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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
prolonged periods. A tool with a vibration value of 2.8 m/s
2
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 gener-
ally 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.