The damage tolerance approach to structural safety is centered on a philosophy of insuring safe operation in the presence of flaws. Accordingly, flaws are assumed to be present at all critical locations and it is demonstrated that these flaws will not grow to a critical size in the usage environment during the next period of operation. This process requires bounds on the sizes of the flaws that may be in the structure and the bounds must be quantified in terms amenable to analysis, i.e., in terms of an equivalent crack length, aNDI. Manufacturing quality control and field inspections are intended to eliminate all flaws but the capability of current inspection systems can only be expressed in probabilistic terms at the small crack sizes of interest. Since no guarantee can be given that all flaws greater than aNDI will be detected and eliminated, there is a failure risk associated with the damage tolerance process.