I refer to David Close's letter (NCE last week) on vibration data. I am chairman of the British Tunnelling Society's sub-committee on hand-arm vibration syndrome (HAVS) and we have long recognised that hand driven tunnels can give rise to vibration health problems.
We are about to publish HAVS - a guide to good practice aimed at tunnelling works in 'easy to read' language. It cites recognised vibration emissions for tools that might be used for estimating vibration dose periods or 'trigger times'.
I believe it is not unreasonable for the Health & Safety Executive (HSE) to provide guidance in choosing a vibration estimate, which is related in some way to the manufacturer's quoted figure. Whether the HSE's blanket advice of doubling the manufacturer's data is correct in all cases is not certain but it does highlight that, like me, the HSE has seen vibration equipment that has not been properly maintained by often reputable contractors.
What this figure does not do is provide an alternative to insitu testing. Manufacturers test their machines to ISO 8662-5, which provides guidance for a standard test but this does not represent the actual use of vibrating equipment in the field.
There is no test that can possibly replicate site conditions. The standard test is the starting point from which contractors can modify results gained from their own experience and testing, published data and HSE guidance.
Jack Knight (F), technical director - tunnelling, Charles Haswell and Partners, Equipoint Centre, 1506-1508 Coventry Road, Yardley Birmingham, B25 8AQ