Shattered tempered glass

Please advise of recorded experiences of tempered glass shattering without any potential accidental source. Any recorder experience of this occurring as a result of manufacturing defect?
My experience is with my car, put into my garage at 9PM with glass in perfect condition. The following morning at 8 AM there was a hole in the lift gate's window with the balance of the broken glass still hanging in there. There was no thermal stress, i.e both inside and outside temperature were between 60 and 70 degrees. Theree was no opportunity for anything to drop on the lift gate, which was within 3" of the garage door.
Would appreciate any reference to authoratative source of a posssible non-accidental cause, or referral to a potential source of this information.
Thank you.
Fred Henning

Guest User
Mon, 21/03/2005 - 13:29


There are numerous articles on "spontaneous" glass breakage. Spontaneous breakage could be the result of nickel sulfide inclusions in the glass, but could just as easily be from a sharp impact and taken a while to fully fracture or a number of other causes. You can have the glass tested, if you need to know why the break occurred. You need to locate the origin of the fracture and have it looked at under an electron microscope.

Tony L. Cummings, AIA, CSI
Construction Forensics, Inc.

Joel Feingold
Mon, 21/03/2005 - 14:35

Fred - tempered glass can shatter spontaneously when the mid-plane tensile stresses are not in equilibrium with the compressive stresses at the surface. Other than induced stress (thermal or mechanical), this can be caused by:

1) Poor process control (furnace or cooling nozzle problems)

2) Undetected defects in the glass, typically Nickel Sulfide inclusions and bubbles. Undetected microfractures or hairline cracks caused by these defects can "run" and cause a rupture.

3) Under- or Over-tempering (over reliance on fragmentation testing or time/temp recipes instead of measuring actual surface stress with an instrument such as the Strainoptics GASP surface polarimeter for quality control)

If your lift gate window is curved and/or has a black band around the perimeter, then residual stresses in the edge region could be at fault. This situation requires measurement with an Edge Stress meter, such as the Strainoptics GES-100 or VRP-100 polarimeters. Many major auto glass manufacturers already use these instruments as part of their QC procedures, but not all.

Hope this helps.

Guest User
Tue, 29/03/2005 - 19:17

The breakage you describe is probably due to one of the two following causes.

1. Nickel sulfide inclusions in the raw glass from which the part was made can change state, causing enough tension to fracture tempered glass. the problem is less common now than a decade ago. Most raw glass manufacturers have eliminated stainless steel from their processing equipment, a major source of nickel through abrasion by raw materials. (Sulfur is abundant in the melt.) They also do a better job of avoiding nickel contamination of raw materials. Sometimes, tempered parts are heat-soaked in a manner designed to destroy nickel-sulfide contaminated parts before they are sold.

2. Because the fracture resistance (modulus of rupture) of glass is time dependent, some abrasions that penetrate through the layer of surface compression are not propagated as fracture until the core tension breaks many silica-oxygen (SiO2) bonds in the fissure front over time. Then, the fault reaches "criticality" and the tempered part suddenly shatters. (Tempered glass fractures as it does because during cooling the warmer core continues to cool and contract after the surface freezes. That core contraction pulls the surface into high compression - the reason the surface is strong - and pulls the core into high tension. When a fracture occurs in the high tension core, it is propagated by that tension.) Water molicules reduce the energy required to separate the SiO2 bond. Capillary condensation assures that water molicules will accumulate in the fissure fronts in the glass surface. The capillary condensation process can influence the time dependence of fracture propagation in abraded tempered glass.

Enough of that! The bottom line is that if you have enough of the broken pieces, an expert can determine whether your glass broke from NiS inclusions (a manufacturing defect) or abrasion (bad luck). Without that evidence, the manufacturer will deny the presence of NiS in their glass parts (bad luck).

Guest User
Wed, 30/03/2005 - 04:32

Bottom Line - The dealer replaced the liftgate window under warranty after forwarding my photographs to higher places.

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