¹ Center for Mechanical & Environmental Systems Technology (CMEST), University of Nevada, Las
   Vegas, Nevada, USA

INTRODUCTION

In the field of personal protective equipment, gloves were being manufactured and marketed that claimed to significantly reduce the magnitude of vibration transmitted from vibrating tools to the hand. Most of these claims proved to be false. As a result, the International Organization for Standardization adopted ISO Standard 10819 to define test procedures that must be used to measure the vibration attenuation characteristics of gloves that were designed to reduce vibration into the hand.⁽¹⁾ This standard also specified the vibration attenuation values that must be achieved for a glove to be labeled as an "antivibration glove".

A project was undertaken at the Center for Mechanical & Environmental Systems Technology (CMEST) at the University of Nevada, Las Vegas in the USA to develop a test system that can be used to conduct glove vibration transmissibility tests per the test procedures specified in ISO Standard 10819. The test system that was developed during this project is described in a companion paper by the authors of this paper.⁽³⁾ The test protocol for measuring the vibration transmissibility of gloves per the test procedures specified in ISO Standard 10819 were examined and evaluated as part of this project. The results of this analysis are discussed in this paper.

ISO STANDARD 10819 TEST PROCEDURES

ISO Standard 10819 specifies the test procedures that must be used to measure the vibration transmissibility of gloves.⁽¹⁾ The vibration transmissibility of a glove per ISO Standard 10819 is the ratio of the vibration amplitude directed into the palm of the hand inside of a glove divided by the vibration amplitude directed into the palm on the outside surface of the glove. The vibration signals that are measured at the handle and into the palm are the overall acceleration signals that are passed through an ISO weighting filter that is specified by ISO Standard 5349.⁽²⁾ Figure 1 shows the ISO weighting filter. The vibration transmissibility of a glove is a measure of the attenuation of vibration into the hand and arm by means of a resilient or vibration-damping material placed in the glove. The lower the vibration transmissibility, the more effective a glove is in reducing vibration energy into the hand and arm.

ISO Standard 10819 specifies the amplitude of vibration transmissibility that must be achieved for a glove to be classified as an antivibration glove. The standard requires the overall vibration transmissibility of a glove to be measured for mid frequencies (16-400 Hz) and for high frequencies (100-1,600 Hz). Figure 2 shows the third octave amplitudes of the vibration spectra for the mid and high frequency test signals, respectively. Tables 1 and 2 shows the third octave band amplitudes and required band tolerance values for the mid and high frequency test signals, respectively. Vibration first corresponding to the mid frequency test spectrum and then to the high frequency test spectrum are directed into the hand by means of a 40 mm diameter handle attached to a vibration shaker. Sets of two measurements on each of three test subjects for a total of six measurements are made for each frequency range. Three different gloves, one for each test subject, are used for each test series. The six individual transmissibility values for each of the mid and high frequency test signals are averaged to obtain the respective average ISO Standard 10819 vibration transmissibility values. The average mid-frequency transmissibility is designated TR_M, and the average high-frequency transmissibility is designated TR_H. For a glove to be classified as an antivibration glove:

• TR_M must be less than 1.0, and TR_H must be less than 0.6.

• The resilient or vibration-damping material must be placed in the palm and the full finger and thumb stalls of the glove.

Table 1  ISO Standard 10819 Mid Frequency Acceleration and Tolerance Values

Table 2  ISO Standard 10819 High Frequency Acceleration and Tolerance Values

GLOVE VIBRATION TRANSMISSIBILITY TESTS

Table 3  Legend for Gloves that Were Tested

Thirteen different gloves were tested. The type of vibration-damping material that was placed in each glove is listed in Table 3.

Manual Method of Controlling Shaker Handle Acceleration Values

The ISO Standard 10819 mid and high frequency test spectra for this project were manually adjusted for the glove vibration transmissibility tests. Three methods for adjusting the shaker handle acceleration spectra were examined:

Method 1: The third octave mid and high frequency acceleration values of the shaker handle were adjusted with no one clasping the handle. When the handle was clasped for a test, the acceleration amplitudes in the third octave frequency bands below 160 Hz decreased as is shown in Figure 3. ISO Standard 10819 tests were conducted where no adjustments were made to compensate for these decreased acceleration values.

Figure 3  Typical Handle Mid Frequency Acceleration Spectra (Spectrum-M) and High
                  Frequency Acceleration Spectra (Spectrum-H) for Methods 1, 2, and 3 (The
                  triangular symbols represent the lower and upper acceleration limits specified
                  by ISO Standard 10819.)

Method 2: The acceleration values of the shaker handle were adjusted per the procedures used in Method 1. The decreases in third octave acceleration values were measured for each of the three test subjects that were used for a specific test series. The corresponding average values were calculated for each affected third octave frequency band. The third octave graphic equalizer that was used to control the input spectrum to the shaker handle was then adjusted to compensate for the "averaged" changes in acceleration values. Figure 3 shows the effectiveness of this method in controlling the ISO Standard 10819 mid and high frequency acceleration values of the shaker handle. ISO Standard 10819 tests were conducted with no further adjustments being made to the shaker handle vibration amplitudes.

Method 3: The acceleration values of the shaker handle were adjusted per the procedures used in Method 1. As each test subject clasped the shaker handle for a test, the third octave graphic equalizer was manually adjusted until the handle acceleration values for the test were within the third octave amplitude limits specified by ISO Standard 10819. Method 3 was used for all of the "official" ISO Standard 10819 vibration transmissibility tests that were conducted at CMEST.

ISO Standard 10819 vibration transmissibility tests were conducted using the ISO weighting filter as specified by the standard and a linear weighting filter (Figure 1). Table 4 shows a comparison of the test results for Methods 1, 2, and 3. Table 4 indicates that the method of adjusting the shaker handle acceleration values had little effect on the ISO and linear glove transmissibility values.

Table 4  Test Results for Gloves 1, 9, and 12 Using
Methods 1, 2, and 3

Figure 4  Filter Setup for Measuring the ISO Weighted Acceleration Value

Weighting Filter Bandwidths

ISO Standard 10819 requires that the rms acceleration values at the shaker handle and at the palm of the hand be measured using the ISO weighting filter that is specified in ISO Standard 5349. Figure 4 shows a schematic of the filter setup for measuring the ISO weighted acceleration amplitudes. Figure 1 shows the overall results of the filter setup when the corner frequencies of the bandpass filter are 6.3 Hz and 1,250 Hz.

Different laboratories have interpreted the above requirements differently. Table 5 shows how the requirements of ISO Standard 10819 have been interpreted by the Berufagenossenschaftliches Institut fur Arbeitssickerheit (BIA), Delta Acoustic & Vibration (DELTA), and the Center for Mechanical & Environmental Systems Technology (CMEST). Each of these laboratories have selected different corner frequencies for the bandpass filter for the mid and high frequency measurements. Table 6 shows a comparison of the vibration transmissibility test results that were obtained at CMEST and the corresponding results that were obtained at DELTA and BIA.

Table 6 indicates that the ISO Standard vibration transmissibility results that were obtained at the above three laboratories agreed well with each other. This good agreement occurred because the ISO mid and high frequency spectra to the shaker handle was properly controlled at the three laboratories. Vibration energy outside of the frequency bandpasses for the mid frequency spectrum (16-400 Hz) and for the high frequency spectrum (100-1,600) were properly attenuated (at least -12 dB/octave at the low and high corner frequencies). When this is the case, any of the corner frequencies given in Table 5 can be used for a bandpass filter that is placed before an ISO weighting filter and yield similar results.

Table 6  Comparison of ISO Standard 10819 Glove Vibration Transmissibility Test Results

ISO Weighted Versus Linear Vibration Transmissibility Values

ISO Standard 10819 requires that glove vibration transmissibility values be obtained using the ISO weighted acceleration values at the shaker handle and palm of the hand. One of the problems with this is that the ISO weighted vibration transmissibility values tend to underestimate the vibration attenuation characteristics of antivibration gloves. Figure 5 shows the effects of the ISO weighting filter on the mid and high frequency input spectra for ISO Standard 10819. This figure indicates that the ISO weighting biases the ISO weighted values of acceleration to the third octave acceleration values that are closest to the lower frequency limits of the respective input spectra. Thus, the attenuation effectiveness of a glove at the third octave frequencies near the upper frequency limits of the respective input spectra is significantly underestimated.

Figure 5  Effects of the ISO Weighting Filter on the Mid and High                   Frequency Vibration Input Spectra

This problem can be addressed by measuring the glove vibration transmissibility values, using a linear weighting filter (Figure 1). Table 7 shows the ISO and linear weighted vibration transmissibility values of the gloves that were tested during this project. There was not a significant difference between the ISO and linear transmissibility values for the mid frequency vibration input. However, the linear transmissibility values were substantially less than their corresponding ISO weighted values for the high frequency input.

Table 7  Summary of ISO 10819 Vibration Transmissibility Test Results

Figure 6 shows the relations that exist between the ISO and linear weighted vibration transmissibility values for the ISO 10819 mid and high frequency input spectra. The equation for the mid frequency input spectrum is:

The correlation coefficient for this equation is 0.98 and the standard error of fit is 0.028. The equation for the high frequency input spectrum is:

The correlation coefficient for this equation is 0.99 and the standard error of fit is 0.042. These two equations can be used to convert from ISO weighted vibration transmissibility criteria values to their corresponding linear criteria values. This yields the following:

TR_M(Lin) < 1 and TR_H(Lin) < 0.37.

Figure 6  Relationship between ISO and Linear Weighted Vibration
                 Transmissibility Values

OBSERVATIONS ASSOCIATED WITH ISO STANDARD 10819 TESTS

Observations Associated with Test Subjects

• The test subjects had a significant effect on the vibration transmissibility test results. Proper posture during a test was very important, There were a few test subjects who had consistently high transmissibility values, while there were a few who had consistently low transmissibility values. Proper training of the test subjects was necessary to obtain reliable and repeatable test results.

• Those test subjects who consistently had unusually high transmissibility values could result in a glove not meeting the requirements of ISO Standard 10819 to be classified as an antivibration glove.

• It took training and great care to ensure that the palm accelerometer adapter was properly placed between the palm of the hand and the glove during a test.

• When only three test subjects are used for the ISO Standard 10819 tests, a test subject who consistently has unusually high vibration transmissibility tests results can negatively bias the transmissibility tests for a glove. Increasing the number of test subjects to four or five can minimize this problem.

Observations Associated with the Test Procedures

• It was very difficult to generate the mid and high frequency vibration input spectra within the amplitude band limits that are specified by ISO Standard 10819 without the use of a vibration feedback controller.

• Allowing the mid and high frequency input spectra to deviate from the amplitude band limits specified by ISO Standard 10819 did not have a significant effect on the measurement of the mid and high frequency vibration transmissibility values.

• Vibration energy outside of the lower and upper frequency band limits of the mid and high frequency test spectra must be sufficiently attenuated to prevent this energy from negatively biasing the mid and high frequency test results. This is particularly important for the high frequency test spectra.

• If a feedback vibration controller is used to generate the vibration test signals, the controller output must be checked to ensure that the controller significantly attenuates the controller output signal outside of the lower and upper frequency limits of the test signal.

• When a vibration feedback controller is not used to generate the vibration test signals, a bandbass filter must be placed after the signal generator to attenuate the vibration signal outside of the test frequency bandpass. This filter must have a minimum attenuation of -12 dB/octave at the lower and upper frequency limits of the test signal.

• When the ISO Standard 10819 test signals are properly processed before the signals enter the power amplifier for the electromechanical shaker, it does not make any difference whether or not the output signals from the accelerometers on the shaker handle and on the palm accelerometer adapter are directed through bandpass filters before they are directed through ISO weighting filters. If the test signals are not properly processed before they enter the shaker power amplifier, the use of bandpass filters before the ISO weighting filters and the selection of the corner frequencies for these filters can have a significant effect on the ISO Standard 10819 vibration transmissibility test results.

• ISO weighting of the acceleration signals for the ISO Standard 10819 tests biases the measured glove vibration transmissibility values to the lower frequency limits of the mid and high frequency test signals. This often causes the ISO weighted vibration transmissibility values to underestimate the effectiveness of a glove in attenuating vibration to the hand. This is particularly true for the high frequency vibration transmissibility tests. This problem can be resolved by using linear weighting filters instead of ISO weighting filters (Figure 1).

• Shaker handle resonance frequencies within the test frequency band limits of the mid and high frequency test signals can negatively bias the ISO Standard 10819 test results. This is particularly true for the high frequency vibration transmissibility tests. A shaker handle should be tested for resonance frequencies before it is used for ISO Standard 10819 tests. If resonance frequencies are found to exist within the test signal frequency limits, the handle must be redesigned to eliminate the resonance frequencies.

• Sharp edges on the vibration-damping material side of the palm accelerometer adapter can cause the adapter to "dig" into the vibration-damping material. This can negatively effect the ISO Standard 10819 vibration transmissibility test results. This problem can be resolved by rounding the edges of the accelerometer adapter.

CONCLUSIONS

• Use only trained test subjects for ISO Standard 10819 vibration transmissibility tests.

• Test subjects who consistently yield unusually low or high vibration transmissibility values should not be used as test subjects.

• Consideration should be given to increasing the number of test subjects to four or five.

• The allowable amplitude band limits for the mid and high frequency test spectra should be increase to +2 for all third octave band frequencies.

• Care must be taken to ensure that the vibration energy into the shaker power amplifier outside of the of mid and high frequency test spectra lower and upper frequency limits is significantly attenuated.

• The ISO weighting of the acceleration signals for the ISO Standard 10819 vibration transmissibility tests causes the ISO Standard 10819 vibration transmissibility values to understate the effectiveness of a glove in attenuating vibration to the hand.

• Linear filters should be used instead of the ISO weighting filters should be used on the acceleration signals before they are processed to obtained the ISO Standard 10819 vibration transmissibility values.

• When linear filters are used on the acceleration signals to obtain the ISO 10819 vibration transmissibility values, the criteria levels should be changed to TR_M(Lin) < 1.0 and TR_H(Lin) < 0.37.

• The shaker handle must not have any resonance frequencies in the frequency bandpass of the mid and high frequency test signals.

• The sharp edges on the bottom side of the palm acceleration adapter must be rounded to prevent the adapter from "digging" into the glove vibration-damping material during an ISO 10819 test.

REFERENCES

1. ISO Standard 10819: Mechanical vibration and shock - Hand-arm vibration - Method for t he measurement and evaluation of the vibration transmissibility of gloves at the palm of the hand, 1996, International Organization for Standardization, Geneva, Switzerland.

2. ISO Standard 5349: Mechanical vibration - Guidelines for the measurement and the assessment of human exposure to hand-transmitted vibration, 1986, International Organization for Standardization, Geneva, Switzerland.

3. Reynolds, D.D. and Stein, J.K., Design and Evaluation of an Inexpensive Test Fixture for Conducting Glove Vibration Tests per ISO Standard 10819, 8^th International Conference on Hand-Arm Vibration, Umea, Sweden, June 9-12, 1998.

Paper presented at:
8th International Conference on Hand-Arm Vibration
Umea, Sweden
June 9-12,1998