Analysis of Scaffolding Accident Records and

Related Employee Casualties

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

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

January 1980

I Prepared for

! National institute of Occupational Safety and Health

PIP Department of Health, Education and Welfare

Washington, D.C.

100

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79-1955

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• A • ANALYSIS OF SCAFFOLDING ACCIDENT

RECORDS AND RELATED EMPLOYEE CASUALTIES

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S. G. Fattal

C. L. Mullen

B. J. Hunt

R. S. Lew

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

January 1980

Prepared for National Institute of 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., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
OAVan JAHOIT*«

086t
ACKNOWLEDGEMENT

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 the Bureau of Labor

Statistics (BLS) and the Occupational Safety and Health Administration

(OSHA) for their special assistance in providing the information

used in compiling this paper.

In addition, to Ms. Ava I. Moore, University of Kansas School of Architecture, for capturing the special effects for the cover photograph

and to Mr. Larry Hale, NBS Photographic Services, in making these effects

part of this publication. A special thank you to Ms. Tracey Kistler,

Ms. Ulesia B. Gray and Mrs. Mary Rams burg for the typing of this paper.

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TABLE OF CONTENTS

Page

ABSTRACT . . . ill

ACKNOWLEDGMENTS iv

1. INTRODUCTION 1

2. APPROACH 3

3. BASIS OF STUDY 9

4. ANALYSIS OF ACCIDENT CAUSES 14

4.1 Presentation of the Data 14

4.2 Interpretation of General Trends 15

4.3 System Failures 18

4.3.1 Work Platforms 18

4.3.2 Support Elements 20

4.3.3 Connections 20

4.3.4 Anchors 22

4.3.5 Foundation 23

4.3.6 Accessways 24

4.3.7 Safety Devices 24

4.4 Environmental Factors 25

4.5 Human Factors 26

5. SUMMARY AND CONCLUSIONS 29

6. RECOMMENDATIONS 31

7. REFERENCES 33

APPENDIX A Twenty One Major Scaffold Types Addressed by the Codes

and Standards A-1

APPENDIX B Types of Scaffolds Identified in the Questionnaire of

the Work Injury Survery by the Bureau of Labor

Statistics B-1

V

1 . INTRODUCTION

This report presents an analysis into the causes of scaffolding accidents resulting in employee casualties based on statistical data of such

incidents compiled by other sources. The study constitutes part of a multi-phase research effort consisting of a series of inter-related

tasks to develop a technical basis for the improvement of the safety

aspects of scaffolding practices.

In general terms, safety research may be defined as an effort to develop

practices by which potential accidents and their consequences can be

mitigated to achieve an acceptably low level of risk of human casualties.

The word "practices" applies to a given segment of industry which,

in this case, denotes the design, erection, operation and maintenance

of scaffolding systems used in construction work or other work-related

applications such as building renovation or maintenance. The subject

of interest in this study is the protection of employees from occupational

hazards during the conduct of their assigned tasks. Safety aspects

of scaffolding uses in non-occupational or voluntary applications that

may be different from those encountered within an employer-employee work

environment are, therefore, not addressed directly in this study.

To bring critical research needs for scaffolding systems into focus,

a number of avenues may be explored, such as an analysis of accident

data, evaluation of applicable codes and standards, or field investigations of current practices. An analysis of accident statistics, if

such statistics are available and sufficiently detailed to allow meaningful

interpretation, should go a long way in providing the type of information

sought. For example, it may point out the specific nature of structural,

environmental and human factors that are the principal perpetrators

of accidents; it may indicate which types of scaffolds are experiencing

the most frequent problems and which are the ones most commonly used;

it may indicate the rate and trend of scaffold accidents; and it may

indirectly highlight specific deficiencies in existing code provisions

for scaffolding systems.

The information used in this analysis provides answers on some of the

above-noted trends and was derived primarily from two sources. The

first source consists of survey records of scaffold accidents involving

work-related injuries documented by the Bureau of Labor Statistics (BLS)

for approximately a six-month period [1]*. The second source contains

information on scaffold-related accidents involving worker fatalities

for a four-year period compiled by the Occupational Safety and Health

Administration (OSHA) [2], Both these sources utilize backup data

in the form of questionnaires or standard accident forms containing

witness accounts of the individual accidents. By examining the narrative

sections of this backup material, it was usually possible to identify

*The numbers in brackets indicate references listed at the end of

the report.

1
the primary cause of the accident and the type of scaffold used. There

were, however, a few cases that were not considered because of inadequate

information. The scope and type of specific information contained

in the source documents examined are discussed in Section 3.

2
2 . APPROACH

Before reviewing the source documents from BLS and OSHA, a set of criteria was devised by which the contents of the accident data could be

interpreted and classified (see Figure 2.1). Noting that an accident is

usually characterized as a chain of events of discrete time duration

rather than as a single instantaneous incident, it is possible that more

than one factor may contribute to its occurrence and resulting consequences. Wherever possible, the factor responsible for the initiation

of the accident was identified as the primary cause and the factor that

could have mitigated the consequences of an accident in progress, but

did not, was identified as a secondary cause. For any accident there

may be several secondary causes but only one primary cause.

For the purpose of this study, accidents were classified as resulting

from three major causes;

(a) system failures

(b) environmental factors

(c) human factors.

In the case of system failures, it was necessary to identify the cause

of the accident more explicitly at the component level as follows;

(1) platform

(2) support elements

(3) connections

(4) anchorages

(5) foundation

(6) accessways

(7) safety devices.

The foregoing breakdown allows also the representation of all scaffolding systems in terms of basic components, or units used in the

assembly of scaffolds. For clarity and consistency, the following

definitions are introduced;

Accessway

Anchor

Anchorage

Connection

Element

system which provides access of personnel to and from

scaffolds

component used for securing scaffold to foundation

same as anchor, assembly of anchors

component used for the attachment of scaffolding

elements

component or structural unit other than connection or anchor

Foundation - means providing support to the scaffold

system

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

scaffold

3
Figure 2.1. Systematic approach used in interpreting and

classifying the accident data.

4
Safety devices

Structural

system

physical devices installed for the protection of

employees, such as guardrails, nets, belts,

lanyards and lifelines, screens, etc.

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

platform and transmits applied loads to the

foundation.

System assembly of components serving a specified function.

System failures occur as a result of inadequate strength or lack of

stability. The failure of any component, foundation, accessway or safety device due to a lack of strength is considered as a system

failure. Similarly, any system Instability such as rolling, sliding,

tilting, settlement or overturning of the scaffold, as well as buckling,

sliding, tilting or loss of support of an unsecured platform or any

other component is considered as a system failure. If a system failure

initiates the set of events resulting in an employee casualty, it is

classified as the primary cause of the accident. If, however, a system

failure affects only the potential consequences of an accident already

in progress, it is classified as a secondary cause .

Unsafe environmental conditions inherent to the work space could produce

accidents or fail to mitigate their potential consequences. Environmental failures are often characterized by unexpected occurrences that can throw employees off balance during the conduct of work, such as sudden

release of heat, noise, or wind gust. Environmental failures may also

be attributed to exposure of employees to toxic fumes; the presence of

ice, debris and other obstructions on the work platform that create

slippery or unsafe walking and working conditions; or insufficient cues

to other physical hazards which the worker fails to perceive, such as openings and precipitous edges without appropriate warning signs. It

should be noted that as a matter of choice, the absence of protective

devices, where responsible for the initiation or progress of the accident, is treated as a system rather than environmental failure.

Furthermore, depending on the situation, wind or ice may be classified

in one of two categories. Structural failures precipitated by wind or ice loads are treated as system failures. On the other hand, in cases where ice creates slippery conditions on the work surface or where a wind gust throws a worker off balance (which happens often when carrying a sheet of construction material with large surface area), the

resulting accident is attributed to environmental factors.

5
Human factors contributing to accidents are somewhat more difficult to

identify from the available information than those noted above. Humancreated hazards in the work environment may be attributed to perceptual

or behavioral failures. In other words, an individual may fail to

perceive a danger or fail to act. Perceptual and behavioral failures

are often due to the absence of environmental characteristics which

indicate danger (as in a dark surrounding), or due to unreliable physical characteristics of the system (such as a guardrail which is weak but

looks sturdy). In such cases, the factors contributing to the accident

are not treated as human failures. On the other hand, perceptual and

behavioral failures may occur even when environmental and system characteristics are present and reliable. For instance, perceptual failures

may occur because of: (a) defects in the sensory apparatus, (b) immaturity in the sensory apparatus, (c) temporary incapacity due to drugs

or illness, (d) untrained discrimination, or (e) inattention. Likewise,

behavioral failure, or failure to react to a perceived danger, may

occur because of defective, inadequately trained, or temporlly incapacitated behavior. The solutions to these performance failures often involve

training, education and proper safety orientation for the job. However, even with adequate preparation for the job, it is not entirely possible

to eliminate human failures which may occur as a result of inadvertent

unsafe acts or voluntary and deliberate abuse. In reviewing the accident

records, whenever a clear indication was given that the accident occurred

as a result of a voluntary unsafe act, such as an employee extending

over or through the railing to reach the work area, human failure was classified as the primary cause of the accident. If the worker inadvertently misused the scaffold, or was compelled by a supervisor to

do so, human failure was classified as a secondary cause of the accident.

In order to determine whether certain types of scaffolds may be susceptible to specific kinds of failures, it is also desirable to classify

accidents according to the types of scaffold used. Twenty one major

types of scaffolds were identified for the purpose of this study. Most

of these are addressed by the OSHA regulations [3]

.

In addition, a twenty second category titled "improvised scaffolds" was created to

classify all those scaffolds which could not be identified with any

one of the major types. The types of scaffolds and the numbering system

used for identification are illustrated in appendix A.

6
TABLE 3.1

Profile of Scaffolding Accidents Involving Worker Injuries

(Based on Survey by the Bureau of Labor Statistics)

Organization No. (out of 803) 1

General: Craftsmen and kindred workmen 479 60

Laborers, except forman 190 24 Operatives, except transport 90 1195*

Specific

Carpenters 216 27 Construction laborers, except carpenters' helpers 130 16 Brickmasons, stonemasons 53 7 Painters, construction, maintenance 41 5 Drywall installers, lathers 30 4

59*

Type of Scaffold No. (out of 779) %

General

Self-supporting 476 61 Improvised 131 17 Supported by structure or other methods 95 12 Suspended 15 2 92*

Specific

Welded tubular 241 31 Ladder scaffold 142 18 Tube and coupler 60 8 Bracket 41 5 Pump jack 23 3 Ladder jack 23 3 Double pole 17 2 Bricklayer's square 16 2 Two-point suspension 10 1 Single-pole 5 1 74*

Description of work activity No. (out of 800) %

Working directly from scaffold 476 60

Climbing up to or down from scaffold 120 15 Stepping on to or off of scaffold 78 10 Building or tearing down the scaffold 77 10 Moving the scaffold 42 5 100

Description of the accident No. (out of 801) %

H or I** Fell off - nothing happened to scaffold 222 27

C Plank slipped 126 16 A Plank broke 62 8 D Support poles tilted or tipped over 57 7 C Wheels on bottom of scaffold rolled 45 6 B Cross-bracing gave way 45 6 D Anchoring into structure gave way 43 5 H Slipped on work materials 42 5 B Wood or metal support pole(s) broke 41 5 E Scaffold tilted on unlevel ground 35 4

E Scaffold base slipped on slick surface 31 4 H Struck by falling object while on scaffold 21 3 E Support poles sank in soft ground 16 2 D High winds moved scaffold 8 1 B Cable or suspension line broke 6 1 G Scaffold guardrail broke 1 - 100

* Specific items that could be identified were less than total number of cases.

** Alphabetic coding corresponds to categories specified in Tables 4.1 and 4.2.
TABLE 3.1 (Continued)

E. Number of workers on the scaffold No. (out of 754) %

1 429 57

2 200 27

3 67 9 4 22 3 0 20 3 >10 2 - 99

Description of work platform

(1) Composition No. (out of 795) %

wood plank 659 83

solid metal 74 9 metal grate 35 496

(2) Height above ground (ft) No. (out of 793) %

<10 402 51 >10 377 48

99

(3) Width (ft) No. (out of 780) %

2-4 354 45

<2 266 34

>4 134 1796

(4) Length (ft) No. (out of 730) %

8-12 365 47 >12 213 27 <8 174 2296

Description of platform support system

No. (out of 782) %

metal tube frame 511 65 wheels 218 28 guyed or anchored to structure 168 21 wood frame 93 12 screw jacks 37 5 suspended by wire cable 13 2

If scaffold had metal tube frame, was frame No. (out of 428) % cross-braced?

yes 362 85 no 47 1196

If wood frame, was frame cross-braced? No. (out of 88) %

yes 56 64

no 28 3296

8
3. BASIS OF STUDY

This section describes the scope and type of information found iu the

BLS and OSHA scaffolding accident records involving work-related

injuries and fatalities, respectively. As noted earlier, these were

the two major sources of Information utilized in this study.

The BLS study [1] compiles scaffolding accident and injury statistics

from May through mid-November, 1978. The study derix'es accidcar information from accounts given by the Employers' First Report of Injury

required by State laws on worker’s compensation, and from special survey

questionnaires sent to injured employees whose reported accidents were

judged to be within the scope of the survey. The information was collected from seventeen States named in the survey and described as providing a rough balance of geographic and industrial characteristics.

A total of 2237 cases of scaffolding accidents resulting in work-related

injuries were reported within the specified period of the survey. Out

of this total, 1007 cases were eliminated from the survey because they

were: (a) out-of-scope accidents, (b) accidents involving fatalities,

(c) cases more than ninety days old or (d) non-mailable. Of the remaining 1230 cases for which BLS issued survey questionnaires, there were

803 responses which were subsequently examined and used in the preparation of the accident statistics report issued by BLS.

The BLS survey provides a profile of scaffold accident characteristics

based on injured workers' reports. The questionnaire was designed to

provide information on (a) occupation; (b) type of scaffold; (c)

description of work activity; (d) description of the accident;

(e) number of workers on the scaffold; (f) type of work platform

including composition, length, width and height above ground; (g)

description of support system for the platform; (h) presence or absence

of crossbracing; and (i) personnel data (such as nature of injury, age, sex and training of the workers) which are not directly related to the

scope of this study.

Table 3.1 summarizes the responses received by BLS for the type of information sought in this study, shown in the order of decreasing frequency

for each of the categories specified above. By examining the given data

some useful inferences can be drawn. For instance, an interesting

aspect of the BLS survey, and one that is of primary concern to this

study, is the type of failures triggering the accident or the factor

falling to mitigate its consequences (item D in table 3.1). Heading

the list (27 percent) are falls without apparent damage to the scaffold.

The preponderance of planks either breaking or slipping off supports,

which accounts for the next highest rate of incidents (24 percent),

points to definite targets for improvement in scaffolding applications.

The illustration of the types of scaffolds (16 in all) appended to the

BLS survey questionnaire is shown in appendix B. The percentages of the

scaffold types given in item B of table 3.1 are percentages of reported

9
accident-related scaffolds. If an attempt were made to correlate frequency

of accidents with type of scaffold, these values would have to be weighted

by percentages of the types of scaffolds in use. At this writing, information

is not at hand to determine frequency of use according to type of scaffold.

The BLS data is, nonetheless, relevant in pointing out the trend of

scaffold use and the need for further corroboration through a comprehensive

field study. It is encouraging to note, with regard to coverage of various

scaffold designs, that the sixteen scaffold descriptions offered with

the BLS questionnaires apparently cover more than 90 percent of the reported

scaffold accident cases.

The BLS document notes that 800,000 cases of Employers First Reports of

Injuries were reviewed during the survey period. Of these, approximately

2200 cases involved scaffold accidents, which represent a seemingly low

value of about 0.3 percent of the workers' compensation cases reviewed.

This figure alone does not lend itself to meaningful interpretation without

having comparable figures for the number of employees involved in scaffold-related work versus the total number of employees. More precisely,

for a representative base period, total employee-hours of scaffold use

should be compared to total employee-hours in other occupations.

In an attempt to gather any available information on the above subject,

inquiries to BLS indicated that total wage and salary workers in the

construction industries were about 5.7 percent of the total wage and

salary workers in the U.S. Thus, for a given base period, if total scaffold

work constitutes 5% of the total employee-hours in construction industries,

then it would represent 0.3% of total wage and salary employee-hours (viz.

5% X 5.7% _ 0.3%). Since this figure is the same as the percent rate

of scaffold accidents reported, it may be concluded that the frequency

of scaffold Injuries is comparable to the average for all other industries

taken collectively. If the scaffolding use is less than 5% of the total

construction employee-hours, it would indicate potential safety problems for

scaffold users. This still leaves the question on the rate of scaffold

use unanswered but points out survey possibilities as a means of estimating the severity of safety problems of one segment of Industry

relative to other industries.

The other major source of information for this study was acquired from

OSHA. The OSHA document [2] is based on scaffolding accident data

involving worker fatalities covering a period from May, 1974 through

April, 1978. Among 386 working surface accident reports, 82, or 21

percent, were identified as fatal incidents relating to scaffolds.

Four of the incidents Involved more than one death bringing the total

to 86 deaths. The study excludes cases that occurred on permanent platforms, catwalks, oil derrick platforms, window washer belts or cases where scaffolds should have been used but were not. It should also be

noted that the OSHA study excludes the 51 worker fatalities resulting

from the Willow Island cooling tower collapse in West Virginia on April

27, 1978, which was the worst construction disaster in U.S. history [4].

The OSHA study identifies types of scaffold used as belonging to one of

three general categories (suspended, self-supporting and other) which

10
encompass the types of scaffolds specified in the OSHA regulations. It

also provides a description of the types of incidents, employee activities at the time of the incident (but not necessarily those causing the

incident), and a breakdown of causes into four categories: ev^uipment

failure, operating procedure, environmental and other. The OSHA study

shows that equipment failure and failure to follow operating procedures

accounted for 48 percent and 37 percent of the total incidents,

respectively, while environmental and "other" conditions together

accounted for 15 percent. It also shows that: 70 percent (17 out of

25) of suspended scaffold incidents and 31 percent (11 out of 35) of

the self-supporting scaffold incidents involved equipment failures; 49

percent (17 out of 35) of self-supporting scaffold incidents were attributed to operating procedure; and, equipment failure accounted for 50

percent (11 out of 22) of the incidents in the "other" category of

scaffolds. One-half of the total (11 out of 22) in this category were

improvised scaffolds.

Although the definitions of the various classifications of accident

causes in the OSHA report are somewhat different from those used in this

study, the term "equipment failure" approximately corresponds to the

term "system failure" referred to herein. The OSHA report Indicates

that connection failures or the absence of same account for the maximum

number of incidents, followed in decreasing order of incident frequency

by support element failures (referred to as scaffold component failures),

failures due to faulty or improvised construction, insufficient strength,

insufficient anchors, and failure of safety devices. As will be noted

in section 4.2, this study categorizes all system type failures at the

component level and therefore, has no direct counterpart to failures

attributed to improvised construction or insufficient strength in the

OSHA report.

11
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12

Table

4.1

Injury

Statistics

of

Scaffold

Accidents
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SlN3N0dW00 W3ISAS aiOddVOS STVIOI

13

Table

4.2.

Fatality

Statistics

of

Scaffolding

Accidents
4. ANALYSIS OF ACCIDENT RECORDS

The following sections present an analysis of the causes of the accidents examined. Section 4.1 describes the method used to present these causes according to the breakdown discussed in section 2. Section 4.2

notes the general trends observed in the accident data. Section 4.3 and

its subdivisions present itemized descriptions of accident causes attributed to system component failures, and sections 4.4 and 4.5 describe

respectively, accident causes attributed to environmental and human

factors

.

4.1 PRESENTATION OF THE DATA

In order to identify the types of failures associated with the reported

accidents according to the breakdown noted in section 2, it was necessary to examine, in addition to the BLS and OSHA reports, the individual

accident records upon which these documents are based.

In the case of the OSHA study, all of the 82 accident files were reviewed,

of which 3 were dropped because of insufficient information. Typically,

an accident file contained the following: (a) a standard Safety and

Health or Accident Inspection Report which provided accident data in

numerical code format corresponding to a specified legend, (b) a standard

Citation and Notification of Penalty form which specified any violations

of OSHA employee safety regulations, and (c) various witness accounts

of the accident in narrative form, where available. Some of the records

showed sketches and photographs of the accident site as well.

As noted earlier, the BLS study of scaffold Injuries was backed up by

more that 800 individual accident accounts. They were reported by the

respondents (parties injured in the accident) using standard questionnaires which also provided spaces for narrating the incident and sketching the type of scaffold involved, when different from the 16 types

Illustrated in the questionnaire (see appendix B).

An initial examination of the BLS questionnaires indicated that in most

instances the narrative section and the space for sketching non-typical

scaffolds were left blank, and as a result, were of limited use as backup material for the purpose of this study. Consequently it was decided to select 10 percent of the available reports on the basis of

the amount of Information supplied by the respondents. Furthermore, at

least one but not more than 10 percent of the reports from any given

state was Included in the sample to maintain approximately the geographic

distribution of the original source data. Ultimately, 58 cases or slightly

over 7 percent of those reported satisfied these requirements and were

retained for further evaluation.

Tables 4.1 and 4.2 compile accidents Involving injuries and fatalities

based on the respective source data from BLS and OSHA. In order to present

the selected data from both sources in a consistent fashion, the matrix

format indicated in these tables was adopted.

14
The rows of the matrix represent the primary (and secondary) cause of

each accident while the columns represent the corresponding type of

scaffold used. The three major categories of factors leading to the

accidents are identified as follows: system failures, rows A through

G; work environment, row H; and human factors, row 1. The system failure

subdivisions A through G correspond to those already defined in section

2. Columns labeled 1 to 21 correspond to the types of scaffolds illustrated

in Appendix A. Improvised scaffolds are indicated in column 22.

Each matrix is supplemented with additional rows and columns that sum

up the results. The last two rows represent the number of incidents

Involving each scaffold type and the corresponding percentage of the

total number of cases considered. The last two columns show the number

of incidents associated with each category of failure and the corresponding

percentage of the total.

In both tables, a distinction is made with regard to whether any- particular factor was the primary or secondary cause of the accident in

accordance with the concept Introduced in section 2. The numbers representing secondary causes are shown in parentheses to distinguish them

from primary causes. However, the percentage figures in the last row

and column represent only the primary causes and should add up to 100

percent (lower right-hand number) because only one primary cause is

identified for each accident investigated.

4.2 INTERPRETATION OF GENERAL TRENDS

The interpretation of injury statistics compiled in table 4.1 is subject

to possible errors that may have been introduced in the sampling process.

To estimate any differences between the 7 percent sample used in this

study and the BLS data source, the percentage values of the various

causes of accidents shown in table 4.1 were compared with the corre- sponding values from the BLS report after identifying the latter (item D,

table 3.1) according to the categories used in table 4.1. This leads to

the following results:

Type of Failure

Percent of 801 cases

(table 3.1)

Percent of 58 cases

(table 4.1)

A - Platform 8 7 B

- Support elements 12 14

C - Connections 21 17

D

- Anchorages 13 17

E

- Foundation 10 14

F

- Accessways < 1 0

G

- Safety devices < 1 3

H -

I - Environmental andHuman factors 36 27

It is seen from the above that differences between sample and source

data are not major for the purpose of examining the trend of accident

causes on the basis of the figures in table 4.1. The difference between

15
the values for environmental and human failures taken collectively may

be due to different interpretations of the source data, because the

definition of causal factors used in this study are not coincident with

those used by BLS. For example, a "fall with no apparent damage to the

scaffold" may be interpreted here as a fall precipitated by movement

or instability of the scaffold if the data examined gave any indication

that this may have been the case.

Possible differences between sample and source data may also be investigated by comparing the percentage values of the scaffold types shown in

table 4.1 with the corresponding values for the specific types shown

under item B of table 3.1. Sampling distortions were generally more

apparent in this case, the sample being most heavily biased toward

bracket and pole types (30 percent) relative to the source (8 percent).

On the other hand, the highest rate of accidents Involved (collectively)

frame type and manually propelled mobile (or ladder type) scaffolds, and was about the same for both sample and source data (approximately 50

percent of the cases).

The accident statistics involving fatalities compiled in table 4.2 do

not present any sampling problems because they represent almost all of

the cases on record. The data in tables 4.1 and 4.2 exhibit certain

similarities and differences worthy of note. For instance, they agree

remarkably well by pointing out that in about 3 out of 4 cases the primary cause of the accident is attributable to a system failure. Within

that category, they both show that about 30 percent of all accidents are triggered by connection and anchorage failures, and 7 or 8 percent are triggered by work platform failures. On the other hand, the rate of

incidents attributed to foundation or support element failures resulting

in injuries is about three times the corresponding rate of incidents

resulting in fatalities.

A comparison of accident rates for the various types of scaffolds is not

very meaningful because no information is available on the frequency of

scaffold use according to type. If, for example, a particular type of

scaffold is used 90 percent of the time but accounts only for 50 percent

of all accidents, its accident rate per unit time of use will be much

less than indicated by the 50 percent figure. This points out the need

for compilation of statistical data of frequency of scaffold use according

to type through field studies or other means.

It should be emphasized that extreme care must be exercised in comparing

the Injury and death statistics compiled in tables 4.1 and 4.2. The data

in tables 4.2 constitutes nearly all of the scaffold-related work fatalities

in the U.S. over a period of four years. On the other hand, the Injury

data in table 4.1 represents a 2.6-percent sampling of all scaffold-related

injuries (58 out of 2200 cases) occurring within a period of 6-1/2 months

in states representing about 47 percent of the U.S. population. If the

injury statistics are adjusted to the same time span and population

bases as those for the death statistics, the number of cases involving

16
injuries will be about 35,000, or about 410 Injuries per fatality.

Therefore, the Individual figures shown in these tables (the matrix

elements) cannot be compared directly for the purpose of estimating

incident rates according to the various categories listed. Rather,

they should be viewed in relation to each other by comparing the

given percentage values and the relative figures of Injury and fatality

rates for a common base period. It should also be kept in mind that

the information in table 4.1 is subject to sampling distortions and

the possible effect of seasonal factors on the BLS data which was assembled during a period of peak construction activity.

In way of Illustrating a possible pitfall in the interpretation of the

data catalogued in tables 4.1 and 4.2, the following example may be

cited. According to table 4.2, the second highest rate of death incidents is associated with two-point suspension scaffolds, while the

corresponding rate of injuries is among the lowest of the group (table

4.1). At first glance, this may suggest erroneously that two-point

scaffold accidents involving casualties almost always result in death.

However, a comparison drawn on a common time span and population basis

will show that two-point suspension scaffold injuries occur about 20

times more frequently than fatalities. This ratio is probably on

the high side because of the seasonal factors mentioned above. Note

that for the limiting (unlikely) case of no scaffolding activity

occurring outside the 6-1/2 month (BLS survey) period in a year, the

ratio would still be 10 to 1.

For the reasons stated above, there appears to be no expedient way of

combining the data in tables 4.1 and 4.2 for the purpose of developing

total casualty statistics of scaffolding accidents. Where the corresponding

percentage figures from the two sets of data are in close agreement, they

will Indicate a definite trend. If, however, differences in the corresponding percentages are appreciable, the rate of the injury data in

table 4.1 will, in general, indicate the dominant trend (exceptions are noted below), because the frequency of scaffold-related injuries is at

least two orders of magnitudes higher than the frequency of fatalities.

Keeping these factors in mind, the following observations of general

trends in scaffold-related work casualties can be made.

System failures are by far the major causes of casualties accounting for

almost 3 out of 4 cases reviewed. At the component level, the most common

primary cause of casualties was the failure of connections and anchorages

(17 percent each), followed by foundation and support element failures

(14 percent each), failure of work platforms (7 percent), failure of

safety devices (between 3 and 21 percent), and accessway failures (1 percent).

The major difference between the data in the two tables is in the percentage

figures identifying a safety device failure as the cause of the accident

both in the primary sense (3 percent injuries vs. 21 percent fatalities)

and secondary sense (8 out of 39 injuries versus 48 out of 90 fatalities).

In an attempt to find a logical explanation for these large discrepancies,

the following were observed. The BLS source data (the questionnaires)

17
do not specify explicit violations of the OSHA regulations on safety

devices as do the citations which are part of the fatality statistics.

Consequently, it was simpler to identify any evidence relating the

fatality incidents to deficiencies (primary cause) or the absence

(secondary cause) of safety and fall protection devices than in the case

of injury data. However, the BLS report does indicate that only 33

percent of the scaffolds (out of 803 cases) were equipped with guardrails

and of these, only 54 percent (or 18 percent of the total) provided

protection on all exposed sides. The BLS report also states that 80

percent of the accidents were falls from scaffolds. Based on these

observations, it is estimated that failure of safety devices is a leading cause of scaffolding casualties both in the primary sense and

secondary sense, and therefore, the percentage figures in table 4.2 are more indicative of this trend than those shown in table 4.1.

Only in about one out of four cases was the primary cause of an accident

attributed to an environmental and human factor (17 and 10 percent,

respectively). Note that in the secondary sense, human factors contributed to the accidents in about twice as many instances as environmental

factors

.

The highest number of incidents involved manually propelled mobile,

fabricated frame, bracket, wood pole and improvised scaffolds, which

collectively represent about 90 percent of the cases considered. Twopoint suspension scaffolds are not among this group because their

casualty rate is low (the 2 percent figure in table 4.1 prevails for reasons noted above). However, because the severity of the consequences

of an accident is a primary safety concern, the high rate of accident

fatalities attributed to two-point suspension scaffold failures (25 percent,

table 4.2) takes on more significance as a critical safety problem than

the above-observed trend of the total casualty statistics would indicate.

4.3 SYSTEM FAILURES

In the preceding section, the breakdown of accident causes into specific

categories was helpful in developing an overall grasp of major safety

problem areas with regard to scaffolding practices. It was observed

that about three-quarters of the accidents were a result of failure

of the scaffolding systems and that connection and anchorage failures

were the most common. In this section, failure of the various components

of scaffolding systems will be discussed in detail in order to establish

the nature of these component failures, such as stability or strength.

4.3.1 Work Platforms

The work platform is the component of the scaffolding system in direct

contact with the loads which Include workers, materials, and equipment.

The work platform also transmit other loads such as ice or wind to the

scaffolding structure. Furthermore, the platform can be the location

of many environmental hazards due to the presence of work materials and

slippery surfaces. Such hazards of the work environment are discussed

in Section 4.4.

18
Approximately 7 percent of all scaffolding accidents reviewed were caused

by structural failure of the platform which usually consists of wooden

planks. Failure occurred as the result of defective pieces of Ivfmber,

Inadequate number of planks, planks of insufficient size and strength,

or excessive loads. The majority of such failures occurred on improvised

scaffolds where less care was probably given to provide adequate support

to anticipated loads.

Accident descriptions reveal that some planks x^ers split and splintered;

however, even after inspection these planks were used for the platform

surface, sometimes repeatedly. One injured worker stated that after

having fallen when a plank broke, he returned to the site and discovered

that the same piece of wood had been put back. The ends had simply been

squared and 2 x 4-ln cleats had been nailed to the bottom. Furthermore,

only a short time thereafter, he fell again when another plank split

diagonally.

Examination of some of the schemes for constructing platforms (derived

from sketches in the reports) reveals that in some cases planks were

not placed in sufficient nvimbers on the scaffold or did not have sufficient cross-sectional area to support the imposed loads. For example,

due to limited space, improvised scaffolds consisted of one plank

with nominal dimensions of 50 x 250 mm (2 x 10 in). This may or may

not be sufficient to support one person depending on the span and the

condition of the plank. Such a condition is also hazardous as well

from the viewpoint of protection against falls. Loading conditions can

be critical where such improvised scaffolds exist. In one instance, a worker fell to his death when another worker stepped down from a platform

two feet above causing the plank to fail. Dangers are not limited to

improvised platforms consisting of wood. One platform where aluminum

planks were used failed when a third worker stepped on carrying two

buckets of fresh cement.

In some of the accidents which involved platforms, it was found that the

platform elements themselves were not the primary cause of the accident.

Rather, the cause was attributed to lack of adequate connections to the

supporting elements, gaps between planks, or slippery surfaces.

When planks are not secured to the supporting elements they become laterally unstable. In some cases, when workers were getting the platform the

planks moved as a result of the applied horizontal thrust. The consequences

of such movements varied from a jammed finger to death of the worker. This

problem is also related to openings between adjacent planks. When planks

are secured against lateral movement, openings remain fixed. If the gap

becomes large and the worker begins to fall through, he may still have an opportunity to grab onto the planks and impede the fall.

If the planks are not secured against lateral movement, it is less

likely that a woker will be able to impede his fall by such countermeasures. Incidents caused by movement of unsecured planks are identified with connection failures (sec. 4.3.3).

19
4.3.2 Support Elements

By reference to appendices A and B, it is apparent that there are a variety of ways to support a work platform. In all cases, however, the

supporting elements act to transfer the loads acting on the work platform to the foundation. Various work environments necessitate different foundations and thus different support systems. When the foundation

is the ground below, a framework or some type of mechanical elevating

system is required. If height, space, or access are restraints, particularly during a construction process, it may be necessary to anchor the

scaffold onto the structure itself. In such cases the platform must

cantilever outward from the structure and an outrigger or bracket may

be utilized. When a secure foundation exists above the level of the

work platform, the platform may be suspended by ropes or cables.

When an accident can be related to the supporting elements, consideration of the type of support system is necessary in order to understand

the nature of the consequences. The modes of failure of a framework

are different from those of a suspension cable or bracket. Furthermore,

if one element of a framework fails, the system may not collapse; whereas, if one of the two cables from which a platform is suspended snaps,

it will precipitate collapse. About 14 percent of the total number

of accidents were attributed to support system failures. The distribution

of such failusres according to type of scaffold shows no definite trend.

Support system failures were responsible for a larger share of accidents leading to injury than accidents leading to death. Collapse depends

on whether each supporting element involved in the failure is vital

to the transfer of loads to the foundation. When redundancies or alternate

load paths are present, failure of one element may only result in local

instability, such as in a fabricated tubular frame scaffold. Two of

the three accidents reviewed which led to injuries were attributed to

the use of a diagonal brace as a means of access; not designed for

this purpose, the brace broke or yielded. The primary function of this

brace is to resist loads applied laterally to the structure. Consequently,

failure of the brace did not cause collapse of the structure nor death

to the worker. Rather, the worker probably lost his balance and either

struck the hard metal or fell (some distance less than the height

of the platform level which he was accessing). It is also interesting

to note that no accidents involving fabricated tubular frame scaffolds were reviewed where death occurred primarily as a result of support

system failure. However, two-point suspension scaffolds, in which failure

of the support system occurred, were involved in three accidents resulting

in death and none resulting in injuries. The failures were attributed

to breakage of the suspension rope or, in one case, the safety line

which was secured to the suspension cable.

4.3.3 Connections

According to the definition in section 2, a connection is a component

used for the attachment of scaffolding elements. Any physical device

used for the purpose of Interconnecting scaffold support elements or

20
braces, or securing work platforms, accessways, and safety devices to

the scaffold, fall within the scope of this definition. Examples of

commonly encountered mechanical connecting devices used in scaffolding

applications are nails, bolt, wires, clamps, locks, clips, sleeves,

inserts, devices, couplers, hooks, splices and turnbuckles.

As noted in section 4.2, connection and anchorage failures top the list

of all accident causes, accounting for 17 percent each of all the cases

reviewed. Examination of the individual accident descriptions revealed

that absence of proper connections as well as failure of connections in

place were about equally responsible for the initiation of the accidents.

Connection failures in frame and manually propelled mobile scaffolds

were by far the most common. In manually propelled mobile scaffolds,

connection failures were often characterized by such incidents as the

collapse or detachment of a wheel, or the malfunctioning of a worn

locking device, causing the scaffold to tilt, roll or tip over.

In one case, the detachment of a brace secured to an improvised scaffold by one nail precipitated its collapse. Other instances where the

failure of a single connection brought about the collapse of the entire

scaffold or work platform were: the rupture of a clip causing the slippage of a cable clamp and consequent collapse of the suspended scaffold;

and detachment of a platform support bar causing the work platform to

collapse. Descriptions indicating such occurrences as the detachment of

a bolt, the slippage of a loose frame connection, the snapping of a locknut not securely fastened, or the dislodging of a notched angle bar from

its support (not a positive connection against pull) were instances of

improper use and maintenance of connections in place.

In nearly all of the cases reviewed where the absence of adequate connection was judged to be the primary factor causing the accident, the work

platform was either not secured or partially secured to the scaffold.

It thus appears that lack of proper connection between platform and

scaffold is a major cause of instability of working surfaces. In view

of the nature of construction work activities, this hazard cannot be

eliminated by training and safe conduct of work alone, as indicated by

the following accounts: The platform overturned when a worker stepped

over a 0.9 m (3 ft) overhang section. The overhang had been supported

earlier by a frame which had been removed before the incident; a worker

fell when attempting to step down on a board which slid backwards causing

him to lose his balance; another worker fell through an opening between

planks which were not tightly placed or secured.

The absence of platform connections create the kind of environmental

hazard that is difficult to perceive or anticipate. An unsecured

overhanging platform, for instance, may not provide an adequate visual

cue to the construction worker as to the exact location of its support

point which it conceals. Workers in the act of carrying materials or equipment often have their field of vision temporarily narrowed or impeded and may well fail to perceive and stay clear of openings between

21
unsecured planks. A worker descending on the platform may assume erroneously that the platform is secured or has sufficient friction to

take a horizontal thrust without movement. A horizontal thrust will

also occur in many other work situations such as when an employee is

pushing a screw gun to fasten facade elements on a building.

Based on the foregoing arguments it would be reasonable to expect that

work platforms, especially in construction work, will be subjected

frequently to horizontal thrusts, overturning forces, or wind-induced

uplift. To resist such forces, the platforms must be adequately secured

to the scaffold frame. Considering the available accident casualty

evidence, there exists strong justification for banning the use of

unsecured platforms on scaffolds where the platform is to serve the

function of a working or walking surface. Accident statistics also

indicate the need to develop a technical basis for improvement of the

structural performance of scaffold connections.

4.3.4 Anchors

According to the definition in section 2, anchors are used to connect

and secure the scaffold to its foundation. The scope of this definition

includes any device that connects the scaffold to its supports at the

support points. In the case of a guy wire, its point of attachment to

the scaffold is treated as a connection point and its point of attachment to the support or foundation is treated as an anchorage point. The

guy wire itself braces the scaffold and, therefore, is treated as an element of the system.

Anchorage failures were one of the two leading causes of scaffold accidents

within the system component group. Unlike failure associated with connections,

in most cases anchorage failures were actual failures of anchors which

were in place. Bracket and two-point suspension scaffolds experienced

the most frequent anchorage problems resulting in injury and death,

respectively.

Incidents of anchorage failures in two-point suspension systems included

the following accounts: the cable at one end of the work platform slipped through the U-clamp at the anchorage point causing loss of support;

a hook of a cable broke at the support point. The hook was reported to

have been cracked before the accident; the wire tie securing the platform to the building broke and the platform swayed out causing the

worker to fall. This happened when the screw gun, which the worker was pushing against the building, suddenly yielded; the inside support of one

of the outriggers failed causing the scaffold to collapse. Where the

collapse of the scaffold was attributed to lack of anchorage, one incident

was described as having occurred because there were no safety clips at

anchorage points. Another accident occurred when rollers supporting the

suspended platform slipped off the end of an I-beam flange where no roller

stops were provided.

Anchorage failures involving bracket scaffolds were of two types: fail- ure due to lack of strength or failure due to insufficient embedment.

22
Embedment failures were described as triggered by nails or walls ties

pulling out at points where the bracket was attached to the building;

while failures due to lack of strength were Identified in cases vhere

there was evidence that an anchor had ruptured. In two cases of anchorage failures Involving other types of scaffolds, the Inadequacy of anchors

to resist wind was cited as a cause that precipitated a collapse or overturning of the scaffold. Other instances cited included a weld

failure of an angle attaching a work platform to a steel tank, rcpture

of cleats anchoring a board to the wall (improvised scaffold), and a bracket which became disengaged from the wall.

Many of the examples cited above are indicative of a majior problem area

in structural design, namely, the paucity of research information for

formulating an adequate design basis for anchorage systems. Of particular concern is the load capacity of nails, inserts and similar mechanical devices driven into concrete, masonry or mortar for the piorpose of

anchoring scaffolds. The use of such anchorage devices is encountered

quite frequently in scaffolding and shoring operations and the decision

as to what constitutes a proper anchorage for a given support system

Is often left to the contractor or field supervisor. Technical information is needed to aid in the development of a rational design approach

for anchorages to such support systems, in order to minimize the occurrence of anchorage failures which have been shown to produce major collapses rather than localized failures. Such information should address

not only the design strength of anchorage devices but also identify the

magnitude of construction loads.

4.3.5 Foundation

A foundation may be conveniently defined as the means that lends support

to the scaffold system (section 2). This broad definition allows a structure or any other object to which the scaffold is attached for

support, as well as the ground upon which it bears, to be classified as foundation.

On the basis of the data compiled in section 4.2, the number of accidents

attributed to foundation failures was the same as that attributed to

support element or platform failures, each representing about 14 percent

of the total accident cases reviewed. There were, howe/ar, some cases which were classified as foundation failures but could have been interpreted differently as the following examples will indicate. One accident was attributed to the movement of a mobile scaffold reportedly caused

by debris on the floor upon which it was resting. Another accident occurred

when a wheel of the mobile scaffold sank into a floor depression. In either

case, the movement of the scaffold was assumed to have occurred without

rolling. Had there been any indication of rolling, the cause of the

accident would have been identified as a connection failure. In another

instance, hooks and tiebacks pried loose from a brick veneer wall which

was being restored (loose bricks and mortar were being replaced). A

judgment was made that in view of the conditions of the wall, it did

not have retention capacity for anchors and, therefore, the accident

was attributed to a foundation rather than anchorage failure.

23
Like anchorage failures, foundation failures appear to affect the

stability of the entire scaffold system rather than remain localized.

Thus, foundation failures have the potential to precipitate major

disasters, particularly in the construction of large structures using

well-populated scaffolds. This point was dramatically Illustrated by

the Willow Island cooling tower collapse in West Virginia, on April 27,

1978, as a result of which 51 employees were kllled[4]. At the time of the

collpase, the employees were working from scaffolds suspended from the

partially-cured portion of the concrete shell 52 m (170 ft) above ground.

A 1.5 m (5 ft) top section of the shell collapsed causing the scaffold and

workers to plunge to the ground. Even though this incident is not

included in the OSHA death statistics records used in this study (it

did not occur within the specified time period), it clearly falls within

the definition of foundation failures adopted in this study. The scaffold was entirely supported by the concrete shell which functioned as its foundation, but was not capable of resisting the imposed construction loads.

It is extremely unlikely that in practice much engineering attention is

given to ascertain that the foundation used will provide sound and

stable support to the scaffold and the Imposed loads. In view of the

potential hazards noted above, it is important that foundation problems

receive high priority in any investigative effort aimed at the improvement of safety aspects of scaffolding practices.

4.3.6 Accessways

Accessways should provide the means for safe access of workers, materials or equipment to and from the work area of the scaffold. Examination of the accident statements revealed that in most instances Improper

accessways, or more often the absence of accessways, caused unsafe

employee acts which led to accidents as highlighted by the following

accounts. Accidents typically occurred in the absence of accessways

when employees used the scaffold rungs, braces, frame sections, etc.,

to ascend onto or descend from the work platform. In all these cases

an accessway failure was classlfed as the secondary cause of the accident. In another instance, the absence of a proper accessway tempted an employee to jump down on the work platform which ruptured under the

Impact. In this case the absence of an accessway was interpreted

as the primary cause of the accident. The conclusion drawn from these

examples is that the problem is one of proper implementation of accessway regulations to keep employees from being tempted to perform an improper or unsafe act to gain access to the work area.

4.3.7 Safety Devices

Safety devices protect employees from falls, air-borne objects and other

environmental (natural or human-made) hazards. Examples of Installed

safety devices are: guardrails, to keep employees from accidentally

entering into hazardous areas such as falling from heights; safety

nets, to capture employees in the act of accidental falls; and screens.

24
to protect employees from air-borne (mostly falling) objects. Examples

of devices worn by the workers are hard hats, goggles, safety shoes,

heat- toxic fume- or electric shock-resistant apparel, etc. Once in

progress, accidental falls can also be checked by a "fall protection

system" (a term herein used) consisting of a safety belt worn by the

employees, an independently suspended lifeline, and a lanyard hooked to

the lifeline at one end and to the safety belt at the other. The OSHA

employee and construction safety regulations spell out requirements for

the various safety devices to be used in the workplace.

In reviewing the individual records of accident fatalities, it was noted

that a significant portion of the cases involved non-compliance with

existing OSHA regulations for safety devices. The explicit citations

found among these records allowed an assessment to be made of the nature

of primary causes of accidents attributed to safety device failures, as indicated by the following accounts: the top rail broke where an employee

leaned over it to reach his work; another employee fell over a top rail

reportedly less than 1.07 m (42 in) in height; in one case an employee

fell where a lanyard which was rubbing against a toeboard broke; two

instances were cited where the lanyard had too much slack in it and

broke under the impact of the fall.

Explicit citations also helped identify numerous instances where a safety device was judged to have been the contributing factor to the

accident in a secondary sense. These were predominantly cases where

a guardrail was not present to prevent a fall, or fall protection systems

were not independently suspended.

Based on the evidence at hand, it may be concluded that better utilization and maintenance of safety devices will have a significant impact

in reducing the severity of the consequences of scaffold accidents.

4.4 ENVIRONMENTAL FACTORS

While reviewing the accident accounts, it became apparent that the cause

of some accidents could not be related to failure of the scaffold system.

Rather, other factors contributed to the events leading up to the accident or to the consequences of the accident. Many of these factors were

related to conditions of the work environment while others Involved some human element. Human factors are discussed in Section 4.5.

Conditions of the work environment are highly variable and often unique.

Each job where a scaffold is utilized has peculiar space requirements

and exposure to the natural environment. Also, there are many scaffold

types and various uses of the same scaffold.

Conditions of the work environment were considered to be responsible for

17 percent of all accidents reviewed. Over 40 percent of the fatalities

(6 out of 14), caused by factors related to the work environment, occurred

on Improvised scaffolds. The remaining 60 percent were distributed among

other types. However, of those accidents whose consequences included

25
injury to the worker, 40 percent occurred on manually propelled mobile

scaffolds and 30 percent occurred on fabricated tubular frame scaffolds.

At first glance, it might seem that scaffold type should not necessarily

correlate with the occurrence of accidents where the work environment

was a factor. However, after reviewing the descriptions of accidents

involving the improvised and metal scaffolds mentioned above, the cited

statistics take on some meaning. Improvised scaffolds are generally

erected because space or access conditions prohibit the use of manufactured scaffolds. Examples of locations described in the accident

reports include elevator shafts and the interior of a boiler hopper.

In some cases where the accidents occurred on fabricated tubular frame

or manually propelled mobile scaffolds (both manufactured scaffolds)

the scaffold itself presented environmental hazards. For example, after

a rain the metal tubes became slippery and made access difficult, or bolts protruded which scraped one worker. During normal operations

these items of the scaffold constitute part of the work environment

with which the worker has to deal. Manually propelled mobile scaffolds

present the same hazards, but in the accidents reviewed problems were

associated mainly with the wheels falling into ruts or striking objects

or clutter on the ground surface.

Most of the instances where the work environment contributed to the

accident involved hazardous circumstances due to the nature of the work

that was being carried out. Several accidents occurred as a result of

hazardous conditions in the work environment where the danger was implicit

in the work. The workers violated the prescribed modes of work, exposing

themselves to the hazardous conditions. In a few instances, a sudden

event occurred during the course of work to disrupt the equilibrium

of the worker. The inadequacy of fall protection then allowed the

accident to proceed. In other instances fall protection was present

and adequate, but the worker took a voluntary risk in order to complete

some aspect of his work which could not be done easily from the work

platform provided.

Several accidents involved hazardous conditions in which the nature of

the work and the type of scaffold had no part. These conditions were

attributed to such factors as slippery surfaces, materials on the work

platform, or the natural environment which somehow disrupted the equilibrium of the worker. Conditions of the natural environment such as ice

or gusts of wind can be disruptive to the stability of the scaffolding

system as well. When this was the case, the particular accident was attributed to a system failure.

4.5 HUMAN FACTORS

The human element pervades through all activities during which accidents

occur. There is interaction between the workers, the supervisor, the

safety officer, and possibly the contractor during erection, maintenance,

and dismantling operations. Coordination and perception are involved

26
dur^aj a jrker’s access to the platform level and the performance

of his normal tasks while on the platform. Furthermore, during many

of the operations performed on the platform, there is communication

and interaction between the people on the platform and others on the

ground or at some other level.

It is often a matter of judgment as to whether or not the human element

is actually responsible for a particular accident. If the scaffold

system does not fail in any respect and no factor of the work environment appears to be responsible, it may indicate that an unsafe act was the cause of the accident. Most of the accidents reviewed, however,

did not appear to be caused in a primary sense by the action of a person. Rather, the human element was merely one factor contributing

to the set of events leading to the accident or to its consequences.

Referring to table 4.1 it is noted that human factors were the primary

cause of about 10 percent of all the accidents reviewed. Most of the

the accidents where a hviman action was primarily responsible occurred

on manually propelled mobile scaffolds. These scaffolds appear to be

prone to misuse. In one case, six scaffolds were lined up in a row

and the worker fell while moving from one to the other. In another

case, a worker jumped from a roof to the platform. Other cases involved

coordination and memory: one man simply missed a step, another forgot

that he had raised the platform to a higher level and fell because

he descended directly from the platform. Several accidents Involved

the collective misuse by several persons. For example, workers who were

on the scaffold while it was being pushed from below, died from the

subsequent falls; a coworker's neglect in locking the brakes on the

wheels of a mobile scaffold was the source of injury to a man working on

the platform.

The highest percentage of accidents where human factors were Involved

in a seconday sense, occurred on two-point suspension scaffolds. The

consequence of the accidents was death to a worker in every case. The

human element involved here was failure of the worker to be adequately

safeguarded against falls. Several reasons were found to have permitted

this situation to exist: (1) a safety belt and lifeline or lanyard

were not provided by the contractor or company supervisor, or (2) the

equipment was provided and not used or (3) the equipment was not attached

or used properly.

The human element in many accidents involved Inadequate training or an involuntary situation. One drywall installer who fell from an improvised

scaffold stated that the contractor had failed to supply a proper scaffold

which he could use. One worker who overextended himself and fell commented

that he had not been advised on the proper use of the scaffold. Another

worker who fell as a result of defective planking pointed out the lack of

safety inspection of the scaffold. In one case, a worker reported a defective brace to the union job steward. The steward ignored the comment and

required that the man return to his work. Upon return to the scaffold

the brace failed and the worker fell.

27
Some accidents occurred as the result of improper construction or use of

the scaffold. One man removed a support and inadvertently stepped onto

the scaffold thereafter. An accident occurred when a man tried to do

work at a height of 2.7 m (9 ft) on a scaffold designed for work done at

1.2 m (A ft). One telescoping scaffold was put into free-wheeling position

downward when a hammerhead flew off and struck a makeshift crank. A

pump jack collapsed when the worker standing on it tried to raise the

center jack higher than the end jacks in order to do work at the top of an A-frame building. Also, the use of supporting elements as means

of access was a frequent abuse and a source of many casualties.

28
5. SUMljyiY AlID CONCLUSIONS

This study Identifies and interprets the causes of scaffold accidents

based on information acquired from two different sources. One source

provided individual accounts of scaffold accidents involving work-related

fatalities resulting from scaffold accidents and supplementary records

describing the incidents. The other source provided information on work-related injuries resulting from scaffold accidents reported by

the injured workers on standard questionnaires.

The causes of accidents have been identified in this report with one of

the following categories: system failures, environmental factors or human factors. In cases where an accident is attributed to a system

failure, it is further identified with one of the sub-categories at the

component level. A concept is introduced that allows an accident to

be identified with a primary or secondary cause. The factor triggering

the incident is viewed as its primary cause while a factor that fails

to impede an accident in progress is viewed as a secondary cause. The

following summarizes the major findings of this study.

In three out of four cases reviewed, the primary cause of the accident

was identified with a system failure. At the component level within the

system failure category, nearly one-half of the accidents were interpreted

as having been triggered by connection and anchorage failures, and about

one-fourth by safety device failures. The rest of the accidents were

attributed to support element, foundation or platform failures. In one case the primary cause of the accident was classified as an accessway

failure.

Primary system failures were caused by inadequate strength or lack of

stability. The rupture of an anchor, platform, connection or support

element, or yielding of a foundation were treated as conditions of

inadequate strength to support the imposed loads. Among these, anchorage and foundation failures frequently created conditions of overall

system instability. Several other instances were noted where conditions

of local Instability due to the absence of positive connections precipitated the accident. This was particularly true in cases of work

platforms sliding or overturning under human-induced loads because they

were unsecured or inadequately secured to the support systems. In other

cases, connections and locking devices were not tight enough to prevent

slippage or rolling.

Within the system group, there were numerous instances where the absence,

defectiveness or improper use of a safety device was judged to have failed

to impede an accident in progress. This represented about 80 percent of

all secondary causes attributed to component failures. The problem appears

to be related to non-compliance with existing safety regulations which

give comprehensive coverage to provisions for the installation and proper

use of such devices in the work place.

29
In one out of four cases, the primary cause of the accident was attributed to a human or environmental factor. In such cases, environmental

factors occurred about twice as frequently as human factors. On the other

hand, two to three times as many human factors as environmental factors

were considered to have been the secondary causes of the accidents.

Environmental conditions triggering accidents were typified by sudden

or unexpected occurrences such as an electric flash or ignition of gas,

the presence of toxic fumes, excessive heat, slippery surfaces, debris

and other obstructions in the work area, or impact by a crane or other

moving equipment. The primary cause of an accident was attributed to a human factor in cases where such incidents were triggered by what were

judged voluntary unsafe acts. Inadvertent misuse or involuntary acts

were classified as human factors contributing to accidents in a secondary

sense.

This report also classified the frequency of accidents according to the

various types of scaffolds used. The trend of the accident data indicates

that the highest rates of incidents, which collectively represent about

90 percent of all the casualties, occurred on manually-propelled mobile,

tubular frame, bracket, wood pole and improvised scaffolds. Improvised

scaffolds are less likely to comply with safety regulations than other

types while manually-propelled mobile scaffolds appear to lend themselves

to misuse. However, the incident rates Indicated for the various types

of scaffolds cannot be used for the purpose of assessing the proneness

of a particular scaffold to accidents relative to other types without

statistical information on the frequency of use of each type. At this

time, information on the frequency of use of each type is not available.

A particular trend was the number of cases involving two-point suspension

scaffolds where the secondary cause of the accident was attributed to a safety device failure. Ten out of 22 types of scaffolds Identified in

this study were not associated with any of the accidents reviewed.

30
6. RE w..EMENDATIONS

The analysis of scaffold accidents presented in this report brings into

focus potential safety problems in the design, erection, operation and

maintenance of scaffolding systems used in construction work and other

applications. The following statements suggest an approach to trace

the source of these problems and to develop an appropriate course of

remedial action.

To understand the need for identifying the source of a particular safety

problem, it must be recognized that an analysis of accident records

alone will not suffice and further investigative efforts must be performed. Without identifying or having proper knowledge regarding the

problem, it is not possible to prescribe the best course of remedial

action for its resolution.

Limitations of the available accident data must be recognized as well.

The records that were examined were post-facto witness statements

usually made by laypersons in the technical sense. Therefore, the

accounts generally lack the type of specifics by which a complete and

technical evaluation of the problem can be performed. This limitation

in itself warrants the need for an on-site study, performed by a technically oriented team. However, before such a program is implemented,

a review of all applicable codes and standards must be performed. Such

a review should Identify any major deficiencies in existing scaffolding

provisions such as inconsistencies, inadequacies, lack of clarity,

noncomprehensiveness or unenforceability and their possible correlation

with the problem areas encountered in this accident study. This assessment is further warranted in a review of a recent independent study which

revealed major discrepancies in pertinent OSHA regulations regarding

allowable design properties of wood used in scaffolding [5]

.

It is further recommended that a comprehensive literature search for

technical and non-technlcal information regarding scaffolding systems

be performed. This task would serve as a means to determine whether

any code deficiencies which may exist are due to a lack of technical

information or a lack of recognition of such existing information.

The foregoing tasks are viewed essential in corroborating the findings

of this accident study and in identifying prime targets of needed

research to develop the technical basis for the improvement of scaffolding practices. Once such tasks have been substantially performed,

a field technical evaluation of scaffolding systems and practices

with documentation is recommended.

Such an exploratory field investigation of selective scaffolding installations during operation will enable the Identification of realistic

and common scaffolding practices. The purpose of this effort would be

to evaluate the intensity and distribution of construction loads

(including dynamic effects), to identify the types and conditions of

31
system components in prevalent use and to develop an understanding of

safety problems due to those factors identified in this accident study

and the other studies recommended above. Once the origin of the major

safety problems have been identified in conjunction with the other

information mentioned above, it would then be possible to develop a comprehensive research plan that would address and resolve these problems in the most effective manner.

A research plan formulated on the basis of this study alone, will have

to place heavy emphasis on structural investigations of system components

in recognition of the finding that indicates three out of four accidents

are attributable directly to system failures. It should be noted that even without taking into consideration such casual factors as the absence

or improper use of components (which fall within the broad definition

of system failures adhered to in this study) the structural failures

of system components accounted for more than 50 percent of all the accidents reviewed.

Anchorage and connection problems appear to be particularly critical in

light of the high rate of incidents attributed to their failure. However, noting that significant problems exist with regard to platform,

foundation and support element failures observed, they should also be

given research recognition.

Based on all of the above mentioned efforts, a final recommendation

would consist of formulating a comprehensive set of construction standards

that will promote and facilitate safe scaffolding practices. The abovementioned research efforts would enhance and develop the scientific and

technological base by which such a set of safety standards could be

formulated.

32
7. REjr’ERENCES

1. Study of Scaffolding Accidents Resulting in Injury, Conducted by the

Bureau of Labor Statistics (BLS) under the auspices of the

Occupational Safety and Health Administration (OSHA) for the period

of May to November, 1978. No publication, for administrative use

only.

2. OSHA Fatality/Catastrophe Investigations, Occupational Safety and

Health Administration, U.S. Department of Labor, Washington, D.C.,

May, 1979.

3. Occupational Safety and Health Standards (Federal Register 1910 and

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

4. Lew, H.S., Fattal, S.G., Shaver, J.R., Relnhold, T.A., Hunt, B.J.,

Investigation of Construction Failure of Reinforced Concrete Cooling

Tower At Willow Island, West Virginia, NBSIR 78-1578, Center for

Building Technology, National Engineering Laboratory, National Bureau

of Standards, Washington, D.C.

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

News Shipbuilding, Newport News, Virginia, January, 1979.

33
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APPENDIX A

Twenty-One Major Scaffold Types Addressed By The Codes and Standards

A-1
TABLE OF CONTENTS

TYPE Name Page

1 Wood pole scaffold a) single post A-3

b) independent post A-4

2 Tube and coupler scaffold A-5

3 Fabricated tubular frame scaffold A-6

4 Manually-propelled mobile ladder stand and scaffold (tower) . A-8

5 Vehicle-mounted elevating and rotating A-9

6 Telescoping work platform A-9

7 Self-propelled elevating work, platform A-9

8 Outrigger scaffold A-10

9 Adjustable multiple-point suspension (masons' or stonesetters') scaffold A-11

10 Two-point suspension (swinging) scaffold A-11

11 Single-point suspension scaffold . A-11

12 Boatswains' chair A-12

13 Needle beam scaffold A-12

14 Float or ship scaffold A-12

15 Catenary scaffold A-12

16 Bracket (carpenters' bracket) scaffold A-13

17 Square (bricklayers' square) scaffold A-14

18 Horse scaffold A-14

19 Ladder jack scaffold A-15

20 Window jack scaffold A-15

21 Pump jack scaffold A-16

A-2
Type la

pole scaffold - (a) single post.

A3

Figure A.l. Wood
Type lb

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Type 2

Figure A. 3. Tube and coupler scaffold.

A5
1

Figure A. 4. Fabricated tubular frame scaffold.

AFigure A. 5. Tubular frame subsystems*

A7
(b) Type 4

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

A-8

J
(b) Type 6 (c) Type 7

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

(c) self-propelled elevating work platforms.

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A-10
(a) Type 9

(b) Type 10

(c) Type 11

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

A-11
DROP PIN

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(a) Type 12

(b) Type 13

(c) Type 14

(d) Type 15

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
(b) Type 18

Figure A. 12. (a) Square (bricklayers' square) and (b) horse scaffolds.

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
A

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B-2
APPENDIX B

Types of Scaffolds Identified in the Questionnaire of the

Work Injury Survey of the Bureau of Labor Statistics

B-1
NBS-114A (REV. 9-78)

U.S. DEPT. OF COMM. 1. PUBLICATION OR REPORT NO. BIBLIOGRAPHIC DATA

SHEET NBSIR 79-1955

Z, Acee$»io>t No»

4. TITLE AND SUBTITLE

Analysis of Scaffolding Accident Records and Related

Employee Casualties

5. Publication Date January 1980

7. AUTHOR(S) s. George Fattal , Christopher Mullen,

Hai S, Lew, Bernard J. Hunt

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

10. Project/Task/Wofk Unit No.

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS rsfreef, 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

14. Spoil

15. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 20(hword or leaa factual summary of moat aignificar\t information. If document includes a significant bibliography or

literature survey, mention it here,) This report analyzes the causes of scaffold accidents involving employee

casualties based on existing records of such incidents. Where possible,

the causes are identified with system failures, environmental factors or

human factors. System failures are further subdivided into categories

to pinpoint the exact nature of the event that triggered the accident.

The study provides an insight into the major safety-related aspects of

scaffolding practices and points out the types of remedial measures that

should be instituted to mitigate the frequency and consequences of scaffolding incidents. Simultaneously, it identifies critical research needs

to develop the technical basis for the improvement of the safety aspects

of scaffolding practices.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the firat letter of the first key word unless a proper name;

separated by semicolons)

Accidents, accident statistics; construction regulations; construction safety;

employee casualties; environmental hazards; human factors; occupational safety;

scaffolds; scaffold failures.

18. AVAILABILITY ^Unlimited

I I For Official Distribution. Do Not Release to NTIS

I I Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003-

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF

PRINTED PAGES

22. Price

USCOMM-DC
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