scaffolds.pdf

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Guidelines for Multi-PointSuspended Scaffolds (MPSS)


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An electronic copy of this publication is available on the Ministry of Labour website atwww.labour.gov.on.ca

A hardcopy of this publication can be ordered:

Online at www.serviceontario.ca/publications By phone through the ServiceOntario Contact CentreMonday to Friday, 8:30 am to 5:00 pm

416 326-5300

416 325-3408 (TTY)

1 800 668-9938 Toll-free across Canada

1 800 268-7095 TTY Toll-free across Ontario

Published January 2006

Queen's Printer for Ontario, 2006

ISBN 0-7794-9926-3
http://www.labour.gov.on.ca/http://www.serviceontario.ca/publicationshttp://www.serviceontario.ca/publicationshttp://www.labour.gov.on.ca/


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TABLE OF CONTENTS

Section 1 Introduction....................................................................................... Page 1

Section 2 Purpose of the Guideline................................................................... Page 2

Section 3 Definitions......................................................................................... Page 3

Section 4 Multi-Point Suspended Scaffolds (MPSS) Overview....................... Page 5

Sec. 4.1 - Platform Uses.................................................................. Page 5Sec. 4.2 - Description of Major Components ................................. Page 5

Section 5 Design Requirements ........................................................................ Page 3

Sec. 5.1 - Load Considerations ....................................................... Page 8Sec. 5.2 - Methods for Designing MPSS ...................................... Page 11Sec. 5.3 - Redundancy of the System Design ............................... Page 14Sec. 5.4 - Other Design Considerations ........................................ Page 15

Section 6 General Requirements .................................................................... Page 16

Sec. 6.1 - Engineering Drawing Requirments .............................. Page 16Sec. 6.2 - Specific Duties: Professional Engineer,

Constructor, Employer, Worker and Supervisor .......... Page 17

Appendix A Typical Components of MPSS........................................................ Page 22


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2. PURPOSE OF THE GUIDELINE

The purpose of this guideline is to clarify the requirements for MPSSs in sections 142.1 to 142.8of the Regulations for Construction Projects.

The guideline highlights the major components of an MPSS, design methods, design loads, loadfactors and safety factors to be considered in the design, system redundancy, design drawingsand what they should include. Not withstanding the requirements made under the OccupationalHealth and Safety Act, the guideline explains the sections of the regulations for MPSS that dealwith the responsibilities of the professional engineer and responsibilities of the constructor,employer, supervisor and worker.

In designing an MPSS, a professional engineer must ensure that the minimum design criteria setout in the Regulations are met when following other applicable codes and standards.

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4. MULTI-POINT SUSPENDED SCAFFOLDS (MPSS) OVERVIEW

4.1 USE OF MPSS

Multi-point suspended scaffolds are suspended from a permanent building or structureand are used as a work platform for a variety of tasks on construction projects andindustrial workplaces. Multi-point suspended scaffolds vary in size and capacitydepending on their application.They range from large area MPSS commonly used for

bridge repair and restoration work to small scaffolds used for access and inspectionapplications. MPSS are also used for masonry work particularly in high-rise buildingconstruction.

Multi-point suspended scaffold may be designed and constructed to move or traversehorizontally, or move vertically along the structure from which they are suspended, or toremain stationary.

4.2 DESCRIPTION OF MAJOR COMPONENTS OF AN MPSS

A Multi-Point Suspended Scaffold generally consist of the following major components:(refer to sketch 1):

Platform assembly: the platform surface and structure, which may be onelevel or multiple levels.

Suspension system: the suspension system includes wire ropes, chains andcables, and the anchorage system. It also includes a hoisting mechanism: anassembly that will allow the platform to be moved by mechanical means.

4.2.1 Platform Assembly

The platform consists of three main components:

1-

The main supporting beams or trusses2- The joists

3- The deck surface

The platform may be constructed of wood, steel or aluminium.

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4.2.2 Suspension System

The suspension system contains the following:

1- Suspension assembly includes wire ropes, chains or cables andrigging hardware to connect the platform to the overhead structure,which is normally a permanent structure;

2- Hoisting mechanism, where the scaffold is to be raised or lowered;and

3- Anchorage system, which includes outrigger beams, beam clamps,cross tubes, trolley mechanism and other related hardware.

4.2.2.1 Suspension assembly

The suspension assemblies are the primary support system forMulti-Point Suspended Scaffolds. The suspension system assemblyconnects the platform structure to the overhead structure. Thesuspension assembly consists of wire ropes, chains or cables.

Wire Ropes and Chains

The most common type of suspension system assembly is steel wire ropeor chains to support or suspend the platform from a permanent ortemporary structure. Threaded steel rods and steel tubes are alsocommonly used. This type of assembly normally includes the wire ropeor chain, the appropriate rigging hardware, the stirrups or clamps used toattach the wire rope or chain to the main support beams of the platform,and the beam clamps or outrigger beams. The beam clamps andoutrigger beams are part of the anchorage system and are attacheddirectly to the permanent structure.

4.2.2.2 Hoisting Mechanism

A hoisting mechanism is connected to the suspension system when theMPSS is designed to move vertically. The two main categories of hoistsare manually operated and power operated hoists.

Manually Operated Hoists

The most common hoists are traction type, which are used with a wireropes suspension system.

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5.1.2.1.2 Loads due to Abrasive (Sand) Blasting operations

If the MPSS is to be used for abrasive blasting operations,then an additional live load allowance for 25 mm gritaccumulation across the entire platform area must be

included. It is recommended that the unit weight of the grit be specified and verified during field inspection.

5.1.3 Wind Loads

Subsection 142.2(3)(b) indicates that the MPSS shall be designed for wind loadsdetermined in accordance with Table 2.5.1.1 (Design Data for Selected Locationsin Ontario) as per section 4.1.8 of the Building Code, assuming a probabilityfactor of at least one in ten.

The effect of wind loading on any environmental enclosures on the MPSS must be taken into account.

5.1.3.1 Special consideration for the wind loading

The wind load derived from Table 2.5.1.1 of the Building Code, may bereduced by up to 30% if the professional engineer who designs theMPSS determines it appropriate to do so. If the professional engineer

does reduce the wind load, he/she must provide the rational for doing soin writing.

5.1.4 Any Other Applied Loads

Subsection 142.2(3)(c) indicates that in addition to the above loads, the MPSSshall be designed for any other loads likely to be applied to it.

Examples include:

Stock piling or storage of material

Dynamic effects of moving equipment

Material receiving areas

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( D) = Dead load factor (refer to Table 1).

D = Anticipated dead load of MPSS and its components.

= Importance factor applied to factored loads other than dead load whichtakes into account the consequences of collapse or failure as theyrelate to the use of the structure (refer to section 4.1.3.1 of theBuilding Code). The value of shall not be less than 1.0 and may beincreased greater than 1.0 in some cases for critical components.

= Load combination factor applied to factored loads other than dead loadto take into account the reduced probability of a number of loads fromdifferent sources acting simultaneously (refer to section 4.1.3.1 of theBuilding Code).

( L) = Live load factor (refer to Table 1)

L = Specified live load for platform surface.

( W) = Wind load factor (refer to Table 1).

W = Wind load in accordance with section 4.1.8 of the Building Code using the probability factor of at least one in ten for temporarystructures.

Note: The above definitions have been modified to reflect the terms related to Multi-pointSuspended Scaffolds .

Table 1 provides a comparison of the load factors for the design of an MPSS.

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Table 1Load Factors

Structure/component L D W

MPSS and structuralmembers (platformstructure)

3.0 1.5 1.5

Suspension andAnchorage system

4.0 2.0 2.0

5.2.2 Working Stress Design

Subsection 142.2(9) of the Regulation allows the designer the option to design theMPSS and its components using Working Stress Design. However, the safetyfactors for the scaffold and its structural members are required to be at least equalto what would otherwise be provided under the Limit States Design.

5.2.3 Ultimate Strength Design (Determination Of Failure Load By Testing)

Subsection 142.2(10) of the Regulation indicates that if a component is tested tofailure, then a suitable safety factor may be applied to the failure load to

determine the capacity of the component. Where the failure load of a componenthas been determined by testing and verified in writing by a professional engineer,the minimum safety factors listed in Table 2 shall be used.

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Table 2Minimum Safety Factors for Testing

MPSSComponent/structure

Minimum SafetyFactor

Component of theMPSS (PlatformStructure)

3.0

Components of theSuspension andAnchorage System

4.0

Hoisting system (wireropes, chains or cables

used for hoisting)

10.0

5.3 REDUNDANCY OF THE SYSTEM DESIGN

Subsection 142.2(12) of the Regulation requires that an MPSS be designed, constructedand maintained in such a way that the failure of one means of support or suspension willnot cause any part of the scaffold to collapse or fail under the most adverse loadingconditions as determined by the professional engineer who designs the scaffold incompliance with section 142.2.

This requirement means that the suspension system and its components must be designedsuch that if a suspender or a suspension component fails under any loading condition, theremaining suspension system shall continue to support the platform with the load factorsand safety factors specified in subsections 142.2 (7)(8)(9)(10). A failure mode analysis isnormally required to be carried out to determine this design requirement.

The above suspension system redundant design feature is required where the MPSS is both stationary or when it is being moved or traversed to another anchorage position.

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5.4 OTHER DESIGN CONSIDERATIONS

5.4.1 Fall Arrest System

Section 142.7 requires a worker on an MPSS to use a fall arrest system when theMPSS is being erected, dismantled, traversed or otherwise moved. The fall arrestsystem is independent of the MPSS and must be designed in accordance withsubsections 26.1, 26.6, 26.7 and 26.9 of the Regulation such that the worker is

protected at all times. The design and layout of the fall arrest system must takeinto consideration the design of the MPSS.

It is recommended that the design engineer of the MPSS evaluate the loadsinduced by the fall arrest system on the permanent structure.

5.4.2 Movement limi ting devices

The design engineer of the MPSS shall consider and specify movement-limitingdevices to prevent the unintended movement of the scaffold when traversing orotherwise moving (refer to section 142.2(13)).

5.4.3 Wind speed

It is recommended that the design engineer of the MPSS specify on the designdrawing the maximum wind speed at which operations such as traversing ormoving of the platform should cease or when further precautions would berequired. A wind speed indicator may be provided and located on the platform toallow the workers to monitor wind conditions.

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6.0 General Requirements

6.1 ENGINEERING DRAWINGS

In accordance with subsection 142.2(15). the design drawings of the MPSS shall include:

a statement by the professional engineer who designs the MPSS indicatingthat the design meets the requirements of this Regulation;

the size and specifications of all components, including the type and grade ofall materials to be used (for specific products this may be supplemented bylisting the product name, model and size, i.e. beams, trolleys, tensioningdevices);

the load factors and safety factors for the scaffold and all its components;

all the specified loads, including the loads during erection, dismantling,traversing and otherwise moving. Load patterns and location of concentratedloads should also be included;

the procedures for erection, dismantling, traversing and otherwise moving.

6.1.1 Addit ional Considerations For Engineering Drawings

It is recommended that the professional engineer who designs the MPSS show the

following requirements on the design drawings:

the maximum wind speed as referenced in Part 5.4.3 of the guidelineshould also be on the drawing;

the professional engineer specify the wind load at which work on theMPSS shall stop;

movement-limiting devices as referenced in Part 5.4.2 of the guideline;

procedures to be followed where the MPSS becomes skewed or jammed during traversing or moving;

a checklist of the items including the critical components to beinspected, to assist the competent worker during the inspection of theMPSS;

where proprietary components are used for the MPSS, the professionalengineer who designs the scaffold must ensure that appropriate testingand certifications of components have been done.

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6.2 SPECIFIC DUTIES

The following are specific duties imposed by the Regulation on professional engineersand other workplace parties related to the design, erection, use, moving, traversing,maintenance, and dismantling of MPSS.

6.2.1 Professional Engineers Duties

In addition to designing the MPSS in accordance with Parts 6.1 and 6.1.1 of theguidelines and the requirements of section 142.2 and subsections 142.3(2),(3),(4)and (5) of the Regulation, the professional engineer shall prepare, sign and sealdesign drawings of the MPSS.

6.2.2 Constructors Duties

In addition to the general duties and responsibilities as per section 23 of theOccupational Health and Safety Act, R.R.O. 1990, c. O.1, the constructor hasadditional duties related to MPSS:

Section 142.2

that the MPSS is designed by a Professional Engineer

the design drawings are signed and sealed by the ProfessionalEngineer

the drawings include written procedures for the erection, dismantlingand traversing the MPSS

any deviations from the drawings are approved by a ProfessionalEngineer in writing

Professional Engineer responsible for the structural integrity of the permanent structure from which an MPSS is suspended provideswritten report approving the design loads on the permanent structure

by the MPSS

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Section 142.3

to notify the Ministry of Labour that the MPSS is to be erected ordismantled

ensure that a Professional Engineer inspects the MPSS after it iserected and before it is first used (including inspection when MPSS ismoved to Canada and before it is first used on a project in Ontario),and after it has been moved to a new anchorage

that the Professional Engineer provides a written report that the MPSScomplies with the drawings subject to any deviations and stateswhether or not all components are in adequate condition

before erecting or dismantling a multi-point suspended scaffold, theconstructor shall give notice, in person, by telephone, by fax or byelectronic means, to the Ministry office located nearest the project.

Section 142.4

keep all written reports and drawings regarding the MPSS at the project

Section 142.8

keep, at the project, a written record of all inspections, tests, repairs,modifications and maintenance performed on the MPSS while theMPSS is at the project.

6.2.2.1 Addit ional elements to be considered by Constructor

It is recommended that the MPSS is equipped with a wind speed-measuring device and that work is stopped if the wind speedspecified in the Professional Engineers drawing is reached.

A copy of the written records of inspection under section 142.8 aremaintained with the MPSS when it is moved off site.

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6.2.3 Employers Duties

In addition to the general duties and responsibilities as per sections 25 and 26 ofthe Occupational Health and Safety Act, R.R.O. 1990, c. O.1 , the employer hasadditional duties related to MPSS:

Section 142.2

that the MPSS is designed by a Professional Engineer

the design drawings are signed and sealed by the ProfessionalEngineer

the drawings include written procedures for the erection, dismantlingand traversing the MPSS

any deviations from the drawings are approved by a ProfessionalEngineer in writing

Section 142.3

ensure that a Professional Engineer inspects the MPSS after it iserected and before it is first used (including inspection when the MPSSis moved to Canada and before it is first used on a project in Ontario),and after it has been moved to a new anchorage position

ensure the Professional Engineer provides a written report that the

MPSS complies with the drawings and that all components are inadequate condition

ensure that the MPSS is equipped with a wind speed-measuring deviceand that work is stopped if the wind speed specified in the ProfessionalEngineers drawing is reached.

appoint a competent worker to inspect the MPSS prior to each daysuse and ensure that the inspection is done.

Section 142.5

ensure that the MPSS is erected, dismantled and traversed by acompetent worker under the supervision of a competent person inaccordance with all design drawings,

provide adequate oral and written instruction to the workers workingon the MPSS on the use and limitations of the scaffold

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provide adequate oral and written instruction for the workers engagedin the erection, dismantling and traversing of the MPSS

provide the constructor with the drawings, reports and approvals forthe MPSS

Section 142.6

ensure the MPSS is not overloaded

post signs on the MPSS indicating the loading of the platform

Section 142.7

during erection, dismantling, traversing or otherwise moving, a workershall use personal fall protection equipment at all times.

provide written instruction to workers on operation procedures whenMPSS is jammed or skewed.

6.2.3.1 Addit ional consideration forEmployer

It is recommended that the competent worker inspects the MPSS based on a check-list prepared by the design engineer or by themanufacturer.

6.2.4 Workers Duties

In addition to the general duties and responsibilities as per section 28 of the OccupationalHealth and Safety Act, R.R.O. 1990, c. O.1, the worker has additional duties related toMPSS:

Section 142.3

the competent worker shall inspect the MPSS daily, prior to its use.

Section 142.5

work in accordance with the manufacturers or Professional Engineersinstruction for the MPSS

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Section 142.7

use appropriate fall arrest equipment while the MPSS is being erected,dismantled or traversed . The workers shall use double lanyards orequivalent to ensure 100% protection where needed.

6.2.5 Supervisors Duties

In addition to the general duties and responsibilities as per section 27 of the OccupationalHealth and Safety Act, R.R.O. 1990, c. O.1, the supervisor has additional duties related toMPSS

Section 142.5

under his or her supervision, only a competent worker or workers shallerect, dismantle, or otherwise move an MPSS

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Appendix A

Sketch 1, Multi-point suspended scaffold assemblies

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ISBN 0-7794-9926-3 January 2006

Documents

scaffolds.pdf