Key Terms

A scaffold refers to any temporary elevated platform and its supporting structure (including points of anchorage) used to support employees or materials or both. Most scaffolds fall into one of the following categories:

• A supported scaffold refers to one or more platforms supported by outrigger beams, brackets, poles, legs, uprights, posts, frames, or similar rigid support. Supported scaffolds include but are not limited to the following:
  • Bricklayer's square scaffolds, carpenter's bracket scaffolds, crawling boards (chicken ladders), double pole scaffolds, fabricated frame scaffolds (tubular welded frame scaffolds), form scaffolds, horse scaffolds, ladder jack scaffolds, lean-to scaffolds, mobile scaffolds, outrigger scaffolds, pump jack scaffolds, repair bracket scaffolds, and tank builders' scaffolds
• Considered a subcategory of supported scaffold, an aerial lift refers to a vehicle-mounted aerial device used to elevate personnel to an above-ground worksite. Types include the following:
  • Extensible boom platforms, aerial ladders, articulating boom platforms, and vertical towers
• A suspension scaffold refers to one or more platforms suspended by ropes or other non-rigid means from an overhead structure(s) usually deployed on a building roof. Suspension scaffolds include but are not limited to the following:
  • Adjustable suspension scaffolds, boatswain's chairs, catenary scaffolds, chimney hoists, continuous run scaffolds, float (ship) scaffolds, interior hung scaffolds, single-point or multi-point adjustable suspension scaffolds, and two-point suspension scaffolds (swing stages)

Scaffold components include the following:

• Bearer (putlog): a horizontal transverse scaffold member upon which the scaffold platform rests and which joins scaffold uprights, posts, poles, and similar members.
• Brace: a rigid connection that holds one scaffold member in a fixed position with respect to another member, or to a building or structure.
• Cleat: a structural block used at the end of a platform to prevent the platform from slipping off its supports. Cleats are also used to provide footing on sloped surfaces such as crawling boards.
• Fabricated decking and planking: manufactured platforms made of wood, metal, or other materials.
• Guardrail system: a vertical barrier erected to prevent employees from falling off a scaffold platform or walkway to lower levels.
• Hoist: a manual or power-operated mechanical device used to raise or lower a suspended scaffold.
• Outrigger: the structural member of a supported scaffold used to increase the base width of a scaffold in order to provide support for and increase the stability of the scaffold.
• Outrigger beam (thrustout): the structural member of a suspension scaffold or outrigger scaffold which provides support for the scaffold by extending the scaffold point of attachment to a point out and away from the structure or building.
• Platform: a work surface elevated above lower levels.
• Runner (ledger or ribbon): the lengthwise horizontal spacing or bracing member which may support the bearers.
• Walkway: a portion of a scaffold platform used only for access and not as a work level.

A personal fall arrest system (PFAS) comprises the parts used to arrest an employee's fall. A PFAS consists of an anchorage, connectors, and a body harness. It may include a lanyard, deceleration device, lifeline, or combinations of these. Each employee more than 10 feet above a lower level must be protected from falls by guardrails, a PFAS, or both.

Key terms related to a PFAS include the following:

• Body harness: a system of straps worn by an employee in a way to distribute the fall arrest forces over at least the thighs, pelvis, waist, chest and shoulders; the harness can be attached to other components of a personal fall arrest system.
• Deceleration device: any mechanism, such as a rope grab or lanyard, that dissipates a substantial amount of energy during a fall arrest or limits the energy imposed on an employee during fall arrest.
• Lifeline: a flexible line that connects to an anchorage at one end to hang vertically (vertical lifeline), or that connects to anchorages at both ends to stretch horizontally (horizontal lifeline), and which serves as a means for connecting other components of a personal fall arrest system to the anchorage.

To understand the risks of scaffolds, users must understand their load-bearing nature, including the following concepts:

• Loads:
  • Maximum intended load: the total load of all persons, equipment, tools, materials, transmitted loads, and other loads reasonably anticipated to be applied to a scaffold or scaffold component at any one time.
  • Failure: breakage, separation of component parts, or load refusal. Load refusal is the point where the ultimate strength of the scaffold is exceeded.
  • Rated load: the manufacturer's specified maximum load to be lifted by a hoist or to be applied to a scaffold or scaffold component.
  • Stall load: the load at which a power-operated hoist stalls or the power is automatically disconnected.

Other key terms in this course include the following:

• Competent person: someone capable of identifying working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them.
• Equivalent designs, materials, or methods: these protect against a hazard as well as or better than those specified in the Code of Federal Regulations.
• Exposed power lines: electrical power lines that are accessible to employees but not shielded from contact. Such lines do not include extension cords or power tool cords.
• Lower level: an area below where the employee is located onto which an employee can fall. Such areas include ground levels, floors, roofs, ramps, runways, excavations, pits, tanks, materials, water, and equipment.
• Qualified person: someone who, by possession of a recognized degree, certificate, or professional standing, or who, by extensive knowledge, training, and experience, has successfully demonstrated his or her ability to solve or resolve problems related to the subject matter, the work, or the project.
• Unstable object: an object whose strength, configuration, or lack of stability may allow it to become dislocated and shift and therefore may not properly support the loads imposed on it. Unstable objects are not a safe base support for scaffolds, platforms, or employees. Examples include barrels, boxes, loose bricks, and concrete blocks.

To learn more about Scaffolding Safety visit our Construction Scaffolding Safety Online Training web page.