact on people and buildings considerably greater.

The good news is that modern fire simulations can help us get this problem under control. We can calculate in advance where the weak points are, how to fix them, and what measures will save lives in an emergency.

👉 Want to know how your underground car park will hold up in an emergency? We'll simulate it for you and provide you with the basis for making safe decisions.