Christopher S. Pan

The impact of keyboard design on comfort and productivity in a text-entry task

Concerns have arisen that the keyboard is a causal factor in the development of work-related musculoskeletal disorders (WRMDs) among video display terminal (VDT) operators. A number of alternative keyboard designs have been developed with altered geometry in an effort to improve comfort in keyboard operation. However, few data are available to substantiate whether these new keyboard designs are actually effective in reducing discomfort and musculoskeletal problems in users. The purpose of this study was to provide data on the efficacy of certain alternative keyboard design features (e.g. splitting the keyboard in half, and laterally inclining the keyboard halves) in reducing fatigue and musculoskeletal discomfort among keyboard operators. The study also explored the effects of these design features on performance. Fifty subjects performed a text-entry task for one day on a standard keyboard, then were assigned to one of five keyboard conditions for an evaluation period of two days (i.e. 10 subjects/condition). Outcome measures included performance (i.e. keystrokes/h, errors/h) and self-report measures of discomfort and fatigue. The results indicated an initial decline in productivity when subjects began typing on two of the alternative keyboards, but these productivity losses were recovered within the two-day evaluation period. The results also indicated no significant differences between keyboard conditions in discomfort and fatigue. These results suggest a minimal impact of the keyboard design features examined in this study on productivity, comfort and fatigue, at least after two days of exposure.

Assessment of perceived traumatic injury hazards during drywall hanging

Abstract Workers who handle massive and bulky drywall sheets are at a high risk of traumatic injuries. The objective of this study is to identify the drywall handling tasks and activities which are directly perceived as hazardous by workers. A questionnaire survey was conducted for the study. In the questionnaire, three hanging tasks were included: (1) hanging drywall on the ceiling; (2) hanging drywall on the upper half of the wall; and (3) hanging drywall on the lower half of the wall. Each of the three tasks was divided into 10 to 12 constituent activities. Supportive elevated equipment was also evaluated. Workers were instructed to rate the drywall-hanging tasks/activities and elevated equipment in regard to fall potential, perceived physical stress, and risk of being struck by or against objects, using a seven-point scale (1=hardly at all to 7=a great deal). Results from this study indicate that all the ratings of fall potential, perceived physical stress, and risk of being struck by or against objects while hanging drywall on the ceiling were greater than while performing the other two tasks. Activities involving lifting/carrying/holding drywall sheets were rated as most physically stressful. Workers perceived greatest physical stress and fall potential when wearing stilts as compared to using ladders or scaffolds. The findings of this study provide detailed information directly from the workers about the hazards associated with drywall hanging. Results from this study will assist in focusing future research efforts on the most hazardous tasks and activities of drywall hanging. Relevance to industry Construction workers who perform drywall installation have high occupational incident rate for traumatic injury. Handling massive and bulky drywall sheets increases the potential for physical stress, falls and struck by and against objects. A questionnaire was designed to collect injury information directly from construction workers who performed drywall hanging and to identify perceived hazards associated with drywall hanging. Prior to this study, there has been little substantive research to evaluate the excessive stresses imposed on this workforce.

Traumatic Injury among drywall installers, 1992 to 1995

This study examined the traumatic-injury characteristics associated with one of the high-risk occupations in the construction industry—drywall installers—through an analysis of the traumatic-injury data obtained from the Bureau of Labor Statistics. An additional objective was to demonstrate a feasible and economic approach to identify risk factors associated with a specific occupation by using an existing database. An analysis of nonfatal traumatic injuries with days away from work among wage-and-salary drywall installers was performed for 1992 through 1995 using the Occupational Injury and Illness Survey conducted by the Bureau of Labor Statistics. Results from this study indicate that drywall installers are at a high risk of overexertion and falls to a lower level. More than 40% of the injured drywall installers suffered sprains, strains, and/or tears. The most frequently injured body part was the trunk. More than one-third of the trunk injuries occurred while handling solid building materials, mainly drywall. In addition, the database analysis used in this study is valid in identifying overall risk factors for specific occupations.

Analysis of musculoskeletal loadings in lower limbs during stilts walking in occupational activity.

Construction workers often use stilts to raise them to a higher level above ground to perform many tasks, such as taping and sanding on the ceiling or upper half of a wall. Some epidemiological studies indicated that the use of stilts may place workers at increased risk for knee injuries or may increase the likelihood of trips and falls. In the present study, we developed an inverse dynamic model of stilts walking to investigate the effects of this activity on the joint moments and musculoskeletal loadings in the lower limbs. The stilts-walk model was developed using the commercial musculoskeletal simulation software AnyBody (version 3.0, Anybody Technology, Aalborg, Denmark). Simulations were performed using data collected from tests of four subjects. All subjects walked without or with stilts through a 12-m straight path. The moments of the knee, hip, and ankle joints, as well as forces in major muscles or muscle groups in the lower limbs, for stilts walking were compared with those for normal walking. Our simulations showed that the use of stilts may potentially increase the peak joint moment in knee extension by approximately 20%; induce 15% reduction and slight reduction in the peak joint moments in ankle plantar flexion and hip extension, respectively. The model predictions on the muscle forces indicated that the use of stilts may potentially increase loadings in five of eight major muscle groups in the lower extremities. The most remarkable was the force in rectus femoris muscle, which was found to potentially increase by up to 1.79 times for the stilts walking compared to that for the normal walking. The proposed model would be useful for the engineers in their efforts to improve the stilts design to reduce musculoskeletal loadings and fall risk.

Mood disturbances and musculoskeletal discomfort: effects of electronic performance monitoring under different levels of VDT data-entry performance

The effects of electronic performance monitoring (EPM) work management on mood disturbances and musculoskeletal discomfort were evaluated under three levels of data‐entry task performance. EPM work management (i.e., performance monitoring and feedback) was used to induce compliance with data‐entry performance standards of greater than or equal to 200 keystrokes per minute and less than or equal to six errors per minute. Forty‐seven female office workers who had difficulty maintaining the data‐entry speed standard were assigned at random to EPM work management or no EPM work management. Participants in both work management conditions were divided into three keystroke performance groups (low, moderate, high). Self‐ratings of mood disturbance and musculoskeletal discomfort were recorded at periodic intervals over three consecutive workdays. Regardless of the level of data‐entry performance, the increase in perceived time pressure across the workdays was greater under EPM work management than under no EPM wor...

Assessment of perceived traumatic injury hazards during drywall taping and sanding

The objective of this study was to identify the drywall finishing tasks which are directly perceived as hazardous by workers. A questionnaire survey was conducted to evaluate workers’ perceived injury hazards (physical stress, fall potential, and struck by/against an object) for six finishing tasks (4 taping and 2 sanding tasks) and three items of elevated support equipment. Thirty experienced drywall finishers participated in this study. The ratings of perceived physical stress and fall potential varied significantly among the six tasks (both p values <0.05). Subjects perceived greater physical stress for the two drywall sanding tasks than the four taping tasks. Sanding skimmed drywall without the use of pole sanders, in particular sanding ceiling joints, nails, and corners was rated most stressful. Wrists/hands and shoulders were identified as the most affected body part subject to physical stress during drywall taping and sanding. Tasks performed with the use of stilts were rated as having greater fall potential than those without using stilts. The activity of putting on stilts and getting up on them was most likely to cause loss of balance. Results from this study provide information directly from experienced workers to help identify hazardous tasks and activities associated with drywall finishing. The findings will assist in focusing future research efforts on the most hazardous tasks and activities of drywall finishing. Construction workers who perform drywall installation, including taping and sanding drywall sheets, have the highest incidence/injury rate compared to any other workforce. Taping and sanding drywall sheets increases the potential for physical stress, falls and struck by and against objects. A questionnaire was designed to collect injury information directly from painters who performed drywall taping/sanding and to identify perceived hazards associated with drywall taping and sanding. Prior to this study, there has been little substantive research to ergonomically evaluate the excessive stresses and potential injuries imposed on this workforce.

Kinematics and kinetics of gait on stilts: Identification of risk factors associated with construction stilt use

This study investigated kinematics and kinetic strategies and identified risk factors associated with gait on stilts. A six-camera motion-analysis system and two force platforms were used to test 20 construction workers for straight walking or turning, with or without carrying tools while wearing safety shoes or stilts at different heights. The results indicated that gait on stilts is characterised by increases in stride length, step width and the percentage of double support period, decreases in cadence, minimum foot clearance and a weaker heel-strike and push-off. Stilts place greater joint loadings on lower extremities to compensate for the added weight and limitation in joint mobility. Smaller foot clearances found for gait on stilts constitute an increased risk for tripping over obstacles. Workers may need to avoid prolonged use of stilts to alleviate stresses on the joints. This study was conducted to determine to what extent stilts alter the gait strategies and to explain the compensatory movements. Prior to this study, there has been little substantive research to evaluate the stresses and potential injuries associated with stilts.

Estimation of the kinetic energy dissipation in fall-arrest system and manikin during fall impact

Fall-arrest systems (FASs) have been widely applied to provide a safe stop during fall incidents for occupational activities. The mechanical interaction and kinetic energy exchange between the human body and the fall-arrest system during fall impact is one of the most important factors in FAS ergonomic design. In the current study, we developed a systematic approach to evaluate the energy dissipated in the energy absorbing lanyard (EAL) and in the harness/manikin during fall impact. The kinematics of the manikin and EAL during the impact were derived using the arrest-force time histories that were measured experimentally. We applied the proposed method to analyse the experimental data of drop tests at heights of 1.83 and 3.35 m. Our preliminary results indicate that approximately 84–92% of the kinetic energy is dissipated in the EAL system and the remainder is dissipated in the harness/manikin during fall impact. The proposed approach would be useful for the ergonomic design and performance evaluation of an FAS. Statement of Relevance: Mechanical interaction, especially kinetic energy exchange, between the human body and the fall-arrest system during fall impact is one of the most important factors in the ergonomic design of a fall-arrest system. In the current study, we propose an approach to quantify the kinetic energy dissipated in the energy absorbing lanyard and in the harness/body system during fall impact.

EVALUATION OF A COMPUTER-SIMULATION MODEL FOR HUMAN AMBULATION ON STILTS

Stilts are elevated tools that are frequently used by construction workers to raise workers 18 to 40 inches above the ground without the burden of erecting scaffolding or a ladder. Some previous studies indicated that construction workers perceive an increased risk of injury when working on stilts. However, no in-depth biomechanical analyses have been conducted to examine the fall risks associated with the use of stilts. The objective of this study is to evaluate a computer-simulation stilts model. Three construction workers were recruited for walking tasks on 24-inch stilts. The model was evaluated using whole body center of mass and ground reaction forces. A PEAK™ motion system and two Kistler™ force platforms were used to collect data on both kinetic and kinematic measures. Inverse- and direct-dynamics simulations were performed using a model developed using commercial software — ADAMS and LifeMOD. For three coordinates (X, Y, Z) of the center of mass, the results of univariate analyses indicated very small variability for the mean difference between the model predictions and the experimental measurements. The results of correlation analyses indicated similar trends for the three coordinates. Plotting the resultant and vertical ground reaction force for both right and left feet showed small discrepancies, but the overall shape was identical. The percentage differences between the model and the actual measurement for three coordinates of the center of mass, as well as resultant and vertical ground reaction force, were within 20%. This newly-developed stilt walking model may be used to assist in improving the design of stilts.

Assessment of Fall-Arrest Systems for Scissor Lift Operators Computer Modeling and Manikin Drop Testing

Objective: The current study is intended to evaluate the stability of a scissor lift and the performance of various fall-arrest harnesses/lanyards during drop/fall-arrest conditions and to quantify the dynamic loading to the head/neck caused by fall-arrest forces. Background: No data exist that establish the efficacy of fall-arrest systems for use on scissor lifts or the injury potential from the fall incidents using a fall-arrest system. Method: The authors developed a multibody dynamic model of the scissor lift and a human lift operator model using ADAMS™ and LifeMOD™ Bio-mechanics Human Modeler. They evaluated lift stability for four fall-arrest system products and quantified biomechanical impacts on operators during drop/fall arrest, using manikin drop tests. Test conditions were constrained to flat surfaces to isolate the effect of manikin-lanyard interaction. Results: The fully extended scissor lift maintained structural and dynamic stability for all manikin drop test conditions. The maximum arrest forces from the harnesses/lanyards were all within the limits of ANSI Z359.1. The dynamic loading in the lower neck during the fall impact reached a level that is typically observed in automobile crash tests, indicating a potential injury risk for vulnerable participants. Conclusion: Fall-arrest systems may function as an effective mechanism for fall injury protection for operators of scissor lifts. However, operators may be subjected to significant biomechanical loadings on the lower neck during fall impact. Application: Results suggest that scissor lifts retain stability under test conditions approximating human falls from predefined distances but injury could occur to vulnerable body structures.