Don't think your sunroof could ever explode? Think again.

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Why Do Sunroofs Explode?
Don't think your sunroof could ever explode? Think again.

— Owning a vehicle means problems, from bad gaskets to ailing alternators.  One thing we shouldn’t have to worry about is the vehicle glass spontaneously exploding.  Yet that is exactly what many drivers have faced over the years with their sunroofs.

The U.S. National Highway Traffic Safety Administration has received enough complaints on the matter to open an investigation into exploding sunroofs in the 2012 Hyundai Veloster.  Hyundai drivers report glass raining down on them after their sunroofs suddenly shattered while cruising down the highway at 70 mph, as well as reports of sunroofs that exploded while the vehicles were parked and unattended.

The thought of glass exploding above your head might seem absurd, but it can occur to any make and model of vehicle.

One owner of a 2005 Volvo S40 contacted immediately after her sunroof exploded while she was driving down a North Carolina highway.

“It sounded like a gunshot right above my head and I had no idea where it was coming from,” said Alexandra, of North Carolina.  “I could hear air coming into the car even though all my windows were up.”

Alexandra was understandably upset when she described what took place.

“It looked like a meteor bounced through my car upwards and out the sunroof glass.  The remaining sunroof glass was pointed toward the sky, so I knew nothing hit the glass from the outside,” Alexandra said.

What she described is exactly what many drivers have reported.  The sunroof has clearly blown upward, not toward the inside of the vehicle as you would see if an object struck the glass from the outside.

“I lucked out on my side of the car because the passenger/backside got the brunt of it,” Alexandra said.  “I used to nanny in college and drive the babies around. My first thought was, ‘Imagine if I had those kids in here when this happened!’"

While the government investigates Hyundai over the problem and Volvo must answer to Alexandra about her S40, has heard about the problem for years from drivers of the Honda Accord, Audi Q5, Mazda CX-9, Chrysler 300M, Honda CR-V, and many other vehicles.

The story is always the same.  Whether the incident occurred when the vehicle was parked or traveling at highway speeds, the remaining glass structure is always pointed toward the sky.  Owners must then face the task of convincing the dealership and manufacturer that the sunroof wasn’t hit from the outside, a battle that can lead to expensive repairs and denial of insurance or warranty coverage.

Additionally, Alexandra was fighting with the dealer to fix the scratched paint caused by flying glass.

What could cause a sunroof to explode or shatter? contacted four of the top university mechanical engineering professors and asked that very question.  All agreed the problem could be found in the glass itself, not necessarily how it was installed in the vehicle.  In fact, all types of glass products can explode, including ovenware, patio tables, even glass balconies.  It’s occurred for years and the problem has grown in vehicles because more cars come standard with a sunroof/moonroof, something that was once considered a luxury option.

A sunroof is made with tempered glass that is designed to break into small pieces for safety.  Any imperfection in the glass--whether caused by a bad batch of glass or a scratch from a rock--can cause the glass to shatter when under pressure.  The pressure might come from the vehicle itself because every vehicle is more airtight than ever.

Because a glass sunroof is under a lot of compression, air pressure or temperature changes can all contribute to pressure on the glass.  All it takes is one microscopic imperfection and time to allow the problem to reach a level where the glass explodes.

Previous unrelated investigations found nickel sulfide crystals in shattered glass.  These crystals can grow and if their growth is in the correct direction, the glass will shatter from the pressure.

Hyundai Veloster owners are waiting for an answer to why their sunroofs exploded.  The National Highway Traffic Safety Administration would not discuss the case because the investigation is currently open.

What Alexandra Saw When She Pulled to the Side of the Highway


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