205
BIOMECHANICAL EVALUATIONS OF FOOT PLACEMENT FOR CONSTRUCTION WORKERS ON STILTS.
C. Pan, S. Chiou, T. Kau, D. Ammons, D. Cantis, NIOSH, Morgantown, WV.
Stilts are elevated tools that are frequently used by construction workers to raise workers 18 to 40 inches above the ground. Previous studies indicated that construction workers perceive risk of injury when working on stilts. However, no in-depth biomechanical analyses have been conducted. The objective of this laboratory study was to evaluate joint loadings on lower extremities and potential loss of balance associated with the use of stilts in various foot placements. Twenty construction workers (mean age = 36 ± 7 years) with at least 12 months (mean experience = 10 ± 7 years) of experience in the use of stilts participated in this study. A PEAKTM motion system and two KistlerTM force platforms were used to collect data on both kinetic and kinematic measures. Subjects were tested under six foot-placement conditions. These six experimental conditions were statically tested under all combinations of three levels of elevation: 0” (no stilts), 24” stilt height, and 40” stilt height. SAS mixed procedure was used to evaluate the effect of different experimental conditions. The results of univariate analysis and principal component analysis demonstrated that stilt height, foot placement direction, and foot placement width all had significant effects on whole body postural stability, as well as on joint loadings for lower extremities. This study found that the higher the stilts were elevated, the greater the postural instability and joint loadings. A foot position in which one foot was placed forward of the other foot produced greater postural instability and joint loadings than a position with two feet parallel and directly beneath the body. This study also found that placing the feet parallel and directly beneath the body, with the feet positioned either one shoulder width apart or 1½ shoulder width apart, caused less postural instability and joint loadings than at half shoulder width.
206
ERGONOMIC ASSESSMENT OF TANK TRUCK DRIVERS.
C. Chang, Exxon Mobil Corporation, Annandale, NJ.
One of the major tasks that a tank truck driver does during a delivery is removing the product and vapor recovery hoses from a storage area prior to off-loading petroleum products at gas stations and returning them back to the storage area. In general, a hose box was used to store the hoses for some trucks while a hose tray was used for others. Back and shoulder strains were reported, allegedly caused by pulling/pushing the hoses out of/into the hose box before/after off-loading the products. Using the Ergonomic Job Measurement System, a tool developed by Applied Ergonomics Technology Inc., two assessments were conducted to evaluate/compare the potential relative ergonomic risks of tank truck drivers handing the hoses stored in the hose box versus the hose tray. The assessment evaluated various elements of three major task categories, i.e., repetitive motion/awkward postures (Part I), lifting (Part II), and the ratio (%) of employee complaints (Part III). A score or ranking was assigned to each element and the sum of all elements (total score) was used to identify the risk ranking of the task with the following scale: high risk = 85 or more; moderate risk = 45–84; low risk = 0–44. The assessment resulted in a total score of 76 for handling hoses stored in the hose box, versus a total score of 53 for the hose tray, i.e., upper moderate risk and Lower Moderate Risk. This finding resulted in all tank trucks manufactured thereafter to be equipped with a hose tray as a standard design.
207
EVALUATION OF CAB DESIGN IN EARTHMOVING CONSTRUCTION EQUIPMENT.
M. Viswanathan, M. Jorgensen, Wichita State University, Wichita, KS; N. Kittusamy, NIOSH–SRL, Spokane, WA.
Awkward postures while operating construction equipment are due to improper cab design and work procedures. If not addressed, awkward posture of any body part can result in increased risk of fatigue, pain, or injury. The objective of this study was to use a checklist for evaluating cab design of construction equipment. This checklist has 31 questions that can be used to evaluate different characteristics of cab design. Eighteen pieces of earthmoving construction equipment were analyzed, including excavators, dozers, and dump trucks. An overall score for each cab was calculated by assigning equal weight to all questions. Results showed that the overall total cab design scores for all equipment ranged from 77 to 97%, the higher the score the better the design. Some design concerns were: (1) the seat did not swivel in the majority of the equipment (94%), (2) the controls in most of the dump trucks were not adjustable, (3) among the various dump trucks, some of the operators felt vibration through the floor, seat, and/or controls of the cab, and (4) noise was a common problem among the dozers. This checklist was useful in identifying several design characteristics of the cab that may need further improvement, which in turn can be useful in reducing awkward postures and improving the working environment.
208
EFFECT OF WORKPLACE RISK FACTORS ON GAIT TASK PERFORMANCE BY LOW-SEAM MINERS.
A. Bhattacharya, J. Gordon, P. Succop, T. Sobeih, University of Cincinnati, Cincinnati, OH; L. Kincl, University of Oregon, Eugene, OR.
The performance of tasks in mines with low ceilings requires work in restricted postures. Under these conditions the performance of dynamic (gait) tasks in stooping postures will cause potential loss of stability/balance to increase. A study was designed to quantify postural instability of 25 low-seam miners while carrying out mine-related tasks (walking with 20 lbs weight) under exposure to individual and combined risk factors of environmental lighting, surface slipperiness (DCOF range for firm-dry, uneven dry and firm-slippery surfaces: 0.9 to 0.22), and footwear (leather steel-toe boot and rubber steel-toe boot) used. The miners’ kinematic and kinetic data, incidence of slip and fall events and perceived exertion (RPE) levels and perceived sense of slip (PSOS) were collected during the experiments. The type of walking surface was significantly (p < 0.0001) associated with maximum medial force, maximum braking force, maximum propulsion force, and maximum lateral force with highest response observed for the uneven-dry surface followed by firm-dry and firm slippery surface. This was expected, as the firm-slippery surface does not provide the necessary foot-floor surface friction to allow development of adequate ground reaction forces and moments necessary for safe upright balance. This is supported by the fact that firm-slippery surface produced the highest level of slip (83% of trials produced slips) and fall incidences (8% of trials produced falls). Carrying a weight also significantly affected both RPE and PSOS (p < 0.0001) inducing 20.5% greater RPE and 40.6% greater PSOS than not carrying a weight. This increased perceived level of exertion and slips during carrying weight was consistent with the body’s response to an increase in braking force/power and contact time. Carrying a weight was associated with an increased probability of slip (p < 0.004, OR = 2.0). Wearing a rubber boot led to an increased probability of fall (p < 0.02, OR = 5.7).
209
ASSESSMENT OF REPETITION IN AUTOMOTIVE ASSEMBLY JOBS.
M. Ebersole, T. Armstrong, A. Johnson, University of Michigan, Ann Arbor, MI.
The American Conference of Governmental Industrial Hygienists has published a Threshold Limit Value (TLV) for repetitive work. This TLV uses a metric, the Hand Activity Level (HAL), which relates repetition to exertion frequency and duty cycle. The HAL can be determined using an observational scale with verbal anchor points or through a calculation using duty cycle and exertion frequency. The aim of this study was to compare the observational and calculation methods. Over 500 automotive assembly jobs with a cycle time of approximately one minute were assessed by a pair of analysts using a visual analog scale. From these jobs, 25 were selected to maximize the range of HAL values. An independent analyst was then chosen to calculate the exertion frequency and duty cycle of the subset of 25 jobs using a fixed interval sampling method. This method required the analyst to observe the video at 0.25-s intervals and assess hand force. An exertion was defined as “a conspicuous increase in hand force.” The duty cycle was defined as the percent of time the worker’s hand force was greater than 2.5%. A paired t-test between the observed HAL rating and the calculated HAL value showed that there was a statistical difference between the two samples (p = 0.01). When a linear regression was performed, the analysis showed a correlation between the two samples (r = 0.44). While the two values are significantly different, there is a general trend that both follow. The calculation method tended to underestimate the HAL when compared to the observational method with an average difference of 1.6 pts on a 10-pt scale. In addition, the calculation method did not accurately depict jobs with a low exertion frequency and high duty cycle.
210
INDIVIDUAL CAPABILITIES ASSOCIATED WITH THE PERFORMANCE IN THE JOB-RELATED TEST
DRILL FOR FIRE FIGHTERS.
S. Lusa, A. Punakallio, H. Lindholm, R. Ilmarinen, Finnish Institute of Occupational Health, Helsinki, Finland; V. Louhevaara, Finnish Institute of Occupational Health and University of Kuopio, Kuopio, Finland.
Objective. The best way for occupational health and safety personnel to evaluate the physical work capacity of fire fighters is the job-related test. The test needs to be reliable and safe. The objective of this study was to identify individual capabilities, which are associated with the performance in the job-related test drill developed for fire fighters for evaluating their physical work capacity. Methods. Forty-eight male fire fighters aged 30–54 years performed a job-related test drill including five typical fire-fighting tasks: walking with two rolls of hose (ca. 32 kg), stair climbing with two hose carriers (ca. 36 kg), hammering, going over and under bars (height of 60 cm), and hose rolling. The drill was carried out as rapidly as possible using proper work techniques and wearing fire protective clothing and equipment (ca. 26 kg). Anthropometrics, cardio-respiratory capacity, and muscular fitness were measured in the laboratory. Performance time, heart rate (HR), oxygen consumption (VO2), and ratings of perceived exertion (RPE) were assessed in the drill. Results. The mean performance time was 10.5 min, and respectively HR, VO2, and RPE were 163 beats/min, 2.52 l/min (22.9 ml/min·kg-1), and 15. The results obtained in the squatting (40 kg, repetitions/min), bench press (40 kg, repetitions/ min), and pull-up (maximal repetitions) tests correlated significantly (-0.42, p = 0.009; -0.39, p = 0.020, and -0.43, p = 0.009, respectively) with the performance time. Correspondingly, the significant correlations were observed between the absolute maximal VO2 (-0.50, p = 0.002) and the maximal VO2 related to body mass (-0.42, p = 0.010) and the performance time. Conclusions. Good cardio-respiratory capacity and muscle endurance and strength were associated with short and successful performance time in the job-related test drill. However, further development, also for safety reasons, is needed to reduce the static and to increase dynamic workload in the drill.
211
EFFECTS OF CONSTRUCTION STILTS ON GAIT CHARACTERISTICS AND JOINT LOADINGS.
S. Chiou, C. Pan, J. Zwiener, M. Ronaghi, NIOSH, Morgantown, WV.
Falls and overexertion are the leading causes of traumatic injuries in the construction industry, largely attributable to the nature of construction work, which continually requires workers to maintain awkward postures and perform tasks at elevations. Stilts are elevated equipment commonly used for drywall finishing, painting, and ceiling work. Previous researchers suggested that stilts may place workers at increased risk for knee injuries and falls. This study was undertaken to quantify stresses and changes in gait biomechanics associated with stilts. Ground reaction forces and body dynamics of 20 subjects (age: 35.8 ± 7.7 years) were evaluated during walking with stilts at different heights (24 or 40 inches). Subjects walked on different paths (straight or curved) with or without holding a mud pan and a trowel in hands. Results from repeated measure ANOVA revealed significant gait adaptations associated with stilts, including increases in stride length, step width, stride period, and reductions in velocity at heel contact (p < 0.0001). Furthermore, lower extremity joint moments (peak ankle dorsiflextion, knee extension, and hip extension) were significantly affected by stilt height (p < 0.001). As the height of the stilt increased, lower extremity joint moments increased, suggesting more muscle activities were needed to ensure steady and safe progression. The maintenance of dynamic balance on stilts is achieved by incorporating compensatory joint torques into the normal gait pattern so as to minimize the destabilizing forces at elevations. The effect of tool carrying did not show any significance, possibly due to the light weights carried in each hand. The findings of this study provide a better understanding of important aspects related to the biomechanics of gait on stilts. To reduce the potential for loss of balance and overexertion, it is suggested that workers avoid or limit prolonged use of stilts, especially when stilts are elevated at high levels.
212
FOOTWEAR EFFECTS ON WORKERS’ INSTABILITY IN A VIRTUAL ROOF WORKPLACE.
P. Simeonov, H. Hsiao, A. Amendola, J. Powers, D. Ammons, T. Kau, D. Cantis, NIOSH/DSR, Morgantown, WV.
Falls from elevation remain the leading cause for fatal injuries in the construction industry, with building roofs as the major source of falls. Previous research has recognized that many of these falls initiate as loss-of-balance incidents. Workers rely heavily on sensory information from their feet to maintain balance in the visually degraded environment at elevation. Shoes act as a sensory interface between the worker’s feet and the support surface, and their design can modify balance control. This study evaluated the effect of footwear type/style on workers’ instability in a simulated roof workplace.
Twenty-four construction workers performed walking tasks with three athletic and three work shoe styles on 10”- and 6”-wide roof planks. The planks were positioned in a surround-screen virtual reality system which simulated visually the environment on the roof of a residential building. A simulated ground environment served as a baseline. Trunk and foot kinematics and instability perceptions were collected using a balanced experimental design. Dependent variables included the angular velocities of the trunk and the shoe rear end in the frontal plane, and the rated perceived instability.
Repeated measures ANOVA demonstrated significant environment-shoe type interaction effect on all dependent variables. The differences between the shoe types were significant only at the narrow planks at simulated height but not in the baseline conditions. Overall, the shoes with improved motion control characteristics, e.g., tennis and basketball athletic styles, appeared to enhance workers’ stability, while the running shoes increased instability. Further, shoes with a higher upper, e.g., work and safety boots style vs. low-cut work shoes, improved considerably workers’ balance on the narrow roof planks.
In conclusion, proper shoe selection and improvements in the design of specialized work footwear would enhance workers’ stability at height, and can be an effective intervention strategy to reduce the risk of falling.
Posted May 30, 2005