Chernobyl accident, that happened on April, 26, 1986 is the only one attributed to the highest 7 level of “safety significance” (in common words we might say “danger”) on the international nuclear events scale (INES). Neither to nor after such heavy accident have taken place in nuclear industry nor power engineering. The erroneous actions of personnel of the station drove reactor to a state, not considered by regulations, in which its technical failures showed up. On experts’ conclusion the severe accident arose through a low probability coincidence of a number of factors. Every factor separately could not result in an accident. But their coincidence was, on one side, casual, on the other - appropriated, in the sense, that first or last it must happen however. Because the attitude toward procedures of safety was too careless at the atomic station, and in all links of the soviet production system related to nuclear power.