The glass breakage pictures presented in this chapter will be structured, focusing on the essence of glass breakage. Identification of unambiguous causes of glass breakage always requires big experience, so such causes should be determined by specialists.

In certain cases it is impossible to identify a clear unambiguous cause on site just on the basis of the glass breakage view. Then checking of the glass cross-section through a microscope might be useful in order to identify the basic or primary breakage, when breakage lines are complicated. As this method is highly expensive, it can be applied only in exceptional cases. It also requires big experience. Only a limited number of institutes are capable to perform an analysis and define the clear cause. However, in most cases, the cause(s) of glass breakage can be defined quite precisely on site after precise and comprehensive analysis.

There always exist several basic rules which prove out for the cases with non-tempered glass and thus they should be taken into account.

Three rules of breakage:

1. Breakageg is always expanding in the direction of spread.
   If such expanded breakage is traced back, the primary breakage an splitting centre is reached.
2. A crack can never overleap the existing crack.
   A crack ends at the place of reached another crack. This fact often enables to establish the sequence of crack emergence as well as place/cause of the primary crack. This feature is used by glass specialists for "catching" of cracks.
3. The average number of cracks depends on the degree of load at the time of cracking.
   A denser network of cracks is usually formed when the glass has to hold a bigger load than vice-versa.

When assessing the pictures of cracking, one should always start from the question about thermal causes, in order to initially ensure clear division of the cracks into the groups of thermal or mechanical cracking.