An employee and his co-worker were removing a sheet metal air duct fitting from a scissor lift. After removing two of the four bolts, they brought the lift down to the floor to get additional tools. While the co-worker left to get the tools, the employee raised the lift back up to remove the remaining two bolts. The employee then lowered the lift back to the floor to wait on the co-worker. While standing in the lift at the floor level, the employee was struck by the fitting when it came loose and fell, injuring the employee's back and nose and fracturing a vertebra.