A maintenance access system for a storage and retrieval system having a storage and retrieval space and automated transport vehicles disposed in the space. The system includes at least one maintenance access control unit associated with a portion of the space, at least one barrier in the space and defining a boundary of the portion of the space and configured to substantially prevent the passage of the vehicles past the at least one barrier, and a controller connected to the control unit, the controller being configured to receive a signal from the at least one control unit for isolating the portion of the space associated with the at least one control unit, where the controller in response to the signal closes the at least one barrier isolating the portion of the space and effects the removal from or shutting down of vehicles within the portion of the space.