Review of Current Codes and Standards for Scaffolds

S G. Fattal, C L Mullen, H. S. Lew, B. J. Hunt

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D C. 20234

April 1980

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Prepared for National Institute for Occupational Safety and Health

Department of Health, Education and Welfare

Washington, D.C.

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* REVIEW OF CURRENT CODES

AND STANDARDS FOR SCAFFOLDS

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S. G. Fattal

C. L. Mullen

H. S. Lew

B. J. Hunt

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

April 1980

Prepared for National Institute for Occupational Safety and Health

Department of Health, Education and Welfare

Washington, D.C.

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr. r Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

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REVIEW OF CURRENT CODES

AND STANDARDS FOR SCAFFOLDS

S. G. Fattal, C. Mullen

H. S. Lew and B. J. Hunt

ABSTRACT

This report presents a critical review of the provisions in existing

codes and standards for the design, erection, operation and maintenance

of scaffolds used in construction work and other applications. The

requirements in these documents were examined from the standpoint of

clarity, consistency and completeness. Ambiguities arising from

conflicting requirements or from provisions that led to more than one interpretation, and lack of consideration of major safety-related

structural, environmental and human factors are highlighted. In

addition, the adequacy of, and the rationale behind, the prescribed

provisions are examined. These are supplemented by a specific application to wood platform design appearing in Appendix B. Appendix A

illustrates common types of scaffolding systems that have been addressed

by at least one of the codes or standards examined. The findings of this

study serve to identify principal areas of needed research to improve

present scaffolding practices.

Keywords: Codes and standards; construction safety; design; loads;

maintenance; occupational hazards; scaffolds; stiffness;

strength; structural safety; work surfaces.

iii
ACKNOWLEDGMENTS

This report was sponsored by the National Institute for Occupational

Safety and Health (NIOSH) , Department of Health, Education and Welfare.

The authors wish to express their gratitude to those persons of the NBS

staff, in particular Mr. Lou E. Cattaneo and Mr. Robert M. Eisenhard,

whose efforts were of tremendous value In the compiling of this report.

Also Dr. N. J. Carino for his untiring review efforts and Ms. Ana Sanchez

and Ms. Ulesia B. Gray for the typing of this report.

iv
TABLE OF CONTENTS

Page

ABSTRACT iii

ACKNOWLEDGMENT iv

1. INTRODUCTION 1

2. REVIEW OF GENERAL PROVISIONS FOR SCAFFOLDING SYSTEMS 4

2 . 1 General 4

2.2 Work Platform 5

2.3 Support System 6

2.4 Connections and Anchorages 8

2.5 Foundation 9

2.6 Accessway 10

2.7 Strength 11

2.8 Stability 13

2.9 Physical Protection 15

2.10 Environmental Safety Criteria 16

2.11 Special Provisions 17

3. SCAFFOLDING VARIANCES 17

4. SUMMARY AND CONCLUSIONS 19

5. RECOMMENDATIONS 20

6. REFERENCES 23

APPENDIX A - TYPICAL SCAFFOLDINGS SYSTEMS A-l

APPENDIX B - APPLICATION SUMMARY AND REVIEW OF EXISTING

STANDARDS FOR THE DESIGN OF WORK PLATFORMS

CONSISTING OF WOOD PLANKING B-l

v
.
1 . INTRODUCTION

At the present time, there exists no all-encompassing set of technically

based criteria by which construction scaffolds can be evaluated for

structural integrity, serviceability and personnel safety. In response

to the need to minimize scaffolding accidents and consequent work-related

human casualties, a research program has been initiated at the National

Bureau of Standards (NBS) to develop the necessary technical basis for the

improvement of current scaffolding provisions in existing codes and standards.

The scaffolding research program is organized into several phases consisting

of a series of inter-related studies which may be identified by their subject

matter as follows: Analysis of scaffold accident records and related casualties; review of scaffolding provisions of existing codes and standards;

review and evaluation of existing technical literature on scaffolds; field

study of scaffolding practices; analytical and experimental investigations;

and development of performance standards for the design, erection, operation,

maintenance and evaluation of construction scaffolds.

The initial phase of the scaffolding research program was sponsored by the

National Institute mf Occupational Safety and Health (NIOSH) and consisted

of two separate studies. The first study, which dealt with the analysis of

scaffolding accidents and related casualties, has been documented in a separate report [1].* The second study, which evaluates the scaffolding

provisions of current codes and standards, is documented in this report.

A total of 25 codes and standards were initially examined for prescriptive

content on safety requirements for scaffolds. This choice of documents

represented a reasonable profile of scaffolding provisions in the U.S.

and Canada. They consisted of four national codes, seven model codes and

voluntary standards, five state codes and nine city codes. The number

was narrowed down to eleven after eliminating those documents which either

provided minimal or no coverage on the subject, or contained provisions

similar to those in one of the retained documents. Nationally applicable

documents retained for this study are the following:

(1) American National Standard, ANSI A10.8, A92.1, A92.2, A92.3,

and A92.6 (ANSI)**[2]

.

(2) Occupational Safety and Health Standard, Part 1910

(OSHA 1910) [3]

* Numbers In brackets designate references listed at the end of this

report.

** The terms in parentheses are abbreviations used for citing the corresponding documents in the text of this report.

1
(3) Construction Safety and Health Regulations, Part 1926

(OSHA 1926) [4]

(4) State of California Construction Safety Orders

(CAL/OSHA) [5]

(5) American Insurance Association National Building Code

(NBC) [6]

(6) The Building Officials and Code Administration (BOCA)

Basic Building Code [7]

(7) The National Research Council of Canada Construction

Safety Code (NRCC) [8]

These documents were selected on the basis of the following considerations. The OSHA 1910 and OSHA 1926 documents are federally-enforced

employee safety regulations applicable in the United States. The Occupational Safety and Health Administration (OSHA) exercises a mandate

over all such regulations in accordance with the Occupational Safety

and Health Act of 1970. The CAL/OSHA document is part of the State of

California Administrative Code [9]. The CAL/OSHA employee safety regulations are applicable in the State of California by agreement with

OSHA, and as such constitute an extension of OSHA employee safety jurisdiction to California. The ANSI document is a voluntary consensus standard which was used extensively as the basis for the development of the

current OSHA regulations (OSHA 1910 and OSHA 1926). As a result, a marked similarity exists between these documents with regard to format,

scope and technical content. The NBC Code is an enforceable document

in the sense that it prescribes safety requirements for insurability.

The BOCA Code is widely adopted by state and local regulatory agencies,

especially in the eastern parts of the U.S. A number of other

nationally-referenced documents, such as the Uniform Building Code and

the Southern Building Code, either did not provide detailed requirements

for scaffolds or did not reference other major codes or standards for

such detailed requirements. The Canadian document was retained because

it is the enforceable safety code in Canada.

In addition to national codes and standards, 13 state and city codes were examined. Of these, the following four were selected on the basis

of the extent of specifics and detailed provisions for scaffolds contained therein:

(1) State of Connecticut Labor Department Construction Safety

Code (Connecticut) [10]

(2) The Wisconsin Administrative Code (Wisconsin) [11]

(3) City of Atlanta Building Code (Atlanta) [12]

(4) City of New York Building Code (New York) [13]

The scaffolding safety requirements in the above documents were reviewed

in terms of the following criteria: (1) comprehensiveness, (2) consistency,

(3) clarity, (4) adequacy and (5) enforceability. A document is considered

to be comprehensive if it contains those provisions that are deemed

2
necessary for the maintenance of employee safety. Consistency refers

to the absence of conflicting requirements. Clarity denotes absence

of ambiguity such as statements which lead to more than one interpretation. Adequacy is judged according to whether a provision meets,

exceeds or falls short of the intended level of safety. Enforceability

is judged according to whether or not the user (designer, fabricator,

contractor, inspector, compliance officials, etc.), to whom the require

ment is addressed, can interpret and implement it in accordance with

the intent of the code.

The following definitions are introduced to avoid possible ambiguities

in the text of this paper when referring to parts and portions of the

scaffolding systems.

Accessway - system which provides access of personnel to and from

scaffolds

Anchor - component used for securing scaffold to foundation

Anchorage - same as anchor, assembly of anchors

Component - unit used in the assembly of scaffolding system.

Connection - component providing the means of attachment of

other scaffolding components together.

Element - component or structural unit other than connection or anchor

Foundation - means providing total support to the scaffold system

Platform - component(s) comprising the work surface of the scaffold

Safety devices - physical devices installed for the protection of

employees, such as guardrails, nets, belts, lanyards

and lifelines, screens, etc.

Structural

system - assembly of components serving a structural function

Subsystem - assembly of part of a system consisting of more than

one element and one or more connections and/or

anchors

Support element - element of scaffold subsystem which supports the plat

System

form and transmits applied loads to the foundation

- assembly of components serving a specific function

3
2. REVIEW OF GENERAL PROVISIONS FOR SCAFFOLDING SYSTEMS

2 . 1 GENERAL

Most of the documents reviewed are patterned after ANSI A10.8. These

documents are organized into general and type-specific provisions.

The OSHA 1910 and OSHA 1926 documents closely maintain this organizational structure while CAL/OSHA and others adhere to ANSI A10.8 in

varying degrees. The general provisions are those which apply to scaffolding systems of all types, while the type-specific provisions appear

only under the heading of a particular type of scaffold.

Table 1 lists the types of scaffolds found in the ANSI (A10.8 and A92.X)

and OSHA (1910, 1926 and CAL/OSHA) documents. Note that there is no com- plete agreement among these documents with regard to the terms used

to describe specific scaffolding types, although in many instances they are the same. For example, it is difficult to discern whether Tower and

Rolling Scaffolds of CAL/OSHA and Manually-Propelled Mobile Ladder Stands

and Scaffolds of ANSI A92.1, OSHA 1910 and OSHA 1926, describe the same category of scaffold types. Another difficulty is that certain scaffold

types appear only in some of the documents. A case in point is the

Catenary Type which is addressed by ANSI 10.8 and CAL/OSHA but not by

OSHA 1910 and OSHA 1926. Confusion is further compounded by the fact

that many of the scaffolding types used by the construction and other

industries do not belong to any of the specified categories. It should

be noted, however, that these documents make provisions for conditions

under which different scaffolding types could be used. ANSI A10.8

stipulates that exception may be granted by the enforcing authority to

permit the use of other devices and methods when it is clearly indicated

that equivalent protection is secured. The vehicle by which OSHA implements this provisions is to grant variances which are in effect only for

a specific type of scaffold used for a specific job application. The

mechanism by which variances are administered is discussed in Section 3.

Tables 2a through 2e provide a summary of the general scaffolding

requirements contained in the documents reviewed. For purposes of com- parison, the provisions from the various sources are broken down into the

following categories. It Is noted that these categories do not exist within

the documents reviewed per se, and that they are used only within the

context of this report.

(1) Work platform

(2) Supporting elements

(3) Connections and anchorages

(4) Foundation

(5) Accessway

(6) Strength

(7) Stability

(8) Physical protection

(9) Environmental safety criteria

(10) Special provision*

4
The first five items collectively identify basic components in terms of

which all scaffolding systems can be defined. Strength and stability

(items 6 and 7) relate to the structural safety of the system while

item 9 refers to environmental safety considerations. In this respect,

failure of any component of the system (items 1 through 5) could

precipitate partial or complete collapse and therefore can be viewed

from the standpoint of structural safety or stability (items 6 and 7).

Similarly, items such as openings on the work platform or between the

platform and the adjacent wall, various obstructions, etc. can be

viewed as non-structural design factors or environmental factors

affecting the safety of employees in the workplace. Physical protection devices (item 8) relate to both structural and environmental safety

aspects. Under special provisions (item 10), situations requiring

special consideration are listed (e.g. conditions under which the ser- vices of a professional engineer are required).

In most instances the type-specific provisions can be fitted into these

categories as well. However, they are too numerous to be presented in

tabular form. Instead, these will be cited at the appropriate places

in the discussions of the general provisions in accordance with the

specified format.

2.2 WORK PLATFORM

In many situations a work platform can be treated as a structurally

independent element of the scaffolding system. Simply supported platforms

or platforms continuous over more than two supports, for instance, can be

analyzed for imposed loads by considering them separately from the

system. Such an analysis then will provide information about the structural adequacy of the platform and can be used to set structural safety

requirements.

Requirements listed in tables 2a through 2e show that many specific

provisions are prescribed for wood platforms by the various standards.

Those of ANSI, OSHA 1910, OSHA 1926 and CAL/OSHA are essentially the

same: a 2 in (50 mm) thick (nominal) scaffold grade plank is specified

with maximum spans for loads of 25, 50 and 75 psf (1.2, 2. A and 3.7 N/m^).

For a summary and review of other provisions for the design of wood platforms, refer to Appendix B. Spans are also identified for use with planking having a minimum thickness of 1 1/2 in (38 mm). However, no sizes are specified for loads exceeding the 75 psf (3.7 N/nr) limit.

The approach which prescribes specific designs for platforms limits the

scope of the standards. Similarly, the restrictive policy on acceptable

lumber grades could create difficult situations in the event that the

specified grades or species were to become scarce or unavailable. It

should be noted that for certain types of scaffolds, OSHA permits the

use of fabricated planking if it can safely support the specified load.

There seems to be no apparent reason why such a clause should not be

equally applicable to all scaffold types. In this respect, the Wisconsin

Code uses a more general approach by requiring that safe loads be in

5
proportion to the allowable stress and width of plank for a given span

and that load distribution be considered in design. By emphasizing a design approach rather than prescribing a preconceived design, the

provision is thereby rendered less restrictive with regard to choice

of grade and plank size. The BOCA Code is likewise less restrictive

in that it calls for the design of platforms to support specified levels

of loading which are the same as those used by ANSI and OSHA. The rest

of the State and local codes generally make reference to platform provisions in ANSI or BOCA.

Disparities are also found between the various standards and codes with

regard to non-structural design requirements. ANSI allows a 1 in (25 mm)

opening between adjacent planks while in most other codes no spacing is

allowed. The Canadian Code requires platforms to be securely tied in

place. In the New York City Code, a similar requirement is specified

but only for "inclined planking", a term which is left undefined. On

the other hand, ANSI and OSHA require platforms to be tied down or secured only for certain types of scaffolds (types 4, 8, 13, 21, appendix B). Generally, the required proximity of the scaffold to the face

of the structure under construction is not adequately addressed.

2.3 SUPPORT SYSTEM

The term support system is used to designate the structure which provides direct support to the work platform and transmits all loads to

the foundation. This could mean, for instance, a braced framework

consisting of elements, connections and anchorages; a flexible or non- flexible (wire rope or bar) platform suspension system; a mobile or vehicle unit integrating a work platform; or any other system serving

the defined support function. Appendix A illustrates various scaffold

types and their support systems. The support system frequently identifies

the characteristic feature of a scaffold and thereby constitutes the basis

for making the distinction between the types appearing in Appendix A.

The provisions for support systems are primarily related to structural

safety requirements for the individual elements, connections and anchorages to achieve a desired level of performance. In Table 2 "support

systems" Is not listed as a separate item because requirements for

connections, anchorages, strength and stability can be treated more appropriately under separate headings. This section, therefore, dwells on provisions which affect the structural performance of the individual

elements of the support systems.

Most of the provisions for support systems appear under type-specific

headings for the various scaffolding configurations that are addressed.

Because of the close similarity between the ANSI, OSHA 1910 and OSHA

OSHA 1926 provisions for scaffolding support systems, it is convenient

to address only one of these documents (OSHA 1926 is selected) and point

out marked differences between it and the other standards and codes

examined.

6
A potential structural safety problem for support systems is degradation

of strength from repetitive use and exposure to the exterior environment.

This is particularly true for systems which use wood elements in their

construction. By referring to Appendix A, it is noted that at least 11

of the 21 scaffold types fall in this category. Degradation of wood mani

fests itself in the form of warping and bowing, decay, wear or cumulative construction damage (dents, cracks, delamination, nail perforations,

etc. )

.

None of the documents reviewed contained definitive criteria to compensat

for strength degradation of materials and components through such means

as design modifications or repair and replacement of support elements.

The extent of direct reference given to the topic by OSHA 1926 is a clause under the general provisions calling for the immediate repair or replacement of damaged and weakened parts. However, what constitutes

damage that requires replacement is left to the judgement of the user. The CAL/OSHA Code calls for the inspection of scaffolding lumber before

and at (unspecified) periods during use, and for replacement of pieces

incapable of supporting 4 times the maximum imposed load. In many

instances, there is no simple and practical set of rules to follow for

determining compliance. Usually, verification is not feasible without

an engineering analysis and/or some physical testing.

Similar inadequacies can also be found with regard to the lack of provisions for the repair, maintenance or replacement of support systems

assembled wholly or partly from fabricated metal products. Noting that

metal sections are relatively thin-walled, they would be more susceptible to physical damage or corrosion than wood. The type-specific

requirements for metal support systems (such as types 2 through 7,

Appendix A) contained in ANSI and the other documents make no provision

for the determination of strength loss due to these factors for the purpose of acceptance or rejection. The problem may be even more critical

in the case of open metal sections in compression, such as diagonal steel

angle braces that are often used in many scaffolding systems such as carpenter's brackets (type 16, Appendix A), because the stability of

the entire system can be seriously impaired by the presence of bends,

dents and other local damage.

In general, the problem related to the degradation of members such as noted above cannot be resolved without undertaking a comprehensive program to devise a practical approach (for instance, expedient field measurement and/or testing techniques) whereby the level of unacceptable

damage can be established.

As in the case of platforms, the type-specific provisions for support

systems appearing in OSHA 1926 (and most other codes as well) are limited in scope to specific prototype systems. In this respect, the

provisions are similar to a set of instructions for assembling a commercial product. Even though this approach possibly simplifies the standard

provisions for the layman, there are some obvious pitfalls. For example,

under the Wood Pole category, the standard spells out sizes, lengths,

7
projections and orientations of wood members to assemble a scaffold having

a preconceived shape and layout. This inhibits the use of wood pole

scaffolds having different framing arrangements, member sizes, allowable

stresses, level and distribution of loads, etc., from those specified.

It is true that in such cases variances may be granted by OSHA upon

proof that the system provides "equivalent" protection. However, in all

likelihood, the contractor will have to engage the services of an engineer

to produce the required justification, in which case, a contradiction of

sorts occurs because OSHA does not require the procurement of variances

for engineered scaffolds in the first place.

Problems such as the above can be avoided by modifying the scope of the

provision requiring engineered design so that it is equally applicable

to systems not conforming with specific requirements in the standards.

Another concept that might deserve consideration as a means of simplifying present OSHA scaffolding regulations and at the same time ren- dering them less restrictive for other systems, is to issue all specific designs under an appropriately titled separate reference (such as

a Manual of Specific Scaffolding Systems and Practices Conforming with

OSHA Regulations).

2.4 CONNECTIONS AND ANCHORAGES

Connections are components which fasten individual scaffolding components

together to form the complete system. Any physical device used for the

purpose of interconnecting support elements or braces, or securing work

platforms, accessways or safety devices to the scaffold falls in this

category. Common examples of scaffolding connections are nails and bolts

for wood systems and pins, couplers and (shop) welds for metal systems.

In general, the codes and standards reviewed did not contain definitive

provisions to ensure the integrity of scaffolding connections. ANSI

A10.8 and OSHA 1910 call for the use of nails or bolts of adequate size

and sufficient numbers to develop design strength (OSHA 1926 does not

have specific provisions for connections). The obvious omission of

quantitative criteria in this statement underscores the need for verification of strength through design or testing. The lack of a welldocumented design approach or a practical standard test method makes

it difficult to exercise either of these options in a consistent and

reliable manner. Furthermore, because the term "design strength" is

neither explicitly defined nor a universally accepted term, it lends

itself to misinterpretation. If, for instance, it is taken to mean the

allowable stress level of the incident elements at a joint, which incorporates a factor of safety, and the connection is proportioned using its

ultimate capacity, the resulting desigh will not have the margin of safety

to ensure connection integrity beyond working load levels.

A similar situation is encountered in an overall strength provision in

both ANSI A10.8 and OSHA 1910 stating that scaffolds and their components

shall be capable of supporting without failure at least four times the

maximum intended load (see sec. 2.7). In this case, unlike connections,

8
scaffolding elements are required explicitly to have a factor of safety

of four. However, the terms "intended load" and "failure" are not clearly

defined. If failure is associated with the load at which the element

attains its peak resistance level, it should be so stated. Similarly,

"intended load" needs classification because it could mean the "working

load" anticipated by the design, or a recommended "working load" by the

fabricator-supplier of system components directed to the erector and

contractor to ensure that the system does not get overloaded under normal

operating conditions.

Among the standards and codes reviewed, CAL/OSHA and the Wisconsin code

address connections in greater detail than the other documents by specifying the quantity and type of fasteners and nails to be used in various

applications. On the other hand, the Canadian Construction Safety Code

is the only document that requires explicitly the connection strength

be equal to the member strength. It further requires that the horizontal

members shall not be spliced between two support points. This requirement provides against the possibility of premature failure of horizontal

members which support the work platform.

Anchorages refer to those components which secure the scaffolding system

to its foundation. Because anchorages provide either partial or total

support to a scaffolding system, failure of an anchorage could bring

about a catastrophic collapse of the entire system. Except for a brief

statement that scaffolds shall be secured to permanent structures, none

of the standards and codes provided adequate coverage on anchorages.

Furthermore, it is not clear whether a structure under construction can

be classified as a permanent structure for anchoring purposes.

According to a recent study of scaffold-related accidents [1], a substantial portion of system failures were triggered by failures of anchors

and connections. The present study suggests the possibility that the high

rate of incidents involving such failures may be at least partially

attributable to the absence of prescriptive technical provisions in the

existing codes and standards applicable to the design of connections and

anchorages. The source of the problem may be a lack of research information on the capacity of connections and anchors used for scaffolding

applications. It is also possible that such information does exist but

has not yet been fully utilized by the present codes and standards.

2 . 5 FOUNDATION

Foundation designates the total system which provides support to the

scaffold. In this context, it may be the ground (footing or flooring)

upon which the scaffold bears as well as any other supporting structure

such as the partially completed wall of a building to which the scaffold

is attached for lateral support. Connections between the scaffold and

foundations are treated as anchorages (Section 2.4).

Referring to Tables 2a through 2e, a general lack of substantive provisions for scaffolding foundation is noted. The Canadian Code states that

9
footings and supports shall carry the maximum load without unsafe settlement but fails to prescribe specific criteria by which a safe or unsafe

settlement condition may be evaluated. The ANSI and OSHA documents state,

in effect, that footings and anchorages be sound, rigid and capable of sup

porting the maximum intended load without settling or displacement.

This is a requirement of several expected performance attributes without specifying the necessary criteria by which the level of performance

can be established. In the absence of prescriptive criteria, the meaning of terms such as "sound" or "rigid" are subject to different interpretations by different users. In addition, the requirement that no displacement or settlement occur under loading is ambiguous in the sense

that in a real-life situation loads always produce settlement and displace

ment. The ambiguity can be removed by restating the requirement so that settlements and displacements produced by the intended loads be

kept within tolerable limits to provide adequate margins of safety

against instability and structural distress.

Some of the type-specific provisions of ANSI and OSHA contain foundation

clauses which use different wording but are otherwise just as ambiguous

and void of prescriptive content as the general provision. For instance,

under wood-pole scaffolds, OSHA 1926 states that poles shall bear on

a foundation of sufficient size and strength to spread the load from

the pole over a sufficient area to prevent settlement. This clause also

appears almost identically in the Wisconsin Code. However, the latter

does specify a footing size for wood scaffolds. This still leaves open

questions with regard to the adequacy of the subgrade to safely support

the specified footing irrespective of the type of soil, height of scaffold

and anticipated loads.

It is also noted that none of the documents addresses the adequacy of

the foundation when it consists of the partially completed or partially

cured (in the case of concrete) part of a structure. There have been

cases where the failure of a partially cured foundation has precipitated

collapse and high employee casualties. For example, the Willow Island

Cooling tower collapse in West Virginia on April 27, 1978, which claimed

the lives of 51 workers, may be viewed as an foundation failure because

of the inadequacy of the concrete shell (to which the scaffolding was

attached) to resist the imposed construction loads without failure [14]

.

Since foundations have a direct bearing on both structural strength and

stability (items 6 and 7), it is concluded that the present codes and

standards do not contain adequate foundation provisions relating to

scaffolding practices to insure structural safety in the work environment.

2.6 ACCESSWAY

Accessway refers to the means of access to and egress from the work

platform. Except for two-point suspended scaffolds, most standards and

codes call for ladder or other type access devices to the work surface.

10
The Canadian code further requires that an accessway must be provided

if the working platform is 1.7 meters (5 ft) above the ground or floor

level while U.S. standards or codes have no such requirement. According

to the accident study [1], injuries have occurred in the absence of access ladders as a result of workers jumping onto platform surfaces from higher

elevations or workers falling while climbing on tubular metal scaffolds.

Only a small percentage of accidents were attributed to failure of the

accessway itself.

All the codes and standards reviewed fail to define accessway in terms

of the above established criteria (i.e. comprehensiveness, consistency,

clarity, adequacy, etc.). This situation occurs even under type-specific

categories. Without the clear definition of accessway for all scaffolding

types, the current provisions are incomplete, thus making enforceability

impractical.

The standards and codes (OSHA 1910 and ANSI 10.8) cite the general requirement mentioned above that an access ladder or equivalent be provided to

work platforms of all types. Under the type-specific category of tubular

frame scaffolds (Type 3, Appendix A), only ANSI addresses a means by which

access is to be provided. One such means is the attachable metal ladder

which most manufacturers provide with this type of scaffold. However,

the manufacturer also provides end frames, often titled 'step* or 'ladder'

type (Fig. A. 5). These frames provide support for working platforms

(which must extend beyond the support) as well as an indirect means of access

To enhance safe practices of scaffolding uses, the codes and standards

must clearly define the system components and address their function and

use. The general trend indicates a worker using various system components

for access to and egress from the scaffolding system. Horizontal

elements, cross-bracing, platforms, platform rungs, etc., are typically

used as accessways.

The codes and standards contain provisions on ladders, stairways, handrails, etc. (typical accessway components) under separate sections. By

cross-referencing these existing provisions, the scaffolding requirements

can be rendered more specific with regard to the use of proper accessways.

It is noted that there exist no accessway provisions for the expedient

evacuation of personnel from well populated scaffolds in the event of

disaster. Attention is drawn to well-documented building code requirements for the evacuation of personnel in case of fire. These regulations

can be used to model similar requirements for the safe evacuation of

personnel from scaffold work platforms.

2.7 STRENGTH

ANSI A10.8 and OSHA 1910 and 1926 contain a provision stating that

"scaffolds and their components shall be capable of supporting without

failure at least four times the maximum intended load". With the

11
exceptions of the Wisconsin, Connecticut, and New York codes cited in

Table 2, all of the other authorities reviewed contained a similar

statement.

The above clause is so general that it appears to be an attempt to

insure, in a single statement, that all scaffolds be sufficiently strong

to protect people on or near the scaffold. Such a general statement is

open to much criticism. No basis appears to have been given consideration in the selection of the value of four. Furthermore, interpretation

and implementation are difficult and sometimes confusing. A recent technical review of OSHA regulations regarding scaffolding loads and actual

margins of safety revealed major discrepancies [15]. Appendix B

provides a summary and review of general provisions for strength in the

design of work platforms consisting of wood planks and highlights

problems inherent in interpreting the general requirements in terms of

a factor of safety.

Safe design is primarily based on two major factors:

1. Adequate assessment of imposed loads, and

2. Provision of adequate resistance to imposed loads.

Without insight to actual loading configurations it is not possible to

properly assess the safety of the design. It is important that the

designers have at their disposal explicit guidelines of loads and loading

ranges anticipated in service. In the case of scaffold design, such

loads would include weights of the workers and materials, and equipment

to be placed on the work platform. In addition, the effects of wind

(lateral or uplift forces), falling objects (impact loads) or timevariation of loads (dynamic amplification) must be addressed. The ANSI

reference to "maximum intended load” is open to numerous interpretations.

There exist two major design approaches used in determining the resistence of a structure. In the first approach, designers proportion com- ponents according to a specified allowable stress for the given material

comprising the components. This approach is prescribed by steel and

and wood design specifications [16, 17]. In the second approach, the

designer utilizes the ultimate* strength concept which represents a specific limit state. This approach is prescribed in the ACI concrete

code [18] .

Under the working (or allowable) stress design, the service loads (or

unfactored loads) are used in proportioning the structural members so that

the working stress developed does not exceed the allowable stress for that

given material. This specified allowable stress is determined by applying

a code-specified factor of safety to the ultimate limit state of the

* Ultimate is a term which defines a peak or maximum characteristic for

a specific material.

12
material; the state at which a uniquely defined failure or unsatisfactory

performance occurs (e.g., steel begins to yield).

Under the ultimate strength approach, the service loads imposed are increased by certain load factors to account for overloads for design

purposes. The structural elements are then sized so that their expected

capacities equal or exceed the factored design loads. In making the

comparison between load and capacity, the theoretical capacities of the

members are reduced by strength reduction factors to account for uncertainties in material properties and construction workmanship. The reason

for these different approaches to structural design are manifold and are beyond the scope of this paper.

The ANSI statement of "support without failure" lacks clarity because

failure of a structure can be defined in several ways. It can be defined

in terms of the failure of either the system (global) or an element (local)

that serves a load-carrying function. Excessive deflection or vibration

may impair the proper conduct of work on the work platform to such a degree

as to constitute failure. Furthermore, the inability to provide adequate

strength margins against accidental abnormal loads, fire, or errors in

fabrication or erection may contribute to failure. A review of statistical data in the accident study [1] provided evidence of failure of the

latter type, particularly in regard to overloads and erection errors.

The above-mentioned design approaches must be consistent with specified

definitions of failure modes. For a particular ultimate limit state, the

problem that remains to be resolved is the significance of element failure

or subsystem failure in relation to total collapse of the scaffold system.

Considering a fabricated tubular frame scaffold (Type 3, Appendix A), for

example, failure of a weld or a leg, or the absence of a brace may result

only in local damage. Each constitutes failure according to an ultimate

limit state. The accident study [1] indicated that the consequences

of such local failures are usually not severe.

Different critical failure modes have different consequences. To establish a safety margin, the severity of the consequences should be considered. Either explicitly or by reference to other documents, all of the

documents reviewed include a provision for a higher safety margin for

suspension rope. The provisions call for support without failure of six

times (vs. four times for erected scaffolds) the maximum intended load

although the wording varied and was subject to different interpretations.

Compared to erected scaffolds, the consequences of failure of a suspended

system would be expected to be more severe because of a lack of built-in

structural redundancies. This provides a logical explanation of the

higher margin of safety prescribed for suspended systems.

2.8 STABILITY

The basic stability requirements for erected and suspended scaffolds are somewhat different. In erected scaffolds, where elements of the support

system are in compression, structural instability or compressive buckling

phenomena, at both local and global (system) levels, needs to be addressed

13
in design. In suspended scaffolds, where the support elements (cables)

are in tension, this type of instability is not a problem. Local structural instability, such as the buckling of a single compression strut,

is usually confined to a small region, particularly when the system has

built-in redundancies. On the other hand, global structural instability,

such as out-of-plane buckling of a frame-type scaffold, often leads to

total collapse. To ensure structural stability, bracing and lateral

support requirements for the various systems will have to be determined

either individually by design, or with the aid of tables and charts based on analysis.

Scaffolding systems must also be secured to prevent geometric instability

such as rolling or overturning. This means that the scaffold must be

anchored to its foundation in such a way as to inhibit rigid body displacements, and the foundation itself must be stable and capable of

supporting the applied loads.

Lastly, "recoverable" displacements must be maintained within tolerable

limits to ensure "stability" of working surfaces. This may be achieved

by designing the structure for a required minimum stiffness and providing

sufficient anchors to control excessive drift or vibration under certain

types of loads such as wind and uplift. In the accident study [1], numerous

casualties resulted from workers losing their balance because of excessive

movements of the scaffold. Suspended scaffolds are particularly susceptible to this type of movement due to the inherent flexibility in the

support system.

The codes and standards reviewed were found to be generally not cognizant

of the types of stability problems noted above. The limited amount of

information contained in these documents seldom meet the criteria of com- prehensiveness, clarity, consistency, adequacy and thus enforceability.

The type of statement such as "to prevent swaying or displacement" or "restrained from tipping by guying or other means", often encountered in

these documents, is not accompanied by quantitative information by which

the stability characteristics of scaffolding systems can be identified

and controlled. The following ANSI A10.8 provisions, which are frequently

cross-referenced by other codes and standards (table 2) are cited as examples to illustrate the point.

ANSI required vertical structural elements to be "securely and rigidly

braced to prevent swaying and displacement" and free standing towers with

a height-to-base ratio of 4 to 1 or more to be "restrained". The quoted

terms, which can be interpreted in different ways, underscore the need to

establish displacement tolerences by analyzing the effects of system com- ponent movements for the various scaffold types, configurations and loading

conditions

.

In a similar type of statement, support elements are required to bear on foundations of a size and strength capable of distributing the load safely.

However, once again, criteria by which such a requirement can be met are

not cited.

14
Most of the documents require scaffolds to be "securely anchored" at specified horizontal and vertical intervals which vary according to the type of

scaffold. Anchorage spacing requirement for the purpose of providing stability to the scaffold in the transverse direction will, in general, depend

on the structural characteristics and spatial configuration of the system

as well as on the magnitude and distribution of the applied loads. There

is no indication that the effect of these factors have been considered in

the development of the prescribed anchorage spacing requirements.

The effect of casters or wheels and locking devices on system stability

must be studied as well. Criteria for locking devices under long-term

repetitive use must be formulated because their performance is critical

in maintaining the stability of mobile systems.

Another stability-related item is the use of cross bracing which is a requirement cited by all the documents. However, no specific guidelines

are provided by which an adequate bracing system can be selected. A study

by the Scaffolding and Shoring Institute [19] on tubular frame-type scaffolds

indicates that the failure mode of the scaffolding assembly is characterized

by out-of-plane buckling of the transverse frame units. This response is

understandable in view of the high in-plane rigidity of the frame units

coupled with the high flexibility and slenderness of the bracing elements.

It would be of interest to study the effect of varying the frame-bracing

stiffness ratio on the overall response of the system with the aim of

developing criteria for optimizing the load response of the system. For

instance, if the study shows that increasing the relative stiffness of

the cross bracing elements produces a more favorable load distribution in

the system and increases its ultimate load response, a revision of current

practice to reflect this finding could lead to more economical designs and,

at the same time, provide bracing elements which are less susceptible to

accidental damage.

2.9 PHYSICAL PROTECTION

Most of the documents contain specific requirements for protective devices

such as guardrails, safety belts, screens, etc., and, in addition, specify

where and under what conditions they shall be used. However, there are some fundamental environmental safety-related differences in the prescribed

values which cannot be logically explained. For example, where guardrail

use is specified, ANSI, OSHA 1910 and OSHA 1926 require that they be

installed on open sides and ends of all platforms higher than 10 ft (3.1 m)

above ground, while according to CAL/OSHA, the corresponding figure is

7.5 ft (2.3 m).

OSHA 1926, additionally requires that on a scaffold having a minimum

width less than 45 in (1.1 m) , guardrails be installed at platform heights

greater than 4 ft (1.2 m) above ground. This height is also a requirement

of the Canadian Code, but the stated reason is not minimum width but

rather the presence of wheel barrows and other vehicles on the platform.

Lastly, the Atlanta Code contains the somewhat ambiguous requirement that

guardrails be installed on platforms greater than 20 ft above ground

15
or 6 ft above floor level. Similar discrepancies can be found when con- sidering the various code provisions on the use of safety belts and lifelines as indicated in tables 2a through 2e. The OSHA documents are not

altogether clear whether the lifeline should be independently supported

or wether the employee is required to "wear" it during the conduct of

work.

The issue of major concern from the standpoint of employee safety, is

the height of platform above which protective safety devices should be

made mandatory. Insight into the problem was gained by analyzing the

existing accident records involving falls of employees from heights

and related consequent injury and death statistics. It is difficult

to reconcile with the implication that if an employee falls from an unprotected work platform just under 10 ft (3.1 m) high, the likelihood

of serious injury or death is such that the absence of guardrail or other

protection will constitute an acceptable level of risk by one standard

but not by another.

Finally, a point of somewhat less concern, but nonetheless one that makes

the present OSHA documents unnecessarily voluminous, less readable, and

confusing is the duplication of text on the provisions for guardrails

and other safety devices. In OSHA 1926, for instance, specific guardrail

provisions are first stated under the general heading, and repeated, almost

identically, 15 different times under various type-specific headings. It

will take only minimal modification to consolidate under general provisions

a substantial amount of repetitive text on safety devices that now appear

under the type-specific headings, and thereby render the OSHA regulation

more concise and effective.

2.10 ENVIRONMENTAL SAFETY CRITERIA

With the exceptions of the Wisconsin and Connecticut codes, all codes

and standards reviewed contain at least one or two provisions relating

to safety of the work environment. These provisions deal with five sources of environmental hazards: objects falling from above, the

natural environment (wind, snow, ice), clutter or protruding objects,

corrosive substances, and fire. The accident study [1] corroborates the

existence of these hazards. Usually these conditions cause the worker

to lose his balance. The consequences of the loss of balance varied,

depending on the support system, from a critical fall to a bruised

leg. Injury from a falling object or a protruding nail can be serious,

depending on which part of the body is contacted and the magnitude of

force applied by the object striking the person.

The ANSI and OSHA documents offer the most comprehensive coverage of the

environmental hazards mentioned. ANSI calls for overhead protection

where needed, treatment of rope (suspension cable or lifeline) in the

presence of corrosive substances, and protection of rope or other members

in the presence of heat-producing processes. It prohibits workers from

working on scaffolds during storms or high winds, or working on platforms

covered with ice and snow unless they are removed and the planking sanded.

It prohibits tools, materials, or debris, from accumulating on platforms

16
and the use of corrosive substances unless approved by the manufacturer.

OSHA adds to these a provision for the use of wire ropes when acid solutions are used for cleaning buildings which are higher than 50 ft (15.2 m).

The model codes cited in table 2c (NBC and BOCA) have fewer provisions on

the conditions under which fire protection is needed as well as on type

and level of protection that should be provided. NBC limits the maximum

height of overhead protection to 10 ft (3.1 m) above the platform. NRCC

includes provisions for protection against splinters and protruding nails.

CAL/OSHA has provisions similar to ANSI but excludes the item of fire protection. Permission is granted for some reason for workers to access platforms with slippery conditions if these conditions are a necesary part

of the work. The other state authorities cited in table 2f (Wisconsin and

Connecticut) do not have any provisions for environmental safety.

The environmental provisions in the New York and Atlanta Building Codes are

few and focus on combustibility of materials, a hazard which none of the

other codes address. The scaffold accident study [1], however, provided

evidence that such a hazard exist and may lead to serious injury or death.

2.11 SPECIAL PROVISIONS

This section addresses situations requiring special attention and consideration by the scaffold designer or user. These situations are grouped

under the category of Special Provisions in table 2. Many of the special

provisions call for engineering services when unique design conditions

occur that are not addressed specifically. In most instances, the special

provisions are general in nature; however, clarification of numerous items

is needed if deviations by the user are to be prevented.

Under the category of 'general' in ANSI, exceptions are permitted to the

literal requirements if granted by the enforcing authority, if equivalent

protection is provided. Where the various types of scaffolds are provided

with more than one working level, the existing provisions require that professional services be used for their design. For clarity, such requirements should be factored out from the type-specific provisions and categorized as special provisions under the general heading.

3. SCAFFOLDING VARIANCES

The possibility exists that some situations in the field are deviations

from the OSHA scaffolding requirements but are net actual infractions.

The application for, and authorization of variances, and other relief

from occupational safety and health standards and regulations are discussed

in CFR Title 29 (Labor) 1905.10. A brief discussion of OSHA variances

is given below together with examples abstracted from cases documented

in the Occupational Safety and Health Reporter published by the Bureau

of National Affairs, Inc. (BNA).

When considering the many types of scaffolding used, both in general

industrial occupations (1910.28) and in construction activities (192.6

17
451), the OSHA regulations set forth numerous general and specific

requirements. The purpose of enforcing these scaffolding requirements

is, of course, to reduce hazards to personnel in various occupations.

However, there have been instances in which none of the scaffold types,

supplied and used as required (i.e., in compliance with the OSHA Scaffolding Regulations), were suited to accomplish the job at hand satisfactorily. In some of these cases, the employing companies have

required and have been granted permission to bypass the regulations by

using a specially designed scaffold or by introducing some non-complying

modification. Such variances, nevertheless, usually include the addition of other compensating requirements intended to offer the employee

equivalent safety under the working conditions of the particular job

for which the variance is granted. For example, additional requirements

might be imposed for the posting of danger warning signs or of maximum

load limits. It is important to note that the granting of the variance

applies only to the requesting company for the situation described and

not to other companies even though they might have the same working

conditions with which to contend. Some illustrative situations for which

OSHA variances have been granted, follow:

case 1:

The applicant was engaged in chimney construction and maintenance and

stated that in constructing a chimney, the elevated platform or scaffolding is moved upward with the construction. As the height of con- struction reaches 122 m (400 ft) or more, it becomes impractical to use an access ladder [OSHA 1926.552 (c) requires the construction of hoist towers

when hoisting personnel]. The applicants claimed that there was insufficient room on the small chimneys to build a hoist tower.

For these and additional claims of difficult conditions, the company was authorized (1) to transport personnel to and from the elevated platform

on chimneys under construction using a special workmen's hoist in lieu

of complying with 1926.552 (c) and (2) to transport personnel one at

a time, to and from an elevated scaffold on small diameter chimneys under

construction; or from a bracket scaffold outside the chimney using a boatswain's chair (in place of the material bucket) attached to a material

hoist bucket, with the worker's safety belt attached to a safety clamp

and lifeline according to the authorized instructions. These variations

were allowed provided additional conditions were met regarding the

construction and the operation of the hoist.

case 2:

The applicants were involved in constructing tanks made of steel plates

consisting of ring segments. This activity required special scaffolding

which is highly portable and is raised up the shell of the tank as new

steel plate ring segments are added. If 1926.451 (a) (4) were compiled

with (guardrail supports not to exceed 8 ft (2.4 m), and table L-3 were

followed (1926.451 (a) (10) - maximum allowable planking span), it would

be necessary to attach brackets to the ring plates at 7.8 ft (2.4 m)

intervals. A spacing of 10.5 ft (3.2 m) was required for the plates

18
which were 31.4 ft (9.6 m) long. In addition, the tank scaffolds do

not have toe boards as required by 1926.451 (a) (4) (5), and there were

some guardrail discrepancies caused by the goemetric difference between

the curved face of the tank and the straight adjacent edge of the scaffold

platform which led to the use of taut wire rope as a safety line.

Consideration of the applicants' claim resulted in their being authorized to use the special scaffolds provided that: (1) loose tools were

kept in well-designed containers secured to prevent their upset; (2) areas beneath working zones were roped off and posted with warning

signs; and (3) additional precautionary measures were taken regarding

scaffold occupancy and assemblage.

Because variance is granted only to one applicant (or a group of applicants involved in a given operation), similar requests and decisions

are to be found documented for different applicants. Since the frequency

of requests for a particular variance may have some influence on recom- mendations for future modifications of scaffolding requirements, a more detailed examination of documented scaffolding variances should be performed.

4. SUMMARY AND CONCLUSIONS

this report presents a review and assessment of scaffolding safety provisions in existing codes and standards. The documents examined are voluntary consensus standards and mandatory codes and regulations under Federal,

state and local jurisdictions. The study is part of an NBS research

project to develop the technical basis for the improvement of current

scaffolding practices.

The review places emphasis on the structural and environmental aspects of

safety. For the purpose of comparison, each document is broken down into

ten categories and each category is examined separately in the text. Table

2 presents a summary of the various provisions under the appropriate categories. Appendix A illustrates 21 specific types of scaffolds addressed

by the codes and standards. Appendix B discusses the technical basis

used in the design of wood platforms and highlights differences between

it and the scaffolding regulations.

The findings of this study bring into focus critical deficiencies in the

present scaffolding provisions. A prevalent trend is the inclusion of

requirements for compliance with certain expected performance attributes

without giving any specifics by which the level of performance can be

judged. Most notable is the absence of definitive criteria for the design

or evaluation of the adequacy of anchorages, connections and foundations.

It is significant that the failure of these same components were found

to be the leading causes of scaffolding accidents according to an earlier

study [1 ]

.

For work platforms and the support system, the provisions tend to be

generally more specific, sometimes to the extent of recommending actual

scaffolding systems. This latter approach, however, tends to inhibit

19
the use of alternative schemes which provide equivalent protection, unless

permission is granted through the variance process in the case of OSHA

Construction Safety Regulations.

For load supporting elements, most of the documents have adopted a simplified approach by recommending a factor of safety of 4 against failure.

However, in many instances, this approach is not consistent with present

materials-oriented codes and standards which taken into consideration

strength as well as ductility and other structural response characteristics of the product in developing the prescribed safety margins.

Some of the documents reviewed prescribed quantitative requirements related

to system stability, such as the provision of longitudinal and transverse

bracing and spacing of anchorages. However, it is judged that these

requirements will have to be supplemented by additional requirements, such

as strength-based criteria for determining sizes of bracing elements,

sizes and embedment lengths of anchorages, and displacement tolerances of

supports, before they can adequately cover for the stability of scaffolding used in construction practice.

In general, the documents examined do provide for the protection of personnel from environmental hazards by prescribing requirements for keeping

working surfaces free of debris, clutter, ice, sharp projections and

unguarded openings, and for the installation and use of safety devices.

There are cases, however, where the required level of protection against

a specific environmental hazard varies from one document to another, and

not all documents address the same set of environmental hazards.

Deficiences are also noted with regard to the lack of definitive guidelines for the evaluation of strength and stiffness degradation in service,

or provision of appropriate criteria for the repair, maintenance and

replacement of damaged components.

5 . RECOMMENDATIONS

Based on the review of existing scaffolding provisons presented in this

report as well as an analysis of scaffolding accidents documented in a separate report [1], the following areas of research are recommended:

1) Conduct a comprehensive review of the technical literature

regarding the scaffolding topics outlined in this paper.

2) Conduct a field study to identify scaffolding designs, loads,

specific applications and practices.

3) Develop a technical research plan by which construction scaffolding can be analyzed, and implement this plan so that necessary data

can be obtained for further analytical use.

4) In accordance with the technical basis estalished above, develop

improved criteria for the design and evaluation of scaffolding

systems used in construction work.

20
A review of technical literature serves two important functions. It

identifies pertinent research data that can be translated into criteria

for adoption by codes and standards. It also identifies areas of

needed research where technical information is scarce or unavailable.

Based on the findings documented in this report, the study of technical

literature should concentrate on the following items:

° Identify technical research information on anchors and connections

used in scaffolding applications. Topics of major concern are the

strength characteristics of nails, fasteners, bolts, clamps, couplers,

and anchoring devices.

° Review current literature regarding structural testing and evaluation

of scaffolding system and their components, including fabricators'

data.

° Identify existing evaluative techniques to assess bearing and displacement characteristics of foundation materials and their suitability to support scaffolding structures at grade level. Identify

literature on transfer of stress from thin-walled tubes across

end bearing configurations.

° Review the literature on movement, instability and displacement limitations of scaffolding systems, and the effects of such movements on human

subjects

.

° Review the technical basis by which safety and physical protection

devices were developed, and criteria for their application to scaffolding

systems

,

° Review technical literature on impact and dynamic effects on scaffolding

systems and their components.

In conjunction with the literature search, it is recommended that a con- current field survey be performed, to gather pertinent information on the

practical aspects of scaffolding applications for use in the later ana- lytical portion of the study. Recommended areas of specific interest are

the following:

° Collect information on the range and distribution of construction loads

according to type of construction and type of scaffold. This information is mandatory for the analytical research phase.

° Assess support system degradation and maintenance conditions and practices, especially weathering effects on lumber and corrosion effects

on steel.

Identify prevalent types of anchors and connections with emphasis on material type and application.

21
° Identify types and configurations of foundations and relate them to

type and size of scaffold used.

° Identify types of accessways in conjunction with the various types of

scaffolding uses.

° Assess susceptibility of system components to accidental damage which

might lead to instability problems.

° Identify environmental conditions regarding clutter, protrusions,

exposure of workers to falling objects, fire, corrosion, etc.

The literature and field study information will be used to develop the

remaining analytical research program. Therefore, it is important that

the majority of these efforts be completed before the research plan is

developed.

The analytical research effort will include the use of pertinent data

obtained from the above studies and it should consist of modeling techniques aided by laboratory investigations. It is recommended that the

following topics receive priority:

° Formulate a consistent approach for the structural analysis and

design of work platforms with major emphasis on material properties,

loading configuration, capacity reduction factors, safety factors and

a defined design strength.

° Develop mathematical models for computer analysis of the various types

of scaffolds, including constraints, support displacements, connection

and anchorage force resultants and displacements, and tie down and

guying effects, under various loading configurations.

Apply ultimate and working stress design concepts to scaffolding systems

and their components.

Develop minimum performance criteria for anchors, connections, wheels

and locking devices by laboratory investigations.

Perform anchor-foundation pull-out strength studies to establish ultimate anchor limit states, especially on anchors embedded in partially

cured concrete.

Conduct human loading effects on scaffold platforms and other components

including step-down and impact tests via human subjects and an anthropomorphic dummy.

The technical data obtained from the above effort will be analyzed and used

as basis for establishing a set of scaffolding safety criteria. These

criteria can then be used to upgrade scaffolding provisions in existing

codes and standards to enhance safety in the design and application of

scaffolding systems to construction practice.

22
6.

REFERENCES

1. Fattal, S.G., Mullen, C.L., Hunt, B . J . , Lew, H.S., Analysis of Scaffolding Accident Records and Related Employee Casualties, NBSIR 79-1955

National Bureau of Standards, Washington, D.C., January 1980.

2. American National Standard, Safety Requirements for Scaffolding,

et al. (ANSI A10.8, A92.1, .2, .3, .6), The American National

Standards Institute, New York, NY, 1971.

3. Occupational Safety and Health Standards, (Federal Register 29 CFR Part

1910), Occupational Safety and Health Administration, U.S. Department of Labor, Washington, D.C., 1974.

4. Construction Safety and Health Regulations, (Federal Register 29 CFR

Part 1926), Occupational Safety and Health Administration, U.S. Department of Labor, Washington, D.C., 1974.

5. State of California Construction Safety Orders (CAL/OSHA), Building

News, Inc., Los Angeles, CA, January 1976.

6. The National Building Code, American Insurance Association, New

York, NY, 1976.

7. The BOCA Basic Building Code, Building Officials and Code Administrators International, Inc., Chicago, IL, 1978.

8. Canadian Construction Safety Code, National Research Council of

Canada, Ottawa, Canada, 1977.

9. State of California Administrative Code, Fifth printing, Sacramento,

CA., 1926.

10. Construction Safety Code, State of Connecticut Labor Department,

Wethersfield, CT.

11. Wisconsin Administrative Code, Madison, WI, 1971.

12. Building Code of Atlanta, Atlanta, GA, 1973.

13. Building Code of the City of New York, Chapter 26, Administrative

Code, New York, NY, 1974.

14. Lew, H.S., Fattal, S.G., Shaver, J.R., Reinhold, T.A., Hunt, B.J.,

Investigation of Construction Failure of Reinforced Concrete

Cooling Tower at Willow Island, West Virginia, NBSIR 78-1578 National

Bureau of Standards, Washington, D.C., November 1979.

15. Eisenacher, E.A., Evaluation of OSHA Scaffolding Standards, Newport

News Shipbuilding, Newport News, VA, 1979.

23
16. Manual of Steel Construction, American Institute of Steel Construction, Inc., New York, NY

17. Timber Construction Manual, American Institute of Timber Construction, John Wiley and Sons, New York, NY, 1974.

18. Building Code Requirements for Reinforced Concrete, ACI 318-77,

American Concrete Institute, Detroit, MI, 1977.

19. Results of Steel Scaffold Testing, Scaffolding and Shoring Institute, Cleveland, OH, 1961, 1963, 1966.

24
TABLE 1. TYPES OF SCAFFOLDS ADDRESSED BY ANSI AND OSHA

ANSI (1977)-^ OSHA 1910„(1974) OSHA 1926 (1974) Cal/OSHA (1976) Wood pole do-' do do Tube and coupler do

Metal: Fabricated tubular frame Tubular welded frame Tubular welded frame - tube and coupler

- tubular welded frame

Manually-propelled mobile ladder stands do do Tower and rolling

and scaffolds (towers) (A92.1 - 1977)

Vehicle-mounted elevating and rotating 3/ Elevating and rotating Scaffolds on vehicles

work platforms (A92.2 - 1979) work platforms

Telescoping work platforms — — (A92.3 - 1973)

Self-propelled elevating work platforms — — — (A92.6 - 1979)

Outrigger do do do Masons' adjustable multiple-point Suspended:

suspension - brick layers' or masons' Two-point suspension (Swinging) (applies to stone

setters'

)

do do - load < 425 lbf Stone-setters' adjustable - ladder type

Multiple-point suspension - closed hook

Single-point adjustable suspension - load 425-1000 lbf

- power driven

Boatswains' chair do do do Carpenters' bracket do do Bracket

Carpenters' bracket

Bricklayers' square do do do Horse do do do Needle beam— do do do Plasterers, decorators, do — and large area Interior hung do do Wood pole-light trade interior

Ladder jack do do do Window jack— do do do Roofing brackets do — — Crawling boards or do — chicken ladders

Float or ship do do Float Catenary — — Staging supported by

catenary or horizontal — — wire ropes Form — Pump jack — do do

2/ Unless otherwise noted, ANSI A10.8 is referenced.

2/ "do" is an abbreviation for "ditto", implying that the same term is used as that which

is used in the first column by ANSI.

2/ A dashed line implies that the type is not discussed in the particular standard.

25
Table 2a. General Provisions for Scaffolding (ANSI)

AMERICAN NATIONAL STANDARDS INSTITUTE

AMERICAN NATIONAL STANDARD

ANSI A10.8 (1977)

1. Work Platform a. Planking 2-in (nominal) thickness selected for plank use recognized by grading rules-'' for species used.

b. For 2 x 10-in (nominal) or 2 x 9-in (rough) planks:

10 25

Span (ft) 1 8 for Working Load (lbf/ft^) £ 50

7 75

c^ Span _£ 4 ft for 1-1/4 x 9-in or wider plank of full thick- ness with medium loading of 50 lbf/ft . d. Fabricated planking may be used if it meets general strength

requirement (item 6).

e. Planks laid with opening <

1 in between adjacent planks

or scaffold member.

f. Planks or platforms in continuous run overlapped > in

or secured from movement.

g. Unless restrained at both ends, planks extend 6-18 in over

end supports.

2. Supporting

Elements

a. Load-carrying timber members of scaffold framing minimum of

1500 lbf/in^ (stress grade) construction grade lumber.

b. Rope for suspension supports ^ 6 x (intended load).

3. Connections a. Nails or bolts develop at each connection designed

and Anchorages strength of scaffold.

b. Scaffolds secured to permanent structures. Do not use window cleaner's anchor bolts.

c. Check ties and scaffold components to which ties are attached for additional load due to wind and weather if

scaffold partly or wholly enclosed.

4. Foundation Footing or anchorage sound, rigid, capable of supporting

maximum intended load without settling or displacement.

5. Accessway Ladder or equivalent safe access to platform. Both ladder

and platform restrained from movement.

6. Strength Scaffolds and their components support without failure ^ 4 x (maximum intended load).

1 / Grading rules approved by the board of review of the American Lumber Standards

Committee.

26
/ . Stability a. Poles, legs, uprights plumb, rigidly and securely braced

to prevent swaying and displacement.

b. Free-standing towers with height:base ratio >4:1

restrained from tipping by guying or other means.

8. Physical

Protection

2 / a. GR- (sizes specified) installed on all open sides and

ends of platforms > 10 ft above ground or floor.

b. Exceptions: 1) scaffolds wholly enclosed in building;

2) scaffold types 12-15, 19- with lifeline and

belt required if > 10 ft above ground.

c. GR with screens (size specified) in areas where persons

must work or pass under scaffold, except types 12, 13, 15,

19.

9. Environmental a. Overhead protection for men on a scaffold exposed to overSafety Criteria head hazards . b. Workers shall not work on scaffolds during storms

or high winds or on scaffolds covered with ice or snow unless removed and planking sanded.

c. Tools, materials, debris not accumulated on platforms.

d. Treat fiber or synthetic rope if corrosive substance used.

Acids or corrosive substances not used on scaffolds unless

approved by manufacturer.

e. Protect scaffold members, wires, fiber, synthetic rope

when using heat producing process.

10. Special a. Scaffolds not to be loaded in excess of load for which

Provisions intended

.

b. Manufactured scaffolds used in accordance with manufacturers

recommendations

.

c. Scaffolds not named or defined in this standard prohibited

unless exception granted by enforcing authority.

d. Scaffold designed by qualified engineer for type 1 > 60 ft

high or types 2, 3 > 125 ft high.

'GR' is an abbreviation for 'gaurdrails' assumed to consist of toprail, midrail and

toeboard

.

3Ul/ Scaffold types numbered and described in Appendix B.

27
Table 2b. General Provisions for Scaffolding (OSHA)

UNITED STATES DEPARTMENT OF LABOR

OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION A

Occupational S. & H. Standards OSHA 1910 (1974)

B Construction S. & H. Standards OSHA 1926 (1974)

1. Work Platform a. All planking shall be Scaffold Grade cf . OSHA 1910 recognized by grading rules for species

used.

b. For 2 x 9-in or wider planks: For 2 x 10-in or wider planks:

Full thick. Norn. Undressed thick. 10 — 25 Spans < 8 8 W.L. < 50 cf. OSHA 1910

(ft) 6 6 (lbf/ft2

) 75

c • cf ANSI cf. ANSI

d. o 0

e. o o

f

cf . ANSI cf. ANSI

g. cf . ANSI Planks extend 6-12 in. over end (End restraint not mentioned.) supports.

2. Supporting a. cf. ANSI*-^ cf. OSHA 1910 Elements *("1500 cf.")

b. cf. ANSI cf. ANSI*

*( "rated load”)

3. Connections and a. cf. ANSI Anchorages o Also nails not subjected to straight pull;

nails driven full length.

b. cf. ANSI o o o

4. Foundation cf • ANSI cfANSI

5. Accessway cf

ANSI cf

OSHA

(Restraint not mentioned.)

'Confero' , Latin meaning 'compare with' connoting 'similar to' as used. ^ An open-dot depicts items not addressed by the particular code or standard.

6^ A single asterisk depicts an unclear situation where wording lacks definition,

thus inhibiting interpretation of intent.

28
6. Strength cf . ANSI cf. ANSI

7. Stability

a. cf. ANSI cf. ANSI

b. 0 o

8. Physical

Protection

a. cf. ANSI cf. ANSI

Also, GR for scaffolds 4-10 ft high,

having minimum horizontal dimension

< 45 in.

b. Exceptions: 1) cf. ANSI Exceptions: types 13, 14.

2) scaffold types 13, 14 in use by structural

iron workers

.

c. cf . ANSI (noexceptions stated) cf. OSHA 1910

9. Environmental a. cf. ANSI cf. ANSI

Safety Criteria

b. cf. ANSI Slippery conditions eliminated as soon as possible after they occur.

c. cf. ANSI o

d. cf. ANSI When acid solutions used for cleaning

buildings > 50 ft high use wire rope supported scaffolds.

cf. ANSI

e. cf. ANSI No welding, burning, riveting, open

flame work on staging suspended by

fiber or synthetic rope.

10. Special a • cf. ANSI o Provisions

b. o . C o

c. o 0

d. cf. ANSI cf. ANSI

29
Table 2c. General Provisions for Scaffolding (NBC and BOCA)

American Insurance Association Building Officials and Code Administrators

National Building Code Basic Building Code

NBC 1201 (1976) BOCA 1314 (1978)

1. Work Platform a. Where wood planking used,

cf. OSHA 1910. Platforms and supporting elements**

designed, constructed to support uniform

minimum live loads in lbf/ft of platform

area in accordance with following:

Class Service Type Load

Light

Duty

Carpenters

Stone setters Miscellaneous(no

(no

stone)

material)

25

Medium Bricklayers

Duty Stucco 50 Lpthers, Plasterers

Heavy

Duty Stone masons 75

2. Supporting

Elements

b.

Where load carrying members are wood, use stress graded lumber, having extreme

fiber stress in bending, f > 1200 psi.

cf. ANSI

**

3. Connections and Anchorages

** o

4. Foundation ** o

5. Accessway ** o

6. Strength cf. ANSI but > 100 lbf/ft2 cf. ANSI

TT The double asterisk shows which categories within a code share the same cross-reference.

30
7. Stability o

8. Physical

Protection

cf. OSHA 1926

b. Exceptions: 1) 02) cf. OSHA 1910 All floor and wall openings shall be protected with substantial guardrails

and toe boards in accordance with

accepted engineering practice.

cf. ANSI

9. Environmental

Safety Criteria

a. Overhead protection (< 10 ft above platform) capable of supporting objects likely o

to fall.

b-d o

e. Provisions (specified) where scaffolds

materials require fire protection.

cf. NBC

10. Special c. On matters not detailed in this code**

Provisions conformance with provisions of ANSI A10.8 evidence that scaffold is reasonably safe. o
Table 2d. General Provisions for Scaffolding (NRCC)

National Research Council of Canada

Canadian Construction Safety Code

NRCC 15562 (1977)

1. Work Platform a. Wood** platforms have planks of same thickness

> 2 x 10-in (nominal). _ b . For 2 x 10-in (nominal) planks, span _< 8 ft, and

25 8 Load (lbf/ft^) if span (ft) < 50 6

d. o

e. Planks laid tightly together.

g. Platform securely fastened tied in place; planks extend over

end supports 6-12 in.

(Planking subject to general strength requirement-item 6.)

2. Supporting

Elements

a. Material used in construction of scaffold shall be

suitable for intended use. Where lumber used** it

shall be > strength of No. 1 Spruce.

b. No general provision.

3. Connections and

Anchorages

Horizontal members shall not be spliced between points of

support

(Joints subject to general strength requirement-item 6.)

4.

Foundation cf. ANSI

5.

Accessway Except for suspended scaffolds, platform > 5 ft above

level workman may fall provided with means of access

and egress (specified).

6.

Strength Scaffold including joints and planking shall be

capable of supporting _> 4 x (maximum intended load).

32
7. Stability a. Uprights shall be adequately braced diagonaxly and

horizontally to prevent lateral movement.

b. Scaffold adequately secured to suitable supports at

vertical intervals < 3 x (least base dimension).

8. Physical a. GR at areas to which workman has access and may fall

Protection into water or vertical drop > 10 ft; where wheelbarrows or other vehicles used GR when drop > 4 ft.

b. Use wood GR (sizes specified); wire cable and snow fencing may be used unless prohibited by appropriate

authority having jurisdiction.

c. GR with screens (size specified) where required by

appropriate authority having jurisdiction.

d . Safety belt and independent lifeline for suspended scaffolds.

9. Environmental

Safety Criteria

Barrels, boxes or similar loose objects shall not

be used to stand upon while working; top rails of

GR shall be free from splinters or protruding nails.

10. Special a-b o Provisions c. Scaffolds or components thereof that do not comply

in all respects with provisions of this code shall

not be used unless approved for such use.

d. Temporary works shall be designed by a professional

engineer competent and experienced in this type of work

where required by appropriate authority having

jurisdiction or scaffold > 30 ft high.

33
Table 2e. General Provisions for Scaffolding (Cal/OSHA)

State of California

Administrative Code-Industrial Relations

Construction Safety Orders

Cal/OSHA 29 (1976)

1. Work Platform a. Except when specified, planks 2-in (nominal) material

selected for scaffold grade plank (defined).

b. cf. ANSI

c. cf. ANSI

d. cf. ANSI

e

No general provision.

f No general provision.

g. Plank overhang its support < 18 in, unless access

to overhanging portion prevented or unless other

end of plank anchored.

2. Supporting

Elements

a. No general provision.

b. cf. ANSI,*

under type-specific provision

*( "factor of safety of 6")

3. Connections and cf. ANSI; also, nailed joints not support concrete

Anchorages hoppers with capacity > 1/2 yd , nails 8-penny

size; minimum number of nails specified for various

connection types and size lumber; lubricated or wax-coated nails not used.

4. Foundation No general provision.

5. Accessway Safe and unobstructed means of access, such as walkway,

stair, or ladder provided to platform.

6. Strength cf. ANSI* (Inspection and replacement of pieces

not meeting requirement called for - test implied.)
7. Stability a. Anchorage and bracing shall prevent scaffold from

swaying tipping, or collapsing.

b. o

8. Physical a. GR (sizes specified) on all open sides and ends of

Protection elevations > 7-1/2 ft above level below.

b. Exceptions: scaffold types 15, 19

c. cf. ANSI, if material on a railed scaffold is piled

higher than the toeboard (canvas and equivalents to

1/2-in wire mesh permitted).

d. Provisions for use of safety belts and nets.

9. Environmental a. cf. ANSI

Safety Criteria b. Worker not permitted to work on platform where

slippery conditions exist unless such conditions are

a necessary part of the work.

c. cf. ANSI

d-e o

a-b cf. ANSI

10. Special c. Scaffolds constructed of wood or suitable materials

Provisions such as steel or aluminum members of known strength

characteristics. Where materials other than wood used or scaffold designs differ from provisions in these orders,

equivalent strength, rigidity, safety must be provided.

d. cf. ANSI, professional engineer currently registered in

California; some reductions in permissible height for

several working levels on same scaffold.

35
Table 2f. General Provisions for Scaffolding (Stare Authorities)

1. Work

Platform

State of Wisconsin

Wisconsin Administrative Code

Rules of Industry, Labor, and Human Relations

(1971)

cf. NRCC

State of Connecticut

Labor Department

Construction Safety Code

(1971)

Except where otherwise specified:

b. Span <_ 8 ft, except for printing, decorating,

and paper work (conditions given). Safe load

is proportional to allowable stress, also varies according to load distribution assumed

(examples shown for one species and one

2x9 or 2x10 10 Plank size > 2x12 Span < 12 (in) 2x14 (ft) 14 2x16 16 2x20 or 3x10 20

c-d o o e. Platform to be solid, except spacing < 18 in

permitted for Jlght work (defined).

f

Two successive planks not to abut on a single bearer; where overlap, ends of upper

and lower planks overlap bearer > 6 in.

o

g- Planks shall project over last bearer

6-12 in. cf. Cal/OSHA

(Subject to general strength requirements - item 6.)

(Subject to general strength requirements

item 6.)

2. Supporting

Elements a-b (Subject to general strength requirements - item 6.

)

(Subject to general strength requirements

item 6.)

3. Connections

and Anchorages

4. Foundation

5. Accessway

6. Strength

fft2 /

cf. OSHA 1910 except for type 14 (Minimum nail sizes given for various

material thicknesses).

Load-supporting members have 5 nails at each connection.

braces and GR have 2 nails at each connections

cf. Cal/OShA

b-c

Post not to stand directly on ground. Foot- ing or foundation (size specified for wood)

to spread load to prevent settlement.

No general provision.

Lumber to be stress grade material, carrying

imposed loade safely without exceeding

allowable working stresses (specified). Metal

to conform with ASTM^' standards (given). All scaffolds designed and built so unit stresses

in material under maximum loading >_ specified. Factor of safety of 4:1 for metal scaffolds.

cf. Cal/OShA

Lumber equivalent of "selected lumber" free from damage that affects its strength.

Replace pieces of lumber that cannot support

4 x (maximum load to be imposed). Refer- ence SSSI-' for allowable stresses and safety factors for metal scaffolds. Factors

of safety of 6 for suspension rope.**

American Society for Testing and Materials.

Steel Scaffolding and Showing Institute.

36
7.

Stability a. Scaffold types 1, 8, 17 braced to prevent cf. Cal/OSUA

lateral movement or distortion of the whole

or any part (guidelines for removal of braces).

Free-standing towers or rolling scaffolds to

b. o have least base dimension _> 1/3 height unless

guyed.

8.

Physical

Protection

a • cf. ANSI o

b. Exceptions: riveter's platforms, scaffold

types 18, 19, and single plank

painters' scaffolds.

Exceptions: 1) cf. ANSI

2) cf. ANSI

c. cf. Cal/OSHA

o

d. Independent lifelines for suspended

scaffolds o

9.

Environmental

Safety Criteria

o o

10. Special a-b o o Provisions c. Suspended scaffold systems must be approved

by industrial commission.

cf . Cal/OShA

d. o o Also, plates in appendix provide all

e. History of certain provisions referenced provisions for pole scaffolds.

by industrial commission. Metal scaffolds are to be of standard manufacture.
Table 2g. General Provisions for Scaffolding (Municipal Authorities)

City of New York

Building Code

(1968 - amendments through 1974)

City of Atlanta

Building Code

(1973)

1. Work Platform

b. For 2-in planks:

25

If W.L. < 50

(lbf/ft 2

) 75

Planks >_ 2-in (nominal) thickness of sound, seasoned lumber.

Full thick,

undressed

10 Span _< 8 (ft) 6

Nominal

thickness

8

6

5

c. For 1-1/4-in plank of full thickness

span < 6 ft, working load < 50 lb/ft

**

,1

d. o

e. Planks laid tight and fastened if Inclined

f

o

g- cf. ANSI

2. Supporting ** Elements Test suspended scaffolds; must carry 4 x (load

to be carried) through distance of 1 ft; wire

rope support 6 x (actual load).

**

3. Connections

and Anchorages

a. cf. ANSI

(Minimum requirement for sizes and number

of nails specified).

)

**

b. cf. ANSI ;<

4. Foundation cf. ANSI; also, secure against movement

in any direction.

Provide adequate footings for uprights.

5. Accessway

6. Strength Strength and quality of lumber used in scaffolds or their supports** >_ construction grade Douglas fir. Loads

not concentrated so that allowable

stresses > (specified).

38

cf. ANSI, but > 125 lbf/ft
7. .stability Adequate cross-bracing fo r upri g hts .

cf. ANSI

8. Physical

Protection

a. cf . ANSI unless otherwise specified for particular type of scaffold.

b. o

cf. ANSI

GR (heights specified, not sizes) if platform > 20 ft above ground or 6 ft above

floor level. Exceptions: iron workers' scaffolds and

type 16 Screens (size not specified) if material

higher than toe boards.

Environmental a • o cf. ANSI

Safety Criteria b.c.d. Falling tools orodebris prevented.

0

e. Except planking,

rial (conditions

use noncombusitble matespecified) . Platforms and supports noncombustible

material or treated wood (conditions

specified)

10. Special a. cf . ANSI (standard loads defined). ** Provisions b. Construction of designed scaffolds in

accordance with designs.

c. Materials or dimensions other than specified may be used if equivalent to compar- cf. NBC** able scaffold and approval of commissioner

obtained

d. Type 1 scaffolds > 75 ft and all

type 9 scaffolds shall be ** designed; drawings kept at site.

39

APPENDIX A

2.1 Major Types of Scaffolds Under Study

A1
TABLE OF CONTENTS

Type Name Page

1 Wood pole scaffold a) single post A-3

b) double post A-A

2 Tube and coupler scaffold A-5

3 Fabricated tubular frame scaffold A-6

A Manually propelled mobile ladder stand and scaffold tower A-8

5 Vehicle-mounted elevating and rotating A-9

6 Telescoping work platform A-9

Self-propelled elevating work platform A-9

8 Outrigger scaffold A-10

9 Adjustable multiple-point suspension (masons' or stonesetters') scaffold A-ll

10 Two-point suspension (swinging) scaffold A-ll

11 Single-point suspension scaffold A-ll

12 Boatswains' chair A-12

13 Needle beam scaffold A-12

1A Float or ship scaffold A-12

15 Catenary scaffold A-12

16 Bracket (carpenters' bracket) scaffold A-13

17 Square (bricklayers' square) scaffold A-1A

18 Horse scaffold A-1A

19 Ladder jack scaffold A-15

20 Window jack scaffold A-15

21 Pump jack scaffold A-16
Type la

Figure A.l. Wood pole scaffold - (a) single post.

A3
Figure A.l. Wood pole scaffold - (b) double post

AType 2

Figure A. 3. Tube and coupler scaffold,

A5

a/cuT

£ OH 0IMHII WX.lt.) — fciVOkJfr'T TVPfe' -JklLi'tTOgl,

- fcA'ci ?i-4Tfr\, TO

• OOP <3 -L*. ACTVB.

feBfc't.TilJa Glff^T

i.feMfc'o OF CaA^fcV

•-POST OC Lfc'i

OKTtiu'fc'
Figure A. 4. Fabricated tubular frame scaffold.

AFigure A. 5. Tubular frame subsystems.

A7
Figure A. 6. Manually propelled mobile (a) ladder stand and (b) scaffold (tower).

A-8
wmULLLLlilffll

(b) Type 6 (c) Type 7

Figure A. 7. (a) Vehicle-mounted elevating and rotating, (b) telescoping, and

(c) self-propelled elevating work platforms.

A9
UALU

THIS INB I

; StCURCD

StCUtCD

| | GAINST

•itiocr

1

; I ovuruta

t — _-

WW/Ww/7W.

=*

iUULB.

gA^Ai? _

TOC Bg*m^

3 » a' n

' l

’ m*'--'1

.)

-4-- t' TO <*- 0

*

Type 8

Figure A. 8. Outrigger scaffold

f igi

A- 1
WL 1

:]T

KIMMflt >TWt

(b) Type 10

^ -41 n»* i » ii »««««. *T 2

V ft.lfl.gAP MtltTWI

k

m

i

I

i

r

4W ! ^-a r ^ i*‘ —

H

j

(a) Type 9

(c) Type 11

Figure A. 9. (a) Adjustable multiple-point (masons' or stone-setters'), (b) twopoint (swinging), and (c) single-point suspension scaffolds.

A-ll
(a) Type 12

(b) Type 13

Prhip* rx offi«r C»w Srnx-fi/r*

JE^r-v n n—ft n c

J r

"" ^ 1 N

v

r*0'**'

(d ) Type 13

Figure A. 10. (a) Boatswain's chair, and (b) needle beams, (c) float or ship,

and (d) catenary scaffolds.

A-12
Type 16

Figure A. 11. Bracket (carpenters' bracket) scaffold.

A- 13
figure

(b) Type 18

• L2, (aj Square kDnckiayers square; ana (.d; norse scarroias.

A- 14
(b) Type 20

Figure A. 13. (a) Ladder jack and (b) window jack scaffolds.

A-15
Type 21

Figure A. 14. Pump jack scaffold.

A- 16
APPENDIX B

SUMMARY AND REVIEW OF EXISTING STANDARDS FOR THE DESIGN OF

SCAFFOLD WORK PLATFORMS CONSISTING OF WOOD PLANKING

B-l
INTRODUCTION

This Appendix provides a summary and review of certain existing

standards used in determining strength and design values for wood

construction. These standards are listed below and are referred to

throughout this section. The original formats have been maintained in

order that clarity and cross-referencing might be facilitated.

The purpose of this section is to identify the technical bases by which

wood design values are obtained and to convey, through the scaffolding

provisions of ANSI and OSHA, the need to recognize these bases. In particular, the actual factor of safety determined by these technical bases is

is different from that specified by the codes and standards for scaffolding. It is recommended that the reader become familiar with the following

documents

0 ASTM: D245-74 , Standard Methods for Establishing Structural

Grades and Related Allowable Properties for Visually Graded

Lumber.

ANSI/ASTM: D2555-78 , Standard Methods for Establishing Clear

Wood Strength Values

° National Design Specification for Wood Construction; 1977.

B.l APPLICABLE PROVISIONS IN EXISTING STANDARDS

B.1.1 ANSI A10. 8-1974

3 . General Requirements for All Scaffolds

3.4 Scaffolds and their components shall be capable of supporting without failure at least four times the maximum intended load. (except)

3.9 All planking shall be 2-in (nominal) selected for scaffold plank

use as recognized by grading rules approved by the Board of Review

of the American Lumber Standards Committee for the species of wood

used. 1 '* The maximum permissible spans for 2 x 10-in (nominal) or

2 x 9-in (rough) planks shall be as shown in the following table.

Working Load Permissible Span

psf (KN/nT ) ft (m)

25 (1.2) 10 (3.1)

50 (2.4) 8 (2.4)

75 (3.7) 7 (2.1)

* Numerical superscripts designate notes listed at the end of this Appendix.

B-2
The maximum permissible span for 1-1/4 x 9-in or wider plank of full

thickness is 4 ft with medium loading of 50 lb/ft . Fabricated

planking may be used if designed in accordance with 3.4 of this

section. (excerpt)

B.1.2 ASTM D245-74

3. Foreword

3.2 Visual grading procedure:

1. Examine all four faces and ends of piece.

2. Evaluate location, size, and nature of knots and other features

appearing on the surfaces over the entire length.

3. Assign strength ratio for pieces representing strength in relation to strength without presence of weakening characteristics.

3.3 Use classification of structural lumber

The various factors affecting strength such as knots, deviations of

grain, shakes, and checks, differ in their effect, depending on the kind

of loading and stress to which the piece is subjected. Structural lumber

is therefore often classified according to its size and use. (excerpt)

Classes: joists and planks, beams and stringers, posts and timbers, and

structural boards.

Planks - pieces of rectangular cross section, 2-4 in in least dimensions,

graded primarily for strength in bending flatwise.

3.4 Essential elements of stress grade description:

1. Grade name identifying use class.

2. Permissible growth characteristics that affect mechanical properties .

3. Allowable properties for the grade related to its strength

ratio.

6 . Determination of Allowable Properties for Timber Design

6.1 1. Average wood property values and their standard deviation are obtained from Tables 1-3, ASTM D2555-78, for a particular

species of wood.

2. Allowable properties for green lumber are computed according

to the permitted growth characteristics. It is assumed that

design loads act for a normal duration (taken to be 10 yr) and

B-3
are realistic, and that each member carries its own load.

A 5 percent exclusion limit is assumed, that is, the allowable

stresses are intended to be less than the stress permissible for

95 percent of the species in a species group and stress grade.

6.2 The 5 percent exclusion limit value for bending strength, et. al.

obtained from ASTM D2555-78 when divided by an adjustment factor

(given in Table 9) gives the allowable design properties for

clear straight-grained wood. The factor includes an adjustment

for normal load duration and a factor of safety .

6.4 The properties obtained in 6.2 are further modified according to

the permitted characteristics in any stress grade by multiplying

the properties by the appropriate strength factors. These

factors include slope of grain, knot size and location, variation

in lumber size, defects etc., and are cited in 4.2 and are highlighted

below

1. Grading factor - reduces the strength value in accordance with

the growth characteristics (slope of grain, knots, shakes,

checks, and splits) permissible for a particular grade. (Note - unsound knots and limited amounts of decay in its early stages

are permitted in some of the lower stress - rated grades used

in light framing.)

2. Density factor - increases the strength value for the effect of

specific gravity greater than the average value of the particular

species. Density is in part determined by the rate of growth of

a particular species (number of annual rings per radial strength).

3. Seasoning factor - increases strength value for effect of moisture content below that of green lumber. (Note - maximum moisture

content expected in the field must be estimated by the designer.)

4. Temperature factor - increases or decreases the strength value

for the effect of temperature substantially different from the

laboratory temperature of 68 + 7 F (20 + 3 C) specified for the

text. The effect of temperature depends on the moisture content,

but generally increases strength during cooling and decreases

strength during heating. (Note - the range and effect of temperature expected in the field must be estimated by the designer.)

5.

Load duration factor - decreases the strength value for the

effect of duration of load and stress different than the 5 min

load duration specified for testing. (Note - grading procedures

incorporate this assuming a normal duration of 10 years; the

variation from the normal condition of the load duration expected

in the field must be estimated by the designer and the effect

ascertained from the appropriate curve or equation expressing

the strength - load duration relation.)

B-4
7 . Modification of Allowable Properties for Design Use

Note 2 - The principal modifications made in design properties

are summarized in Table 10. It is assumed to be the final responsibility of the designing engineer to relate design assumptions and

allowable properties, and to make modifications of the allowable

properties for seasoning and duration of load to fit a particular

use. These modifications are often subject to the requirements of

a building code. This section contains some recommended modification criteria. (excerpt)

B.1.3 ASTM D2555-78

Note 9 - An exclusion limit is a level of strength below which a selected percentage of the strength values are expected to fall and

corresponds to a selected probability point from the frequency

distribution of strength values. A 5 percent exclusion limit for a species or regional subdivision is obtained by multiplying the

standard deviation for the strength property under consideration

by 1.645^ and subtracting the product from the average strength

values, (excerpt)

A1 . Principals for Conversion to Working Stresses

A1.7 Factor of safety.

Working stress standards for marketed wood products should take

into account, after applying the foregoing factors (duration of

load, moisture content, temperature, strength reducing characteristics, and shape and form), whether a further reduction of stress

for factor of safety should be made, and if so how much. The

accounting should be made preferably by considering the factor of

safety to be multivalued and as depending upon conditions of both

strength and use. The factor of safety may recognize differences

in the hazards and the consequences of failure appropriate to the

expected uses of the various marketed wood products. An extended

discussion of the factor of safety is found in ASCE Transactions , Paper No. 3051, "Factor of Safety in Design of Timber Structures,"

(1960). (excerpt)

B .2 APPLICATION TO DESIGN OF WOOD WORK PLATFORMS

Structural design parameters:

1. Loads - depend on service type and the natural environment.

2. Species and section properties of planking - depend on availability.

3. Bending stress - depends on span, section properties,

magnitude and distribution of loads, and support conditions.

4. Factor of safety - ratio of expected strength to expected stress

and its magnitude depends on uncertainties in the estimation

of loads and resistance and on the consequences of failure.

B-5
Application of code provisions by a design example:

1. Estimate working loads, w: 25, 50 and 75 psf (1.2, 2.4 and 3.7 KN/m2

) 2. Select, for example, 2 x 10 in (51 x 254 mm) (nominal) eastern

spruce

3. Assume uniform load w acts over entire span, L, and that the

planks are simply supported at their end. According to the

technical theory of mechanics of solids the maximum bending

stress, f, occurs at the extreme fibers (top and bottom of the

section at midspan) and has magnitude computed as follows:

3 2

f = 4 W (L/h) B.l

4

where w = load per unit of platform area

L/h = span to thickness ratio of planking

Typically, the designer selects appropriate values for the above listed

parameters in accordance with code provisions. ANSI A10.8 provision

3.4 (which is adopted by OSHA and several other authorities with

enforcement powers) presents an overriding strength requirement of 4 times

the intended load. Maximum spans for planks subject to various loading

levels are then prescribed in provision 3.9. Provision 3.4 can be interpreted to mean that a factor of four should be applied to the maximum

intended working load thus generating an ultimate design stress. Applying Equation B.l and using the span permitted for this working load, the

designer would compute the bending stress below which failure should not occur. The prescribed level of safety would presumably be assured by

selecting a grade of wood with a modulus of rupture higher than the

computed value. However, if this method is used in obtaining a final

factored ultimate stress, it is not consistent with the National Design

Specification for Wood Construction (NDSWC) procedure used in establishing the allowable design stress for wood construction as will now be

demonstrated

Table 4A of the supplement to the (NDSWC) gives allowable bending stresses

derived using the procedure outlined in ASTM D245-74. Review of these

procedures reveals that the allowable values trace back to an average

modulus of rupture for a clear-grained, green specimen 1.25 x 1.25 x 48 in

(32 x 32 x 1219 mm) tested in the laboratory. As was mentioned above,

these values must be modified to incorporate variation in the properties

of wood. To illustrate the complexity concerning the varying factor

of safety arising when applying the provisions of NDSWC, the following

example will be considered.

Selecting an eastern spruce which according the Agriculture Handbook No. 71

(.USDA), dries easily and is stable after drying, is moderately light in

weight and easily worked, has moderate shrinkage, and is moderately strong,

stiff, tough, and hard... The largest use of eastern spruce is in plywood,

it i s also used for framing material, general millwork, boxes and crates,

B-6
ladder rails, scaffold planks , and piano sounding boards." (Note - No. 1 eastern spruce is specified by the National Research Council of Canada

(NRCC) to be a minimum standard grade for lumber used in the construction

of scaffolds.)

Given: ° w = 25 psf (1.2 KN/m^)

° 2 in x 9 in (51 x 229 mm) (Rough)

° L = 10 ft (3.1 m)

° flatwise repetitive use

° density = 36 pcf (576 kg/m^)

The allowable bending stress for No. 1 grade eastern spruce 2 x 9 in

planking when there are repetitive members is 1250 psi. This value is

increased by a factor of 1.22 for the case of flatwise bending, thus the

allowable stress is 1525 psi. This represents the allowable stress for

wood used at a maximum moisture content of 19% and under a 10 year load

duration. To calculate the expected ultimate of this wood, the procedures

of ASTM D-245 may be used:

where f = the allowable stress

k f = adjustment factor given in table 9 f =5% exclusion limit strength under short-term test

condition.

lor the case of bending the adjustment factor is 2.1; this value is derived

as the product of a load duration factor and a partial safety factor. The

load duration factor is used to convert the short-term strength from

laboratory tests to strength under sustained load. For a 10-year load

duration the load reduction factor is estimated to be 0.625 (using Figure

5 of ASTM D245) . Thus, according to B.2, the short-term ultimate strength

would be (1525) (2.1) = 3200 psi, and the ultimate strength under 10-year

load duration would be (3200) (0.625) = 2000 psi.

The parameter of major interest is the actual factor of safety which exists

for a given situation. This actual factor of safety is defined by the

following ratio;

F.S. = (ultimate strength) /(actual stress). B.3

The actual stress can be calculated for the given problem by equation

B.l. Using the prescribed span, loads and board dimensions, the actual

stress is found to be;

f act = 580 psi (4 N/mm^)

B-7
The ultimate strength (that is, 5% exclusion limit) for the No. 1 grade

eastern spruce planking would be 2000 psi if the moisture content does

not exceed 19% and the load duration is assumed to be 10 years. The

provisions of NDSWC specify a strength reduction factor of 0.86 in cases where moisture content exceeds 19%. In addition, there are modification

factors for load duration other than 10 years as follows:

load duration modification factor

> 10 years 0.90

2 months 1.15

_< 7 days 1.25

wind or earthquake 1.33

impact 2.0

The ultimate strength in this problem will depend on moisture content

and load duration and thus the computed safety factor can have one of

many values. To illustrate the possible range, the upper and lower

bounds of the actual factor of safety are computed as follows:

Upper bound :

Impact loading, less than 19% moisture content.

Ultimate strength = 2000 x 2 x 1 = 4000 psi

F.S. = 4000 _ 6 9

580

Lower bound

Greater than 10 year loading, more than 19% moisture content.

Ultimate strength = 2000 x 0.9 x 0.86 = 1550 psi

F.S. = 1550 = 2 7 580

Of these two limits, the upper is unlikely in that it assumes that the

entire design load is due to impact. It would seem reasonable to use a 10-year load duration and moisture content above 19% for routine scaffolding application. Under these conditions the safety factor would be:

_ c _ 2000 xlx 0 . 86 _o n F - S ' ' “580 3-0

The above has illustrated a serious inconsistency in scaffolding standards modeled after ANSI A10.8. Using the prescribed design loads and

maximum spans can lead to a factor of safety less than the overriding

prescribed value of 4.

The complex and technical procedures by which wood design values are obtained are due to the anisotropic and variable nature of wood; that

is, wood has properties that vary with orientation of the wood relative

B-8
to the applied loads and these properties are altered by natural and

manufacturing defects. Consequently, the general provision of ANSI and

OSHA, which specifies a 4 to 1 strength factor reflects incognizance

regarding the existing technical bases by which wood design values are determined.

Therefore, technical research addressing strength and safety requirements must be performed in order that a more meaningful safety factor can be identified per scaffolding type and be incorporated in the codes

and standards.

Notes

1 Grading rules are promulgated by associations of manufacturers and

approved by the Board of Review of the American Lumber Standards

Committee, the National Grading Rule Committee, and the National

Bureau of Standards. The National Design Specification for Wood

Construction (NDSWC), 1977, presents allowable strength values for

various species based on the rules set forth by seven agencies

having jurisdiction in different parts of the United States and

Canada. The design values for visually graded lumber are based on

the provisions of ASTM D245-74, "Methods for Establishing Structural

Grades and Related Allowable Properties for Visually Graded Lumber."

These values are published in Table 4A of this supplement to (NDSWC)

(1977).

2 The value of 1.645 is derived from an assumed normal (bell-shaped)

probability distribution function.

B-9
I J...4A ’ *» e. V . 9- / 8

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 79-1937

4. TITLE AND SUBTITLE

Review of Current Codes and Standards for Scaffolds

X * Action Nc.

5. Publication Date APRIL 1980

mmm

7. AUTHOR(S)

S. George Fattal , Christopher Mullin,

Hai S. Lew, Bernard J. Hunt

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, city, state, ZIP)

National Institute of Occupational Safety and Health

Department of Health, Education and Welfare

Washington, D.C.

13. Type of Report & Period Covered

15. SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

IS. ABSTRACT (A 200-word or leaa factual aummary of moat aighificant information . If document includea a aignificant bibliography or

literature aurrey, mention it here.) This report presents a critical review of the provisions in existing codes and

standards for the design, erection, operation and maintenance of scaffolds used

in construction work and other applications. The requirements in these documents were examined from the standpoint of clarity, consistency and completeness,

Ambiguities arising from conflicting requirements or from provisions that led to

more than one interpretation, and lack of consideration of major safety-related

structural, environmental and human factors are highlighted. In addition, the

adequacy of, and the rationale behind, the prescribed provisions are examined.

These are supplemented by a specific application appearing in Appendix B.

Appendix A illustrates common types of scaffolding systems that have been

addressed by at least one of the codes or standards examined. The findings

of this study serve to identify principal areas of needed research to improve

present scaffolding practices.

17. KEY WORDS (aix to twelve entriea; alphabetical order; capitalize only the firat letter of the firat key word unleaa a proper name;

aeparated by memicolona)

Codes and standards; construction safety; design; loads; maintenance; occupational

hazards; scaffolds; stiffness; strength; structural safety; work surfaces.

II. AVAILABILITY Q£) Unlimited

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Qj Order From Sup. of Doc.. U.S. Government Printing Office, Washington, DC

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K~] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

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