Window blow-out by itself?

When I returned to my car after my morning gym workout the other day, I discovered my car’s side window was smashed. I assumed it was a break-in, but the manager at the gym told me he thought it was more likely that the window just blew out on its own due to rapidly warming morning temperatures. This sounded far-fetched (and CYA) to me, but he offered in support of his theory these factoids:

– nothing was stolen (I didn’t leave anything in there worth taking)

– most of the glass, including a roughly 12 x 8 inch chunk, was outside the car (there were still plenty of chunks inside the car)

– it was cold when I got to the gym (10 or 15 degrees) but that side of the car faced the morning sun and it got up to about 30 in the hour that I was gone

– when we reviewed the security tape, we didn’t see anyone loitering around the parking lot, but the camera didn’t capture the row where my car was, so someone could have been messing around out of the camera’s range.

Is the gym manager’s theory likely or even plausible? If so, why aren’t car windows blowing out all over Denver on winter mornings? We often have rapidly warming winter temperatures here.

What do you think?


I think it’s possible, especially if there was a manufacturing defect or a small chip that you didn’t notice in the glass.

I should add that I’ve never noticed a chip in that window. Also, the car is 8 years old and I’ve lived in Denver for 5 years. Winter conditions this year are pretty much like every other year.

Anything’s possible, but it seems less likely than the possibility that someone broke in and then discovered nothing to steal. Where the doors still locked?
Another possibility is that some object impacted the window and broke it, without any evil intent. Is it near an area where children play?

Well, I assume he didn’t mean the air made it blow out, rather, the temperature change made the window expand unevenly, causing a fracture. I guess it could occur, unlikely as it is, but I’m more inclined to thing that something hit it, either intentionally or unintentionally.

When I was in college years ago a friend’s car was parallel parked and a truck parked behind it rolled forward and bumped his car (a hatchback), shattering a rear side window but doing no other damage to his car. I saw him and the car with the truck still against it while my friend was waiting for the police to arrive. Most of the glass was outside the car. Based on that experience I’m wondering if a driver bumped your car in such a way that, along with the cold weather, caused the window to shatter.

Doors were stil locked but the window was completely gone, so it would’ve been easy for someone to reach in. It was not near an area where children play.

In these snowy conditions there may have been ciders layed down in the parking lot by the snow crew. Another car, pulling out from a space two or three away from yours could have kicked up those rocks when accelerating away from their space and not even have realized it.
This has, in fact, happened to me while parked in my driveway, behind my other car, with the back end jutting out only into the parking portion by the curb. When I went out an hour later to get into the Explorer, the left rear door glass was shattered. As best as I could determine from the evidence at hand, another vehicle kicked up the road cinders when accelerating away from the stop sign.
Lots of glass fell outside too because that tempered glass just goes everywhere when not being assisted by the force of a person swinging an implement from the outside.

That’s entirely possible, since it was in a parking lot. But there’s no video of that area to review.

Honestly, I’d rather believe that the window blew out, rather than think that someone broke in. It just seems unlikely. Wouldn’t there be windows blowing out all over Denver?

Considering all the evidence I consider the gym manager’s theory very plausible. Especially with a 12x8 inch chunk of glass still intact.

Cars’ side windows are required by law to be tempered. Tempered means that they’re heat treat with a procces that leaves the structure under residual stresses, such that if the glass is broken via impact it breaks into lots of tiny pieces rather than large sharp-edged sections. I suspect your window had a defect and fractured from thermal stress the point of origin being at the defect.