The blast at the 620-megawatt, Siemens combined cycle gas- and oil- fired power plant[5][6] occurred at 11:17 am,[7] and was reported at 11:25 am EST.[2] The plant's manager, Gordon Holk, said that contractors and other workers from O & G Industries, Ducci Electric, and Keystone Construction and Maintenance Services were at the site when the blast occurred.[8] The explosion occurred at the rear of the largest building, the turbine hall, which was destroyed.[9] Some residents reported "earthquake-like tremors"[2][10] from at least 10 miles (16 km) away,[9] although the blast proved not to be seismically detectable.[11] Another resident of the area felt that it was more like a sonic boom.[12]