An employee used a safety cage with a gangway stair that is attached to an overhead catwalk and lowered onto the tanker truck to disconnect a hose on top of the tanker and close the tanker. The truck started moving back while the employee was on top of the truck and her legs were caught between the tanker trailer and the lowered gangway stair. The employee suffered two broken bones in the right leg, a fractured left leg, and a fractured spine.