1. A safety system for identifying safe regions in a three-dimensional workspace including controlled machinery, the system comprising: a plurality of sensors distributed about the workspace, each of the sensors being associated with a grid of pixels for recording images of a portion of the workspace within a sensor field of view, the workspace portions partially overlapping with each other; a controller configured to: register the sensors with respect to each other so that the images obtained by the sensors collectively represent the workspace; generate a three-dimensional representation of the workspace as a plurality of volumes; for each sensor pixel having an intensity level above a threshold value, preliminarily marking as unoccupied volumes intercepted by a line-of-sight ray path through the pixel and terminating at an estimated distance from the associated sensor of an occlusion, marking as occupied the volumes corresponding to a terminus of the ray path, and marking as unknown any volumes beyond the occlusion along the ray path; for each sensor pixel having an intensity level below the threshold value, preliminarily marking as unknown all voxels intercepted by a line-of-sight ray path through the pixel and terminating at a boundary of the workspace; finally marking as unoccupied volumes that have been preliminarily marked at least once as unoccupied; and mapping one or more safe volumetric zones within the workspace, the volumetric zones being outside a safety zone of the machinery and including only volumes marked as unoccupied.