Distributed vibration power absorption of the human hand-arm system in different postures coupled with vibrating handle and power tools

This study presents vibration power absorption (VPA) of different hand-arm substructures in the bent-arm and extended arm postures excited by broadband random and power tool vibrations. VPAs are estimated using biomechanical models of the hand-arm system derived from both the driving-point mechanical impedance and distributed vibration transmissibility. VPAs due to the vibrations of selected hand-held power tools are also estimated. The results show that distributed VPAs of the arms are greater below 25 Hz than those of the hand (fingers and palm) for both postures, while the hand VPAs are greater above 100 Hz, although the values are smaller than those below 25 Hz. The power absorbed during the extended arm posture is about 2.5 times greater than the power absorbed with the bent-arm posture for similar hand forces and vibration magnitude. Similar trends are observed in distributed VPAs due to broadband random as well as typical tool excitations, while the VPA due to tool vibration revealed peaks near the operating frequencies of the power tools and their harmonics. Furthermore, the percentage of power absorbed in different hand-arm substructures was dependent on the operating speed of the power tools, the higher the operating speed the higher the power absorbed in the hand and vice versa. The results showed relatively lower VPA values in the fingers and palm in the 60–160 Hz range than those obtained for the arms in the 5–16 Hz range. The study revealed the need for different frequency weightings for assessment of potential injury risk of different hand-arm substructures.Relevance to industryOperators of hand-held power tools are exposed to hand-transmitted vibration and the associated potential injuries. This study showed that the extended arm posture should be avoided when operating hand-held power tools because large vibration power is absorbed in the human hand-arm system, which may cause hand-arm injury.     

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

The objective of this study is to enhance the understanding of the vibration transmission in the hand-arm system in three orthogonal directions (X, Y, and Z). 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 Y 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 X and Y directions and around 200 Hz in the Z direction. In the fingers, the resonance magnitude in the Z direction was generally the lowest, and the resonance magnitude in the Y 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 industryProlonged, 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.     

An analytical investigation of an energy flow divider to attenuate hand-transmitted vibration

A five-degrees-of-freedom (DOF) bio-mechanical model of the hand-arm system is developed to study the vibration transmissibility characteristics of the human hand-arm. The model parameters are identified from the characteristics of vibration transmitted to the hand, forearm and upper arm, measured in the 10–200 Hz frequency range under a constant 25.0 N grip force. A concept of an energy flow divider is proposed to reduce the flow of vibration energy into the hand. The coupled hand-arm-divider is modeled as a six-DOF dynamical system and the response characteristics are evaluated for handle excitations caused by a palm-grip orbital sander. The response characteristics of the coupled hand-arm-divider model are compared to those of the hand-arm model to demonstrate the potential performance benefits of the proposed energy flow divider. The hand-transmitted vibration is further assessed using the overall weighted acceleration response, and it is concluded that the proposed energy flow divider can reduce the magnitude of hand-transmitted vibration considerably.     

The vibration transmissibility and driving-point biodynamic response of the hand exposed to vibration normal to the palm

Prolonged, intensive exposure to vibrations from palm and orbital sanders could cause finger disorders. They are likely to be associated with the biodynamic responses of the fingers. Although the biodynamic responses of the hand-arm system have been studied by many researchers, the detailed biodynamic responses distributed in the hand substructures have not been sufficiently understood. To advance the knowledge in this aspect and to aid in the development of improved finite element models of the substructures, this study simultaneously measured the overall driving-point biodynamic response and the distribution of vibration transmissibility at the fingers and back of the hand exposed to a flat plate vibration (as an approximate simulation of the operations of the palm and orbital sanders) and examined the relationship between these two measures of biodynamic responses. Ten subjects (five males and five females) participated in the experiment. A scanning laser vibrometer was used to measure the distributed vibration. This study confirmed that the distributed hand responses generally varied with locations on each finger, vibration frequencies, and applied hand force. Two major resonances were observed in the vibration transmissibility. At the first resonance, the transmitted vibrations at different locations were more or less in phase; hence, this resonance was also observed in the driving-point biodynamic response that measures the overall biodynamic response of the system. The second resonance was observed at the fingers. Because this resonant frequency varied greatly among the fingers and the specific segments of each finger, it is difficult to identify this resonance in the driving-point biodynamic response. The implications of the findings for further model developments and applications are discussed.

Relevance to industry

This study enhanced the understanding of the biodynamic responses of the fingers and hand exposed to vibrations on a contact surface with a large effective radius such as that found on palm and orbital sanders. The results can also be used to develop and/or validate models of the substructures of the hand-arm system, which can be further used to help design and analyze these tools and associated anti-vibration devices. The results may also be applicable to help develop location-specific frequency weightings to assess the risks of the finger vibration exposure.     

Experimental Investigation To Study the Influence of Handle Diameter on Low‐Frequency,Hand–Arm Vertical Vibration

Handle vibration from equipment or machines influences musculoskeletal activity as well as comfort in handling the same. New technology can be worse than no technology if it was not developed correctly as ergonomic research has clearly demonstrated the relationship between injury risk and poorly designed hand tools. Clinical and epidemiological studies have shown that operators of handheld power tools are prone to develop various vibration‐induced disorders of the hand and arm, which are collectively referred to as “hand–arm vibration syndrome.'' The vibration direction has a great influence on the transmitted vibration. The present study focuses the effects of low‐frequency vertical vibration on hand to shoulder from handles of different size. The electrodynamic exciter is used for simulating vibration to a vertical handles of four different diameters. PULSE LabShop software is used for evaluating the magnitude of vibration in different frequency bands. The vibration characteristic data were acquired in the y_h axis at the wrist, elbow, and shoulder for bent arm and extended arm postures with vibration excitation of 4.5 m/s². Transmissibility characteristics are computed to determine the influence of handle diameter in y_h vibration transmitted to the hand–arm system. The magnitude of vibration transmitted within the hand, elbow, and shoulder was observed to be dependent on the handle size; larger handles cause higher vibration transmissibility. The results also show that the human hand–arm system in an extended arm posture amplifies the vibration transmitted than bent arm in a small difference. © 2011 Wiley Periodicals, Inc.     

The effects of vibration-reducing gloves on finger vibration

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.     

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

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 industryHand-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.     

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

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.     

The effects of shoulder posture on neck and shoulder musculoskeletal loading and discomfort during smartphone usage

While using their smartphone, users tend to adopt awkward neck and shoulder postures for an extended duration. Such postures impose the risk of MSDs on those body parts. Numerous studies have been undertaken to examine neck posture; however, few studies have investigated shoulder postures. This study examined various shoulder postures during smartphone use and their effect on neck and shoulder kinematics, muscle loading, and neck/shoulder discomfort. Thirty-two asymptomatic young adult smartphone users randomly performed texting tasks for 3 min at four different shoulder flexion angles (15°, 30°, 45°, and 60°), while maintained a neck posture in the neutral position (0° neck flexion angle). Measures were taken of neck and shoulder muscle activity of the cervical erector spinae (CES), anterior deltoid (AD), upper trapezius (UT) and lower trapezius (LT), and kinematic data (angle, distance and gravitational moment). Results showed AD and LT muscle activity significantly increased when the shoulder flexion angle increased with an opposite effect on CES and UT. A recommended shoulder posture was identified as 30° flexion, as this yielded the best compromise between activation levels of the four muscles studied. This angle also induced the lowest neck/shoulder discomfort score. The findings suggest smartphone users hold their device at approximately 30° shoulder flexion angle with their neck in a neutral posture to reduce the risk of shoulder and neck musculoskeletal disorders when smartphone texting.Relevance to industrySmartphone use in the manufacturing and service industries is an integral part of work and useful means of communication tool. Awkward postures during extensive smartphone use impose an increased risk of both neck and shoulder musculoskeletal disorders. Shoulder flexion angles need consideration when making recommendations about safe work postures during smartphone use.     

Subjective response of standing persons exposed to fore-aft,lateral and vertical whole-body vibration

The aims of this study were to propose multiply scale factors for evaluation of discomfort of standing persons and to investigate whether there exist differences between multiplying factors used for evaluation of discomfort of standing persons and those of seated persons exposed to WBV. Twelve male subjects were exposed to twenty-seven stimuli that comprise three acceleration magnitudes (0.2, 0.4, and 0.8 m/s² r.m.s.) along fore-aft (x), lateral (y) or vertical (z) direction. The subjects with seated or standing posture on the platform of the vibration test rig rated the subjective discomfort for each stimulus that has frequency contents ranging from 1.0 Hz to 20 Hz with a constant power spectrum density. The order of presentation of the test stimuli was fully randomized and each stimulus was repeated three times. The subjective scale for discomfort was calculated by using the category judgment method. The best combinations of multiplying factors were determined by calculating correlation coefficients of regression curves in-between subjective ratings and vibration magnitudes. In all the directions, body posture significantly influenced on subjective discomfort scales. Particularly in the fore-aft and lateral direction, the upper limit of all the categories for the standing posture resulted in higher vibration acceleration magnitudes than those for the seated posture. In contrast, in the vertical direction, only the upper limit of category “1: Not uncomfortable” for standing posture was observed to be higher than that for seated posture. The best agreement for ISO-weighted vibration acceleration occurred at x factor of 1.8 and y factor of 1.8 in the standing posture and x factor of 2.8 and y factor of 1.8 in the seated posture. The results suggest that seated people respond more sensitively and severely in perception of discomfort to fore-aft and lateral vibration than standing people do while standing people respond more sensitively and severely to vertical vibration than seated people do. Thus the effects of body postures on multiplying factors should be considered in evaluation of discomfort caused by whole-body vibration.Relevance to industryThis study reports differences in subjective response of standing persons to fore-aft, lateral and vertical whole-body vibration. The results obtained in this study propose the fundamental data on the sensitivity to whole-body vibration exposed with standing posture.     

Validity and inter-observer reliability of subjective hand-arm vibration assessments

Exposure to mechanical vibrations at work (e.g., due to handling powered tools) is a potential occupational risk as it may cause upper extremity complaints. However, reliable and valid assessment methods for vibration exposure at work are lacking. Measuring hand-arm vibration objectively is often difficult and expensive, while often used information provided by manufacturers lacks detail. Therefore, a subjective hand-arm vibration assessment method was tested on validity and inter-observer reliability.     

Development of a new frequency weighting filter for the assessment of grinder exposure to wrist-transmitted vibration

The risk assessment of hand tool workers exposed to hand-arm vibrations is still problematic. It is based, accordingly to ISO 5349, on a frequency-weighted measurement recorded at the handle of the tool. Unfortunately, the frequency-weighted filter recommended by ISO 5349 does not take into account any amplification of the hand-arm system and underestimates the global rms acceleration transmitted to the hand. In this study, the vibration transmitted from the tool handle to the worker's wrist is investigated in an industrial environment for seven commercial grinders, two subjects and three push forces. The results are compared with the ISO-5349 and ACGIH threshold limit values, and a new frequency weighting filter is proposed, by which the amplification close to the natural frequencies of the hand-arm system can be considered in the evaluation of the vibration transmitted to the wrist from vibration measurements at the tool handle in a grinding operation.     

Influence of reading format on reading activity under uniaxial whole body vibration

In a railway vehicle, the vibrations are transmitted to the passengers through the various interfaces such as floor, seat, backrest etc. These vibrations affect the passenger comfort as well as their performance to do any work such as reading, writing, typing etc. In the present work, effects of vibration magnitude, direction of vibration, postures and reading formats have been studied on the reading activity. Thirty healthy male subjects have performed reading task, one at a time. All subjects were exposed to uni-axial whole body vibration in 1–20 Hz frequency range at 0.5, 1 and 1.5 m/s² rms vibration magnitude. The experimental task involved reading a paragraph under the different 54 experimental conditions (three magnitude, three direction, two posture and three reading format). The task performance has been evaluated in terms of time taken by the subjects to read a given paragraph and also the subjective evaluation of perceived difficulty on Borg's CR 10 scale. Perceived difficulty and performance degradation in reading have been found to increase with the increase in vibration magnitude in each direction of vibration. The perceived difficulty and performance degradation in reading have been observed to be higher in the fore-&-aft direction in with-backrest posture. In vertical and lateral vibration, perceived difficulty and performance degradation have been higher in without-backrest posture compare to with-backrest posture. The perceived difficulty and performance degradation have been lower for the triple-column format.     

Feasibility analysis of low-cost flexible resistive sensors for measurements of driving point mechanical impedance of the hand-arm system

This study explored the feasibility of the flexible resistive (FlexiForce) force sensors for measurement of the hand-arm biodynamic response. Two FlexiForce sensors were installed on an instrumented handle to measure the palm-handle and finger–handle interface dynamic forces. The measurements were performed with six subjects grasping a 38 mm diameter instrumented handle with nine different combinations of grip (10, 30 and 50 N) and push (25, 50 and 75 N) forces and two levels of broad-band random vibration (1.5 and 3.0 m/s² weighted rms acceleration) in the 4–1000 Hz frequency range. The data acquired from the instrumented handle was analyzed to determine the palm and finger impedance responses, which served as the reference values to evaluate feasibility of the FlexiForce sensors. The comparisons revealed very similar trends, while the impedance magnitude responses obtained from the FlexiForce sensors were substantially lower in the entire frequency range than the reference values, except at very low frequencies. A correction function was subsequently developed and applied to the FlexiForce measured data, which resulted in similar hand-arm impedance response trends compared to the reference values. It was concluded that the low-cost FlexiForce sensors could be applied for measurements of biodynamic responses of the hand-arm system in real tool handles in the field. Due to the physiological risks associated with prolonged exposure to tool vibration the applicability of a low-cost biodynamic response measurement system can be used as a preventative measure for such risks.Relevance to industryThe measurement of hand–handle interface forces is vital for assessing the hand-transmitted vibration exposure and the biodynamic responses of the hand-arm system to vibration. The low cost and flexible sensors, proposed in the study, could be conveniently applied to the curved surfaces of real power tool handles in the field. The most significant benefit of the sensors lies with its negligible mass and thereby the instrumented handle inertia-induced errors in the biodynamic responses can be eliminated.     

Predictive validity of the Hand Arm Risk assessment Method (HARM)

The Hand Arm Risk assessment Method (HARM) is a simplified risk assessment method for determining musculoskeletal symptoms to the arm, neck and/or shoulder posed by hand-arm tasks of the upper body. The purpose of this study was to evaluate the predictive validity of HARM using data collected from a three year prospective cohort Study on Musculoskeletal disorders, Absenteeism and Health (SMASH). Structured observations of video recordings using HARM were made of 88 participants performing hand-arm tasks. These video recordings were made at baseline of the SMASH study, whereas self-reported musculoskeletal symptoms were assessed both at baseline and during a three year follow-up. The receiver operating characteristic (ROC) curves showed an area under the curve (AUC) of 0.75 (CI: 0.65–0.86) for symptoms at baseline and 0.70 (CI: 0.58–0.83) for symptoms during follow-up. For a HARM score of 50, the sensitivity and specificity were 64% and 79% at baseline and 53% and 82% during follow up. Participants with a HARM score of 50 or more (considered a high risk) had a significantly higher risk of upper limb symptoms than those with a HARM score of less than 50 at baseline (OR = 5.31; 95%CI: 2.10–13.39) and 3 year follow-up (OR = 5.11; (95%CI: 1.61–16.27). This study has shown that HARM can be used to assess work tasks of the hands and arms and discriminate between tasks that pose a high or low risk of neck or upper limb symptoms.     

Factors affecting the perception of whole-body vibration of occupational drivers: an analysis of posture and manual materials handling and musculoskeletal disorders

Due to the high cost of conducting field measurements, questionnaires are usually preferred for the assessment of physical workloads and musculoskeletal disorders (MSDs). This study compares the physical workloads of whole-body vibration (WBV) and awkward postures by direct field measurements and self-reported data of 45 occupational drivers. Manual materials handling (MMH) and MSDs were also investigated to analyse their effect on drivers' perception. Although the measured values for WBV exposure were very similarly distributed among the drivers, the subjects' perception differed significantly. Concerning posture, subjects seemed to estimate much better when the difference in exposure was significantly large. The percentage of measured awkward trunk and head inclination were significantly higher for WBV-overestimating subjects than non-overestimators; 77 and 80% vs. 36 and 33%. Health complaints in terms of thoracic spine, cervical spine and shoulder–arm were also significantly more reported by WBV-overestimating subjects (42, 67, 50% vs. 0, 25, 13%, respectively). Although more MMH was reported by WBV-overestimating subjects, there was no statistical significance in this study.     

受振动影响的手部操作仿真与操作精度研究

在手及手臂参与控制的操作中,由操作端传递给手及手臂的振动会对操作精度产 生影响。利用计算机程序仿真了一种在虚拟空间中的直线路径追踪操作,以可编程的力觉交互 设备Phantom 作为操作端,研究低频率段不同参数的振动对用户操作精度的影响。振动频率对 操作误差的影响呈非线性,显著的影响出现在2 Hz 附近。振动幅值对操作误差的影响近似线性, 振动方向对操作误差也有一定影响。     

The design and development of suspended handles for reducing hand-arm vibration in petrol driven grass trimmer

The portable petrol driven grass trimmer is identified as a type of machine whose operator can be subjected to large magnitude of hand-arm vibration. These vibrations can cause complex vascular, neurological and musculoskeletal disorder, collectively named as hand-arm vibration syndrome. The vibration total level on the handle of grass trimmer of 11.30 m/s² was measured, and it has reached the exposure limit value of 5.0 m/s² for daily vibration exposure A(8). New suspended handles were designed to reduce the vibration level. Three different prototype handles with rubber mounts were designed. Handles were made of different materials, and the distance of rubber mounts were varied. From the study, it was observed that not all the handles with rubber mounts were effective in reducing hand-arm vibration. The reduction of vibration depended on the handle material and distance installed between rubber mount and vibration transmissibility of handle-isolation system. Subjective ratings of perception of vibration were measured, and the results indicated that operators were not fully aware of the level of vibration. A prototype handle that is made of heavier material results in the lowest hand-arm vibration of 2.69 m/s². The new handle has significantly reduced the vibration total value by 76% compare with the existing commercial handle.

Relevance to industry

Large numbers of workers are employed to perform grass trimming job in many developing countries. This paper presents the effect of handle types (commercial and prototype) on the commonly used grass trimmer.     

A finite element modeling-based approach to predict vibrations transmitted through different body segments of the operator within the workspace of a small tractor

Agricultural tractor drivers are subjected to high levels of whole-body vibrations and hand arm vibrations during most part of the farm activities due to unevenness of field surface, uneasy posture, improper workplace design, moving parts of the tractor, and other unavoidable circumstances. The comfort level of the operator inside a dynamic tractor is dependent on the level of vibration generated inside the different human body segments. In the present study, a finite element modeling was proposed to predict vertical vibrations (Z-axis) and frequencies at the different body segments of the seated small tractor operator. The forces required for different controls of the tractor were measured to be used as input parameters in the finite element modeling. The maximum mean forces of the brake (172.8 N) and clutch (153.2 N) were used as the input parameters for the simulation study. The simulated results were validated with the field measured values of vertical accelerations at selected body segments of the operator. The simulation could successfully predict vertical vibrations at selected points of interest (i.e., foot, leg, thigh, lower arm, upper arm, back, and head) except the chest of the body, as the buttock of the operator model was fixed (degree of freedom is equal to zero) in the simulation. The obtained results were compared with the international standards ISO 2631-1 (1985/1997) and ISO 5349-1 (2001) to assess the vibration characteristics at the different body segments of the operator. The foot, leg, lower arm, and upper arm of the operator were subjected to vertical vibration frequencies from 10 to 200 Hz. Most of the resonance of vertical accelerations occurred in one-third octave bands of 20–80 Hz frequencies. The thigh, chest, back, and head of the operator were exposed to vibration frequencies below 40 Hz during field operation. At these parts of the body, the vertical acceleration resonated at lower frequencies, between 2 and 8 Hz.     

Occupational hazards survey among coal workers using hand-held vibrating tools in a northern China coal mine

ObjectiveProlonged exposure to hand-transmitted vibration (HTV) is associated with an increased risk of hand-arm vibration syndrome (HAVS). This study aimed to identify the signs and symptoms associated with coal workers using hand-held vibrating tools in a northern China coal mine, and to determine the risk factors for HAVS.MethodsA cross-sectional survey was conducted of 167 male workers with part-time exposure to HTV. A structured questionnaire was administered to the workers along with a series of function tests. The frequency-weighted vibration acceleration of hand-held tools was measured. The prevalence ratio and symptom correlation to HAVS among the different subgroups were evaluated.ResultsThe prevalence of hand numbness, carpal tunnel syndrome, hand ache, tinnitus, memory loss, dizziness and headache showed significant differences in the longer-exposure groups (working years > 3 years or the daily-exposure duration > 2 h), compared with the control group (P < 0.05). Function tests showed abnormal findings only in vibration sensation and the X-ray examination of the longer-exposure groups (P < 0.05). The logistic regression analysis showed that longer working years, higher daily exposure and alcohol consumption were risk factors, while wearing anti-vibration gloves showed protective effects for hand numbness.ConclusionsThis study has identified the main signs and symptoms of HAVS among coal workers exposed to HTV in China. More information related to occupational safety and health programs are required to reduce the risk of HAVS.