The progress of a unimolecular chemical degradation reaction is used in representing a component failure mechanism. The component is said to fail when the concentration of reaction product accumulates beyond an acceptable level. The process of accumulating reaction product is modelled as a Markov pure birth process which, in turn, is used in developing the failure time distribution. The model is analyzed under the assumption that the reaction rate is constant. Also, the initial state and the final state of the degradation process are assumed to be Poisson variables. Based on numerical examples, it is found that the failure model can be described as a three-parameter or two-parameter Weibull distribution.