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Q: Deafening sound from something blowing out through sunroof

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My family and I were travelling on the interstate around 60 mph and a sound went off inside the car that sounded deafening. I looked on all sides of our car to see what might have caused the noise or to see if something had hit the car on top of it. We pulled back the sunroof a few inches and there was a large hole in it. I exited at the next off ramp and got out. The sunroof looked like something had crashed up through it from the inside, outward to the exterior of the car. The hole was around 5” x 15” and it was very evident that it had come from inside the car because the edges were arched upward and outward. On top of the sunroof were safety glass fragments and there were also some on the inside visor. The visor had been closed at the time, so no glass had entered the car. There were no bridges nearby at the time of the incident and we did not see any rocks. It was around 75-80 degrees outside and we had the air conditioning on inside the car. We can not find any evidence of anything having hit the car. Please tell me what caused this very frightening thing to happen and how to keep it from occurring again.

A: Hi there, and thank you for asking about th...

Hi there, and thank you for asking about the event that happened with your 2013 Lexus RX450h. Although certainly frightening, this is likely a truly rare event. Most automotive glass has multiple layers of glass, joined by a plastic layer that holds shards together as slightly smoother bits when it shatters like this. When manufactured, there are sometimes residual heat stresses in the glass layers. Additional heat, thermal differences between sides of the glass, vibration, flexing in the body of the vehicle, and other seemingly minor impacts can cause these stresses to "release", sometimes explosively as in your case.

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