Every covering provided for an opening shall be
(a) so constructed as to prevent the fall of persons, materials and
articles; and
(b) clearly and boldly marked as to show its purpose or be securely fixed
in position.
Every board or plank forming part of a working platform, gangway or run shall
(a) be of sound construction, adequate strength and free from patent
defect;
(b) be of a thickness capable of affording adequate security having regard to the distance between the supports and be not less than
200 millimetres in width and not less than 25 millimetres in thickness or not less than 150 millimetres in width when the board or plank exceeds
50 millimetres in thickness;
(c) not protrude beyond its end support to a distance exceeding
150 millimetres unless it is sufficiently secured to prevent tipping;
(d) rest securely and evenly on its supports; and
(e) rest on at least 3 supports unless, taking into account the distance between the supports and the thickness of the board or plank the conditions are such as to prevent undue or unequal sagging.
(1) Subject to subsection (2), every working platform, gangway and run shall
be closely boarded or planked.
(2) Subsection (1) shall not apply to a working platform, gangway or run
(a) consisting of open metal work having interstices none of which exceeds 4 000 square millimetres in area; or
(b) the boards or planks of which are so secured as to prevent their moving and so placed that the space between adjacent boards or planks does not exceed 25 millimetres.
if there is no risk of persons below the platform, gangway or run being struck by materials or articles falling through the platform, gangway or run.
(1) Subject to subsections (2) and (3), the width of any working platform,
gangway or run shall be not less than 400 millimetres.
(2) Subject to subsection (3), the width of any gangway or run used for the
movement of materials shall be not less than 650 millimetres.
(3) Where it is impracticable by reason of limitations of space to provide a working platform, gangway or run of the width required by subsection (1) or (2), then, in lieu of complying with that subsection, the working platform, gangway or run shall be as wide as is reasonably practicable.
6.2 Dismantling of metal scaffolds
6.2.1 The dismantling work shall be done by trained workmen under the immediate supervision of a competent person. (Regulation 38E of the CSSR)
6.2.2 Sufficient time should be allowed for the dismantling work to be
conducted safely.
6.2.3 The scaffold to be dismantled should be checked for its strength and stability beforehand.
6.2.4 No components, which endanger the stability of the remaining structure, should be removed. Unless necessary precautions have been taken, all the ties and bracings should remain secured in positions.
6.2.5 If dismantling has reached the stage at which a critical member has to be removed, for example, a tie or a brace, the stability of the structure should be assured by fixing a similar or otherwise adequate member in place lower down before the member to be taken out is removed.
6.2.6 All the stacked materials and debris placed on the scaffold should be removed.
6.2.7 Dismantling sequence should be planned and that sequence of dismantling sections of the scaffold should be logical and determined with due consideration of the scaffolders’ safety. Dismantling work should be carried out according to the plan. Because changes may have been 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. Also, the procedure of dismantling should be orderly and planned and should proceed generally from the top in horizontal sections.
6.2.8 If the scaffold is defective, it should be made good before dismantling
commences.
6.2.9 Scaffolds should not be dismantled in vertical sections from one end towards the other unless special consideration is given to ties and bracings.
6.2.10 A scaffold might have been temporarily stabilized during construction by rakers that have been subsequently removed. If the level of the lowest tie point is high, temporary rakers or other structurally adequate means of supports should be built up from the ground to achieve stability of the partly dismantled scaffold.
6.2.11 Safe access to and egress from the place of work should be provided for the scaffolders.
6.2.12 The scaffold to be dismantled should be fenced off at the ground level/ public area to prevent persons entering the work area and warning notices should be posted up in the vicinity.
6.2.13 Steps shall be taken to ensure that scaffolding materials are not thrown, tipped, or shot down from a height where they are liable to cause injury to any person on or near the construction site; and where practicable, properly lowered in a safe manner by means of a lifting appliance or lifting gear (Regulation 49 of the CSSR). Scaffolding materials should include the tubes, the scaffold boards or planks, the metal couplers for scaffolding purposes, etc.
6.2.14 All materials should be lowered to the ground and not stored on the scaffold. In the case where the 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, by using the materials recovered from the upper lifts.
6.2.15 Every scaffolder involved in the dismantling work at height should wear safety belt attaching to suitable and sufficient anchorage and suitable fixings, for example, the provision of an independent lifeline that extends from an independent anchorage point to which a lanyard of a safety belt is attached using a fall arresting device. Scaffold members should not be used for anchorage purpose. Whenever practicable, safety nets for fall protection of scaffolders should be used. Further reference should be made to the Guidance Notes on Classification and Use of Safety Belts and their Anchorage Systems prepared by the Labour Department.
6.2.16 All the trades on the site should coordinate and collaborate closely with the contractor engaging in scaffold dismantling work regarding the safety precautions necessary during various stages of the work.
6.1 Inspection and maintenance of metal scaffolds
6.1.1 The scaffold shall not be used on a construction site unless the scaffold has been inspected by a competent person before being taken into use for the first time and at regular intervals not exceeding 14 days immediately preceding each use. (Regulation 38F of the CSSR)
6.1.2 The scaffold shall not be used on a construction site unless the scaffold has been inspected by a competent person after any substantial addition, partial dismantling or other alteration. (Regulation 38F of the CSSR)
6.1.3 The scaffold shall also be inspected by a competent person since exposure to weather conditions likely to have affected its strength or stability or to have displaced any part (Regulation 38F of the CSSR). Such weather conditions would be heavy rain, storm, etc. affecting its strength and stability.
6.1.4 The competent person should check the strength and stability of the scaffold and ascertain whether it is safe for workers to stay on or it needs to be repaired. Inspection may be done more frequently depending on the usage and conditions of the scaffold.
6.1.5 Defects found during the inspection should be rectified immediately.
The scaffold shall not be used unless a report has been made in Form 5, which specifies the location and extent of the scaffold on the site and includes a statement to the effect that the scaffold is in safe working order, by the competent person carrying out the inspection referred to in Sections 6.1.1, 6.1.2 and 6.1.3 above (Regulation 38F of the CSSR). The Form 5 should be displayed in prominent positions on the scaffold.
6.1.6 For unsafe scaffolds, effective measures should be taken to prohibit their use. They should be marked to show that they are unsafe and should not be used.
5.4 Falsework
Falsework is a temporary structure used to support a permanent structure while the latter is not self-supporting. In Hong Kong, falsework is commonly used to support formwork for in-situ concrete construction, and from time to time, workers have to work on or in the vicinity of the falsework. Total or partial collapse of falsework may lead to serious accidents. Inadequate design, defective or sub-standard materials, faulty setting out, inadequate supervision and procedural inadequacies such as improper loading and dismantling are the common causes of their collapses.
The design, construction, use and dismantling of falsework should comply with BS 5975 or other equivalent national/international standards or provisions. The falsework should be designed by professional engineer and when the case is warranted, an independent checking professional engineer should be arranged to cross-check the design and the erected falsework. The followings highlight the good practices sometimes overlooked in order to prevent collapse of falsework on construction sites in Hong Kong:
5.4.1 Engineering considerations
(a) The framing of structural members and details of construction should be justified in accordance with recognized engineering principles to meet the loads to which the falsework may be subjected. The loads include vertical loads and lateral loads, and the common ones are given below:
Vertical Loads from: (i) Self-weights.
(ii) Permanent works to be supported.
(iii) Impact due to placing permanent works (e.g. free fall of wet concrete).
(iv) Construction operations: A minimum of 1.5kN/m2 should be allowed for the operations.
(v) Temporary storage of materials.
(vi) Traffic loads.
(vii) Plant: The operating loads should include the weight of plant,
dynamic effects and vibration effects. (viii) Induced wind loads.
(ix) Uplift loads due to wind and floatation.
Lateral Loads from:
(i) Wind loads.
(ii) Hydrostatic pressure: It may come from wet concrete or an external source.
(iii) Lateral earth pressure.
(iv) Differential movements of supports such as ground movements.
(v) Vibration effects such as those due to concrete vibrations,
concrete pumping operations or piling operations nearby. (vi) Flowing current.
(vii) Unsymmetrical distribution of vertical loads, such as effects
due to unbalanced concrete placing.
(viii) Unsynchronized jacking of permanent works against
falsework.
(ix) Sway of falsework.
(x) Buckling of props.
(xi) Eccentricity of vertical loads due to construction deviations,
especially for falsework on sloping ground. (xii) Dynamic effects from plant and equipment. (xiii) Casting up of concrete against existing works. (xiv) Discontinuity in the soffit formwork.
(b) The minimum lateral loads should be taken as the greater of:
(i) the most adverse combination of the above lateral loads; or
(ii) 2.5% of the vertical loads taken as acting at the points of contact between the vertical loads and the supporting falsework.
(c) Each falsework member should be designed for the most adverse combination of vertical loads and lateral loads. The reduction of permissible axial stress for used materials and the reduction in strength with the increase in the number of stages of scaffold should be considered.
5.4.2 Structural steel works
(a) Use structural steel in accordance with the Code of Practice for the Structural Use of Steel issued by the Buildings Department or other equivalent national/international standards or provisions.
(b) Steel hollow sections exposed to the weather should have walls not less than 4mm thick, unless protection against corrosion is effectively provided and maintained.
(c) Steel members of hollow sections are often used repeatedly. As some damage is expected after each cycle of use, they should be inspected prior to reuse and be discarded if found unsatisfactory. For reused members, an allowance for strength reduction should be considered.
5.4.3 Lateral stability
(a) The key to keep falsework safe is the provision of adequate lacing and bracing to prevent the falsework from buckling or sway.
(b) Lacing are horizontal members connecting props together to reduce the unsupported length of the props. They may behave as struts or ties, and help to transmit lateral forces to bracing members.
(c) Bracing generally are inclined members connecting lacing members and props. They transmit lateral forces to the foundations.
(d) Lacing and bracing must be recognized as critical members
in falsework. They should be adequately provided in compliance with recognized engineering principles. They should be clearly shown in the drawings in the three principal directions to illustrate professional engineer’s intentions. Undue movement due to lateral forces, torsion or impact forces should be prevented. A properly planned loading sequence will alleviate torsional effects.
(e) If possible, the falsework should be tied back to stiff parts of
completed permanent structures to enhance lateral stability.
(f) The framing of falsework should give a robust and stable structure, especially for falsework near vehicular traffic. The structure should be designed and constructed so that it is not unreasonably susceptible to effects of impacts or vibrations. Damage to small areas of a structure should not lead to collapse of major parts of the structure. To avoid accidents, adequate headroom, lighting, warning signs and signals, and impact protection measures should be provided.
5.4.4 Cantilever members
(a) The end portion of a prop protruding beyond a lacing member should be considered as a cantilever member unless adequate means is used to brace the end portion. Such end portion often occurs at the top or at the base of a prop.
(b) If a prop has an extensible portion at the end, the joint between the extensible portion and the prop itself allows a little angular movement. Such movement constitutes a weak point in the falsework. Unless otherwise justified by recognized engineering principles, the extensible portion should be adequately laced and braced at the end where the extension exceeds 300mm.
5.4.5 Fastenings to concrete or masonry
All fastenings to concrete or masonry for structural uses should be designed in accordance with recognized engineering principles and the manufacturer’s recommendations. The construction details and instructions for use should be clearly specified in the drawings and specifications.
5.4.6 Lacing, bracing & wedging
Falsework will not be safe without adequate lacing, bracing and wedging. Workmen should not be permitted to install lacing, bracing or wedging in favour of their own decisions. All the details shown in the drawings and specifications should be followed.
5.4.7 Test on falsework equipment
(a) In Hong Kong, much of the falsework equipment in use is of proprietary design that has been purchased or hired. Detailed information, such as that provided by the manufacturer, is of great importance in inspecting such equipment if the inspection is to be carried out by those not familiar with its usage. Very often, technical information relating to the performance of such material has been compiled from test carried out during the
development of the equipment. It is desirable that test procedures for similar systems or components should be standardized in such a way as to make the critical properties comparable. Worldwide accepted methods of test for falsework equipment such as those laid down in BS 5507 and BS EN 1065 can be used by manufacturers in compiling the necessary design data.
(b) Where the strength of a manufactured component cannot be ascertained by applying design criteria recommended in this Code, testing should be carried out at the prototype stage of development in order to obtain results, including ultimate behaviour, on which design data for the component or system can be based.
5.4.8 Loading sequence/pattern
(a) Sequence of placing loads on the falsework including loads due to temporary storage and prestressing should be planned and taken into account in the design.
(b) The sequence of placing permanent works such as wet concrete should comply with professional engineer’s intentions expressed in the drawings and specifications. If such a sequence has not been specified, advice on the loading sequence should be sought from the professional engineer. If the professional engineer considers that no specific sequence is needed, then the sequence of working should be planned by spreading the loads evenly on the falsework. Uneven distribution of loads, such as out-of-balance effects due to unsynchronized jacking of permanent works against the falsework by more than one jack may lead to uplifting or instability.
(c) Concrete pouring by crane, skip, barrow, dumper or pumping produces impact forces. The free fall should not exceed 0.5m unless otherwise permitted by professional engineer. Heaping of wet concrete within a small area should be avoided. Unless otherwise permitted by the professional engineer, equipment for concrete pumping should not be fastened to the falsework.
5.4.9 Undue movement of falsework
The works under construction should be suspended immediately when any undue movement of the falsework occurs. In addition, the falsework should be labelled to show that it is unsafe and should not be used. Investigation on the causes of the undue movement should be carried out immediately by competent person with the help of the drawings and specifications. If any doubt still exists, the competent person should immediately seek professional engineer’s advice.
5.3.3 Modular scaffolds
(a) Modular scaffolds are mainly made of tubes, angle steel, I-beams, channels, steel columns, etc. Most systems of modular scaffold are composed of standards with preformed connectors welded at intervals along their length to which ledgers are fixed with a proprietary clamping or wedging arrangement. (See Figure 9)
(b) Each scaffold should be constructed in accordance with the design and drawings of professional engineer. If there is any need to deviate from the original design and drawings, the scaffold should be re-designed by professional engineer.
(c) A modular scaffold system mainly consists of the following components:
(i) Standards
They come in a variety of lengths and have preformed connectors welded at fixed distances along their length. A spigot arrangement or socket is provided at one end of the standard for extension purposes.
(ii) Ledgers
They are in varying lengths with connectors welded to each end. The connection is made when the wedge, cup or bolt is hammered or screwed tight.
(iii) Transoms
They are generally made to support scaffold boards or stagings. The ends of the transoms are connected to the standards in the same way as the ledgers. Some systems might require intermediate transoms to support the boards or stagings.
(iv) Bracings
Bracings in each direction are made to fit the different bay sizes. Some systems use standard tubes and fittings for bracings.
(v) Scaffold boards
They are also called stagings and come in a variety of lengths, thicknesses and widths. Decking is seldom interchangeable as each system is designed to sit exactly on the narrow lip of the transom. Scaffold boards are often made from steel with a slip resistant surface and pre-drilled drainage holes. These systems allow for the attachment of proprietary toe-boards.
(vi) Ties
Ties are generally formed in tube and fittings.
(vii) Adjustable base plates
They are essential and care should be taken to establish their safe working loads and whether they are designed for heavy or light duty use.
(d) These scaffolds all employ different patented locking devices (wedges, locking pins, etc.) and are designed to different specifications. It is therefore difficult and sometimes dangerous to interchange one system with another. As such, there should not be a mixing of two different systems in one scaffolding system.
(e) It is vital that specific instruction, training or an erection handbook be provided for the workmen erecting any modular scaffold. Users should pay strict attention to their loading capacities and methods of erection published in the manufacturer’s instructions. There is no common specification for modular scaffolds.
5.3.2 Plane frame scaffolds
(a) This type of scaffolds is commonly used for access to ceiling, soffits, walls and columns for carrying out light work, for examples, plastering, painting, conduit installation, cleaning and similar operations. Each scaffold comprises an arrangement of vertical frames and bracings supporting closely boarded working platforms at required levels.
(b) The design and loading of plane frame scaffolds should be in accordance with Section 5.1 of this Code. The height of a vertical frame is normally 1.7m to 2m (depending on the type of the frame used) to give adequate headroom for passage. The height limits of the free-standing plane frame scaffolds and tied plane frame scaffolds should follow professional engineer’s design.
(c) A plane frame scaffold system mainly consists of the following components:
(i) Ties
– It is essential for all plane frame scaffolds to be securely tied either to surrounding walls, columns or such similar structures throughout the length and height to prevent the scaffolds from movement, tipping into or away from the wall and structure.
– The ties should be located not more than one bay from the ends of the scaffold and thereafter at intermediate spacing of not more than 3 bays or 7.5m apart, whichever is the lesser. The ties should be as far as practicable be fixed at staggered positions at every two lifts.
– The ties should be perpendicular to the longitudinal plane of the scaffold and where it is not practicable, the deviation from the perpendicular should not exceed 15o. Every tie should be capable of withstanding tensile or compression force applied along the length of the tie.
– Besides, corner-ties are also necessary to maintain the
stability of plane frame scaffolds. (See Figure 5 for details) (ii) Bracings
– Each plane frame scaffold should be effectively
braced to restrain from lateral movement. Cross bracing should be of such length as to square and align vertical members while diagonal bracing should be braced at about 45o to the horizontal. (See Figure 6 for details)
– The scaffolds should also be braced horizontally at intervals of not more than every five lifts. The joints for the bracings should be continuous or lapped. All the brace connections should be made secure.
(iii) Joints
A joint tube is an internal fitting for joining two standards end to end. A joint tube should be self-centring so that equal length of the tube can be embedded into each of the standards. When uplift may occur, plane frames should be locked together vertically by pins/bolts & nuts. (See Figure 7 for details)
(iv) Flip locks
Flip locks should be installed at upright position so as to prevent the cross bracing from detaching out of the standards. (See Figure 6)
(v) Base plates
Legs of the plane frame scaffold should be set on adjustable base plates or plain bases on foundations adequate to support the maximum designed vertical and horizontal loads. The erected scaffold should be plumbed and levelled. (See Figure 6)
(vi) Fork-heads
A fork-head is a U-shaped assembly at the top of a standard for bearers of formwork to rest on. Fork-heads should not be used as base plates in supporting the scaffold.
(vii) Castors
A castor is a swiveling wheel secured to the base of a vertical member for the purpose of mobilizing the scaffold. All scaffold castors should be designed for strength and dimension to support the designed working load. Castors should be provided with a positive wheel and swivel lock, or equivalent means, to prevent movement and rotation while the scaffold is in place. Castor stems should be secured in the scaffold to prevent them from accidentally falling out at any time.
(d) Safety requirements relating to the boards or planks forming a working platform, guard-rails and toe-boards of a working platform, access to and egress from a scaffold, etc. for prevention of falls are the same as described in Section 5.1.4. (See Figure 8 for details)
5.3 Proprietary scaffold systems
5.3.1 A proprietary scaffold system comprises a complete set of prefabricated components of unique design, capable of erection without any other components. It will be necessary for the manufacturer of the system to provide a complete set of instructions, compatible with this Code and sufficient to ensure the safe erection and use of the scaffold. Plane frame scaffolds and modular scaffolds are the most commonly used proprietary scaffold systems in Hong Kong. When using a proprietary type scaffold system, the scaffold system should be designed by professional engineer making reference to the manufacturer ’s instructions and in accordance with recognized engineering principles or other national/international standards or provisions. Reference should also be made to Section 5.4 of this Code. An independent checking professional engineer should be arranged to cross-check the design and the erected scaffold when the case is warranted. As a general guidance, the following safety procedures should be taken into account:
(a) The scaffold should be erected in accordance with professional engineer’s design in which reference should also be made to the manufacturer’s recommendations or national/international standards or provisions. However, the professional engineer should avoid using two or more standards in one single design.
(b) Regarding the strength of steel elements and frame scaffold, sampling tests, loading tests and mechanical tests (for example, yield stress, tensile strength, compressive strength, elongation, bend and buckling tests), reference should be made to the procedures laid down in relevant standards of the International Organization for Standardization or equivalent procedures.
(c) Design involving structural steel should be in accordance with the Code of Practice for the Structural Use of Steel issued by the Buildings Department or other equivalent national/international standards or provisions.
(d) The height limit of each proprietary scaffold system should be checked.
When the number of stages of scaffold increases, the strength of the
scaffold would be reduced.
(e) Rusting of scaffold members would reduce the strength of the scaffold. Therefore, attention should be paid to the severity of rusting of scaffold members. When deciding the strength reduction factor, reference should be made to relevant national/ international standards or provisions.
(f) The scaffold should be levelled until proper fit can easily be made.
Frames or braces should not be forced to fit.
(g) Each frame or panel should be effectively braced to restrain from lateral movement. All brace connections should be made secure in accordance with the manufacturer ’s recommended procedures.
(h) A mixed structure of different proprietary systems should not be used.
(i) When there is any deviation from the standard scaffold, or when sheeting or fan is added, or when other changes are made which will vary the structural loading or arrangement of the scaffold, professional engineer should be consulted well beforehand.
(j) The tying and its attachment to appropriate points on the scaffold should be arranged in accordance with the design.
(k) Suitability of the support should be checked against those requirements mentioned in Section 5.1.2.
Metal Scaffold Systems | Access Tower | Working Platform | Repropping| Formwork 