Supernumerary robotic arms have a high potential to increase human capacities to perform complicated tasks; e.g., having a third arm could increase the user's strength, precision, reachability, and versatility. However, having a robotic manipulator working in extreme proximity to the user raises new challenges in terms of safety; i.e., uncontrolled and hazardous collisions with the user's body parts and the environment. In this preliminary work, we show that most of these safety considerations can be extracted from standardized norms and translated into kinematics constraints for the robot. Thus, we propose a quadratic programming approach to achieve safe inverse-kinematics and physical interaction for supernumerary arms. We validate our approach in designing a safe supernumerary arm using the 7-Dof Kinova ® Gen3 robot.