A note on worker blocking in narrow-aisle order picking systems when pick time is non-deterministic

The focus of this work is to develop analytical models to estimate worker blocking in narrow-aisle order picking systems. The situation with deterministic pick times has already been reported in the literature but the case with non-deterministic pick times remains an open question. Models that use a non-deterministic pick time for cases where the pick: walk-time ratios are 1:1 and infinity:1 are presented. It is shown that the results obtained using deterministic pick times are in fact sensitive to this assumption.