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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.
2
'a' values in excess of 2.5 m/s
are considered hazardous when used for prolonged
periods. A tool with a vibration value of 2.8 m/s
2
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 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 resulant 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.
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