I.W. sat down on the Rippers of the Case Loader during EE's conversation with another emp. The loader rippers hydraulic pressure was suddenly released and the rippers dropped to the floor while the I.W. was sitting on them. This caused the I.W. to fall backwards into the scraper box. The I.W.'s lower back hit against the scraper box resulting in fracture to the L1 & L2 vertebrae.