An employee was operating a three-wheeled forklift to hoist metal material with a sling system. While driving downhill in a gravel driveway, the front tire caught a root and the forklift lost momentum. This caused the hoisted material to sway and the forklift tipped forward. Inside the forklift, the employee struck against the dash and roof of the cage, sustaining a contusion to the forehead, abrasions to both legs, and later had a seizure.