A phenomenological formulation of Si-O bond dissociation is utilized to interpret stable crack velocity and static and dynamic fatigue phenomena. The resulting model has an exponential form and is applicable to a wide range of flaw sizes, service stresses, and test environments. Furthermore, it is readily reduced to the power law by retaining the first term of the series expansion of the exponential function. The model provides a sound physical basis for comparing different fiber compositions, service environments, and stress-time histories (static versus dynamic) from the fatigue point of view. The application of the model to silica and titania-doped silica optical fibers provides valuable insight into their relative fatigue behaviors and sheds further light on the fundamental mechanisms controlling such behavior.