International Journal of Industrial Ergonomics

Published by Elsevier
Print ISSN: 0169-8141
Publications
Health information technology (IT) is widely endorsed as a way to improve key health care outcomes, particularly patient safety. Applying a human factors approach, this paper models more explicitly how health IT might improve or worsen outcomes. The human factors model specifies that health IT transforms the work system, which transforms the process of care, which in turn transforms the outcome of care. This study reports on transformations of the medication administration process that resulted from the implementation of one type of IT: bar coded medication administration (BCMA). Registered nurses at two large pediatric hospitals in the US participated in a survey administered before and after one of the hospitals implemented BCMA. Nurses' perceptions of the administration process changed at the hospital that implemented BCMA, whereas perceptions of nurses at the control hospital did not. BCMA appeared to improve the safety of the processes of matching medications to the medication administration record and checking patient identification. The accuracy, usefulness, and consistency of checking patient identification improved as well. In contrast, nurses' perceptions of the usefulness, time efficiency, and ease of the documentation process decreased post-BCMA. Discussion of survey findings is supplemented by observations and interviews at the hospital that implemented BCMA. By considering the way that IT transforms the work system and the work process a practitioner can better predict the kind of outcomes that the IT might produce. More importantly, the practitioner can achieve or prevent outcomes of interest by using design and redesign aimed at controlling work system and process transformations.
 
Although a risk of occupational musculoskeletal diseases has been identified with age-related strength degradation, strength measures from working group are somewhat sparse. This is especially true for the lower extremity strength measures in dynamic conditions (i.e., isokinetic). The objective of this study was to quantify the lower extremity muscle strength characteristics of three age groups (young, middle, and the elderly). Total of 42 subjects participated in the study: 14 subjects for each age group. A commercial dynamometer was used to evaluate isokinetic and isometric strength at ankle and knee joints. 2 × 2 (Age group (younger, middle-age, and older adult groups) × Gender (male and female)) between-subject design and Post-hoc analysis were performed to evaluate strength differences among three age groups. Post-hoc analysis indicated that, overall, middle-age workers' leg strengths (i.e. ankle and knee muscles) were significantly different from younger adults while middle-age workers' leg strengths were virtually identical to older adults' leg strengths. These results suggested that, overall, 14 middle-age workers in the present study could be at a higher risk of musculoskeletal injuries. Future studies looking at the likelihood of musculoskeletal injuries at different work places and from different working postures at various age levels should be required to validate the current findings. The future study would be a valuable asset in finding intervention strategies such that middle-age workers could stay healthier longer.
 
Feedback of information has consistently shown positive results in human inspection, provided it is given in a timely and appropriate manner. Feedback serves as the basis of most training schemes; traditionally this has been performance feedback. Other forms of feedback which provide strategy information rather than performance information may have a role in improving inspection. This study compared performance feedback and cognitive feedback in a realistic simulation of an aircraft structural inspection task. Performance (time, errors) feedback showed the greatest improvements in performance measures. Cognitive feedback enhanced efficiency measures of search strategy. When cognitive feedback consisted of visual representations of the path and the coverage of the search sequence, subjects also were able to use this task information to improve their search performance.
 
More than 90% of the critical skills that an aviation maintenance technician uses are acquired through on-the-job training (OJT). Yet many aviation maintenance technicians rely on a `degenerating buddy system', `follow Joe around', or unstructured approach to OJT. Many aspects of the aviation maintenance environment point to the need for a structured OJT program, but perhaps the most significant is the practice of job bidding which can create rapid turnover of technicians. The task analytic training system (TATS), a model for developing team-driven structured OJT was developed by the author, and first introduced in Boeing Commercial Airplane Group to provide competency-based OJT for aviation maintenance and inspection personnel. The goal of the model was not only to provide a comprehensive, highly structured training system that could be applied to any maintenance and inspection task, but also to improve team coordination, attitude and morale. The first goal was accomplished by following the systems eight-step process, the latter through incorporating human factors principles such as decision making, communication, team building and conflict resolution into the process itself. In general, the process helps to instill mutual respect and trust, enhance goal-directed behavior, strengthen technicians’ self-esteem and responsiveness to new ideas and encourage technicians to make worthwhile contributions. The theoretical background of the model is addressed by illustrating how the proven training methodologies of job task analysis and job instruction training are blended with human factors principles resulting in a unique team-driven approach to training, The paper discusses major elements of the model including needs identification, outlining targeted jobs, writing and verifying training procedures, an approval system, sequencing of training, certifying trainers, implementing, employing tracking mechanisms, evaluating, and establishing a maintenance/audit plan.
 
The objective of this investigation was to use published literature to demonstrate that specific changes in workplace biomechanical exposure levels can predict reductions in back injuries. A systematic literature review was conducted to identify epidemiologic studies which could be used to quantify relationships between several well-recognized biomechanical measures of back stress and economically relevant outcome measures. Eighteen publications, describing 15 research studies, which fulfilled search criteria were found. Quantitative associations were observed between back injuries and measures of spinal compression, lifting, lifting ratios, postures, and combinations thereof. Results were intended to provide safety practitioners with information that could be applied to their own work situations to estimate costs and benefits of ergonomic intervention strategies before they are implemented.
 
Medication label design is frequently a contributing factor to medication errors. Design regulations and recommendations have been predominantly aimed at manufacturers' product labels. Pharmacy-generated labels have received less scrutiny despite being an integral artifact throughout the medication use process. This article is an account of our efforts to improve the design of a hospital's intravenous (IV) medication labels. Our analysis revealed a set of interrelated processes and stakeholders that restrict the range of feasible label designs. The technological and system constraints likely vary among hospitals and represent significant barriers to developing and implementing specific design standards. We propose both an ideal IV label design and one that adheres to the current constraints of the hospital under study.
 
The purpose of this study was to examine nonfatal occupational injury data associated with slip and fall accidents by extracting the latest information from the database of the Bureau of Labor Statistics (BLS). Systematic information on the cost and causes of industrial slip and fall accidents are not readily available from statistical and survey data sources, as such, detailed information regarding the slip-/fall-related injuries in US industries categorized by various factors are presented in this study. Nonfatal injuries resulting in days lost from work due to fall and slip were categorized by the number and incidence rate by various characteristics such as major US industry, nature of injury, source of injury, types of fall, occupation, part of body injured, age of the injured, gender of the injured and number of lost workdays utilizing the BLS database. Additionally, cost per claim associated with industrial slip and fall accidents are reviewed using the National Safety Council database. This information may be used to focus our attention toward most relevant intervention strategies associated with workplace slip and fall accidents.
 
A laboratory study was conducted to examine gait changes between younger and older subjects as they walked across different floor surfaces. Twenty subjects participated in the experiment (five each of older and younger males and females). For half of the trials, subjects carried light loads that blocked their view of the floor surface immediately in front of them. Subjects walked on slippery (soapy water on vinyl) and stable (outdoor carpet) floor surfaces, as well as transitioning from one surface to another. Responses studied included: required coefficient of friction (RCOF), stride length (SL), and minimum toe clearance (MTC). Significant effects were found for the floor surface, load versus no load condition, and some interactions involving age (older versus younger subjects). Not all expected differences due to age were found in this experiment. The lack of significant differences between younger and older subjects could be due to the older subjects that participated in the experiment. They were volunteers at a local medical center, were in good physical shape, and were probably not typical of the population of people over 65 years of age. RELEVANCE TO INDUSTRY: Slips and falls in industry are costly safety issues in terms of human suffering as well as financial compensation. In many facilities and at home, people make transitions from one floor surface to another many times each day, while carrying loads or just walking. A better understanding of characteristics of people as they walk on slippery floor surfaces and the changes that might occur with age, will allow engineers to design better floor surfaces to reduce the incidence of slips and falls.
 
Stability of the body during manual material handling is an important issue in the prevention of falls and over-exertion injuries. This research investigated stability limits while standing and holding loads in different positions relative to the body. Theoretically, the stability region is the full base of support defined by the perimeter of the foot contact area. However, the functional stability region may be smaller. The purpose of this study was to locate functional stability limits with respect to the base of support. Fifteen male subjects leaned as far as possible in four directions in the sagittal and frontal planes. Their center of gravity location at these extremes determined the stability limit. The results showed that functional stability limits reached only about 60% of the distance to the maximum base of support limits under the conditions of this study. The sway angles reached at the stability limits averaged 9.2 degrees anteroposteriorly and 15.3 degrees laterally. External load positions which lowered the center of gravity of the body-and-load system extended those stability limits. This study provides a postural stability perspective of load-holding which may be applied in establishing safe lifting and reach limits.
 
According to the current rule-based risk management approach at the National Aeronautics and Space Administration (NASA), the effort is directed to contain all identified risks of a program. The identification of hazards and mitigation effort proceeds along with the development of the system hardware, till all the tradable resources for a program is exhausted. In this process, no conscious effort is made to evaluate risks and associated cost, and the final design is likely to have undesirable residual risks. This approach also results in allocating a significant amount of resources to gain only marginal mitigation of hazard and leave some undesirable hazards in the system due to the budget limitation. The approach in the proposed knowledge-based risk planning system makes a conscious attempt to trade risk with other resources, e.g., schedule, cost, reliability, performance, and others in a judicious and cost-effective way. A knowledge of the feasible option sets requiring high incremental cost for a marginal gain in hazard reduction helps the management to make decision for residual risk that falls within an acceptable range for an option set.
 
Realizing that the availability of a practical recognition system for Korean handwritten characters without any constraints has a long way to go, we have attempted to find a set of writing constraints which significantly improves the machine-readability. Based on our observation that the majority of the misrecognitions reported are caused by ambiguous characters, we have developed a set of writing constraints which maximally disambiguate those characters. Through experiments, we have confirmed that the recognition rate of those handwritten data could be improved significantly by applying the proposed set of constraints
 
A current United States trend in alternative work schedules is to increase the length of the workday while decreasing the number of days in the work week. Referred to as compressed work schedules (CWS), they are popular amongst shiftworkers although the longer work shifts may be associated with increased fatigue and may create additional risk of accidents and health problems in the workplace. The specific aim of the current study is to evaluate a CWS to better understand its influence on the sleep and fatigue of shiftworkers. A 10 h day/14 h night rotating CWS was introduced to a fire department to replace an 8 h, three shift rotating schedule. This study is comprised of an assessment of a 10 h day/14 h night rotating CWS and an evaluation of the impact of a change in work schedules, comparing 8 h shifts to the extended work periods. The results of the current study revealed no significant differences between the compressed and non-compressed work schedules. Subjective measures of sleepiness and mood were shown to increase over the course of the extended work shifts. Despite the increase, the CWS is deemed acceptable because it did not negatively impact on the workers who participated to a greater extent than when they worked on the non-compressed schedule.Relevance to industryApproximately twenty present of all United States workers are employed on some form of shiftwork. Previous research has demonstrated that negative outcomes may be associated with shiftwork, especially nightwork. The current study aims to evaluate a compressed work schedule, one that may minimize the deleterious impact of night and shiftwork.
 
The purpose of this study is to examine sleep structure under the hyperbaric environment to obtain fundamental data so that a desirable sleep environment for divers may be organized using the polysomnography. Using standard polysomnography, the total sleep time (TST), sleep efficiency index (SEI), number of awakenings (No A), lengthening of stage 1 sleep (LS1S), and lengthening of stage 4 sleep (LS4S) for 12 divers were measured over a period of 268 nights in three simulated conditions under a hyperbaric saturation environment of a He–O2 mixture at a depth equivalent to 16, 19, and 24 ATA. In the three diving conditions during the bottom nights and during the decompression nights (at 16, 19, and 24 ATA), the statistically significant results were shown: a reduction of TST, a decrease of SEI, an increase of No A after sleep or from rapid eye movements (REM) sleep, a LS1S deviation, and a reduction of LS4S deviation. The amount of LS4S was largest in the 16 ATA diving condition on the bottom nights and the decompression nights, and tended to decrease in order of 19 and 24 ATA diving conditions. The No A from REM sleep and interruption of REM sleep were significantly higher on the bottom nights and decompression nights than predive nights, and tended remarkably to increase in the order of 16–24 ATA on decompression nights. The sleep patterns under the three saturation diving conditions showed disorders in the bottom nights and decompression nights. However, these disorders continually worsened with increasing depth from 16 to 24 ATA. The psychological stress in the divers that gives rise to sleep disorders is caused by compression and decompression and from long periods of stay under closed conditions.
 
The National Institute for Occupational Safety and Health has expanded its research program investigating agricultural injuries. Data from the Supplementary Data System (SDS), maintained by the Bureau of Labor Statistics, U.S. Department of Labor, indicate that injuries to the back and lower extremities of agricultural workers are quite common. Injury data from SDS were examined for agricultural employees for the years 1985 through 1987 from the 21 states that consistently provided records for each year. During this 3-year period, a total of 71,098 injuries were reported to SDS for the agricultural Industry Groups included in this study. Of these, 26,450 (37.2%) were classified as sprains and strains. Analysis of the data indicate that workers in industries within the major groupings of crop production and agricultural services have an increased potential for sustaining a sprain or strain injury.
 
Functional forms of the NIOSH asymmetry multiplier and theoretical injury function (after Dempsey et al., 1995). 
Graphical summary of asymmetry values from: (a) Karwowski and Brokaw (1992), (b) Marras et al. (1993), and (c) a recent pilot study conducted by the authors. 
The lifting equation developed by the National Institute for Occupational Safety and Health in 1981 was revised in 1991. One goal of the revision was to accommodate non-sagittal lifting tasks, since sagittal lifting tasks are an exception rather than the rule in many industrial settings. This goal of expanding the equation to non-sagittal tasks was accomplished by adding an asymmetry multiplier to the lifting equation. This paper examines the rationale behind the development of the asymmetry multiplier and provides an alternative perspective by reviewing additional literature. The usability of the asymmetry multiplier in industry is discussed with particular emphasis on the applications manual for the 1991 NIOSH equation. The concept of operational definitions required to be able to use the equation as intended is presented. Data from three different sources illustrate the problems and variability associated with measuring asymmetry, as required by the NIOSH equation, in industrial settings. Finally, recommendations for further research and potential modifications to the asymmetry multiplier are presented.Relevance to industryThe discussion of measuring asymmetry in industry has particular relevance to industrial settings where the NIOSH equation is applied and asymmetry must be measured.
 
Although many product developers may have high hopes for developing a new product in their respective domains, most product development efforts focus on incremental innovations. Accordingly, most research on the product development process focuses on the development of evolutionary products. In a project seeking the means for achieving breakthrough innovations, the fundamental question is: How do we integrate the innovative ideas into the product development process? To provide an answer to the question, the concept of High Touch is presented with case studies conducted between 1994 and 1998. This study also presents a systematic model for identifying the consumer needs and for generating new product ‘ideas’ based on the identified needs. High Touch is a product development strategy initiated and promoted by the first author since the 1980s. The insight gathered from the model and case studies of High Touch showed that the process for innovative product development should allow exploration and diversion of the project team facilitated with heavily consumer-driven development process. The key success factor for all the case studies presented in this study seems to come from the systematic convergence of technological competence and the visionary role of the development team. In the front end of the successful new product development, the vision and implicit potential of the product should sometimes override the typical feasibility analysis, market assessment, and financial analysis of the product.Relevance to industryNew product development is a key factor to the successful product strategy and thus, one of the most important components of a firm's competitiveness. The method and case studies presented in this paper will be useful to any industry that designs and produces consumer products. Especially, the case studies are very well suited to the manufacturers of consumer electronic products.
 
Riders of twelve motorcycles, comprising 6 full-scale motorbikes and 6 motor-scooters, and 5 sedan vehicles, performed test runs on a 20.6 km paved road composed of 5 km, 5 km, and 10.6 km of rural, provincial and urban routes, respectively. Each test run of motorcycle was separately performed under speed limits of 55 km/h and 40 km/h. Tri-axial accelerations of whole-body vibration (WBV) were obtained by using a seat pad and a portable data logger, and the driver's view was videotaped with a portable media recorder. Root mean square (RMS) acceleration, 8-h estimated vibration dose value (VDV(8)) and 8-h estimated daily dose of static compression dose (Sed) were determined from the collected data in accordance with ISO 2631-1 and ISO 2631-5 standards. Experimental results indicate that the WBV values of the sedan vehicle drivers have low RMS, VDV(8) and Sed values (RMS 0.27–0.32 m/s2; VDV(8) 6.3–8.3 m/s1.75; Sed 0.21–0.26 MPa). However, over 90% of the motorcycle riders had VDV(8) (mean 23.5 m/s1.75) exceeding the upper boundary of health guidance caution zone (17 m/s1.75) recommended by ISO 2631-1, or had Sed (mean 1.17 MPa) exceeding the value associated with a high probability of adverse health effects (0.8 MPa) recommended by ISO 2631-5. Over 50% of the motorcycle riders reached these boundary values for VDV and Se in less than 2 h. The WBV exposure levels of the full-scale motorbikes riders and motor-scooter riders were not significantly different. However, the RMS and VDV(8) values of motorcycle riders indicate significant roadway effect (p < 0.001), while their Sed values indicate significant speed limit effect (p < 0.05). This study concludes that the WBV exposure levels of common motorcycle riders are distinctively higher than those of sedans, even on a regular paved road. The impact on health of WBV exposure in motorcycle riders should be carefully addressed with reference to ISO 2631-1 and ISO 2631-5.
 
Lateral radiographs were taken of 16 subjects in the upright position through 90° flexion, in 30° increments. The radiographic sacral angle was compared with the angle estimated from the external stick marker technique. Three observers independently and repeatedly examined the sacral angles using these two methods. Results showed that the radiographic and marker techniques yielded significantly different sacral angles, with the latter tending to underestimate the angle. These differences in the measurements of sacral angle will lead to overestimating the compression (with an average 115 N) and to underestimating the shearing force (with a range of 57–268 N) at L5/S1 disc in a biomechanical analysis. The inter-observer reliability of the stick marker measurements were poor for the four trunk positions, however the measurements did show good intra-observer reproducibility.Relevance to industryMeasurements of sacral angle are important in assessing the stresses acting on the low back in lifting. Our findings indicate that the stick marker technique does not yield accurate or reliable estimates of the sacral angle. The result implied that the use of this noninvasive method should be interpreted cautiously.
 
The semiconductor industry is moving from the production of 200 mm wafers to 300 mm wafers. With the increase in wafer size, the workload of wafer handling tasks is also increasing. This study evaluated the operator's handling capability, and the risk of having musculoskeletal disorders (MSDs) for handling 300 mm wafers. Twenty-four female operators from a semiconductor manufacturing company participated in the experiment. Subject’s psychophysical, and physiological responses were measured. Posture analysis and biomechanics analysis were also conducted to evaluate the local strain at different joints. The results suggest that loading and unloading front opening universal pod (FOUP) at 90/90 cm is best for enhancing handling capability, wrist posture, and minimizing L5/S1 compression force. About 30% of the operator's FOUP handling capabilities were lower than the safe load limit (25%ile Maximal alleptable weight of lift) recommended by SEMI (Semiconductor Equipment and Materials International). Handling wafers at 90/125 tends to increase the risk of causing shoulder and wrist injuries. Handling wafers at 90/35 tends to induce greater strength loading at hip joint, and cause greater wrist radial deviation. To minimize the risk of having MSDs, countermeasures such as training appropriate method of FOUP handling, minimizing manual carrying, specifying ergonomic machine equipment interface, and assigning male operators for high frequency FOUP handling tasks were proposed. Positive feedbacks are obtained.Relevance to industryThe results of this study provided useful information to improve the design of 300 mm wafer handling task, which enhanced the safety and health of operators in the semiconductor manufacturing workplace.
 
The objective of this study was to investigate the effects of target location on the temporal coordination of the upper body in 3D seated reaches over an extensive range of motion. Sixteen subjects reached to 64 targets distributed in the right hemisphere over four azimuths, with four heights and four radial distances from the right shoulder. The results showed that (1) all the joints did not start to move simultaneously (2) they did not stop their movements in synchrony (3) inter joint delays were significantly influenced by target location (4) tangential velocity profiles of the hand were also affected by target location. The results can be applied to develop a new seated reach prediction model that takes inter joint delays into account and simulate more natural and realistic seated reach motions. Such model can be applied to evaluate and develop products and workplaces more effectively.Relevance to industryIn order to evaluate products and workplaces more efficiently, digital human models have been an absolute need to reduce development cost and implement pro-active ergonomics. Among the many ergonomic evaluations, reach analysis has been one of the most important applications of digital human models since this activity is present in all industrial tasks requiring human operation. This study deals with seated reach behavior characteristics considering the three-dimensional range of motion.
 
The aim of this study was to get a preliminary picture of how aged female workers use typical applications of new technology in daily life. The study group consisted of 29 sixty-year-old female workers and recently retired women who had mainly worked in light physical indoor work. The subjects completed a questionnaire, dexterity of the hands and reaction time of the subjects were measured, and user-trials with a computer and remote control device were performed. Almost all subjects had used remote control device daily at home. In a user-trial 28% of the subjects had experienced difficulties in using the device, although the model of the device used was a simple one. A computer had been used by 31% of the subjects. In a user-trial with a word processor most of the subjects experienced difficulties in operating the mouse. Measured dexterity of the hands was slightly better among the subjects who performed well on the computer test. The attitudes towards new technology varied greatly, but most of the opinions were positive. The present study illustrates that a lot of work is still needed to design technological products suitable to the needs of an aged population.Relevance to industryThere are many cases where technology has been converted for use in the work environment. However, knowledge is lacking concerning how the aged worker manages and copes with the technical environment.
 
A study was conducted with an objective of evaluating cumulative probability distribution of force (CPDF) as a method for assessing exposures to mechanical workload during dynamic activities. In a supine posture, participants adopted 90° shoulder abductions, and maintained this posture against time-varying resistance until exhaustion (1 hr max.). External forces were generated by a mechanism consisting of a rotating dynamometer connected to a set of springs and light steel cables, with the other end of the mechanism connected to an elbow strap. Since the participant's arm was held at a fixed location, cyclic rotating movements of the dynamometer resulted in repetitive, isometric non-isotonic exertions. The 10th and the 90th percentiles of the external CPDF were set at 2.5% or 10% and 20% or 30% of maximum strength, respectively. The dynamometer angular velocity was set at 20° or 45°/s, to impose different rates of muscle contraction. Response variables included endurance time, rates of muscle strength reduction, and rates of perceived discomfort increase. The findings indicated that the CPDF method reflected differing exposures to mechanical workload, but failed to capture information on task repetitiveness. Additionally, the findings suggested the potential benefit of shorter work cycles and the use of subjective ratings for rapid assessments of short-term performance outcomes.Relevance to industryThe ability to quantify mechanical exposures is a prerequisite for task evaluation and determining dose–response relationships. This study evaluated the effectiveness of such an exposure assessment method.
 
The objective of the study was to determine the cognitive abilities of cut-to-length single-grip timber harvester operators and operator students. The study focused in more detail on their visuospatial abilities, which have grown in importance in previous psychological studies and are congruent with the demand description of modern harvester work. The visuospatial abilities of six professional harvester operators and 40 operator students were tested using psychological tests. The findings of the study confirmed that comprehensive perception, wide use of memory functions, non-verbal deduction, spatial perception, coordination, concentration and motivation are characteristics of a productive operator. The most productive operators did not possess any superior abilities and, therefore, the most important attribute appears to be a good mastering of different kinds of abilities. The correlation between speed tests and productivity was low, which indicates that speed is not the most essential element to increase productivity. A good harvester's steering abilities can be explained by comprehensive work planning and schemas.Relevance to industryWhen selecting new harvester operators using psychological tests, the test battery should widely evaluate the following abilities: comprehensive perception, wide use of memory functions, non-verbal deduction, spatial perception, coordination, concentration and motivation. This study also provides information for harvester operator teachers to design exercises to practice harvester operating skills.
 
This study investigated the dynamic characteristics and human perception of higher-frequency multi-axis vibration associated with a military propeller aircraft environment. Triaxial accelerations were measured at the interfaces between the occupant and aircraft seat surface (seat pan and seat back) to evaluate and compare the effects of the aircraft seat fitted with different cushions. While all cushions showed a significant reduction in the X-axis seat pan vibration as compared to the original operational seat cushion at the blade passage frequency (BPF∼73.5 Hz), the associated accelerations remained significantly higher than the floor input accelerations. Transmissibility data confirmed these seat system characteristics at higher frequencies. A body region perception survey suggested that the subjects were most sensitive to the BPF component of the operational exposure. In contrast, the weighted acceleration levels (ISO 2631-1: 1997) suggested that the subjects would perceive the highest vibration in the vertical (Z) direction at the seat pan with substantial contributions in the X direction from the seat back, particularly at the propeller rotation frequency (PRF∼18.5 Hz). The overall Vibration Total Value (ISO 2631-1: 1997) suggested that the operational exposures would be perceived as being “not uncomfortable” to “a little uncomfortable.”Relevance to industryEffective multi-axis vibration mitigation strategies depend on the relationships between the location, direction, and level of vibration entering the occupant and human perception of the exposure. Current human exposure guidelines may not optimally reflect these relationships for assessing higher-frequency propeller aircraft work environments and should be applied with caution.
 
Footwear sole wear by natural use or artificial abrasion either increases or decreases slip resistance on floors with and without lubricant. The objectives of this paper were to study the effect of footwear sole abrasive wear on slip resistance on ice with respect to temperature, and to compare the slip resistance of abraded soles on melting and hard ice with that on lubricated steel plate. The kinetic coefficient of friction (COF) of nine pairs of footwear were measured with the stationary step simulator developed at the Finnish Institute of Occupational Health, before and after the new footwear soles were artificially abraded. Two-way factorial ANOVA showed that the abrasion of nine pairs of footwear had no significant effect on COF on melting ice (Mean COF with abrasion=0.056, std=0.0158, COF without abrasion=0.055, std=0.0205, P=0.805). On hard ice, however, the COF of abraded soles measured (mean COF=0.244) was significantly higher than without abrasion (mean COF=0.180, p<0.001), and than abraded soles on lubricated steel (mean=0.137, p<0.001). There is statistical significance between the three types of surfaces (p<0.001). On hard ice, regardless of abrasion, curling footwear with crepe rubber soling showed significantly higher COF (mean=0.343 after abrasion, 0.261 before abrasion) than other types (p<0.001). The results indicate that artificially abraded footwear is more slip resistant than new one for use on hard ice. The abrasion requirement could be specified if developing a new standard to measure COF on ice in the future. Of the footwear measured, the curling footwear with crepe rubber soling performed best in terms of slip resistance property. Therefore, Crepe rubber soling is highly recommended for use on hard ice. Melting ice is much more slippery, in which sole abrasion does not improve slip resistance. Thus, additional measures should be taken to reduce slip and fall risk.
 
This study investigated the correlation between reported injury and illness occurrence, estimated absolute aerobic capacity, exercise and smoking in a sample of 212 young male (average age 21.5 yr, SD=2.86) manual material handlers from the Southeastern (n=75), Midwest (n=77), and Western (n=60) areas of the United States.Analysis results indicate a significant association with exercise and absolute VO2MAX. No significance was noted with smoking and absolute VO2MAX. Significant associations were observed with smoking and injury (RR=2.5, P=0.0082) and higher total lost workdays injuries and illnesses (P=0.0070).Overall, this study demonstrated supporting evidence to existing literature, that data obtained via questionnaire is valid as demonstrated by the self-report of exercise and corresponding higher aerobic capacity, obtained via objective measurement. Additional support is verified by the association of smoking and injury. One deviation from the existing literature is that smoking did not appear to have an adverse impact on aerobic conditioning.Relevance to industryThis article conveys important information providing more insight into the non-occupational and personal risk factors, exercise and smoking. Smoking is correlated to injury case incidence rate and lost work day case incidence rate not just employee absenteeism as reported by other researchers.
 
In recent years there has been a discussion as to whether shock-type vibration from hand tools has stronger effects on the hand-arm system in comparison with non-impulsive vibration. The purpose of the investigation is to compare the influence of these two types of vibration on the absorption of mechanical energy in the human hand and on the grip and feed forces applied by the subjects.The energy absorption has been measured by use of a specially designed laboratory handle. The grip and feed forces applied by the subject to the handle were measured simultaneously. In the study two different frequency weighted acceleration levels were used.The outcome showed that the vibration exposure levels made a significant contribution to the vibration absorption as well as to the strength of the grip and feed forces. Moreover, it was found that the hand forces decrease while the absorption of energy increases during the experiment. Furthermore, the influence of shock-type exposure gave a significantly higher hand forces and absorption of energy compared with the non-impulsive exposure. It was, therefore, concluded that the vibration response characteristics of the hand and arm differ, depending upon whether the exposure is of shock or non-impulsive type.Relevance to industryThe paper discusses the dynamic response of the hand and arm during exposure to shock and non-impulsive vibration. Whenever possible, a tool that requires low grip and feed forces should be used as well as tools that not generate shock-type excitation. This can be helpful in choosing the proper tool for the job.
 
The power absorption characteristics of 27 male and female seated subjects, exposed to vertical vibration in the 0.5–40 Hz frequency range, are characterized under different sitting postures. The measurements are performed for a total of 36 different sitting postural configurations realized through variations in hands position (in lap and on steering wheel), seat heights (510, 460 and 410 mm), and seat design factors involving pan (0° and 7.5°) and backrest (0° and 12°) orientations, and different back support conditions. The measured data, expressed in terms of the vertical absorbed power density, are analyzed to study the effects of sitting posture on the biodynamic response under whole-body vertical vibration. An indirect method of computing absorbed power from the apparent mass response is formulated and validated using the directly measured absorbed power data. The measured data were analyzed to study the dependence of vibration energy absorption on various factors related to anthropometry (body mass, fat and mass index), seat geometry and sitting postures. The strong linear dependence between the absorbed power and the body mass and body mass index were revealed over the frequency range considered. The results clearly validate that the power absorption strongly depends upon the magnitude of whole-body vibration. Both the absorbed power near the primary resonance and the total power increase nearly quadratically with the exposure level. The hands in lap sitting posture yields to higher power absorption, irrespective of the back support condition. The sitting with a backrest reduces the energy dissipation at low frequencies and increases the energy absorption at frequencies above resonance, irrespective of the hands position, while the influence of seat pan inclination is negligible within the range of angles investigated.
 
Manual materials handling on a moving platform, like a ship, might be a risk factor for the development of low back pain due to the influence of accelerations on low back loading. In the current simulation study, 3-D accelerations, measured on a frigate were applied to the kinematics of symmetrical and asymmetrical lifting movements and to a pulling task that had been performed under stable conditions. The aim was to find out to what extent low back loading is increased when the task execution is not adapted to the ship accelerations.Unfavorable timing, analyzed using the 99th percentile of predicted low back moments, resulted in only a moderate (up to 15%) increase of extending and total low back moments, and in a substantial increase of the twisting moment (up to 67%) during asymmetrical lifting. Moments in the pulling task were low and were relatively unaffected by ship accelerations, but adaptation of the movement pattern to prevent falling would be needed more often than during lifting. It furthermore appeared that a substantial reduction of low back loading by favorable timing is not a realistic option. Designing tasks in such a way that they are located midship would reduce the 99th percentile of predicted low back moments. During lifting, orienting the task in such a way that the feet are pointing sideward relative to the ship reduces the predicted peak twisting moment at the low back compared to pointing the feet forward or backward.Relevance to industryAccelerations on a ship may influence safety and loading of workers during manual materials handling. This study investigates potential effects of moderate accelerations on low back loading during lifting and pulling tasks. It is shown that working midship reduces the risk of low back overloading, compared to working at the front deck.
 
Vector projection on the XY plane. 
Static test setup. Fig. 3. Dynamic test setup. 
Static test setup. Fig. 3. Dynamic test setup. 
One of the main issues in occupational studies focusing on musculoskeletal disorders of the upper extremity is how to best quantify workers' exposures to risk factors during a workday. Direct measurement is preferred because it is objective and provides precise measurements. To measure elevation angle exposure of the upper extremity, accelerometers are commonly used. The main problem with the use of accelerometers is the fact that they are sensitive to linear acceleration and can only assess two axes of rotation. In the present study the Virtual Corset, a pager-sized, battery powered, tri-axial linear accelerometer with an integrated data logger, was validated in vitro for the reconstruction of elevation angles under static conditions and angle error prediction under dynamic conditions. For static conditions, the RMS angle error was less than 1°. Under dynamic conditions the elevation angle error was influenced by the radius and angular acceleration. However, the angle error was predicted well with an RMS difference of 3°. It was concluded that the Virtual Corset can be used to accurately predict arm elevation angles under static conditions. Under dynamic conditions, an understanding of the motion being studied and the placement of the Virtual Corset relative to the joint are necessary.Relevance to industryA device is tested that could capture posture exposure of the shoulder at the workplace during a workday. Such exposure measurement can be used to test interventions and to develop preventive guidelines to reduce risk factors associated with musculoskeletal injuries of the upper extremity.
 
Pneumatic shut-off nut runners may produce large reaction forces to the operator's hand, especially at the end of the securing of threaded fasteners. These reaction forces depend on the shut-off mechanism, the joint hardness, tool torque level and to some extent the physical properties of the tool. The objective of this study was to find acceptability limits for the discomfort from pneumatic tool torque reaction forces that could be related to technical test measures of the tools.In a study at a truck assembly industry 38 workers participated. Reaction forces, tool handle displacements and subjective discomfort ratings were measured. The tools were first tested according to ISO 6544 in the laboratory and the tool torque impulse was calculated. Strong correlations between tool handle displacements (r = 0.952), reaction forces (r = 0.981, vertical force) and ratings were found. Acceptability limits for ratings, tool handle displacements and reaction forces were also determined. No subject would accept to work a whole workday at a discomfort level over 9 on a 20-point scale and all would work a whole workday at a discomfort level of 2. These limits could then be correlated to the tool torque impulse measures from the technical test, thus making it possible to predict how many of the assemblers would work within acceptance limits.
 
Several guidelines for manual material handling have been derived using psychophysical methods. Despite ease of use and interpretation, such guidelines have received limited verification and can be criticized for their dependence on subjective measures. In this study, 10 participants reported both maximum acceptable loads and subjective ratings. This was done statically, and in postures that isolated the elbow, shoulder, or lower torso joint demands. Two major conclusions were reached from examination of the relationships among maximum acceptable loads, ratings of perceived exertion, and relative joint demands (external/strength moment). First, relative joint demands appeared to be used in determining acceptable limits, but this use differed both within and between individuals. Second, linear relationships were found between relative joint demands and perceived exertion, though again inconsistencies were found among individuals.Relevance to industryToward the end of providing a stronger theoretical/objective basis for psychophysical methods, the present results, along with existing evidence, provide only mixed support. Guidelines for material handling based on psychophysical methods, while of clear value, should be interpreted with some caution until future evidence indicates the source upon which acceptable limits are obtained by experimental participants.
 
In the development of our present manual materials handling (MMH) guidelines (Ergonomics 34 (1991) 1197), the assumption was made that the effects of frequency on maximum acceptable weights (MAWs) of lifting with a large box (hand distance, 38 cm from chest) were similar to frequency effects on MAWs of lifting with a small box (hand distance, 17 cm from chest). The first purpose of the present experiment was to investigate this assumption. The second purpose was to study the effects of extended horizontal reach lifting (hand distance, 48 cm from chest) on MAWs as a confirmation of the results of a previous study on this variable. Lastly, we studied the effects of high frequency (20 lifts/min) on MAWs of lifting. Eight male industrial workers performed 15 variations of lifting using our psychophysical methodology. As expected, the results revealed that MAWs of lifting with the large box was significantly effected by frequency. Frequency factors based on the 1 lift/min task illustrated less change to higher frequencies (>1 lift/min) and more change to slower frequencies (<1 lift/min) as compared to lifting with the small box. It was concluded that our existing guidelines present a conservative estimate of lifting large boxes in the spectrum of frequencies studied. The results also verified the extreme effects of lifting with an extended horizontal reach and quantified the effects of the 20 lifts/min lifting frequency.Relevance to industry:Lifting is the most common MMH task but certain variables such as large containers and extended hand distance have been given considerably less attention in research. This study investigated these select variables of lifting in an effort to improve estimation of MAWs for ergonomic redesign.
 
The purpose of this experiment was to replicate a previous psychophysical experiment [Ciriello, V.M., McGorry, R.W., Martin, S.E., Bezverkny, I.B., 1999b. Maximum acceptable forces of dynamic pushing: comparison of two techniques. Ergonomics 42, 32–39] which investigated maximum acceptable initial and sustained forces while performing a 7.6 m pushing task at a frequency of 1 min−1 on a magnetic particle brake treadmill versus pushing on a high-inertia pushcart. Fourteen male industrial workers performed both a 40-min treadmill pushing task and a 2-h pushcart task, with a unique water loading system, in the context of a larger experiment. During pushing, the subjects were asked to select a workload they could sustain for 8 h without “straining themselves or without becoming unusually tired, weakened, overheated or out of breath.” The results revealed that similar to the previous study maximum acceptable sustained forces of pushing determined on the high inertia cart were significantly higher (21%) than the forces determined from the magnetic particle brake treadmill. These results were countered by an 18% decrease in maximum acceptable forces for the criterion magnetic particle brake treadmill task, perhaps due to secular changes in the industrial population. Based on the present findings, it is concluded that the existing pushing data [Snook, S.H., Ciriello, V.M., 1991. The design of manual tasks: revised tables of maximum acceptable weights and forces. Ergonomics 34, 1197–1213] still provides an accurate estimate of maximal acceptable forces for this pushing distance and frequency.Relevance to industryJobs are often redesigned to eliminate lifting and to include carts for transporting loads. Our database on maximum acceptable forces of pushing on a magnetic particle braked treadmill has been used as a tool to design manual handling tasks. This article links the existing database with actual cart pushing.
 
Fifteen female subjects (21–59 years) were trained to execute simulated automobile hose insertion tasks using a psychophysical approach. Tasks were performed at 3 frequencies and in 5 postures. Subjects were instructed to apply their maximum acceptable force, during 750 ms, static insertion efforts, performed repetitively for 18 h of training and 9 h of testing. Maximum acceptable peak forces and impulses were calculated from the last 20 min of testing. Average within-subject coefficients of variation for acceptable peak forces and impulses were 9.0% and 8.1%, respectively. Mean acceptable peak forces for the pull back condition were 46% greater than those in the medial push far reach condition and decreased, on average, as exertion frequency increased. An average decrease of 17% was observed, across all postures, as frequency increased from 1 to 5 insertions/min. A significant main effect for posture was also found for acceptable impulse, following a similar trend as peak force. Subjects selected acceptable forces that were an average of 63% of their maximum voluntary effort, when averaged across all postures at a frequency of 1 per minute.Relevance to industryThe current study provides maximal acceptable peak forces and impulses for females during rubber hose installations in automotive manufacturing. These data can be employed to establish tolerance limit values for females to reduce the incidence of injury associated with hose installation tasks, as well as ensuring quality.
 
The purpose of this experiment was to investigate maximum acceptable initial and sustained forces while performing a 7.6 m pushing task at a frequency of 1 min−1 on a magnetic particle brake treadmill and a high-inertia pushcart. Eleven female industrial workers performed a 40-min treadmill pushing task in the context of a larger experiment and two 2-h push cart tasks with a unique water loading system. A psychophysical methodology was employed, whereby the subjects were asked to select a workload they could sustain for 8 h without “straining themselves or without becoming usually tired, weakened, overheated or out of breath”. The results revealed that maximum acceptable initial and sustained forces of pushing determined on the high inertia cart were not significantly different than pushing forces determined on the magnetic particle brake treadmill. It was concluded that adjustments to the female pushing and pulling data bank by Snook and Ciriello (Ergonomics 34 (1991) 1197) may not be necessary if replication of this experiment yields similar results.Relevance to industryJobs are often redesigned to eliminate lifting and to include pushing. Our data bank on maximum acceptable forces of pushing on our magnetic particle braked treadmill has been used as a tool to design manual handling tasks. This article links the data bank with actual cart pushing.
 
A study on maximum acceptable weight limit (MAWL) was conducted on ten adult Indian female building construction workers (CW) and eight household workers (HW), following the psychophysical methodology. All these workers were in the age group of 28-32 years. In this study, three different body heights (i.e. knee, waist and maximum reach) in sagittal plane were considered. The lifting frequency was fixed at 1 lift min−1. The subjects were instructed to lift the load from the ground. Each set of experiments was conducted for 45 min work period using free-style lifting technique. Subjects were using a load container with no handle, which is typically used in the field. Both the working heart rates (WHR) and pause heart rates (with 4.4 s interval) were collected for the entire duration. The subjects were requested to rate their perceived exertion level after each load adjustment. The average MAWL working heart rates of CW group are 106.2(±8.3), 108.7(±9.3) and 106.8(±11.0) beats min−1 for knee, waist and maximum reach heights, where the load levels were estimated as 18.2(±0.8), 17.4(±1.4) and 16.3(±1.2) kg, respectively. For HW group, the MAWL working heart rates obtained were 101.3(±8.0), 99.6(±6.2) and 105.2(±6.1) beats min−1 for knee, waist and maximum reach heights and the corresponding load levels were 15.4(±0.5), 14.4(±0.7) and 13.9(±1.2) kg, respectively. Both the groups psychophysically rated the work in moderate to heavy category. A best-fit curve was obtained from average normalized baseline pause heart rates with work duration as Avg. . It has been observed that with extrapolation of the work duration to 8 h from 45 min experimental observation, the heart rate would increase to about 6-8 beats min−1 for both the groups of workers. This equation can be used to approximate the effect of work-duration on heart rate.
 
An experimental study was conducted to determine an appropriate adjustment period using the psychophysical approach for evaluating acceptable work limits for a task involving sloped walking/working surface. A workstation was designed and constructed to simulate a sloped residential roof. Twelve healthy males from a university population served as subjects. The subjects were provided training until the experimenter was confident in their ability to perform the simulated roof-shingling task, while comparing to the experienced roofers’ performance. Results indicated that 198 shingles/h is an acceptable roof shingling frequency for a workday. Time period had significant effect on psychophysical, postural sway, and selected physiological responses. Appropriate adjustment period using the psychophysical approach for evaluating acceptable work limits for tasks involving sloped surface was determined to be 2 h. Postural sway and physiological variables support these findings. The results from this study could aid in setting safe work limits in roofing construction for males. This study may prove to be useful for practical applications for the reduction of the risk of occupational injuries and fatalities, while improving productivity and safety in the roofing industry.Relevance to industryResults from this study could aid in setting acceptable work limits for roof shingling operations. Ergonomic intervention may decrease the risks of falls from roof thus reducing workers compensation costs and lost productivity of the worker.
 
The purpose of the current study was to use a psychophysical methodology to establish acceptable impact severity levels for this automotive trim installation. Two studies were conducted. In the first study, 17 male and 12 female subjects (6 assembly line workers and 23 students) performed 5 hand impacts/min on a device that simulated the process of seating push pins during door trim panel installation. In both studies, subjects were asked to impact the simulation device as hard as they found acceptable without causing injury, numbness or pain. Subjects were trained for 11 h. Force and hand acceleration time-histories were recorded from the simulation device and a hand-mounted accelerometer, respectively. The magnitude of each impact was quantified with eight dependent measures: peak, time-to-peak, load rate and impulse, from both the force and acceleration transducers. Statistics were used to determine the effects of gender, skill level and impact location on acceptable impact severity. In the second study, 8 male and 8 female subjects performed repeated hand impacts on a wall-mounted force plate at three different frequencies (2, 5 and 8 impacts/min) over three separate sessions. Force measures and statistics were the same as in Study 1. In the first study, impact location did not appear to have a consistent effect on the acceptable impact severities and there was no significant differences observed between male and female values. For both force and acceleration, impulse was the most reliable variable followed by the peak. In the second study an increase in impact frequency was observed to result in a significant decrease in the acceptable levels of peak force and force impulse. This effect was largest when going from 2 to 5 impacts/min and was less pronounced when going from 5 to 8 impacts/min (especially for force impulse). Male subjects demonstrated significantly higher acceptable impulse levels. Based on the combined results from both studies, acceptable limits were recommended for peak force and impulse that would be acceptable to 75% of the population for a range of frequencies. These limits were observed to range from 181 (8/min) to 259 N (2/min) for peak force and 2.53 (8/min) to 3.52 N s (2/min) for force impulse. It was concluded that force impulse and peak force were the variables most likely being controlled by the subjects.Relevance to industryAutomotive assembly includes a number of tasks that involve hand impacts within the manufacturing process. One such task is the door trim panel installation process where the base of the hand is used to impact the door trim panel and drive fastening push pins through holes in the metal door frames. The current study provides tolerance limits so that industrial tasks involving hand impacts can be evaluated for their injury risk.
 
The asymmetrical lifting of postal sacks without handles was simulated. Type-2 and Type-3 postal sacks (those typically used by the U.S. Postal Service) were loaded and unloaded from and to different cart and conveyor levels. An adjustable table was used to simulate the different conveyor levels. There were six combinations of lift for each of twenty participants (ten male and ten female). A modified version of the psychophysical methodology was used to determine the maximum acceptable weight of lift. A significant difference was found between the weights lifted across cart heights. Specifically, the mean load lifted over the 96.5 cm (38.0 in) cart height was 15.337 kg (33.74 lb) and was significantly greater than the average load lifted across the 20.40 cm (8.0 in) and the 104.20 cm (41.0 in cart heights. However, this difference is not practically significant different (mean difference = 1.44 kg). There was no significant difference (p > 0.05). This lifted across table heights. A significant interaction occurred between cart height and conveyor height (p < 0.05). This interaction indicated that as the vertical distance between the cart height and the conveyor height increased, the acceptable load handling capabilities of the participants decreased. The mean MAWL for Type-2 postal sacks (14.5 kg, 31.91 lb) was similar to the mean weight lifted at the postal distribution center (16.4 kg, 36.0 lg). The mean MAWL for Type-3 sacks (14.5 kg, 31.9 lbs) was less than half of the mean weight lifted at the postal distribution center (24.6 kg, 54.1 lb).The results of this study have direct implication regarding the design of postal operations, the types of lifting and lowering tasks that should and should not be performed, as well as more practical weight limitations than are previously employed in these types of operations.
 
The purpose of this experiment was to investigate horizontal and vertical components of maximum acceptable initial and sustained forces while performing push cart tasks on high and low coefficient of friction (COF) floors. Eight male industrial workers performed two sessions of 120 push cart tasks on a high COF floor and one session of 120 push cart tasks on a low COF floor. Each push cart task was 7.6 m long and initiated once a minute. A psychophysical methodology was employed, whereby the subjects were asked to select a workload they could sustain for 8 h without “straining themselves or without becoming unusually tired, weakened, overheated or out of breath”. The results revealed maximum acceptable weights of the push cart tasks on the low COF floor were significantly lower (31%) than the maximum acceptable weights on the high COF floor. That coincided with a significant reduction in the initial and sustained horizontal forces of push (41% and 38%, respectively) on a low COF floor. Push durations on the low COF floor were also longer (62%) than on the high COF floor. Vertical forces and ratios of the vertical to horizontal forces were not significantly different comparing both floors. Calculated slip potential and probability of slipping was borne out by the observation of repeated slipping by the subjects during pushing on the low COF floor. Ergonomic strategies should include the maintenance of sufficient COF on floors to maximize the psychophysical pushing capabilities of the industrial worker.Relevance to industryJobs are often redesigned to eliminate lifting and to include pushing. This article emphasizes the need to maintain floors with appropriate COF to take advantage of the maximum acceptable pushing capabilities of the industrial worker.
 
An experimental study was conducted to determine an appropriate adjustment period using the psychophysical approach for evaluating acceptable work limits for a task involving sloped walking/working surface. A workstation was designed and constructed to simulate a sloped residential roof. Twelve healthy males from a university population served as subjects. The subjects were provided training until the experimenter was confident in their ability to perform the simulated roof-shingling task, while comparing to the experienced roofers’ performance. Results indicated that 198 shingles/h is an acceptable roof shingling frequency for a workday. Time period had significant effect on psychophysical, postural sway, and selected physiological responses. Appropriate adjustment period using the psychophysical approach for evaluating acceptable work limits for tasks involving sloped surface was determined to be 2 h. Postural sway and physiological variables support these findings. The results from this study could aid in setting safe work limits in roofing construction for males. This study may prove to be useful for practical applications for the reduction of the risk of occupational injuries and fatalities, while improving productivity and safety in the roofing industry.Relevance to industryResults from this study could aid in setting acceptable work limits for roof shingling operations. Ergonomic intervention may decrease the risks of falls from roof thus reducing workers compensation costs and lost productivity of the worker.
 
This paper presents a study on a combination lift and lower manual handling task and was designed to simulate the loading of grocery bags into car trunks. Eighteen male subjects performed an externally-paced task of lifting grocery bags loaded with steel shots from 15 cm above the floor and over a wooden sill. There were two different sill heights of 70 cm and 90 cm, and for each of these heights there were three different sill depths of 28 cm, 43 cm, and 57 cm. The dependent variables were the maximum acceptable weight of lift. Constant conditions were temperature (23–26°C), humidity (52–62%), horizontal distance of lift (136 cm), and time of day the subjects performed the lifting. A unique lifting sequence and a modified version of the psychophysical methodology were used to determine the maximum acceptable weight that subjects were willing to lift. There were no significant differences in the weights lifted across the two sill heights but weights lifted over the 28 cm sill depth was significantly more than the weights lifted for either the 43 cm depth or the 57 cm depth.
 
The purpose of this study was to investigate the influence of adjustment periods (20, 30, 40, and 50 min) on the maximum acceptable weights of lift (MAWL) and the resulting responses (heart rate and rating of perceived exertion) on participants during lifting a container from the floor to knuckle height at various frequencies (1, 2, 4, and 6 lifts/min). A total of 6 males were recruited as the participants to perform 16 different combinations of lifting tasks. The results show that: (1) The adjustment period had a significant effect on the MAWL, and the MAWL decreased significantly as adjustment period increased. However, the effect of the adjustment period on the heart rate was not significant. In addition, the effect of the adjustment period on the rating of perceived exertion was significant. The ratings of perceived exertion (RPE) value increased as the adjustment period increased; (2) Even though the lifting frequency significantly affected the maximum acceptable weights, the lifting frequency had no significant effect on the percentage of decrease in MAWL from the 20-min adjustment period values. The participants lifted 3%, 11% and 11% less MAWL when the lifting task was performed at 30, 40, and 50 min adjustment periods, respectively.Relevance industryAt the current time, there are not only extensive databases on lifting and lowering tasks, but also various multipliers and correction factors to extend the range of applicability for this data. Though many researchers have investigated the validity and reliability of the psychophysical data generated in short trials for 8-h or more of work, a very important issue concerning the effect of the adjustment period of psychophysical approach on the lifting capacity has been overlooked and not been studied.
 
Twenty males and 20 females participated in a study undertaken to provide an ergonomic basis for deciding between the conventional steel access cover (less expensive and heavier, and therefore undesirable) and a new composite access cover (relatively more expensive but lighter, and therefore more desirable). The results indicated that the conventional steel cover (weighing 80.35 kg and 91.44 cm in diameter) is too heavy for safe manual handling. The steel cover weight not only exceeded the average individual psychophysical lifting capacity of males and females (33.83 kg and 29.56 kg, respectively), it exceeded the average psychophysical lifting capacity of two-member male and female teams as well (76.04 kg and 67.08 kg, respectively). The spinal compression, if lifting the steel access cover was permitted, would have been approximately 13210 N for individual lifting and 6190 N for team lifting. Only 4 males were able to lift the composite access covers (weighing 38.13 kg and 91.44 cm in diameter) straight up using built-in handles, individually. The average spinal compressive force generated in this case (5849 N) also exceeded the spinal column strength of most males and females. Lifting the composite cover by a two-person team was found to be much safer (average spinal compression for team lifting the composite cover = 2501 N) and is a viable solution. The factor of safety for team lifting the composite access cover is at least 36% for females and 56% for males. Removing the composite cover individually using a rod type handle (unseating the cover by first rotating it and then pulling it for removal) resulted in somewhat greater physical stress (21.33 kg vertical force and 2898 N spinal compressive force) than lifting it by a team but, on the average, provided a factor of safety of at least 49% for males and 26% for females. Removing the composite access cover with the aid of the rod handle was also perceived to be “light” (average RPE value of 10.25 for males and 10.00 for females).
 
The objective of the study was to determine if restriction to access, asymmetry of posture, and reduced headroom in lifting and palletizing tasks affect biomechanical stresses on the lumbar spine significantly. Eleven male blue collar workers with a mean age of 29.1 yr, mean weight of 67.6 kg, and mean height of 174.1 cm with no musculoskeletal disorders were required to lift a 22 kg weight box measuring 46×30×30 cm to a shelf 125 cm high which allowed either 5 or 10 mm clearance for the weight box. The lifts were performed in sagitally symmetrical and 45° asymmetric planes under headroom adjusted to 80% and 90% of the subject's stature and unrestricted headroom. The 12 tasks were randomized and each task was performed three times. During these 12 tasks the xyz coordinates at 15 nodal points were recorded and were inputted to a biomechanical model. The disc compressive and shear forces, and the muscle forces for spinal and abdominal muscles were computed for six lumbar intervertebral discs for six stages of the lift. The results indicated that the take-off stage was most stressful followed by to- the-shelf stage. The multivariate analysis of variance revealed that the headroom affected the biomechanical loads significantly (p<0.004). Symmetry affected the disc compressive load during take-off only (p<0.01). The clearance had no impact on the biomechanical loading.Relevance to industryLifting and palletizing are very common industrial activities. By breaking down the components of tasks and variables affecting them one can determine more clearly the effect of each of these variables. This will help in managing the risk at workplace.
 
It is well accepted that with even very simple tasks, a user's performance with a manual control device improves substantially over some period of time before stabilizing. Past studies with computer input devices have shown that the overall period of time required to learn to physically interact with a system is, however, generally quite short. For users with mobility impairments, however, not only may the overall physical learning phase be significantly longer than for nondisabled users, but certain features of the interface design may require a longer learning period than others. Depending on how different “initial” performance is from “practiced” performance, systems intended for “walk up and use” applications or casual use may need to be designed differently to allow easy access for persons with mobility impairments. Twenty persons with impaired hand and arm function (as a result of spinal cord injury) performed a target acquisition task with five manual computer input devices. Task completion times and errors were recorded. The results indicate that some devices and screen design features required significantly longer periods of time than others for the participants to become proficient at using them. The results also suggest not only that some physical design attributes negatively effect performance, but that the magnitude of the effects differ for “initial” performance and “practiced” performance. In fact, in some cases attributes which had no effect once performance had asymptoted were shown to have a significant effect on novice performance. The implications for interface design are discussed.
 
Two sets of experiments were carried out with 15 young industrial male subjects participating in each. In the first set, the subjects palletized a box with and without handles weighing 11 kg and 22 kg in sagittally symmetrical and 45° asymmetrical plane to the right on to a 125 cm high shelf with four clearances (15 mm, 20 mm, 25 mm, and 30 mm) at a frequency of 2 lifts per minute. In the second set of experiments, the subjects palletized a box weighing 11 kg and 22 kg in sagittally symmetrical and 45° asymmetrical planes on to a 125 cm high shelf with three clearances (15 mm, 20 mm, and 25 mm), and headroom adjusted to 90% and 95% of individual stature of the subjects. Heart rate, oxygen uptake, ventilation volumes were measured and rate of perceived exertion (RPE) was determined. The statistical analyses of the results showed that the load of lift significantly affected all physiological and psychophysical variables (p < 0.002). The handle affected the heart rate, oxygen uptake and ventilation volume (p < 0.01). The headroom significantly affected the RPE and oxygen uptake (p < 0.02). The asymmetry and the restriction to access had no significant effect on any physiological or psychophysical variables.
 
In the aircraft industry, the design of floor assembly jigs (FAJs) is an important activity that directly affects productivity. It involves tool frame generation and locator and clamp placement to ensure that the assembly components are held properly with respect to each other to meet the required tolerances. The tool designer also has to analyze the design to ensure that the assembly process does not pose accessibility and ergonomics related problems. The current approach is dependent on the experience of the tool designer and the limited visualization possible on commercial CAD systems. This leads to extensive redesign when accessibility and ergonomic related problems are detected on the physical prototype. In this research, an integrated Virtual Reality-based environment is being developed for the analysis of assembly product and jig designs. CAD models of the assembly product and jig are imported into a Virtual Reality (VR)-based visualization system for accessibility analysis. A motion tracking system is integrated to allow ergonomic posture analysis. The combined VR and motion tracking system allows evaluation of alternate assembly sequences and the jig design. In this paper, the theoretical basis for the analysis environment is presented along with details of the prototype implementation of this system.Relevance to industryFloor assembly jigs are used extensively by the aircraft industry. Improvement of their design process will lead to savings in better design and reduced development time and cost. Better designs will require fewer changes after the jigs have been fabricated. The overall result will be a reduction in product realization time and cost and improved product quality.
 
Top-cited authors
Mitsuo Nagamachi
  • Hiroshima International University
Waldemar Karwowski
  • University of Central Florida
Subhash Rakheja
  • Concordia University Montreal
Shrawan Kumar
  • University of Alberta
Joseph H. Goldberg