D.E. Welcome

Estimation of tool-specific isolation performance of antivibration gloves

Abstract A methodology to estimate vibration isolation effectiveness of antivibration gloves as a function of handle vibration of specific tools is proposed on the basis of frequency response characteristics of the gloves. The handle vibration spectra of six different tools are synthesized in the laboratory and attenuation performances of two different gloves are characterized under tools vibration, and M- and H-spectra defined in ISO-10819 (1996). The vibration characteristics of gloves are measured using three male subjects in the laboratory under different excitation spectra. The results suggest that tool-specific vibration isolation performance of a glove cannot be derived from the standardized M- and H-spectra. Frequency responses of the gloves are thus characterized under broad-band vibration excitations of two different magnitudes, and grip and feed forces recommended in ISO-10819. The results suggest that frequency response characteristics of gloves are relatively insensitive to magnitude of vibration but strongly dependent upon visco-elastic properties of the glove materials. The mean measured frequency response characteristics are then applied to derive an estimate of tool-specific isolation effectiveness of the gloves. The estimated acceleration transmissibility characteristics of gloves are compared with the mean measured responses to demonstrate validity of the proposed methodology. From comparisons, it is concluded that the isolation effectiveness of gloves for selected tools can be effectively predicted using the proposed methodology. The deviations between the predicted and measured transmissibility values are within 8% for majority of the glove–spectra combinations, well within the intra- and inter-subject variabilities reported in different studies. Relevance to industry The methodology proposed in this study and the results can be applied to effectively assess the antivibration performance of the gloves for specific tools, and thereby select near optimal gloves to reduce the health hazards posed by the hand-transmitted vibration.

Effectiveness of a new method (TEAT) to assess vibration transmissibility of gloves

Abstract A test method based upon total effective acceleration transmissibility (TEAT) is proposed to study the vibration isolation performance of anti-vibration gloves. The vibration transmission characteristics of three different gloves are investigated under predominantly axial vibration using the proposed method and the procedure outlined in ISO-10819 (Mechanical Vibration and Shock—Hand–Arm Vibration—Method for the Measurement and Evaluation of the Vibration Transmissibility of Gloves at the Palm of the Hand, International Standard Organization, Geneva, Switzerland, 1996). The measured data are systematically analyzed to illustrate the measurement and evaluation errors arising from misalignments of the response accelerometer within the palm-held adaptor, unintentional non-axial vibration caused by the vibration exciter and dynamics of the coupled hand–handle system. The degree of adaptor misalignment, estimated from the measured data, was observed to vary from 5.9° to 59.6°. Such variations could cause measurement errors in excess of 20%. The vibration transmission characteristics of selected gloves, evaluated using the proposed method, are compared with those derived from the standardized method to demonstrate the effectiveness of the TEAT approach. From the results, it is concluded that the TEAT method, based upon vector sums of both the source and response accelerations, can effectively account for the majority of the measurement errors, and yield more repeatable and reliable assessments of gloves. Relevance to industry Prolonged exposure to hand-transmitted vibration has been related to the possible occurrence of several health disorders by affecting the bones, joints, muscles and nervous system. The epidemiological studies show that millions of industrial workers are being exposed to hand vibration throughout the world. It is thus vital to develop improved methods for assessment of effectiveness of anti-vibration gloves. The proposed methodology could be applied to assess the effective vibration attenuation performance of anti-vibration gloves, and it could contribute towards developing an improved test method.

Increased Oxidant Activity Mediates Vascular Dysfunction in Vibration Injury

Occupational exposure to hand-operated vibrating tools causes a spectrum of pathological changes in the vascular, neurological, and musculoskeletal systems described as the hand-arm vibration syndrome (HAVS). Experiments were performed to determine the effects of acute vibration on the function of digital arteries. Rats paws were exposed to a vibrating platform (4 h, 125 Hz, constant acceleration of 49 m/s2 root mean squared), and digital artery function was assessed subsequently in vitro using a pressure myograph system. Constriction to phenylephrine or 5-hydroxytryptamine was reduced in digital arteries from vibrated paws. However, after endothelium denudation, constriction to the agonists was no longer impaired in vibrated arteries. Inhibition of nitric-oxide synthase (NOS) with Nω-nitro-l-arginine methyl ester (l-NAME) increased constriction to phenylephrine or 5-hydroxytryptamine in vibrated but not control arteries and abolished the vibration-induced depression in constrictor responses. However, nitric oxide (NO) activity, determined using the NO-sensitive probe 4-amino-5-methylamino-2′, 7′-difluorofluorescein, was reduced in vibrated compared with control arteries. Endogenous levels of reactive oxygen species (ROS), determined using the ROS-sensitive probe 5-(and 6)-chloromethyl-2′,7′-dichlorodihydro-fluorescein, were increased in vibrated compared with control arteries. The increased ROS levels were abolished by l-NAME or by catalase, which degrades extracellular hydrogen peroxide. Catalase also increased constriction to phenylephrine or 5-hydroxytryptamine in vibrated but not control arteries and abolished the vibration-induced depression in constrictor responses. The results suggest that acute vibration causes vascular dysfunction in digital arteries by increasing ROS levels, which is probably mediated by uncoupling of endothelial NOS. Therefore, therapeutic strategies to inhibit ROS or augment NO activity may be beneficial in HAVS.

Effects of Hand-Tool Coupling Conditions on the Isolation Effectiveness of Air Bladder Anti-Vibration Gloves

The goals of this study were to determine the vibration isolation effectiveness of a typical (air bladder) anti-vibration glove as a function of vibration frequency, and to investigate the effects of hand-tool coupling action and applied force level on the effectiveness. Six male volunteers were used in the study. A palm adapter method similar to that recommended in the current ISO standard for anti-vibration glove testing (ISO-10819, 1996) was used to measure the transmissibility of the glove. Three different handgrip actions (grip-only, push-only and combined grip and push), three force levels (50, 75 and 100 N), and a broad-band random spectrum were used in the experiment. This study found that the effectiveness of the glove generally increased with an increase in vibration frequency, while the glove did not provide any effective vibration isolation at frequencies less than or equal to 25 Hz. Under the same force level, the push-only action produced the greatest vibration attenuation while the grip-only action resulted in the lowest glove performance among the three actions. Increasing the force tended to increase vibration transmissibility at low frequencies (< 31.5 Hz), while transmissibility decreased at the middle frequencies (63 – 250 Hz). The knowledge generated by this study can be used to augment vibration exposure risk assessments and to promote the appropriate application of anti-vibration gloves at workplaces.

An Evaluation of Impact Wrench Vibration Emissions and Test Methods

In the interest of providing more effective evaluations of impact wrench vibration exposures and the development of improved methods for measuring vibration emissions produced by these tools, this study focused on three variables: acceleration measured at the tool surface, vibration exposure duration per test trial, and the amount of torque required to unseat the nuts following a test trial. For this evaluation, six experienced male impact wrench operators used three samples each of five impact wrench models (four pneumatic models and one battery-powered model) in a simulated work task. The test setup and procedures were based on those provided by an International Organization for Standardization (ISO) Technical Committee overseeing the revision of ISO 8662-7. The work task involved the seating of 10 nuts onto 10 bolts mounted on steel plates. The results indicate that acceleration magnitudes vary not only by tool type but also by individual tools within a type. Thus, evaluators are cautioned against drawing conclusions based on small numbers of tools and/or tool operators. Appropriate sample sizes are suggested. It was further noted that evaluators could draw different conclusions if tool assessments are based on ISO-weighted acceleration as opposed to unweighted acceleration. As expected, vibration exposure durations varied by tool type and by test subject; duration means varied more for study participants than they did for tool types. For the 12 pneumatic tools evaluated in this study, torque varied directly with tool handle acceleration. Therefore, in order to reduce vibration exposure, tools should be selected and adjusted so that they produce no more than the needed torque for the task at hand.

Effectiveness of a Transfer Function Method for Evaluating Vibration Isolation Performance of Gloves When Used With Chipping Hammers

Anti-vibration gloves have been used as personal protective equipment to reduce the exposure intensity of hand-transmitted vibration. Although a method based upon the measured transfer function has been recently proposed to predict the tool-specific anti-vibration performance of these gloves, its validity for real tool applications has not been sufficiently evaluated. In this study, the effectiveness of the proposed prediction method was examined using two typical vibration-attenuation gloves when used in conjunction with two different pneumatic chipping hammers. Six adult male subjects were employed in the experiments involving measurement of gloves transmissibility while operating the selected tools. A comparison of the measured vibration transmissibility with the predicted values revealed that the transfer function method provides a reasonably good prediction of the vibration isolation performance of the gloves. The differences between the predicted and measured mean values of the weighted transmissibility were surprisingly small. It is concluded that the transfer function method can serve as an effective and convenient approach for estimating the effectiveness of anti-vibration gloves when used with pneumatic chipping hammers. A pneumatic chipping hammer is considered to represent a critical case for the evaluation of the method because they are typical percussive tools that generate impact vibration. It is thus anticipated that the transfer function method may also be widely employed to predict anti-vibration glove performance when used with many other vibrating tools.

Antivibration gloves: effects on vascular and sensorineural function, an animal model.

Anti-vibration gloves have been used to block the transmission of vibration from powered hand tools to the user, and to protect users from the negative health consequences associated with exposure to vibration. However, there are conflicting reports as to the efficacy of gloves in protecting workers. The goal of this study was to use a characterized animal model of vibration-induced peripheral vascular and nerve injury to determine whether antivibration materials reduced or inhibited the effects of vibration on these physiological symptoms. Rats were exposed to 4 h of tail vibration at 125 Hz with an acceleration 49 m/s2. The platform was either bare or covered with antivibrating glove material. Rats were tested for tactile sensitivity to applied pressure before and after vibration exposure. One day following the exposure, ventral tail arteries were assessed for sensitivity to vasodilating and vasoconstricting factors and nerves were examined histologically for early indicators of edema and inflammation. Ventral tail artery responses to an α2C-adrenoreceptor agonist were enhanced in arteries from vibration-exposed rats compared to controls, regardless of whether antivibration materials were used or not. Rats exposed to vibration were also less sensitive to pressure after exposure. These findings are consistent with experimental findings in humans suggesting that antivibration gloves may not provide protection against the adverse health consequences of vibration exposure in all conditions. Additional studies need to be done examining newer antivibration materials.

Estimation of the Transmissibility of Anti-Vibration Gloves when Used with Specific Tools

Anti-vibration gloves are increasingly being used as personal protective equipment to help reduce the hazards of hand-transmitted vibration. A vibration transfer function method for estimating the tool-specific performance of anti-vibration gloves has been proposed to help select appropriate gloves for particular tools and to assess the potential risks posed by tool vibration. This study evaluates the validity of the method by comparing the predicted vibration transmissibility with the measured value. Two typical vibration-attenuating gloves (air-bladder and visco-elastic material gloves) were used in the study. Two series of experiments were performed for the evaluation. In the first series, the isolation efficiency of selected anti-vibration gloves was evaluated in the laboratory under synthesized handle vibration spectra of six different tools. The second series of tests involved the measurement of the glove transmissibility, while operating two different pneumatic chipping hammers. The results of the study show reasonably good agreements between the predicted and measured acceleration transmissibility values of the candidate gloves. It is thus concluded that the transfer function method provides a reasonably good estimate of vibration attenuation performance of gloves for specific tools.