Comparison of Anti-Vibration Glove Performances in the Laboratory and in the Field: Similarities and Differences †

: Anti-vibration gloves undergo a certiﬁcation procedure that is described in the EN ISO 10819:2013. This is a laboratory practice that, in this paper, is compared with a standardized ﬁeld method. Two methods are implemented in the tests: a direct method and an experimental one. The results show that some transmissibility is above the limit suggested by the standard. The difference between the transmissibility measured in the ﬁeld, using the direct transmissibility as a reference, and the values declared by the manufacturers is very small. In the case of the experimental transmissibility, two out of three gloves amplify vibrations instead of reducing them.


Introduction
The certification of anti-vibration gloves is performed following the directives of UNI EN ISO 10819:2013 [1,2]. This standard describes the standardized measurement protocol to be performed in the laboratory in order to certify an anti-vibration glove. When, on the other hand, measurements are taken in the field, the standardized measurement conditions are missing: the posture, grip strength, and vibration frequency of the tools, for example, are very different. The standard only recommends determining the transmissibility as a function of the frequency; then, the transmissibility varies depending on the tool used [3,4].
The purpose of this work is to compare the transmissibility of some anti-vibration gloves measured in the field with their certification in the laboratory, taking the manufacturer's certification data as the reference and comparing them with the data obtained from the measurements performed on a chainsaw.

Methods
The measurements were assessed on six male participants, experienced in using a chainsaw. The required task was to cut a pine trunk with a diameter of 15-20 cm perpendicular to the axis of the trunk in thin slices. Each operator first performed a bare hand measurement to obtain the transmissibility of the hand (T 0 ) and then a measurement with the anti-vibration glove to obtain the relative transmissibility (T 1 ). The following transmissibility was defined in line with the aforementioned UNI standard: T 0 = a hv,h /a c , T 1 = a hv,g /a c , where a hv,h , a hv,g , and a c represent the total acceleration value as defined by UNI EN ISO 5349-1 measured on the bare hand, on the gloved hand, and directly on the chainsaw handle, respectively. The accelerations on the hand and on the handle were measured by means of two SEN026 PCB triaxial accelerometers, one inside the glove, inserted in a palmar adapter, and one fixed on the handle. A load cell was inserted inside the handheld adapter to measure the grip force. The operators were asked to comply with the real working conditions that arise during wood cutting operations, unlike in the laboratory where a standardized posture is prescribed [1].
The calculation of the transmissibility value was performed using the UNI EN ISO 10819:2013 model, i.e., 3 measurements for each of the 6 subjects, with and without gloves. Two methods were used to calculate the transmissibility, which we call the direct method and the experimental method: 1.
Direct method: acceleration inside the glove/acceleration on the handle; 2.
The chainsaw transmissibility signal acquired in the field was divided into medium and high frequency for better comparability with the laboratory transmissibility described by the standard.

Results
The results were calculated using both the chainsaw handle and the bare hand as a reference and are described in Tables 1 and 2. The values declared by the manufacturer were also reported, where available. The values in bold are those that were beyond the limit value allowed by UNI EN ISO 10819 (T m ≤ 0.9; T h ≤ 0.6).

Discussion
The difference between the transmissibility measured in the field, using the direct transmissibility as a reference, and the values declared by the manufacturers was very small, with some exceptions, and the standard deviation of the values measured in the field had good values. In the case of the experimental transmissibility, however, two out of the three gloves would not pass the certification because, for some subjects, they amplified rather than reduced the vibrations.
The transmissibility values obtained respectively with reference to the bare hand and with the values declared by the manufacturers were quite close to each other. This was even more evident by comparing the standard deviation obtained on several measurements and that obtained for each individual subject. These data were not reported for reasons of space.
The current data seemed to confirm the effectiveness of the certification protocol by comparing the measured data with those declared. It seems reasonable to assume, given the high standard deviation, that in the field it would be right to measure a larger number of subjects to account for the high variability. The next step to conclude the work will be to carry out laboratory measurements by reproducing the average signal obtained in the field on the chainsaw and adopting the indications of the UNI EN ISO 10819:2013 certification standard.