vibration risk.

22

If the emission level provided by the supplier is below the threshold of

2.5 m/s2 but the likely level in the workplace is much higher, the emission level data

has failed to inform of a residual vibration risk likely to require management. In such

cases suppliers are obliged to make the likelihood of a vibration risk evident. This

may be done by pictograms; reporting the results of alternative tests; or by giving a

written report (see the appendix). Similarly, if the supplier reports a level above the

threshold of 2.5 m/s2 but unrepresentative of the emission level likely to be found

during `intended use', the supplier should provide further information to the user.

23

The 8-hour time weighted average vibration exposure is given by:

A(8) = a %

Where a is the value (in m/s2) reported by the supplier (or, in some cases, measured

in the workplace) and t  used is the time for which the tool is used during the day (in

24

If several tools are used in the day it will be necessary to sum the

contributions of each tool to the daily vibration exposure. The total exposure for the

day is then:

where A1(8), etc are the 8-hour time weighted averages calculated for each tool

according to equation (1). The procedure, including a nomogram, is presented in

more detail in HS(G)88 pages 42-43. Alternatively a `calculator' is included in HSE's

CD-ROM (see paragraph 35).

Note: Most data currently provided with hand-held power tools is reported for the

dominant axis and exposures should be estimated as above for comparison with

HSE's recommended action level of 2.8 m/s2 A(8) which is also dominant axis.

Future data will increasingly be for the sum of three axes of vibration - often referred

to as `root-sum-of-squares', `rss', or `vector sum'. The rss equivalent of HSE's action

level is approximately 4 m/s2 A(8). HSE's action level is expected to be superseded

by implementation of a proposed new European Directive on vibration which is likely

to include an rss exposure action level and limit value (draft values at February 2001

are 2.5 and 5 m/s2 A(8) respectively).

AVOIDING HIGH VIBRATION HAND-HELD POWER TOOLS

25

Vibration emissions of hand-held power tools vary greatly from user to user

and task to task often by factors of 2 or 3:1 between worst and best circumstances.

Figure 1 shows typical vibration emission data for 3 tools. Each tool has a range of

levels which will be found during `intended' use. This is shown by the vertical line.

The average (mean) of these use levels is shown by the mark to the right of the