Tensile strength of structural glass elements is highly influenced by flaws. For this paper, the study concentrates on the fracture origin i.e. the critical flaw, situated at the edge of a glass element. In the current study the influence of two different edge finishings, two stress rates and two suppliers on the edge strength of glass have been investigated by means of experiments. Microscope observations have been performed to determine the flaw dimensions and the fracture mirror zone. The critical flaw initiating the failure is characterized by the depth and by the geometry factor. In addition, the environmental conditions are taken into account in the study due to strength degradation as a function of loading time. In this paper, a relation found in the literature between the critical flaw and the mirror radius at the fracture zone is presented and compared to obtained experimental values. From the study it is concluded that the failure strength as a function of loading time can be determined for failed specimen using a proposed procedure on flaw measurements. (C) 2014 Elsevier Ltd. All rights reserved.