Last data update: Nov 04, 2024. (Total: 48056 publications since 2009)
Records 1-18 (of 18 Records) |
Query Trace: Pan CS[original query] |
---|
Testing the shock protection performance of Type I construction helmets using impactors of different masses
Wu JZ , Pan CS , Ronaghi M , Wimer BM . Biomed Mater Eng 2024 BACKGROUND: Wearing protective helmets is an important prevention strategy to reduce work-related traumatic brain injuries. The existing standardized testing systems are used for quality control and do not provide a quantitative measure of the helmet performance. OBJECTIVE: To analyze the failure characterizations of Type I industrial helmets and develop a generalized approach to quantify the shock absorption performance of Type I industrial helmets based on the existing standardized setups. METHODS: A representative basic Type I construction helmet model was selected for the study. Top impact tests were performed on the helmets at different drop heights using two different impactor masses (3.6 and 5.0 kg). RESULTS: When the helmets were impacted with potential impact energies smaller than the critical potential impact energy values, there was a consistent relationship between the peak impact force and the potential impact energy. When the helmets were impacted under potential impact energies greater than the critical potential impact energy values, the peak impact forces increased steeply with increasing potential impact energy. CONCLUSION: A concept of safety margin for construction helmets based on potential impact energy was introduced to quantify the helmets' shock absorption performance. The proposed method will help helmet manufacturers improve their product quality. |
A finite element analysis of the effects of anchorage reaction forces and moments on structural stability of mast climbing work platforms
Wu JZ , Pan CS , Wimer BM , Warren CM , Villeneuve F , Dong RG . J Multiscale Modell null [Epub ahead of print] Mast climbing work platforms (MCWPs) have been increasingly used for construction projects, whereas their safety remains an important issue. As the mast in the Mast climbing work platform (MCWP) system is "slender" structurally, its anchorages must play an important role in maintaining its stability. Therefore, the anchorages and their attachments to a construction structure are likely among the most critical components for the MCWPs. This study developed finite element models of a representative MCWP and applied them to analyze the characteristics of the reaction forces at the anchorages when the work platform operates at different heights and under different loading conditions and to simulate the mast structure responses to the failure of one of the three anchorages. The results of this study indicate that the anchorage reaction forces are sensitive to the loading and operational conditions of the MCWP. The responses of the anchorage reaction forces may reflect the stability status or risk potential of the mast structure of the MCWP to collapse. The characteristics of the anchorage forces identified in this study can be used to help develop a structural safety monitoring system, to minimize the risk of catastrophic failures of MCWPs. The knowledge obtained in the study would help improve MCWP safety management at construction sites and help MCWP manufacturers to improve anchorage design and installation procedures to reduce the risk of the mast structure's instability or collapse. |
Evaluation of the fall protection of Type I industrial helmets
Wu JZ , Pan CS , Cobb C , Moorehead A , Kau TY , Wimer BM . Ann Biomed Eng 2022 50 (11) 1565-1578 The performance of Type I industrial helmets for fall protection is not required to be tested in standardized tests. The current study analyzed the fall protection performance of Type I industrial helmets and evaluated if the use of a chin strap and the suspension system tightness have any effect on protection performance. Head impact tests were performed using an instrumented manikin. There were 12 combinations of test conditions: with or without chin strap usage, three levels of suspension system tightness, and two impact surfaces. Four representative helmet models (two basic and two advanced models) were selected for the study. Impact tests without a helmet under all other applicable test conditions were used as a control group. There were four replicates for each test condition-a total of 192 impact tests with helmets and eight impact tests for the control group. The peak acceleration and the calculated head impact criteria (HIC) were used to evaluate shock absorption performance of the helmets. The results showed that all four helmet models demonstrated excellent performance for fall protection compared to the barehead control group. The fall protection performance of the advanced helmet models was substantially better than the basic helmet models. However, the effects of the use of chin straps and suspension system tightness on the helmets' fall protection performance were statistically not significant. |
Application of polyethylene air-bubble cushions to improve the shock absorption performance of Type I construction helmets for repeated impacts
Wu JZ , Pan CS , Ronaghi M , Wimer BM , Reischl U . Biomed Mater Eng 2020 32 (1) 1-14 BACKGROUND: The use of helmets was considered to be one of the important prevention strategies employed on construction sites. The shock absorption performance of a construction (or industrial) helmet is its most important performance parameter. Industrial helmets will experience cumulative structural damage when being impacted repeatedly with impact magnitudes greater than its endurance limit. OBJECTIVE: The current study is to test if the shock absorption performance of Type I construction helmets subjected to repeated impacts can be improved by applying polyethylene air-bubble cushions to the helmet suspension system. METHODS: Drop impact tests were performed using a commercial drop tower test machine following the ANSI Z89.1 Type I drop impact protocol. Typical off-the-shelf Type I construction helmets were evaluated in the study. A 5 mm thick air-bubble cushioning liner was placed between the headform and the helmet to be tested. Helmets were impacted ten times at different drop heights from 0.61 to 1.73 m. The effects of the air-bubble cushioning liner on the helmets' shock absorption performance were evaluated by comparing the peak transmitted forces collected from the original off-the-shelf helmet samples to the helmets equipped with air-bubble cushioning liners. RESULTS: Our results showed that a typical Type I construction helmet can be subjected to repeated impacts with a magnitude less than 22 J (corresponding to a drop height 0.61 m) without compromising its shock absorption performance. In comparison, the same construction helmet, when equipped with an air-bubble cushioning liner, can be subjected to repeated impacts of a magnitude of 54 J (corresponding to a drop height 1.52 m) without compromising its shock absorption performance. CONCLUSIONS: The results indicate that the helmet's shock absorbing endurance limit has been increased by 145% with addition of an air-bubble cushioning liner. |
An approach to characterize the impact absorption performance of construction helmets in top impact
Pan CS , Wimer BM , Welcome DE , Wu JZ . J Test Eval 2020 49 (3) The helmets used by construction site workers are mainly designed for head protection when objects are dropped from heights. Construction helmets are also casually called hard hats in industries. Common construction helmets are mostly categorized as type 1 according to different standards. All type 1 helmets have to pass type 1 standard impact tests, which are top impact tests--the helmet is fixed and is impacted by a free falling impactor on the top crown of the helmet shell. The purpose of this study was to develop an approach that can determine the performance characterization of a helmet. A total of 31 drop impact tests using a representative type 1 helmet model were performed at drop heights from 0.30 to 2.23 m, which were estimated to result in impact speeds from 2.4 to 6.6 m/s. Based on our results, we identified a critical drop height that was used to evaluate the performance of helmets. The peak impact forces and peak accelerations varied nonproportionally with the drop height. When the drop height is less than the critical height, the peak force and peak acceleration increase gradually and slowly with increasing drop height. When the drop height is greater than the critical height, the peak force and peak acceleration increase steeply with even a slight increase in drop height. Based on the critical drop height, we proposed an approach to determine the safety margin of a helmet. The proposed approach would make it possible to determine the performance characteristics of a helmet and to estimate the safety margin afforded by the helmet, if the helmet first passes the existing standardized tests. The proposed test approach would provide supplementary information for consumers to make knowledgeable decisions when selecting construction helmets. |
Application of air-bubble cushioning to improve the shock absorption performance of type I industrial helmets
Wu JZ , Pan CS , Ronaghi M , Wimer BM , Reischl U . Eng Fail Anal 2020 117 104921 The industrial helmet is the most used and effective personal protective equipment to reduce work-related traumatic brain injuries. The Type I industrial helmet is a basic helmet model that is commonly used in construction sites and manufacturers. The purpose of the current study was to investigate if shock absorption performance of these helmets could be improved by using an air-bubble cushioning liner to augment the helmet's suspension system. Drop impact tests were performed using a commercial drop tower test machine according to the ANSI Z89.1 Type I drop impact protocol. Typical off-the-shelf Type I industrial helmets were utilized in the study. The effects of the air-bubble cushioning on the helmets' shock absorption performance were evaluated by comparing the original off-the-shelf helmet samples to the helmets equipped with an air-bubble cushioning liner. The air-bubble cushioning liner (thickness 5 mm) was placed between the headform and the helmet when being tested. The impactor had a mass of 3.6 kg and was free-dropped from different heights. The maximal peak transmitted forces for each of the tests have been evaluated and compared. Our results show that the shock absorption effectiveness of the air-bubble cushioning is dependent on the magnitude of the impact force. At lower drop heights (h < 1.63 m), the air-bubble cushioning liner has little effect on the transmitted impact forces, however, at higher drop heights (h>/= 1.73 m) the air-bubble cushioning liner effectively reduced the peak transmitted forces. At a drop height of 1.93 m (the highest drop height tested), the air-bubble cushioning liner reduced the peak transmitted force by over 80%. Our results indicate that adding an air-bubble cushioning liner into a basic Type I industrial helmet will substantially increase shock absorption performance for large impact forces. |
Biomechanical assessment while using production tables on mast climbing work platforms
Pan CS , Ning X , Wimer B , Zwiener J , Kau TY . Appl Ergon 2020 90 103276 The objective of this study was to assess the impact of using alternative mast climbing work platform (MCWP) designs on trunk motion and postural stability with masonry workers while performing bricklaying and stepping down tasks using a conventional MCWP setting (i.e. with a step deck) as well as two types of production tables (straight- and L-shaped). The trunk angles and postural sway parameters of twenty-five masonry workers were recorded for the following tasks: (1) standing on a simulated MCWP and laying bricks on an adjacent wall, and (2) stepping down onto the step deck to get into position for doing the bricklaying task. Results indicated that the use of the L-shaped production table resulted in the lowest trunk ranges of motion and significantly reduced the workers' trunk angles in all three planes when compared to both the straight-shaped production table and the conventional approach of not using a production table. Data showed that both body sway velocity and area were significantly reduced when using either one of the production tables. The use of production tables significantly reduced impact sway forces when workers stepped from the main platform to the step deck. The use of production tables on MCWPs improved workers' postures and overall stability, which could reduce the risk of injury. |
Evaluation of the shock absorption performance of construction helmets under repeated top impacts
Wu JZ , Pan CS , Wimer BM . Eng Fail Anal 2019 96 330-339 It is accepted in industries that an industrial helmet should be disposed of when it is subjected to a significant impact. There is no scientific evidence that supports this well-accepted belief. The current study was intended to evaluate the shock absorption performance of industrial helmets under repeated impacts. Common industrial or construction helmets are categorized as Type I according to ANSI Z89.1 and they are designed to mainly protect top impacts. A representative basic Type I construction helmet model was selected in the study. Helmets were repeatedly impacted ten times using a commercial drop tower tester with an impactor (mass 3.6?kg) at different drop heights from 0.30 to 2.03?m. A total of 80 impact trials were performed in the study. The relationships of the transmitted force with the drop height and with impact number were analyzed. A new parameter - the endurance limit - was proposed to evaluate the shock absorption performance of a helmet. The helmets were observed to experience cumulative structural damage with increasing impact number, resulting in a degrading shock absorption performance, when being impacted repeatedly with magnitudes greater than the endurance limit. Repeated impacts with magnitudes smaller than the endurance limit did not cause measurable cumulative structural damage to the helmets in our study. |
Evaluation of postural sway and impact forces during ingress and egress of scissor lifts at elevations
Pan CS , Chiou SS , Kau T , Wimer BM , Ning X , Keane P . Appl Ergon 2017 65 152-162 Workers are at risk when entering (ingress) or exiting (egress) elevated scissor lifts. In this study, we recorded ground impact forces and postural sway from 22 construction workers while they performed ingress and egress between a scissor lift and an adjacent work surface with varying conditions: lift opening designs, horizontal and vertical gaps, and sloped work surfaces. We observed higher peak ground shear forces when using a bar-and-chain opening, with larger horizontal gap, with the lift surface more than 0.2 m below the work surface, and presence of a sloped (26) work surface. Similar trends were observed for postural sway, except that the influence of vertical distance was not significant. To reduce slip/trip/fall risk and postural sway of workers while ingress or egress of an elevated scissor lift, we suggest scissor lifts be equipped with a gate-type opening instead of a bar-and-chain design. We also suggest the lift surface be placed no more than 0.2 m lower than the work surface and the horizontal gap between lift and work surfaces be as small as possible. Selecting a non-sloped surface to ingress or egress a scissor lift is also preferred to reduce risk. |
An improved finite element modeling of the cerebrospinal fluid layer in the head impact analysis
Wu JZ , Pan CS , Wimer BM , Rosen CL . Biomed Mater Eng 2017 28 (2) 187-199 The finite element (FE) method has been widely used to investigate the mechanism of traumatic brain injuries (TBIs), because it is technically difficult to quantify the responses of the brain tissues to the impact in experiments. One of technical challenges to build a FE model of a human head is the modeling of the cerebrospinal fluid (CSF) of the brain. In the current study, we propose to use membrane elements to construct the CSF layer. Using the proposed approach, we demonstrate that a head model can be built by using existing meshes available in commercial databases, without using any advanced meshing software tool, and with the sole use of native functions of the FE package Abaqus. The calculated time histories of the intracranial pressures at frontal, posterior fossa, parietal, and occipital positions agree well with the experimental data and the simulations in the literature, indicating that the physical effects of the CSF layer have been accounted for in the proposed modeling approach. The proposed modeling approach would be useful for bioengineers to solve practical problems. |
Finite element simulations of the head-brain responses to the top impacts of a construction helmet: Effects of the neck and body mass
Wu JZ , Pan CS , Wimer BM , Rosen CL . Proc Inst Mech Eng H 2017 231 (1) 58-68 Traumatic brain injuries are among the most common severely disabling injuries in the United States. Construction helmets are considered essential personal protective equipment for reducing traumatic brain injury risks at work sites. In this study, we proposed a practical finite element modeling approach that would be suitable for engineers to optimize construction helmet design. The finite element model includes all essential anatomical structures of a human head (i.e. skin, scalp, skull, cerebrospinal fluid, brain, medulla, spinal cord, cervical vertebrae, and discs) and all major engineering components of a construction helmet (i.e. shell and suspension system). The head finite element model has been calibrated using the experimental data in the literature. It is technically difficult to precisely account for the effects of the neck and body mass on the dynamic responses, because the finite element model does not include the entire human body. An approximation approach has been developed to account for the effects of the neck and body mass on the dynamic responses of the head-brain. Using the proposed model, we have calculated the responses of the head-brain during a top impact when wearing a construction helmet. The proposed modeling approach would provide a tool to improve the helmet design on a biomechanical basis. |
Accelerated evaluation of automated vehicles safety in lane-change scenarios based on importance sampling techniques
Zhao D , Lam H , Peng H , Bao S , LeBlanc DJ , Nobukawa K , Pan CS . IEEE Trans Intell Transp Syst 2016 18 (3) 595-607 Automated vehicles (AVs) must be thoroughly evaluated before their release and deployment. A widely used evaluation approach is the Naturalistic-Field Operational Test (N-FOT), which tests prototype vehicles directly on the public roads. Due to the low exposure to safety-critical scenarios, N-FOTs are time consuming and expensive to conduct. In this paper, we propose an accelerated evaluation approach for AVs. The results can be used to generate motions of the other primary vehicles to accelerate the verification of AVs in simulations and controlled experiments. Frontal collision due to unsafe cut-ins is the target crash type of this paper. Human-controlled vehicles making unsafe lane changes are modeled as the primary disturbance to AVs based on data collected by the University of Michigan Safety Pilot Model Deployment Program. The cut-in scenarios are generated based on skewed statistics of collected human driver behaviors, which generate risky testing scenarios while preserving the statistical information so that the safety benefits of AVs in nonaccelerated cases can be accurately estimated. The cross-entropy method is used to recursively search for the optimal skewing parameters. The frequencies of the occurrences of conflicts, crashes, and injuries are estimated for a modeled AV, and the achieved accelerated rate is around 2000 to 20 000. In other words, in the accelerated simulations, driving for 1000 miles will expose the AV with challenging scenarios that will take about 2 to 20 million miles of real-world driving to encounter. This technique thus has the potential to greatly reduce the development and validation time for AVs. |
Gap acceptance during lane changes by large - truck drivers - an image - based analysis
Nobukawa K , Bao S , LeBlanc DJ , Zhao D , Peng H , Pan CS . IEEE Trans Intell Transp Syst 2015 Pp (99) 1-10 This paper presents an analysis of rearward gap acceptance characteristics of drivers of large trucks in highway lane change scenarios. The range between the vehicles was inferred from camera images using the estimated lane width obtained from the lane tracking camera as the reference. Six-hundred lane change events were acquired from a large-scale naturalistic driving data set. The kinematic variables from the image-based gap analysis were filtered by the weighted linear least squares in order to extrapolate them at the lane change time. In addition, the time-to-collision and required deceleration were computed, and potential safety threshold values are provided. The resulting range and range rate distributions showed directional discrepancies, i.e., in left lane changes, large trucks are often slower than other vehicles in the target lane, whereas they are usually faster in right lane changes. Video observations have confirmed that major motivations for changing lanes are different depending on the direction of move, i.e., moving to the left (faster) lane occurs due to a slower vehicle ahead or a merging vehicle on the right-hand side, whereas right lane changes are frequently made to return to the original lane after passing. |
Assessment of fall-arrest systems for scissor lift operators: computer modeling and manikin drop testing
Pan CS , Powers JR , Hartsell JJ , Harris JR , Wimer BM , Dong RG , Wu JZ . Hum Factors 2012 54 (3) 358-72 OBJECTIVE: The current study is intended to evaluate the stability of a scissor lift and the performance of various fall-arrest harnesses/lanyards during drop/fall-arrest conditions and to quantify the dynamic loading to the head/ neck caused by fall-arrest forces. BACKGROUND: No data exist that establish the efficacy of fall-arrest systems for use on scissor lifts or the injury potential from the fall incidents using a fall-arrest system. METHOD: The authors developed a multibody dynamic model of the scissor lift and a human lift operator model using ADAMS and LifeMOD Biomechanics Human Modeler. They evaluated lift stability for four fall-arrest system products and quantified biomechanical impacts on operators during drop/fall arrest, using manikin drop tests. Test conditions were constrained to flat surfaces to isolate the effect of manikin-lanyard interaction. RESULTS: The fully extended scissor lift maintained structural and dynamic stability for all manikin drop test conditions. The maximum arrest forces from the harnesses/lanyards were all within the limits of ANSI Z359.1. The dynamic loading in the lower neck during the fall impact reached a level that is typically observed in automobile crash tests, indicating a potential injury risk for vulnerable participants. CONCLUSION: Fall-arrest systems may function as an effective mechanism for fall injury protection for operators of scissor lifts. However, operators may be subjected to significant biomechanical loadings on the lower neck during fall impact. APPLICATION: Results suggest that scissor lifts retain stability under test conditions approximating human falls from predefined distances but injury could occur to vulnerable body structures. |
An investigation on the dynamic stability of scissor lift
Dong RG , Pan CS , Hartsell JJ , Welcome DE , Lutz T , Brumfield A , Harris JR , Wu JZ , Wimer B , Mucino V , Means K . Open J Saf Sci Technnol 2012 2 (1) 8-15 The tip-over of scissor lifts in operation has frequently resulted in the death and/or severe injuries of workers. The objective of this study is to enhance the understanding of its major mechanisms and factors influencing scissor lift stability. Both experimental and modeling approaches were used in this study. Two series of experiments were performed under possible tip-over scenarios: curb impact and pothole depression. Based on the dynamic characteristics identified from the experimental results, a lumped-parameter model of the scissor lift was developed. It was applied to investigate the effect of scissor structure flexibility on the tip-over potential of the lift, to understand tip-over mechanisms, and to explore preventive strategies. This study found that the fundamental natural frequencies of the lift were generally in a range of 0.30 - 2.08 Hz, which are likely related to the tip-over. Increasing flexibility of the lift structure generally increased the tip-over potential. The tip-over threshold was also a function of both ground slope and tilt speed of the lift. The results suggest that the lift should not be elevated on largely deformable and/or uneven surfaces such as bridged wood board or a soft soil base. The worker on the lift platform should avoid any large continuous periodic movement or forceful action in the horizontal plane, especially when the lift is fully elevated. Besides the tilt angle of the lift, the tilt speed should be monitored to help prevent the tip-over. |
Estimation of the kinetic energy dissipation in fall-arrest system and manikin during fall impact
Wu JZ , Powers JR , Harris JR , Pan CS . Ergonomics 2011 54 (4) 367-379 Fall-arrest systems (FASs) have been widely applied to provide a safe stop during fall incidents for occupational activities. The mechanical interaction and kinetic energy exchange between the human body and the fall-arrest system during fall impact is one of the most important factors in FAS ergonomic design. In the current study, we developed a systematic approach to evaluate the energy dissipated in the energy absorbing lanyard (EAL) and in the harness/manikin during fall impact. The kinematics of the manikin and EAL during the impact were derived using the arrest-force time histories that were measured experimentally. We applied the proposed method to analyse the experimental data of drop tests at heights of 1.83 and 3.35 m. Our preliminary results indicate that approximately 84-92% of the kinetic energy is dissipated in the EAL system and the remainder is dissipated in the harness/manikin during fall impact. The proposed approach would be useful for the ergonomic design and performance evaluation of an FAS. STATEMENT OF RELEVANCE: Mechanical interaction, especially kinetic energy exchange, between the human body and the fall-arrest system during fall impact is one of the most important factors in the ergonomic design of a fall-arrest system. In the current study, we propose an approach to quantify the kinetic energy dissipated in the energy absorbing lanyard and in the harness/body system during fall impact. |
Fall arrest characteristics of a scissor lift
Harris JR , Powers JR Jr , Pan CS , Boehler B . J Safety Res 2010 41 (3) 213-20 PROBLEM: Census of Fatal Occupational Injuries (CFOI) data indicate 306 aerial lift fatalities between 1992-2003. Seventy-eight of these fatalities specifically involved scissor lifts. Members of standards committees have requested that NIOSH conduct research to determine the effects of safety-control practices related to using fall-protection systems for scissor lifts. METHOD: This research examined the structural and dynamic stability of a scissor lift subjected to fall arrest forces. This was accomplished by conducting drop tests from a scissor lift. Anchorage locations evaluated included manufacturer-supplied anchorage points on the scissor lift platform as well as mid-rail and top-rail locations. RESULTS: Preliminary drop tests determined that a 2400lb maximum arrest force (MAF) could be generated by dropping 169lb through a fall height of 36" using Nystron(R) rope as a lanyard. The scissor lift maintained structural and dynamic stability for all drop tests when fully extended and on an incline. DISCUSSION: Anchoring a fall arrest system to either the mid-rail or top-rail is not a recommended practice by the scissor lift manufacturer. Anchor points are provided on the platform floor of the scissor lift for this purpose. However, our results demonstrate that the mid-rail and top-rail absorb substantial energy from an arrested fall and may have potential as appropriate anchorage points. IMPACT TO INDUSTRY: Employers and workers should consider implementing fall arrest systems when using scissor lifts as part of their overall risk mitigation plan for fall injury prevention. |
Effects of foot placement on postural stability of construction workers on stilts
Pan CS , Chiou S , Kau TY , Bhattacharya A , Ammons D . Appl Ergon 2009 40 (4) 781-9 Stilts are elevated tools that are frequently used by construction workers to raise workers 18-40 inches above the ground. The objective of this laboratory study was to evaluate the potential loss of postural stability associated with the use of stilts in various foot placements. Twenty construction workers with at least 1 year of experience in the use of stilts participated in this study. One Kistler force platform was used to collect kinetic data. Participants were tested under six-foot-placement conditions. These 6 experimental conditions were statically tested under all combinations of 3 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 the multivariate analysis of variance (MANOVA) and repeated measures of univariate analyses of variance (ANOVAs) demonstrated that stilt height, foot-placement direction, and foot-placement width all had significant effects on the whole-body postural stability. This study found that the higher the stilts were elevated, the greater the postural instability. A stance position with one foot placed forward of the other foot produced greater postural instability than a position with the feet parallel and directly beneath the body. This study found that placement of the feet parallel and directly beneath the body, with the feet positioned a half shoulder width apart, caused a greater amount of postural sway and instability than one and one-and-half shoulder width. This study also found that construction workers using the stilts could perceive the likely postural instability due to the change in foot placements. |
- Page last reviewed:Feb 1, 2024
- Page last updated:Nov 04, 2024
- Content source:
- Powered by CDC PHGKB Infrastructure