S. Chervak, U.S. Army CHPPM, Aberdeen Proving Ground, MD
A large organization conducted a study to evaluate the effectiveness of various types of ergonomic training with respect to increased ergonomic knowledge and reduced reports of physiological disorders. The study consisted of 840 subjects at 48 different locations. Participation in the study was voluntary. The subjects were divided into six groups based on the type of ergonomic training to be received: (1) no training (the control group), (2) training via self-instructional reading material, (3) video training, (4) one-on-one training, (5) train-the-trainer training, and (6) group training. Subjects completed a questionnaire before the training, two weeks after training, and five months after the training. The questionnaire contained inquired about the subject’s general office ergonomic knowledge, body part discomfort and workstation arrangement.
Regardless of the training the subjects received, their knowledge of ergonomics increased immediately after the training and remained significant at the follow-up 5 months later. Initially, subjects who received the one-on-one training had a dramatic increase in their knowledge of ergonomics when compared to the other groups. After the trainer left, however, there was no follow-up, and the employees’ knowledge soon decreased. Those who had the opportunity to reinforce their training (i.e., self-instructional reading material) retained their knowledge at the 5-month follow-up interval.
Those employees who received the more personal or involved training (one-on-one and train-the-trainer) had the opportunity to make changes to their workstations, thus showing a significant increase in the number of ergonomic alterations made when compared to the other groups. Also, the train-the-trainer group was the most successful in terms of reducing the degree of body part discomfort.
J. Blas, H. Gomez, University of California, Los Angeles, CA; W. Liu, California State University, Northridge, Northridge, CA
The paper describes the results of an assessment of the ergonomic stress experienced by workers in a Maquiladora factory manufacturing heat sinks for computer components. The assessment focused on the washing and tapping operations in the factory. The workforce consisted of 47% males and 53% females. Job tenure ranged from 2 months to 42 months. The annual turnover rates were 33% and 40% for the washing and tapping operations, respectively. Age of the workers ranged from 17 years to 57 years. Stature of the workers ranged from143 cm to 172 cm. Workers in the tapping operation were required to handle more than 14,000 pieces per day, while workers in the washing operation were required to carry and push heavy baskets. The results of the assessment indicate that the design of most of the workstation does not match anthropometric characteristics of the Maquiladora workers. This mismatch may result in a higher risk for the development of musculoskeletal disorders/discomfort. A simplified survey was also conducted at the factory. The results of the survey indicate that though workers did complain of muscular fatigue and even neck and back pain, these workers perceived fatigue and pain as a normal component of the job. This study indicates the imminent need for ergonomic training for both production engineers and workers in the Maquiladora industry.
M. Lu, A. Bhattacharya, P. Succop, University of Cincinnati, Cincinnati, OH
Fall-related fatal and non-fatal injuries remain a major safety problem in the workplace. Improper visual cues, fatigue and task performance have been known as major risk factors for falls on a level surface. The effects of the aforementioned risk factors on workers’ safety while working on inclined surfaces are not clear. This study investigated the effects of visual cues, muscular fatigue of the lower limbs and reach task on workers’ postural stability on three different inclinations—0º, 14º and 26º. Nineteen subjects from roofing-related industries participated in the study. Postural stability was measured in terms of sway length and area by a force platform. Additionally, a questionnaire was administered to acquire workers’ subjective perceived sense of sway and postural instability (PSPSI) for each test condition. The test conditions included 3 inclinations ´ 2 visual cues settings (with or without) ´ 3 levels of fatigue (full, half and no) ´ 2 tasks (forward reach and stationary). Results from a repeated measure analysis of covariance showed that inclination, reach task and their interaction were found to have significant effects (p<0.001) on sway length and area, whereas visual cues were significant on sway length (p<0.001). Both workers’ PSPSI and sway were significantly affected by inclination (p<0.001). A correlation analysis showed that the workers’ PSPSI was not found to be significantly related to both sway variables. Visual cues and reach task significantly decreased and increased the workers postural instability, respectively. These effects, however, were not perceived by the workers. On the contrary, fatigue caused the workers’ PSPSI to increase significantly, which however, was not found to be a significant factor affecting their postural stability. These mismatches between the workers’ subjective PSPSI and objective sway variables imply that training for proper perception of postural control while working on inclined surfaces is needed for fall prevention.
J. Pentikis, M. Lopez, U.S. Army CHPPM, Aberdeen Proving Ground, MD
There has been significant emphasis placed on injury prevention in the military and the Federal government in recent years. The Federal Worker 2000 Presidential Initiative requires a reduction in the overall occurrence of injuries, a reduction in the occurrence of injuries at the highest rate work sites and a reduction in the rate of lost production days for all Federal agencies and departments.
Accurate and timely ergonomic assessments leading to redesigns of the workplace, tools and equipment are essential to facilitate a soldiers’ return to full duty status following an injury. However, the shortage of trained ergonomists to conduct assessments have resulted in poorly focused return to duty efforts, frequent re-injuries, eventual increases in hospitalizations and disabilities.
Data on 125 physically demanding, high injury risk tasks were collected by on-site ergonomist and evaluated by them. Data from these same tasks were also collected on-site by technicians and evaluated by off-site ergonomists. The results of the assessments conducted by on site ergonomists and off site ergonomists showed good agreement with the Borg scale, fair agreement was seen with the DOD Level 1 Guides and fair agreement was seen with the NIOSH Lifting Equation. Both the Ovaco Working Posture Analysis System and the Rapid Upper Limb Assessment tool were dependent on the quality of the videotape and showed poor agreement between the on- and off-site ergonomists.
The results indicate which assessment tools lend themselves for off-site analysis and what changes in procedure are needed so that on-site technicians can more accurately collect data.
P. Sung, University of California at Los Angeles, Los Angeles, CA; V. Liu, California State University, Northridge, Northridge, CA
Repeated and sustained forceful exertions have been associated with the development of musculoskeletal disorders in hands, wrists and fingers. In industry utilizing gloveboxes, workers may wear up to three layers of gloves while performing tasks, resulting in aggravated stress. This study investigated the glove/tool contact force differences due to gloves and task positions.
A factorial experiment in a randomized block design was employed. Four glove conditions (barehanded, one glove, two gloves, and three gloves) and three task positions (near-7”, center-16”, and far-25” inside a glovebox) are the independent variables and each subject is a block. Four hand tools (a ball-pin hammer, a roller, a crescent wrench, and a pair of tweezers) were used for tasks simulation at constant task demand. The contact force, as a dependent variable, at the glove/tool interface was measured using a thin-film force sensor.
Data were analyzed using analysis of variance. Task position was found statistically significant at the tip of thumb during hammer (F=3.86, p<0.05) and wrench (F=3.5, p<0.05) simulations. The contact force was highest at the far position followed by near and center positions suggesting moving tasks to the center. Glove was statistically significant factor at the following glove/tool contact areas: tip of thumb when using hammer (F=2.75, p<0.05) and roller (F=10.1, p<0.01); 1st phalange of the index finger when using hammer (F=2.76, p<0.05) and wrench (F=3.19, p<0.05); 2nd phalange of index finger when using roller (F=3.81, p<0.05); and 3rd phalange of the middle finger when using hammer (F=2.74, p<0.05). The lowest contact forces were found when wearing triple gloves. The stress in the high contact force areas could be minimized by increasing the thickness of gloves around those areas without increasing the overall thickness of the whole glove.
W. Keyserling, S. Sudarsan, B. Martin, A. Haig, The University of Michigan, Ann Arbor, MI
Non-neutral trunk postures can cause fatigue and discomfort in the lower back. These effects may be amplified in persons suffering from chronic low back pain due to aggravation of pre-existing conditions. A laboratory study was conducted to determine the effects of personal factors (age, gender and back disability status) and task factors (flexion angle and work-rest cycle) on endurance time and perceived discomfort during continuous and intermittent trunk flexion. Eighty subjects (40 males, 40 females) participated. Half of the subjects suffered chronic low back pain with an associated work restriction; the remaining subjects had healthy backs (controls). The trunk was flexed to 15°, 30°, 45°, and 60° under three conditions: 1) continuous static flexion (no rest), 2) cyclical static flexion with 20 percent rest, and 3) cyclical static flexion with 40 percent rest. Each condition was performed for up to 600 seconds or until the subject reached his/her pain tolerance limit. The total endurance time (TET) for each condition was recorded. At 30-second intervals, perceived discomfort was measured with a visual analog scale.
For continuous exertions, the chronic-pain subjects had lower TET (p < .001) and greater perceived discomfort (p < .001) when compared to controls. In both groups, TET decreased and perceived discomfort increased as the trunk flexion angle increased.
Chronic-pain subjects also reported greater perceived discomfort during the intermittent tasks (p < .001); and the difference between chronic-pain subjects and healthy controls increased over time for all conditions tested (p < .001). Increasing the rest component decreased discomfort in both groups.
This study demonstrated that persons with chronic back pain have decreased tolerance for jobs with high trunk flexion demands. To better accommodate these workers, consideration should be given to reducing both the magnitude (angle) and duration of trunk flexion required by their jobs.
Posted June 14, 2002