If there’s something that is currently controversial in the world of HAV measurements, then it has to be concerned with the placement of the accelerometer (or sensor) when measuring tool vibration levels. This controversy arises because some measurements are taken with the accelerometer either mounted on the wrist of the operative or attached to a glove that the operative wears.
According to the HSE, the accelerometer must be mounted firmly and directly on the vibrating surface of the tool, which is what the relevant international standards specify. In an online Q and A publication of theirs, the HSE has made a statement about the accelerometer location when carrying out vibration measurements.
Where you place the accelerometer could determine the validity (or invalidity) of your tool vibration level results, when predicting the employee’s daily exposure against the exposure values of the Control of Vibration at Work Regulations (2005). Employers are legally obliged to comply with these regulations to protect employees from the ill effects of HAV.
So what DO the HSE publication and the Control of Vibration at Work Regulations (2005) say about the sensor placement positions for measurements?
The HSE publication (8 Questions about Vibration Exposure Monitoring) (see http://www.hse.gov.uk/vibration/hav/advicetoemployers/vibration-exposure-monitoring-qa.pdf) answers the following question (Question 7):
“Do hand-arm vibration measurements need to be taken “on the tool? (NEW)
Yes – Hand-arm vibration measurements should be made with the transducer firmly attached to the vibrating surface.”
The publication then goes on to make the following statement (in Question 7):
“Any measurement away from the palm of the hand or where the measurement position is on the back of the hand, fingers or wrist is unlikely to provide reliable measurement. Further advice is given in BS EN ISO 5349-2:2001. There is currently no wrist or glove mounted device which measures vibration suitable for use in a vibration risk assessment...”.
The Control of Vibration at Work (2005) Regulations makes reference to the standards as per the following:
Under the heading “Vibration measurement and instrumentation” (paragraph 281), it states: “Anyone making hand-arm vibration measurements should be familiar with BS EN ISO 5349-1:2001 and BS EN ISO 5349-2:2002 which contain detailed practical guidance on measurement of vibration in the workplace.”
And what does BS EN ISO 5349-2 specifically state about the measurement position of the accelerometer?
It states: “The accelerometers should be rigidly attached to the vibrating surface”. It is important to note that the action and limit values in the regulations are based upon measurements performed in accordance with these BS EN ISO Standards.
Measurements conducted with accelerometers that are mounted elsewhere other than on the tool’s vibrating surface, or tool handle, could produce significantly different results. This may impact the outcome of any court cases with possible expensive consequences.
When carrying out vibration measurements either in-house or by hiring external expertise, you should ensure that this exercise is carried out in accordance with BS-EN-ISO 5349 parts 1 and 2 for compliancy against the regulations. Make this clear to the assessor.
Further research, however, upon alternative methods of hand arm vibration measurement with respect to accelerometer placement should be encouraged as technology advances. If the outcome of such research is accepted by leading experts and recognised organisations that exert influence on the standards and regulatory committees, then the standards and regulations can evolve and therefore be amended accordingly.
Until then you should look to measurements being conducted in accordance with BS EN ISO 5349 parts 1 and 2 standards. This will ensure compliance with the regulatory and HSE requirements.
A free guide to conducting a hand arm vibration (HAV) risk assessment is available for download. It explains, amongst other things, when you should carry one out, and what constitutes a competent risk assessment. Click here to receive it.