How the hand-arm vibration is measured?
According to BS EN ISO 5349, hand vibration should be measured in place, or at the point of contact with the hand tool. The best location in the center of the handle is the most representative location. BS EN ISO 5349 suggests using lightweight sensors to reduce measurement errors. Measurements directly at the hand are performed using special adapters and measurement in all three axes is recommended.
Hand-arm vibration exposure
The average duration of vibration exposure consists of short periods in which the operator is in contact with the tool. Measuring hand-transmitted vibration time should include a representative tool operation time and the measurement should start from the moment the vibrating device is touched and should end when the contact is broken or the vibration stops (BS EN ISO 5349-2).
The fundamental parameter used in the measurement of hand-arm vibration is the vector sum of tri-axial vibration called ahv which is the basis for the calculation of daily exposure A(8). To identify the daily exposure it is necessary to identify all the sources of vibration, which means identifying all working modes of tools (e.g. drilling with a hammer and without), and changes in the conditions of use of the device. This information is necessary for the proper organization of measurement and to include as many common tasks of the operator during which he is exposed to hand-arm vibration. Daily exposure should be calculated for each source of vibration.
After determining the sources of mechanical vibrations affecting the employee, the next step is to choose the most appropriate accelerometer mounting.
Vibration limit values
When it comes to hand-arm vibration syndrome, exposure duration is a key factor. Studies have shown that workers exposed to vibration who exceed limit values are at risk of developing the condition. Symptoms include numbness, tingling, and pain in the hand and fingers. In severe cases, workers may also experience difficulty gripping or holding objects. If you work with power tools or other machinery that produces vibration, it’s important to take breaks every few hours to reduce your risk of hand-arm vibration syndrome.
Hand-Arm Vibration Chart
The hand-arm vibration chart is used for hand-arm vibration testing. The chart is based on BS EN ISO 5349-1 Wh frequency weighting for hand-arm vibration. The top of the chart is located at 8 to 10 Hz where are the most harmful resonant frequencies for hands and arms. A hand-arm vibration chart is a valuable tool for exposure assessment and the prevention of vibration white finger (hand-arm vibration syndrome).
Improved methods of hand-arm vibration exposure measurement have been defined by BS EN ISO 5349 as the ones using additional factors such as contact force to decrease the uncertainty of exposure time. Contemporary, very small force transducers can be fitted right next to the MEMS-technology-based vibration accelerometer in a form of a hand-arm adapter as specified by BS EN ISO 5349-2 and BS EN ISO 10819. With such an effective solution it became possible to perform continuous measurements throughout the whole working day which decreases the uncertainty of the sample limitation. The time-history of contact force values proved important in determining the true exposure time by simple selection of the force threshold level and this was backed up by the analysis of spectrograms.
Simultaneous measurement of contact force and the vibration is necessary because different coupling forces applied by operators on handheld vibrating tools influence differently the stage of transmission of vibration in the upper limbs. Contact force modifies exposure to vibration and the health effects it causes. Moreover, the cumulative exposure of force and vibration on the cardiovascular system, nervous system, joints, and muscles should be considered.