Glenda

The only logical explanation I would have...
1- someone or something hit the window. You may not hear the glass being hit and it shattering, 'cause there isn't enough time difference between the two events.
2- the window was under a lot of stress by the window mechanism - does it have electric window lifts? It may have overstressed the window pane and a little extra vibration can shatter the glass.
3- poor quality glass

Glenda

I was driving my Wrangler soft top home from work in one of the South's infamous ice storms. Had about 2 inches of ice on the rear side windows that I didn't feel like waiting to melt off (can't use an ice scraper on a plastic window). So I'm on the highway and an 18 wheeler passes me and throws up a huge chunk of ice into the driver side rear window. It shattered just like glass! Also scared the bejeesis out of me. When I called the insurance company, he said "broken window- take it to a glass shop" and connected me right away before I could say anything. Talk to the glass shop- which of course does not replace plastic windows. Called insurance company again- quickly explained that my PLASTIC window broke and the GLASS shop can't fix it. Stunned silence. Ended up writing me a check and I got a new aftermarket window.

This is indeed unusual.
Hope no-one ended up with any glass in their eyes ..
I think this is caused by a sharp stone or piece of debris being thrown up by a passing vehicle.
All cars should have "mud-flaps" to prevent this..
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Yea, mud flaps would look really cool on my vette, or better still on my neighbors Ferrari !!

The side windows of your car are tempered glass. Tempered glass is heat strengthened by taking the glass up to 1200F and then rapidly cooling it. This causes the exterior surface of the glass to compress while the interior of the glass is still quite warm and still in expansion mode. Ultimately, this translates into an exterior compression layer and an interior tension layer.

When the compression layer is breached, then all that tension is released (kind of like a spring) and POW! there goes the window.

Okay, then why did the side window break? It is certainly possible that it was impacted by a rock or bb or something similar, but I am guessing that it was spontaneous breakage based on the description.

As mentioned, tempered glass is tough on the face, but the edges are quite fragile.

One characteristic of tempered glass is that if it has edge damage it might not "release" immediately, preferring to wait around for awhile until it has a chnace to scare the @$#%@^@%#$@ out of someone sitting at a stoplight or else eating breakfast in their home. It makes for great conversation!

When glass is manufactured, it might have what are called "inclusions". Usually nickle sulfide or perhaps other trace elements, these inclusions can cause significant problems in tempered glass. While most glass with inclusions will break during the tempering process, some of them are just stubborn enoungh to make it past that process and into the actual finished product. These inclusions, like their edge damaged cousins, love to wait around awhile until everyone is quietly relaxing and then POW! no more glass in the window frame.

Typical breaking stress for annealed (regular) glass is around 6000psi. Typical windload breaking stress for tempered glass is around 24,000psi, thus the "four times stronger" comparison that many folks like to quote.
When impacted, tmepered glass is about double the strength of annealed glass. One typical lab test is to impact 1/4" lites with a 5gm missile. The tempered glass can withstand the impact up to about 60ft/sec while the annealed can withstand the missile to about 30ft/sec.

Ultimately, very few folks insure against glass breakage. Although spontaneous breakage does happen, I would suggest that proving it will be difficult and the last thing that any glass company wants to do is to deal with about 10,000,000 claims for spontaneous breakage - definitely a losing situation. And realistically, way more glass is broken for reasons other than spontaneous breakage...

Hopefully this made some sense!

I was sitting at a stoplight in the left turn bay, when all of a sudden...BOOM! Almost my entire back window was gone. The guy in the car next to (and slightly behind) me had his mouth open and a stunned look on his face. He asked ME what happened!

There were was another witness from the car behind me who just shrugged his shoulders when asked what happened.
Initially, many things went through my mind:
1) Did somebody with a baseball bat and smash my window and run off? --No. He would have been seen.
2) How about a kicked up rock from a passing car? --No. All cars around me were at a standstill and there was no oncoming traffic.
3) Maybe I was shot at by a gun or BB-rifle? --Unlikely. The intersection is in the middle of an open field, so there is no place to hide. Plus a handgun or rifle shot would have hit something else in my car when the bullet passed through. I've seen windows that were broken by a small projectile and usually you can easily define the impact spot. There was no such spot.
4) Did something fall off of an airplane and hit my window? (I actually did look up at the sky after exhausting all of the other possibilities.) --No. I looked over every inch of the car and could find no trace of a projectile.

When I took my car to the police station, they said that since it wasn't vandalism or caused by an accident, that they "really didn't have a form for spontaneously exploding car windows." She did tell me that she has heard of this happening on 4 different occasions before.

SO WHAT REALLY HAPPENED?
I'm guessing that it was a combination of several events:
1) A big storm was rolling in at the time so the pressure was dropping
2) It was a warm day, but the storm was bringing with it much cooler air
3) I had had my car serviced the week before at the dealer for problems with my rear window washer fluid dispenser, which actually sits on the rear window glass

EVIDENCE
The only evidence I have is a lack of a projectile and the broken glass was about 60% inside my car, 40% outside...suggesting that the window just exploded.
I've attached a link to some pictures that I'll post later tonight.

Scary and wierd!

I have a friend that owns a body shop. He had a customers car in to replace a side glass that had exploded. The car was finished and parked out side in front of the shop around 3:30pm. The customer showed up around 4:00pm walked into the shop and asked when the car was going to be finished. The owner said it was all done and ready to go. When they walked outside to inspect the new glass that one had exploded too. So it is not uncommon for them to explode. But I don't think they are as bad as they use to be.

BN