Publications by authors named "Daniel Welcome"

49 Publications

An investigation of the effectiveness of vibration-reducing gloves for controlling vibration exposures during grinding handheld workpieces.

Appl Ergon 2021 Sep 12;95:103454. Epub 2021 May 12.

Health Effects Laboratory Division, National Institute for Occupational Safety and Health (NIOSH), Morgantown, WV, 26505, USA.

Prolonged and intensive vibration exposures during the grinding of handheld workpieces may cause hand-arm vibration syndrome. The objectives of this study are to develop an on-the-hand method for evaluating vibration-reducing (VR) gloves, and to determine whether VR gloves can significantly reduce the vibration exposures. A worker holding and pressing a typical workpiece (golf club head) against a grinding wheel or belt in order to shape the workpiece was simulated, and the input vibration and those on the workpiece and hand-arm system were measured. Ten human subjects participated in the experiment. The results demonstrate that VR gloves significantly reduced the vibrations at the palm, hand dorsum, and wrist. The grinding interface condition and hand feed force did not substantially affect glove effectiveness. The use of gloves slightly increased the workpiece resonant response, but the resonant response did not significantly affect glove effectiveness. This study concluded that the use of VR gloves can help control vibration exposures of workers performing grinding of handheld workpieces.
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http://dx.doi.org/10.1016/j.apergo.2021.103454DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8262383PMC
September 2021

Development of a finger adapter method for testing and evaluating vibration-reducing gloves and materials.

Measurement (Lond) 2019 Apr;137:362-374

Physical Effects Research Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.

The objective of this study was to develop a convenient and reliable adapter method for testing and evaluating vibration-reducing (VR) gloves and VR materials at the fingers. The general requirements and technical specifications for the design of the new adapter were based on our previous studies of hand-held adapters for vibration measurement and a conceptual model of the fingers-adapter-glove-handle system developed in this study. Two thicknesses (2 mm and 3 mm) of the adapter beam were fabricated using a 3-D printer. Each adapter is a thin beam equipped with a miniature tri-axial accelerometer (1.1 g) mounted at its center, with a total weight ≤ 2.2 g. To measure glove vibration transmissibility, the adapter is held with two gloved fingers; a finger is positioned on each side of the accelerometer. Each end of the adapter beam is slotted between the glove material and the finger. A series of experiments was conducted to evaluate this two-fingers-held adapter method by measuring the transmissibility of typical VR gloves and a sample VR material. The experimental results indicate that the major resonant frequency of the lightweight adapter on the VR material (≥800 Hz) is much higher than the resonant frequencies of the gloved fingers grasping a cylindrical handle (≤300 Hz). The experimental results were repeatable across the test treatments. The basic characteristics of the measured glove vibration transmissibility are consistent with the theoretical predictions based on the biodynamics of the gloved fingers-hand-arm system. The results suggest that VR glove fingers can effectively reduce only high-frequency vibration, and VR effectiveness can be increased by reducing the finger contact force. This study also demonstrated that the finger adapter method can be combined with the palm adapter method prescribed in the standardized glove test, which can double the test efficiency without substantially increasing the expense of the test.
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http://dx.doi.org/10.1016/j.measurement.2019.01.034DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6444365PMC
April 2019

Vibration characteristics of golf club heads in their handheld grinding process and potential approaches for reducing the vibration exposure.

Int J Ind Ergon 2017 Nov;62:27-41

Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, Wv, USA.

To control vibration-induced white finger among workers performing the fine grinding of golf club heads, the aims of this study are to clarify the major vibration sources in the grinding process, to identify and understand the basic characteristics of the club head vibration, and to propose potential approaches for reducing the vibration exposure. The vibrations on two typical club heads and two belt grinding machines were measured at a workplace. A simulated test station was also constructed and used to help examine some influencing factors of the club head vibration. This study found that the club head vibration was the combination of the vibration transmitted from the grinding machines and that generated in the grinding process. As a result, any factor that affects the machine vibration, the grinding vibration, and/or the dynamic response of the club head can influence the vibration exposure of the fingers or hands holding the club head in the grinding process. The significant influencing factors identified in the study include testing subject, grinding machine, machine operation speed, drive wheel condition, club head model, mechanical constraints imposed on the club head during the grinding, and machine foot pad. These findings suggest that the vibration exposure can be controlled by reducing the grinding machine vibration, changing the workpiece dynamic properties, and mitigating the vibration transmission in its pathway. Many potential methods for the control are proposed and discussed.

Relevance To Industry: Vibrations on handheld workpieces can be effectively transmitted to the hands, especially the fingers. As a result, a major component of the hand-arm vibration syndrome - vibration-induced white finger - has been observed among some workers performing the grinding and/or polishing tasks of the handheld workpieces such as golf club heads. The results of this study can be used to develop more effective methods and technologies to control the vibration exposure of these workers. This may help effectively control this occupational disease.
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http://dx.doi.org/10.1016/j.ergon.2016.08.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6275093PMC
November 2017

An evaluation of the contact forces on the fingers when squeezing a spherical rehabilitation ball.

Biomed Mater Eng 2018 ;29(5):629-639

National Institute for Occupational Safety and Health, Morgantown, WV, USA.

The rehabilitation squeeze ball is a popular device to help strengthen the hand, fingers and forearm muscles. The distributions of the contact pressure in the interface between the therapy ball and hand/fingers can affect the joint moment of each of the individual fingers, thereby affecting rehabilitation effects. In the current study, we evaluated the contact force distributions on the fingers when gripping a spherical object. Eight female adults [age 29 (9.1) years, mass 64.6 (7.1) kg, height 163.5 (1.9) cm, hand length 17.2 (0.7) cm] participated in the study. Contact force sensors were attached to the middle of the palmar surfaces of the distal, middle, and proximal phalanges of the four fingers in the longitudinal direction. In order to evaluate the effects of the ball stiffness on the contact force distributions on the fingers, subjects were requested to perform quasi-static gripping on a standard tennis ball and on a rehabilitation ball. The tennis ball is much stiffer and experiences smaller deformation under compression compared to the rehabilitation ball. We analyzed the force share among the distal, middle, and proximal finger segments, when subjects gripping balls of different stiffnesses (tennis ball vs. rehabilitation ball) and at three different grip efforts. Our results indicated that the grip force is contributed about 60% and 40% by the middle/ring fingers and by the index/little fingers, respectively. These characteristics are independent of the grip force levels and stiffness of the contact surface.
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http://dx.doi.org/10.3233/BME-181013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6388416PMC
February 2019

Vibrations transmitted from human hands to upper arm, shoulder, back, neck, and head.

Int J Ind Ergon 2017 Dec 22;62:1-12. Epub 2016 Jul 22.

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, USA.

Some powered hand tools can generate significant vibration at frequencies below 25 Hz. It is not clear whether such vibration can be effectively transmitted to the upper arm, shoulder, neck, and head and cause adverse effects in these substructures. The objective of this study is to investigate the vibration transmission from the human hands to these substructures. Eight human subjects participated in the experiment, which was conducted on a 1-D vibration test system. Unlike many vibration transmission studies, both the right and left hand-arm systems were simultaneously exposed to the vibration to simulate a working posture in the experiment. A laser vibrometer and three accelerometers were used to measure the vibration transmitted to the substructures. The apparent mass at the palm of each hand was also measured to help in understanding the transmitted vibration and biodynamic response. This study found that the upper arm resonance frequency was 7-12 Hz, the shoulder resonance was 7-9 Hz, and the back and neck resonances were 6-7 Hz. The responses were affected by the hand-arm posture, applied hand force, and vibration magnitude. The transmissibility measured on the upper arm had a trend similar to that of the apparent mass measured at the palm in their major resonant frequency ranges. The implications of the results are discussed.

Relevance To Industry: Musculoskeletal disorders (MSDs) of the shoulder and neck are important issues among many workers. Many of these workers use heavy-duty powered hand tools. The combined mechanical loads and vibration exposures are among the major factors contributing to the development of MSDs. The vibration characteristics of the body segments examined in this study can be used to help understand MSDs and to help develop more effective intervention methods.
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http://dx.doi.org/10.1016/j.ergon.2016.07.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5672949PMC
December 2017

The relationships between hand coupling force and vibration biodynamic responses of the hand-arm system.

Ergonomics 2018 Jun 17;61(6):818-830. Epub 2017 Nov 17.

a Engineering and Control Technology Branch, Health Effects Laboratory Division , National Institute for Occupational Safety and Health , Morgantown , WV , USA.

This study conducted two series of experiments to investigate the relationships between hand coupling force and biodynamic responses of the hand-arm system. In the first experiment, the vibration transmissibility on the system was measured as a continuous function of grip force while the hand was subjected to discrete sinusoidal excitations. In the second experiment, the biodynamic responses of the system subjected to a broadband random vibration were measured under five levels of grip forces and a combination of grip and push forces. This study found that the transmissibility at each given frequency increased with the increase in the grip force before reaching a maximum level. The transmissibility then tended to plateau or decrease when the grip force was further increased. This threshold force increased with an increase in the vibration frequency. These relationships remained the same for both types of vibrations. The implications of the experimental results are discussed. Practitioner Summary: Shocks and vibrations transmitted to the hand-arm system may cause injuries and disorders of the system. How to take hand coupling force into account in the risk assessment of vibration exposure remains an important issue for further studies. This study is designed and conducted to help resolve this issue.
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http://dx.doi.org/10.1080/00140139.2017.1398843DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6530558PMC
June 2018

Modeling of the interaction between grip force and vibration transmissibility of a finger.

Med Eng Phys 2017 07 9;45:61-70. Epub 2017 May 9.

Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.

It is known that the vibration characteristics of the fingers and hand and the level of grip action interacts when operating a power tool. In the current study, we developed a hybrid finger model to simulate the vibrations of the hand-finger system when gripping a vibrating handle covered with soft materials. The hybrid finger model combines the characteristics of conventional finite element (FE) models, multi-body musculoskeletal models, and lumped mass models. The distal, middle, and proximal finger segments were constructed using FE models, the finger segments were connected via three flexible joint linkages (i.e., distal interphalangeal joint (DIP), proximal interphalangeal joint (PIP), and metacarpophalangeal (MCP) joint), and the MCP joint was connected to the ground and handle via lumped parameter elements. The effects of the active muscle forces were accounted for via the joint moments. The bone, nail, and hard connective tissues were assumed to be linearly elastic whereas the soft tissues, which include the skin and subcutaneous tissues, were considered as hyperelastic and viscoelastic. The general trends of the model predictions agree well with the previous experimental measurements in that the resonant frequency increased from proximal to the middle and to the distal finger segments for the same grip force, that the resonant frequency tends to increase with increasing grip force for the same finger segment, especially for the distal segment, and that the magnitude of vibration transmissibility tends to increase with increasing grip force, especially for the proximal segment. The advantage of the proposed model over the traditional vibration models is that it can predict the local vibration behavior of the finger to a tissue level, while taking into account the effects of the active musculoskeletal force, the effects of the contact conditions on vibrations, the global vibration characteristics.
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http://dx.doi.org/10.1016/j.medengphy.2017.04.008DOI Listing
July 2017

Tool-specific performance of vibration-reducing gloves for attenuating fingers-transmitted vibration.

Occup Ergon 2016 ;13(1):23-44

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health, Morgantown, WV, USA.

Background: Fingers-transmitted vibration can cause vibration-induced white finger. The effectiveness of vibration-reducing (VR) gloves for reducing hand transmitted vibration to the fingers has not been sufficiently examined.

Objective: The objective of this study is to examine tool-specific performance of VR gloves for reducing finger-transmitted vibrations in three orthogonal directions (3D) from powered hand tools.

Methods: A transfer function method was used to estimate the tool-specific effectiveness of four typical VR gloves. The transfer functions of the VR glove fingers in three directions were either measured in this study or during a previous study using a 3D laser vibrometer. More than seventy vibration spectra of various tools or machines were used in the estimations.

Results: When assessed based on frequency-weighted acceleration, the gloves provided little vibration reduction. In some cases, the gloves amplified the vibration by more than 10%, especially the neoprene glove. However, the neoprene glove did the best when the assessment was based on unweighted acceleration. The neoprene glove was able to reduce the vibration by 10% or more of the unweighted vibration for 27 out of the 79 tools. If the dominant vibration of a tool handle or workpiece was in the shear direction relative to the fingers, as observed in the operation of needle scalers, hammer chisels, and bucking bars, the gloves did not reduce the vibration but increased it.

Conclusions: This study confirmed that the effectiveness for reducing vibration varied with the gloves and the vibration reduction of each glove depended on tool, vibration direction to the fingers, and finger location. VR gloves, including certified anti-vibration gloves do not provide much vibration reduction when judged based on frequency-weighted acceleration. However, some of the VR gloves can provide more than 10% reduction of the unweighted vibration for some tools or workpieces. Tools and gloves can be matched for better effectiveness for protecting the fingers.
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http://dx.doi.org/10.3233/OER-160235DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5113028PMC
January 2016

The Efficacy of Anti-vibration Gloves.

Acoust Aust 2016 Apr 3;44(1):121-127. Epub 2016 Feb 3.

Engineering & Control Technology Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.

Anyone seeking to control the risks from vibration transmitted to the hands and arms may contemplate the use of anti-vibration gloves. To make an informed decision about any type of personal protective equipment, it is necessary to have performance data that allow the degree of protection to be estimated. The information provided with an anti-vibration glove may not be easy to understand without some background knowledge of how gloves are tested and does not provide any clear route for estimating likely protection. Some of the factors that influence the potential efficacy of an anti-vibration glove include how risks from hand-arm vibration exposure are assessed, how the standard test for a glove is carried out, the frequency range and direction of the vibration for which protection is sought, how much hand contact force or pressure is applied and the physical limitations due to glove material and construction. This paper reviews some of the background issues that are useful for potential purchasers of anti-vibration gloves. Ultimately, anti-vibration gloves cannot be relied on to provide sufficient and consistent protection to the wearer and before their use is contemplated all other available means of vibration control ought first to be implemented.
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http://dx.doi.org/10.1007/s40857-015-0040-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5003016PMC
April 2016

Review and Evaluation of Hand-Arm Coordinate Systems for Measuring Vibration Exposure, Biodynamic Responses, and Hand Forces.

Saf Health Work 2015 Sep 19;6(3):159-73. Epub 2015 Jun 19.

Engineering & Control Technology Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, WV, USA.

The hand coordinate systems for measuring vibration exposures and biodynamic responses have been standardized, but they are not actually used in many studies. This contradicts the purpose of the standardization. The objectives of this study were to identify the major sources of this problem, and to help define or identify better coordinate systems for the standardization. This study systematically reviewed the principles and definition methods, and evaluated typical hand coordinate systems. This study confirms that, as accelerometers remain the major technology for vibration measurement, it is reasonable to standardize two types of coordinate systems: a tool-based basicentric (BC) system and an anatomically based biodynamic (BD) system. However, these coordinate systems are not well defined in the current standard. Definition of the standard BC system is confusing, and it can be interpreted differently; as a result, it has been inconsistently applied in various standards and studies. The standard hand BD system is defined using the orientation of the third metacarpal bone. It is neither convenient nor defined based on important biological or biodynamic features. This explains why it is rarely used in practice. To resolve these inconsistencies and deficiencies, we proposed a revised method for defining the realistic handle BC system and an alternative method for defining the hand BD system. A fingertip-based BD system for measuring the principal grip force is also proposed based on an important feature of the grip force confirmed in this study.
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http://dx.doi.org/10.1016/j.shaw.2015.05.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4674512PMC
September 2015

An examination of an adapter method for measuring the vibration transmitted to the human arms.

Measurement (Lond) 2015 Sep;73:318-334

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, USA.

The objective of this study is to evaluate an adapter method for measuring the vibration on the human arms. Four instrumented adapters with different weights were used to measure the vibration transmitted to the wrist, forearm, and upper arm of each subject. Each adapter was attached at each location on the subjects using an elastic cloth wrap. Two laser vibrometers were also used to measure the transmitted vibration at each location to evaluate the validity of the adapter method. The apparent mass at the palm of the hand along the forearm direction was also measured to enhance the evaluation. This study found that the adapter and laser-measured transmissibility spectra were comparable with some systematic differences. While increasing the adapter mass reduced the resonant frequency at the measurement location, increasing the tightness of the adapter attachment increased the resonant frequency. However, the use of lightweight (≤15 g) adapters under medium attachment tightness did not change the basic trends of the transmissibility spectrum. The resonant features observed in the transmissibility spectra were also correlated with those observed in the apparent mass spectra. Because the local coordinate systems of the adapters may be significantly misaligned relative to the global coordinates of the vibration test systems, large errors were observed for the adapter-measured transmissibility in some individual orthogonal directions. This study, however, also demonstrated that the misalignment issue can be resolved by either using the total vibration transmissibility or by measuring the misalignment angles to correct the errors. Therefore, the adapter method is acceptable for understanding the basic characteristics of the vibration transmission in the human arms, and the adapter-measured data are acceptable for approximately modeling the system.
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http://dx.doi.org/10.1016/j.measurement.2015.05.039DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4731869PMC
September 2015

Theoretical foundation, methods, and criteria for calibrating human vibration models using frequency response functions.

J Sound Vib 2015 Nov;356:195-216

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.

While simulations of the measured biodynamic responses of the whole human body or body segments to vibration are conventionally interpreted as summaries of biodynamic measurements, and the resulting models are considered quantitative, this study looked at these simulations from a different angle: model calibration. The specific aims of this study are to review and clarify the theoretical basis for model calibration, to help formulate the criteria for calibration validation, and to help appropriately select and apply calibration methods. In addition to established vibration theory, a novel theorem of mechanical vibration is also used to enhance the understanding of the mathematical and physical principles of the calibration. Based on this enhanced understanding, a set of criteria was proposed and used to systematically examine the calibration methods. Besides theoretical analyses, a numerical testing method is also used in the examination. This study identified the basic requirements for each calibration method to obtain a unique calibration solution. This study also confirmed that the solution becomes more robust if more than sufficient calibration references are provided. Practically, however, as more references are used, more inconsistencies can arise among the measured data for representing the biodynamic properties. To help account for the relative reliabilities of the references, a baseline weighting scheme is proposed. The analyses suggest that the best choice of calibration method depends on the modeling purpose, the model structure, and the availability and reliability of representative reference data.
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http://dx.doi.org/10.1016/j.jsv.2015.06.047DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4699322PMC
November 2015

An examination of the vibration transmissibility of the hand-arm system in three orthogonal directions.

Int J Ind Ergon 2015 Feb;45:21-34

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, USA.

The objective of this study is to enhance the understanding of the vibration transmission in the hand-arm system in three orthogonal directions (, and ). For the first time, the transmitted vibrations distributed on the entire hand-arm system exposed in the three orthogonal directions via a 3-D vibration test system were measured using a 3-D laser vibrometer. Seven adult male subjects participated in the experiment. This study confirms that the vibration transmissibility generally decreased with the increase in distance from the hand and it varied with the vibration direction. Specifically, to the upper arm and shoulder, only moderate vibration transmission was measured in the test frequency range (16 to 500 Hz), and virtually no transmission was measured in the frequency range higher than 50 Hz. The resonance vibration on the forearm was primarily in the range of 16-30 Hz with the peak amplitude of approximately 1.5 times of the input vibration amplitude. The major resonance on the dorsal surfaces of the hand and wrist occurred at around 30-40 Hz and, in the direction, with peak amplitude of more than 2.5 times of the input amplitude. At higher than 50 Hz, vibration transmission was effectively limited to the hand and fingers. A major finger resonance was observed at around 100 Hz in the and directions and around 200 Hz in the direction. In the fingers, the resonance magnitude in the direction was generally the lowest, and the resonance magnitude in the direction was generally the highest with the resonance amplitude of 3 times the input vibration, which was similar to the transmissibility at the wrist and hand dorsum. The implications of the results are discussed.

Relevance To Industry: Prolonged, intensive exposure to hand-transmitted vibration could result in hand-arm vibration syndrome. While the syndrome's precise mechanisms remain unclear, the characterization of the vibration transmissibility of the system in the three orthogonal dimensions performed in this study can help understand the syndrome and help develop improved frequency weightings for assessing the risk of the exposure for developing various components of the syndrome.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4666322PMC
http://dx.doi.org/10.1016/j.ergon.2014.11.001DOI Listing
February 2015

The Effect of a Mechanical Arm System on Portable Grinder Vibration Emissions.

Ann Occup Hyg 2016 Apr 30;60(3):371-86. Epub 2015 Nov 30.

Health Effects Laboratory Division, National Institute for Occupational Safety and Health (NIOSH), 1095 Willowdale Road, Morgantown, WV 26505, USA.

Mechanical arm systems are commonly used to support powered hand tools to alleviate ergonomic stressors related to the development of workplace musculoskeletal disorders. However, the use of these systems can increase exposure times to other potentially harmful agents such as hand-transmitted vibration. To examine how these tool support systems affect tool vibration, the primary objectives of this study were to characterize the vibration emissions of typical portable pneumatic grinders used for surface grinding with and without a mechanical arm support system at a workplace and to estimate the potential risk of the increased vibration exposure time afforded by the use of these mechanical arm systems. This study also developed a laboratory-based simulated grinding task based on the ISO 28927-1 (2009) standard for assessing grinder vibrations; the simulated grinding vibrations were compared with those measured during actual workplace grinder operations. The results of this study demonstrate that use of the mechanical arm may provide a health benefit by reducing the forces required to lift and maneuver the tools and by decreasing hand-transmitted vibration exposure. However, the arm does not substantially change the basic characteristics of grinder vibration spectra. The mechanical arm reduced the average frequency-weighted acceleration by about 24% in the workplace and by about 7% in the laboratory. Because use of the mechanical arm system can increase daily time-on-task by 50% or more, the use of such systems may actually increase daily time-weighted hand-transmitted vibration exposures in some cases. The laboratory acceleration measurements were substantially lower than the workplace measurements, and the laboratory tool rankings based on acceleration were considerably different than those from the workplace. Thus, it is doubtful that ISO 28927-1 is useful for estimating workplace grinder vibration exposures or for predicting workplace grinder acceleration rank orders.
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http://dx.doi.org/10.1093/annhyg/mev084DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4779390PMC
April 2016

Laboratory and workplace assessments of rivet bucking bar vibration emissions.

Ann Occup Hyg 2015 Apr 7;59(3):382-97. Epub 2014 Nov 7.

National Institute for Occupational Safety and Health (NIOSH), Health Effects Lab, 1095 Willowdale Road, Morgantown, WV 26505, USA.

Sheet metal workers operating rivet bucking bars are at risk of developing hand and wrist musculoskeletal disorders associated with exposures to hand-transmitted vibrations and forceful exertions required to operate these hand tools. New bucking bar technologies have been introduced in efforts to reduce workplace vibration exposures to these workers. However, the efficacy of these new bucking bar designs has not been well documented. While there are standardized laboratory-based methodologies for assessing the vibration emissions of many types of powered hand tools, no such standard exists for rivet bucking bars. Therefore, this study included the development of a laboratory-based method for assessing bucking bar vibrations which utilizes a simulated riveting task. With this method, this study evaluated three traditional steel bucking bars, three similarly shaped tungsten alloy bars, and three bars featuring spring-dampeners. For comparison the bucking bar vibrations were also assessed during three typical riveting tasks at a large aircraft maintenance facility. The bucking bars were rank-ordered in terms of unweighted and frequency-weighted acceleration measured at the hand-tool interface. The results suggest that the developed laboratory method is a reasonable technique for ranking bucking bar vibration emissions; the lab-based riveting simulations produced similar rankings to the workplace rankings. However, the laboratory-based acceleration averages were considerably lower than the workplace measurements. These observations suggest that the laboratory test results are acceptable for comparing and screening bucking bars, but the laboratory measurements should not be directly used for assessing the risk of workplace bucking bar vibration exposures. The newer bucking bar technologies exhibited significantly reduced vibrations compared to the traditional steel bars. The results of this study, together with other information such as rivet quality, productivity, tool weight, comfort, worker acceptance, and initial cost can be used to make informed bucking bar selections.
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http://dx.doi.org/10.1093/annhyg/meu091DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4733632PMC
April 2015

Anti-vibration gloves?

Ann Occup Hyg 2015 Mar 7;59(2):127-41. Epub 2014 Nov 7.

Engineering and Control Technology Branch, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.

For exposure to hand-transmitted vibration (HTV), personal protective equipment is sold in the form of anti-vibration (AV) gloves, but it remains unclear how much these gloves actually reduce vibration exposure or prevent the development of hand-arm vibration syndrome in the workplace. This commentary describes some of the issues that surround the classification of AV gloves, the assessment of their effectiveness and their applicability in the workplace. The available information shows that AV gloves are unreliable as devices for controlling HTV exposures. Other means of vibration control, such as using alternative production techniques, low-vibration machinery, routine preventative maintenance regimes, and controlling exposure durations are far more likely to deliver effective vibration reductions and should be implemented. Furthermore, AV gloves may introduce some adverse effects such as increasing grip force and reducing manual dexterity. Therefore, one should balance the benefits of AV gloves and their potential adverse effects if their use is considered.
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http://dx.doi.org/10.1093/annhyg/meu089DOI Listing
March 2015

Tool-specific performance of vibration-reducing gloves for attenuating palm-transmitted vibrations in three orthogonal directions.

Int J Ind Ergon 2014 Nov;44(6):827-839

Biodynamics Laboratory, University of Connecticut Health Center, Farmington, CT 06030-2017, USA.

Vibration-reducing (VR) gloves have been increasingly used to help reduce vibration exposure, but it remains unclear how effective these gloves are. The purpose of this study was to estimate tool-specific performances of VR gloves for reducing the vibrations transmitted to the palm of the hand in three orthogonal directions (3-D) in an attempt to assess glove effectiveness and aid in the appropriate selection of these gloves. Four typical VR gloves were considered in this study, two of which can be classified as anti-vibration (AV) gloves according to the current AV glove test standard. The average transmissibility spectrum of each glove in each direction was synthesized based on spectra measured in this study and other spectra collected from reported studies. More than seventy vibration spectra of various tools or machines were considered in the estimations, which were also measured in this study or collected from reported studies. The glove performance assessments were based on the percent reduction of frequency-weighted acceleration as is required in the current standard for assessing the risk of vibration exposures. The estimated tool-specific vibration reductions of the gloves indicate that the VR gloves could slightly reduce (<5%) or marginally amplify (<10%) the vibrations generated from low-frequency (<25 Hz) tools or those vibrating primarily along the axis of the tool handle. With other tools, the VR gloves could reduce palm-transmitted vibrations in the range of 5%-58%, primarily depending on the specific tool and its vibration spectra in the three directions. The two AV gloves were not more effective than the other gloves with some of the tools considered in this study. The implications of the results are discussed.

Relevance To Industry: Hand-transmitted vibration exposure may cause hand-arm vibration syndrome. Vibration-reducing gloves are considered as an alternative approach to reduce the vibration exposure. This study provides useful information on the effectiveness of the gloves when used with many tools for reducing the vibration transmitted to the palm in three directions. The results can aid in the appropriate selection and use of these gloves.
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http://dx.doi.org/10.1016/j.ergon.2014.09.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4696608PMC
November 2014

Analysis of the effects of surface stiffness on the contact interaction between a finger and a cylindrical handle using a three-dimensional hybrid model.

Med Eng Phys 2014 Jul 13;36(7):831-41. Epub 2014 Apr 13.

National Institute for Occupational Safety and Health, Morgantown, WV, USA.

Contact interactions between the hand and handle, such as the contact surface softness and contact surface curvature, will affect both physical effort and musculoskeletal fatigue, thereby the comfort and safety of power tool operations. Previous models of hand gripping can be categorized into two groups: multi-body dynamic models and finite element (FE) models. The goal of the current study is to develop a hybrid FE hand gripping model, which combines the features of conventional FE models and multi-body dynamic models. The proposed model is applied to simulate hand-gripping on a cylindrical handle with covering materials of different softness levels. The model included three finger segments (distal, middle, and proximal phalanxes), three finger joints (the distal interphalangeal (DIP), proximal interphalangeal (PIP), and metacarpophalangeal (MCP) joint), and major anatomical substructures. The model was driven by joint moments, which are the net effects of all passive and active muscular forces acting about the joints. The finger model was first calibrated by using experimental data of human subject tests, and then applied to investigate the effects of surface softness on contact interactions between a finger and a cylindrical handle. Our results show that the maximal compressive stress and strain in the soft tissues of the fingers can be effectively reduced by reducing the stiffness of the covering material.
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http://dx.doi.org/10.1016/j.medengphy.2014.03.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4573534PMC
July 2014

An examination of the handheld adapter approach for measuring hand-transmitted vibration exposure.

Measurement ( Mahwah N J) 2014 Jan;47:64-77

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health, 1095 Willowdale Road, Morgantown, WV 26505, USA.

The use of a handheld adapter equipped with a tri-axial accelerometer is the most convenient and efficient approach for measuring vibration exposure at the hand-tool interface, especially when the adapter is incorporated into a miniature handheld or wrist-strapped dosimeter. To help optimize the adapter approach, the specific aims of this study are to identify and understand the major sources and mechanisms of measurement errors and uncertainties associated with using these adapters, and to explore their improvements. Five representative adapter models were selected and used in the experiment. Five human subjects served as operators in the experiment on a hand-arm vibration test system. The results of this study confirm that many of the handheld adapters can produce substantial overestimations of vibration exposure, and measurement errors can significantly vary with tool, adapter model, mounting position, mounting orientation, and subject. Major problems with this approach include unavoidable influence of the hand dynamic motion on the adapter, unstable attachment, insufficient attachment contact force, and inappropriate adapter structure. However, the results of this study also suggest that measurement errors can be substantially reduced if the design and use of an adapter can be systematically optimized toward minimizing the combined effects of the identified factors. Some potential methods for improving the design and use of the adapters are also proposed and discussed.
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http://dx.doi.org/10.1016/j.measurement.2013.08.037DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4701056PMC
January 2014

The effects of vibration-reducing gloves on finger vibration.

Int J Ind Ergon 2014 Jan;44(1):45-59

Engineering and Control Technology Branch, HELD, National Institute for Occupational Safety and Health, CDC, MS L-2027, 1095 Willowdale Road, Morgantown, WV 26505, USA.

Vibration-reducing (VR) gloves have been used to reduce the hand-transmitted vibration exposures from machines and powered hand tools but their effectiveness remains unclear, especially for finger protection. The objectives of this study are to determine whether VR gloves can attenuate the vibration transmitted to the fingers and to enhance the understanding of the mechanisms of how these gloves work. Seven adult male subjects participated in the experiment. The fixed factors evaluated include hand force (four levels), glove condition (gel-filled, air bladder, no gloves), and location of the finger vibration measurement. A 3-D laser vibrometer was used to measure the vibrations on the fingers with and without wearing a glove on a 3-D hand-arm vibration test system. This study finds that the effect of VR gloves on the finger vibration depends on not only the gloves but also their influence on the distribution of the finger contact stiffness and the grip effort. As a result, the gloves increase the vibration in the fingertip area but marginally reduce the vibration in the proximal area at some frequencies below 100 Hz. On average, the gloves reduce the vibration of the entire fingers by less than 3% at frequencies below 80 Hz but increase at frequencies from 80 to 400 Hz. At higher frequencies, the gel-filled glove is more effective at reducing the finger vibration than the air bladder-filled glove. The implications of these findings are discussed.

Relevance To Industry: Prolonged, intensive exposure to hand-transmitted vibration can cause hand-arm vibration syndrome. Vibration-reducing gloves have been used as an alternative approach to reduce the vibration exposure. However, their effectiveness for reducing finger-transmitted vibrations remains unclear. This study enhanced the understanding of the glove effects on finger vibration and provided useful information on the effectiveness of typical VR gloves at reducing the vibration transmitted to the fingers. The new results and knowledge can be used to help select appropriate gloves for the operations of powered hand tools, to help perform risk assessment of the vibration exposure, and to help design better VR gloves.
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http://dx.doi.org/10.1016/j.ergon.2013.10.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4630214PMC
January 2014

Analysis of the musculoskeletal loading of the thumb during pipetting--a pilot study.

J Biomech 2014 Jan 15;47(2):392-9. Epub 2013 Nov 15.

National Institute for Occupational Safety & Health, Morgantown, WV 26505, USA.

Previous epidemiological studies indicate that the use of thumb-push mechanical pipettes is associated with musculoskeletal disorders (MSDs) in the hand. The goal of the current study was to analyze the loading in the muscle-tendon units in the thumb during pipetting. The hand is modeled as a multi-body linkage system and includes four fingers (index, long, ring, and little finger), a thumb, and a palm segment. Since the current study is focused on the thumb, the model includes only nine muscles attached to the thumb via tendons. The time-histories of joint angles and push force at the pipette plunger during pipetting were determined experimentally and used as model input; whereas forces in the muscle-tendon units in the thumb were calculated via an inverse dynamic approach combined with an optimization procedure. Results indicate that all nine muscles have force outputs during pipetting, and the maximal force was in the abductor pollicis brevis (APB). The ratio of the mean peak muscle force to the mean peak push force during the dispensing cycle was approximately 2.3, which is comparable to values observed in grasping tasks in the literature. The analysis method and results in the current study provide a mechanistic understanding of MSD risk factors associated with pipetting, and may be useful in guiding ergonomic designs for manual pipettes.
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http://dx.doi.org/10.1016/j.jbiomech.2013.11.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4782592PMC
January 2014

Theoretical relationship between vibration transmissibility and driving-point response functions of the human body.

J Sound Vib 2013 Nov;332(24):6193-6202

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.

The relationship between the vibration transmissibility and driving-point response functions (DPRFs) of the human body is important for understanding vibration exposures of the system and for developing valid models. This study identified their theoretical relationship and demonstrated that the sum of the DPRFs can be expressed as a linear combination of the transmissibility functions of the individual mass elements distributed throughout the system. The relationship is verified using several human vibration models. This study also clarified the requirements for reliably quantifying transmissibility values used as references for calibrating the system models. As an example application, this study used the developed theory to perform a preliminary analysis of the method for calibrating models using both vibration transmissibility and DPRFs. The results of the analysis show that the combined method can theoretically result in a unique and valid solution of the model parameters, at least for linear systems. However, the validation of the method itself does not guarantee the validation of the calibrated model, because the validation of the calibration also depends on the model structure and the reliability and appropriate representation of the reference functions. The basic theory developed in this study is also applicable to the vibration analyses of other structures.
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http://dx.doi.org/10.1016/j.jsv.2013.07.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4671508PMC
November 2013

Vibration-reducing gloves: transmissibility at the palm of the hand in three orthogonal directions.

Ergonomics 2013 25;56(12):1823-40. Epub 2013 Oct 25.

a Health Effects Laboratory Division (HELD) , National Institute for Occupational Safety and Health (NIOSH) , Morgantown , WV , USA.

Vibration-reducing (VR) gloves are commonly used as a means to help control exposures to hand-transmitted vibrations generated by powered hand tools. The objective of this study was to characterise the vibration transmissibility spectra and frequency-weighted vibration transmissibility of VR gloves at the palm of the hand in three orthogonal directions. Seven adult males participated in the evaluation of seven glove models using a three-dimensional hand-arm vibration test system. Three levels of hand coupling force were applied in the experiment. This study found that, in general, VR gloves are most effective at reducing vibrations transmitted to the palm along the forearm direction. Gloves that are found to be superior at reducing vibrations in the forearm direction may not be more effective in the other directions when compared with other VR gloves. This casts doubts on the validity of the standardised glove screening test. Practitioner Summary: This study used human subjects to measure three-dimensional vibration transmissibility of vibration-reducing gloves at the palm and identified their vibration attenuation characteristics. This study found the gloves to be most effective at reducing vibrations along the forearm direction. These gloves did not effectively attenuate vibration along the handle axial direction.
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http://dx.doi.org/10.1080/00140139.2013.838642DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4592941PMC
August 2014

The musculoskeletal loading profile of the thumb during pipetting based on tendon displacement.

Med Eng Phys 2013 Dec 6;35(12):1801-10. Epub 2013 Sep 6.

National Institute for Occupational Safety & Health, Morgantown, WV 26505, USA. Electronic address:

Strong evidence indicates that highly repetitive manual work is associated with the development of upper extremity musculoskeletal disorders (MSDs). One of the occupational activities that involves highly repetitive and forceful hand work is manual pipetting in chemical or biological laboratories. In the current study, we quantified tendon displacement as a parameter to assess the cumulative loading exposure of the musculoskeletal system in the thumb during pipetting. The maximal tendon displacement was found in the flexor pollicis longus (FPL) tendon. Assuming that subjects' pipetting rates were maintained constant during a period of 1 h, the average accumulated tendon displacement in the FPL reached 29 m, which is in the lower range of those observed in other occupational activities, such as typing and nail gun operations. Our results showed that tendon displacement data contain relatively small standard deviations, despite high variances in thumb kinematics, suggesting that the tendon displacements may be useful in evaluating the musculoskeletal loading profile.
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http://dx.doi.org/10.1016/j.medengphy.2013.08.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5014230PMC
December 2013

Modeling of the biodynamic responses distributed at the fingers and palm of the hand in three orthogonal directions.

J Sound Vib 2013 Feb;232(4):1125-1140

Engineering & Control Technology Branch, National Institute for Occupational Safety and Health Morgantown, WV 26505, USA.

The objectives of this study were to develop models of the hand-arm system in the three orthogonal directions ( , and ) and to enhance the understanding of the hand vibration dynamics. A four-degrees-of-freedom (DOF) model and 5-DOF model were used in the simulation for each direction. The driving-point mechanical impedances distributed at the fingers and palm of the hand reported in a previous study were used to determine the parameters of the models. The 5-DOF models were generally superior to the 4-DOF models for the simulation. Hence, as examples of applications, the 5-DOF models were used to predict the transmissibility of a vibration-reducing glove and the vibration transmissibility on the major substructures of the hand-arm system. The model-predicted results were also compared with the experimental data reported in two other recent studies. Some reasonable agreements were observed in the comparisons, which provided some validation of the developed models. This study concluded that the 5-DOF models are acceptable for helping to design and analyze vibrating tools and anti-vibration devices. This study also confirmed that the 5-DOF model in the direction is acceptable for a coarse estimation of the biodynamic responses distributed throughout the major substructures of the hand-arm system. Some interesting phenomena observed in the experimental study of the biodynamic responses in the three directions were also explained in this study.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4656148PMC
http://dx.doi.org/10.1016/j.jsv.2012.10.003DOI Listing
February 2013

A proposed theory on biodynamic frequency weighting for hand-transmitted vibration exposure.

Ind Health 2012 ;50(5):412-24

Engineering and Control Technology Branch, National Institute for Occupational Safety and Health, USA.

The objective of this study is to propose a theory on the biodynamic frequency weighting for studying hand-transmitted vibration exposures and vibration-induced effects. We hypothesize that the development of a vibration effect is the result of two consecutive but synergistic processes: biodynamic responses to input vibration and biological responses to the biomechanical stimuli resulting from the biodynamic responses. Hence, we further hypothesize that the frequency-dependency (W) of the effect generally includes two components: a biodynamic frequency weighting (W1) and a biological frequency weighting (W2), or W=W1• W2. These hypotheses are consistent with the stress and strain analysis theory and methods widely used in structural dynamics and biomechanics. The factorization may make it easier to study the complex frequency-dependency using different approaches: the biodynamic frequency weighting depends on the passive physical response of the system to vibration, and it can thus be determined by examining the biodynamic response of the system using various engineering methods; on the other hand, the biological frequency weighting depends on the biological mechanisms of the effects, and it can be investigated by studying the psychophysical, physiological, and pathological responses. To help test these hypotheses, this study reviewed and further developed methods to derive the finger biodynamic frequency weighting. As a result, preliminary finger biodynamic frequency weightings are proposed. The implications of the proposed theory and the preliminary biodynamic frequency weightings are also discussed.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4684643PMC
http://dx.doi.org/10.2486/indhealth.ms1380DOI Listing
April 2013

Frequency-dependent effects of vibration on physiological systems: experiments with animals and other human surrogates.

Ind Health 2012 ;50(5):343-53

Engineering and Controls Technology Branch, National Institute for Occupational Safety and Health, USA.

Occupational exposure to vibration through the use of power- and pneumatic hand-tools results in cold-induced vasospasms, finger blanching, and alterations in sensorineural function. Collectively, these symptoms are referred to as hand-arm vibration syndrome (HAVS). Currently the International Standards Organization (ISO) standard ISO 5349-1 contains a frequency-weighting curve to help workers and employers predict the risk of developing HAVS with exposure to vibration of different frequencies. However, recent epidemiological and experimental evidence suggests that this curve under-represents the risk of injuries to the hands and fingers induced by exposure to vibration at higher frequencies (>100 Hz). To improve the curve, better exposure-response data need to be collected. The goal of this review is to summarize the results of animal and computational modeling studies that have examined the frequency-dependent effects of vibration, and discuss where additional research would be beneficial to fill these research gaps.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4694567PMC
http://dx.doi.org/10.2486/indhealth.ms1378DOI Listing
April 2013

Assessment of hand-transmitted vibration exposure from motorized forks used for beach-cleaning operations.

Ann Occup Hyg 2013 Jan 5;57(1):43-53. Epub 2012 Sep 5.

Health Effects Laboratory Division, National Institute for Occupational Safety & Health, Morgantown, WV, USA.

Unlabelled: Motorized vibrating manure forks were used in beach-cleaning operations following the massive Deepwater Horizon oil spill in the Gulf of Mexico during the summer of 2010.

Objectives: The objectives of this study were to characterize the vibration emissions of these motorized forks and to provide a first approximation of hand-transmitted vibration exposures to workers using these forks for beach cleaning.

Methods: Eight operators were recruited to operate the motorized forks during this laboratory study. Four fork configurations were used in the study; two motor speeds and two fork basket options were evaluated. Accelerations were measured near each hand as the operators completed the simulated beach-cleaning task.

Results: The dominant vibration frequency for these tools was identified to be around 20 Hz. Because acceleration was found to increase with motor speed, workers should consider operating these tools with just enough speed to get the job done. These forks exhibited considerable acceleration magnitudes when unloaded.

Conclusions: The study results suggest that the motor should not be operated with the fork in the unloaded state. Anti-vibration gloves are not effective at attenuating the vibration frequencies produced by these forks, and they may even amplify the transmitted vibration and increase hand/arm fatigue. While regular work gloves are suitable, vibration-reducing gloves may not be appropriate for use with these tools. These considerations may also be generally applicable for the use of motorized forks in other workplace environments.
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http://dx.doi.org/10.1093/annhyg/mes049DOI Listing
January 2013

Laboratory and field measurements and evaluations of vibration at the handles of riveting hammers.

Ann Occup Hyg 2012 Oct 26;56(8):911-24. Epub 2012 Apr 26.

NIOSH Health Effects Laboratory, National Institute for Occupational Safety and Health, Morgantown, WV 26505, USA.

The use of riveting hammers can expose workers to harmful levels of hand-transmitted vibration (HTV). As a part of efforts to reduce HTV exposures through tool selection, the primary objective of this study was to evaluate the applicability of a standardized laboratory-based riveting hammer assessment protocol for screening riveting hammers. The second objective was to characterize the vibration emissions of reduced vibration riveting hammers and to make approximations of the HTV exposures of workers operating these tools in actual work tasks. Eight pneumatic riveting hammers were selected for the study. They were first assessed in a laboratory using the standardized method for measuring vibration emissions at the tool handle. The tools were then further assessed under actual working conditions during three aircraft sheet metal riveting tasks. Although the average vibration magnitudes of the riveting hammers measured in the laboratory test were considerably different from those measured in the field study, the rank orders of the tools determined via these tests were fairly consistent, especially for the lower vibration tools. This study identified four tools that consistently exhibited lower frequency-weighted and unweighted accelerations in both the laboratory and workplace evaluations. These observations suggest that the standardized riveting hammer test is acceptable for identifying tools that could be expected to exhibit lower vibrations in workplace environments. However, the large differences between the accelerations measured in the laboratory and field suggest that the standardized laboratory-based tool assessment is not suitable for estimating workplace riveting hammer HTV exposures. Based on the frequency-weighted accelerations measured at the tool handles during the three work tasks, the sheet metal mechanics assigned to these tasks at the studied workplace are unlikely to exceed the daily vibration exposure action value (2.5 m s(-2)) using any of the evaluated riveting hammers.
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http://dx.doi.org/10.1093/annhyg/mes022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4677776PMC
October 2012

Evaluation of anti-vibration effectiveness of glove materials using an animal model.

Biomed Mater Eng 2011 ;21(4):193-211

National Institute for Occupational Safety and Health, Morgantown, WV, USA.

Gloves with anti-vibration features are increasingly used to reduce impact vibrations or shocks transmitted to the hands of power tool operators. Selection and evaluation of the glove materials are important steps in the designs of such gloves. In the current study, we proposed an approach to objectively evaluate the effectiveness of the glove materials using a rat-tail impact model. As a critical part of a systematic investigation, we examined the vibration reduction characteristics of typical resilient glove materials (air bladders and viscoelastic gels) and the impact vibrations transmitted to the rat tail. A special test platform that mimics impact tool vibrations was constructed and used in the experiment. A scanning laser vibrometer was used to measure the vibration at points across the platform surface under several different test conditions. The peak acceleration was found to be greatly attenuated by the glove materials, especially by using strips from a gel-filled glove. The rat tail was found to effectively absorb the high-frequency vibration. However, the glove materials and the rat tail did not reduce the frequency-weighted acceleration. The implications of the experimental results are discussed.
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http://dx.doi.org/10.3233/BME-2011-0669DOI Listing
April 2012
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