Lesson 4-2 SCAFFOLDS
Scaffolds are temporary elevated platforms that are used to support workers and tools. They may range from individual planking that is placed across structural members of a building to steel mobile work platforms. Well-constructed or erected scaffolds are safer for you to work from than a ladder. The types of scaffolds most commonly used by painters include horse, independent metal, swing stage, and boatswain's chair.
a. Scaffold Horse. Use a scaffold horse (Figure 4-13) to construct a simple scaffold. Scaffold horses are used in pairs; however, a stairway, porch, or any other stationary object may be used to hold one end of a work platform while a scaffold horse holds the other. Before each use, check the nailing of the horse's legs and braces.
Figure 4-13. Scaffold horse
b. Independent Scaffold (Figure 4-14). A double-pole, built-up scaffold (metal or wood) is completely independent of the main structure. Several types of patented independent scaffold are available for simple and rapid erection. Brace the scaffold uprights (scaffold legs) with diagonal members, and cover the working level with a planking platform. All bracing must form triangles, and the base of each column requires adequate footing plates (Figure 4-15) for the ground-bearing area. If the ground is fairly even, secure the footing plate by bolting it to a 2-by-8 board that is placed on the ground.
Figure 4-14. Independent scaffold topped with platforms
Figure 4-15. Footing plate
(1) Patented steel scaffold. Erect patented steel scaffolds by placing the first and second uprights on footing plates and insert diagonal braces, thus completing the first set of tiers. The diagonal braces have rapid locking end fittings (Figure 4-16) that permit rapid locking into position. The first-tier set is set at ground level on steel bases. Erect the second-tier set by placing the third and fourth uprights on footing plates and insert diagonal braces. Lock the second set to the first set with diagonal braces. Elevate scaffolds by placing a second tier on the first tier, and lock the bottom of each upright to the top of the lower tier. Build the scaffold as high as desired, but tie a high scaffold into the main structure with building tie-ins (Figure 4-17).
Figure 4-16. Rapid-locking end fitting
Figure 4-17. Building tie-in
(2) Side bracket. A side bracket (Figure 4-18) is damped on the scaffold uprights to provide platforms at various height levels.
Figure 4-18. Side bracket
(3) Rolling tower. Use a rolling tower if the scaffold will be subjected to frequent moves; however, use a rolling tower only on solid floors. To construct a rolling tower, replace the scaffold footing plates with locking casters. For safe operation, the tower's height must not exceed four times its smallest base dimension; in addition, the tower must have a guardrail above the working platform.
c. Swing-stage scaffold. A swing-stage scaffold (Figure 4-19) is used to reach the upper surfaces of an exterior wall, and it is suspended from the building's roof or cornice with ropes or steel cables. The scaffold consists of the following parts: two block-and-tackle sets, two cornice hooks, two swing stirrups, a guardrail, and a platform.
Figure 4-19. Swing-stage scaffold
(1) Cornice hook. A cornice hook is a large metal hook that hooks securely over the top of a substantial portion of the building's roof or cornice. Fasten one end of a tieback rope to an eye located at the top of the hook. For your safety when working on scaffolds, you should fasten the other end of the tieback rope to the base of a chimney, a soil pipe, or any other securely attached projection that will support the weight of the scaffold and the working load being placed on it. Attach a set of block and tackle to an eye which is located at the lower end of a cornice hook.
(2) Stirrup. A stirrup is a metal unit that supports the scaffold's platform. Two stirrups are required for the scaffold. Attach a set of block and tackle to a ring located at the top of each stirrup. Use rollers to prevent the scaffold from hitting the wall.
(3) Guardrail. A guardrail is constructed of 2- by 4-inch material, and it helps to protect you from falling from the scaffold platform.
(4) Platform. A scaffold platform is the working space on which you move about as you work. It is from 20 to 24 inches wide and no greater than 26 feet long. A platform is made of well-seasoned, 2-inch lumber that is straight-grained, and free of knots or other defects.
(5) Toeboards. Use toeboards to prevent material from slipping or accidentally being knocked off the scaffold. Toeboards run the full length of the scaffold, are constructed of 2- by 4-inch material, and are located at the front and back of the scaffold.
(6) Block and tackle. To raise and lower the unit a special type of block and tackle is used on each end of the swing-stage scaffold. A hoisting machine may be substituted for the block and tackle.
(7) Safety. Observe the following salty rules when using swing-stage scaffold:
- Test the scaffold before using it by hoisting it 1 foot off the ground, then load it with four times the working load.
- Prevent the scaffold from swinging outward after hoisting by lashing it to a building or a structural wall as soon as possible.
- Ensure that no more than two painters work on the scaffold at one time. Each painter should wear a safety belt that is attached to an individual lifeline. Fasten the safety-belt line above and free from the scaffold.
- Use steel cable whenever possible when using acid solutions with hoisting equipment. Immediately replace all fiber ropes exposed to acids or acid solutions.
- Lower the scaffold to the ground when it is not in use.
- Keep weights on the outside of a platform when raising the scaffold until it is secured to the building.
- Do not touch the wall next to the scaffold until the scaffold is secured to the building. A light push against the wall may swing the scaffold out in such a way that you may lose your balance and fall.
- Check the hoisting machine's operation before each use.
- Inspect the tackle-block assembly before each use.
- Lubricate the tackle-block pulley wheels when necessary.
- Keep tackle-block ropes under cover to guard the ropes against deterioration when weather threatens.
- Do not expose tackle-block ropes to acids. Ropes exposed to acids will deteriorate and become unsafe.
- Do not permit tackle-block ropes to scrape against sharp projections such as scaffolds, windowsills, beams, or building walls.
- Ensure that the ropes are not pinched between hard surfaces when ropes are subjected to heavy loads.
- Do not run ropes through sheaves that are too small because the sheave's size will increase the wear on ropes.
- Lubricate the ropes with beef tallow when required.
- Do not allow ropes to slip over pulley wheels that do not turn.
- Inspect hooks for cracks or bends before using them again when cornice hooks have been subjected to strain.
- Inspect each plank before its use when planking is used as a part of a scaffold.
- Always inspect swing-stage stirrups before each use.
- Do not walk under a scaffold.
- Do not reeve a set of blocks on the ground where dirt, dust, or mud will get on the ropes.
- Do not use a scaffold without a guardrail.
(8) Inspection. Before each use, inspect all units that form a part of the scaffold and the units used in conjunction with the scaffold. You should inspectó
- Wooden platforms, guardrails, toeboards, metal stirrups, and hooks for worn parts.
- Steel cables for wear signs, kinks, worn parts, broken wires, or corrosion.
- Fiber ropes for any strands that are broken, cut, or weakened.
(9) Storage. Store scaffolds in a dry place to prevent the warping or splintering of wood sections; the rusting of wire cables, tackle blocks, or hoisting machines; or the rotting of fiber ropes.
d. Boatswain's Chair.
(1) The boatswain's chair shown in Figure 4-20 is made to support one man. Use the chair to paint small areas that cannot be reached by ladders or where it is impractical to erect scaffolds. A double bowline knot is used to make up the chair. For short periods of time, the chair can be used without the notched board by inserting your legs through the loops.
Figure 4-20. Boatswain's chair
(2) The boatswains chair with suspending tackle (Figure 4-21) is supported by securing block and tackle to the building's roof, ceiling joists, or rafters. Before using the chair, ensure that it is attached securely. You can either raise or lower yourself or be assisted by a person on the ground. When working alone, the fall line (control) is attached to the suspending tackle (two double blocks) with a rolling hitch. The fall line allows you to lower yourself. When receiving assistance from the ground, the fall line should be tied to a tree or a building member that will hold your weight.
Figure 4-21. Boatswain's chair with suspending tackle