As it is predicted that mobile traffic demand will reach an astonishing 190 exabytes by 2018, current methods of spectrum allocation and management need to be rethought towards more advanced sharing of frequency bands. To this end, a novel regulatory framework has recently emerged, named Licensed Shared Access (LSA), which enables guaranteed spectrum access for a limited number of sharers. However, realistic LSA band operation may result in its abrupt unavailability, causing traffic delays and even network access failures in case of unsuccessful evacuation of a user back to conventional cellular bands. In this paper, we formulate an adequate queuing-theoretical model for evaluating such service failure and interruption probability for users that attempt to operate within a cell of a network with the LSA capability. © 2015 IEEE.