Two people are dead after their Tesla turned into a fireball upon striking a tree in Spring, Texas, a town just north of Houston, local news station .

According to the report, authorities used 23,000 gallons of water to finally extinguish the Tesla’s flames because the battery kept reigniting no matter how hard they tried to get it out. It took over four hours. At one point, authorities attempted to contact Tesla for guidance on how to extinguish the flames.

Right now, it is unclear what exactly happened. Authorities note that it appears the car failed to fully make a cul-de-sac turn, which saw them run off the road into the tree. It is also unclear whether or not the car was using Tesla’s Level 2 driver assistance program, which it calls Self-Driving, because neither of the car’s two passengers was behind the wheel. One was in the passenger seat in the front of the car while the other was in the rear. In any case, two lives have been lost.

There have been recurring concerns with Tesla’s Autopilot system, especially regarding the fact that there is no aggressive driver-monitoring system that ensures the person behind the wheel is still alert and ready to take control of the car if anything goes wrong.

Level 2 driver assist programs are not designed for a driver to take their hands off the wheel. Tesla’s Autopilot system is currently only able to steer, accelerate, and brake in some circumstances but not all. The driver still needs to remain alert behind the wheel to do things like change lanes or correct a car-initiated maneuver that is unsafe.

However, the deceptive name of Tesla’s program has resulted in a common misconception that the car is capable of performing fully-autonomous maneuvers that can allow the driver to sleep, swap seats, or take their hands off the wheel for long periods of time.

Battery fires, too, are a big concern for electric cars. While battery packs are designed to avoid penetration, they are not invincible, and the nature of a battery fire makes it far more difficult to extinguish than the traditional gasoline fire.

The investigation is currently ongoing. We will keep you updated as we receive more information.