vented to release overpressure and then re-filled with water and boric acid for cooling, and to inhibit further nuclear reactions. Unit 2 was possibly suffering a lower than normal water level, but was thought to be stable; although pressure inside the containment vessel was high. The Japan Atomic Energy Agency announced that it was rating the situation at unit 1 as level 4 (an accident with local consequences) on the International Nuclear and Radiological Event Scale. Monday, 14 March 11:01: The unit 3 reactor building explodes. According to TEPCO, there was no release of radioactive material beyond that already being vented, but blast damage affected the water supply to unit 2. 11 workers were injured in the explosion. 13:15: The reactor core isolation cooling system for reactor 2 stops and, shortly afterwards, the water level within the reactor starts falling. 15:00: A major part of the fuel in reactor 3 drops to the bottom of the reactor pressure vessel. 18:00 (approximate): The water level in reactor 2 reaches the top of the fuel. 20:00: Core damage starts occurring in reactor 2. The president of the French nuclear safety authority, Autorité de sûreté nucléaire (ASN), said that the accident should be rated as a 5 (an accident with wider consequences) or even a 6 (a serious accident) on INES. Tuesday, 15 March approx. 06:00 According to TEPCO, an explosion damaged the 4th floor area above the reactor and spent-fuel pool of the Unit 4 reactor. 20:00: A majority of the fuel in reactor 2 drops to the bottom of the reactor pressure vessel. Damage to the temporary cooling systems on unit 2 from the explosion in unit 3, plus problems with its venting system, meant that water could not be added to the extent that unit 2 was in the most severe condition of the three reactors. Initially, it was thought that an explosion had occurred at unit 2 because its pressure indicator dropped at the same time as unit 4 exploded. However, later it was confirmed that there was no explosion at unit 2. A fire breaks out at unit 4. Radiation levels at the plant rise significantly but subsequently fall. Radiation equivalent dose rates of 400 millisieverts per hour (400 mSv/h) are observed at one location in the vicinity of unit 3. Wednesday, 16 March At approximately 14:30 TEPCO announces its belief that the fuel rod storage pool of