When the reactor power had decreased to approximately 500 MW, the reactor power control was switched to a different mode in order to manually maintain the required power level. Around that moment, the power suddenly fell into an unintended near-shutdown state, with a power output of 30 MW thermal or less. The exact circumstances that caused the power fall are unknown because Akimov died in hospital on 10 May and Toptunov on 14 May; early reports attributed it to Toptunov's mistake, but it has also been suggested it was due to an equipment failure.