The basis for the approval was enhanced safety measures, in particular raising the previous assumption for the Sendai plant of 540 gal for maximum earthquake strength to 620 gal, and similarly the assumption of maximum tsunami height from 4 meters to 5 meters. Furthermore, a 10-meter-high protection wall was built. Design standards were further enhanced to take into account all other natural disasters, in particular volcanic eruptions and tornadoes, along with plans to address terrorist attacks. Further details on the tests may be found in the Special Bulletin.