Glass Expert at Read Consulting is asked to assess whether a broken window or shower door was fully tempered. One method is to select the ten largest “crack free” pieces and determine if these can fit into a 10 square inch area. In the photo above, a 3″ X 3″ (approximately 10 square inches) “frame” is placed over the broken glass. In this example there are many more than 10 pieces in the opening. Before breaking this glass door, the temper stress was measured to be 16,000 psi using a Strainoptics grazing angle surface profilometer (GASP). However, it is important to note that there are cases where the fully tempered glass will not fragment properly. The larger pieces result from the stresses applied to break the tempered glass door or tempered glass window.