Information on this page is drawn from "A Checklist for Evaluating Cab Design of Construction Equipment" Reported by N. Kumar Kittusamy and published by the NIOSH
General
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.
Studies
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 Hagberg7 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
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. This was done by assigning equal weights to each of the answers, and a percentage of affirmative answers were determined. The closer the calculation was 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
Checklist for Construction Equipment Design
Results
All seven equipment types listed in Table III 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 fof the equipment (57%), vibrations were felt at the seats and the controls
- The seat did not swivel in more than half of the equipment.
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
The checklist is a general assessment tool. The checklist was 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 13 14
References
1 Chaffin, D.B.: Localized Muscle Fatigue---Definition and Measurement. J Occup Med 15(4):346-354 (1973).
2 Punnett, L.; Fine, L.J.; Keyserling, W.M.; et al.: Back Disorders and Nonneutral Trunk Postures of Automobile Assembly Workers. Scand J Work Environ
Health 17(5):337-346 (1991).
3 Magora, A.: Investigation of the Relation Between Low Back Pain and Occupation: Part I. Indus Med Surg 39(11):465-471 (1970).
4 Chaffin, D.B.; Andersson, G.B.J.: Occupational Biomechanics. John Wiley and Sons, New York, NY (1991).
5 Kelsey, J.L.; Hardy, R.J.: Driving of Motor Vehicles as a Risk Factor for Acute Herniated Lumbar Intervertebral Disc. Am J Epidemiol 102(1):63-73 (1975).
6 Hagberg, M.: Local Shoulder Muscular Strain — Symptoms and Disorders. J Hum Ergol 11(1):99-108 (1982).
7 Hagberg, M.: Occupational Musculoskeletal Stress and Disorders of the Neck and Shoulder: A Review of Possible Pathophysiology. Int Arch Occup Environ Health 53(3):269-278 (1984).
8 National Institute for Occupational Safety and Health: Musculoskeletal Disorders (MSDs) and Workplace Factors — A Review of Epidemiologic Evidence for Work-Related Musculoskeletal Disorders of the Neck, Upper Extremity, and Low Back. DHHS (NIOSH) Pub. No. 97-141. NIOSH,Washington, DC (1997).
9 Lifshitz, Y.; Armstrong, T.J.: A Design Checklist for Control and Prediction of Cumulative Trauma Disorders in Intensive Manual Jobs. In: Proceedings of the Human Factors Society 30th Annual Meeting. Human Factors and Ergonomics Society, Dayton, OH (1986).
10 Zimmermann, C.L.; Cook, T.M.; Rosecrance, J.C.: Operating Engineers: Work-Related Musculoskeletal Disorders and the Trade. Appl Occup Environ Hyg 12(10):670-680 (1997).
11 Easterby, R.S.: Ergonomics Checklist: An Appraisal. Ergonomics 10(5):549- 556 (1967).
12 Kittusamy, N.K.; Okogbaa, O.G.; Babu, A.J.G.: A Preliminary Audit for Ergonomics Design in Manufacturing Environments. Indus Eng (July, 1992).
13 Kittusamy, N.K.; O'Reilly, J.T.: Ergonomics Program. In: Accident Prevention Manual for Business & Industry: Administration & Programs (Occupational Safety and Health Series), 12th ed., chap. 16. P. Hagan; J.F. Montgomery; J.T. O'Reilly, eds., National Safety Council, Chicago, IL (2001).
14 Keyserling, W.M.; Brouwer, M.; Silverstein, B.A.: A Checklist for Evaluating Ergonomic Risk Factors Resulting from Awkward Postures of the Legs, Trunk and Neck. Int J Indus Ergon 9:283-301 (1992).
