In this study we revisit the problem of on-line human-robot collision avoidance for industrial manipulators, where the robot is operating in non-static surrounding with moving obstacles/humans. The objective is to leverage the power of concurrent simulation packages for validating human-robot collision avoidance algorithm. The simulations are carried out on a robotic cell in which a human co-worker and a robot share the same working area. The robot is required to perform a task while the co-worker is moving freely in the space around the robot. Experimental tests were conducted recurring to the real-time virtual-reality simulations carried out using the Virtual Robot Experimentation Platform (V-REP).