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VIBRATION EMISSIONS
HAND-ARM VIBRATION
Employers are advised to refer to the HSE publication "Guide for Employers".
All hand held power tools vibrate to some extent, and this vibration is transmitted
to the operator via the handle, or hand used to steady the tool. Vibration from
about 2 to 1500 hertz is potentially damaging and is most hazardous in the range
from about 5 to 20 hertz.
Operators who are regularly exposed to vibration may suffer from Hand Arm
Vibration Syndrome (HAVS), which includes 'dead hand', 'dead finger', and
'white finger'. These are painful conditions and are widespread in industries
where vibrating tools are used.
The health risk depends upon the vibration level and the length of time of
exposure to it......in effect, a daily vibration dose.
Tools are tested using specialised equipment, to approximate the vibration level
generated under normal, acceptable operating conditions for the tool in question.
For example, a grinder used at 45° on mild steel plate, or a sander on softwood
in a horizontal plane etc.
These tests produce a value 'a ' , expressed in metres per second per second,
which represents the average vibration level of all tests taken, in three axes where
necessary, and a second figure 'K', which
represents the uncertainty factor, i.e. a value
in excess of 'a', to which the tool could
vibrate under normal conditions. These
values appear in the specification panel
below.
You will note that a third value is given in the
specification - the highest measured
reading in a single plane. This is the maximum
level of vibration measured during testing in
one of the axes, and this should also be
taken into account when making a risk
assessment.
2
' a ' values in excess of 2.5 m/s
are considered hazardous when used for prolonged
2
periods. A tool with a vibration value of 2.8 m/s
may be used for up to 8 hours
2
(cumulative) per day, whereas a tool with a value of 11.2 m/s
may be used for
½ hour per day only.
The graph shows the vibration value against the maximum time the respective
tool may be used, per day.
14
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