Yes, I agree, the station personnel must hold responsible, but they was only engineers and couldn't to know all about positive reactivity in reactor. In the operation instructions was no information about this effect. And instructions had no restrictions to use reactor in these modes (number of raised rods, for example). I am an engineer and often must operate sophisticated equipment, but I don't know, how works many things inside of the devices and operate only according to instructions, written by developers. Only if personnel violated an instruction, it must hold responsible. And another fact, the reactor exploded after pressing the emergency stop button. It's impossible in normal system. On forum.ixbt.com there is an interesting thread, where people discussing this disaster, and there is an many posts from the lead engineer of reactor operation on chernobyl station. There discusses a many aspects of reactor control and personnel actions in different situations. And another thing. If the oficial version of this disaster was a design mistake, then IAEA would require the closure of all similar reactors, and this variant was impossible for USSR goverment, and a version of human error was the most convenient. By the way, all similar reactors have been upgraded to prevent a similar catastrophe in future. This suggests that not all was so safe. Where the truth, I don't know, but the personnel is not only one, who is guilty...