An employee was using small material handling equipment (MHE) to place a box of product onto a shelf. Another employee was operating a larger MHE to retrieve empty pallets from the shelf racks in the same aisle. The second employee's MHE equipment was raised in the air approximately 20 feet as it was being moved to the next pallet. The second employee did not see the first employee working below him or her MHE sitting in the aisle, and the MHE equipment collided. The first employee's left ankle was caught and crushed between the two pieces of equipment, requiring hospitalization.