An employee was walking into the control galley room on the ground level. On the floor was a removeable steel plate (60 x 90) that covers the boot pit. The steel plate slipped when the employee stepped on it causing them to fall approximately 22 feet down into the boot pit, landing on the concrete ground. The employee was hospitalized with two fractured vertebrae, bilateral arm fractures, a left elbow dislocation, and an abdominal injury.