Applies to the erection or construction of iron or steel dwellings including assembling or fabricating at the job site. Contemplates any iron or steel work on one or two family residences or other buildings used for dwelling purposes, including Quonset huts not over two stories in height. Contemplates the erection of iron or steel in connection with military reservation construction not over two stories in height such as barracks, hospitals, mess halls, canteens, storage and ammunition warehouses etc. Welding operations are considered incidental to the overall operations.