Applied Occupational and Environmental Hygiene

Volume 16(7): 723–726, 2001

1047-322X/01 $12.00 + .00

Ergonomics

Scott P. Schneider, Column Editor

723

An Ergonomic Evaluation of Excavating Operations: 

A Pilot Study 

Reported by N. Kumar Kittusamy and Bryan 

Buchholz 

Previous studies indicate that operators of heavy construction equipment 

are aff icted by musculoskeletal injuries 

of the arms, shoulders, neck, and lower 

back. These injuries appear to be due 

to excessive periods of sitting (static 

posture), work intensity, whole-body vibration, high resistance levers, repetitive 

motions, and awkward postures.(2 5) Although numerous studies have shown an 

association between operation of heavy 

construction equipment and symptoms 

of musculoskeletal disorders, very little 

research has been performed that systematically characterizes operating engineers’ exposure to ergonomic hazards. 

The objective of this study was to systematically characterize the ergonomic 

hazards associated with excavating operations. As such, the following were 

performed: (1) vibrations were measured 

at the operator/seat interface (X, Y, and 

Z axes), and at the f oor of the cab 

(Z axis); (2) psychophysical ratings of 

whole-body vibration (WBV) level and 

overall seat design were obtained; and 

(3) postural assessments of the job were 

made. 

Methodology 

This study evaluated an inexperienced female operator performing excavation, utilizing two different pieces of 

equipment. The operator was 37 years 

old, 162 cm tall, and weighed 80 kg. 

She had approximately 15 hours of operation time (experience) on the equipment evaluated. The two pieces of equipment used were: a Case Super 580E 

(1986) backhoe/loader, and an Insley 

H-2000 excavator (1975) (see Figures 1 

and 2). More evaluations were performed on the backhoe/loader than on 

the excavator. The following evaluations 

were performed on the Case equipment: 

1) vibration levels at the seat and f oor; 

2) psychophysical ratings of the overall 

seat design and vibration levels (for the 

task duration, and for an 8 hour duration); 

and 3) postural assessments. For the Insley equipment, all of the evaluations 

were performed except vibration measurements. When the evaluations were 

conducted, the following environmental 

conditions were noted: the temperature 

was 31 F, and soil and terrain conditions 

were rough and frozen. 

Whole-Body Vibration 

Whole-body vibration was analyzed 

at the seat/operator interface using a triaxial piezoresistive seat pad accelerometer (Model VT-3), and at the f oor 

level using a single-axis piezoresistive 

accelerometer (Model 7265A-HS), both 

from Endevco Corporation (Canton, 

MA), as well as a f eld computer system (Model 2100 FCS) from Somat Corporation, to f lter and store the data in 

the f eld. The vibration measurements 

were performed in accordance with the 

ISO 2631 standard.(6) Calibration procedures and mounting of the test equipment 

were done according to the manufacturers’ guidelines. 

The f eld computer system (FCS) was 

connected to a rechargeable lead-acid 

battery and the tri-axial (Channels 2– 4) 

and single axis (Channel 1) accelerometers. A laptop was used to calibrate the 

accelerometers, to start and stop the data 

collection process, and f nally to download the data from the FCS after evaluating each of the activities. Figure 3 shows 

the location of the accelerometers, and a 

general schematic of the instrumentation 

used for data collection. 

The vibration data were f ltered using a Butterworth f lter with a 100 Hz 

break frequency. The data were sampled 

at a rate of 500 Hz. A Hanning window was applied to the time domain 

data. A windowing function is necessary to reduce the leakage in calculating 

the frequency content of a signal. The 

crest factors (CFs) were calculated, and 

then compared with the limit established 

by the American Conference of Governmental Industrial Hygienists (ACGIH R ) 

standards.(1) Crest factor is def ned as the 

ratio of peak to RMS acceleration, measured in the same direction for X, Y, and 

Z axes. 

A Fast Fourier Transform (FFT) and 

one-third octave band analysis were performed using the Matlab software. FFT 

analysis converted the time-domain data 

into frequency domain data. The data 

were broken down into one-third octave bands, which provide greater detail 

than one-octave frequency bands, especially at the lower frequencies. Also onethird octave band analysis of the spectra 

is needed to use the WBV limits established by ISO/threshold limit value 

(TLV R ) limit.(1) The total vector sum 

acceleration for the X, Y, and Z axes 

was calculated using the appropriate axis 

weighting factors from ACGIH.(1) The 

total weighted vector sum was then compared with the 8-hour action level of 

0.5 m/s2. 

Psychophysical Rating 

Psychophysical rating was used to 

estimate physical strain as perceived by 

the operator. The ratings(discrete scales) 

were recorded for the overall seat design, 
724 N. K. KITTUSAMY AND B. BUCHHOLZ

FIGURE 1 

A Case Super 580E Backhoe/Loader. 

FIGURE 2

An Insley H-2000 Excavator. 
ERGONOMIC EVALUATION OF EXCAVATING OPERATIONS 725

and the equipment’s vibration level for 

each task. The operator was asked for a 

rating after completion of each activity. 

Responses were recorded for the following questions: 

1. The vibration level of the equipment is: (1 low to 5 high). 

2. The seat design of the equipment 

is: (1 good to 5 bad). 

The ratings were compared with the 

quantitative measurement of vibration at 

the seat, and the transmissibility of vibration due to the design characteristics 

of the seat. 

FIGURE 3 

A schematic of the instrumentation used for WBN data collection. 

Postural Assessment 

Postural assessments were performed 

by videotaping the jobs (digging a 

trench), and then evaluating it using the 

real-time postural assessment system.(7) 

The trunk, right shoulders, and neck were 

analyzed. For the postural analysis, the 

operator was observed for 42.3 and 62.4 

seconds while operating the Case and 

Insley equipment, respectively. 

Results and Discussion 

A Hanning window was applied to 

the time domain data, and then a Fast 

Fourier Transform was performed using 

Matlab software. For the tasks performed 

by the Case (backhoe/loader) equipment, 

the overall weighted (vector sum) total 

RMS accelerations, crest factors, psychophysical ratings, and sample times 

(for vibration measurements) are provided in Table I. 

The digging and riding with load tasks 

resulted in higher levels of vibration as 

compared to idling. If these were the 

WBV levels for an 8-hour day, all tasks 

except idling would exceed the limit of 

0.5 m/s2 recommended by the European 

Commission. In general, the seat was 

amplifying the vibration levels, particularly at lower frequencies. The ratings 

show that both the digging and riding 

with a load resulted in a higher rating of 

perceived vibration from the subject. The 

operator rated the overall seat design for 

the Case equipment as a 3. In general, 

high crest factors were present in both 

digging and riding with a load. This 

indicates that the operator was exposed 

to random jolts and jerks in performing 

the different activities. When CFs are 

greater than 6, ISO 2631(6) methodology 

may underestimate the true effects of 

WBV, and the results should be used with 

caution. 

The postural analysis of the operator performing the trench digging operation was performed on both pieces 

of equipment (Case and Insley). For the 

Case equipment, the trunk was in neutral 

and twisted 75 percent and 25 percent 

of the observed time (42.3 seconds), respectively. The neck was in neutral and 

twisted 45 percent and 55 percent of the 
726 N. K. KITTUSAMY AND B. BUCHHOLZ

observed time, respectively. The right 

shoulder was in elevation (45 to 90 ) 

for a majority of the time period (98%). 

For the Insley equipment, the trunk was 

in neutral, f exion (more than 20 ), and 

twisted or bent (more than 20 ) 18 percent, 65 percent, and 17 percent, respectively, for the observed time (62.4 seconds). The neck was in neutral, twisted, 

and severe forward f exion (> 45 ) 78 

percent, 21 percent, and 1 percent of 

the time, respectively. The right shoulder was in elevation the majority of the 

observed time period (77%). The view 

of the videotape made the analysis challenging for the other body parts. For the 

Insley, the operator rated the overall seat 

design as a 3, the vibration level for the 

task duration as a 3, and for an 8 hour 

operation of digging the trench the rating was a 5. 

TABLE I 

Summary of results for the case equipment 

Riding with 

Idling Digging load 

Weighted total RMS 0.053 2.66 6.07 

accelerations (m/sec2) 

Crest factors (range for all axes) 2.2 to 17.7 13.5 to 26.6 6.2 to 8.8 

Sampling times (minutes) 2.05 6.08 0.82 

Psychophysical ratings of 2 3 to 5 3 to 5 

vibrationA 

ANote: The psychophysical ratings are for the sampling time and for an 8-hour job. 

Conclusions 

This f eld study was conducted to 

evaluate the ergonomic hazards associated with the use of construction 

equipment to perform excavating operations. One female operator performed 

excavations using two different pieces of 

construction equipment. Whole-body vibration measurements, psychophysical 

ratings of the overall seat design and vibration, and postural assessments were 

performed. The job was broken down 

into tasks to characterize the vibration 

levels of each task. The study was carried 

out in accordance with the measurement 

and evaluation techniques outlined in 

the ISO 2631 standard.(6) The machines 

studied were relatively old, resulting in 

higher WBV exposures (due to no vibration attenuation), and awkward postures (due to poor cab design). The 

results revealed that the digging operation and traveling with a load (in the 

loader-bucket) had higher levels of total 

weighted acceleration than idling. The 

seats in the equipment demonstrated that 

they are not suff cient to protect the operator from long-term effects of vibration exposure. The psychophysical ratings were consistent with the vibration 

levels. Also, the postural evaluation revealed that the operator assumed awkward postures of the trunk, neck, and 

shoulders while performing the excavations. 

Recommendations 

The construction equipment sampled 

in this study were older pieces of equipment. Newer equipment is expected to be 

ergonomically designed, yielding better 

attenuation of vibration and visibility of 

the job. Some controls for whole-body 

vibration and awkward postures are as 

follows: 

Whole-Body Vibration 

1. Design and select seats based 

on the transmissibility characteristics, and not solely on the immediate comfort of the operator. 

2. Design and select seats that will 

adequately damp vibration at all 

frequencies, but importantly, in the 

lower frequencies (1 to 8 Hz). 

3. Properly maintain the equipment 

to reduce wear and tear that could 

result in increased vibration. 

4. Limit the speed of the equipment 

when driven, especially over bumpy or irregular surfaces. 

5. Workers should avoid jumping 

off their equipment when exiting, 

since this introduces a shock to the 

body that has just been vibrated for 

several hours. 

Awkward Posture 

1. Redesign cabs to accommodate 

better upward and/or downward 

visibility. 

2. Have co-worker or foreman guide 

the operator (hand signals) when 

visibly challenging jobs are performed (i.e., jobs below ground). 

3. Install mirrors to provide better 

visibility (sideways, and below 

ground). 

REFERENCES 

1. American Conference of Governmental 

Industrial Hygienists: Threshold Limit 

Values and Biological Exposure Indices, 

pp. 126–133, ACGIH, Cincinnati, OH 

(2000). 

2. Bongers, P.M.; Boshuizen, H.C.; Hulshof, 

C.T.J.; et al.: Back Disorders in Crane 

Operators Exposed to Whole-Body Vibration. Int Arch Occup Environ Health 

60:129–137 (1988). 

3. Buchholz, B.; Moir, S.; Virji, M.A.: An 

Ergonomic Assessment of an Operating 

Engineer: A Pilot Study of Excavator 

Use. Appl Occup Environ Hyg 12:23–27 

(1997). 

4. Burdorf, A.; Zondervan, H.: An Epidemiological Study of Low-Back Pain 

in Crane Operators. Ergonomics 33:981– 

987 (1990). 

5. Hansson,	 J.E.: Ergonomic Design of 

Large Forestry Machines. Intl J Ind Ergon 

5:255–266 (1990). 

6. International Standards	 Organization: 

Evaluation of Human Exposure to 

Whole-Body Vibration, ISO 2631/1. ISO, 

Geneva (1985). 

7. Keyserling, W.M.: Postural Analysis of 

the Trunk and Shoulders in Simula 

ted Real Time. Ergonomics 29:569–583 

(1986).