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Course 804 - Safe Scaffold Erection and Inspection

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Inspecting Suspended Scaffolds

Introduction

Suspended scaffolds are platforms suspended by ropes, or other non-rigid means, from an overhead structure. Because two-point scaffolds are the most common type of suspended scaffold, this module uses the Two-Point scaffold to describe requirements that apply to all suspended scaffolds. Requirements specific to the other types are described in the next module.

intbracket

Two-Point Scaffolds

two point

Two-point adjustable suspension scaffolds, also known as swing-stage scaffolds, are perhaps the most common type of suspended scaffold. Hung by ropes or cables connected to stirrups at each end of the platform, they are typically used by window washers on skyscrapers, but play a prominent role in high-rise construction as well.

Note: Except where indicated, the same basic scaffold requirements that appear in this module also apply to single-point adjustable, multi-point adjustable, catenary, interior hung, needle-beam, multi-level, and float (ship) scaffolds which will be covered in the next module.

Let’s take a look at important inspection criteria for this scaffold.

Inspecting the Anchorage

two point
Two Point Suspension Scaffold
Click to enlarge

The safe use of a suspended scaffold begins with secure anchorage. The weight of the scaffold and its occupants should be supported by both the structure to which it is attached and by each of the scaffold components that make up the anchorage system.

We will discuss each of the scaffold components below.

  • tiebacks
  • counterweights
  • direct connections

Note: Except where indicated, these requirements for anchorages also apply to multi-level, single-point adjustable, multi-point adjustable, interior hung, needle-beam, catenary, and float (ship) scaffolds.

outrigger
This image is a two-point suspension scaffold suspended from outriggers with counterweights. There are no tiebacks. The yellow lifelines should not be attached to outriggers.

Anchorage Tiebacks

The tiebacks should be secured to a structurally sound anchorage on the building or structure, which may include structural members. A good example would be an anchor mounted in concrete with drilled-in fasteners. In your inspection, make sure tiebacks are:

  1. not secured by vents, electrical conduit, or standpipes and other piping systems
  2. installed perpendicular to the face of the building or structure, or opposing angle tiebacks should be installed (single tiebacks installed at an angle are prohibited)
  3. equivalent in strength to the suspension ropes and hoisting rope

Real-Life Example

Workers Killed When Scaffolds Without Tiebacks Fall

Two employees were working on a two-point suspension scaffold without safety belts, lifeline, or tiebacks. They attempted to move a hook to reposition it when the hook slipped off the parapet, causing one end of the scaffold to drop. The victim fell five stories to his death. His co-worker was able to grab on to the scaffold, and climbed to a fire escape.

inspecting
Counterweights are to be secured. These have pulled away by fall protection rope. Fall protection must be independent of the scaffold.

Anchorage Counterweights

Safety factors for the counterweights, riggings, and direct connections to roofs, floors, and suspension ropes of adjustable suspension scaffolds should be based on the rated load and the stall load of the hoist, not the maximum intended load.

  1. Make sure suspended scaffold outrigger beams are stabilized by:
    1. counterweights
    2. bolts or other direct connections to the floor or decks
  2. Check that counterweights used to balance adjustable suspension scaffolds are capable of resisting:
    1. at least 4 times the tipping moment imposed by the scaffold when it is operating at the rated load of the hoist (see counterweight formula to the right)
    2. a minimum of 1½ times the tipping moment imposed by the scaffold when it is operating at the stall load of the hoist, whichever is greater
    cwformula
    Counterweight formula
    Click to enlarge
  3. Ensure only items specifically designed as counterweights are used to counterweight scaffold systems.
  4. Check to make sure masonry units, rolls of roofing felt, and other similar construction materials are not being used as counterweights.
  5. Ensure counterweights are not made of flowable materials such as sand, gravel, and similar materials that can be easily dislocated. An acceptable material for use would be a counterweight made of cast iron.
  6. Make sure counterweights are secured by mechanical means to the outrigger beams to prevent accidental displacement.
  7. Counterweights should not be removed from an outrigger beam until the scaffold is disassembled.

Real-Life Example

Inadequate Counterweights Cause Two Deaths

A 53-year-old painting foreman and a 28-year-old painter were killed when their scaffold collapsed. They were working on a 48-foot-high tank from a two-point suspension scaffold supported by two steel outriggers. The scaffold manufacturer specified 600 pounds of counterweight for this scaffold and load, but the painters had rigged the scaffold using only 200 pounds of counterweight (100 pounds per outrigger). The outriggers were not tied off or otherwise secured. No personal fall protection equipment was being used by either worker. While the two men were working on the scaffold, their weight caused the outriggers to slip, and the scaffold, rigging, and victims fell to the ground.

Direct Connections

cwformula
Steel outrigger for two-point scaffold on top of a power cord for a portable grinder. Can this scaffold become energized?
Click to enlarge

Direct connections and counterweights used to balance adjustable suspension scaffolds should resist at least four times the tipping force of the scaffold. A competent person who directs the rigging of the scaffold should calculate the potential loads.

  1. Inspect to make sure scaffold outrigger beams are stabilized by:
    1. bolts or other direct connections to the floor or deck
    2. counterweights
  2. Make sure direct connections to roofs and floors are capable of resisting:
    1. at least 4 times the tipping moment imposed by the scaffold when it is operating at the rated load of the hoist
    2. a minimum of 1½ times the tipping moment imposed by the scaffold when it is operating at the stall load of the hoist, whichever is greater

Inspecting the Support

support

Adjustable suspension scaffolds are designed to be raised and lowered while occupied by workers and materials, and should be capable of bearing their load whether stationary or in motion. We will look at inspecting each of the following topics related to supports:

  • capacity
  • components
  • outrigger beams
  • suspension ropes
  • hoists

Note: Except where indicated, these requirements also apply to multi-level, single-point adjustable, multi-point adjustable, interior hung, needle beam, catenary, and float (ship) scaffolds.

Real-Life Example

Scaffold with Improvised Components Fails; Worker Dies

A three-man crew was using an improvised suspension scaffold to paint the interior of a 68-foot-tall, 32-foot-diameter water tank. The scaffold consisted of an aluminum ladder used as a platform, and secured to steel "stirrups" made of steel bar stock bent into a box shape and attached to each end of the ladder. Wire cables from each stirrup ran to a common tie-off point. A cable from this common tie-off was rigged to a block-and-tackle used from ground level to raise and lower the platform. The block-and-tackle supporting the system was secured to a vertical steel pipe on top of the tank by a cable, which was fashioned into a loop by U-bolting the dead ends of a piece of wire rope.

The victim had been painting from one end of this scaffold while wearing a safety belt and lanyard attached to an independent lifeline. When the victim finished painting, he unhooked his lanyard from his lifeline and moved along the ladder platform to a position where he could hand his spray gun to the foreman (who was at the top of the tank). As the foreman took the spray gun, he heard a "pop" and saw the scaffold and the victim fall 65 feet to the floor of the tank.

Investigation of the incident revealed that the two U-bolts on the loop of cable supporting the block-and-tackle had loosened enough to allow the cable ends to slip through, causing the scaffold to fall. This particular rig had been used without incident every day for two weeks preceding this fatal fall.

Support Capacity

bricklayer
Can this parapel support at least 4X the imposed load by the cornice hook? Should the cornice hook be tied back, and supported with bearing blocks?
  1. Ensure scaffolds and scaffold components are capable of supporting, without failure, their own weight and at least 4 times their maximum intended load.
  2. Make sure each suspension rope, including connecting hardware, is capable of supporting, without failure, at least 6 times the maximum intended load applied to that rope while the scaffold is operating at the greater of either:
    1. the rated load of the hoist
    2. 2 times the stall load of the hoist
  3. Inspect to ensure all suspension scaffold support devices, such as outrigger beams, cornice hooks, and parapet clamps:
    1. Rest on surfaces capable of supporting at least 4 times the load imposed on them by the scaffold operating at the greater of either:
    2. rated load of the hoist
    3. 1½ times the stall capacity of the hoist
    4. capacity
    5. are supported by bearing blocks
    6. are secured against movement by tiebacks installed at right angles to the face of the building or structure, or by opposing angle tiebacks installed and secured to a structurally sound point of anchorage (structurally sound points of anchorage include structural members, but not vents, electrical conduit, or standpipes and other piping systems)
  4. Ensure no more than two employees occupy suspension scaffolds designed for a working load of 500 pounds (non-mandatory).
  5. Ensure no more than three employees occupy suspension scaffolds designed for a working load of 750 pounds (non-mandatory).
  6. Make sure scaffolds are altered only under the supervision and direction of a competent person.

Real-Life Example

Foreman Dies When Overloaded Scaffold Falls

Six other boilermakers had just left a suspension scaffold when it fell about 392 feet along with the foreman, who was killed. The superintendent had ordered the scaffold's main support be disassembled before the scaffold was lowered to ground level. Rigging, welding machines, materials and supplies, etc., were placed on the scaffold, and two 1-inch wire rope hoist lines were cut free. This put the load on a single 3/4-inch wire rope hoist line, which was overloaded by 255 percent, and on the diesel hoist located outside the chimney, which was overloaded by 167 percent. The superintendent was in a rush to get the system disassembled because a helicopter had been contracted to remove the structural members of the scaffold support system on Monday.

Support Outrigger Beams

capacity
Click to Enlarge
  1. Make sure outrigger beams are made of structural metal, or other material of equivalent strength.
  2. Ensure outrigger beams are restrained to prevent movement.
  3. Check to make sure inboard ends of outrigger beams are stabilized by bolts or other direct connections to the floor or roof deck, or by counterweights.
  4. Make sure before the scaffold is used, direct connections of outrigger beams are evaluated by a competent person to determine that the supporting surfaces are capable of bearing the loads that will be imposed on them.
  5. If outrigger beams are not stabilized by bolts or other direct connections to the floor or roof deck, make sure they are secured by tiebacks.
  6. Ensure outrigger beams are placed perpendicular (90-degree angle) to their bearing support when feasible (usually the face of the building or structure).
  7. When perpendicular outrigger placement is not possible because of obstructions that cannot be moved, check to ensure outriggers have been placed at some other acceptable angle, and that opposing angle tiebacks are used.
  8. Check to make sure outrigger beams:
    1. have stop bolts or shackles at both ends
    2. are securely fastened together with the flanges turned out when channel iron beams are used instead of I-beams
    3. are installed with all bearing supports perpendicular to the beam center line
    4. are set and maintained with the web in a vertical position
    5. are attached to the scaffold ropes by a shackle or clevis placed directly over the stirrup

Real-Life Example

Failed Outrigger Leads to Fatality

Two employees were painting the exterior of a three-story building when one of the two outriggers on their two-point suspension scaffold failed. One painter safely climbed back onto the roof while the other fell approximately 35 feet to his death. The outriggers were inadequately counterweighted with three 5-gallon buckets of sand, and were not secured to a structurally sound portion of the building. Neither painter was wearing an approved safety belt and lanyard attached to an independent lifeline.

Inspecting Suspension Ropes

wire rope
This wire rope has a thimble secured by an eyesplice, as required on the load end of suspension ropes.
wire rope
Looks for wires and strands that are broken.
bird caged
This wire rope has “bird-caged” and became unsuitable for use.
twisted
The constant rotation of this rope as it ran through the hoist has caused the free end to twist and split.
clips
There are only 2 clips fastening this wire rope. Is it safe? The standard requires 3 clips.
right vs. wrong
Right vs. Wrong
Click to enlarge
  1. Check suspension ropes supporting adjustable suspension scaffolds to ensure they have a diameter large enough to permit proper functioning of brake and hoist mechanisms.
  2. Make sure the use of repaired wire rope as suspension rope is prohibited.
  3. Ensure wire suspension ropes are not joined together except through the use of eye splice thimbles connected with shackles or coverplates and bolts.
  4. Make sure the load end of wire suspension ropes are equipped with proper-size thimbles, and secured by eyesplicing or equivalent means.
  5. Ensure competent persons are inspecting ropes for defects prior to each work shift, and after every occurrence which could affect a rope's integrity. 
  6. Check that ropes are replaced when any of the following conditions exist:
    1. any physical damage which impairs the function and strength of the rope
    2. kinks that might impair the tracking or wrapping of the rope around the drum or sheave of the hoist
    3. six randomly distributed wires are broken in one rope lay, or three broken wires in one strand in one rope lay
    4. loss of more than one-third of the original diameter of the outside wires due to abrasion, corrosion, scrubbing, flattening, or peening
    5. heat damage caused by a torch, or any damage caused by contact with electrical wires
    6. evidence that the secondary brake has been activated during an overspeed condition and has engaged the suspension rope
  7. Ensure swaged attachments or spliced eyes on wire suspension ropes are not used unless they are made by the manufacturer or a qualified person.
  8. When wire rope clips are used on suspension scaffolds, ensure:
    1. A minimum of 3 clips are installed, with the clips a minimum of 6 rope diameters apart.
    2. Clips are installed according to the manufacturer's recommendations.
    3. Clips are retightened to the manufacturer's recommendations after the initial loading.
    4. Clips are being inspected and retightened to the manufacturer's recommendations at the start of each subsequent work shift.
    5. U-bolt clips are not being used at the point of suspension for any scaffold hoist.
    6. When U-bolt clips are used, the U-bolt is placed over the dead end of the rope, and the saddle is placed over the live end of the rope.
  9. Make sure suspension ropes are being shielded from heat-producing processes.
  10. When acids or other corrosive substances are used on a scaffold, ensure the ropes are:
    1. shielded
    2. treated to protect against the corrosive substances
    3. are of a material that will not be damaged by the substances

Real-Life Example

Broken Suspension Ropes Result in Worker Death

Two victims and a co-worker were painting the side of a building in San Francisco. They were on a two-point suspension scaffold that did not have guardrails; the ropes suspending the scaffold were old and had not been inspected; and the employees were not wearing safety belts. When the left scaffold rope broke and the scaffold collapsed, one employee was killed and another fell to a nearby roof and broke both arms. The co-worker was left hanging on to the remaining scaffold rope.

Inspecting Hoists

suspended scaffold
If a suspended scaffold becomes stuck while traveling, the hoist motor may strain and cause too much load for tiebacks, counterweights or the structure, causing a possible fatal fall.

A mechanical device is used to raise or lower a suspended scaffold. It can be mechanically powered or manually operated. When inspecting hoists check each of the following:

  1. Verify the stall load of the scaffold hoist does not exceed 3 times its rated load.
  2. When winding drum hoists are used and the scaffold is extended to its lowest point of travel, ensure there is enough rope to wrap four times around the drum.
  3. When other types of hoists are used, make sure the suspension ropes are long enough to allow the scaffold to travel to the level below without the rope end passing through the hoist, or else make sure the rope end provides a means to prevent the end from passing through the hoist.
  4. Make sure power-operated and manual hoists have been tested and listed by a qualified testing laboratory.
  5. Ensure gasoline-powered hoists are not used on suspension scaffolds.
  6. Check gears and brakes of power-operated hoists used on suspension scaffolds to make sure they are properly enclosed.
  7. In addition to the normal operating brake, make sure that both power-operated and manual hoists have a braking device or locking pawl which engages automatically when a hoist experiences:
    1. instantaneous change in momentum
    2. accelerated overspeed episode
  8. Verify manually operated hoists have a positive crank force to descend.

Note: Many scaffold failures occur early in the morning, after condensation has collected on the wire ropes overnight. The preferred industry practice at the beginning of a shift is to raise the scaffold 3 feet, hit the brakes, then lower the scaffold and hit the brakes again. This ensures that moisture on the wire rope will not allow it to slip through the braking mechanism, causing the scaffold to fall.

Real-Life Example

Failed Scaffold Hoists Cause Worker Death

Three workers were on a two-point suspension scaffold rated at 500 lbs. working weight. As the employees went up in the scaffold, the right side fell to the ground from an elevation of 20 feet. One worker managed to hold on, the other two fell with the scaffold, resulting in one worker dying and the other being hospitalized for extensive injuries. Investigation indicated that the scaffold motor assembly was improperly connected to the scaffold platform. The workers were wearing the available safety harnesses and lifelines but had not connected the lifelines.

Video

Instructions

Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. Which of the following is the most common type of suspension scaffold?

2. Which of the following components is "the beginning" of the safe use of a suspended scaffold?

3. Which of the following scaffolds is designed to be raised and lowered while occupied by workers and materials?

4. While inspecting work being conducted on an adjustable suspension scaffold you notice that repaired wire rope is being used. What do you tell the workers?

5. When inspecting hoists, verify that power-operated and manual hoists have been tested and listed by _____.


Have a great day!

Important! You will receive an "error" message unless all questions are answered.