Another type of scaffold, the tube and coupler, is often used when a work platform is required to be built around an irregular structure. The tube and coupler scaffold usually consists of two inch outside diameter steel tubing used to make posts, bearers, runners, and braces. The runners are placed along the length of the scaffold and interlocked to form continuance lengths, and connected by coupling devices to each post for stability.
The bearers which help carry the load are installed across the width between posts and securely coupled to the posts to form a level base for the work platform. Cross bracing is installed across the width of the scaffold at at least every third post horizontally. Diagonal bracing is used and installed at approximately a 45-degree angle from near the base of the first outer post upward to the extreme top of the inner post, to maintain structural integrity. For stability, the entire scaffold must be tied to and securely braced against the building or structure at intervals not to exceed 30 feet horizontally, and 25 feet vertically.
Manually propelled mobile tubular welded scaffolds, commonly known as the mobile scaffold, is primarily designed for use on level concrete or other smooth floors, to access elevated work areas or simply to install equipment or parts. Mobile scaffolds which are supported by casters must consist of cross braces and diagonal braces secured laterally to the vertical end sections, or members, to maintain stability. The cross braces and diagonal braces must be of a length that will automatically square and align vertical members so that the erected scaffold is always plumb, square, and rigid. To insure further stability and reduce the possibility of tipping, the height must not exceed four times the least base dimension. For safe access ladders or stairs must be provided, either built-in or attached to the scaffold.
Mobile scaffolds are limited in height to a single unit or section unless the entire system is approved in writing by a registered professional engineer, or it is erected in accordance with instructions furnished by the manufacturer. Casters or wheels are attached for mobility. Outriggers which are also equipped with wheels, can be added for additional stability. Prior to any personnel getting onto a mobile type scaffold, all wheels must be secured and locked. Casters must be pinned to the scaffold leg or screw jack. Horizontal diagonal braces must be installed at the base, and the work platform must be fully planked.