Richard W. Marklin

Case study report. Business case for implementing battery-powered tools for direct-bury line workers at an electric power utility.

C utting cable and crimping compression connectors are the two most commonly performed tasks by direct-bury line workers who repair and bury underground cable for electric power utilities. Battery-powered tools, rather than manual (Figure 1), do the demanding work of cutting cable and crimping connectors while the worker holds the tool in place.(1) The focus of this case study is whether the cost of batterypowered tools for direct-bury line workers can be justified based on injury and illness data and other factors.

Wrist and Forearm Posture From Typing on Split and Vertically Inclined Computer Keyboards

A study was conducted on 90 experienced office workers to determine how commercially available alternative computer keyboards affected wrist and forearm posture. The alternative keyboards tested had the QWERTY layout of keys and were of three designs: split fixed angle, split adjustable angle, and vertically inclined (tilted or tented). When set up correctly, commercially available split keyboards reduced mean ulnar deviation of the right and left wrists from 12° to within 5° of a neutral position compared with a conventional keyboard. The finding that split keyboards place the wrist closer to a neutral posture in the radial/ulnar plane substantially reduces one occupational risk factor of workrelated musculoskeletal disorders (WMSDs): ulnar deviation of the wrist. Applications of this research include commercially available computer keyboard designs that typists can use and ergonomists can recommend to their clients in order to minimize wrist ulnar deviation from typing.

Wrist and forearm postures of users of conventional computer keyboards

The aim of this study was to perform a comprehensive investigation to document wrist and forearm postures of users of conventional computer keyboards. We instrumented 90 healthy, experienced clerical workers with electromechanical goniometers to measure wrist and forearm position and range of motion for both upper extremities while typing. For an alphabetic typing task, the left wrist showed significantly greater (p < .01) mean ulnar deviation (15.0° ± 7.7°) and extension (21.2° ± 8.8°) than the right wrist (10.1° ± 7.2° and 17.0° ± 7.4° for ulnar deviation and extension, respectively). Conversely, the right forearm had greater mean pronation (65.6° ± 8.3°) than the left forearm (62.2° ± 10.6°). We noted minimal functional differences in the postures of the wrists and forearms between alphabetic and alphanumeric typing tasks. Ergonomists should consider the statistically significant and probable practical difference in wrist and forearm posture between the left and right hand in ergonomic interventions in the office and in the design of computer keyboards. Actual or potential applications of this research include guiding the design of new computer keyboards.

Quantitative biomechanical analysis of wrist motion in bone-trimming jobs in the meat packing industry

This study was motivated by the serious impact that cumulative trauma disorders (CTDs) of the upper extremities have on the meat packing industry. To date, no quantitative data have been gathered on the kinematics of hand and wrist motion required in bone-trimming jobs in the red-meat packing industry and how these motions are related to the risk of CTDs. The wrist motion of bone-trimming workers from a medium-sized plant was measured, and the kinematic data were compared to manufacturing industrys preliminary wrist motion benchmarks from industrial workers who performed hand-intensive, repetitive work in jobs that were of low and high risk of hand/wrist CTDs. Results of this comparison show that numerous wrist motion variables in both the left and right hands of bone-trimming workers are in the high-risk category. This quantitative analysis provides biomechanical support for the high incidence of CTDs in the meat packing industry. The research reported in this paper established a preliminary database of wrist and hand kinematics required in bone-trimming jobs in the red-meat packing industry. This kinematic database could augment the industrys efforts to reduce the severity and cost of CTDs. Ergonomics practitioners in the industry could use the kinematic methods employed in this research to assess the CTD risk of jobs that require repetitious, hand-intensive work.

Effect of keyswitch design of desktop and notebook keyboards related to key stiffness and typing force

This study aimed to compare and analyse rubber-dome desktop, spring-column desktop and notebook keyboards in terms of key stiffness and fingertip typing force. The spring-column keyboard resulted in the highest mean peak contact force (0.86N), followed by the rubber dome desktop (0.68N) and the notebook (0.59N). All these differences were statistically significant. Likewise, the spring-column keyboard registered the highest fingertip typing force and the notebook keyboard the lowest. A comparison of forces showed the notebook (rubber dome) keyboard had the highest fingertip-to-peak contact force ratio (overstrike force), and the spring-column generated the least excess force (as a ratio of peak contact force). The results of this study could aid in optimizing computer key design that could possibly reduce subject discomfort and fatigue.

Measurement of Stiffness and Damping Characteristics of Computer Keyboard Keys

To determine the stiffness and damping of computer keyboard keys, a computer-controlled test rig that can measure computer key displacement, velocity, and contact force has been designed. The test rig, consisting of a single-axis stage carrying a probe for contacting keys, has been used to collect contact force and motion data as computer keys are depressed and released at constant velocities up to 80mm∕s. Keys that employ a rubber-dome under their caps to achieve the necessary compliance and toggling action were tested. The results demonstrate a nonlinear stiffness force versus displacement characteristic at a given speed and the presence of damping-type forces that increase with key depression speed at a given displacement. In particular, the results indicate that the peak force at the 80mm∕s rate of depression increases relative to the quasistatic (0.5mm∕s) force level by over 12% for the “Enter,” “K,” and “Spacebar” keys. This paper describes the hardware and software configuration, and presents sample results of the stiffness and damping characteristics of keys during depression-return stroke tests.

Are posture data from simulated tasks representative of field conditions? Case study for overhead electric utility workers

Many ergonomics studies are conducted in laboratory-simulated work environments to assess risks for the development of musculoskeletal disorders under more controlled conditions. However, the simulated conditions could be of questionable validity with respect to reproduction of field conditions involving risk factors. The objective of this study was to verify whether the postures recorded for neck extension/flexion and upper arm elevation of overhead electric utility workers in a simulated environment were similar to those recorded in a field environment. Of the three frequently performed tasks analysed, two presented similar exposure in both conditions. However, differences were identified for a more complex task (relay replacement). These results suggest that simulated tasks may be more representative for more standardised tasks. This may indicate that researchers investigating risks should avoid simplifying complex tasks when reproducing field posture exposure in laboratories, since omitting extra subtasks may lead to an inaccurate reproduction of field exposure. Practitioner Summary: Studies comparing results from field and simulated environments are necessary to evaluate to what degree postural exposure reproduced in laboratory is representative of the exposure occurring in real work situations. This is particularly relevant for tasks involving training in simulated environment due to safety constraints.

Biomechanical Effects of Mobile Computer Location in a Vehicle Cab

Objective: The objective of this research is to determine the best location to place a conventional mobile computer supported by a commercially available mount in a light truck cab. Background: U.S. and Canadian electric utility companies are in the process of integrating mobile computers into their fleet vehicle cabs. There are no publications on the effect of mobile computer location in a vehicle cab on biomechanical loading, performance, and subjective assessment. Method: The authors tested four locations of mobile computers in a light truck cab in a laboratory study to determine how location affected muscle activity of the lower back and shoulders; joint angles of the shoulders, elbows, and wrist; user performance; and subjective assessment. A total of 22 participants were tested in this study. Results: Placing the mobile computer closer to the steering wheel reduced low back and shoulder muscle activity. Joint angles of the shoulders, elbows, and wrists were also closer to neutral angle. Biomechanical modeling revealed substantially less spinal compression and trunk muscle force. In general, there were no practical differences in performance between the locations. Subjective assessment indicated that users preferred the mobile computer to be as close as possible to the steering wheel. Conclusion: Locating the mobile computer close to the steering wheel reduces risk of injuries, such as low back pain and shoulder tendonitis. Application: Results from the study can guide electric utility companies in the installation of mobile computers into vehicle cabs. Results may also be generalized to other industries that use trucklike vehicles, such as construction.

Comparison of Anthropometry of U.S. Electric Utility Field-Workers With North American General Populations

Objective: The primary purpose of this study was to determine whether conventional anthropometric databases of the U.S. general population are applicable to the population of U.S. electric utility field-workers. Background: On the basis of anecdotal observations, field-workers for electric power utilities were thought to be generally taller and larger than the general population. However, there were no anthropometric data available on this population, and it was not known whether the conventional anthropometric databases could be used to design for this population. Method: For this study, 3 standing and 11 sitting anthropometric measurements were taken from 187 male field-workers from three electric power utilities located in the upper Midwest of the United States and Southern California. The mean and percentile anthropometric data from field-workers were compared with seven well-known conventional anthropometric databases for North American males (United States, Canada, and Mexico). Results: In general, the male field-workers were taller and heavier than the people in the reference databases for U.S. males.The field-workers were up to 2.3 cm taller and 10 kg to 18 kg heavier than the averages of the reference databases. Conclusion: This study was justified, as it showed that the conventional anthropometric databases of the general population underestimated the size of electric utility field-workers, particularly with respect to weight. Application: When designing vehicles and tools for electric utility field-workers, designers and ergonomists should consider the population being designed for and the data from this study to maximize safety, minimize risk of injuries, and optimize performance.

Effects of Computer Keyboard Setup Parameters and User's Anthropometric Characteristics on Wrist Deviation and Typing Efficiency

Two questions that computer keyboard operators face when using keyboards that can be separated into halves (split keyboards) are at what angle should the keyboard halves be opened and at what distance should the keyboard halves be placed apart. The objective of this study was to investigate the effects of the opening angle and separation distance between halves of a split keyboard on wrist radial/ulnar deviation and typing efficiency. Eleven experienced typists participated in this study and typed on a split keyboard configured in the following four arrangements. 1. The keyboard halves were setup the same way as a conventional keyboard. 2. The keyboard halves were contiguous but angled, based on the users anthropometry, to maintain a theoretical neutral posture of the users wrists in the radial/ulnar plane. 3. The keyboard halves were separated at a fixed distance of 20 cm, and the halves were angled to maintain a theoretical neutral posture of the users wrists in the radial/ulnar plane. 4. The keyboard halves were separated at a distance equal to the users shoulder width, and the halves were parallel to each other, resulting in a theoretical neutral posture of the users wrists in the radial/ulnar plane. The findings from testing these four keyboard configurations are the following: 1. The mean ulnar deviations from the alternative configurations of the split keyboard (configurations 2, 3, and 4 above) ranged from 7.0 to 8.4 for the left wrist and 2.7 to 5 deg. for the right wrist. There were no significant differences in ulnar deviations among the three alternative configurations. 2. The three alternative configurations resulted in ulnar deviation of both wrists that were significantly less than ulnar deviation from typing on the conventional setup (configuration 1 above). The mean ulnar deviations from the conventional setup were 18.9 deg. for the left wrist and 14.2 deg. for the right wrist. 3. There were no significant differences in typing speed and accuracy between the alternative and conventional configurations.