For human-robot interaction, a 3D representation of the robot's close environment based on depth measurements is proposed. First, the current close range is defined by computing the reachable space of the robot. Then obstacles and occluded space within the close range are represented in an octree structure considering obstacle occlusions as well as robot occlusions. Based on the obstacle octree, the minimum distance between the robot and the surrounding obstacles is determined. Experimental results with depth sensor data from multiple on-board sensors of a mobile manipulator are shown.