nbr 6494scaffolding engl

ABNT STANDARD NBR 6494

SCAFFOLDING SAFETY Procedure

1. Objective

This standard establishes the required conditions for the safety in scaffolding in relation to structural conditions as well as safety of personnel working or walking on it.

This standard is applicable to scaffolding used as aids for vertical development of construction, as well as the ones that are installed for repair, finishing, painting, access towers and others, in already erected buildings.

This standard is not applicable to the safety of third parties, which should be directed by the specific laws from public services.

This standard covers scaffolding according to their class as follows:

a) suspended scaffolding, mechanical, - heavy; - light;

b) cantilevered scaffolding;

c) laid scaffolding, - fixed - mobile

Note: Scaffolding not included in this classification shall be subject to design and/or calculation prepared by a licensed professional and shall follow the safety conditions established in this standard.

2. Definitions

The definitions in 2.1 to 2.1.3 are used throughout this standard. 2.1 Scaffolding

Platforms necessary to perform work in elevated places where it cannot be safely performed from the floor. They are used in construction services, repairs, demolishing, painting, cleaning and maintenance.

2.1.1 Suspended scaffolding, mechanical

Scaffolding, heavy or light, where the floor is supported by metallic or wooden beams, suspended by wire ropes, moving vertically by means of winches.

2.1.1.1 Suspended scaffolding, mechanical, heavy

Scaffolding with structure and dimensions able to support maximum working loads of 4 kPa (400 kgf/m2), considering the safety factors on each one of its components.

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2.1.1.2 Suspended scaffolding, mechanical, light

Scaffolding with structure and dimensions able to support maximum working load of 3 kN (300 kgf), considering the safety factors on each one of its components.

Note: Working load is defined as the sum of material loads, tools and personnel on the scaffolding.

2.1.2 Cantilevered scaffolding

Scaffolding that projects out of the building and are supported by beams or cantilever structure, with ensured safety, either clamped or using other counterbalance system inside the building, and may be either fixed or mobile.

2.1.3 Laid scaffolding

Scaffolding which structure works just by laying flat, and may be fixed or mobile.

3. General conditions

The following conditions shall be observed. 3.1 Design and construction of scaffolding

3.1.1 All scaffolds shall be designed to bear the loads which they will be subject to.

3.1.2 All scaffolds shall have a safety device suitable for the work to be performed.

3.1.3 Each equipment used shall be of good quality and shall be in good working conditions, meeting the Brazilian standards.

3.1.4 Scaffolding design shall present the admissible working loads.

3.1.5 Scaffolding shall not be subject to loads above that specified in the design, and the load shall be uniformly distributed without blocking passageways.

3.1.6 Access to scaffolding during assembly and disassembly shall be prohibited to all personnel, except the assembly team responsible for the work.

3.1.7 The gap between scaffold and floor shall be in accordance with its resistance and with the loads to be applied. Sagging of more than 1/200 of the span is not permitted.

3.1.8 Board or plank floors shall be laid preferably over 3 cross beams with anti-sliding devices at the ends. In case of using 2 cross beams, it is mandatory that the ends are fixed. The wood used on floors shall be of good quality, dry, and without nodes or cracks.

3.1.8.1 Planks or boards laid side by side in the transversal direction shall not present gaps or spaces and shall cover the entire floor width, and shall be fixed to avoid shifting.



3.1.8.2 Floors with boards of 0.025m thick shall not have spans of more than 2.00 m, and shall be interlocked one to another. For spans of up to 1.5 m, interlocking is not required.

3.1.8.3 When joining together, planks or boards shall touch each other, and a cross beam shall be located under each end. In exceptional cases, overlapping is acceptable provided that the joint is located over a cross beam with at least 0.20 m each side (i.e., the overlapping will be at least 0.40 m). In this case, proper signage shall be posted (to inform the existence of a step, and a warning stripe shall be painted on the floor), as well as the ends shall be carefully fixed to prevent the ends of moving upwards.

3.1.8.4 Planks or boards shall not have more than 0.20 m in balance.

3.1.9 Floors shall not be slick, and even being metallic, shall present enough roughness to avoid shoes from slipping, even when wet.

3.1.10 All external scaffolding shall have fixed floor boards to avoid fall caused by the wind.

3.1.11 Working floors shall be horizontal.

3.2 Scaffolding safety and protection

3.2.1 Scaffolding shall be provided with rails on all its external faces, located 0.5 m and 1.0 m above the floor, and with kick plates at least 0.15 m high in the working floors. The handrail assembly shall resist to a punctual horizontal load of 350N, applied in its least favorable section, without presenting permanent deformation. The handrail shall be always fixed so that it will not move, under any circumstances.

3.2.2 If there is a possibility of personnel fall towards the internal face of the scaffold during work on the scaffold floor, suitable handrail shall be provided.

3.2.3 If spacing between stanchions is less than 1.0 m, the handrail referred to on 3.2.1 and 3.2.2 may be made of chain or wire rope, considering the height.

3.2.4 On hanging scaffolding, the space between the handrail and the kick plate shall be closed with a mesh or other equivalent material, including the ends.

3.2.4.1.1 In addition to the closure of the space between the handrail and the kick plate, a net shall be installed along the external perimeter to prevent objects from falling. The net shall have mesh size no greater than 25 mm.

3.2.5 Working place and accesses shall be properly illuminated.

3.2.6 Special care shall be taken during assembly, moving and use of scaffolding close to power lines. All electric cables for lighting and power in scaffolding shall be isolated.

3.2.7 When necessary, scaffolding shall be protected and provided with warning signals against vehicles and equipment impact.

3.2.8 Suspended scaffolding shall be duly anchored in a way that it is protected against movement in any direction.



3.2.9 Platforms of light suspended scaffolding shall be located a maximum of 0.30 m away from the work surface.

3.2.10 Wire ropes used in scaffolding shall be long enough to have at least two full turns left in the reel when the floor is on its lower position.

3.2.11 The hanging wire main sheave shall turn freely and its groove shall be maintained in a good working condition, clean and preserved; as well as it shall be suitably sized for the rope diameter.

3.2.12 Lifting devices shall be inspected before each service by a qualified professional.

3.3 Safety Use of Scaffolding

3.3.1 Care shall be taken to prevent objects from falling from the scaffolds. No material shall be piled up or stacked up on scaffolding.

3.3.2 All scrape or drop material shall be removed duly conditioned or by the use of a discharge chute.

3.3.3 Vertical movement of components and accessories used for the scaffolding assembly or disassembly shall be done by means of ropes or suitable lifting devices. Dropping parts or components is not permitted.

3.3.4 Personnel shall not be permitted to work on scaffolding during severe weather such as heavy rain or wind.

3.3.5 Services on scaffolding shall never be performed by only one person. At least one more person shall be available to help in case of emergency.

3.3.6 Personal protection equipment such as hard hats, safety belts and others shall be used as necessary. The equipment shall be in good conditions and available to the workers at any time.

3.3.7 Personnel working on scaffolding suspended more than 2.00 m above the ground shall use safety belts with fall restraining device connected to a safety lanyard attached to the building, independent from the scaffolding structure.

3.3.8 Scaffolding shall be provided with protection net to prevent objects from falling, as well as with a protecting platform at the same elevation of the building’s first floor.

4. Specific Conditions

4.1 Suspended scaffolding ropes

4.1.1 Wire ropes shall have a breaking load equal to at least five times the maximum working load.

4.1.2 Every time a suspension wire rope makes contact with a corner, it shall be protected against friction, and a minimum bending radius of eight times the diameter shall be maintained by a device tightly fixed to the structure.



4.1.3 Suspension wire ropes shall have fiber core (FC) and shall be of 6x19 type, with right regular lay, galvanized, with wire breaking load between 1600 Mpa and 1800 Mpa. The minimum diameter of wire ropes for light scaffolds shall be 7.95 mm, with a minimum breaking load of 34.8 kN, and for heavy scaffolds it shall be 9.5 mm with a minimum breaking load of 49.8 kN.

4.1.4 Suspension wire ropes shall be inspected before assembly, and periodically during use, and shall not present any of the following defects:

a) rust of the wires, reducing its characteristics;

b) broken wires in a quantity above 1 for each turn;

c) permanent deformation, such as kinks, crushed parts, damaged strands, etc;

- rope nominal diameter reduction of more than 10%;

- wear on external wires due to friction on more than 30% of wires.

Note: turn is the distance on which the wire completes one turn around the core.

4.1.5 All slings shall be provided with thimbles suitable for the rope diameter and shall be fixed with clips or sockets. In case of using clips, a reduction of 20% shall be considered on the rope admissible load. Clips shall be of Crosby type, heavy, in accordance with the figure. Quantity and spacing of clips shall follow the manufacturer’s tables, and at least three clips shall be used on each connection.

4.1.6 Wire ropes and accessories shall follow Brazilian standards.

4.2 Heavy duty suspended scaffolding, mechanical

The assembly of the heavy duty suspended scaffolding, mechanical, is composed of a mechanical winch system and steel cross beams to support a continuous platform with minimum width of 1.50 m.

CORRECT

WRONG

WRONG

Figure – Correct use of clips on slings.

4.2.1 Wire ropes supporting beams shall be a steel “I” shape, with minimum height of 0.15 m at the web, and minimum length of 4.00 m, installed in a cross direction from the surface where the services are being done.



4.2.2 The cantilever length of the 0.15 m high supporting beams shall be a maximum of 1.60 m from the building wall, so as to allow the working platform to stay up to 0.10 m away from the working surface.

4.2.3 The portion of the supporting beams that extends inside the building shall be not less than one and a half times the length in balance outside the building.

4.2.4 The internal ends of the supporting beams shall be tightly secured to the building structure.

4.2.5 The resisting moment to be considered in the sizing of the beams shall be at least thee times the applied moment.

4.2.6 The suspending wire ropes shall be fixed to the “I” beams by means of clamps with supporting bolts.

4.2.7 The clamps shall be arranged so that the wire loops are aligned with the winches and perpendicularly located to them, in a way to maintain the wire rope always vertical.

4.2.8 To prevent the clamps from sliding, end bolts shall be installed at the ends of each beam.

4.2.9 All parts and components of the scaffold shall be provided with easy access for inspection and repair, as well as free longitudinal access.

4.2.10 The connection between winches and scaffold floor shall be ensured by steel frames duly sized and suitably fixed.

4.2.11 Suspension winches shall meet the following conditions:

a) shall have devices to block the retro-action of the drum;

b) shall have a safety lock.

4.3 Light Suspended Scaffolding, mechanical

4.3.1 Light suspended scaffolding, mechanical, shall be supported by balanced beams or hooks with dimensions suitable for the intended application, fixed to avoid horizontal stresses.

4.3.2 The end of the hook or other special device facing the building shall be tied by a wire rope to a holding point that is suitable to hold the tensions to which it will be subject.

4.3.3 It is not permitted to fix hooks or tying devices directly to brick walls.

4.3.4 Wood boards shall be inserted between the edge and the hook to shim it.

4.3.5 Winches of light suspended scaffolds, mechanical, shall be fixed to the end of the working platforms, and the interconnection of platforms or the extension of platforms in balance are not allowed.

4.3.6 The floor shall be firmly secured to the supporting frame, as well as the handrails to the stanchions, to prevent movement. A bodyguard shall be provided in the interior side.



4.3.7 Winches shall be provided at least with three safety devices, two of those shall be automatic.

4.4 Cantilevered Scaffolding

4.4.1 Cantilevered scaffolding does not have platforms suspended by wire ropes.

4.4.2 The attachment system of the scaffold to the existing structure shall ensure that the resistant moment is at least three times the applied moment.

4.4.3 The cantilevered scaffolding structure shall be calculated and designed to the applied stresses in each case.

4.4.4 During assembly, the projected area of the scaffold on the floor plus 3.00 m for each side shall be blocked and made inaccessible.

4.4.5 All components of the scaffold shall be fixed, and loose parts are not allowed at all.

4.4.6 The scaffolding structure shall be suitably braced and anchored to a point of no movement.

4.5 Laid Scaffolding

4.5.1 They may be made of metal or wood, and shall have beams laid on bases suitable to resist to the applied loads, and compatible with the soil resistance.

4.5.2 The structure shall be duly braced and anchored, or tied down, to obtain a no movement condition. Quantity of these tied-downs on vertical surface scaffolding shall be of one for each 36.00 m2, and they shall have a 6.00 m spacing in any direction. The beams shall be perfectly aligned.

4.5.3 Work in scaffolding laid on workhorses is permitted provided that the height is not greater than 2.00 m above the ground where it is laid, and the width shall be a minimum of 0.60 m.

4.5.4 It is recommended that beams on wooden scaffolding shall not have a cross section with a side of less than 0.075 m or diameter of less than 0.085 m, braced, and its height shall not exceed 12.00 m, without specific design. Nails for wooden scaffolding shall not be smaller than 18 x 27 (3 mm x 60 mm).

4.5.5 Beams for metallic scaffolding shall have a minimum wall thickness of 2.65 mm and minimum diameter of 42.20 mm (note 1).

4.5.6 Scaffolding platforms shall have a minimum width of 0.60 m and a minimum free height of 1.75 m.

4.5.7 Before installing any material lifting device to the scaffold, the installation point shall be chosen so that the safety and stability of scaffolding are not compromised.

4.5.8 Any scaffolding shall be provided with suitable personnel access to each level without blocking passageways and compromising personnel safety. Vertical access




shall be by ladders, rope ladders are allowed, fixed to the scaffolding system or by independent staircase.

4.5.9 Mobile scaffolding shall consider that the moving system (casters or similar) resists at least one and one half times the average loaded scaffolding weight. In case of casters, they cannot have a diameter less than 0.13 m, and shall be provided with brakes.

4.5.10 The structure of mobile scaffolding shall have convenient bracing to support stresses during movement without deformation, and shall be fixed and tied down during use.

4.5.11 Mobile scaffolding shall make a rigid assembly, without loose elements that may represent a fall risk or that will disassemble during moving. During movement, the assembly shall be perfectly balanced, without risk of tilting. It shall not be permitted moving scaffolding with people or loose material on any point of the scaffolding.

4.5.12 No mobile scaffolding shall have its height greater than four times the smallest dimension of the base.

4.5.13 On mobile wooden scaffolding, the connection between beams, cross members, bracings and longitudinals shall be with passing-through bolts of french or machine type.

4.5.14 Mobile scaffolding shall be permanently locked, except when in movement.

Note (1): BS 1387

nbr 6494scaffolding engl

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