An employee was operating a powered pallet jack and heading to the north cooler door. When the employee made it to the north cooler, another pallet jack operator was leaving the cooler. The employee backed out to allow the other pallet jack operator to exit the cooler. After the other pallet operator exited, the employee turned the handle on his pallet jack and the machine went backwards. The pallet jack then hit the cooler guard and the employee's lower left leg was caught between the jack and guard, resulting in a broken lower left leg.