Similarities and Differences between Scaffolds and Formwork Structures

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1 Coverage of Talk 27 Mar N. KRISHNAMURTHY SAFETY CONSULTANT AND TRAINER Website: Similarities and differences between scaffolds and formwork structures 2.Why temporary structures are more critical than permanent structures 3.Case studies of scaffold and formwork structure accidents 4.How risk management can be used to reduce scaffold and formwork failures Acknowledgements and References 1. Mr. Tan Kai Hong for certain information and pictures of workplace accidents. 2. Case Studies of Construction Industry, WSH Council, Singapore, June 2008, 116p. 3. Formwork and Scaffolding Collapses, IMIA Working Group Paper WGP 80 (13), IMIA Conference, New Delhi, India, Sept It is better to be careful a hundred times than to get killed once. Mark Twain 2 Scaffold and Formwork Structure Scaffold & falsework are similar, structurally & functionally 1. Similarities and Differences between Scaffolds and Formwork Structures Formwork Structure (=Formwork + Falsework) 3 4 Scaffold & Formwork Structure Similarities If we consider the pure formwork part as mould for wet concrete until it hardens, the comparison may be limited to scaffolds and falsework, i.e. the support for formwork. Similarities: Both are temporary structures Both bear loads during construction of permanent structures Both will be reused a number of times for short periods Both are susceptible to incidents and accidents Both involve working at height Both are given the same secondary importance compared to permanent structures Both need special design, fabrication, inspection, maintenance and supervision to be safe 5 Scaffold & Formwork Structure Differences Scaffolds bear weight of persons and tools (and occasional supplies), while falsework must bear the much heavier weight of wet concrete and its formwork. Scaffolds bear mostly static loads, while falsework must bear widely variable dynamic loads in addition. Scaffold is dry work while formwork is wet work. Rescues must be made before concrete sets. 6 1

2 2. Why temporary structures are more critical than permanent structures 7 Permanent vs. Temporary Structures Unlike permanent structures, temporary structures Do not have assured or well-prepared foundations Are not designed as well or in as much detail Are not used or even seen by the ultimate customer Have often built-in compromises in quality and strength Are put together at site from numerous components Most components are already used and some damaged Are erected generally by less skilled temporary workers Are not checked as rigorously or as frequently Are not inspected as meticulously Are not supervised as strictly Are not maintained as well Do not have their faults rectified as promptly or fully Are the first to compromise on safety when time or budget presses hard 8 Permanent vs. Temporary Structures Unlike permanent structures, temporary structures Do not have assured or well-prepared foundations Are not designed as well or in as much detail Are not used or even seen by the ultimate customer Have often built-in compromises in quality and strength Are put together at site from numerous components Most components are already used and some damaged Are erected generally by less skilled temporary workers Are not checked as rigorously or as frequently Are not inspected as meticulously Are not supervised as strictly Are not maintained as well Do not have their faults rectified as promptly or fully Are the first to compromise on safety when time or budget presses hard 9 The handicaps of being temporary Temporary structures cannot be a line-item to customer. The word temporary suggests that: We can get by with compromises, deficiencies, and even occasional violations Fact: As the ultimate user is not around and the public does not see temporary structures, accidents are more likely to happen, and any flaws may have far- reaching adverse effects. We can occasionally subject the structure to temporary over-loads. Fact: This implies over-stressing the material which may not be put together in the correct fashion, and which may already be damaged or yielded in even hidden locations. Inexperienced people can design and erect them. Fact: Temporary structures need more expertise! 10 Increased Risks in Temporary Structures The increased risks in temporary structures formwork and falsework in particular are as follows: Design by site staff who may not have the necessary design background to be doing it; A general view that temporary work should be designed by the more junior staff (such structures not deserving the serious attention of 'real' structural engineers); Design-in-a-hurry i or Design-by-guess ; Insufficient consideration of possible accidental loads; Careless assembly; Lack of proper quality control, or quality control by personnel with insufficient experience of temporary work and the realities of site operations; Overloading of temporary work by personnel who do not understand these matters. Adapted from: Case studies of scaffold and formwork structure accidents 12 2

3 Fall from Mobile Scaffold, 2/7/2002 Fall from Scaffold, 21/4/2001 Two workers were wet- ting 4th storey RC beam for skim coat, with one of them walking backwards on the work platform. Either the worker fell while working or while climbing li bi d down. Guardrails at the two ends were only secured on one side to allow access from the ends. No access ladder. Subcontractor s partner fined $9000, and occupier fined $5000 Fall from scaffold, 18/4/2004 fallen with the mobile tower from 4th storey to the ground floor and died. Mobile tower s Height/Width ratio = 4.3 (>3)*, not tied, legs on uneven floor, hence unstable. No supervision during erection** and use Occupier fined $18,000 for*, and $15,000 for ** workers dismantling external scaffolding When leaving for lunch break, one fell from scaffold, hitting worker already on the ground, and died. Safety y harness worn but had been disconnected from lifeline for descent. Supervisor not present. Deceased and one other worker had no work at height training, and were not certified for rigging. Occupier fined $12,000 A worker tidying up metal scaffolds fell down and died. He had safety belt on, but had no anchor of lifeline to clamp it to. None of them was trained th storey worker fell on to scaffold platform through openings on all floors. Supervisor did not actually check work area for hazards. Worker not wearing safety harness; not attended SCOC* Occupier & Site Mgr., $18K for no SWP+Occ.$2K for no* 17 Scaffold Collapse 23/10/2004 Fall from Height, 3/7/2004 He appeared to have 13 Fall from Scaffold, 6/6/2003 While getting ready for painting work at Worker instructed to install bonding bars at duct area One worker killed. No supervision Design flaw inadequate training no Risk Assessment A simple tie would have been enough to prevent the fall 18 3

4 Worker fell 9 storeys & died. He was not wearing safety belt or harness. Scaffold had not been checked and d certified tifi d for f 3 years. No Risk Assess. No SWP No safe access plan Inadequate safety training Fines: $25K & $40K Table Form Mishandling, 15/5/2005 Fall from Scaffold 9/5/2005 While workers were shif- ting table form from Floor 15 to Floor 18, obstructed by overhead beam. Worker separated table form into two parts and started pushing it. It hit some planks, toppled and killed the worker. Did not follow safe work procedure No guidance at site No supervision Fall from Scaffold Mobile Scaffold Collapse 7/2006 Mobile scaffold fell over worker during shifting Worker killed Scaffold may have struck obstruction during shifting, and pp it. momentum toppled No proper planning No RA No supervision Worker tasked to paint roof elements under roof of 6-storey building He fell off the scaffold work platform and died. No guardrails around p work platform No proper access to working platform Fall from Suspended Scaffold Fall from Scaffold Worker tasked to dis- mantle metal platform fell 4.5m to the ground and died. No proper access No risk assessment Required PPE not provided 23 Worker intending to paint walls adjacent to a ledge tried to climb out of a suspended scaffold onto the building ledge but lost his footing and fell from the 9th storey, died. No RA, no PPE No supervision 24 4

5 Scaffolds are generally for workers and tools while falsework is for formwork, and concrete casting loads Scaffold live loads are of the order of 1.5 to 2kN/m2, while falsework live load is mainly concrete weighing 25kN/m3, which even for 300mm depth slab is 7.5kN/m3. Scaffold work is generally dry, static work, while falsework wet dynamic work of concrete casting and is subject to wet, vibration, with very hazardous materials which will set hard within a short time. Scaffold erection is relatively better organised and more visible at all times than falsework which involves more components and variable sizes, and more adjustments and actions. Scaffold failures may generally be localised while formwork/falsework collapse can be massive and progressive 25 Formwork Failure, 7/1/1999 Why must we be stricter with formwork/falsework than with scaffolds? assessment done 27 Compassvale Primary School Seven workers injured Overloading during concreting Inadequate supervision Formwork Failure, 23/4/ There were inadequate bracing in shoring system 28 Demarcation of heavy loading zones Zones designed for heavy loading must be demarcated. The formwork structure was not designed by PE Formwork Collapse 15/6/1999 supervision No risk Dead load of collapsed beam in excess of 2160Kg/m2 26 Formwork Collapse 15/5/1999 NIE Complex, collapsed Saturday Not scaffold as reported but formwork Five workers fell 8m, badly injured but survived Rush job, at night and during weekend Not enough Condominium transfer beam collapsed while being cast Vehicular ramp for a 6-storey industrial building collapsed at the sloped portion. Ramp was supported with conventional steel frames. Lack of diagonal bracing Defective & deformed members reduced loading capacity 30 5

6 Formwork panel fixed at 16th storey, fell to ground, killing site supervisor and worker on it. It had just been shifted from 15th storey by tower crane. Bracket not secured to support. No RA or SWP for the modified system. No safety training record Occupier fined $30,000 Subcontractor fined $160,000 Fall from Formwork 11/2005 Formwork Collapse, 19/11/2004 No proper supervision No RA Viaduct, Portugal, 2010 No edge protection 32 Bridge Formwork Collapse, Poland, 2009 buting to collapse: The main cause was Whole length of fresh concreted section of deck, together with supporting structure collapsed at once during pouring One dead, 8 injured Uneven load distribution during pouring of the concrete Formwork Panel Failure BUGIS MRT Incident, 19/7/2013 Fell 8m 31 Two factors contri- lack of bracing to adequately counter lateral forces. Large quantities of reinforcing bars were temporarily stored on the bridge deck. These bars imposed a load not considered in the falsework design. Collapse similar to Fusionpolis in S pore Worker plunged to death through opening in formwork Formwork collapse 2 dead, 9 injured The company allegedly failed: To ensure that the formwork structures were inspected and certified by a professional engineer before the placement of concrete, and, To ensure a formwork supervisor regularly inspected the structures. 35 Formwork wall panel gave way; worker fell 6m, and panel fell on him, killing him. Foreman knew top tie rods of panel had been removed but did nothing about it. 36 6

7 Fall from Concrete Hopper Worker was riding cage attached to hopper to release control lever for hopper to dump concrete in formwork. Cage caught on a re-bar, dislodged and hit another rebar, and fell 20m with worker, killing him instantly. No securing device to prevent accidental dislodgement. No risk assessment No proper SWP 37 Bracing, a most critical element Many scaffold and falsework failures are due to missing or inadequate bracing. Mere horizontal bracing completely useless to prevent sway Unless one or both ends are prevented from moving Buckling will reduce capacity to a fraction of designed value! 38 Unsafe Act or Unsafe Condition? THE RIGHT WAY Is this unsafe act Ladder and? Fall by worker Prevention by Travel or unsafe Restraint condition by mana- gement? No need for body harness 39 Give Everybody Body Harness? 1. As PPE, it is the least effective control, to be chosen after all other controls have been explored & exhausted 2. Cannot be used below about 5.5m ( Fall Clearance ) 3. Need well-designed anchors, and correct anchoring. 4. Must fit the user, and must be stocked in various sizes 5. Must be worn correctly, if loosely worn, can be injurious 6. Must be used correctly, with 100% tie-off 7. Much more costly than other PPE 8. Needs more training, better maintenance, and more supervision, than other PPE 9. Introduces fresh hazards like hitting objects during fall 10. Needs a prompt and proper on-site rescue system Otherwise, death by suspension trauma likely 11. Make the all-day wearer very uncomfortable Causing him to make mistakes, and/or Reducing productivity ( will discard!) USE ONLY WHEN AND WHERE REQUIRED BY CODE! More in author s paper on body harness in his website How risk management can be used to reduce scaffold and formwork failures 41 Causes of Scaffold/Formwork Failures No or improper risk assessment Inadequate or incomplete design for the actual loading No or inadequate bracing Inadequate implementation of design in erection Loading of unstable structure Overloading of structure Lack of training of supervisor/worker and/or SWP Worker not following SWP (i.e. Supervisor Almost all not ensuring that SWP is followed) these are No proper access/egress failures of Work platform not provided guardrails existing Worker not given proper PPE controls! Worker not wearing or correctly using PPE Worker not given proper anchorage for harness Worker not anchoring harness to available anchor No or inadequate supervision 42 7

8 Design of Formwork Str. (MOM 18/1/2014) PE appointed to design any formwork structure should be appointed in writing with a detailed work scope; PE shall comply with Part IX of the WSH (Construction) Regulations 2007, and make reference to the Singapore Standard 580:2012 (or any revision thereafter) and the various formwork guidelines published by WSH Council; All formwork structures shall be capable of sustaining the total dead load, live load and impact load imposed on the formwork structures with a minimum safety factor of 2; PE shall ensure that his design can be executed safely by any person who constructs or uses the formwork struct.; PE should ensure that he is competent in the use of any proprietary formwork system used in his design; and Mix-and-match of formwork systems and components should be avoided. If unavoidable, PEs shall ensure that overall strength & integrity of such systems are retained. 43 SS580: Risk assessment A risk assessment specific to the project shall be conducted to identify hazards prior to commencement of the formwork activity. By assessing the risks that may occur, appropriate risk control measures can be undertaken so that reasonably practicable measures can be taken to eliminate or control the risks arising from such hazard. The risk assessment and control measures shall be documented in a risk register and the information made available. Other vital information on safety, design, erection, transfer, alteration and dismantling shall be included in the risk register to ensure complete documentation and enable effective communication of the risks and controls to parties involved, and for inspection by authorities. 44 Risk Management Risk management, to eliminate risks or mitigate their effects, consists of three steps: Hazard identification Assessment of risk from likelihood and severity, by risk matrix Risk control according to recommended hierarchy Most of the accidents in Singapore have been declared to be due to lack of an adequate risk assessment, meaning the safety team had not identified or controlled some risk. Use risk management principles to cover hazards beyond conventional harm to health, such as the ones listed: Structural weaknesses Construction flaws Worker behaviour errors Supervision deficiencies Safety violations Almost all these are failures of existing controls! 45 Risk Management in Practice We know the hazards in scaffold and formwork accidents We know the existing controls to eliminate these hazards or to mitigate their effects. We provide enough safeguards, PPE, and training to implement the controls. What we lack is supervision to ensure that these safeguards are actually implemented and followed by all concerned, at all times the work is taking place. Increased and tighter supervision is the key to improved safety more than new rules. (Means more inspection!) Supervisor should be alert to any deviations from standard practice and specs, and report any significant or potentially dangerous problems when he finds them. Incident reporting is now mandatory, as per the WSH Act (2006), Incident Reporting Regulations. 46 CoP Appendix C. Risk Assessment Form Almost all scaffold and formwork accidents are failures of existing controls! SOLUTION? 1. Tighten up existing controls through normal compliance regime of inspection, maintenance, and supervision. 2. In recognition of special problems with immigrant labour, provide additional continuous supervision 47 The End 48 8