When dropping material through a hole in the floor without a chute, the barricade around the collection area should be at least: ?

The barricade around the collection area should be at least 42 inches tall and not less than 6 feet back from the opening above the projected edge. Warning signs of the hazard of falling materials should always be posted at every level. The removal of waste should not be permitted in the lower areas until the handling of debris above is stopped. This is done to ensure safety in the working area.