Welder #2 was cutting a strip of steel loose from the rear of the girder cutout. The strip of steel was cut loose & allowed to free fall uncontrolled, approx. 7'-8' to the ground, where it fell over and struck the work platform & broke it loose from the girder. It caused the ladder that Welder #1 was standing on to topple over, and fall approximately 8'-9' to the ground.