NIOSH HEALTH HAZARD EVALUATION REPORT 

HETA #2003-0146-2976 

Genesis Steel Services, Inc. 

Baltimore, Maryland 

July 2005 

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health
ii 

PREFACE

The Hazard Evaluation and Technical Assistance Branch (HETAB) of the National Institute for 

Occupational Safety and Health (NIOSH) conducts field investigations of possible health hazards in the 

workplace. These investigations are conducted under the authority of Section 20(a)(6) of the Occupational 

Safety and Health (OSHA) Act of 1970, 29 U.S.C. 669(a)(6) which authorizes the Secretary of Health and 

Human Services, following a written request from any employers or authorized representative of 

employees, to determine whether any substance normally found in the place of employment has 

potentially toxic effects in such concentrations as used or found. 

HETAB also provides, upon request, technical and consultative assistance to federal, state, and local 

agencies; labor; industry; and other groups or individuals to control occupational health hazards and to 

prevent related trauma and disease. Mention of company names or products does not constitute 

endorsement by NIOSH. 

ACKNOWLEDGMENTS AND AVAILABILITY OF REPORT

This report was prepared by Jim Albers, Steve Hudock and Yong-Ku Kong, OSHFB, Division of Applied 

research and Technology (DART). Field assistance was provided by Dwight Werren (OSHFB). 

Analytical support was provided by Brian Lowe (OSHFB/DART), Sunil Sudhakaran (OSHFB/DART), 

and Ed Krieg (CST/DART). Desktop publishing was performed by Juanita Nelson. Review and 

preparation for printing was provided by Rick Hartle and Ellen Galloway. 

Copies of this report have been sent to employee and management representatives at Genesis Steel 

Services, Inc. and the OSHA Regional Office. This report is not copyrighted and may be freely 

reproduced. The report may be viewed and printed from the following internet address: 

http://www.cdc.gov/niosh/hhe. Single copies of this report will be available for a period of three years 

from the date of this report. To expedite your request, include a self-addressed mailing label along with 

your written request to: 

NIOSH Publications Office 

4676 Columbia Parkway 

Cincinnati, Ohio 45226 

800-356-4674 

or visit the NIOSH web site at: 

http://www.cdc.gov/niosh/hhe 

After this time, copies may be purchased from the National Technical Information Service (NTIS) at 5825 

Port Royal Road, Springfield, Virginia 22161. Information regarding the NTIS stock number may be 

obtained from the NIOSH Publications Office at the Cincinnati address. 

For the purpose of informing affected employees, copies of this report 

shall be posted by the employer in a prominent place accessible to the 

employees for a period of 30 calendar days.
iii 

Highlights of the Health Hazard Evaluation 

Highlights of the NIOSH Health Hazard Evaluation

Evaluation of NIOSH Health Hazard Evaluation

NIOSH Investigator evaluated workers’ risk of developing back and wrist disorders associated with tying 

rebar and the possible benefits of using a battery powered tier (BPT) as a substitute for manual tying to 

prevent upper extremity and low back musculoskeletal disorders. 

What NIOSH Did

• Measured the posture of the dominant wrist 

and the low back when workers tied rebar 

with wire using one of three techniques: 1) a 

pliers, 2) a battery powered tier (BPT), and 

3) the battery powered tier with an extension 

handle (BPT+E). 

• Made measurements of workers tying rebar 

on a freeway bridge deck. 

• Videotaped workers tying rebar and 

evaluated the videotape later for trunk 

posture. 

• Talked to reinforcing iron workers to see 

how they liked the BPT and BPT+E. 

What NIOSH Found

• Manually tying rebar with a pliers involves 

rapid and repetitive hand and forearm 

movements associated with increased risk of 

developing a hand, wrist, or elbow disorder. 

• Using the extension handle with the BPT 

requires the least deep forward bending. 

• The risk for developing a hand and wrist 

musculoskeletal disorder was reduced when 

the BPT or BPT+E are used. 

• Workers supported their upper body weight 

with their free arm when tying at ground 

level using the BPT. 

• Minimize the frequency and time employees 

manually tie rebar using the pliers. 

• Provide BPTs to employees when they tie 

rebar more than 1 hour per day. 

• Provide an extension handle for the BPTs 

for ground level tying. 

• Provide employees information describing 

the signs and symptoms of low back and 

hand, wrist and elbow disorders. 

What the Employees Can Do 

• Minimize the time spent in deep forward 

bending when tying rebar using the pliers. 

• Use the BPT and the extension handle when 

they are available. 

 Report to management any low back or 

upper limb aches, stiffness, or pain that may 

be due to work.

What Managers Can Do

What To Do For More Information:

We encourage you to read the full report. If you 

would like a copy, either ask your health and 

safety representative to make you a copy or call 

1-513-841-4252 and ask for 

HETA Report 2003-0146-2976#
iv 

Health Hazard Evaluation Report 2003-0146-2976 

Genesis Steel Services, Inc. 

Baltimore, Maryland 

June 2005 

Jim Albers, MPH, CIH 

Steve Hudock, PHD, CSP 

Yong-Ku Kong, PHD 

SUMMARY

During February 2003, the National Institute for Occupational Safety and Health (NIOSH) received a 

management request for a Health Hazard Evaluation (HHE) from the Genesis Steel Services, Inc. (GSSI). 

GSSI requested that NIOSH: 

• Evaluate the risk that reinforcing ironworkers have for developing back and hand disorders as a result 

of hand-tying reinforcement steel on concrete bridge decks and other large concrete slab jobs; and 

• Investigate whether the use of reinforcing steel battery powered tying tools can be an effective 

intervention for the prevention of work-related musculoskeletal disorders (WMSDs) of the upper 

limbs and back. 

In response to the request, NIOSH investigators evaluated GSSI employees’ biomechanical loading 

during rebar tying on a freeway-bridge construction site. 

NIOSH investigators measured employees’ wrist and forearm movement with goniometers while crew 

members tied reinforcing steel using three different tying methods. The employees were videotaped and 

the tape was analyzed to record trunk postures. NIOSH investigators analyzed the data collected and 

compared the results with criteria used to describe and contrast the levels of hand-wrist and low-back 

biomechanical loading for GSSI employees for each rebar tying technique used. 

Manually tying rebar at ground level using a pliers and wire involved sustained deep 

trunk bending and rapid, repetitive, and forceful hand-wrist and forearm movements that 

would require limits on the amount of time workers can safely do the work. Using a 

battery powered rebar tying tool significantly reduced the use of rapid and repetitive 

hand-wrist and forearm movements and freed one hand to support the trunk during tying. 

Adding an extension handle to the battery powered rebar tying tool allowed workers to tie 

rebar standing erect 

Keywords: NAICS 23412 (SIC 1622), ergonomics, reinforcement steel, bridge deck construction, workrelated musculoskeletal disorders, low back, hand-wrist 
Table of Contents 

Preface..........................................................................................................................................................ii

Acknowledgments and Availability of Report..........................................................................................ii

Highlights of the Health Hazard Evaluation ...........................................................................................iii

Summary.....................................................................................................................................................iv

Introduction.................................................................................................................................................1

Background .................................................................................................................................................1

Springfield Interchange Freeway Bridge..............................................................................................1

Installing and Fastening Rebar for the Bridge.....................................................................................1

Methods........................................................................................................................................................2

Data collection .........................................................................................................................................2

Data Analyses ..........................................................................................................................................3

Goniometric data ................................................................................................................................3

Positional data .....................................................................................................................................3

Evaluation Criteria .....................................................................................................................................3

Results ..........................................................................................................................................................5

Discussion ....................................................................................................................................................6

Conclusions..................................................................................................................................................8

Recommendations.......................................................................................................................................8

References....................................................................................................................................................9

Health Hazard Evaluation Report No. 2003-0146-2976 Page 1 

INTRODUCTION

In February 2003, the National Institute for 

Occupational Safety and Health (NIOSH) 

received a request for a Health Hazard 

Evaluation (HHE) from the vice-president of the 

Genesis Steel Service, Inc (GSSI). GSSI, a 

construction reinforcing and structural steel 

contractor in Baltimore, MD, GSSI asked 

NIOSH to do the following: 

• Evaluate the risk that GSSI reinforcing 

ironworkers have for developing back and 

hand musculoskeletal disorders as a result of 

hand-tying reinforcement steel on concrete 

bridge decks, and 

• Investigate whether the use of a battery 

powered tier (BPT) for rebar tying can be an 

effective intervention for the prevention of 

work-related musculoskeletal disorders 

(WMSDs) of the upper extremities and 

back. 

In response to the request, NIOSH investigators 

conducted a field investigation of GSSI 

employees’ exposures to biomechanical loading 

when tying rebar for the concrete deck of an 

elevated freeway bridge in Springfield, VA. The 

investigation was conducted on October 27-30, 

2003. 

BACKGROUND

Genesis Steel Service, Inc. is a minority owned 

construction specialty subcontractor providing 

structural and reinforcing steel services for new 

construction projects in the greater BaltimoreDistrict of Columbia metropolitan area. The 

distribution of GSSI’s work is approximately 

60% concrete reinforcement, 25% structural 

(bridge and buildings < 4 stories), and 15% 

miscellaneous metals, including ornamental. 

GSSI does not operate a fabrication shop and 

reinforcing steel used on projects is 

predominantly pre-cut and pre-formed. 

At the time of the HHE request, GSSI employed 

100 ironworkers (IWs). Around 40% of the IWs 

employed by GSSI were minority workers - 20% 

African-American and 20% Hispanic. GSSI 

estimated that for 2/3 of the Hispanic workers 

English is their second language. The IWs are 

members of the International Association of 

Bridge, Ornamental, and Reinforcing Iron 

Workers. GSSI estimated that 25-30% of the 

IWs employed at the time of the study had been 

employed by the contractor since 1988. Genesis’ 

IWs tend to specialize in structural or 

reinforcing work, and most reinforcing 

ironworkers (RIW), also known as ‘rodmen’, 

work exclusively on concrete reinforcing jobs. 

Springfield Interchange 

Freeway Bridge 

As a subcontractor on the Springfield 

Interchange Improvement Project, GSSI 

installed reinforcing steel bars for the concrete 

deck of the bridge connecting westbound I-495 

traffic to the southbound I-95 interstate highway. 

The bridge is approximately one mile long by 

60 feet wide. GSSI employees were responsible 

for placing and tying the steel bars used to 

reinforce the concrete deck and walls of the 

bridge. An estimated 2.2 million wire ties were 

made on the bridge to secure the rebar at a rate 

of 7 wire ties per square foot (ft2

) for the bridge. 

For most of the project, weather permitting, 

GSSI IWs worked a 5 day and 40 hour work 

week. The amount of rebar placed and tied on a 

given day depended on several factors, including 

the number of workers on the job, the 

environmental conditions, and the pace of the 

work preceding rebar installation. 

Installing and Fastening Rebar 

for the Bridge 

Before pouring the concrete deck that will be the 

surface of the bridge, steel reinforcing bars (aka 

rebar) must be placed inside the concrete forms. 

The rebar is used to reinforce and increase the 

tensile strength (i.e., bending and stretching) of 

the concrete in the deck and sidewalls. Two 

rebar ‘mats’ were placed one above the other 

inside the concrete form over the full length of 
Page 2 Health Hazard Evaluation Report No. 2003-0146-2976 

the bridge. Each mat consisted of a series of bars 

placed perpendicular to each other and spaced 

about seven (7) inches on-center. The bottom 

mat was kept above the metal decking using 

wire supports (aka chairs). Chairs were used to 

separate the top mat from the bottom mat. The 

rebar are tied together to prevent the bars from 

shifting when the concrete mixture is poured 

into the form, although the ties do not add 

strength to the bridge. 

The specifications for the job, common for 

freeway bridge decks in the Unites States, 

required tying 50% of the intersecting rebar on 

the bottom mat and 100% of the intersections on 

the top mat. GSSI employees used two 

techniques to tie the intersecting rebar together, 

including: 1) pliers and spool of wire and 2) the 

battery operated RB392 rebar tier (MAX USA 

Corp., Garden City, New York) (Figure 1). The 

BPT tier was used most frequently to make the 

‘snap’ or simple ties used to keep the rebar from 

shifting. Pliers were used when more secure ties 

(i.e., ‘saddle’ or ‘figure 8’) were necessary to 

frame the sidewalls of the bridge deck or make 

the first ties for each mat (Figure 2). 

Traditional tying (Figure 3) required the use of 

two hands – one to use the pliers to pull, wrap, 

twist, and cut the wire and the other to pull and 

push the wire. Only one hand was necessary to 

operate the BPT (Figure 4). Both techniques 

required frequent and sustained deep trunk 

bending (aka stooping) (>90o trunk inclination) 

to tie the rebar. 

NIOSH introduced a commercially available 

extension handle developed for use with the 

BPT (Figure 5 and 6). This was the third rebar 

tying technique used during the investigation. 

METHODS

GSSI employees were directed to tie the rebar 

placed for the bottom mat using three different 

tying techniques: 1) pliers; 2) the RB392 BPT 

and 3) the BPT with an extension handle 

(BPT+E). All employees were familiar with the 

first two techniques and used each on the site. 

NIOSH brought the extension handle to the site 

and none of the employees had previously used 

the device. Participants were encouraged, but 

not required, to use the extension before 

measurements were made. 

GSSI had purchased the BPTs approximately 2 

years prior to the study in part to reduce 

employees’ exposures to biomechanical loading 

related to tying using pliers. The power tier still 

required deep forward bending when tying at 

deck level, but workers now used one hand to 

hold the tier and the other to support their upper 

body while tying. 

The investigation was conducted to answer the 

following questions: 

1. How does the use of a battery powered rebar 

tier (MAX USA RB392) affect the 

biomechanical loading of the hand-wrist 

and/or of the low back? 

2. How does the use of an adjustable extension 

handle with the battery powered rebar tier 

(MAX USA RB392) affect the 

biomechanical loading of the hand-wrist 

and/or low back? 

3. How does the use of the battery powered 

rebar tier (MAX USA RB392) with and 

without the adjustable handle affect the 

productivity of rebar tying? 

Data collection 

Each worker tied rebar for about 30 minutes 

using the: 1) pliers; 2) BPT; and 3) BPT+E. A 

twin-axis goniometer (Biometrics SG Series) 

and torsiometer (Biometrics Q110) were used to 

measure the dominant wrist motion and position 

(aka posture) in the flexion/extension, 

ulnar/radial, and pronation/supination planes 

(Figure 7) during tying.1

Observational methods were used to record the 

position of the trunk during tying and the 

number of ties each worker made. This consisted 

of videotaping each worker from three different 

angles so that the trunk could be later viewed 

from both the side and front. 

Each worker was asked to describe the physical 

effort they used with their hand-wrist and lowback on a scale from 0 (‘nothing at all’) to 10 
Health Hazard Evaluation Report No. 2003-0146-2976 Page 3 

(‘extremely strong’) when using the three tying 

methods.2

 Prior to conducting the study, the 10-

point scale was translated into Spanish by a 

NIOSH contractor. 

Personal information and work history was 

obtained using self administered questionnaires 

available in English and Spanish. 

Data Analyses 

Goniometric data 

The goniometric data were converted to readable 

files using proprietary Biometrics Ltd. 

management and analysis software. Statistical 

analysis, including summary and inferential 

statistics, was conducted using SAS® Institute 

software. 

Positional data 

Video tape was analyzed using the Multimedia 

Video Task Analysis (MVTATM) software 

program, which allowed the analyst to run video 

tape through the computer.3

 The analyst 

recorded the frequency and duration of the trunk 

posture angles and the time required to tie rebar 

for each of the three tying techniques. 

Analysts used the computer-based 3-D Static 

Strength Prediction ProgramTM to estimate the 

pressure (compressive forces) on the spinal disc 

between the fifth lumbar vertebrae and the first 

sacral vertebrae (aka L5/S1 spinal disc) during 

rebar tying in stooped postures.4

 Disc pressure is 

known to vary depending on the amount and 

type (e.g., forward, sideward, twisting) of 

bending. 

EVALUATION CRITERIA

Overexertion injuries and musculoskeletal 

disorders, such as low back pain, tendinitis, and 

carpal tunnel syndrome, are often associated 

with job tasks that include: 

1. Repetitive, stereotyped movement about the 

joints; 

2. Forceful manual exertions; 

3. Lifting, pushing, and pulling; 

4. Awkward and/or static body positions; 

5. Direct pressure on nerves and soft tissues; 

6. Work in cold environments; 

7. Exposure to whole-body or segmental 

vibration; or 

8. Work-related psychosocial factors, such as 

high job demand, low decision latitude, and 

monotonous activity, etc. 

The risk of injury appears to increase as the 

intensity and duration of exposures to the risk 

factors increases and the recovery time (i.e., rest 

time) decreases. Individual characteristics (e.g., 

age, gender, weight, fitness) are seen as 

“contributing and modifying influences in the 

development of pain and disability and in the 

transition from acute to chronic pain.”5

The preferred method for preventing and 

controlling work-related musculoskeletal 

disorders (WMSDs) is to reduce or eliminate 

exposure to the risk factors. The most effective 

way to do this is to design jobs, workstations, 

tools, and other equipment to match the 

physiological, anatomical, and psychological 

characteristics and capabilities of the worker. 

Under these conditions, exposures to task factors 

considered potentially hazardous will be reduced 

or eliminated. 

The following criteria were used to evaluate the 

biomechanical loading of GSSI employees’ low 

back and upper limbs during rebar tying tasks on 

the Springfield Interchange Improvement 

Project: 

1. the American Conference of Governmental 

Industrial Hygienists (ACGIHTM) Hand 

Activity Level (HAL) Threshold Limit 

Value (TLV)TM, 6

 

2. recommendations for acceptable hand-wrist 

motion (e.g., velocity and acceleration) to 

prevent wrist cumulative trauma disorders 

(CTD),7 8

 

3. the Michigan 3-Dimensional Static Strength 

Prediction ProgramTM to estimate the 

compressive and shear forces on the L5/S1 

spinal disc,4

 

4. the Evaluation of Static Working Postures, 

International Organization for 

Standardization (ISO) 11226,9

 and 
Page 4 Health Hazard Evaluation Report No. 2003-0146-2976 

5. risk assessment of spinal disease as a result 

of cumulative physical work load on the 

lumbar spine.10

ACGIHTM Hand Activity Level TLVTM

The ACGIHTM Hand Activity Level (HAL)5

TLVTM is based on epidemiological, 

psychophysical, and biomechanical studies and 

is applied to "mono-task" jobs performed for 

four hours or more per day. (A mono-task job 

involves performing a similar set of motions or 

exertions repeatedly such as working on an 

assembly line or using a keyboard for 

transcription.) The HAL is based on the 

frequency of hand exertions and the duty cycle 

(distribution of work and recovery periods). The 

HAL can be determined by a trained observer or 

calculated using information on the frequency of 

exertions and the work/recovery ratio. Peak 

force is normalized on a scale of 0 to 10, 

corresponding to 0% to 100% of the applicable 

population reference strength. Peak force can be 

determined with ratings by a trained observer, 

ratings using subjective exertion scales (i.e., 

Borg 10 point perceived effort scale)2

, or 

measured using instrumentation such as strain 

gauges. Peak force requirements can be 

normalized by dividing the force required to 

perform the job by the strength capability of the 

work population for that activity. The total 

exposure is characterized in terms of average 

hand activity level and peak hand force. 

Hand-Wrist Motion Guidelines

Marras and Schoenmarklin studied the 

relationship between wrist movement, including 

the angle, repetition, velocity, and acceleration 

levels, and the risk of developing a CTD.7

 The 

study found that high wrist and forearm motion 

(i.e., angular velocity and angular acceleration) 

during an 8-hour day were significantly 

associated with risk of developing an upper 

extremity CTD. Non-neutral wrist position (aka 

posture) alone was not associated with an 

increased risk of developing CTDs. Mean wrist 

acceleration levels associated with high and low 

CTD risk in the radial/ulnar, flexion/extension, 

and pronation/supination planes were, 

respectively, 494 and 301 angular 

degrees/second2

 (d/s2), 824 and 494 d/s2 , and 

1824 and 1222 d/s2

. In follow-up analysis of the 

data, wrist acceleration in the flexion/extension 

plane was determined to be the best predictor of 

a hand/wrist CTD.8

 

3-D Static Strength Prediction Program

The Michigan 3-Dimensional Static Strength 

Prediction ProgramTM (3DSSPPTM) is a 

computerized model which can be used to 

evaluate the physical demands of a prescribed 

job.4

 Typical inputs to the model are the 

magnitude and direction of forces at the hands, 

angles of body segments, and worker 

characteristics. The model calculates forces (i.e., 

moments) on the joints of the body and 

estimates the percentage of the workforce able to 

sustain the inputted loads. Compressive and 

shear forces for the L5/S1 disc are calculated. 

The program allows the analyst to estimate the 

compressive forces acting on the spine relative 

to the revised NIOSH lifting equation.11. In 

order to prevent low back disorders, NIOSH 

recommends L5/S1 disc compression force 

never exceed 3400 Newtons (N) during any 

single job activity (1 N = 0.225 pound-force). 

The 3DSSPPTM can be used to evaluate the 

biomechanical demands of an existing task or to 

predict the physical demands of a task that is 

being designed or modified. The joint angles for 

the program’s mannequin were set to represent 

postures used during rebar tying and estimate the 

forces exerted on the L5/S1 spinal disc. 

ISO Evaluation of Static Work Postures

The ISO developed the consensus standard titled 

Ergonomics – Evaluation of Static Working 

Postures (ISO 11226-2000).9

 ISO 11226 was 

written to control pain, fatigue and disorders of 

the musculoskeletal system that may result from 

the use of non-neutral body postures for long 

durations without sufficient recovery time. The 

standard describes acceptable trunk postures and 

maximum acceptable holding times for 

potentially harmful postures. 
Health Hazard Evaluation Report No. 2003-0146-2976 Page 5 

Cumulative spinal loading and back 

disease

Seidler et al investigated the relationship 

between the cumulative (e.g., added over time) 

forces on the lumbar section of the back and 

symptomatic spinal disease, e.g., spondylosis of 

the lumbar spine.12 Specifically, the study 

compared the stress (i.e., forces) over time on 

the lumbar spine due to lifting, carrying, and 

extreme forward flexion (>90°) with the 

occurrence of back disease (i.e., osteochondrosis 

or spondylosis) diagnosed using x-rays. The 

authors reported significantly more spinal 

disease in the group of workers with the higher 

cumulative physical stress on the back compared 

with workers with less back stress. The risk of 

back disease also increased with the amount of 

physical force applied to the L5/S1 spinal disc. 

RESULTS

Summary 

Manually tying rebar at ground level using pliers 

and wire involved sustained deep trunk bending 

and rapid and repetitive hand and wrist 

movements. Using a BPT significantly reduced 

the use of rapid and repetitive hand-wrist and 

forearm movements characteristic of tying with 

the pliers, and freed one hand to support the 

weight of the trunk during tying. Adding an 

extension handle to the BPT allowed workers to 

tie rebar standing erect. The results show that 

manually tying rebar using a pliers involves 

greater risk of developing a low back WMSD 

than tying with either the BPT or BPT+E. The 

study indicates that tying with the BPT+E also 

involves less risk of developing an upper limb 

WMSD. 

Demographics 

All eight GSSI employees (six Hispanic, two 

Caucasian) installing rebar on the freeway 

bridge agreed to participate in the study. 

Participant mean age was 37 years old and mean 

height, weight and body mass index (BMI) were, 

respectively 69 inches, 184 lbs., and 27.4 BMI 

(Table 1). Table 2 shows participants’ mean 

time working as a rodbuster, employed by GSSI, 

and working on the study job site. Participants 

reported tying rebar using a pliers and using a 

BPT 8.1 hours/week and 6.1 hours/week, 

respectively. One worker reported a back injury 

occurring during the previous 12 months that 

affected his work. No injuries occurring during 

the previous 12 months were reported by the 

remaining seven workers. 

Electro-goniometric analyses 

Calibration

The calibration results for the electrogoniometers demonstrated that the wrist position 

measurements were accurate and consistent. 

Wrist and Forearm Movements

Wrist mean velocity and mean acceleration were 

higher during pliers tying than BPT or BPT+E 

tying. Differences between the pliers and the 

BPT or BPT+E rates were significantly different 

(Tables 3 and 4). Mean wrist velocities 

measured in the flexion/extension and 

ulnar/radial planes during pliers tying exceeded 

velocities associated with high and low risks of 

developing a CTD (Figure 8).7

 The low CTD 

risk level was exceeded in the ulnar/radial plane 

using each of the three tying techniques. 

Operating the BPT resulted in a mean wrist 

velocity in one plane (ulnar/radial) exceeding 

the level associated with a high CTD risk. 

Figure 9 shows that workers’ mean wrist 

acceleration levels measured during pliers tying 

exceeded levels found to be associated with (a) 

high CTD risk in the flexion/extension (i.e., 

824 d/s2

) and ulnar/radial (i.e., 494 d/s2) planes 

and (b) low CTD risk in the pronation/supination 

plane (i.e., 1222 d/s2

). Use of the BPT exceeded 

acceleration levels related to low CTD risk level 

in the ulnar/radial plane (i.e., 301 d/s2

).7 

Borg Perceived Effort

Five workers completed the perceived effort 

questionnaire. Participants reported the lowest 

‘low back’ effort when using the BPT+E (1.2 on 

the 10 point Borg scale), followed by 2.8 for the 
Page 6 Health Hazard Evaluation Report No. 2003-0146-2976 

BPT and 5.8 for the pliers. The lowest handwrist effort was reported for the BPT (2.8) and 

the BPT+E and pliers were, respectively, 5.0 and 

5.2. (Table 5) 

Observational analyses 

ACGIH Hand Activity Level TLVTM

ACGIH HAL-TLVTM scores were calculated 

using the workers’ perceived effort scores2

 (i.e., 

mean, low and high) for each tying technique. 

Using the mean scores, the HAL-TLVTM (0.78) 

would be greatly exceeded at 2.5 when a pliers 

was used and slightly exceeded at 0.83 when an 

BPT+E (0.83) was used for 4 hours or more 

each day. Use of the BPT alone would not 

exceed the HAL-TLVTM. (Table 6) 

Trunk Positions

Workers were observed tying rebar with severe 

trunk bending (≥ 90°) 94% of the time when 

using the pliers and 93% of the time when using 

the BPT (Table 7). With the BPT+E workers 

tied rebar using neutral trunk positions (< 15° 

flexion) 83% of the time and moderate forward 

flexion (16° – 30°) 16% of the tying time with 

the extension attached to the power tier. 

ISO 11226 recommends that working trunk 

postures not exceed 60° of forward bending at 

any time. Observed trunk postures used during 

pliers and BPT rebar tying greatly exceeded the 

ISO 11226 recommendations. 

When using the BPT, all workers used their free 

hand to support the weight of their torso, e.g., 

resting the hand/forearm on the knee/thigh, 90% 

of the time when they tied at ground level. 

(Table 8) [Note: Workers use two hands to tie 

using the pliers, while only one hand is 

necessary using the BPT or BPT+E.] 

Other 

Cumulative trunk loading

Using the 3D Static Strength Prediction 

ProgramTM (3DSSPP)4

, compressive and shear 

forces acting on the L5/S1disc were estimated to 

be between 1500 N to 2850 N during two-hand 

rebar tying using the pliers without lateral 

bending or trunk rotation. (Table 9) Lateral 

bending (25o left or right) increased both total 

and shear compression forces when the trunk 

inclination did not change. Highest shear forces 

were 501 N and were recorded at the deepest 

trunk inclination (-125o) and 25o lateral bending. 

Although these forces do not exceed the NIOSH 

revised lifting guideline (3400 N), the postures 

must be sustained for several hours each day 

increasing the cumulative force over many years 

of activity. 

Cumulative forces on the L5/S1 were calculated 

(Figure 10/Table 10) for rebar tying (average 2 

and 4 hours duration/day) and carrying 20 kg 

(average 1 hour/day) in front of or beside the 

body for one, five, and ten years.12 Figure 11 

shows that the estimated cumulative forces 

resulted in 2.6 (95% CI 1.2 – 5.7) and 6.0 (95% 

CI 2.7 – 13.4) times greater risk (odds ratios) of 

developing spinal disease, respectively, after 5 

years and 10 years work-exposure. 12 

With the trunk fully flexed, e.g., tying rebar at 

ground level, the muscles that normally support 

the spinal column become ineffective and the 

ligaments take over.13 When the lumbar spine 

becomes stretched out there is a greater potential 

for damage to the spinal discs.13,

14

Productivity 

Tying with the BPT or BPT+E is faster than 

using the pliers. The mean number of ties per 2.5 

minutes completed using the pliers, BPT, and 

BPT+E, respectively was: 42, 84, and 52. (Table 

11) Tying times were significantly different for 

the three techniques when compared to each 

other. 

DISCUSSION

Risks Associated with Pliers Tying 

Both the ACGIHTM HAL-TLVTM and the CTD 

risk estimates developed by Marras and 
Health Hazard Evaluation Report No. 2003-0146-2976 Page 7 

Schoenmarklin8 assume exposure occurs, 

respectively, for ≥4 hours and 8 hours each day. 

Reinforcing ironworkers (RIWs) reported tying 

rebar for about 16 hours per week using the 

pliers or BPT. Tying rebar using the pliers for 4 

or more hours each day exceeded the ACGIHTM 

HAL-TLVTM by 3.2 times. Using the BPT+E for 

4 hours or more each day slightly exceeds the 

HAL-TLVTM. 

During pliers tying, wrist motion (i.e., mean 

velocity and acceleration) in the 

flexion/extension and ulnar/radial planes was 

about twice as fast as the motion associated with 

both low and high CTD risk reported by Marras 

and Schoenmarklin.7

 The upper limb CTD risk 

assessment they conducted was for an 8-hours 

work day. RIWs who do not continuously tie 

rebar with a pliers for 8 hours may not exceed 

these parameters. 

However, pliers tying requires rapid wrist 

movement in all three planes of motion in 

combination with hand forces necessary to pull, 

twist, and cut the wire. Marras and 

Schoenmarklin7

 did not describe the combined 

effect of rapid motion in multiple planes and, 

therefore, the CTD risk levels reported may 

underestimate actual risk when rapid motions 

are required in all three planes. 

The frequency and duration of extreme trunk 

flexion using the pliers increases RIWs’ 

exposure to risk factors for lumbar spine disease 

after 5-10 years of tying in a stooped posture and 

put them at greater risk of developing a low back 

disorder. 

The results of the study clearly show that 

manually tying rebar using a pliers exposes 

workers to serious risk factors for developing 

WMSDs of low back and the upper limbs. 

Tying Using the BPT and BPT+E 

Hand-Wrist

Use of the BPT resulted in mean hand-activity 

level scores below the ACGIH HAL- TLVTM. 

The BPT+E resulted in a mean hand-activity 

level slightly higher than the TLVTM. This 

difference can be explained by the higher 

“perceived effort” scores RIWs gave the BPT+E 

on the Borg2

 questionnaire. Unlike the BPT, 

workers did not have experience using the 

extension prior to the study. Use of the extension 

does increase the distance of the hand to the 

tying location, and possibly reduces control of 

the tool during placement. Perhaps more 

importantly, however, positioning and holding 

the BPT+E away from the body results in higher 

forces on the hand, arm, and shoulder due to the 

larger moment. These factors likely increased 

the “perceived effort” scores during BPT+E use 

and could be addressed with training. 

There was no significant difference between the 

wrist movement (i.e., velocity and acceleration) 

when comparing the use of the BPT and BPT+E. 

Vi described an increase in productivity for the 

BPT+E comparable to the BPT in a study of 

union RIWs in Ontario, Canada, who had 

experience using the extension before the study 

began. 15

Low Back 

Use of the BPT+E resulted in the least forward 

bending during rebar tying. Although the BPT 

tying trunk positions were not significantly 

different from pliers tying positions, it is 

reasonable to assume there is less loading on the 

lumbar spine. The BPT only requires the use of 

one hand to tie rebar and all workers were 

observed using the free hand to support their 

upper body weight during the majority of the 

time they were observed tying with the BPT. 

The use of the hand or arm to support the upper 

body should reduce the compressive forces 

applied to the lumbar spine. Participants appear 

to have confirmed this when they reported 

significantly less perceived effort for the low 

back using the BPT+E than the pliers (2.8 for 

the BPT+E and 5.8 for the pliers), despite the 

similar posture. 

Other Activities 
Page 8 Health Hazard Evaluation Report No. 2003-0146-2976 

NIOSH analyzed only rebar tying during this 

study, although reinforcing ironworkers’ 

perform additional job activities that require 

“maximum muscle force to lift, push, pull, or 

carry objects.”16 For example, in addition to 

lifting and carrying rebar, workers must also 

separate individual rebar from the bundles 

transported to the immediate work area. Rebar 

transported in bundles can become intertwined, 

which makes the separation of individual rebar 

lengths difficult. Workers were observed 

separating rebar using sudden (i.e., jerking) 

muscle forces – often in stooped and 

asymmetrical postures- to separate individual 

rebar from the bundles. 

RIWs’ manual material handling activities can 

comprise a significant percentage of work time. 

Forde17 reported “(m)anual material handling 

(MMH) activities (lifting, lowering, pushing, 

pulling, dragging, carrying, holding, forceful 

motions) were observed 22% and 32% of the 

observed time”, respectively, for reinforcing 

ironworkers building caisson cages and the deck 

and sides of a freeway access tunnel. If these 

additional activities had been evaluated during 

the study, the estimates would be higher and 

indicate greater risk of developing a back 

musculoskeletal disorder. 

Study Limitations 

There are three limitations of this study. First, 

participants’ time using the extension handle 

(BPT+E) was measured in minutes, rather than 

hours. Subsequently, most, if not all, participants 

had insufficient time to become accustomed to 

using the extension (BPT+E). The wrist, elbow, 

and shoulder can be subjected to larger moments 

when the tool is positioned and held further from 

the body. This unfamiliarity may explain some 

participants higher hand-wrist perceived effort 

ratings. 

Second, the study was not conducted in a 

manner that could determine the real 

productivity differences among the three tying 

techniques. Using the BPT nearly doubled the 

number of ties completed during the analysis 

periods, while the BPT+E resulted in a slight 

increase. The observation time, however, was 

too short to consider possible non-productive 

time related to using the BPT, such as the 

additional cost of charging BPT batteries (using 

gasoline powered generator) on the construction 

site and potential productivity loss due to 

changing batteries and BPT mechanical failure, 

i.e., wire jam. Despite this shortcoming, GSSI 

ironworkers and management representatives 

expressed confidence that the MAX USA 

RB392 power tier increased workers’ 

productivity. 

CONCLUSIONS

1. Manually tying rebar using a pliers 

exceeded the ACGIHTM HAL-TLVTM and wrist 

velocity. 

2. Measured mean wrist velocity and 

acceleration rates were high in all planes of 

motion during pliers tying. 

3. Tying rebar using the BPT significantly 

reduced hand and wrist movements that can 

cause upper limb WMSDs. Deep forward 

bending was still necessary to tie the rebar, but 

the ‘free’ arm supported the weight of the trunk, 

reducing forces on the L5/S1 disc. 

4. Tying rebar using the BPT+E eliminated 

the sustained deep forward bending required 

when tying with the pliers and BPT. Wrist 

movement was significantly lower in all three 

planes of motion using the BPT+E. Some 

participants, however, reported hand-wrist effort 

similar to using the pliers, resulting in a mean 

hand-activity level score slightly higher than the 

ACGIH HAL TLVTM. 

5. Worker productivity increased when the 

BPT or BPT+E were used during the study. 

RECOMMENDATIONS

1. Provide battery powered rebar tiers with 

extension handles whenever reinforcing 
Health Hazard Evaluation Report No. 2003-0146-2976 Page 9 

ironworkers tie rebar placed at ground level, i.e., 

bridge and freeway deck, concrete slab, etc. 

2. Provide training to workers who will use the 

extension handle so that they will be able to 

correctly adjust the height of the handle and 

limit the distance they extend the BPT+E during 

tying. 

3. Encourage reinforcing ironworkers to use the 

extension for the battery powered tier when they 

tie rebar at ground level. 

4. Provide ironworkers information to enable 

them to identify the early signs and symptoms of 

low back and upper extremity musculoskeletal 

disorders. 

5. Future research should be conducted to 

characterize the following aspects of tying 

reinforcing steel: 

(a) the types of reinforced concrete construction 

that would benefit from the use of power tiers; 

(b) the optimal design of an extension handle for 

power rebar tiers; and 

(c) reinforcing ironworkers biomechanical 

loading, especially to the back and shoulders, 

during rebar manual material handling. 

REFERENCES

1 Biometric [2003]. Management and Analysis, 

Version 3.0. Biometrics, Ltd., Cwmfelinfach, 

Gwent, United Kingdom 

2 Borg, G. [1982] A category scale with ratio 

properties for intermodal and interindividual 

comparisons. In: Geissler, H.G. and Petzold, P. 

(Eds.), Psychophysical judgment and the process 

of perception. Berlin: VEB Deutscher Verlag der 

Wissenschaften. 

3 UW-Madison [2001] User’s Manual for 

Multimedia Video Task Analysis TM 

(MVTATM). Madison, WI: Ergonomics 

Analysis and Design Research Consortium, 

University of Wisconsin-Madison. 

4 University of Michigan, Center for 

Ergonomics [2001] 3D Static Strength 

Prediction ProgramTM Version 4.3. Ann Arbor, 

MI: University of Michigan Center for 

Ergonomics. 

5 NRC/IOM [2001] Musculoskeletal disorders 

and the workplace: low back and upper 

extremities. Panel on musculoskeletal disorders 

and the workplace. Commission on Behavioural 

and Social Sciences and Education. Washington 

DC: National Academy Press. 

6 ACGIH [2001] Hand Activity Level Threshold 

Limit Value. TLV/BEI Documentation. 

Cincinnati, OH: American Conference of 

Governmental Industrial Hygienists. 

7 Marras WS, Schoenmarklin RW [1993] Wrist 

motions in industry. Ergonomics 36 (4), 342-

351. 

8 Schoenmarklin RW, Marras WS, Leurgans SE 

(1994) "Industrial Wrist Motions and Risk of 

Cumulative Trauma Disorders in Industry," 

Ergonomics, 37(9), 1449-1459. 

9 ISO/CD 11226 [1995] Ergonomics-Evaluation 

of Working Postures International Organization 

for Standardization. Geneva, Switzerland. 

10 Seidler A, Bolm-Audorff U, Heiskel H, 

Henkel N, Roth-Küver B, Kaiser U, Bickeböller 

R, Willingstorfer WJ, Beck W, Elsner G [2001] 

The role of cumulative physical work load in 

lumbar spine disease: risk factors for lumbar 

osteochondrosis and spondylosis associated with 

chronic complaints. Occup Environ Medicine 

58:735–746. 

11 Waters TR, Putz-Anderson V, Garg A [1993] 

Revised NIOSH equation for the design and 

evaluation of manual lifting tasks. Ergonomics 

36 (7) 749-776. 

12 Seidler A, Bolm-Audorff U, Heiskel H, 

Henkel N, Roth-Küver B, Kaiser U, Bickeböller 

R, Willingstorfer WJ, Beck W, Elsner G [2001] 

The role of cumulative physical work load in 

lumbar spine disease: risk factors for lumbar 

osteochondrosis and spondylosis associated with 
Page 10 Health Hazard Evaluation Report No. 2003-0146-2976 

chronic complaints. Occup Environ Medicine 

58:735–746 

13 Pope MH, Goh KL, Magnusson ML [2002] 

Spine ergonomics. Annu. Rev. Biomed. Eng. 

2002. 4:49–68. 

14 Solomonow M, Baratta RV, Banks A, 

Fruedenberger C, Zhou HE [2003] Flexionrelaxation response to static lumbar flexion in 

males. Clinical Biomechanics 18: 273-279. 

15 Vi P, Schneider S [2005]. Promoting Early 

Return to Pre-Injury Job Using a Rebar-Tying 

Machine. J. Occup. Environ. Hyg. 2:D34-D37. 

16 Occupational Information Network [2004] 

Reinforcing iron and rebar workers (47-

2171.00). Occupational Information Network, 

O*Net Online. http://online.onetcenter.org/ 

Date accessed December 2004. 

17 Forde M. [2002] Reinforcing Ironwork: 

PATH (Posture, Activity, Tools, Handling) 

Analysis, Technical Report T-61. Construction 

Occupational Health Program, Department of 

Work Environment, University of Massachusetts 

Lowell, Lowell, MA. 

http://www.uml.edu/Dept/WE/COHP Date 

accessed December 2004. 
Health Hazard Evaluation Report No.: 2003-0146-2976 Page 11 

Figure 1 

MAX-USA RB-392 Power rebar tier (BPT) 

[Click here place Tables, Figures, and Appendices] 

RB-392 Specifications 

Max Wraps per Tie 3 

Tying Speed 1 Second 

Max Rebar Size (in) 3/4 to 1-1/2 

Wire Gauge 21 

Ties per Coil of Wire 180 – 210 

Ties per Battery Charge 8000 

Voltage 9.6 DC 

Weight 4.6 lbs. 
Page 12 Health Hazard Evaluation Report No. 2003-0146-2976 

Figure 2 

Ties used to secure rebar together 

A Snap or simple tie (similar to tie made 

 using power rebar tier, except the power 

 tier wraps wire around bars 3 times) 

B Saddle tie 

A B
Health Hazard Evaluation Report No.: 2003-0146-2976 Page 13 

Figure 3 

Rebar tying using pliers and tie-wire 

Pliers 
Page 14 Health Hazard Evaluation Report No. 2003-0146-2976 

Figure 4 

Rebar tying using MAX-USA RB392 battery powered rebar tier 

Battery 

powered tier 
Health Hazard Evaluation Report No.: 2003-0146-2976 Page 15 

Figure 5 

MAX-USA RB-392 Battery powered tier with adjustable extension (BPT+E) 

(plan to use image from manufacturer) 

Adjustable 

extension 
Page 16 Health Hazard Evaluation Report No. 2003-0146-2976 

Figure 6 

Rebar tying using MAX-USA RB392 power rebar tier with adjustable extension handle 
Health Hazard Evaluation Report No.: 2003-0146-2976 Page 17 

Figure 7 

Wrist, hand and arm position/movement planes 
Page 18 Health Hazard Evaluation Report No. 2003-0146-2976 

Figure 8 

Measured Wrist Velocity during Rebar Tying 

0

20

40

60

80

100

120

P BPT BPT+E P BPT BPT+E P BPT BPT+E

Flexion/Extension Ulnar/Radial Pronation/Supination

Tool Type by Wrist Plane

degrees/second

Mean 

Std Dev

Mean High CTD Risk Mean Low CTD Risk

P= Pliers; BPT= Battery powered tier; BPT+E= BPT + extension 

Wrist acceleration mean and standard deviations measured in three planes 

(flexion/extension, ulnar/radial & pronation/supination) during rebar tying and 

mean high and low CTD risk acceleration rates.7 

48 d/s 29 d/s 

26 d/s 7 d/s

91 d/s 68 d/s 
Health Hazard Evaluation Report No.: 2003-0146-2976 Page 19 

0

200

400

600

800

1000

1200

1400

1600

1800

2000

P BPT BPT+E P BPT BPT+E P BPT BPT+E

Flexion/Extension Ulnar/Radial Pronation/Supination

Tool Type by Wrist Plane

degrees/second2

Mean

Std Dev

Mean High CTD Risk Mean Low CTD Risk 

P= Pliers; BPT= Battery powered tier; BPT+E= BPT + extension 

Wrist acceleration mean and standard deviations measured in three planes 

(flexion/extension, ulnar/radial & pronation/supination) during rebar tying and 

mean high and low CTD risk acceleration rates.7 

494 d/s2 301

824 d/s2

 494 d/s2

1824 d/s2 1222 d/s2

Figure 9 

Measured Wrist Acceleration during Rebar Tying
Page 20 Health Hazard Evaluation Report No. 2003-0146-2976 

Figure 10 

Calculation of one-year cumulative load on L5/S112:

Assumptions: Rodman works 180 days per year tying rebar with pliers an average 4 hours per 

day and carries materials, i.e., rebar, weighing 20 kg an average 1 hour per day. Extreme 

forward bending involved in tying rebar at – (a), -105° (b) and -115° (c) 90°. (Table 16) Force on 

lumbar spine from carrying 20 kg load in front or beside the body equals 2700 N (Seidler et al, 

2001). 

DAYS √ 8h * ∑i Fi * ti Days = working days/year; ti =average daily duration of activity 

(h) 

(a) 

 1 yr = 180 √8h * (17212 N2 * 4h) + (27002 N2 * 1) = 1.8 x 106 Nh 

 5 yr = = 9.1 x 106 Nh 

10 yr = = 18.2 x 106

 Nh 

(b) 

 1 yr = 180 √8h * (20932 N2 * 4h) + (27002 N2 * 1h) = 2.2 x 106 Nh 

 5 yr = = 10.9 x 106 Nh 

10 yr = = 21.8 x 106 Nh 

(c) 

 1 yr = 180 √8h * (26422 N2 * 4h) + (27002 N2 * 1h) = 2.7 x 106 Nh 

 5 yr = = 13.7 x 106 Nh 

10 yr = = 27.3 x 106 Nh 
Health Hazard Evaluation Report No.: 2003-0146-2976 Page 21 

Figure 11 

Estimateda

 Cumulative L5/S1 Spinal Disc Loading During Rebar Tying and Carryingb

and Risk of Developing Spinal Disease with Chronic Complaints12 

a

 See equation in Figure 10.12

b

 See Table 19 for estimated spinal loading during tying and carrying. c Risk of developing lumbar spondylosis with chronic complaints with or without disc herniation 

≥ Odds Ratio (OR) = 2.6 (95% CI 1.2-5.7). 

d Risk of developing lumbar spondylosis with chronic complaints with or without disc herniation 

≥ Odds Ratio (OR) = 6.0 (95% CI 2.7-13.4). 
Page 22 Health Hazard Evaluation Report No. 2003-0146-2976 

Table 1 

Anthropometrics of Subjects 

 Age Ht. (in.) Wt. (lb.) BMI1 

 42 71 185 25.8 

 33 66 160 25.8 

 44 71 210 29.3 

 40 70 210 29.3 

 37 67 160 25.1 

 29 68 190 28.9 

 30 70 185 26.5 

 43 65 170 28.3 

Mean (SD) 37 (6) 69 (2.2) 184 (18.5) 27.4 

(1.6) 

 1 Body mass index (BMI) calculated using CDC BMI calculator. Accessed on 10- 

 29-04. http://www.cdc.gov/nccdphp/dnpa/bmi/calc-bmi.htm. 

Table 2

Ironworker Work History (months) 

 Mean SD Min Max 

Time tying rebar 124 96.4 29 298 

Time with current employer 38 37.7 18 136 

Time on current job site 16 12.6 0 32 
Health Hazard Evaluation Report No.: 2003-0146-2976 Page 23 

Table 3 

Comparison of Mean Wrist Velocity Postures by Rebar Tying Method 

(Chi Square Difference of Least Squares Means) 

Plane Pliers vs. BPT1 Pliers vs. BPT+E2 BPT vs BPT+E

Flexion/Extension <0.0001 <0.0001 NS

Ulnar/Radial NS <0.05 NS

Supination/Pronation <0.0001 0.0001 NS

1

 BPT = MAX RB 392 power tier 

2

 BPT+E = MAX RB 392 power tier plus adjustable extension 

3

 NS = Not significant. 
Page 24 Health Hazard Evaluation Report No. 2003-0146-2976 

Table 4 

Comparison of Mean Wrist Acceleration by Rebar Tying Method 

(Chi Square Difference of Least Squares Means) 

Plane Pliers vs. BPT1 Pliers vs. BPT+E2 BPT vs 

BPT+E

Flexion/Extension <0.001 0.001 NS

Ulnar/Radial <0.05 0.0009 NS

Supination/Pronation <0.0001 <0.0001 NS

 1 BPT = MAX RB 392 power tier 

 2 BPT+E = MAX RB 392 power tier plus adjustable extension 

 3 NS = Not significant. 
Health Hazard Evaluation Report No.: 2003-0146-2976 Page 25 

Table 5 

Participants (n=5) Self Reported Ratings of Perceived Effort1 during Rebar Tying 

Perceived Effort Pliers Power Tier Power Tier + Extension 

Hand-Wrist 5.2 2.8 5.0 

Low Back 5.8 2.8 1.2 

1

 Borg 10 Point Perceived effort scale.2

Table 6 

 ACGIH Hand-Activity Level (HAL)6

 Scoresa for Mean Hand-Wrist Effort 

Tying Rebar Using Pliers, BPT & BPT+E 

Effortb Pliers BPT BPT+E

Mean 2.5c 0.5d 0.8 c

Low 1.0 c 0.3 d 0.3 d

High 3.5 c 1.0 c 1.2 c

a

 Scores <0.56 are acceptable; scores ≥0.56 and ≤0.77 are at the action level; and scores ≥0.78 

exceed the TLV. 

b

 Participants’ (n=5) response (mean, low & high) on Borg 10 point perceived effort 

questionnaire. 

c

. ≥ TLV. 

d

 < TLV. 
Page 26 Health Hazard Evaluation Report No. 2003-0146-2976 

Table 7 

Time (seconds)a in Trunk Postures during Rebar Tying 

Treatment Posture Mean (sec) % Time SD Min Max 

BPT+E Neutral 124b 83 35 55 150 

 16 - 30 24c 16 36 0 95 

 31 - 45 1 <1 3 0 8 

 46 - 60 <1 <1 <1 0 1 

 61 - 75 <1 <1 <1 0 <1 

 76 - 90 0 0 0 0 0 

 > 90 0 0 0 0 0 

BPT Neutral <1 <1 1 0 2 

 16 - 30 <1 <1 <1 0 <1 

 31 - 45 <1 <1 <1 0 <1 

 46 - 60 <1 <1 <1 0 <1 

 61 - 75 <1 <1 <1 0 1 

 76 - 90 5c 3 7 0 18 

 > 90 140b 93 13 110 150 

Pliers Neutral 0 0 0 0 0 

 16 - 30 0 0 0 0 0 

 31 - 45 0 0 0 0 0 

 46 - 60 <1 <1 <1 <1 1 

 61 - 75 <1 <1 1 0 2 

 76 - 90 6c 4 7 1 23 

 > 90 141b 93 9 126 150 a

 Total sample time = 150 seconds 

b

 p < 0.0001 (Comparing differences between BPT + BPT+E and pliers + BPT+E) c

 p < 0.05 (Comparing differences between BPT + BPT+E and pliers + BPT+E) 

Table 8 

Percent Time Free Arm Used to Supported Trunk during Extreme Flexion 

Using Power Rebar Tier per Participant 

a Ironworkers used the free hand or forearm to support an unknown proportion of their 

head/trunk weight. 

 P1 P2 P3 P4 P5 P6 P7 P8 

Supporteda 94.9% 91.0% 92.3% 89.5% 86.4% 98.3% 96.6% 90.0% 

Unsupported 5.1% 9.0% 7.7% 10.5% 13.6% 1.7% 3.4% 10.0% 
Health Hazard Evaluation Report No.: 2003-0146-2976 Page 27 

Table 9 

Estimated Forces on the L5/S1 Disc Using the 3D SSPP4 

Trunk Angle

Total 

Compression 

Total 

Shear 

Flexion

Rotation

Lateral

-90o

0o

0o

2427 N 389 N 

Flexion

Rotation

Lateral 

-90o

0o

+/-

25o

2857 N 306 N 

Flexion

Rotation

Lateral

-105o

0o

0o

1864 N 419 N 

Flexion

Rotation

Lateral

-105o

0o

+/-

25o

2322 N 480 N 

Flexion

Rotation

Lateral

-115o

0o

0o

1511 N 401 N 

Flexion

Rotation

Lateral

-115o

0o

+/-

25o

1930 N 501 N 
Page 28 Health Hazard Evaluation Report No. 2003-0146-2976 

Table 10 

Estimateda Cumulative Physical Workload (N-hb) on the Low Back (L5/S1) 

Due to Extreme Forward Flexion after 1, 5, and 10 Years

 

Flexion Newtons Hrs/Day Days/Wk Wk/Yr N-h/1 Yr N-h/5 Yr N-h/10 Yr

90 deg 2642 2 5 36 0.9E+06 4.8E+06 9.5E+06

 4 5 36 1.9E+06 9.5E+06 19.0E+06

 6 5 36 2.9E+06 14.0E+06 29.0E+06

105 deg 2093 2 5 36 0.7E+06 3.8E+06 7.5E+06

 4 5 36 1.5E+06 7.5E+06 15.0E+06

 6 5 36 2.3E+06 11.0E+06 23.0E+06

115 deg 1721 2 5 36 0.6E+06 3.1E+06 6.2E+06

 4 5 36 1.2E+06 6.2E+06 12.0E+06

 6 5 36 1.9E+06 9.3E+06 19.0E+06

a

 Equation used to calculate annual load on L5/S1 shown in Figure 6.12

b

 N-h = Newton-hours. 
Health Hazard Evaluation Report No. 2003-0146-2976 Page29 

Table 11 

Number of Ties Completed in 2.5 Minutes by Treatment 

Subject Pliers BPT BPT+E

1 47 85 55

2 31 71 41

3 44 89 54

4 48 99 58

5 36a 69 53

6 51 93 66

7 37 79b 38

Mean 42 84 52

SD 6.8 10.3 9.0

a

 Adjusted for 2’15” sample period. 

b

 Adjusted for 2’23” sample period. 
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