Suspended and Mobile Scaffold Requirements

Suspended scaffolds: what is different

A suspended scaffold is a platform hung by ropes or other non-rigid means from an overhead structure. The two-point adjustable suspension scaffold, the swing stage, is the type most people picture, but the family also includes single-point (boatswains' chairs), multi-point, catenary, float, interior hung and needle beam scaffolds. Everything in the general standard applies; 1926.451(d) adds rules for the rigging, and 1926.452(o) through (u) add type-specific rules.

The reason for the extra rules is the failure mode. A frame scaffold with one bad plank drops one worker one level. A swing stage with one bad rope, hook or tieback drops the whole platform and everyone on it, which is why the standard requires both a guardrail and a personal fall arrest system on an independent lifeline.

Rigging and support

• Support surfaces. Every support device (outrigger beam, cornice hook, parapet clamp, roof iron) must rest on a surface capable of carrying at least 4 times the load imposed on it by the loaded scaffold and hoist (1926.451(d)(1)).
• Outrigger beams. Must be made of structural metal or equivalent, restrained from movement, and either stabilized by bearing blocks and tiebacks or secured to the roof structure. The inboard end is anchored by tiebacks or counterweights; the beam is used only in the position and to the length the manufacturer specified (1926.451(d)(3)).
• Counterweights. Only solid, non-flowable materials, mechanically secured to the outrigger beam. Sand, gravel, water and flowable materials are prohibited, and so is using construction materials such as masonry units or rolls of roofing. Counterweights may not be removed until the scaffold is disassembled (1926.451(d)(3)(iii)–(vi)).
• Tiebacks. Equivalent in strength to the suspension rope, secured to a structurally sound anchor on the building or structure, installed perpendicular to the face, or as two tiebacks at opposing angles where perpendicular is not possible. Standpipes, vents, electrical conduit and other piping are not sound anchors (1926.451(d)(3)(ix)–(xi), (d)(5)).
• Suspension ropes. Must support 6 times the maximum intended load. Wire rope is inspected before each shift and after any occurrence, and replaced when it shows kinks, six broken wires in one lay or three in one strand, a third or more wear on outer wires, heat damage, or evidence of contact with a corrosive. Ropes must be long enough to reach the lowest level without passing through the hoist (1926.451(a)(4), (d)(10), (d)(12)).
• Hoists. Power and manual hoists must be tested and listed by a qualified testing laboratory. Gasoline-powered hoists are prohibited. Power hoists must have a brake that engages automatically when power fails, and manual hoists must require a positive crank force to descend (1926.451(d)(13)–(16)).
• Two-point (swing stage) platforms may be no more than 36 inches wide unless designed by a qualified person, and two swing stages may not be bridged together unless the bridge connections are articulated and the hoists are properly sized (1926.452(p)).

Fall protection on suspended scaffolds

Section 1926.451(g)(1)(ii) requires a worker on a single-point or two-point adjustable suspension scaffold to be protected by both a personal fall arrest system and a guardrail system. The PFAS side has its own rules in 1926.451(g)(3):

• Each worker's lanyard connects to a vertical lifeline that is fastened to a fixed, safe anchorage independent of the scaffold, protected from sharp edges and abrasion, and never attached to the same anchor as the suspension rope
• Where vertical lifelines are not practical, a horizontal lifeline designed by a qualified person, or a scaffold structural member on scaffolds engineered for the arrest load, may be used
• Lifelines may not pass through the hoist or share a connection with the suspension line, so a rope or hoist failure does not also take the lifeline
• Two workers on one stage means two independent lifelines

Guardrails on swing stages follow the general dimensions (top rail 38 to 45 inches, midrail) but with lower strength requirements: 100 lb for the top rail and 75 lb for the midrail (1926.451(g)(4)). The fall protection guide has the general rules.

Several cities regulate suspended scaffold work more tightly than federal OSHA. New York City requires Department of Buildings-approved suspended scaffold training for workers and supervisors, and some cities require permits or licensed riggers for swing stage installations. Check the local rules before rigging.

Mobile scaffolds: what is different

A mobile scaffold is a supported scaffold on casters or wheels: a rolling tower, a Baker or Perry scaffold, an aluminum tower. Because it is designed to move, the general rule against moving a scaffold with people on it (1926.451(f)(5)) is relaxed under conditions, and because a narrow tower on wheels tips easily, bracing and ratio rules get stricter. The additional rules are in 1926.452(w).

Mobile scaffold rules

• Bracing. Braced by cross, horizontal or diagonal braces, or a combination, to prevent racking and collapse and to keep the members plumb, level and square. Frames and panels are braced at every level and the whole assembly is stiff enough to move without distorting (1926.452(w)(1)).
• Casters. Casters and wheels must be locked with positive wheel or wheel-and-swivel locks to prevent movement while the scaffold is in use, and caster and wheel stems must be pinned or otherwise secured in the legs (1926.452(w)(2), (w)(9)).
• Height-to-base ratio. The general 4:1 tipping rule applies to mobile scaffolds too; above 4:1 the tower must be tied, guyed or fitted with outriggers. When people ride the scaffold during a move the limit tightens to 2:1 unless outrigger frames are installed on both sides (1926.451(c)(1), 1926.452(w)(6)(ii)).
• Moving the scaffold. Manual force is applied as close to the base as practicable and no more than 5 feet above the supporting surface. Powered moving systems must be designed for that purpose; forklifts, trucks and other motor vehicles may not be used unless the manufacturer designed the scaffold for it (1926.452(w)(3), (w)(4)).
• Riding a mobile scaffold. Permitted only when all of these hold: the surface is within 3 degrees of level and free of pits, holes and obstructions; the height-to-base ratio is 2:1 or less, or outriggers are on both sides; any powered system is designed for the purpose; and nobody is on any part of the scaffold that extends beyond the wheels or supports (1926.452(w)(6)).
• Before every move, each employee on the scaffold is made aware that it is about to move (1926.452(w)(8)).
• Platforms may not extend outward beyond the base supports unless outrigger frames or equivalent devices keep the scaffold stable (1926.452(w)(7)).
• Leveling. Where leveling is necessary, screw jacks or equivalent are used (1926.452(w)(8)).

The general rules still apply and are where small rolling towers most often fall short: platforms fully planked, guardrails above 10 feet, ladder or built-in access when the platform is more than 2 feet up, and a competent person inspection before each shift. A 6-foot Baker scaffold needs no guardrail under federal OSHA, but it still needs locked casters, a full deck and a look before use, and it tips as readily as anything on the site.

Finding compliant equipment and crews

Swing stage and rolling tower suppliers can be found in the directory under swing stage scaffolding, suspended scaffolding, rolling frame scaffolds and aluminum mobile scaffolding. For suspended work, ask the supplier for the hoist listing, the rope certificates and the rigging plan before anything goes on the roof.