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INTR DUCTI N
1.1 Vibration risk and it’s assessment
During human contact with the surface of the vibrating machine mechanical vibrations are transmitted
directly to the human body affecting the individual tissues or even the whole body. Vibration that affects
humans is called human vibration and is divided into whole-body and hand-arm vibration.
In practice the most dangerous are hand-arm vibrations which can cause pathological changes in the
nervous vascular (cardiovascular) and osteoarticular system. Hand-arm vibration occurs when one or both
of the upper limbs is in contact with a vibrating surface. Typical sources of such vibration are any kind of
hand tools that generate vibration steering wheels and levers to control vehicles. The characteristic feature
of hand-arm vibration is their variability in time. Therefore very often measurement results depend on the
point in time that measurement takes place. This is a very important feature that defines both the test
methods and measurements describing this kind of vibration. This variability in time influences another
significant factor in determining the body's response to the vibration which is the exposure time (duration of
exposure to vibration).
The fundamental parameter used in the evaluation of hand-arm vibration is the vector sum of tri-axial
vibration called AEQ 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 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. According to ISO 5349 hand-arm vibration should be measured
in place or at the point of contact with the hand tool. The best location is the centre of the handle which is
the most representative location. 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.
Typical vibration exposure consists of short periods in which the operator is in contact with the tool.
Measuring 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
(ISO 5349-2:2001).