On 26 April 1986, Dyatlov supervised a test at Reactor 4 of the nuclear plant, which resulted in the worst nuclear plant accident in history. During the accident, Dyatlov was exposed to a radiation dose of 390 rem (3.9 Sv), which causes death in 50% of affected persons after 30 days, but he survived.[4] Together with Nikolai Fomin and Viktor Bryukhanov, Dyatlov was tried for failure to follow safety regulations.[5] In 1987, all three were found guilty of gross violation of safety regulations leading to an explosion and were sentenced to ten years in prison.[6] He was granted amnesty after three years.[7]