Nondecay probability of a metastable state: almost exact analytical   description in wide range of noise intensity
  This paper presents a complete description of noise-induced decay of a metastable state in a wide range of noise intensity. Recurrent formulas of exact moments of decay time valid for arbitrary noise intensity have been obtained. The nondecay probability of a metastable state was found to be really close to the exponent even for the case when the potential barrier height is comparable or smaller than the noise intensity. 
Svetlana P. Nikitenkova, Andrey L. Pankratov