While trying to straighten straps across a double-stacked, plastic-wrapped unit of lumber on a flatbed trailer, an employee slipped and fell about 10 feet to the paved ground below. During the fall, the employee struck the edge of the trailer bed. The employee was hospitalized with a head injury with brain bleeding, a cracked T4 vertebra, a cut left ear and contusions. Fall protection was not worn at the time of the incident.