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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.
' a ' values in excess of 2.5 m/s
2
are considered hazardous when used for
2
prolonged periods. A tool with a vibration value of 2.8 m/s
may be used for
up to 8 hours (cumulative) per day, whereas a tool with a value of 11.2 m/s
2
may be used for ½ hour per day only.
The graph below shows the vibration value against the maximum time the
respective tool may be used, per day.
The uncertainty factor should also be taken into account when assessing a
risk. The two figures ' a ' and ' K 'may be added together and the resultant
value used to assess the risk.
It should be noted that if a tool is used under abnormal, or unusual conditions,
then the vibration level could possibly increase significantly. Users must always
take this into account and make their own risk assessment, using the graph
above as a reference.
Some tools with a high vibration value, such as impact wrenches, are
generally used for a few seconds at a time, therefore the cumulative time
may only be in the order of a few minutes per day. Nevertheless, the
cumulative effect, particularly when added to that of other hand held power
tools that may be used, must always be taken into account when the total
daily dose rate is determined.
14
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