The cause of the shower door shattering is all in the manufacturing of the door at the glass works.
If the glass in the door has not been heated and cooled (Annealed) properly while being made, the correct tension and compression is not in the glass, therefore it will shatter under the right conditions.
When the glass is put under a polariscope you can see the forces of the tension and compression in blue and red. Glass will only break under too much tension.
An example of tension and compression;
The rim of a bicyle is in compression, the spokes are in tension. The rim of a wagon wheel (held together with a metal band) is in tension the wooden spokes would be in compression.
I worked with glass for 17 years at Canadian General Electric.
Hope I have not made the waters too muddy.
Geoff
