It could have broke by itself or an impact hard to say unless you saw it happen.Any sign of debri, a branch, a dead bird? If you do a google search you will see here are many reasons.

Your glass was not shattered due to the cold. Tempered glass wouldn't even notice temperature difference that you experienced.

Your glass broke from one of three causes:

1) Something impacted the glass.
2) Nickel-sulfide inclusion.
3) Edge damage to the glass during handling before or during door fabrication.

It isn't particularly difficult for an experienced glass professional to be able to determine the cause of your glass breakage by examining the glass break pattern. Sometimes it can even be done looking at pictures; unfortunately your picture just isn't clear enough or detailed enough to be able to discern the break pattern.

Also unfortunately, most instances of spontaneous tempered glass breakage end up being one of those mysteries of the universe that remain forever unsolved.

If you have other pictures that may be more detailed than the one that you posted...?

+1

Thermal shock is normally reserved for those applications around stoves and smaller applications.

Oberon...is it true that ceramic can break tempered glass?

Tempered glass breaks when a scratch extends through the thin tempering layer.

It then pretty much instantly and completely turns into 'crumbs' as the stress of the tempering process is released.

The tempering layer is VERY thin at edges, making the glass very vulnerable to scratches on the edges of the tempered pane.

Inclusions in the glass can also result in fracture with repeated temperature cycles (a common cause of oven glass breakage).

Tempered glass is used in oven doors, gas fireplaces, stove tops, etc., simply because it is not very susceptible to thermal shock.

Glass is not a particularly good conductor of heat. Thermal breakage in glass is related to stress induced in the glass by the uneven application of heat to the surface of the glass.

If heat is applied to half the face of a sheet of glass and the other half is kept in shadow then the side where the heat is being applied will heat up rapidly while the side where the heat isn't being applied won't be.

What this does is introduce a boundary or terminus between the warmer side and the cooler side (again keeping in mind that "side" is not referring to the front and back of the sheet - it is referring to the side-to-side of the same face).

As the delta T between the warm side and the cold side increases, it causes stress along the boundary. Every one degree F of temperature difference introduces 50psi of stress into the glass.

When dealing with annealed glass you may start to be a little concerned when the delta T reaches 40 degrees or 2000psi differential along that boundary since that would be about the low stress level to potentially crack annealed glass in the right conditions - especially if the glass has any hidden edge damage.

When dealing with tempered glass, and presupposing an undamaged edge, you simply cannot introduce enough temperature differential to break the glass due to thermal stress in any "normal" glass application.

However, a nickel sulfide inclusion is affected by heat/cold cycles (as brickeye mentioned) and an inclusion can definitely cause tempered glass to shatter without warning.

Tempering glass introduces an interior tension layer and an exterior or surface compression layer. The compression layer will be 21% of the thickness of the glass on both sides leaving the center 58% of the total glass thickness under tension.

In 3mm, or 1/8", or double strength tempered glass the surface compression layer is a tiny bit less than 1/32". If that outer 1/32" of glass thickness is penetrated in any way, be it a puncture, a scratch, whatever, caused by a glass cutter, a glass saw, a water jet stream, a laser beam, no matter, then that glass is going to release that inner tension and it's going to turn into a pile of glass chips.

Basically, if enough force is applied to the glass face so that it exceeds the psi level of the surface compression layer then the glass explodes - period.

When dealing with the edge of a piece of tempered glass it is a pretty good idea to leave it alone because the tension layer is going to approach that edge and if you do anything to the edge that happens to pierce the tension layer then bad things happen.

Having said that, how close the tension layer gets to the edge can vary. It is possible to even shave or polish the edge of a piece of tempered glass (so not recommended!), but doing so (assuming it doesn't break in the process), will leave that edge even more vulnerable than it was before. Fun experiment, but not necessarily a good idea.

WoW, glass falls at about a 6.5 hardness on the Moh's scale. Steel falls down around 4-5 and the ceramic used in a spark plug is around 9 or so.

Anything impacting the face of a tempered glass lite that exerts a force that exceeds the surface compression will result in broken glass. Hardness counts when applying force.

This is the BEST Window Forum that I've found on internet. Thank you so much for all of your professional detailed explanation. we have learned a lot and really appreciate!!

We didn't find any debris around our glass door after it was cracked that morning...

Since we bought this glass 2 months ago, should Glass company pay for this damage or we should pay for it? I just uploaded a closer look of my glass, could anyone tell if it is shattered by itself or by an outside object, based on the crack pattern?

Thank you SO MUCH AGAIN!!!!

This post was edited by daveye on Wed, Jan 30, 13 at 20:34

Do you still have the glass that is missing from the door in the picture?

Thank you very much Oberon for your help!! I doubt we still keep the missing glass... I will check! But how can this help to find the cause of cracks? Thanks again!
Dave

This post was edited by daveye on Thu, Jan 31, 13 at 0:35

Once again...Oberon off of the top rope with the facts.

Gotta love it.

Based on the picture that I see Dave, looks like foreign object is probably the culprit.

The new picture sure looks like impact.

Absolutely impact in my opinion as well, probably right about in the center of that "bowtie" for lack of a better term.

I agree as well that it's pretty clear that the break occured right in the middle of the bow tie, and it does look like an impact break to me as well.

But an inclusion will produce a very similar pattern as well.

What I was hoping for, if you had the glass that is missing from the door, was to see if there were two pieces that were shaped like hexagons and that were larger than the rest of the remains.

When the glass "splits" at the point of the nickel-sulfide inclusion it produces two hexagon shaped pieces that are very distinctive and are a positive ID of the cause of the break.

Holy crap, where do you come up with this info oberon? Very interesting posts you always have with great information!

From his glass and window laden brain.

I so cannot take any credit for that one!

The information is based on research done by PPG back in the 80's, and maybe much older, but the oldest reference that I have to the research is a report from 1985 called "Glass Breakage" and "A Guide to the Fracture Analysis Procedure".

Thank you oberon! I really appreciate your time and help!!