Chernobyl turns 40: the human mistake that triggered history worst civilian nuclear disaster

A safety test plus human error set off the blast

Ukraine marks the 40th anniversary of the Chernobyl disaster, the deadliest civilian nuclear accident in history. On April 26, 1986, at 01:23, a human error during a routine safety test triggered an explosion in reactor number four at the plant in what was then Soviet Ukraine. The tragedy reshaped nuclear safety worldwide.