SECTION 7: SUSPENDED SCAFFOLDING

7.1 Scope

7.1.1 Definition

A suspended scaffold is a working platform that:

• Is suspended by ropes from overhead outriggers, needles, parapet hooks or brackets fixed to a building or structure.
• Is capable of being raised and lowered by hand haulage on fibre ropes, or by hoists that are either manually or mechanically operated using wire ropes.

A working platform held by ropes that cannot be raised or lowered, is classified as a hanging scaffold (special duty scaffold), not a suspended scaffold.

7.1.2 Types of suspended scaffolds

The following shows some examples of suspended scaffolds:

• Swinging stage (manual) - This working platform has a minimum of two points of overhead suspension and is raised or lowered by hand haulage, which is controlled from the stage.
• Swinging stage (mechanical) - This working platform has a minimum of two points of overhead suspension and is raised or lowered by power operated or air operated hoists, which are controlled from the stage.
• Boatswain's chair (manual) - This chair has a single overhead suspension and is raised or lowered by hand haulage, which is controlled from the chair.
• Suspended safety chair (mechanical) - This chair has a single overhead suspension and is raised or lowered by a power operated or air operated hoist, which is controlled from the chair.
• Multi-point suspended stage (manual or mechanical) - These are stages that have more than two points of suspension and are raised and lowered by power operated, air operated or manually operated hoists, which are controlled from the stage.

7.2 Motive power

7.2.1 Hand haulage

Fibre rope tackle used for hand haulage must be a minimum of 18mm diameter and preferably be made from natural fibre rope to give a good hand grip. Fibre rope must have a factor of safety of at least 6 when new. Blocks for fibre rope must be made of metal or wood strapped with metal and be no less than 100mm in diameter.

The maximum live load permitted on a hand haul swinging stage is the difference between 360kg and the dead weight of the stage (including the weight of falls and blocks). The relation of width of platform, height of point of suspension on the platform and stage weight must be such that, under a load of 160kg in the extreme position on any side, the cross tilt of the platform is not more than 1 in 6 of the platform width. To prevent end tilt, the overhang of either end beyond the point of support must be such as to ensure that the platform is stable under a load of 160kg at the extreme end.

The total live load permitted on a boatswain's chair must not exceed 115kg. When used by a worker in the seated position, the chair must have a back rail, rope or post not less than 250mm above the seat.

7.2.2 Mechanical haulage

Electric and air operated swinging stages, including cable climbers, need to be controlled from the stage platform or chair. They must have a push button or dead man lever control that will stop and automatically lock the motor and hoist when pressure on the control switch or lever is removed. Each control must be independently operated. Hand operated release to allow faster descent than normal is not permitted.

Ratchet and pawl manually operated swinging stages must have a positive locking device so that the stage can be securely held at any level and the pawl automatically engages when released from the hand control. Wire rope must be of suitable quality and strength with a factor of safety of not less than 10 when new.

The maximum level load permitted on a swinging stage is the difference between 560kg and the dead weight of the stage, including the weight of the hoisting gear or cable climbers. However always check the manufacturer's specifications. No less than two people and no more than three people may use a stage at any one time and the safe lifting capacity must be clearly marked on the hoists. Overload or cut-out switches must be used and must be kept adjusted to provide adequate safeguards should snags be encountered.

The maximum live load permitted on a suspended mechanical chair is 160kg.

The maximum live load permitted on a multi point suspension platform is 240kg, being a maximum of three persons or two persons and materials.

7.3 Anchoring and construction

7.3.1 Anchorages

Hoisting wires or tackle must be anchored to a secure part of the structure, to outriggers (needles), to designed brackets or parapet brackets, or directly to the counterweights.

All structures, parapets, and other supports must be of such condition and design to support the anchorage without danger of failure or distortion and to give a factor of safety of at least 3 under the worst conditions. An engineer's certificate may be required on the suitability of the structure, parapet or support.

7.3.2 Outriggers (needles)

It is accepted engineering practice to use either steel or aluminium outriggers (also called needles) to support mechanical powered swinging stages. For hand hauled swinging stages and boatswain's chairs either steel or timber outriggers may be used.

Design parameters include:

• For a swinging stage with two points of suspension, each outrigger must be designed to carry the entire load of the working platform, including hoists, together with the full live load of persons and materials on the working platform, plus the factor of safety.
• For a swinging stage with more than two points of suspension, each outrigger must be capable of carrying the full dead and live load for each section between suspension points, plus the factor of safety.

Unless specifically designed by a chartered engineer, each outrigger for a mechanically operated swinging stage must be:

• At least equivalent in strength to a 152mm x 89mm x 17.09kg/m rolled steel joist when suspending a maximum load of 400kg.
• At least 3.6m in length when counterweighted.
• Located so as not to project more than 1.5m beyond the outer point of the support on the building or structure (maximum 1.5m outboard from the fulcrum).

The load exerted by the outrigger on the roof structure or parapet needs to be distributed by providing adequate packing at its points of support i.e. the outer or fulcrum end and the inner or counterweighted end.

Needles need to be fixed together to prevent lateral movement of the needle and to prevent overturning with the movement of the stage when it is in use. Alternatively, needles need to be individually secured to prevent movement and overturning.

7.3.3 Stability and counterweighting

Outriggers must be either counterweighted or secured to the building or structure. Where an outrigger is stabilised by counterweights the factor of safety against overturning must be at least 3. Where roof fixings are relied upon as the sole means of achieving stability they must be capable of providing a factor of safety of 3 against uplift.

Needless must be prevented from rolling over or moving laterally due to the movement of the stage. Where counterweights are used to provide stability they must be firmly attached to the outriggers so that they cannot become accidentally dislodged. When strops are used these must be positively secured to the outrigger, which must be provided with stop ends. All shackles must be moused with tie wire through the hole of the shackle and around the shackle itself.

All weights must be stamped or marked with their weight. Sand, water or materials that can run to waste must not be used as counterweights in any form.

7.3.3.1 Counterweighting of outriggers

Where an outrigger is stabilised by counterweights, the factor of safety against overturning must be at least 3.

Figure 90: Suspended scaffold showing counterweights

7.3.3.2 Calculating for counterweights

Terms

Suspended load: The greater of the total of the stage, motors, and ropes plus the total live load in kilograms or the maximum possible line tension allowing for the setting of the motor cut out - typically 125% of the rated pulling power of the motor.

Overhang or outboard: Distance from the fulcrum to the suspension point in metres.

Tail length or inboard: Distance from the fulcrum to the counterweights in metres.

Calculation

Counterweight = overhang (in m) x the suspended load (in kg) x 3

tail length (in m)

For example if the suspended load is 400kg, the overhang is 1.2m and the tail length is 4.5m, the counterweight required for each outrigger is:

1.2m x 400kg x 3

4.5m

= 320kg per outrigger

Note that the safety factor is always a minimum of 3 and that each outrigger must be able to support the total combined loads, should one needle fail.

Figure 91: Supporting outrigger between floor and soffit

7.3.4 Propping needles between the floor and soffit

7.3.5 Brackets and parapet hooks

7.3.5 Brackets and parapet hooks

Brackets, parapet hooks, parapet brackets and attachments must be designed by a chartered engineer. A minimum factor of safety of 3 is required on the combined dead and live loading of the suspended scaffold. All welding for these structural components must be done by a certified welder.

Parapet hooks and brackets may only be used if:

• The parapet is structurally sound - get an engineer's certificate if you are unsure.
• The hook fits the parapet correctly.
• The parapet is deep enough to allow at least 300mm of the hook down the inside of the parapet.

If packing has to be used around the parapet to assist in the tightening of the bracket only adequately sized ply should be used. Never use wedges to pack the front or back of the bracket as they can dislodge with the movement of the suspended platform.

7.3.6 Secondary safety for needles or parapet hooks

It is recommended that every suspended working platform supported by needles or parapet hooks have a secondary safety method of securing the needles or parapet hooks to the supporting structure. This can be achieved by using discarded stage wire ropes and wire rope grips or bulldog clips. Lace the wire rope through the needles or parapet hooks and secure the wire rope around part of the structure with 3 wire rope grips or bulldog clips. While this additional safety precaution is not mandatory, it is recommended. It is also recommended that, where possible, needles are laced together.

7.3.7 Grips and shackles

Rope grips or bulldog clips

Always fit the grips the same way around, with the bridge on the loaded or long part of the rope and the U-bolt on the short part of the rope. On a separate wire rope a minimum of three rope grips must be used and spaced at a distance centre to centre of six rope diameters.

Shackles

Both D and Bow shackles used in scaffolding and suspended scaffolding should have their SWL clearly marked and when in use the pin should be securely screwed in and moused to the body of the shackle.

When using a shackle to form a running noose always fit the back of the shackle to the standing or running part of the rope. Mousing of shackles is usually done by using steelies tie wire or similar, as in figure 92.

Figure 92: Mousing of shackles

7.3.8 Working platforms, guardrails, midrails and toeboards

Platforms may be made of any acceptable material provided it is strong enough for the purpose and provided that platforms are designed, constructed and assembled according to sound and accepted engineering practices.

Guardrails and midrails must be provided on both sides and both ends of swinging stages.

Toeboards must be provided on all types of suspended scaffolds with the exception of boatswain's chairs.

7.4 Use of safety harnesses and lifelines

Every worker on a suspended working platform must wear a safety harness that is secured to a fixed support or to an independent lifeline, except where the platform is:

• A boatswain's chair that has more than one effective means of support.
• So designed and constructed that it would remain safely suspended notwithstanding the failure of one rope or suspension, in which case the harness may be secured to the platform.

A safety harness worn by a worker must suspend the worker not more than 1.5m below the platform if the worker falls from the platform and must be so designed that the force arresting the fall does not exceed 6kN (610kg).

A lifeline must be used by only one worker at a time and must either extend to the ground or be provided with a positive stop to prevent the harness running off the end of the line. This line must have a minimum breaking strength of 29.4kN (3000 kg) and be of nylon at least 12mm in diameter or of polypropylene, or other equally durable material, at least 16mm in diameter.

Where a platform has only one rope at each support the harness lanyard must be attached by a gravity lock device to an independent lifeline. The independent lifeline may be fixed:

• Directly to an anchor set in the building that will withstand a vertical load of 24kN (2450kg); or
• To a separate anchorage other than the needle supporting the platform.

Where a platform has two independent ropes at each suspension the operator's safety harness lanyard may be attached to a suitable anchorage on the platform.

Two ropes used at each support of the platform may be attached to the same outrigger by separate anchorages.

---