Measurement of hand-vibration transmissibility by non-contact measurement techniques

Background: Workers who use hand-held vibrating tools may experience finger blanching attacks due to episodic vasospasm in the digital vessels. In occupational medicine, the pathological consequences to the exposure to handtransmitted vibration are known as vibration induced white finger (VWF). In many cases, workers are recommended to use anti-vibration gloves and a standard procedure (ISO 10819) is used to test and qualify such anti-vibration gloves. Some problems and limits are known for what concerns the measurement and procedure proposed by this standard. Materials and methods: Hand-arm vibration transmissibility (ratio between rms acceleration on different points of the upper side of the hand and the handle rms acceleration) of 13 healthy subjects (main BMI: 24.3 [kg/m]) was measured using a mono-axial accelerometer on the handle and a laser Doppler vibrometer on several points on the hand. The laser vibrometer eliminates any mass loading effect on the hand tissue. Seven single frequency excitations (rms acceleration amplitude: 3 m/s ) have been tested: 15, 20, 30, 50, 70, 90 and 110 Hz. Closed loop control of the handle acceleration is provided. Monitoring of the push force (50 ± 5.0 N) has been carried out during the test. Results: Transmissibility higher then one (1.54) has been measured at the tip of the fingers, especially for vibration frequencies lower then 70 Hz, while transmissibility lower then 1 (0.20) is reported on the hand knuckles for frequencies higher then 30 Hz. Conclusions: The measurement procedure presented a non-contact measurement of the vibration transmissibility of the human hand and in particular its spatial distribution over the hand.