Hongwei Hsiao

Accuracy and precision of two in-shoe pressure measurement systems

The recent rapid adoption of insole pressure measurement systems for clinical and ergonomic evaluations of human gait has necessitated a comprehensive understanding of the accuracy and precision of such systems. Five bench experiments were performed to examine the Pedar and F-Scan in-shoe pressure measurement systems. The insoles examined were the Pedar Y-sized right insole and the F-scan insole trimmed to the size and shape of a Pedar Y-sized insole. Data were sampled at 50 Hz at different levels of applied pressure, calibration procedure, duration of pressure application, insole age of use and experiment day or week. The system accuracy was determined by the per cent error of measurement, the system precision by the 95% tolerance interval of the per cent error. The results show that system accuracy and precision varied among levels of applied pressure, calibration procedure, duration of pressure application and insole age of use. The Pedar system showed the greatest accuracy and precision when the insole was new and measurements were taken (1) after a system calibration as specified by the manufacturer, (2) in the 50 - 500 kPa pressure range and (3) within a few seconds after pressure was applied. Under this condition, the measurement error was in the range -0.6 to 2.7%, and the magnitude (upper bound minus lower bound) of the 95% tolerance intervals was from 13.5 to 18.7%. Measuring less than 35 kPa with the Pedar system is not recommended. To ensure the accuracy and precision of the F-Scan system, users are recommended to estimate the range of the applied pressure and then choose a similar pressure level for calibration. Under this condition, the measurement error was in the range 1.3 - 5.8% and the magnitude (upper bound minus lower bound) of the 95% tolerance intervals was estimated to be in the range 1.1 - 14.8%. When the calibration pressure was outside this range of applied pressure, the per cent errors were considerably higher, ranging from -26.3 to 33.9%.

Functional levels of floor surface roughness for the prevention of slips and falls: Clean-and-dry and soapsuds-covered wet surfaces

Literature has shown a general trend that slip resistance performance improves with floor surface roughness. However, whether slip resistance properties are linearly correlated with surface topographies of the floors or what roughness levels are required for effective slip resistance performance still remain to be answered. This pilot study aimed to investigate slip resistance properties and identify functional levels of floor surface roughness for practical design applications in reducing the risk of slip and fall incidents. A theory model was proposed to characterize functional levels of surface roughness of floor surfaces by introducing a new concept of three distinctive zones. A series of dynamic friction tests were conducted using 3 shoes and 9 floor specimens under clean-and-dry as well as soapsuds-covered slippery wet environments. The results showed that all the tested floor-shoe combinations provided sufficient slip resistances performance under the clean-and-dry condition. A significant effect of floor type (surface roughness) on dynamic friction coefficient (DFC) was found in the soapsuds-covered wet condition. As compared to the surface roughness effects, the shoe-type effects were relatively small. Under the soapsuds-covered wet condition, floors with 50 μm in Ra roughness scale seemed to represent an upper bound in the functional range of floor surface roughness for slip resistance because further increase of surface roughness provided no additional benefit. A lower bound of the functional range for slip resistance under the soapsuds-covered wet condition was estimated from the requirement of DFC > 0.4 at Ra ≅ 17 μm. Findings from this study may have potential safety implications in the floor surface design for reducing slip and fall hazards.

U.S. Truck Driver Anthropometric Study and Multivariate Anthropometric Models for Cab Designs

Objective: This study presents data from a large-scale anthropometric study of U.S. truck drivers and the multivariate anthropometric models developed for the design of next-generation truck cabs. Background: Up-to-date anthropometric information of the U.S. truck driver population is needed for the design of safe and ergonomically efficient truck cabs. Method: We collected 35 anthropometric dimensions for 1,950 truck drivers (1,779 males and 171 females) across the continental United States using a sampling plan designed to capture the appropriate ethnic, gender, and age distributions of the truck driver population. Results: Truck drivers are heavier than the U.S. general population, with a difference in mean body weight of 13.5 kg for males and 15.4 kg for females. They are also different in physique from the U.S. general population. In addition, the current truck drivers are heavier and different in physique compared to their counterparts of 25 to 30 years ago. Conclusion: The data obtained in this study provide more accurate anthropometric information for cab designs than do the current U.S. general population data or truck driver data collected 25 to 30 years ago. Multivariate anthropometric models, spanning 95% of the current truck driver population on the basis of a set of 12 anthropometric measurements, have been developed to facilitate future cab designs. Application: The up-to-date truck driver anthropometric data and multivariate anthropometric models will benefit the design of future truck cabs which, in turn, will help promote the safety and health of the U.S. truck drivers.

Anthropometric criteria for the design of tractor cabs and protection frames

Improved human – tractor interface designs, such as well-accommodated operator enclosures (i.e. cabs and protection frames) can enhance operator productivity, comfort and safety. This study investigated farm-worker anthropometry and determined the critical anthropometric measures and 3-D feature envelopes of body landmarks for the design of tractor operator enclosures. One hundred agriculture workers participated in the study. Their body size and shape information was registered, using a 3-D full-body laser scanner. Knee height (sitting) and another eight parameters were found to affect the cab-enclosure accommodation rating and multiple anthropometric dimensions interactively affected the steering wheel and gear-handle impediment. A principal component analysis has identified 15 representative human body models for digitally assessing tractor-cab accommodation. A set of centroid coordinates of 34 body landmarks and the 95% confidence semi-axis-length for each landmark location were developed to guide tractor designers in their placement of tractor control components in order to best accommodate the user population. Finally, the vertical clearance (90 cm) for agriculture tractor enclosure in the current SAE International J2194 standard appeared to be too short as compared to the 99th percentile sitting height of male farm workers in this study (100.6 cm) and in the 1994 National Health and Nutrition Examination Survey III database (99.9 cm) and of the male civilian population in the 2002 Civilian American and European Surface Anthropometric Resource database (100.4 cm).

A comparison of different postures for scaffold end-frame disassembly.

Overexertion and fall injuries comprise the largest category of nonfatal injuries among scaffold workers. This study was conducted to identify the most favourable scaffold end-frame disassembly techniques and evaluate the associated slip potential by measuring whole-body isometric strength capability and required coefficient of friction (RCOF) to reduce the incidence of injury. Forty-six male construction workers were used to study seven typical postures associated with scaffold end-frame disassembly. An analysis of variance (ANOVA) showed that the isometric forces (334.4-676.3 N) resulting from the seven postures were significantly different (p < 0.05). Three of the disassembly postures resulted in considerable biomechanical stress to workers. The symmetric front-lift method with hand locations at knuckle height would be the most favourable posture; at least 93% of the male construction worker population could handle the end frame with minimum overexertion risk. The static RCOF value resulting from this posture during the disassembly phase was less than 0.2, thus the likelihood of a slip should be low.

Assessment of perceived traumatic injury hazards during drywall hanging

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

Biomechanical evaluation of scaffolding tasks

A field study was conducted to identify tasks and activities that increase the risk of overexertion injury associated with the erection and dismantling of frame scaffolds, and to determine strategies that would prevent or reduce the workers risk of injury. Twelve construction sites involving 29 workers were visited. The investigation identified that lifting scaffold end frames, carrying end frames, handling scaffold planks, removing cross braces, and removing guardrails are activities that increase the risk of overexertion injuries during task performance. This paper has focused on end-frame handling problems. Although the techniques used to handle end frames varied among the construction sites and subjects, six lifting and five carrying strategies were commonly used. Computer simulations of these work techniques show that considerable biomechanical stress occurs to most of the workers at their shoulders, elbows, and hips. To reduce overexertion injuries during erection and dismantling of frame scaffolds, design of an assistive device to lift scaffold end frames and modifications to the end-frame fixtures are suggested. Future research areas for the prevention of injury during scaffolding work are also proposed.

Anthropometric Procedures for Protective Equipment Sizing and Design

Objectives: This article presented four anthropometric theories (univariate, bivariate/probability distribution, multivariate, and shape-based methods) for protective equipment design decisions. Background: While the significance of anthropometric information for product design is well recognized, designers continue to face challenges in selecting efficient anthropometric data processing methods and translating the acquired information into effective product designs. Methods: For this study, 100 farm tractor operators, 3,718 respirator users, 951 firefighters, and 816 civilian workers participated in four studies on the design of tractor roll-over protective structures (ROPS), respirator test panels, fire truck cabs, and fall-arrest harnesses, respectively. Their anthropometry and participant-equipment interfaces were evaluated. Results: Study 1 showed a need to extend the 90-cm vertical clearance for tractor ROPS in the current industrial standards to 98.3 to 101.3 cm. Study 2 indicated that current respirator test panel would have excluded 10% of the male firefighter population; a systematic adjustment to the boundaries of test panel cells was suggested. Study 3 provided 24 principal component analysis-based firefighter body models to facilitate fire truck cab design. Study 4 developed an improved gender-based fall-arrest harness sizing scheme to supplant the current unisex system. Conclusions: This article presented four anthropometric approaches and a six-step design paradigm for ROPS, respirator test panel, fire truck cab, and fall-arrest harness applications, which demonstrated anthropometric theories and practices for defining protective equipment fit and sizing schemes. Applications: The study provided a basis for equipment designers, standards writers, and industry manufacturers to advance anthropometric applications for product design and improve product efficacy.

Evaluation of Fall Arrest Harness Sizing Schemes

Objective: This paper evaluated harness sizing schemes and anthropometric criteria for harness design applications. Background: Updated harness sizing systems are needed to accommodate diverse populations in the current workforce. Method: Three-dimensional torso scan data and human-harness interfaces from 108 women and 108 men were digitally captured. Abounding box approach was employed to quantify the effect of torso shape and size on fall harness fit. Results: A logistic regression model with eight equations was developed and tested to classify more than 96% of participants to the best-fitting size. Conclusion: Study outcomes suggested an alternative system of two sizes for women and three sizes for men over the current four-size unisex system. In addition, thigh strap angle and back D ring location could be utilized along with current harness static fit test criteria to further enhance postfall harness fit predictions. Application: This research could help reduce the risk of worker injury resulting from poor fit, improper size selection, or failure to don the harness properly.

The effect of wearing a back belt on spine kinematics during asymmetric lifting of large and small boxes

Study Design. A crossover design was used to evaluate kinematic measurements collected with an infrared-based motion measurement system. Objectives. To evaluate belt effects on spine kinematics during asymmetric lifting of large and small boxes and to test for carryover effects between trials from belts. Summary of Background Data. Conflicting evidence in the literature exists regarding whether belts are beneficial or detrimental to manual material handlers. Studies have not examined belt effects when lifting different sized boxes, nor carryover effects from belts. Methods. Twenty-eight subjects with manual-handling experience (17 male and 11 female) were randomly assigned to lift either a large or small box (weighing 9.4 kg), from a sagittally symmetric origin at pallet height to a 79 cm height, 60° to the right. Spine flexion, lateral bending and twisting, hip and knee flexion, and angular velocity measurements of the torso with respect to the pelvis were collected for each of three lifting periods, 50 lifts each at 3 lifts per minute, with 18-minute breaks between periods. Results. Belts significantly reduced maximum spine flexion, spine flexion and extension angular velocities, and torso left lateral bending angular velocity, and increased hip and knee flexion, regardless of box size. When lifting large boxes, belts significantly reduced torso right lateral bending and torso left twisting. No significant differential carryover effects were detected from belts. Conclusions. Subjects with belts lifted more slowly and used more of a squat-lift technique, regardless of box size. Belts reduced more torso motions while lifting large boxes.