Kumar Kittusamy ScD, MSPH
Applied Occupational and Environmental Hygiene
Awkward postures
during the operation of heavy construction equipment are a consequence
of improper cab design and work procedures. Poor visibility of the
task, limited room in the cab, excessive forces required to operate
levers/pedals, and improper seat designs are some of the characteristics
of a poorly designed cab. If not controlled, awkward posture of any
body part can result in increased risk of fatigue, pain, or injury.
Exposure to awkward postures, either repetitively or for prolonged
periods, can lead to a variety of musculoskeletal disorders.
Laboratory studies have shown that non-neutral trunk postures (i.e.,
flexion, lateral bending, and/or twisting) caused increased levels
of muscle fatigue and intervertebral disc pressure in the lower back.(1)
Epidemiological studies have shown that flexion, lateral bending,
and twisting of the trunk are factors in the development of low back
pain.(2,3) Spinal disc compression can increase substantially when
the trunk changes from a neutral to a flexed posture.(4) Furthermore,
prolonged sitting can also result in an increased risk of low back
pain.(5)
Laboratory studies of non-neutral shoulder postures have shown that
prolonged elevation of the arms (abduction or flexion of the shoulder)
causes extreme levels of muscle fatigue and discomfort.(1,6) Hagberg(7)
demonstrated a positive relationship between shoulder elevation and
increased risk of tendonitis in a cross-sectional field study. A relationship
between non-neutral neck posture and the development of disorders
has also been well documented.(8)
The objective
of this article is to introduce a one-page checklist for evaluating
cab design of construction equipment. The cab design evaluation
checklist was developed, pilot-tested, and used to measure several
characteristics of cab design (see Table I). The checklist was based
on a literature review and was then discussed with the operators
of construction equipment. The draft checklist was then pilot-tested
with input solicited from and incorporated by trainers, operating
engineers, and apprentices. A case study is presented in which overall
cab design scores were calculated for each type of equipment.
TABLE I
A checklist for evaluating cab design of construction equipment
|
|
Yes |
No |
N/A |
Comments |
1 |
Is
the seat height adjustable? |
|
|
|
1 |
2 |
Can
the seat be adjusted horizontally? |
|
|
|
2 |
3 |
Is
the seat set at proper height? |
|
|
|
3 |
4 |
Does
the seat have a back support? |
|
|
|
4 |
5 |
Does
the seat have a lumbar support? |
|
|
|
5 |
6 |
Are
there armrests available? |
|
|
|
6 |
7 |
Are
the armrests adjustable? |
|
|
|
7 |
8 |
Are
the armrests set at proper height? |
|
|
|
8 |
9 |
Do
you feel any vibration from the equipment through the seat? |
|
|
|
9 |
10 |
Do
you feel any vibration from the equipment through the floor? |
|
|
|
10 |
11 |
Do
you feel any vibration from the equipment through the controls? |
|
|
|
11 |
12 |
Is
the seat firmly mounted to the floor of the cab? |
|
|
|
12 |
13 |
Can
the seat be tilted backward? |
|
|
|
13 |
14 |
Can
the seat swivel? |
|
|
|
14 |
15 |
Is
the location of the controls or levers adjustable? |
|
|
|
15 |
16 |
Can
you easily reach the levers or controls? |
|
|
|
16 |
17 |
Can
you easily operate the levers or controls? |
|
|
|
17 |
18 |
Can
you easily reach the pedals? |
|
|
|
18 |
19 |
Can
you easily operate the pedals? |
|
|
|
19 |
20 |
Is
the cab area large enough (e.g., uncramped area) for you? |
|
|
|
20 |
21 |
Do
you have sufficient upward visibility? |
|
|
|
21 |
22 |
Is
your view of the operation obstructed (e.g., cab guards, pipes/hoses,
etc.)? |
|
|
|
22 |
23 |
Do
you feel the cab is noisy? |
|
|
|
23 |
24 |
Can
you control the temperature of the cab? |
|
|
|
24 |
25 |
Does
the equipment have steps? |
|
|
|
25 |
26 |
Does
the equipment have handrails? |
|
|
|
26 |
27 |
Can
you easily open/close the cab doors? |
|
|
|
27 |
28 |
Does
the equipment have proper means for entering the cab? |
|
|
|
28 |
29 |
Does
the equipment have proper means for exiting the cab? |
|
|
|
29 |
30 |
Do
you have a good general view of the ground? |
|
|
|
30 |
31 |
Are the cab windows free from distracting reflections? |
|
|
|
31 |
Case Study
The checklist was designed to be a systematic evaluation tool that
could be used to assess the characteristics of a cab. A majority
of the questions in the checklist were structured so that satisfactory
ergonomic conditions resulted in affirmative answers to the questions.
There were three questions that had to be worded in an inverse relationship
to avoid ambiguity. If supplying a categorical answer was difficult,
the answer was qualified by an overall assessment of the characteristics
of concern.
After the evaluation of the cab design, an overall assessment score
for the cab was calculated. Thiswas done by assigning equal weights
to each of the answers, and a percentage of affirmative answers
were determined. The closer the calculationwas to 100 percent, the
better the design or the acceptability of the cab. Some features
of the cab may be more important than others, but the simple approach
of equal weights was considered here as used by Lifshitz and Armstrong.(9)
Equipment and Operators Studied
The study was performed at several different construction sites
in the Greater Boston, Massachusetts area. Seven journey-level (experienced)
operators (6 males and 1 female) employed by two major contractors
were studied (see Table II). The operators' ages ranged from 33
to 58 years (43.4�.7); experience ranged from 11 to 40 years (23�.1);
height ranged from 165 cm to 183 cm (172.4�1); and weight ranged
from 52 kg to 129 kg (84.2�.4). Each operator used a different
piece of construction equipment. Operators were briefed about the
study, and they each signed a consent form to participate in this
research.
TABLE II
Background data of operators and equipment evaluated in this study
Characteristics
of the operator
|
Equipment
Information
|
OperatorA |
Height(cm) |
Weight
(kg) |
Age |
Years
of
Exp |
Make |
Model |
Size |
Type |
1 |
165 |
52 |
33 |
11 |
Caterpillar |
CAT
416B |
Small |
Loader/Backhoe |
2 |
178 |
129 |
49 |
30 |
Caterpillar |
CAT
446B |
Small |
Loader/Backhoe |
3 |
183 |
86 |
38 |
17 |
John
Deere |
JD
710D |
Small |
Loader/Backhoe |
4 |
165 |
70 |
58 |
36 |
Caterpillar |
CAT
M318 |
Medium |
Excavator |
5 |
178 |
100 |
56 |
40 |
Caterpillar |
CAT
M318 |
Medium |
Excavator |
6 |
168 |
86 |
35 |
15 |
Daewoo |
DH
200W |
Large |
Excavator |
7 |
170 |
66 |
35 |
12 |
Komatsu |
PC
400LC |
Large |
Excavator |
Mean |
172.4 |
84.2 |
43.4 |
23.0 |
|
|
|
|
SD |
7.1 |
25.4 |
10.7 |
12.1 |
|
|
|
|
Var |
50.4 |
644.6 |
113.6 |
145.3 |
|
|
|
|
AOE
#1 is a female; all others are male operators.
Results
All seven equipment types listed in Table II were evaluated. The
overall total cab score was calculated using all 31 questions in
the cab design evaluation checklist. The results of the overall
cab design score are summarized in Table III. The overall total
cab design scores for the seven equipment types ranged from 71 to
87 percent, with a 6.5-percent standard deviation. The following
concerns were found:
- Seats did
not have lumbar support in all of the equipment (100%).
- In a majority
of the equipment (86%), the vibration could be felt from the equipment
through the floor.
- In a majority
of the equipment (86%), the temperature of the cab could not be
controlled.
- In a majority
of the equipment (71%), the locations of the controls and levers
were not adjustable.
- More than
half of the equipment (57%) did not have adjustable armrests.
- In more
than half of the equipment (57%), vibrations were felt at the
seats and at the controls.
- The seat
did not swivel in more than half of the equipment (57%).
TABLE III
Evaluation of cab characteristics using the cab design checklist
Operator |
Make |
Model |
Type |
Overall
total cab scroreA |
1 |
Caterpillar |
CAT
416B |
Loader/Backhoe |
74 |
2 |
Caterpillar |
CAT
446B |
Loader/Backhoe |
74 |
3 |
John
Deere |
JD
710D |
Loader/Backhoe |
71 |
4 |
Caterpillar |
CAT
M318 |
Excavator |
87 |
5 |
Caterpillar |
CAT
M318 |
Excavator |
81 |
6 |
Daewoo |
DH
200W |
Excavator |
81 |
7 |
Komatsu |
PC
400LC |
Excavator |
71 |
AOverall
total cab score computed using all questions in the checklist.
Discussion and Conclusion
Postural requirements of work should be considered in the design of
work procedures and equipment in construction. The relationship between
awkward posture and the development of fatigue and musculoskeletal
disorders has been reported in laboratory and epidemiological studies.
Despite the fact that operating heavy equipment has been found to
result in a high prevalence of musculoskeletal symptoms and injuries,(10)
there is a lack of quantitative data describing postural stresses
among operators of construction equipment. This could be due to the
time and complexity in collecting and analyzing postural data. The
current study introduced a checklist for evaluating cab design and
presented a case study using the checklist.
The checklist is a general assessment tool. The checklistwas useful
in identifying characteristics that needed improvement. One limitation
of a checklist is that it is, at best, an analytical tool.(11) It
can assist in the process of identifying potential problems within
a system, but for quantifying the problems, a comprehensive and systematic
methodology is required for evaluating the work system. The checklist
provides a static, instantaneous snapshot of characteristics during
a specific time. Nevertheless, this and other checklists provide the
critical point of departure in initiating the ergonomic analysis.(9,12-14)
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EDITORIAL NOTE: N. Kumar Kittusamy is a research engineer at NIOSH's
Spokane,Washington, Research Lab.He conducts research related to safety
and health issues in mining and construction industries. He holds
a B.S. in Industrial Engineering and an M.S. in Public Health with
concentration in Ergonomics and Industrial Hygiene from the University
of South Florida, and a Doctor of Science (Sc.D.) with a major in
Ergonomics and minors in Industrial Hygiene and Epidemiology/Biostatistics
from the College of Engineering at the University of Massachusetts
Lowell. His current research interests include whole-body vibration,
musculoskeletal epidemiology, and workstation design.
For more information, Dr. Kittusamy can be contacted at NIOSH, Spokane
Research Lab, 315 East Montgomery Avenue, Spokane, WA 99207; telephone:
(509) 354-8127; fax: (509) 354-8099; e-mail: nfk8@cdc.gov.
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