KELOWNA, B.C. — On a quiet stretch of the Coquihalla Highway, about 60 km outside of West Kelowna, the sun was shining on a blue-sky February afternoon when the roof of my BMW exploded.


Quite the hole.

The glass sunroof disappeared into the air, a shattering of tempered pebbles drizzled down to the highway behind me. No one was about, so no other cars were at risk from the fallout. The explosion pushed all the pebble-like glass fragments up and away from the 430i xDrive Gran Coupe ($61,250).

I was stunned. In 35 years of testing cars and trucks of all sorts, nothing like this had ever happened to me.

“What the f$%k?”

I took the first exit and parked in a turnout. I reached for the controls of the Harmon Kardon, silencing Lynrd Skynrd’s Free Bird Live at the Fox in Atlanta. I needed a pause. I took a deep breath. What the heck had just happened?

Later, at the BMW dealership in Kelowna, the service manager told me that from time to time a random pebble hits a glass roof at just the right spot, at just the right moment, and that’s that – disintegrating glass. The Coq was covered in plenty of gravelly bits on this late winter day. It had snowed heavily two days earlier; the road crews had been at work with salt and sand.

But in the aftermath, in the moments immediately following the explosion, I had a more immediate problem: What’s next for a Coupe with a gaping hole in the roof?

Cardboard and duct tape filled the hole. BMW of Kelowna acted fast to get me on my way.

I called BMW and they went to work on this Friday afternoon. Minutes later, BMW rang back. Go to the Kelowna store, I was told. There, the service manager and a technician cleaned out the glass bits and plugged the hole with cardboard and duct tape. That allowed me to continue to Silver Star, the brilliant ski hill near Vernon, B.C. My long weekend of skiing was still on.

So, what happened to the glass? Well, according to Consumer Reports, this is not a “freak occurrence.”

“These incidents have happened in every month of the year in every part of the country, in vehicles from all over the world; they have occurred on interstates, on country roads, and even while parked in driveways,” notes the publication.

In a 2017 report, CR noted that in the previous two years, American consumers had filed at least 859 complaints about such an occurrence. This sort of thing had happened to 27 BMW models during those years.

But for the time being, despite a number of different investigations, no car company or government agency has come forward with a definitive explanation for why glass roofs explode from time to time. An act of God or some other greater power? Perhaps there is more than once cause.

“Something is going on. Calling it an act of God feels like an old industry playbook for a new car feature,” an official at the Center for Auto Safety told CR.

Some auto-glass experts and structural engineers told CR that car companies should consider more carefully the kind of glass they use in sunroofs. They called for stronger glass.

South Korean car safety regulators, noted CR, turned their attention to a part of the manufacturing process. They determined that something called “ceramic printing” — used to coat some of the glass, creating a darker area that hides mechanical parts — can make portions of the pane weaker and more vulnerable to shattering, noted CR.

Another expert told CR that modern designs are more three-dimensional and often involve bending glass to the curvature of the roof. That makes them more susceptible to impacts.

The troubling part of the CR investigation, and, indeed, all the investigations into this sort of event, is that, for now, it appears impossible to differentiate a stable glass sunroof from one vulnerable to a shattering incident. And this is not the sort of thing car companies like to talk about, even if only to announce explanations and fixes.

BMW, for its part, took care of the car and me, most likely pleased that no one in my Coupe was injured, and no other car or person was involved. But the mystery of exploding sunroofs, even if it’s a relatively rare occurrence, appears unsolved.

Time for better, more complete answers.

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