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. Together with Nikolai Fomin and Viktor Bryukhanov, Dyatlov was tried for failure to follow safety regulations. 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. He was granted amnesty in late 1990.