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SCAFFOLDING
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SCAFFOLDING

 

Introduction:

Scaffolds are used in refineries as temporary work places to provide support for workmen, plant and materials used in buildings, construction, maintenance, repair and demolition work, etc.

This chapter covers different types of scaffolds and ladders used in conjunction with scaffolds.

Scaffolding hazards:

The accidents to workers that are due to falls from a height or to scaffold collapses show clearly the importance of properly constructed and maintained ladders and scaffolds. Apart from collapses the principal hazards are:

  • Unsecured ladders slipping
  • Use of unsuitable or faulty materials
  • Inadequately supported scaffold boards
  • Inadequate or irregular platform widths
  • Omission of guard rails or toe boards
  • Failure to secure scaffold to the building or to brace it adequately
  • Overloading the platforms and scaffolding , etc

 

General requirements:

Tube:

All steel tubing used for scaffolding shall confirm to BS 1139.

Tube to BS 1139 is nominal 1.5” diameter tube and shall be free of cracks, surface flaws and other defects.

Tube shall not deviate from straight line by more than 1/600 of its length measured at centre of its length. Straightening of tubes shall only be carried out on a straightening machine. Deformed section of tube shall be cut out.

All tubes should be maintained in a clean condition and regularly inspected.

Fittings:

All fittings e.g., couplers, clips, etc., used for scaffolding shall confirm to BS 1139.

Fittings should be regularly examined. Moving parts should be regularly lubricated for easy movement.

Boards:

Timber scaffold boards shall conform to BS 2482.

Looking at the face of the board, the end shall not be split up more than 12” (300 mm) with the hoop iron fixed.

Looking at the edge of the board, not more than half of the depth shall be knot wood.

Looking along the board from one end it must not be twisted by more than ½” (12mm) thick.

Boards which are split, decayed or warped shall not be used, but the parts affected may be cut off to obtain shorter boards.

Boards shall not be painted or treated in anyway that may conceal defects.

Boards used for scaffolding decking shall, for boards up to 2” (20 mm), be not less 8” (200 mm) wide, and for boards exceeding 2” (50mm) thick, not less than 6”(150 mm) wide.

Timber boards shall not be used where they are in contact with hot lines or surfaces which could cause fire. Metallic boards shall be used in this case.

Scaffolding terms:-

Tubular members:

Standard (also known as an upright or column) – a tube used as a column or vertical in the construction of a scaffold, and transmitting a load to the ground via a base plate.

Puncheon:

A vertical tube supported otherwise than upon the ground or a base plate.

Ledger:

A tube spanning horizontally and tying a scaffold longitudinally. It may also act as a support for put logs, transoms or board bearers.

Board bearer:

A tube spanning across ledgers between transoms to support a working platform.

Putlog:

A tube or other member spanning horizontally between a ledger and the wall of a building. It may have a special formed end which may be detachable for the pupose of fitting into brick work.

Raker (also known as a strut or spur):

An inclined load bearing tube having a bearing on the ground or on an adjacent structure.

Brace:

A tube incorporated diagonally across two or more members in a scaffold and fixed to them to afford stability.

Tie:

A tube used to connect a scaffold to a rigid anchorage.

Guardrail (also wrongly known as a handrail):

A tube connected at the edge of a platform and other places to prevent persons falling from platform of place.

Handrail:

Tube used on stairs before permanent handrails, banisters, etc. fitted to prevent the fall of persons.

 

Scaffold fittings:

Base plate:

A 6”*6” (150 mm* 150 mm) – steel plate providing a flat bearing surface for load distribution from standards. It has an integral spigot and fixing holes for use with sole plates.

Adjustable base plate:

Used for compensating variations in ground levels. Also used for strutting and shoring.

Double coupler – (also known as a right angle or ninety degree coupler or clip)

A load bearing coupler used for connecting two tubes together at right angles.

Universal coupler (also known as S.G.B or band and plate coupler):

Load bearing coupler used for connecting two tubes together at right angles or in parallel.

Putlog coupler (also known as a putlog clip)

A non load bearing coupler used for fixing two tubes at right angles, e.g., intermediate put logs or board bearers to ledgers.

Putlog or brace coupler (SGB type)

This coupler whilst primarily designed for securing putlogs and transoms to legers, also confirms to the requirements for a bracing coupler.

Swivel coupler:

Used for connecting two tubes together at any angle through 360 degrees. Not to be used for the load bearing purposes for which a double coupler has been designed.

End to end coupler (also known as a sleeve coupler):

Used for connecting two tubes end to end.

Joint pin (also known as a spigot):

Used for connecting two tubes end to end. Fitted internally it expands to apply grip against the wall of the tube.

Putlog end:

Used for converting an ordinary tube into a put log.

Toe board clip:

Used for fixing toe board to standard.

 

General terms

Sole plate (also known as Spreader)

A timber or other member of adequate size and suitable quality used to distribute the load from the base plate over an area of ground.

Bay:

The space between two adjacent standards along the face fo a scaffold.

Lift:

The height from the ground or floor to the lowest ledger, or the vertical distance between two adjacent ledgers.

Toe board (also known as a kicking board):

A board positioned at the edge of a platform or place so as to prevent persons, tools and materials falling form the platform or place.

Decking:

A close boarded scaffold platform.

Work stage (also known as staging):

Purpose made for use on towers, trestles, roof trusses, etc.

Can be used over greater spans than ordinary scaffold boards.

Unit beam :

A purpose made lattice beam incorporated into a scaffold structure to form a bridge where opening are necessary.

Two way tie:

A tie which prevents movement of the scaffolding both to and from the building or structure to which it is secured.

Column box tie:

Tow way tie secured to a vertical column with tubes forming a ‘box’ round the column.

Parallel coupler :

Short tube secured longitudinally across an end to end joint in tubing to strengthen the joint.

Junction:

The intersection of a series of tubes.

Buttress:

A well braced tubular structure erected against an existing scaffolding structure to strengthen it.

Longitudinal bracing (also known as face or façade bracing)

Tubes secured diagonally across the face of a scaffold to ensure stability.

Ledger bracing (also known as cross or wind bracing):

Tubes secured diagonally between lifts from ledger to ledger or standard to standard to endure stability.

Fan:

A scaffold platform cantilevered from the main structure at point below the working level and designed to catch any materials etc., which might fall.

Scaffold lashing:

Wire rope of ½” (6.4 mm) dia used for lashing ladders, etc. not to be used for suspending or anchoring scaffolds, or for lifting operations.

 

Construction common to all scaffolds:

Foundations:

A good bases is essential, so the ground or floor on which the scaffolding is going to stand should be carefully examined. Soil or made up ground will need consolidating.

Sole plates at least 9”*1.5” (230 mm *40 mm) cross section are required to spread the load on earth, made up ground, asphalted surface etc. Sole plates shall extend under at least two standards and joints shall be positioned so that they fall within one half to one third of the distance between any two adjacent standards. At the end standard the sole plate shall project a similar distance.

Small timber pads may be used on solid bearing, such as concrete, where there is no risk of the standard and base plate sinking or becoming displaced. Any other make shift arrangement e.g. barrels, boxes, lose bricks or concrete blocks shall not be used as a substitute for sole plate for construction of a scaffold.

Standards:

Standards shall be pitched on base plates and sole plates or timber pads. Joints in standards should not occur in the same lift. Joints should be arranged so that they occur as near as possible to a ledger. All standards shall be vertical.

Ledgers:

Ledgers shall be securely fixed to standards with double or universal load bearing couplers and shall be horizontal. Joints in ledgers should be staggered, i.e. joints in adjacent ledgers should not occur in the same bay. It is desirable that these joints be made with sleepe couplers. If joint pins are used they should be placed at about one – quarter to one third the span between the standards, not at mid-span.

Decking:

All decking shall be close-board, each board resting evenly on at least three supports. Boards shall oversail end supports by at least 2” (50mm) but shall not oversail by more than four times their thickness.

Supports for scaffold boards (transoms, putlogs, etc) shall be spaced with due regard to the nature of the platform and the load it will bear. Maximum permissible distances between supports for scaffold boards (transoms, putlogs, etc), is as given below:-

 

 

Thickness of scaffold board

Maximum distance between supports

1 ¼” (32mm)

3’3” (990 mm)

1 ½” (40 mm)

5’0” (1.520 m)

2” (51 mm)

8’6” (2.590 m)

 

Note:

These distances are the maximum allowed for single planking, but these must be reduced whenever the anticipated load or the nature of the platform makes a smaller distance necessary for safety.

Except on decking contiguous to the curved surface of a cylindrical or spherical structure, boards shall be laid flush wherever possible. Where overlaps are unavoidable, suitable beveled pieces shall be provided to reduce the risk of tripping.

Boards shall be laid with no opening more than 1 inch (25 mm) between adjacent boards or scaffold member.

Decking shall be kept free from unnecessary obstructions and from materials, rubbish and projecting nails.

Decking which has become slippery with oil, or other substance shall be immediately sanded, cleaned or otherwise treated.

The slope of a gangway or run, shall not exceed 1 vertical to 11 ½ inch horizontal. Slopes of more than 1 vertical to 4 horizontal shall have stepping laths at suitable intervals. Laths are to extend the full width of the gangway or run, except that gaps of 4” (100mm) may be left at the centre to facilitate the movement of barrows.

Boards shall be secured from movement.

Guardrails and toe boards:

Guardrails and toe boards shall be fitted at edges of decking from which persons or material could fall a distance of more than 6’6” (1980 mm).

Guardrails shall not be less than 3’(920 mm) and not more than 3’9” (1150 mm) high, and the space between toe board and guardrails shall not exceed 2’6” (760 mm).

Guardrails and toe boards shall be fitted to the inside of standards to prevent outward movement, unless they are so designed and used as to prevent such movement.

Toe boards should be 8” (200 mm) high and secured in position by toe board clips or other means.

Guardrails and toe boards may be removed may be removed or remain un-erected for the time and to the extent necessary for the access of men or the movement of materials. They shall be replaced or erected as soon as possible.

Material guards:

Where materials are to be stacked on a working platform or working place above the height of the toe boards, suitable barriers shall be positioned so as to prevent the fall of such material from the platform or place.

Access:

Access to a working platform is best achieved by providing a separate ladder tower or cantilevered access platform so as not to obstruct the platform and to minimize the possibility of persons falling through the gap in the guardrail or decking.

Gin wheels:

Gin wheels are widely used lifting light loads up to 112 lb (50.8 kg) on to scaffolding.  There are two types of wheel in general use, the ring type and the hook type. The ring type is to be preferred.

The supporting tube shall be attached to two standards in the case of an independent tied scaffold. Double or universal load-bearing couplers shallbe used to attach the supporting tube to the standards. The point of suspension of the gin wheel shall not project more than 2’6” (760mm) beyond the outer supporting tube. If the distance between the point of suspension and the outer supporting standard is more than 1’ (300 mm) a diagonal brace should be fitted.

A coupler should be fitted to the supporting tube on either side of the ring to prevent movement.

Ropes used with gin wheel shall be of suitable size and confirm to BS 2052. each rope shall be marked for identification.

Incomplete scaffolding:

Where scaffolding is incomplete, whether it be during erection, dismantling or alteration, access to those parts which are incomplete shall be barred and warning notices displayed.

Workmanship:

Scaffolding shall be erected, altered and dismantled by experienced workmen working under the direction of a competent supervisor.

Standard shall be set accurately, in plan and vertically, by using a spirit level or plumb line at each lift. Ledgers shall be set horizontally with a spirit level, or by using horizontal lines on the building or structure.

Scaffolding couplers should be tightened with the tools recommended by the manufacturers of the couplers. The use of a spanner or tool that gives a leverage greater than that of the tool recommended is liable to cause damage to screw threads with the result that not only will the grip of the coupler on the tube be impaired, but also the coupler will be rendered unserviceable.

Scaffolding materials and other objects shall not be dropped, thrown tipped or shot from heights.

Inspections:

All scaffolding shall be inspected after completion of erection and then at least every seven days and after weather likely to have affected stability. Main points to be checked during inspection are as follows:

Base – standard pitched on base plates and adequate timber sole plates.

Standard- correctly aligned and not damaged or displaced.

Ledgers- no undue deflection.

Ties & braces – adequate and effective.

Couplers- correct type in use and properly tightened.

Boards- sound, close-laid, properly supported and secured from movement.

Guard rails and toe boards- in place to prevent falls wherever men or materials could fall more than 6’6” (1.980 m).

Ladders – In good condition, properly supported and secured.

Inclement weather:

Workers shall not work on scaffolds during storms or high winds.

Load on scaffold platform:

The recommended maximum distribution loading of scaffold platform shall confirm to the following table.

Erection:

The procedure for erection should be such that an unstable condition is not reached at any time. This recommendation is as important in low scaffolds as in taller ones. The ties for the scaffold are to be erected and should reach each tie position.

No portion of the scaffold should be utilized unless that portion is fully decked, braced and tied. Warning notices shall be fixed to draw attention to those parts of a scaffold which are in complete and should not be used.

Dismantling:

During dismantling, no component which endangers the stability of the remaining structure shall be removed.

If dismantling has reached the stage at which a critical member has to be removed, e.g. a tie or a brace, the stability of the structure shall be assured by fixing a similar or otherwise adequate member in place lower down before the member to be taken out is removed.

Because of the changes which are made in a scaffold structure during its working life, it is not safe to assume that dismantling can be carried out in the reverse order to the erection. The scaffold, especially its tying and bracing, should be inspected  prior to dismantling.

If the scaffold is defective, it should be made good before dismantling commences.

 

Recommended maximum distributed loading of scaffold platforms

Type of Scaffold

No. of working platforms in use

Spacing of standards

Width of platforms

Area per bay

Permissible loading

Max. load per bay

Example of max. load per bay

Light duty independent tied

1

9’ (2.7 m)

3 boards

18 ft.sq.

(1.67 sq.mt)

15 lb/ft.sq

(73 kg/sq.mt)

270 lb

1 man, hand tools, paint or plaster

Light duty independent tied

1

9’ (2.7 m)

4 boards

27 sq.ft.

(2.5 sq.m)

15 lb/ft.sq

(73 kg/sq.mt)

405 lb

2 man, hand tools, paint or plaster

Medium duty independent tied

4

7’ (2.1 m)

5 boards

28 sq.ft.

(2.6 sq.m)

37 lb/ft.sq

(180 kg/sq.mt)

1036 lb

1 man, mortar on spot board and 130 bricks

Medium duty independent tied

4

8’ (2.4 m)

5 boards

32 sq.ft.

(2.97 sq.m)

30 lb/ft.sq

(145 kg/sq.mt)

960 lb

2 men, and 620 lb (280 kg) of materials.

Heavy duty independent tied

2 heavy duty 2 light duty

6’ (1.8 m)

5 boards

24 sq.ft.

(2.22 sq.m)

60 lb/ft.sq

(290 kg/sq.mt)

1440 lb

1 man, mortar on spot board and 200 bricks.

Heavy duty independent tied

2 heavy duty 2 light duty

6’ (1.8 m)

5 boards

27 sq.ft.

(2.5 sq.m)

60 lb/ft.sq

(290 kg/sq.mt)

1620 lb

2 men, and 1280 lb (580kg) of materials

Heavy duty independent tied

2 heavy duty 2 light duty

6’ (1.8 m)

5 boards

24 sq.ft.

(2.22 sq.m)

37 lb/ft.sq

(180 kg/sq.mt)

888 lb

2 men and 550 lb (250 kg) of materials

Put log

1

6’ (1.8 m)

5 boards

24 sq.ft.

(2.22 sq.m)

56 lb/ft.sq

(275 kg/sq.mt)

1344 lb

1 man, mortar on spot board and 180 bricks

Put log

1

8’ (2.4 m)

5 boards

32 sq.ft.

(2.97 sq.m)

37 lb/ft.sq

(275 kg/sq.mt)

1184 lb

1 man, mortar on spot board and 160 bricks.

Note: * Assumption made : width of board 9 inch, weight of a man 168 lb (76.2 kg)

          ** Assumption made : Weight of spot board and mortar 70 lb (31.7 kg)

                                                Weight of a brick 6 lb (2.72 kg).

 

The procedure for dismantling shall be orderly and planned and should proceed generally from the top in horizontal sections.

Scaffolds shall not be dismantled in vertical sections from one end towards the other, especially in cases where a hoist tower, which apparently gives support to the scaffold, is to be left standing, unless special consideration is given to ties and bracings.

The following precautions should be observed.

  • DO NOT remove all the ties.
  • DO NOT remove all the bracing first.
  • DO NOT remove all the intermediate and board end transoms.
  • DO NOT remove all intermediate guardrails.

 

An access scaffold may have been temporarily stabilized during construction by rakers that have been subsequently removed. If the level of the lowest tie point is high, e.g. over entrance halls or above tall shop windows, temporary rakers, or other structurally adequate means of support, should be built up from the ground to achieve stability of the part – dismantled scaffold.

Lowering materials:

Materials shall be lowered to the ground and not stored on the scaffold. In the case where a pavement is not to be obstructed and scaffolding materials have to be stored on the lowest lift awaiting collection, this lift should be stiffened and fully braced or propped by rakers, using materials recovered from the upper lifts.

Components shall not be thrown on the ground; they shall be lowered hand to hand in an orderly fashion or brought down by crane, gin wheel or other suitable means.

 

Independent tied scaffold:

An independent tied scaffold (also known as double scaffold) is the most common form of access scaffolding and is divided into three groups:

  • Light duty independent tied scaffold
  • Medium duty independent tied scaffold
  • Heavy duty independent tied scaffold.

Independent scaffold consists of a double row of standards connected together longitudinally with ledgers and with transoms at right angles to the ledgers. Braces and ties are essential for its stability.

Light duty independent tied scaffold:

General requirement:

General construction requirements common to all scaffolds.

Design, loading and dimensions:

Single working platform shall be in use at any one time and the maximum distributed loading on the platform shall not exceed 15 lb/ft.sq (73 kg/m.sq). longitudinal distance between standard shall not exceed 9 foot (2.7 m).

Standards:

The inner row of standards shall be placed as close as possible to the fence of building or structure. However, to avoid projections in the building or structure, they may be placed 13” to 15” (325 mm – 375 mm) away from the wall or structure provided a single board is placed on the transom between the wall/structure and inner standard that should extend to within 2” (50 mm) of the face of the wall or structure. The outer row of standards shall be approximately 3’4”(1.0m) from the inner row to allow for four boards.

Ledgers:

Ledgers shall be vertically spaced between 6’ to 7’ (1.8 to 2.1 m) centres. The first pair of ledger may be up to a maximum height of 8’6” (2.6 m).

Transoms:

Transoms shall be placed on ledgers at 4 (1.2 m) centre for 1 ½” (40 mm)boards. In each bay one transom shall be fixed to, or within 12” (300 mm) of a standard with a load bearing coupler.

Bracing:

Diagonal bracing (or ledger bracing) at right angles to the structure at alternate pair of standards shall be provided for the full height of scaffold. These braces should be fixed to the ledgers close to the standard with swivel couplers. Longitudinal or façade bracing to the full height of scaffold, spaced not more than 100’(30 m) apart along scaffold length, shall be provided.

Ties:

To prevent movement of the scaffold either towards or away from the structure, it shall be securely tied to the structure throughout its entire length and height. Ties should occur at every other lift and not more than 20’ (6 m) interval along the scaffold.

Decking:

The working platform between the standards shall not be more than 36”(920mm) wide, i.e. 4 boards each of 9” (230 mm) width.

Limitation:

This scaffold can be used up to a maximum height of 200’ (60 m).

 

Medium duty independent tied scaffold:

General requirements:

General constructional requirements common to all scaffolds.

Design, loading and dimension:

Four working platforms may be used at any onetime and maximum distributed load on each platform shall not exceed 37 lb/ft.sq (180 kg/mt.sq). longitudinal distance between standards shall not exceed 7’ (2.1 m). this distance may be increased to 8’ (2.4 m) if loading is less than 30 lb/ft.sq (145 kg/mt.sq).

Standards:

The inner row of standards shall be placed as close as possible to the face of building or structure. However to avoid projections in the building or structure, they may be placed 13” to 15” (325 mm-375 mm) away from the wall or structure provided a single board is placed on the transom that should extend to within 2” (50 mm) of the face of the wall or structure. The outer row of standards shall be approximately 3 ft 4 inc (1.0 m) from the inner row to allow for four boards or 4’1” (1.24 m) for five boards with no inside board.

Ledgers:

Ledgers shall be vertically spaced between 6’ to 7’ (1.8 to 2.1 m) centres. The first pair of ledger may be up to a maximum height of 8’6” (2.6 m).

Transoms:

Transoms shall be placed on ledgers at 4’ (1.2 m) centre for 1 ½ “ (40 mm) boards. In each bay one transom shall be fixed to, or within 12” (300 mm) of, a standard with a load bearing coupler.

Bracing:

Diagonal bracing (or ledger bracing) at right angle to the structure at alternate pair of standards shall be provided for the full height of scaffold. These braces should be fixed to the ledgers close to the standards with right angle couplers or to the standards with swivel couplers. Longitudinal or façade bracing to the full height of scaffold spaced not more than 100’ (30 m) apart along scaffold length, shall be provided.

Ties:

To prevent movement of the scaffold either towards or away from the structure, it should be securely tied to the structure throughout its entire length and height. Ties should occurred at every other lift and not more than 20’ (6 m) interval along the scaffold.

Decking:

The working platforms between standards shall not be more than 3’9”(1150 mm) wide i.e. five boards. One of these boards may be placed between inner row of standard and the building or structure.

Limitations:

This scaffold can be used to a maximum height of 150’(45 m).

 

Heavy duty independent tied scaffold:

General requirements:

General constructional requirements are common to all scaffolds.

Design, loading and dimensions:

Two working platforms may be used at any one time and maximum distributed loading on each platform shall not exceed 60 lb/ft.sq (290 kg/mt.sq). an additional two platforms can be used for access or light duty at a loading of 37 lb/ft.sq (80 kg/mt.sq) on each platform. Longitudinal distance between standard shall not exceed 6’ (1.8 m).

Standards:

The inner row of standards shall be placed as close as possible to the face of building or structure. However to avoid projections in the buildings or structure, they may be placed 13” to 15”(325 mm to 375 mm) away from the wall or structure provided a single board is placed on the transom that should extend to within 2” (50 mm) of the face of the wall or structure. The outer row of standards shall be approximately 4’1’’(1.24 m) from the inner row to allow for five boards or 4’ 10” (1.47 m) for six boards with no inside boards.

Ledger:

The vertical distance between each ledger or the first ledger and the level on which standards are pitched (ground level) shall not exceed 6’6”(1.98 m).

Transoms:

Transoms shall be placed on ledgers at 4’(1.2m) centre for 1 ½” (40 mm) boards. In each bay one transom shall be fixed to, or within 12” (300 mm) of, a standard with a load bearing coupler.

Bracing:

Diagonal bracing (for ledger bracing)at right angle to the structure at alternate pair of standards shall be provided for the full height of scaffold. These braces should be fixed to the ledgers close to the standards with right angle couplers or to the standards with swivel couplers. Longitudinal or façade bracing to the full height of scaffold, spaced not more than 100’(30 m) apart along scaffold length, shall be provided.

Ties:

To prevent movement of the scaffold either towards or away from the structure, it shall be securely tied to the structure throughout its entire length and height. Ties should occur at every other lift and not more than 20’ (6m) interval along the scaffold.

Decking:

The working platforms between standards shall not be more than 3’9” (1150 mm) wide i.e. five boards and not more than 4’6” (1380 m) i.e. six boards. One of these boards may be placed between inner row of standard and the building or structure.

Limitations:

This scaffold can be used up to a maximum height of 150’(40 m).

 

Mobile tower scaffold:

A mobile tower scaffold consists of four or more standards connected together longitudinally with ledgers and with transoms at right angle to the ledger, forming a square or rectangular tower mounted on wheels. It has single working platform and is a common form of access scaffolding for painters and others who do work of a light nature and of short duration.

General requirements:

General construction requirements common to all scaffolds.

Design, loading and dimensions:

A mobile tower scaffold shall only have single working platform and the maximum distributed load (in addition to its own weight and the weight of the boards) shall be 30 lb/ft.sq (145 kg/m.sq).

Standards:

Standards shall be set in rows at not more than 8’ (2.438 m) centres.

Ledgers:

The ledger for the first lift may be fixed up to maximum height of 8’6” (2.6 m) and the subsequent lifts should be between 6’6”(1.98 m) and 8’(2.42m) centres.

Transoms:

Transoms on all lifts except the top lift shall be secured to the standards with load bearing couplers.

Transoms on the top lift and other working lifts for access to the walls may be secured to the ledger with right-angle of putlog couplers. These transoms should be at not more than 4’(1.2 m) centres and in each bay one shall be secured to, or within 12” (300mm) of, a standard.

Bracing:

Adequate diagonal bracing for the full height of the scaffold and at least to each corner of the structure in both directions, is required to ensure stability.

Ties:

It is essential that all bird-cage scaffolds are securely tied to surrounding walls throughout their length and height. Ties can be effected by extending alternate ledgers and transoms on alternate lifts to bear against existing walls, or inserting separate tubes at the same intervals, and these should be connected to the standards with load bearing couplers. The ends of the tubes should be packed where necessary to prevent damage to walls. Only load bearing couplers shall be used for securing ties.

Decking:

The working platform shall be close-boarded over the whole working area. Where intermediate platforms are required for access to walls, decking, guardrails, toe boards, etc. shall be provided as for light duty independent tied scaffold.

Guard rails and toe boards:

Unless the working platform finishes with 6” (150 mm) of surrounding walls, guardrails and toe boards shall be provided.

Limitation:

Birdcage scaffold erected in accordance with the foregoing directions with not more than one working platform, may be used up to a maximum height of 200’(60m) where not subjected to wind or other external forces.

 

Truss scaffold:

A truss (also known as cantilever or jib) scaffold is cantilevered out form a building or structure and used where it is impracticable to erect standards bearing on the ground or other surface. It is a form of light independent tied scaffold which is entirely dependent upon the building or structure for support and stability.

General requirements:

General construction requirements common to all scaffolds.

Design, loading and dimensions:

Design, loading and dimensions shall be as for a light independent tied scaffold with spacing and loading as specified as light duty independent tied scaffold.

Foundations:

Before erection work begins, the building or structure shall be carefully examined to ensure that it is structurally sound enough to take the stresses involved in anchoring the scaffold.

Inside anchorage:

The inside anchorage shall be wedged between two adjacent floors or horizontal members of a building or structure by the use of a adjustable base plates or reveal pins with timber sole plates and head plates. Sole plates and head plates shall run at right angles to floor and ceiling joints. Puncheons should be spaced at 4’6” to 5’6”(1.37 m to 1.524 m) centres and generally the spacing of the rows should be 4’6” (1.37 m).

Cantilever tubes:

Cantilever tubes(also known as needles and sometimes as transoms) shall be secured  to the puncheons at right angles with load-bearing couplers and extend through an opening in the building or structure to support an independent tied scaffold on the outside. Two way ties shall be secured to the cantilever tubes on either side of the opening with load bearing couplers.

Ledgers:

Inner and outer ledgers shall be secured to the tops of the cantilever tubes with load-bearing couplers.

Rakers:

Rakers (one for every standard) shall be secured to an outside ledger above the opening and to inside ledger at a lower level. The base of the raker shall bear (through a timber packing) on to a surface inside the building or structure, or on to a ledge outside. Junctions between rakers and ledgers shall be secured with load-bearing couplers. The angle of rakers shall be secured with load bearing couplers. The angle of rakers shall be greater than 35 degrees from the vertical. Rakers more than 10’ (3.0 m) in length shall be braced.

Standards:

Standards shall be secured to the ledgers as close as possible to rakers with load bearing couplers and the junctions reinforced with check couplers.

Braking:

It is not always necessary for bracing to be fixed on the inside anchorage but where it is required it should be fixed with right angle or swivel couplers. No raker to be longer than 10’(3.0 m).

Fittings:

Diagonal braces may be secured to puncheons and standards with swivel couplers. Intermediate transoms used to support the working platform may be secured to ledgers with putlog couplers. All other fittings including those used on rakers, shall be load bearing. Check couplers shall be used immediately above junctions between standards and ledgers and immediately below junctions between rakers and ledgers.

Joints and braces should be avoided where possible. If joints are necessary, parallel couplers shall be use. All other joints in tubing on truss scaffold shall be made with end to end couplers.

Ties:

It is essential that a truss scaffold be securely tied to the building or structure with two-way, through or column box ties. Ties shall be positioned at every other lift at not more than 20’(6.09 m) centres. Reveal ties shall not be used.

Limitations:

Truss scaffolds erected in accordance with the foregoing directions, with not more than one working platform, may be used up to a maximum height of 40’(12.19 m) from truss to working platform.

 

INDEPENDENT SCAFFOLD:

An independent scaffold is used to raise a working platform to the required height like independent tied scaffold where providing ties with the structure for stability is not possible. Independent scaffold shall be erected in accordance with Construction Common To All Scaffolds and Independent Tied Scaffold. Unlike independent tied scaffold, independent scaffold is not tied to the structure for stability and therefore height of independent scaffold shall not be more than 3 times its minimum base dimensions.

 

TRESTLE SCAFFOLD:

Trestle scaffold as a term applied to a working platform supported by trestles, split heads, folding steps, ladder, tripods or similar movable contrivances.

Design, loading and dimensions:

A trestle scaffold shall only have a single working platform in use at one time. It is recommended that the maximum loading on the platform should not exceed 15 lb/ft.sq (73 kg/mt.sq).

Foundation:

A trestle scaffold shall only be erected on a firm level surface with each stile or foot properly supported.

Trestles:

Painter’s folding trestles:

Hinges shall be checked to ensure that they are not broken, rusty or lose. Hinges should be of the self locking type which limits the angle to which the trestles can be opened (not less than 30 degrees or more than 40 degrees for aluminum and not less 24 degrees or more than 36 degrees for timber). Timber trestles shall be checked to ensure that they are not cracked or split, that cross bearers are through tenoned and double-wedged, and that check blocks and tie rods are fitted (four on trestles up to 10’ (3.05 m) and six on trestles over 10’). In order that defects may be easily seen, timber  trestles should not be painted.

Steel extending trestles:

Trestles shall be checked to ensure that they are not twisted or damaged and that all four feet rest evenly on the ground. Adjustable cross bars must be supported by purpose made steel fixing pins which should be chained to the trestle to prevent loss.

Decking:

Painter’s folding trestles:

Working platforms shall consist of at least two 9”(370 mm) scaffold boards placed side by side spanning horizontally between the trestles. Cross-bearers supporting the boards shall be not more than 5’ (1.520 m) apart for 1 ½” (40 mm) boards and not more than 8’6” (2.590 m) apart for 2” (51 mm) thick boards.

Steel extending trestles:

Working platforms are normally four or five boards wide and shall confirm to the requirements specified in section construction common to all scaffolds and sub section decking.

Guardrails and toe boards:

Guardrails and toe boards are not required on scaffolds which are supported by folding trestles, split heads or similar devices, up to a height of 15’(4.572 m).

Limitations:

Trestle scaffolds erected in accordance with the foregoing directions, with not more than one working platform, may be used up to a maximum height of 15’(4.572 m) from base to working platform. It shall be so situated that a person working on the platform would not be liable to fall more than 15’ (4.572 m).

 

System scaffolding:

System scaffolding is also known as unit or frame scaffolding and is composed wholly or partly of prefabricated section. There are many types of system scaffolding available which vary greatly in design and method of erection. In spite of this wide variation the same basic principles described in construction common to all scaffold apply. It should be erected by competent and experienced workmen. Care should be taken that it is erected on a sound base with standards (or equivalent units) vertical and ledgers (or equivalent units) horizontal. It should be adequately braced and securely tied.

 

Slung scaffold.

A slung scaffold is suspended by wire ropes or chains form roof or other structural members where scaffolding from the ground is impracticable. Generally, it is used for painting and other work of a light nature.

General requirements:

General construction requirements common to all scaffolds are to be followed.

Design, loading and dimensions:

A slung scaffold shall only have a single working platform and the maximum distributed loading on the platform shall be taken as 15 lb/ft.sq (73 kg/mt. sq) with ledgers at 8’ (2.438 m) centres and 24.5 lb/ft.sq (120kg/mt.sq) with ledgers at 6’6” (1.981 m) centres.

Suspensions:

Working platforms may be suspended by chains, but wire ropes are more commonly used. Wire ropes should be at least 3.8”(9 mm) in diameter and confirm to BS 302 (Steel Wire Rope). The ¼” or 3 1/8” scaffold lashing must never be used as a means of suspension.

Wire ropes or chains shall be vertical and secured to ledgers as close as possible to transoms. Wire ropes should be secured by two full round turns and three bulldog grips (care being taken to ensure that the bulldog grips are fitted correctly). Chains shall be secured by shackles.

Where wire ropes pass round a sharp edged member, pacing shall be provided to avoid high point loads and to prevent chaffing. A working platform shall have a least six suspension points, evenly spaced, and kept taut. The weight supported by a single wire rope shall not be greater than the safe working load of the rope or of the member to which the rope is attached.

Ledgers:

Ledgers shall span the suspension points and be spaced at 6’6” (1.980 m) centres.

Transoms:

Transoms shall be secured on top of ledgers with load-bearing or putlog couplers at centres not exceeding 4’(1.219 m).

Decking:

The working platforms shall be fitted at edges from which person could fall at distance of more than 6’6”(1.980 m). for exception see below.

Guardrails and toe boards are not needed on a platform suspended from roof members or a roof and used only for light work of short duration if there is adequate handhold at every working position and all material needed can be used safely in the absence of guardrails and toe boards.

Ties:

The stability of the platform shall be ensured by securing adequate and suitable guy lines between the platform and suitable anchorage points. Guy lines shall be as near horizontal as possible and kept taut.

Limitations:

Slung scaffolds erected in accordance with the forgoing directions may be used with single working platforms up to 8’ by8’ (2.438 m by 2.438 m) in area with men and materials spread evenly over the platform. Slung scaffolds departing from these directions, and those required for point loading, shall be specially designed.

 

Drop scaffold:

A drop scaffold is suspended by scaffold tubes from a roof, roof members or other structural members where scaffolding form below is impracticable. Generally it if used for painting and other work of a light nature.

General requirements:

General construction requirements common to all scaffolds.

Design, loading and dimensions:

Design, loading and dimensions for the type of drop scaffold shall be as for light independent tied scaffold with spacing and loading as specified in design, loading and dimensions for the type of drop scaffold and shall be as for a slung scaffold with spacing and loading specified for that.

Suspensions:

The outriggers on the type of drop scaffold may be constructed  on unit beams or tube and fitting. Counterweights shall be securely fixed to the scaffolding and have a safety factor of three to one with the weight of the scaffolding, men and materials being taken into account.

On both types of drop scaffold, check couplers shall be employed at the tops and bottoms of suspension tubes.

Wherever possible vertical suspension tubes should be in one length. Where joints are necessary the tubes should be single lapped using at least two couplers or may be butted and lapped using at least two couplers or may be butted and lapped with a short length of tube. In the latter case, there should be at least two couplers on each side of the lapl.

Ledgers, transoms, decking, guardrails and toe boards, ties and limitations:

For the type of drop scaffold illustrated the requirements shall be as for a light independent tied scaffold.

 

Ladders:

Timber ladders shall confirm to BS 1129. aluminum ladders and steps shall confirm to BS 2037.

The safety of ladders depends upon three important factors:

  • The selection of the right ladder for the job to be done.
  • The condition of the ladder.
  • The safe use of the ladder.

Selection:

A ladder shall be of the proper length for the job to be done. If it is used as a means of access or as a working place it shall rise to a height of at least 3’6” (1.07 m) above the landing place or above the highest rung to be reached by the feet of the person using the ladder.

Metal ladders, wooden ladders with metal reinforced sites, and ladders which are wet shall not be used near electrical equipment with exposed live conductors.

Ladders shall be examined for cracked or split stiles, missing, broken, lose, decayed or damaged rungs and splinters.

Use:

Where a ladder is carried single-handed, the front end should be kept high enough to clear person’s heads and special care taken at corners and blind sports.

The stiles of a ladder shall be equally supported on a firm level surface. Boxes, bricks, barrels, etc., shall not be used as a means of support and under no circumstances shall wedges or other lose material be used as packing.

Ladders shall not be supported on their rungs and rungs shall not be used to support scaffold boards.

Ladders shall be set 1’ (300 mm) out of each 4’ (1.210 m) of height , i.e. at an angle of 75 degrees to the horizontal.

Ladders shall be set with metal reinforcing on the underside of rungs, and where reinforcing is provided on one side of stiles, that too shall be on the underside.

Where extension ladders are used fully extended, the minimum overlap of sections shall be four rungs. Splicing or lashing ladders together to obtain an extension shall not be permitted.

Both stiles of a ladder shall be evenly supported at the upper resting place and securely lashed to prevent any movement.

Where lashing at the upper resting place is impossible, measure must be taken to prevent movement of the ladder, by stationing a man at the foot but it must be borne in mind that a man stationed at the foot can only be expected to control a ladder up to 20’(6.10 m) in height.

Where there is a possibility of a ladder being struck by moving vehicles or plant, a man should be placed on guard or space at the base of the ladder fenced off. Similarly if a ladder is erected close to a door, the door should be locked shut or secured in the open position with a man on guard.

Ladder landing places or platforms are required at every 30’ (9.140 m) of height and shall be provided with guardrails and toe boards. Holes in platforms through which ladders pass shall be as small as practicable.

Tools and materials should not be carried by persons ascending or descending ladders except that tools may be carried in pockets or special belts, provided they do not impair movement.

A person working on or from a ladder must always have both feet on the rungs and a secure handhold. If the work to be done necessitates the use of both hands, safety belts should be used. Only one person should be on a ladder at a time.

 

 

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