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Electrical Failure & Equipment Age Led to Swing Stage Scaffold Failure

Electrical Failure & Equipment Age Led to Swing Stage Scaffold Failure


Four caulking contractors were working on a section of 3-point swing stage scaffold, when one of the end outrigger’s back support leg buckled.  The outrigger beam was tied back and the other two outriggers supported the scaffold, therefore the effect on the platform at the time of the failure was slight.  The contractors on the scaffold felt very little movement, reported no injuries from the incident, and were able to lower the unit to the ground.


The general contractor for the project had set up the swing stage scaffold on the building’s roof to remove and rebuild the brick parapet wall.  The caulking contractors had lowered the platform to perform their work and were attempting to raise it to exit via the roof, when they realized they had lost power to the drive motors.  After calling to the general contractors on the roof to have someone look at the portable temporary power supply, a separate 120 Volt, 20 Amp power supply (being used for their power tools) was connected to the three (3) 10 Amp drive motors.  With this alternative power supply, the caulkers tried to raise the scaffold again and experienced some minor vibration and the drill motors bogging down.  During this process slack had developed in one of the end load lines causing the outrigger to rise in the front, transferring the weight displacement to the back support leg.  This caused the back support leg of the outrigger beam to fail at the top (unused) adjustment hole, buckling the leg, causing the beam and counter weights to fall back, placing the back of the outrigger on a skid located behind it.


The portable temporary power unit had been placed directly on the roof with a sheet of plastic to cover it.  The unit had been inspected and hooked up by an electrician prior to use.  Following the incident, examination of the transformer revealed that it had failed.  The exact cause for this failure could not be determined, however, age and moisture could have been factors. 


The general contractor had a qualified person design the scaffolding and competent persons erect and inspect it each day.  The rigging of the outriggers was determined to be appropriate, following the manufactures specifications for setting them up.  The addition of a truss stanchion assembly was an additional support.  However, consultation with the manufacturer revealed another way to setup the counterbalance weights.  This method places the weights on the roof, transferring the weight to the building.  It was determined that this should be the preferred counterbalancing method on all swing stage outriggers to prevent this type of incident. 


The design of the rolling outrigger support legs supplied by the rental company, appeared to be inferior to the design of the newer components supplied for the first set-up.  The condition of the legs and wheels made it apparent that these were much older components than the tubular dolly support legs supplied for the first set-up.  While visually the legs appeared sound, and they were rated for the load, their age could have been a factor in this incident.  The inspection and certification process of equipment by the rental company could have been a factor as well.

Factors to consider at your site and/or project include, but not limited to the following:

  • Temporary power supplies should be rated for the environment they are required in and protected as necessary.  Alternative power sources should not be used if they are not rated for the equipment being used.
  • Ensure the age and quality of equipment provided by rental companies and the inspection process they have in place to ensure the safety of the equipment they provide you.
  • Standardize on the same manufacturer and type of components for a job to prevent confusion in the set-up of different systems.
  • Ensure the counterbalance set-up on suspension scaffolding places the weights on the roof connected to the I-beam with a cable, as this appears to be a superior set-up to prevent this type of failure and allow easier removal of the weights.
  • Ensure that a qualified person designs the scaffolding for your job; a competent person supervises the erection, moving, dismantling, or altering of the scaffold; that the people performing these duties and inspecting the scaffold each day are experienced and have been trained by a competent person, and the persons working on the scaffold have been trained by a qualified person.


Consider this example as you complete today’s work activities.

Safety Flash Action Items:
  • Date Contractor Safety Flash posted for all employees to review: _______________
  • Safety Talk meeting date: _______________
  • Full employee attendance and participation at safety meeting to review this incident (documentation required).
  • Employees understand urgency in protecting themselves and others.
  • Supervisors and Employees are clear which items shared in this Safety Flash are mandatory.
  • Employees/Supervisors will focus on recommended actions during future work activities of a similar nature.
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THINK about the hazards associated with your particular work, and the steps that can be taken to increase safety on your job.


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