On the night of 16–17 August, the level of vibration increased substantially.[4] There were several attempts to stop the turbine. During 16 August up to 20:30, the load of turbine 2 was 600 MW, then it was reduced to 100–200 MW. On 17 August 2009 at 3:00, the load was increased again to 600 MW; at 3:30, the load was decreased to 200 MW; and at 3:45, it was increased again to 600 MW.[4] During this time, the level of vibration was very high, and was also registered by seismic instruments in the plant. During attempts to shut it down, the rotor inside the turbine was pushed up, which in turn created pressure pushing up on the turbine cover. The cover was kept in place by 80 bolts of 8-centimetre (3.1 in) diameter.