Adjustable Scaffolds–What is it?

By David H. Glabe, P.E. / November 30, 2006

While scaffolds come in all shapes, sizes, and function, they can be categorized as supported, suspended or aerial lifts.  The American National standards Institute, ANSI, has defined an aerial platform as “a mobile device that has an adjustable position platform, supported from ground level by a structure.”  Scissors Lifts, Mast Climbers, and Boom-Supported Elevating Work Platforms (Boom Lifts) are examples of these machines.  While that may explain aerial lifts, what is the difference between supported and suspended scaffolds?  OSHA offers a rather detailed description for each but it can easily be explained this way.  A suspended scaffold is any platform supported by ropes.  That means all other scaffolds are supported scaffolds (if they aren’t aerial lifts).  In other words, a two point wire rope suspended scaffold really is a suspended scaffold.  However, a frame scaffold hanging off the side of a bridge, for example, is a supported scaffold, even if it is “suspended” over the side of the bridge.  While this example may be obvious, other scaffolds may defy easy categorization.

An Adjustable Scaffold is one of those scaffolds.  Which standards apply to this scaffold?  Is an Adjustable Scaffold a supported scaffold or is it a suspended scaffold?  For that matter, what is an Adjustable Scaffold?  By definition, an Adjustable Scaffold is “a scaffold structure with a manually elevating carriage that supports work and material platforms.”  What confuses the situation is that the platform on an Adjustable scaffold is supported by wire ropes.  This would mean that the scaffold is a suspended scaffold.  But not so fast; the wire rope is supported by rigid legs. That would make it a supported scaffold!  Looks to me like it’s both suspended and supported.  Well it is, sort of.  An Adjustable Scaffold is classified as a supported scaffold and here is why.  It is true that all Adjustable Scaffold platforms are supported by wire ropes.  However, unlike the typical suspended scaffold, Adjustable Scaffolds have an additional mechanism, a back-up system if you will, that supports the platform if the wire rope fails.  This mechanism includes a mechanical lever that prohibits the platform from falling very far, typically less than 12 inches.  Because this mechanism exists, the Adjustable Scaffold is not a true suspended scaffold.  That is, if the rope breaks, the scaffold platform will not crash to the ground.  Rather, it will only drop 12 inches, terrorizing the occupants but otherwise staying in the air and keeping them safe.

Adjustable Scaffolds are used almost exclusively by brick masons.  The ability of the platform to be slowly raised as the brick wall is constructed permits the top of the wall to always be at the optimum elevation for the mason.  One of the unique features of some Adjustable Scaffolds is the ability to free stand 28 feet high.  This allows the scaffold to be erected to the full height of a “big box” store (e.g. a Home Depot® or Wal-Mart®) without having to tie it to the structure.  This is a big advantage for masons in terms of efficiency and constructability.  For taller scaffolds, the masts must be tied to the adjacent structure, in compliance with applicable supported scaffold criteria.

As with all scaffolds, Adjustable Scaffolds must have proper fall protection.  This usually is a guardrail system that is installed when the scaffold is initially erected.  However, when the platform is being stocked by a forklift, and the guardrails are removed, the exposed employees must be wearing fall restraint or arrest equipment attached to a suitable anchor.  Since Adjustable Scaffolds are designed for masons, they can support substantial loads.  Consult the manufacturer for the capacity of the scaffold you are using.  Access can be provided by a portable ladder, stairs, a manufacturer supplied ladder or direct access.  Consult your manufacturer if you can use the mast of your scaffold for access.

Adjustable Scaffolds are Supported Scaffolds.  TheUSfederal OSHA standards that apply are the General Requirements, 29 CFR 1926.451, including the Supported Scaffold Criteria, 29 CFR 1926.451(c) which addresses scaffold stability and scaffold foundations.  Additionally, The American National Standards, A10.8-2001 has consensus standards that specifically address Adjustable Scaffolds.

Tags: Fall Protection Scaffolding Scaffolding Platforms adjusted scaffolds Aerial Lifts ANSI Boom Lifts Mast Climber OSHA Standards & Regulations Resources scissor lifts Supported Elevating Work Platforms supported scaffolds

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David H. Glabe, P.E.

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